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Intra-arterial CT-angiography for cerebral arteriovenous malformation—initial experiences for treatment planning of radiosurgery1
Int. J. Radiation Oncology Biol. Phys., Vol. 54, No. 4, pp. 1121–1133, 2002 Copyright © 2002 Elsevier Science Inc. Printed in the USA. All rights reserved 0360-3016/02/$–see front matter
PII S0360-3016(02)03010-9
CLINICAL INVESTIGATION
Brain
INTRA-ARTERIAL CT-ANGIOGRAPHY FOR CEREBRAL ARTERIOVENOUS MALFORMATION—INITIAL EXPERIENCES FOR TREATMENT PLANNING OF RADIOSURGERY ETSUO KUNIEDA, M.D.,* OSAMU KAWAGUCHI, M.D.,* SATOSHI ONOZUKA, M.D.,† SUKETAKA MOMOSHIMA, M.D.,* ATSUYA TAKEDA, M.D.,* NAOYUKI SHIGEMATSU, M.D.,* SUBARU HASHIMOTO, M.D.,* TAKAYUKI OHIRA, M.D.,† AND ATSUSHI KUBO, M.D.* Departments of *Radiology and †Neurosurgery, Keio University, Tokyo, Japan Purpose: To clarify the feasibility and effectiveness of intra-arterial CT angiography (IACTA) for treatment planning of arteriovenous malformation radiosurgery. Methods and Materials: A CT scanner installed in an angiographic examination room was used. Helical IACTA was performed in 22 patients during continuous intra-arterial infusion of contrast medium via the internal carotid or vertebral artery, and dynamic IACTA was performed in 20 of these patients with reconstruction at 0.2-s intervals. The dynamic IACTA was repeated for each 3- or 5-mm increment to encompass the nidus. Subtractions were performed in postembolization cases. A retrospective review of IACTA was performed to assess the effectiveness of dynamic scans. Results: No complications related to the angiographic procedure or CT imaging were detected. High contrast enhancement was obtained for both helical and dynamic IACTA. In 18 of the 20 cases (90%), draining veins were separated from the nidus by using the enhancement patterns, and in 13 cases (65%), feeding arteries were separated. Conclusion: Dynamic IACTA added important information for target-volume determinations. Conventional CT and MRI could be omitted from the protocol, and the period that patients wore the frame was substantially shortened. We conclude that IACTA is a practical and useful method for radiosurgical treatment planning of arteriovenous malformations. © 2002 Elsevier Science Inc. Intra-arterial infusion, CT angiography, Arteriovenous malformation, Dynamic CT, Radiosurgery.
INTRODUCTION Stereotactic radiosurgery performed by steep dose delivery of concentrated gamma- or X-ray beams is one of the major strategies in the treatment of intracranial arteriovenous malformations (AVMs). The probability of cure and the risks of radiation injury are optimized if the target of the beam concentration corresponds to the AVM nidus with minimal irradiation of surrounding normal tissue (1, 2). In particular, irradiation to draining veins may collapse them before the obliteration of the nidus, leading to higher blood pressure in the nidus wall, resulting in a risk of accidental hemorrhage (3, 4). Thus, to minimize the complication, draining veins should be kept outside the radiosurgery irradiation volume. CT angiography performed by injection of iodine contrast material during continuous scanning of the target volume can clearly identify the shape of the lesion three-dimensionally (5–7). In addition, MRI or magnetic resonance angiog-
raphy (MRA) is now often used to define the target volume (8, 9). However, because conventional CT angiography, as well as MRI/MRA, does not provide temporal resolution, the enhanced arteries, nidus, and veins are visualized simultaneously, and no detailed hemodynamic information of the lesion is available. Dynamic CT technique has been used to demonstrate alterations in the intensity of the enhancement of the lesions over time. Nevertheless, CT angiography and dynamic CT evaluation of the cerebral vessels have usually been performed using i.v. injection of contrast material (5, 7, 10). When contrast material is injected i.v. into systemic circulation, only a small portion of the injected material reaches the target area. Thus, at best, only a few series of dynamic scans can be obtained, because the total dose of contrast material that can be used for a single examination is limited by the large volume and potential toxicity of the agent. However, contrast material injected into the supplying arteries of a
Reprint requests to: Etsuo Kunieda, Department of Radiology, Keio University, 35 Shinanomachi, Shinjyuku, Tokyo 160-8582 Japan. Tel: 81-(3)-3353-1211, ext. 62531; Fax: 81-(3)-3359-7425; E-mail: [email protected]
This paper was presented as a scientific paper at RSNA 2000. This paper is submitted as an original research. Received Feb 26, 2002, and in revised form Jun 10, 2002. Accepted for publication Jun 13, 2002. 1121
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target lesion, or intra-arterial CT angiography (IACTA), can produce high contrast enhancement of the vessels with a small amount of the agent (11, 12). Furthermore, dynamic IACTA is able to provide temporal information of AVM blood flow. The purpose of this study was to establish the feasibility and role of IACTA based on our initial experiences in using it for treatment planning of AVM radiosurgery. METHODS AND MATERIALS After stereotactic digital subtraction angiography (stereotactic DSA), we performed helical and dynamic IACTA in patients with AVMs for the purpose of stereotactic determination of the target volumes for radiosurgery. The protocol was approved by the institutional review board. Written informed consent for IACTA was obtained from all patients or, in the case of minors, their parents, after the nature of the IACTA procedure had been fully explained. Patient characteristics A total of 22 consecutive AVM patients between ages 11 and 67 years old (average, 31.7; median, 27.0) underwent IACTA from December 1997 to November 2001. One patient underwent a second radiosurgery with IACTA after an interval of 42 months, because the first radiosurgery failed to completely obliterate the lesion: The abnormal vessels that had embolized before the first radiosurgery had recanalized. Before radiosurgery, therapeutic embolization was performed in five cases in an attempt to reduce flow speed and volume of the nidi. Three patients had undergone surgical resection of hematoma caused by the rupture of AVM, and another patient had experienced radiosurgery without IACTA 3 years earlier. The angiographically calculated volumes of the AVM nidi ranged from 0.4 to 30.8 mL (average, 6.4; median, 4.1). The dimensions of the nidi were measured from the orthogonal DSA images by referring to the fiducial markers located on each face of a box-shaped stereotactic localizer (13). The maximum diameter of the nidus ranged from 11 to 53 mm (average, 27.2; median, 27.5), and the craniocaudal dimensions ranged from 7.8 to 39.3 mm (average, 19.7; median, 17.9). Patient immobilization and imaging The protocol of the stereotactic examinations and irradiation is briefly outlined in Fig. 1. The patient’s head was immobilized by a stereotactic frame (Leksell stereotactic coordinate frame; Elekta Instruments, Atlanta, GA) to prevent movement during stereotactic neuroimaging and irradiation. While the patient was under local anesthesia, the frame was secured to his head with four aluminum screws topped by tiny titanium tips. DSA and IACTA were performed with a hybrid angio-CT system (Advantx ACT; GE Yokogawa Medical Systems Ltd., Tokyo, Japan). The DSA device and CT are
Fig. 1. Flow diagram depicting our protocol for radiosurgery of intracranial vascular lesions. CE ⫽ contrast enhanced; CD-R ⫽ Compact Disk-Recordable.
installed in the same room as the examination table. The frame attached to the patient’s head was fixed to the examination table by an adapter to ensure that the head was rigidly supported throughout the examinations. Before insertion of a catheter into the arterial system, a scout scan and a series of whole cranial scans were performed. These comprehensive scans were used for dose calculation of the treatment irradiation, and as a basis for deciding the range of the more detailed thin-section scans. For each arterial vessel complex supplying the lesion, postero-anterior and lateral exposures were performed separately. Box-shaped acrylic target indicators for DSA and CT were attached to the frame throughout the procedures to determine the stereotactic coordinates of the lesion. Helical IACTA After the DSA, while the catheter tip remained inserted in the internal carotid or vertebral artery, thin-section helical data acquisitions for the target area were carried out (Table 1). The contrast-enhanced helical scans were programmed in a caudocranial direction with a table feed of 2 mm per gantry rotation (0.8 s/rotation) and 1-mm collimation. For patients who required subtraction images, noncontrast scanning with the same range, feed speed, and other scanning parameters was performed before the contrast enhancement scan. The helical scanning ranges were selected according to the craniocaudal size of the nidus, and at least 10-mm margins were used. Transverse sections were reconstructed at intervals equal to half of the pitch by using 180° linear interpolation. The contrast enhancement material (Omnipaque 300; Nycomed Amersham, Princeton, NJ) was diluted with heparinized saline to create a solution having a concentration of
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Table 1. IACTA parameters
No. of examined patients No. of infusion arteries Duration Collimation Table feed Reconstruction Gantry rotation period Subtraction mask Scan range (mm) CM* dose (mL) Max attenuation (HU) Repetitions
Helical
Dynamic
22 24 (18 ICA, 6 VA) 14–29 s 1 mm 2 mm/rotation, helical 1-mm interval 0.8 s Nonenhanced series 36–70 (mean 45.8, median 44.5) 13–26 (mean 17.3, median 16.9) 280–710 (mean 428, median 405) Two (pre- and postcontrast enhancement)
20 20 (17 ICA, 3 VA) 8–9.6 s 3 or 5 mm No feed between scans 0.2 s cine-reconstruction 0.8 s First image of the series 9–45 (mean 24.9, median 24.0) 9–33 (mean 23.3, median 22.5) 438–1320 (mean 862, median 882) 4–12 (mean 8.0, median 8.0) series
Abbreviations: ICA ⫽ internal carotid artery; VA ⫽ vertebral artery; HU ⫽ Hounsfield unit; IACTA ⫽ intra-arterial computed tomography angiography. * CM (contrast medium: 150 mg iodine/mL) dose for dynamic IACTA is the summation of the whole series.
150 mg iodine/mL; this concentration was used throughout the IACTA procedure. A power injector was used for contrast agent injections, which were begun 4 s before the start of the scan and stopped at the completion of the scan. The basic injection speed used for helical IACTA was 0.6 mL/s. However, if the preceding DSA had indicated an apparently high blood flow nidus, an increased speed of not more than 1.5 times the basic speed was used. Dynamic IACTA In addition to the helical scans, 8-s continuous rotation scans (0.8 s/rotation) were performed without table feed (dynamic IACTA). Transcatheter injections of 2.0 to 3.0 mL of contrast material were carried out over 1.5 s, synchronized with the start of dynamic scanning. The scan position was then moved 3 or 5 mm cranially, and the same dynamic scans were repeated up to a maximum of 12 times to encompass the nidus. We programmed repetitions of dynamic scans with intervals of 20 s between the start of each scan. The raw data were reconstructed to form a series with 0.2-s–interval cinereconstruction. Data analysis A Windows 2000 (Microsoft Corp., Redmond, WA) based workstation was used for dose delivery planning. The image data acquired by the CT scanner were transferred to the workstation via Compact Disc-Recordable (CD-R). Treatment planning software based on a threedimensional visualization tool (AVS Express; Advanced Visual Systems Inc., Waltham, MA) was modified to handle the cine-mode display of the dynamic images. The whole cranial scan data, the helical IACTA images, and the cine-reconstruction images were incorporated into the planning database, which was used to determine target volumes and organs at risk, as well as to obtain the dose distributions. In selected patients, such as those who had undergone
prior embolization, subtraction images were made from the pre- and postcontrast enhanced images. To obtain subtraction images from dynamic scans, the first image of the series was selected as a common mask, which was subtracted from each of the enhanced images in the computer memory. RESULTS The total volume of half-diluted contrast material used for the CT examination averaged 38.5 mL. In all cases, there were no neurologic complications, such as any new focal neurologic deficit or changes in mental status, throughout the examinations and the radiosurgery treatments. Helical intra-arterial CT scans were carried out for 24 vessels in 22 patients (Tables 1 and 2). In two cases, multiple vessels were examined, because more than one supplying vessel was suspected of contributing to the blood supply of the nidus at the time DSA was completed (Patient 11 and Patient 17). However, the images from the helical scans seemed to indicate that examination of an internal carotid artery was sufficient to demonstrate the nidus. In two cases, only one vessel was examined by dynamic IACTA series, and complete demonstration of the entire nidus was confirmed. Ranges of 36 mm to 70 mm (average, 45.8 mm) were scanned to obtain the volumetric data for helical arteriography. The average dose of contrast material required for each helical scan was 17.3 mL. The maximum intensity of the helical intra-arterial CT was defined as the highest attenuation at the reference points in the target plane, and the mean value of 24 vessels was 428 ⫾ 117 Hounsfield units (HUs). The dynamic intra-arterial CT scans were completed in 20 out of 22 cases. In one case (Patient 9), improper positioning of the fixation screw led to substantial artifacts from its titanium end, and we decided to discontinue the procedure. In another case (Patient 3), the CT examination was aborted, because of mechanical difficulties with movement
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Table 2. The patients and the dynamic IACTA results Separation from nidus Patient*
Age, yr/gender
Prior treatment
Infusion vessel†
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
19/M 37/M 8/F 27/M 67/M 21/F 33/M 53/F 25/M 47/M 11/F 49/F 18/M 33/M 17/F 24/F 54/F 39/M 28/M 50/M 20/F 18/F
Embolization Embolization Radiosurgery Hematoma evacuation Hematoma evacuation Embolization Embolization Hematoma evacuation Embolization -
L VA R ICA L VA R ICA L ICA L ICA R ICA R VA L ICA R ICA L ICA, L VA R ICA L ICA R ICA R ICA L ICA R ICA L ICA L ICA R ICA L ICA, L VA R VA
Nidus volume (mL)
Draining vein‡
Draining vein
0.4 0.6 0.7 0.9 1.4 1.5 2.3 2.7 3.0 3.8 4.0 4.1 5.4 5.5 5.5 7.5 7.9 10.8 12.6 13.2 17.1 30.8
Deep Deep Deep Deep Superficial Deep Deep Deep Deep Superficial Deep Superficial Deep Deep Superficial Superficial Deep Superficial Deep Superficial Superficial Deep
Poor Poor Good Good No dynamic scans Good Poor Good Good Fair Poor Good Fair Fair Poor No dynamic scans Good Fair Good Fair Good Poor Good Good Good Fair Good Good Good Fair Good Poor Good Good Good Fair Poor Poor Good Fair Good Good
Feeding artery
Abbreviations: IACTA ⫽ intra-arterial computed tomography angiography; L ⫽ left; R ⫽ right; VA ⫽ vertebral artery; ICA ⫽ internal carotid artery. * Patients are sorted by the volume of the nidus. † Lower-case arteries were examined only by helical IACTA. ‡ Deep or superficial is based on the criteria of Spetzler-Martin grade (31)
of the examination table. In both cases, we used data obtained by MRA for treatment planning. The collimation width used for dynamic IACTA was 3 mm in all cases, except in the case with the largest nidus (Patient 22); in this situation, we used a 5-mm collimation width. During each of the examinations, the section interval was the same as the collimation width and kept constant for the entire series of dynamic IACTA. An average of 2.8 mL of contrast material was injected. This dose produced maximum attenuation in the lesion (measured at the reference points) of 862 ⫾ 239 HU. A retrospective review of IACTA was performed to assess the effectiveness of the dynamic scans. First, a dynamic series close to the center of the nidus was selected from the dynamic IACTA, and some reference points were then selected from the target series. The reference points chosen ranged from one of the closest points to the center of the lesion, so as to reflect each vascular component (i.e., the supplying arteries and draining veins and the nidus). The points on the orthogonal DSA images corresponding to the chosen reference points were identified using the stereotactic coordinates of the reference points. The nature of the reference points was confirmed by knowledge of both the connections of the vessels to known vascular structures and the enhancement patterns of the corresponding points on the DSA
series. Separation of each of the vascular components was assessed from the enhancement patterns of the reference points on the IACTA series. From the contrast enhancement pattern of the reference points on the dynamic CT series, the reference points were classified into three categories by peak time in time–attenuation curves. For example, if the peak times of the selected reference points in all of the feeding arteries and in one of the nidi were more than 2 images
Fig. 2. Efficacy of dynamic scan in separating nearby vessels (draining veins, supplying arteries) from the nidi. From the top of the column, “good” (more than 2 images or 0.4 s apart in peak times of the enhancement), “fair” (an image apart), and “poor” (no difference among the peak times).
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Fig. 3. (a) Posterofrontal and (b) lateral DSA, and (c) 3D spoiled gradient-recalled echo MRI images of a left frontal AVM in the territory of the left internal carotid artery (Patient 11). (d) Dynamic IACTA images at the nidus are shown. The elapsed time after the start of scanning is indicated under each image. An averaged image of the dynamic scans is shown at the right bottom. Note that a vascular structure (arrow) was not apparent until the image at 2.0 s, and remained after most of the other vessels had disappeared; this structure was recognized as a vein. The CT images were photographed with a window width of 1500 HU and level of 770 HU. The locations of the reference points are specified on (e) a helical IACTA image, which is at the same craniocaudal position as the (d) dynamic IACTA. The (f) time–attenuation curves of the (e) reference points are also shown. Point 1 is recognized to be a supplying artery and point 2 the nidus. The delayed enhancement pattern of points 3 and 4 indicates that these points are included in a different hemodynamic component than the nidus, and therefore they are recognized to be draining veins.
apart (0.4 s), the rating was “good.” If the peak times were an image apart (0.2 s), it was “fair,” and if there was no difference among the peak times, it was “poor.” Abil-
ity to distinguish nearby draining veins from the nidus was “good” or “fair” in 18 cases (90%) out of 20, and ability to distinguish feeding arteries was “good” or
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Fig. 3. (Cont’d)
“fair” in 13 cases (65%) (Fig. 2). Some of the cases are shown in Figs. 3– 6. DISCUSSION Angiography enables continuous image acquisition in a very short time after the injection of contrast material into the supplying arteries. In other words, it provides temporal resolution that makes it possible to distinguish arteries and the nidus from surrounding late-enhanced veins by the enhancement pattern of each vascular structure. These features make cerebral angiography the primary imaging method for the diagnosis and evaluation of AVM nidi, as well as of feeding arteries and intranidus aneurysms (13, 14). Despite these advantages, conventional biplanar angiography alone is limited in regard to the three-dimensional definition of AVM nidus margins, especially for irregularly shaped lesions (15, 16). If the shape of the nidus includes dimpling or a recess, angiographic planar images, even when many projections other than orthogonal ones are examined, cannot faithfully reflect the real shape of the target volume (8, 17). Tomographic modalities such as MRI and contrast-enhanced CT are indispensable for determining the exact shape of the lesion in three dimensions (6, 7, 9, 10, 18). CT usually provides better spatial resolution than MRI in axial planes. Moreover, X-ray CT is necessary for precise calculation of radiotherapy dose, because it provides a density distribution of the object from the attenuation of the X-ray; the distribution is then used to obtain the attenuation of the treatment beams. Large field-of-view CT images were usually made to depict the positions of the markers, as well as the target lesion; also, if needed for detailed target delinea-
tion, higher-resolution images could be reconstructed from the raw data. MRI/MRA is often preferred over CT angiography for radiosurgery planning. One reason is that when intravenous CT angiography is combined with DSA, the total amount of contrast enhancement agent may exceed the safety limitation dose of the agent. Because of the complementary characteristics of the stereotactic modalities outlined above, the necessary requirement for a radiosurgery database had been DSA (for temporal information), noncontrast CT (for dose calculation), and MRA (for three-dimensional [3D] shape recognition) before we introduced IACTA for AVM radiosurgery. With our current protocol, all the stereotactic examinations— DSA and CT angiography, as well as noncontrast CT for dose calculation—are carried out in the same room and at the same time. Stereotactic MRI was removed from the protocol, and the period that the patient had to wear the stereotactic frame was substantially shortened. Some other benefits are achieved for CT scans if the contrast enhancement agent is injected via the cerebral arteries. Strong and short duration enhancement of the vascular structure is obtained with small doses of the agent. Short duration of the input contrast material to the target area is able to emphasize the small differences in the enhancement peak of each of the vascular components. The large intensity differential between the vessels and the parenchyma reduces the need for intensity resolution. Consequently, the X-ray output power and the load of the X-ray tube can be minimized. In the present study, the high contrast enhancement allowed visualization of small vessels difficult to locate by other modalities (Fig. 6).
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Fig. 4. An (a) anterior and (b) lateral DSA and (c) stereotactic helical IACTA indicate right frontal AVM (Patient 15). (d) Sagittal and coronal AVM sections were reformatted from the 3D data sets in different enhancement phases of multiple dynamic CT series. Each of the 3D data sets consists of multiple sectional images taken from the dynamic CT series at different craniocaudal positions. Because of that, each voxel in the 3D data set is assumed to be at the same phase of the contrast enhancement. Orthogonal images at 0.4 (1), 0.8 (2), 1.6 (3), and 3.6 (4) seconds after the arrival of the contrast material are shown. “Veins” indicated in (4) by the arrows were not seen in (1). This region of “veins” could be excluded from the radiosurgery target volume.
Role of MRA in target delineation Kondziolka et al. studied the accuracy and usefulness of stereotactic MRA for AVM radiosurgery in 28 patients (9). In 24 patients, MRA information equaled that of conven-
tional angiography. In 3 patients, MRA was better because conventional angiography overestimated the size of the AVM nidus. Bednarz et al. evaluated the advantages of using 3D
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Fig. 5. An (a) anterior angiography and a (b) lateral DSA indicate right frontal AVM partially treated by embolization (Patient 2). Helical IACTA images (c) with contrast enhancement and (d) without contrast enhancement are shown (window width 1000, level 40). It is difficult to delineate the nidus, because of the high-density embolic material in the vessels (black arrowheads). Markers of the stereotactic indicator are shown with white arrows. (e) T1-weighted MRI and (f) 3D time-of-flight MRA are not clear in demonstrating the vascular structure of the lesion. (g) Dynamic IACTA was carried out by right internal carotid infusion of the contrast enhancement material. An image of a dynamic scan before the arrival of the contrast enhancement material visualized the embolic material. The embolized material remaining in the vessel hampered clear demonstration of the vascular structures in and around the lesion. When a pre-enhanced image was subtracted from the enhanced images, hemodynamic alteration of the vessels was clearly demonstrated.
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Fig. 5. (Cont’d)
time-of-flight MRA in obtaining three-dimensional information on the nidus (19). The treatment plans were modified by the MRA information in 12 out of 22 cases (55%): The target volumes were reduced. Nevertheless, in 10 cases (45%), both MRI and MRA failed to detect the nidus, because of surgical clip artifacts and the presence of embolization material. Phase-contrast MRA is free from this effect, but it may fail to detect slow blood flow around the nidus (7, 20). Inhomogeneity of the magnetic field in magnetic resonance devices may cause image distortion, and it is often more prominent at the peripheral area of the field of view, where the fiducial markers are (21, 22). Therefore, time-of-flight or phase-contrast MRA, as well as conventional CT angiography, is often useful in delineating target volume for an irregularly shaped nidus. However, because of the nature of the modality, the images are static and do not provide temporal resolution as conventional angiography does. Essig et al. reported the use of dynamic MRA based on a blood bolus tagging technique for the treatment planning of AVM radiosurgery (23). This method has the advantage of providing the hemodynamic information on the vascular lesion. The authors reported that dynamic MRA was able to demonstrate the AVM characteristics and hemodynamics in 12 out of 20 patients. However, because of the low signal: noise ratio, only a single or very limited number of readout sections are applied over the whole range of the lesion; thus, it has substantially no resolution perpendicular to the readout section and lacks a true three-dimensional representation of the vascular structures. Because of this limitation, the role of this method in precise delineation of the radio-
surgery target volume is diminished. In addition, this technique could not reliably depict the malformation in 3 patients with nidi smaller than 1 cm.
Role of dynamic IACTA Possible consequences of irradiation damage to draining veins include venous thrombosis, which in turn could lead to higher blood pressure of the nidus wall, resulting in a risk of accidental hemorrhage (3, 4). Thus, to minimize complications, draining veins should be kept outside the radiosurgery irradiation volume. Dynamic IACTA was performed with 0.8-s rotation of the gantry, and four images were generated from full rotational data using a 180° reconstruction method. Although there was a 90° overlap for each image, the image interval was 0.2 s. Apparently, dynamic IACTA has less temporal resolution than DSA has. A relatively long acquisition time is required for each CT image (0.4 s for 180° reconstruction), whereas for each DSA image, the required duration of acquisition time is very short. Nevertheless, we reconstructed images with 0.2-s intervals to find out when the enhancement of each vessel component begins and where the peaks of the attenuation curves are. Another advantage of dynamic IACTA over DSA is that there are no spatial overlaps of the structure in sectional IACTA. Probably because of the high contrast enhancement effect and the rapid changes in attenuation of the vascular structures, our results indicate a relatively high sensitivity of separation of veins from other vascular components. The nature of the sectional images may also contribute to vessel
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Fig. 6. (a) A right posterior cerebral arterial territory AVM (Patient 1: arrow) was detected by super-selective DSA performed after the onset of the hemorrhage. Because the nidus was small and faint, it was very hard to locate its exact coordinates by stereotactic DSA. Both (b) helical and dynamic scans clearly identified the nidus position. However, the enhancement pattern of the nidus was similar to that of nearby vessels, and it was difficult to separate arteries and veins from the nidus according to the enhancement pattern. (c) MRI could not identify the position of the nidus because of methemoglobin deposition.
separations. The time–attenuation curves and images could indicate fairly well the differences in the enhancement pattern of each vascular structure, as shown in Figs. 3, 4, and 5. Hybrid angio-CT system Our protocol was based on a hybrid angio-CT system (11, 24) that is able to make the IACTA for various organs a practical and safe procedure by eliminating the need for patient transportation and reducing examination time. As far
as we know, more than 100 units of this system, produced by a number of different manufacturers, have already been installed in recent years. However, at this moment, it is not very realistic for every radiosurgery suite to install this system in terms of cost and space for the additional CT scanner. This system was originally developed for use in abdominal interventional radiology, such as in investigating the contribution of portal blood flow to hepatic tumors or in confirming the territory area of a vessel before embolization (24). Hirai et al. used this for preoperative evaluation of
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intracranial aneurysms (11). However, to our knowledge there have been no other published reports on the use of this system for neuroradiologic purposes. The price of a CT scanner is decreasing, and its performance is dramatically improving. New applications for the angio-CT system, such as radiosurgery planning, will increase the range of use and cost-effectiveness of the system. Patient safety Although AVM is already associated with relatively high treatment-related risks as well as risk of hemorrhage from the nidus (25, 26), the risk related to IACTA must still be assessed and minimized. IACTA reduces the need for additional angiographic projections and super-selective procedures. Moreover, the more precise delineation of the nidus is expected to increase the probability of cure and to reduce the risk of complications. The rate of neurologic complications after cerebral angiography has been reported as 1% in most of the recent studies, and the rate of persistent neurologic deficit has been reported as 0.3%– 0.4% (27–29). In their retrospective study of 483 cerebral angiographic examinations, Leffers and Wagner reported a total complication rate of 2.3%, and they found no clear relationship between the incidence rate and the number of series performed (30). Although modern cerebral angiography carries a low risk for permanent neurologic or systemic complications when performed by experienced neuroradiologists (16), the IACTA procedure is potentially associated with some risk of complication, even though this risk is, we believe, much less than that of super-selective or embolization procedures. Therefore, the potential risk factor of IACTA should be assessed and minimized. The time that the catheter is inserted into the infusion vessels should be as short as possible to avoid the potential risk of angiographic complications. Because the X-ray tube is heated by repeated dynamic or helical scans, the IACTA protocol potentially requires relatively long cooling times, so we optimized the X-ray exposure protocol to minimize the tube load. A current of 60 mA is now used throughout the examinations, including the helical and dynamic scans. Duration of the dynamic scan has been minimized to 8 s. Because the start and stop of the anode rotation produce considerable heat in the X-ray tube, a dynamic series set with a constant interval of 20 s between the series was programmed before the start of the scans so that the anode of the X-ray tube continuously rotated. As a result, more than 10 dynamic scans and two helical scans could be performed without having to wait for the tube to cool. Consequently, we have been able to reduce the time required for IACTA to less than 7 min. If a case occurs where multiple vessels need to be examined by multiple helical and dynamic series, adequate cooling time should be allocated during the examination of each of the vessels. We watched the intensity changes of the vessels through real-time reconstruction of CT scans. The injection speed was almost as slow as, and the amount of the contrast agent
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was almost as little as, that of manual test injections performed for confirmation of the catheter position in the vascular system. This low infusion speed reduced the possibility of catheter tip recoil. Comparison with MRA We have not experienced enough cases to assess the exact sensitivity of dynamic IACTA in detecting the separation of the vascular components of AVMs; also, MRA studies were not routinely performed at the same time as IACTA. Therefore, at present, quantitative comparison between IACTA and MRA in precise delineation of the nidus is yet to be performed. Nevertheless, we believe that the nature of IACTA that enables us temporal analysis of the hemodynamics provides some superiority in the delineation, and we experienced a number of cases where MRA failed and IACTA was effective, as shown in the figures. On the other hand, the failed cases give us an indication of the types of cases for which dynamic CT is unlikely to produce meaningful results on the separation of the vascular components. In one of two failed cases in the separation of draining veins (Patient 1, Fig. 6), the dynamic images indicated no prominent draining vein in the target area. (Because of the very small nidus in this case, DSA was not only unable to indicate the draining vein, but also had difficulty in locating the nidus clearly; and MRI/A localization failed, because of methemoglobin deposition.) In another failed case (Patient 20), there was a very high flow nidus, and prominent draining veins were visualized. Probably because of the high flow, there was no substantial difference in enhancement pattern between the nidus and the draining vein. For AVMs that have direct arteriovenous shunts, dynamic IACTA may have limited value in separating nearby draining veins from the nidus. From the standpoint of cost-effectiveness or minimizing examination time, dynamic IACTA is not always required for the patients who have very high flow nidus. However, we believe that helical IACTA is beneficial for all cases. The information from helical IACTA is similar to that of MRI/MRA in terms of radiosurgery planning, and helical IACTA can be performed with one additional injection in a short time when an angio-CT system is used. Advantages for the patients with this procedure are the following: They are not required to be transported to another room for MRI or i.v. CT angiography, and the time that they are required to wear the frame is significantly shortened. One of the inherent advantages of MRA over IACTA is that MRA alone has almost no risk of complication when a contrast enhancement agent is not administered. However, at present a combination of MRA and angiography (DSA) is usually applied for radiosurgery planning, and despite its potential risk, angiography is not omitted. Therefore, the combined risk of MRA and DSA should be compared with that of IACTA and DSA. As we mentioned previously, IACTA and DSA are performed one after the other in the same room with the same kind of contrast agent. A longer
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catheter insertion time, as well as additional infusions of contrast material, is thought to be the only factor that may increase risk. So, we believe that the difference in risk factor with DSA alone (or with MRA) compared with DSA followed by IACTA is minimal. Use of IACTA for radiosurgery planning will be justified when enough benefit is obtained from precise target delineation. On the other hand, we do not recommend the routine use of the IACTA procedure for follow-up studies after radiosurgery. In most cases, MRA and DSA sufficiently evaluate the shrinkage and obliteration of the lesion. Another advantage of MRI/A is that MRI instruments are currently installed in almost every major institute. On the other hand, use of IACTA for neuroradiology is limited, because a special DSA-CT combination is required. We do not recommend carrying a patient from room to room while a catheter is inserted in the carotid or vertebral arteries.
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CONCLUSION In conclusion, intra-arterial CT angiography using a hybrid angio-CT system was safely and effectively performed for radiosurgery planning. All the stereotactic examinations were performed in the same room, and conventional CT and MRI could be removed from the protocol. The period that the patient had to wear the frame was substantially shortened. For these reasons, helical IACTA has an advantage over MRI/A or conventional CT for radiosurgery planning. Because IACTA requires only a small dose of contrast agent, repeated dynamic scans can be performed. In 18 of 20 cases, dynamic IACTA provided temporal information that was helpful in excluding draining veins from the target volume. On the other hand, supplying arteries were rather difficult to separate according to enhancement patterns. If previous stereotactic DSA indicates a very high flow nidus, dynamic IACTA may be omitted.
REFERENCES 1. Lunsford LD, Kondziolka D, Bissonette DJ, et al. Stereotactic radiosurgery of brain vascular malformations. Neurosurg Clin N Am 1992;3:79 –98. 2. Saunders WM, Winston KR, Siddon RL, et al. Radiosurgery for arteriovenous malformations of the brain using a standard linear accelerator: Rationale and technique. Int J Radiat Oncol Biol Phys 1988;15:441– 447. 3. Awad IA, Magdinec M, Schubert A. Intracranial hypertension after resection of cerebral arteriovenous malformations. Predisposing factors and management strategy. Stroke 1994;25: 611– 620. 4. Pollock BE. Occlusive hyperemia: A radiosurgical phenomenon? Neurosurgery 2000;47:1178 –1182 discussion 1182–1174. 5. Levy RP, Schulte RW, Frankel KA, et al. Computed tomography slice-by-slice target-volume delineation for stereotactic proton irradiation of large intracranial arteriovenous malformations: An iterative approach using angiography, computed tomography, and magnetic resonance imaging. Int J Radiat Oncol Biol Phys 1996;35:555–564. 6. Rieger J, Hosten N, Neumann K, et al. Initial clinical experience with spiral CT and 3D arterial reconstruction in intracranial aneurysms and arteriovenous malformations. Neuroradiology 1996;38:245–251. 7. Tanaka H, Numaguchi Y, Konno S, et al. Initial experience with helical CT and 3D reconstruction in therapeutic planning of cerebral AVMs: Comparison with 3D time-of-flight MRA and digital subtraction angiography. J Comput Assist Tomogr 1997;21:811– 817. 8. Bova FJ, Friedman WA. Stereotactic angiography: An inadequate database for radiosurgery? Int J Radiat Oncol Biol Phys 1991;20:891– 895. 9. Kondziolka D, Lunsford LD, Kanal E, et al. Stereotactic magnetic resonance angiography for targeting in arteriovenous malformation radiosurgery. Neurosurgery 1994;35:585–590. 10. Gorzer H, Heimberger K, Schindler E. Spiral CT angiography with digital subtraction of extra- and intracranial vessels. J Comput Assist Tomogr 1994;18:839 – 841. 11. Hirai T, Korogi Y, Ono K, et al. Preoperative evaluation of intracranial aneurysms: Usefulness of intraarterial 3D CT angiography and conventional angiography with a combined unit—initial experience. Radiology 2001;220:499 –505. 12. Tanami Y, Kunieda E, Onozuka S, et al. Intra-arterial an-
13.
14.
15.
16.
17. 18.
19.
20.
21.
22. 23.
gio-CT for radiosurgery of cerebral arteriovenous malformations [published in Japanese]. Rinsyo Housyasen 1998;43: 929 –933. Guo WY, Lindqvist M, Lindquist C, et al. Stereotaxic angiography in gamma knife radiosurgery of intracranial arteriovenous malformations. AJNR Am J Neuroradiol 1992;13:1107–1114. Foroni R, Gerosa M, Pasqualin A, et al. Shape recovery and volume calculation from biplane angiography in the stereotactic radiosurgical treatment of arteriovenous malformations. Int J Radiat Oncol Biol Phys 1996;35:565–577. Blatt DR, Friedman WA, Bova FJ. Modifications based on computed tomographic imaging in planning the radiosurgical treatment of arteriovenous malformations. Neurosurgery 1993;33:588 –595. Pollock BE, Kondziolka D, Flickinger JC, et al. Magnetic resonance imaging: An accurate method to evaluate arteriovenous malformations after stereotactic radiosurgery [see comments]. J Neurosurg 1996;85:1044 –1049. Spiegelmann R, Friedman WA, Bova FJ. Limitations of angiographic target localization in planning radiosurgical treatment. Neurosurgery 1992;30:619 – 623. Guo WY, Nordell B, Karlsson B, et al. Target delineation in radiosurgery for cerebral arteriovenous malformations. Assessment of the value of stereotaxic MR imaging and MR angiography. Acta Radiol 1993;34:457– 463. Bednarz G, Downes B, Werner-Wasik M, Rosenwasser RH. Combining stereotactic angiography and 3D time-of-flight magnetic resonance angiography in treatment planning for arteriovenous malformation radiosurgery. Int J Radiat Oncol Biol Phys 2000;46:1149 –1154. Huston J, Rufenacht DA, Ehman RL, et al. Intracranial aneurysms and vascular malformations: Comparison of time-offlight and phase-contrast MR angiography. Radiology 1991; 181:721–730. Kondziolka D, Dempsey PK, Lunsford LD, et al. A comparison between magnetic resonance imaging and computed tomography for stereotactic coordinate determination. Neurosurgery 1992;30:402– 406. Meuli RA, Verdun FR, Bochud FO, et al. Assessment of MR image deformation for stereotactic neurosurgery using a tagging sequence. AJNR Am J Neuroradiol 1994;15:45– 49. Essig M, Engenhart R, Knopp MV, et al. Cerebral arterio-
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24. 25. 26. 27.
venous malformations: Improved nidus demarcation by means of dynamic tagging MR-angiography. Magn Reson Imaging 1996;14:227–233. Capasso P, Trotteur G, Flandroy P, et al. A combined CT and angiography suite with a pivoting table. Radiology 1996;199: 561–563. Brown RD, Jr, Wiebers DO, Forbes G, et al. The natural history of unruptured intracranial arteriovenous malformations. J Neurosurg 1988;68:352–357. Pollock BE, Flickinger JC, Lunsford LD, et al. Factors that predict the bleeding risk of cerebral arteriovenous malformations. Stroke 1996;27:1– 6. Grzyska U, Freitag J, Zeumer H. Selective cerebral intraarte-
28. 29. 30. 31.
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rial DSA. Complication rate and control of risk factors. Neuroradiology 1990;32:296 –299. Heiserman JE, Dean BL, Hodak JA, et al. Neurologic complications of cerebral angiography. AJNR Am J Neuroradiol 1994;15:1401–1407 discussion 1408 –1411. Waugh JR, Sacharias N. Arteriographic complications in the DSA era. Radiology 1992;182:243–246. Leffers AM, Wagner A. Neurologic complications of cerebral angiography. A retrospective study of complication rate and patient risk factors. Acta Radiol 2000;41:204 –210. Spetzler RF, Martin NA. A proposed grading system for arteriovenous malformations. J Neurosurg 1986;65:476 – 483.
PII S0360-3016(02)03010-9
CLINICAL INVESTIGATION
Brain
INTRA-ARTERIAL CT-ANGIOGRAPHY FOR CEREBRAL ARTERIOVENOUS MALFORMATION—INITIAL EXPERIENCES FOR TREATMENT PLANNING OF RADIOSURGERY ETSUO KUNIEDA, M.D.,* OSAMU KAWAGUCHI, M.D.,* SATOSHI ONOZUKA, M.D.,† SUKETAKA MOMOSHIMA, M.D.,* ATSUYA TAKEDA, M.D.,* NAOYUKI SHIGEMATSU, M.D.,* SUBARU HASHIMOTO, M.D.,* TAKAYUKI OHIRA, M.D.,† AND ATSUSHI KUBO, M.D.* Departments of *Radiology and †Neurosurgery, Keio University, Tokyo, Japan Purpose: To clarify the feasibility and effectiveness of intra-arterial CT angiography (IACTA) for treatment planning of arteriovenous malformation radiosurgery. Methods and Materials: A CT scanner installed in an angiographic examination room was used. Helical IACTA was performed in 22 patients during continuous intra-arterial infusion of contrast medium via the internal carotid or vertebral artery, and dynamic IACTA was performed in 20 of these patients with reconstruction at 0.2-s intervals. The dynamic IACTA was repeated for each 3- or 5-mm increment to encompass the nidus. Subtractions were performed in postembolization cases. A retrospective review of IACTA was performed to assess the effectiveness of dynamic scans. Results: No complications related to the angiographic procedure or CT imaging were detected. High contrast enhancement was obtained for both helical and dynamic IACTA. In 18 of the 20 cases (90%), draining veins were separated from the nidus by using the enhancement patterns, and in 13 cases (65%), feeding arteries were separated. Conclusion: Dynamic IACTA added important information for target-volume determinations. Conventional CT and MRI could be omitted from the protocol, and the period that patients wore the frame was substantially shortened. We conclude that IACTA is a practical and useful method for radiosurgical treatment planning of arteriovenous malformations. © 2002 Elsevier Science Inc. Intra-arterial infusion, CT angiography, Arteriovenous malformation, Dynamic CT, Radiosurgery.
INTRODUCTION Stereotactic radiosurgery performed by steep dose delivery of concentrated gamma- or X-ray beams is one of the major strategies in the treatment of intracranial arteriovenous malformations (AVMs). The probability of cure and the risks of radiation injury are optimized if the target of the beam concentration corresponds to the AVM nidus with minimal irradiation of surrounding normal tissue (1, 2). In particular, irradiation to draining veins may collapse them before the obliteration of the nidus, leading to higher blood pressure in the nidus wall, resulting in a risk of accidental hemorrhage (3, 4). Thus, to minimize the complication, draining veins should be kept outside the radiosurgery irradiation volume. CT angiography performed by injection of iodine contrast material during continuous scanning of the target volume can clearly identify the shape of the lesion three-dimensionally (5–7). In addition, MRI or magnetic resonance angiog-
raphy (MRA) is now often used to define the target volume (8, 9). However, because conventional CT angiography, as well as MRI/MRA, does not provide temporal resolution, the enhanced arteries, nidus, and veins are visualized simultaneously, and no detailed hemodynamic information of the lesion is available. Dynamic CT technique has been used to demonstrate alterations in the intensity of the enhancement of the lesions over time. Nevertheless, CT angiography and dynamic CT evaluation of the cerebral vessels have usually been performed using i.v. injection of contrast material (5, 7, 10). When contrast material is injected i.v. into systemic circulation, only a small portion of the injected material reaches the target area. Thus, at best, only a few series of dynamic scans can be obtained, because the total dose of contrast material that can be used for a single examination is limited by the large volume and potential toxicity of the agent. However, contrast material injected into the supplying arteries of a
Reprint requests to: Etsuo Kunieda, Department of Radiology, Keio University, 35 Shinanomachi, Shinjyuku, Tokyo 160-8582 Japan. Tel: 81-(3)-3353-1211, ext. 62531; Fax: 81-(3)-3359-7425; E-mail: [email protected]
This paper was presented as a scientific paper at RSNA 2000. This paper is submitted as an original research. Received Feb 26, 2002, and in revised form Jun 10, 2002. Accepted for publication Jun 13, 2002. 1121
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target lesion, or intra-arterial CT angiography (IACTA), can produce high contrast enhancement of the vessels with a small amount of the agent (11, 12). Furthermore, dynamic IACTA is able to provide temporal information of AVM blood flow. The purpose of this study was to establish the feasibility and role of IACTA based on our initial experiences in using it for treatment planning of AVM radiosurgery. METHODS AND MATERIALS After stereotactic digital subtraction angiography (stereotactic DSA), we performed helical and dynamic IACTA in patients with AVMs for the purpose of stereotactic determination of the target volumes for radiosurgery. The protocol was approved by the institutional review board. Written informed consent for IACTA was obtained from all patients or, in the case of minors, their parents, after the nature of the IACTA procedure had been fully explained. Patient characteristics A total of 22 consecutive AVM patients between ages 11 and 67 years old (average, 31.7; median, 27.0) underwent IACTA from December 1997 to November 2001. One patient underwent a second radiosurgery with IACTA after an interval of 42 months, because the first radiosurgery failed to completely obliterate the lesion: The abnormal vessels that had embolized before the first radiosurgery had recanalized. Before radiosurgery, therapeutic embolization was performed in five cases in an attempt to reduce flow speed and volume of the nidi. Three patients had undergone surgical resection of hematoma caused by the rupture of AVM, and another patient had experienced radiosurgery without IACTA 3 years earlier. The angiographically calculated volumes of the AVM nidi ranged from 0.4 to 30.8 mL (average, 6.4; median, 4.1). The dimensions of the nidi were measured from the orthogonal DSA images by referring to the fiducial markers located on each face of a box-shaped stereotactic localizer (13). The maximum diameter of the nidus ranged from 11 to 53 mm (average, 27.2; median, 27.5), and the craniocaudal dimensions ranged from 7.8 to 39.3 mm (average, 19.7; median, 17.9). Patient immobilization and imaging The protocol of the stereotactic examinations and irradiation is briefly outlined in Fig. 1. The patient’s head was immobilized by a stereotactic frame (Leksell stereotactic coordinate frame; Elekta Instruments, Atlanta, GA) to prevent movement during stereotactic neuroimaging and irradiation. While the patient was under local anesthesia, the frame was secured to his head with four aluminum screws topped by tiny titanium tips. DSA and IACTA were performed with a hybrid angio-CT system (Advantx ACT; GE Yokogawa Medical Systems Ltd., Tokyo, Japan). The DSA device and CT are
Fig. 1. Flow diagram depicting our protocol for radiosurgery of intracranial vascular lesions. CE ⫽ contrast enhanced; CD-R ⫽ Compact Disk-Recordable.
installed in the same room as the examination table. The frame attached to the patient’s head was fixed to the examination table by an adapter to ensure that the head was rigidly supported throughout the examinations. Before insertion of a catheter into the arterial system, a scout scan and a series of whole cranial scans were performed. These comprehensive scans were used for dose calculation of the treatment irradiation, and as a basis for deciding the range of the more detailed thin-section scans. For each arterial vessel complex supplying the lesion, postero-anterior and lateral exposures were performed separately. Box-shaped acrylic target indicators for DSA and CT were attached to the frame throughout the procedures to determine the stereotactic coordinates of the lesion. Helical IACTA After the DSA, while the catheter tip remained inserted in the internal carotid or vertebral artery, thin-section helical data acquisitions for the target area were carried out (Table 1). The contrast-enhanced helical scans were programmed in a caudocranial direction with a table feed of 2 mm per gantry rotation (0.8 s/rotation) and 1-mm collimation. For patients who required subtraction images, noncontrast scanning with the same range, feed speed, and other scanning parameters was performed before the contrast enhancement scan. The helical scanning ranges were selected according to the craniocaudal size of the nidus, and at least 10-mm margins were used. Transverse sections were reconstructed at intervals equal to half of the pitch by using 180° linear interpolation. The contrast enhancement material (Omnipaque 300; Nycomed Amersham, Princeton, NJ) was diluted with heparinized saline to create a solution having a concentration of
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Table 1. IACTA parameters
No. of examined patients No. of infusion arteries Duration Collimation Table feed Reconstruction Gantry rotation period Subtraction mask Scan range (mm) CM* dose (mL) Max attenuation (HU) Repetitions
Helical
Dynamic
22 24 (18 ICA, 6 VA) 14–29 s 1 mm 2 mm/rotation, helical 1-mm interval 0.8 s Nonenhanced series 36–70 (mean 45.8, median 44.5) 13–26 (mean 17.3, median 16.9) 280–710 (mean 428, median 405) Two (pre- and postcontrast enhancement)
20 20 (17 ICA, 3 VA) 8–9.6 s 3 or 5 mm No feed between scans 0.2 s cine-reconstruction 0.8 s First image of the series 9–45 (mean 24.9, median 24.0) 9–33 (mean 23.3, median 22.5) 438–1320 (mean 862, median 882) 4–12 (mean 8.0, median 8.0) series
Abbreviations: ICA ⫽ internal carotid artery; VA ⫽ vertebral artery; HU ⫽ Hounsfield unit; IACTA ⫽ intra-arterial computed tomography angiography. * CM (contrast medium: 150 mg iodine/mL) dose for dynamic IACTA is the summation of the whole series.
150 mg iodine/mL; this concentration was used throughout the IACTA procedure. A power injector was used for contrast agent injections, which were begun 4 s before the start of the scan and stopped at the completion of the scan. The basic injection speed used for helical IACTA was 0.6 mL/s. However, if the preceding DSA had indicated an apparently high blood flow nidus, an increased speed of not more than 1.5 times the basic speed was used. Dynamic IACTA In addition to the helical scans, 8-s continuous rotation scans (0.8 s/rotation) were performed without table feed (dynamic IACTA). Transcatheter injections of 2.0 to 3.0 mL of contrast material were carried out over 1.5 s, synchronized with the start of dynamic scanning. The scan position was then moved 3 or 5 mm cranially, and the same dynamic scans were repeated up to a maximum of 12 times to encompass the nidus. We programmed repetitions of dynamic scans with intervals of 20 s between the start of each scan. The raw data were reconstructed to form a series with 0.2-s–interval cinereconstruction. Data analysis A Windows 2000 (Microsoft Corp., Redmond, WA) based workstation was used for dose delivery planning. The image data acquired by the CT scanner were transferred to the workstation via Compact Disc-Recordable (CD-R). Treatment planning software based on a threedimensional visualization tool (AVS Express; Advanced Visual Systems Inc., Waltham, MA) was modified to handle the cine-mode display of the dynamic images. The whole cranial scan data, the helical IACTA images, and the cine-reconstruction images were incorporated into the planning database, which was used to determine target volumes and organs at risk, as well as to obtain the dose distributions. In selected patients, such as those who had undergone
prior embolization, subtraction images were made from the pre- and postcontrast enhanced images. To obtain subtraction images from dynamic scans, the first image of the series was selected as a common mask, which was subtracted from each of the enhanced images in the computer memory. RESULTS The total volume of half-diluted contrast material used for the CT examination averaged 38.5 mL. In all cases, there were no neurologic complications, such as any new focal neurologic deficit or changes in mental status, throughout the examinations and the radiosurgery treatments. Helical intra-arterial CT scans were carried out for 24 vessels in 22 patients (Tables 1 and 2). In two cases, multiple vessels were examined, because more than one supplying vessel was suspected of contributing to the blood supply of the nidus at the time DSA was completed (Patient 11 and Patient 17). However, the images from the helical scans seemed to indicate that examination of an internal carotid artery was sufficient to demonstrate the nidus. In two cases, only one vessel was examined by dynamic IACTA series, and complete demonstration of the entire nidus was confirmed. Ranges of 36 mm to 70 mm (average, 45.8 mm) were scanned to obtain the volumetric data for helical arteriography. The average dose of contrast material required for each helical scan was 17.3 mL. The maximum intensity of the helical intra-arterial CT was defined as the highest attenuation at the reference points in the target plane, and the mean value of 24 vessels was 428 ⫾ 117 Hounsfield units (HUs). The dynamic intra-arterial CT scans were completed in 20 out of 22 cases. In one case (Patient 9), improper positioning of the fixation screw led to substantial artifacts from its titanium end, and we decided to discontinue the procedure. In another case (Patient 3), the CT examination was aborted, because of mechanical difficulties with movement
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Table 2. The patients and the dynamic IACTA results Separation from nidus Patient*
Age, yr/gender
Prior treatment
Infusion vessel†
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
19/M 37/M 8/F 27/M 67/M 21/F 33/M 53/F 25/M 47/M 11/F 49/F 18/M 33/M 17/F 24/F 54/F 39/M 28/M 50/M 20/F 18/F
Embolization Embolization Radiosurgery Hematoma evacuation Hematoma evacuation Embolization Embolization Hematoma evacuation Embolization -
L VA R ICA L VA R ICA L ICA L ICA R ICA R VA L ICA R ICA L ICA, L VA R ICA L ICA R ICA R ICA L ICA R ICA L ICA L ICA R ICA L ICA, L VA R VA
Nidus volume (mL)
Draining vein‡
Draining vein
0.4 0.6 0.7 0.9 1.4 1.5 2.3 2.7 3.0 3.8 4.0 4.1 5.4 5.5 5.5 7.5 7.9 10.8 12.6 13.2 17.1 30.8
Deep Deep Deep Deep Superficial Deep Deep Deep Deep Superficial Deep Superficial Deep Deep Superficial Superficial Deep Superficial Deep Superficial Superficial Deep
Poor Poor Good Good No dynamic scans Good Poor Good Good Fair Poor Good Fair Fair Poor No dynamic scans Good Fair Good Fair Good Poor Good Good Good Fair Good Good Good Fair Good Poor Good Good Good Fair Poor Poor Good Fair Good Good
Feeding artery
Abbreviations: IACTA ⫽ intra-arterial computed tomography angiography; L ⫽ left; R ⫽ right; VA ⫽ vertebral artery; ICA ⫽ internal carotid artery. * Patients are sorted by the volume of the nidus. † Lower-case arteries were examined only by helical IACTA. ‡ Deep or superficial is based on the criteria of Spetzler-Martin grade (31)
of the examination table. In both cases, we used data obtained by MRA for treatment planning. The collimation width used for dynamic IACTA was 3 mm in all cases, except in the case with the largest nidus (Patient 22); in this situation, we used a 5-mm collimation width. During each of the examinations, the section interval was the same as the collimation width and kept constant for the entire series of dynamic IACTA. An average of 2.8 mL of contrast material was injected. This dose produced maximum attenuation in the lesion (measured at the reference points) of 862 ⫾ 239 HU. A retrospective review of IACTA was performed to assess the effectiveness of the dynamic scans. First, a dynamic series close to the center of the nidus was selected from the dynamic IACTA, and some reference points were then selected from the target series. The reference points chosen ranged from one of the closest points to the center of the lesion, so as to reflect each vascular component (i.e., the supplying arteries and draining veins and the nidus). The points on the orthogonal DSA images corresponding to the chosen reference points were identified using the stereotactic coordinates of the reference points. The nature of the reference points was confirmed by knowledge of both the connections of the vessels to known vascular structures and the enhancement patterns of the corresponding points on the DSA
series. Separation of each of the vascular components was assessed from the enhancement patterns of the reference points on the IACTA series. From the contrast enhancement pattern of the reference points on the dynamic CT series, the reference points were classified into three categories by peak time in time–attenuation curves. For example, if the peak times of the selected reference points in all of the feeding arteries and in one of the nidi were more than 2 images
Fig. 2. Efficacy of dynamic scan in separating nearby vessels (draining veins, supplying arteries) from the nidi. From the top of the column, “good” (more than 2 images or 0.4 s apart in peak times of the enhancement), “fair” (an image apart), and “poor” (no difference among the peak times).
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Fig. 3. (a) Posterofrontal and (b) lateral DSA, and (c) 3D spoiled gradient-recalled echo MRI images of a left frontal AVM in the territory of the left internal carotid artery (Patient 11). (d) Dynamic IACTA images at the nidus are shown. The elapsed time after the start of scanning is indicated under each image. An averaged image of the dynamic scans is shown at the right bottom. Note that a vascular structure (arrow) was not apparent until the image at 2.0 s, and remained after most of the other vessels had disappeared; this structure was recognized as a vein. The CT images were photographed with a window width of 1500 HU and level of 770 HU. The locations of the reference points are specified on (e) a helical IACTA image, which is at the same craniocaudal position as the (d) dynamic IACTA. The (f) time–attenuation curves of the (e) reference points are also shown. Point 1 is recognized to be a supplying artery and point 2 the nidus. The delayed enhancement pattern of points 3 and 4 indicates that these points are included in a different hemodynamic component than the nidus, and therefore they are recognized to be draining veins.
apart (0.4 s), the rating was “good.” If the peak times were an image apart (0.2 s), it was “fair,” and if there was no difference among the peak times, it was “poor.” Abil-
ity to distinguish nearby draining veins from the nidus was “good” or “fair” in 18 cases (90%) out of 20, and ability to distinguish feeding arteries was “good” or
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Fig. 3. (Cont’d)
“fair” in 13 cases (65%) (Fig. 2). Some of the cases are shown in Figs. 3– 6. DISCUSSION Angiography enables continuous image acquisition in a very short time after the injection of contrast material into the supplying arteries. In other words, it provides temporal resolution that makes it possible to distinguish arteries and the nidus from surrounding late-enhanced veins by the enhancement pattern of each vascular structure. These features make cerebral angiography the primary imaging method for the diagnosis and evaluation of AVM nidi, as well as of feeding arteries and intranidus aneurysms (13, 14). Despite these advantages, conventional biplanar angiography alone is limited in regard to the three-dimensional definition of AVM nidus margins, especially for irregularly shaped lesions (15, 16). If the shape of the nidus includes dimpling or a recess, angiographic planar images, even when many projections other than orthogonal ones are examined, cannot faithfully reflect the real shape of the target volume (8, 17). Tomographic modalities such as MRI and contrast-enhanced CT are indispensable for determining the exact shape of the lesion in three dimensions (6, 7, 9, 10, 18). CT usually provides better spatial resolution than MRI in axial planes. Moreover, X-ray CT is necessary for precise calculation of radiotherapy dose, because it provides a density distribution of the object from the attenuation of the X-ray; the distribution is then used to obtain the attenuation of the treatment beams. Large field-of-view CT images were usually made to depict the positions of the markers, as well as the target lesion; also, if needed for detailed target delinea-
tion, higher-resolution images could be reconstructed from the raw data. MRI/MRA is often preferred over CT angiography for radiosurgery planning. One reason is that when intravenous CT angiography is combined with DSA, the total amount of contrast enhancement agent may exceed the safety limitation dose of the agent. Because of the complementary characteristics of the stereotactic modalities outlined above, the necessary requirement for a radiosurgery database had been DSA (for temporal information), noncontrast CT (for dose calculation), and MRA (for three-dimensional [3D] shape recognition) before we introduced IACTA for AVM radiosurgery. With our current protocol, all the stereotactic examinations— DSA and CT angiography, as well as noncontrast CT for dose calculation—are carried out in the same room and at the same time. Stereotactic MRI was removed from the protocol, and the period that the patient had to wear the stereotactic frame was substantially shortened. Some other benefits are achieved for CT scans if the contrast enhancement agent is injected via the cerebral arteries. Strong and short duration enhancement of the vascular structure is obtained with small doses of the agent. Short duration of the input contrast material to the target area is able to emphasize the small differences in the enhancement peak of each of the vascular components. The large intensity differential between the vessels and the parenchyma reduces the need for intensity resolution. Consequently, the X-ray output power and the load of the X-ray tube can be minimized. In the present study, the high contrast enhancement allowed visualization of small vessels difficult to locate by other modalities (Fig. 6).
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Fig. 4. An (a) anterior and (b) lateral DSA and (c) stereotactic helical IACTA indicate right frontal AVM (Patient 15). (d) Sagittal and coronal AVM sections were reformatted from the 3D data sets in different enhancement phases of multiple dynamic CT series. Each of the 3D data sets consists of multiple sectional images taken from the dynamic CT series at different craniocaudal positions. Because of that, each voxel in the 3D data set is assumed to be at the same phase of the contrast enhancement. Orthogonal images at 0.4 (1), 0.8 (2), 1.6 (3), and 3.6 (4) seconds after the arrival of the contrast material are shown. “Veins” indicated in (4) by the arrows were not seen in (1). This region of “veins” could be excluded from the radiosurgery target volume.
Role of MRA in target delineation Kondziolka et al. studied the accuracy and usefulness of stereotactic MRA for AVM radiosurgery in 28 patients (9). In 24 patients, MRA information equaled that of conven-
tional angiography. In 3 patients, MRA was better because conventional angiography overestimated the size of the AVM nidus. Bednarz et al. evaluated the advantages of using 3D
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Fig. 5. An (a) anterior angiography and a (b) lateral DSA indicate right frontal AVM partially treated by embolization (Patient 2). Helical IACTA images (c) with contrast enhancement and (d) without contrast enhancement are shown (window width 1000, level 40). It is difficult to delineate the nidus, because of the high-density embolic material in the vessels (black arrowheads). Markers of the stereotactic indicator are shown with white arrows. (e) T1-weighted MRI and (f) 3D time-of-flight MRA are not clear in demonstrating the vascular structure of the lesion. (g) Dynamic IACTA was carried out by right internal carotid infusion of the contrast enhancement material. An image of a dynamic scan before the arrival of the contrast enhancement material visualized the embolic material. The embolized material remaining in the vessel hampered clear demonstration of the vascular structures in and around the lesion. When a pre-enhanced image was subtracted from the enhanced images, hemodynamic alteration of the vessels was clearly demonstrated.
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Fig. 5. (Cont’d)
time-of-flight MRA in obtaining three-dimensional information on the nidus (19). The treatment plans were modified by the MRA information in 12 out of 22 cases (55%): The target volumes were reduced. Nevertheless, in 10 cases (45%), both MRI and MRA failed to detect the nidus, because of surgical clip artifacts and the presence of embolization material. Phase-contrast MRA is free from this effect, but it may fail to detect slow blood flow around the nidus (7, 20). Inhomogeneity of the magnetic field in magnetic resonance devices may cause image distortion, and it is often more prominent at the peripheral area of the field of view, where the fiducial markers are (21, 22). Therefore, time-of-flight or phase-contrast MRA, as well as conventional CT angiography, is often useful in delineating target volume for an irregularly shaped nidus. However, because of the nature of the modality, the images are static and do not provide temporal resolution as conventional angiography does. Essig et al. reported the use of dynamic MRA based on a blood bolus tagging technique for the treatment planning of AVM radiosurgery (23). This method has the advantage of providing the hemodynamic information on the vascular lesion. The authors reported that dynamic MRA was able to demonstrate the AVM characteristics and hemodynamics in 12 out of 20 patients. However, because of the low signal: noise ratio, only a single or very limited number of readout sections are applied over the whole range of the lesion; thus, it has substantially no resolution perpendicular to the readout section and lacks a true three-dimensional representation of the vascular structures. Because of this limitation, the role of this method in precise delineation of the radio-
surgery target volume is diminished. In addition, this technique could not reliably depict the malformation in 3 patients with nidi smaller than 1 cm.
Role of dynamic IACTA Possible consequences of irradiation damage to draining veins include venous thrombosis, which in turn could lead to higher blood pressure of the nidus wall, resulting in a risk of accidental hemorrhage (3, 4). Thus, to minimize complications, draining veins should be kept outside the radiosurgery irradiation volume. Dynamic IACTA was performed with 0.8-s rotation of the gantry, and four images were generated from full rotational data using a 180° reconstruction method. Although there was a 90° overlap for each image, the image interval was 0.2 s. Apparently, dynamic IACTA has less temporal resolution than DSA has. A relatively long acquisition time is required for each CT image (0.4 s for 180° reconstruction), whereas for each DSA image, the required duration of acquisition time is very short. Nevertheless, we reconstructed images with 0.2-s intervals to find out when the enhancement of each vessel component begins and where the peaks of the attenuation curves are. Another advantage of dynamic IACTA over DSA is that there are no spatial overlaps of the structure in sectional IACTA. Probably because of the high contrast enhancement effect and the rapid changes in attenuation of the vascular structures, our results indicate a relatively high sensitivity of separation of veins from other vascular components. The nature of the sectional images may also contribute to vessel
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Fig. 6. (a) A right posterior cerebral arterial territory AVM (Patient 1: arrow) was detected by super-selective DSA performed after the onset of the hemorrhage. Because the nidus was small and faint, it was very hard to locate its exact coordinates by stereotactic DSA. Both (b) helical and dynamic scans clearly identified the nidus position. However, the enhancement pattern of the nidus was similar to that of nearby vessels, and it was difficult to separate arteries and veins from the nidus according to the enhancement pattern. (c) MRI could not identify the position of the nidus because of methemoglobin deposition.
separations. The time–attenuation curves and images could indicate fairly well the differences in the enhancement pattern of each vascular structure, as shown in Figs. 3, 4, and 5. Hybrid angio-CT system Our protocol was based on a hybrid angio-CT system (11, 24) that is able to make the IACTA for various organs a practical and safe procedure by eliminating the need for patient transportation and reducing examination time. As far
as we know, more than 100 units of this system, produced by a number of different manufacturers, have already been installed in recent years. However, at this moment, it is not very realistic for every radiosurgery suite to install this system in terms of cost and space for the additional CT scanner. This system was originally developed for use in abdominal interventional radiology, such as in investigating the contribution of portal blood flow to hepatic tumors or in confirming the territory area of a vessel before embolization (24). Hirai et al. used this for preoperative evaluation of
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intracranial aneurysms (11). However, to our knowledge there have been no other published reports on the use of this system for neuroradiologic purposes. The price of a CT scanner is decreasing, and its performance is dramatically improving. New applications for the angio-CT system, such as radiosurgery planning, will increase the range of use and cost-effectiveness of the system. Patient safety Although AVM is already associated with relatively high treatment-related risks as well as risk of hemorrhage from the nidus (25, 26), the risk related to IACTA must still be assessed and minimized. IACTA reduces the need for additional angiographic projections and super-selective procedures. Moreover, the more precise delineation of the nidus is expected to increase the probability of cure and to reduce the risk of complications. The rate of neurologic complications after cerebral angiography has been reported as 1% in most of the recent studies, and the rate of persistent neurologic deficit has been reported as 0.3%– 0.4% (27–29). In their retrospective study of 483 cerebral angiographic examinations, Leffers and Wagner reported a total complication rate of 2.3%, and they found no clear relationship between the incidence rate and the number of series performed (30). Although modern cerebral angiography carries a low risk for permanent neurologic or systemic complications when performed by experienced neuroradiologists (16), the IACTA procedure is potentially associated with some risk of complication, even though this risk is, we believe, much less than that of super-selective or embolization procedures. Therefore, the potential risk factor of IACTA should be assessed and minimized. The time that the catheter is inserted into the infusion vessels should be as short as possible to avoid the potential risk of angiographic complications. Because the X-ray tube is heated by repeated dynamic or helical scans, the IACTA protocol potentially requires relatively long cooling times, so we optimized the X-ray exposure protocol to minimize the tube load. A current of 60 mA is now used throughout the examinations, including the helical and dynamic scans. Duration of the dynamic scan has been minimized to 8 s. Because the start and stop of the anode rotation produce considerable heat in the X-ray tube, a dynamic series set with a constant interval of 20 s between the series was programmed before the start of the scans so that the anode of the X-ray tube continuously rotated. As a result, more than 10 dynamic scans and two helical scans could be performed without having to wait for the tube to cool. Consequently, we have been able to reduce the time required for IACTA to less than 7 min. If a case occurs where multiple vessels need to be examined by multiple helical and dynamic series, adequate cooling time should be allocated during the examination of each of the vessels. We watched the intensity changes of the vessels through real-time reconstruction of CT scans. The injection speed was almost as slow as, and the amount of the contrast agent
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was almost as little as, that of manual test injections performed for confirmation of the catheter position in the vascular system. This low infusion speed reduced the possibility of catheter tip recoil. Comparison with MRA We have not experienced enough cases to assess the exact sensitivity of dynamic IACTA in detecting the separation of the vascular components of AVMs; also, MRA studies were not routinely performed at the same time as IACTA. Therefore, at present, quantitative comparison between IACTA and MRA in precise delineation of the nidus is yet to be performed. Nevertheless, we believe that the nature of IACTA that enables us temporal analysis of the hemodynamics provides some superiority in the delineation, and we experienced a number of cases where MRA failed and IACTA was effective, as shown in the figures. On the other hand, the failed cases give us an indication of the types of cases for which dynamic CT is unlikely to produce meaningful results on the separation of the vascular components. In one of two failed cases in the separation of draining veins (Patient 1, Fig. 6), the dynamic images indicated no prominent draining vein in the target area. (Because of the very small nidus in this case, DSA was not only unable to indicate the draining vein, but also had difficulty in locating the nidus clearly; and MRI/A localization failed, because of methemoglobin deposition.) In another failed case (Patient 20), there was a very high flow nidus, and prominent draining veins were visualized. Probably because of the high flow, there was no substantial difference in enhancement pattern between the nidus and the draining vein. For AVMs that have direct arteriovenous shunts, dynamic IACTA may have limited value in separating nearby draining veins from the nidus. From the standpoint of cost-effectiveness or minimizing examination time, dynamic IACTA is not always required for the patients who have very high flow nidus. However, we believe that helical IACTA is beneficial for all cases. The information from helical IACTA is similar to that of MRI/MRA in terms of radiosurgery planning, and helical IACTA can be performed with one additional injection in a short time when an angio-CT system is used. Advantages for the patients with this procedure are the following: They are not required to be transported to another room for MRI or i.v. CT angiography, and the time that they are required to wear the frame is significantly shortened. One of the inherent advantages of MRA over IACTA is that MRA alone has almost no risk of complication when a contrast enhancement agent is not administered. However, at present a combination of MRA and angiography (DSA) is usually applied for radiosurgery planning, and despite its potential risk, angiography is not omitted. Therefore, the combined risk of MRA and DSA should be compared with that of IACTA and DSA. As we mentioned previously, IACTA and DSA are performed one after the other in the same room with the same kind of contrast agent. A longer
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catheter insertion time, as well as additional infusions of contrast material, is thought to be the only factor that may increase risk. So, we believe that the difference in risk factor with DSA alone (or with MRA) compared with DSA followed by IACTA is minimal. Use of IACTA for radiosurgery planning will be justified when enough benefit is obtained from precise target delineation. On the other hand, we do not recommend the routine use of the IACTA procedure for follow-up studies after radiosurgery. In most cases, MRA and DSA sufficiently evaluate the shrinkage and obliteration of the lesion. Another advantage of MRI/A is that MRI instruments are currently installed in almost every major institute. On the other hand, use of IACTA for neuroradiology is limited, because a special DSA-CT combination is required. We do not recommend carrying a patient from room to room while a catheter is inserted in the carotid or vertebral arteries.
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CONCLUSION In conclusion, intra-arterial CT angiography using a hybrid angio-CT system was safely and effectively performed for radiosurgery planning. All the stereotactic examinations were performed in the same room, and conventional CT and MRI could be removed from the protocol. The period that the patient had to wear the frame was substantially shortened. For these reasons, helical IACTA has an advantage over MRI/A or conventional CT for radiosurgery planning. Because IACTA requires only a small dose of contrast agent, repeated dynamic scans can be performed. In 18 of 20 cases, dynamic IACTA provided temporal information that was helpful in excluding draining veins from the target volume. On the other hand, supplying arteries were rather difficult to separate according to enhancement patterns. If previous stereotactic DSA indicates a very high flow nidus, dynamic IACTA may be omitted.
REFERENCES 1. Lunsford LD, Kondziolka D, Bissonette DJ, et al. Stereotactic radiosurgery of brain vascular malformations. Neurosurg Clin N Am 1992;3:79 –98. 2. Saunders WM, Winston KR, Siddon RL, et al. Radiosurgery for arteriovenous malformations of the brain using a standard linear accelerator: Rationale and technique. Int J Radiat Oncol Biol Phys 1988;15:441– 447. 3. Awad IA, Magdinec M, Schubert A. Intracranial hypertension after resection of cerebral arteriovenous malformations. Predisposing factors and management strategy. Stroke 1994;25: 611– 620. 4. Pollock BE. Occlusive hyperemia: A radiosurgical phenomenon? Neurosurgery 2000;47:1178 –1182 discussion 1182–1174. 5. Levy RP, Schulte RW, Frankel KA, et al. Computed tomography slice-by-slice target-volume delineation for stereotactic proton irradiation of large intracranial arteriovenous malformations: An iterative approach using angiography, computed tomography, and magnetic resonance imaging. Int J Radiat Oncol Biol Phys 1996;35:555–564. 6. Rieger J, Hosten N, Neumann K, et al. Initial clinical experience with spiral CT and 3D arterial reconstruction in intracranial aneurysms and arteriovenous malformations. Neuroradiology 1996;38:245–251. 7. Tanaka H, Numaguchi Y, Konno S, et al. Initial experience with helical CT and 3D reconstruction in therapeutic planning of cerebral AVMs: Comparison with 3D time-of-flight MRA and digital subtraction angiography. J Comput Assist Tomogr 1997;21:811– 817. 8. Bova FJ, Friedman WA. Stereotactic angiography: An inadequate database for radiosurgery? Int J Radiat Oncol Biol Phys 1991;20:891– 895. 9. Kondziolka D, Lunsford LD, Kanal E, et al. Stereotactic magnetic resonance angiography for targeting in arteriovenous malformation radiosurgery. Neurosurgery 1994;35:585–590. 10. Gorzer H, Heimberger K, Schindler E. Spiral CT angiography with digital subtraction of extra- and intracranial vessels. J Comput Assist Tomogr 1994;18:839 – 841. 11. Hirai T, Korogi Y, Ono K, et al. Preoperative evaluation of intracranial aneurysms: Usefulness of intraarterial 3D CT angiography and conventional angiography with a combined unit—initial experience. Radiology 2001;220:499 –505. 12. Tanami Y, Kunieda E, Onozuka S, et al. Intra-arterial an-
13.
14.
15.
16.
17. 18.
19.
20.
21.
22. 23.
gio-CT for radiosurgery of cerebral arteriovenous malformations [published in Japanese]. Rinsyo Housyasen 1998;43: 929 –933. Guo WY, Lindqvist M, Lindquist C, et al. Stereotaxic angiography in gamma knife radiosurgery of intracranial arteriovenous malformations. AJNR Am J Neuroradiol 1992;13:1107–1114. Foroni R, Gerosa M, Pasqualin A, et al. Shape recovery and volume calculation from biplane angiography in the stereotactic radiosurgical treatment of arteriovenous malformations. Int J Radiat Oncol Biol Phys 1996;35:565–577. Blatt DR, Friedman WA, Bova FJ. Modifications based on computed tomographic imaging in planning the radiosurgical treatment of arteriovenous malformations. Neurosurgery 1993;33:588 –595. Pollock BE, Kondziolka D, Flickinger JC, et al. Magnetic resonance imaging: An accurate method to evaluate arteriovenous malformations after stereotactic radiosurgery [see comments]. J Neurosurg 1996;85:1044 –1049. Spiegelmann R, Friedman WA, Bova FJ. Limitations of angiographic target localization in planning radiosurgical treatment. Neurosurgery 1992;30:619 – 623. Guo WY, Nordell B, Karlsson B, et al. Target delineation in radiosurgery for cerebral arteriovenous malformations. Assessment of the value of stereotaxic MR imaging and MR angiography. Acta Radiol 1993;34:457– 463. Bednarz G, Downes B, Werner-Wasik M, Rosenwasser RH. Combining stereotactic angiography and 3D time-of-flight magnetic resonance angiography in treatment planning for arteriovenous malformation radiosurgery. Int J Radiat Oncol Biol Phys 2000;46:1149 –1154. Huston J, Rufenacht DA, Ehman RL, et al. Intracranial aneurysms and vascular malformations: Comparison of time-offlight and phase-contrast MR angiography. Radiology 1991; 181:721–730. Kondziolka D, Dempsey PK, Lunsford LD, et al. A comparison between magnetic resonance imaging and computed tomography for stereotactic coordinate determination. Neurosurgery 1992;30:402– 406. Meuli RA, Verdun FR, Bochud FO, et al. Assessment of MR image deformation for stereotactic neurosurgery using a tagging sequence. AJNR Am J Neuroradiol 1994;15:45– 49. Essig M, Engenhart R, Knopp MV, et al. Cerebral arterio-
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24. 25. 26. 27.
venous malformations: Improved nidus demarcation by means of dynamic tagging MR-angiography. Magn Reson Imaging 1996;14:227–233. Capasso P, Trotteur G, Flandroy P, et al. A combined CT and angiography suite with a pivoting table. Radiology 1996;199: 561–563. Brown RD, Jr, Wiebers DO, Forbes G, et al. The natural history of unruptured intracranial arteriovenous malformations. J Neurosurg 1988;68:352–357. Pollock BE, Flickinger JC, Lunsford LD, et al. Factors that predict the bleeding risk of cerebral arteriovenous malformations. Stroke 1996;27:1– 6. Grzyska U, Freitag J, Zeumer H. Selective cerebral intraarte-
28. 29. 30. 31.
● E. KUNIEDA et al.
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rial DSA. Complication rate and control of risk factors. Neuroradiology 1990;32:296 –299. Heiserman JE, Dean BL, Hodak JA, et al. Neurologic complications of cerebral angiography. AJNR Am J Neuroradiol 1994;15:1401–1407 discussion 1408 –1411. Waugh JR, Sacharias N. Arteriographic complications in the DSA era. Radiology 1992;182:243–246. Leffers AM, Wagner A. Neurologic complications of cerebral angiography. A retrospective study of complication rate and patient risk factors. Acta Radiol 2000;41:204 –210. Spetzler RF, Martin NA. A proposed grading system for arteriovenous malformations. J Neurosurg 1986;65:476 – 483.