- Email: [email protected]
Benefits of 3D Rotational DSA Compared with 2D DSA in the Evaluation of Intracranial Aneurysm
Benefits of 3D Rotational DSA Compared with 2D DSA in the Evaluation of Intracranial Aneurysm Siong Chuong Wong, MD, MRad, Ouzreiah Nawawi, MBBS, FRCR, Norlisah Ramli, FRCR, Khairul Azmi Abd Kadir, MBBS, MRad Rationale and Objectives: The aim of this study was to compare conventional two-dimensional (2D) digital subtraction angiography (DSA) with three-dimensional (3D) rotational DSA in the investigation of intracranial aneurysm in terms of detection, size measurement, neck diameter, neck delineation, and relationship with surrounding vessels. A further aim was to compare radiation dose, contrast volume, and procedural time between the two protocols. Materials and Methods: Thirty-five patients who presented with subarachnoid bleeds on computed tomography and were suspected of having intracranial aneurysms underwent conventional 2D DSA followed by 3D DSA. The 3D digital subtraction angiographic images were displayed as surface shaded display images. Aneurysm detection, sac size, neck diameter, neck delineation, and relationship of aneurysm to the surrounding vessels analyzed from the two protocols were compared. Radiation dose, contrast volume, and procedural time for both examinations were also compared. Results: Three-dimensional DSA detected 44 aneurysms in 31 patients, with negative findings seen in four patients. A false-negative detection rate of 6.8% (three of 44) for 2D DSA was noted. There was no significant difference in aneurysm size between 3D and 2D DSA. The sizes of aneurysm necks were found to be significantly larger in 3D DSA than on 2D DSA. The aneurysm neck and relationship to surrounding vessels were significantly better demonstrated on 3D DSA than on 2D DSA. Radiation dose (entrance surface dose), contrast use, and procedural time with 3D DSA were significantly less than with 2D DSA. Conclusions: Three-dimensional DSA improves the detection and delineation of intracranial aneurysms, with lower radiation dose, less contrast use, and shorter procedural time compared to 2D DSA. The size of the aneurysm neck on 3D DSA tended to be larger than on 2D DSA. Key Words: Imaging; intracranial aneurysm; cerebral angiography; 3D DSA. ªAUR, 2012
C
erebral aneurysm is a potentially life threatening disorder, which may result in spontaneous subarachnoid hemorrhage and is further complicated by hydrocephalus, vasospasm, and brain infarction. Apart from localizing the aneurysm, the aim of imaging is to measure the size and neck of the aneurysm, as well as determine the relationship of the aneurysm to the surrounding vessels. Imaging a cerebral aneurysm can be done using several imaging methods, with the noninvasive techniques being computed tomographic angiography and magnetic resonance angiography. The introduction of three-dimensional (3D) reconstruction of the rotational angiographic images has given reviewers the advantage of viewing the vascular anatomy in
Acad Radiol 2012; 19:701–707 From the Department of Biomedical Imaging, University Malaya Medical Centre, 59100 Kuala Lumpur, Malaysia (S.C.W., O.N., K.A.A.K.); and the Faculty of Medicine, University Malaya Research Imaging Centre, University Malaya, Kuala Lumpur, Malaysia (N.R.). Received October 25, 2011; accepted February 16, 2012. Address correspondence to: O.N. e-mail: [email protected] ªAUR, 2012 doi:10.1016/j.acra.2012.02.012
any angle and plane, thus making it useful for viewing small aneurysms or aneurysms in areas of arterial branching that may be missed on two-dimensional (2D) angiography. Hochmuth et al (1) reported that compared to biplanar digital subtraction angiography (DSA), 3D rotational angiography allows more accurate depiction of anatomic details that are essential in planning surgical and endovascular treatment for intracranial aneurysms in terms of improving the delineation of aneurysmal neck (71%), the parent vessel (45%), and the relationship to adjacent vessels (50%). In addition, 3D DSA allows the detection of more aneurysms, especially small aneurysms (<3 mm), which are not detected on DSA (1–3). With regard to radiation dose, 3D DSA can also reduce the number of exposures compared to 2D DSA, not only to determine the working projection for therapy but also for procedures (1,4,5). However, unlike in previous studies in which only the standard projections of 2D DSA were compared to 3D DSA, in this study, we included additional 2D digital subtraction angiographic views in the evaluation and comparison. In this study, we aimed to confirm the beneficiary role of 3D DSA in the diagnosis and characterization of cerebral aneurysms and to demonstrate the overall reductions of cost, 701
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time, and radiation dose. This is especially important in a developing nation where resources are scarce, so that procuring expensive equipment must be justified with clear benefits in terms of cost and time savings. MATERIALS AND METHODS Study Design
This was a cross-sectional study including 35 patients who underwent angiography for suspected intracranial aneurysm from August 2008 to November 2009. The patients presented with clinical histories of headache, vomiting, dizziness, neck pain, altered sensorium, and diplopia, with computed tomography showing subarachnoid hemorrhages. The study was carried out with the approval of the hospital’s medical ethics committee. Written informed consent was obtained from patients when possible or from close relatives for patients unfit to give consent. Angiography
All patients were imaged using a Siemens angiographic unit (Axiom-Artis VB30E; Siemens Healthcare, Erlangen, Germany). The C-arm system used was a single-plane AXIOM Artis dFa C-Arm Angiography System (Siemens Healthcare). Image acquisition was performed using a dynamic flat-panel detector system with a 48-cm diagonal entrance plane, producing an image with a 1024 1024 matrix. Ultravist 300 mg I/mL (Schering AG, Berlin, Germany) was used for both 2D DSA and rotational angiography. All catheterizations were performed with femoral artery access. Standard 4-Fr or 5-Fr diagnostic catheters were used to cannulate the intracranial arteries and to perform the angiographic examination. In the first phase of the study (2D DSA), selective angiography of both internal carotid arteries (ICA) and vertebral arteries was performed in the Towne’s, lateral, and oblique views (standard projections). If an aneurysm was detected, additional projections were performed until the aneurysm neck was satisfactorily demonstrated. Following 2D DSA, the second phase of the study (3D rotational DSA) was performed on the vessel that showed or was suspected of having the aneurysm, regardless of the findings on 2D DSA. Precontrast data acquisition was performed with 200 of C-arm rotation, at a total rotation time of 5 seconds at 30 frames/s. This resulted in a C-arm speed of 40 /s. A total of 266 images were produced. The angiography arm then was returned to its initial position, after which a postcontrast rotation, taking another 5 seconds, was performed in the same manner. The images from the contrasted rotational angiogram were subtracted from its equivalent mask per scanner protocol, resulting in rotational digital subtraction angiographic images.
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a multimodality workstation (Leonardo; Siemens Healthcare), on which 3D surface shaded displays (SSDs) of the cerebral vascular supply were reconstructed from the rotational digital subtraction angiographic source data. The 2D digital subtraction angiographic images were reviewed first, followed by the 3D digital subtraction angiographic images. The parameters analyzed were aneurysm detection, aneurysm sac size, aneurysm neck delineation, aneurysm neck diameter, and relationship of the aneurysm to surrounding arteries. Measurement was performed using the built-in automated isocenter calibration system available on the Siemens angiographic unit. A neuroradiologist and an interventional radiologist, each with 8 years of experience, reviewed the images independently. The results were reviewed, and the final decision in case of any discrepancy was reached by consensus between the two reviewers. Measurement of Radiation Dose
The parameters measured were entrance surface dose (ESD), which is the radiation dose to skin at the entrance point of the radiation beam, and total dose-area product (DAP). Both parameters were calculated using the built-in electronic dose-measuring chamber available on the C-arm system. The radiation doses for total 2D DSA (standard and additional views) and for additional views on 2D DSA (only additional views) were measured and compared to the measured 3D DSA radiation dose. Measurement of Contrast Volume
The contrast volumes used for total (standard and additional views) 2D DSA and for additional views on 2D DSA (only additional views) were recorded and compared to the contrast volume used for 3D DSA. Measurement of Procedural Time
Procedural time for 2D DSA was calculated from the time taken to perform the first acquisition until the last acquisition, including additional views. As for 3D DSA, procedural time started from the setup position of the mask rotation until the end of 3D computer subtraction. Statistical Analysis
Statistical analysis of differences between the two techniques in aneurysm sac diameter, neck diameter, radiation dose, contrast volume and procedural time were performed using Mann-Whitney U tests. The difference in aneurysm neck delineation and the relationship of the aneurysm to surrounding vessels was determined using Wilcoxon’s test. Statistical significance for all analyses was taken as P < .05.
Image Analysis
RESULTS
The 2D digital subtraction angiographic images and rotational digital subtraction angiographic raw data were transferred to
Four patients (three men, one woman) had no aneurysms detected on either 2D DSA or 3D DSA. There were 22
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Figure 1. Two-dimensional (2D) digital subtraction angiographic image from lateral acquisition of left internal carotid artery (ICA) run (a) showing a large aneurysm (open black arrow) arising from the supraclinoid part of the left ICA. There was another smaller aneurysm (open white arrows) detected on three-dimensional digital subtraction angiographic lateral (b) and oblique lateral (c) views, close to the large aneurysm, which was not seen on 2D digital subtraction angiography.
women and 13 men recruited in our study, for a ratio of about 2:1. The age range was 16 to 71 years, with a mean age of 50.5 13.5 years. Aneurysm Detection
Forty-four aneurysms were detected on 3D DSA, while 41 aneurysms were detected on 2D DSA, for a false-negative detection rate of three of 44 (6.8%) for 2D DSA. The three aneurysms that were not detected on 2D DSA measured <3 mm in size; one was obscured by a larger aneurysm (Fig 1), and two were hidden by bends in the intracavernous portion of the ICA (Fig 2). Number, Sites and Sizes of Aneurysms
The majority of patients had single aneurysms (26 patients [83.9%] on 2D DSA and 25 patients [80.6%] on 3D DSA). Four patients (12.9%) and three patients (9.7%) had two aneurysms on 2D and 3D DSA, respectively. Two patients (6.5%) had three aneurysms detected only on 3D DSA. The largest number of aneurysms detected in a patient on 2D and 3D DSA was seven, in a patient with hypertension who had undergone renal transplantation. The patient had five aneurysms measuring <5 mm and two aneurysms measuring 5 to 10 mm. Most of the aneurysms were found to arise from the ICA (25%), followed by the anterior communicating artery (23%) and posterior communicating artery (23%). Only one aneurysm originated from the basilar artery. The largest aneurysm measured in our study was a left supraclinoid ICA aneurysm, measuring 23.1 mm on 2D DSA and 22.9 cm on 3D DSA in a patient with hypertension. The smallest aneurysm on 2D DSA measured 1.5 mm but measured 1.1 mm in 3D DSA. Twenty-four aneurysms (58.5%) were found to be larger on 3D DSA than on 2D DSA. Four aneurysms (9.8%) had the same measurements
with both techniques, while 13 of 41 aneurysms measured smaller on 3D DSA than on 2D DSA. However, these differences were not statistically significant. The majority of aneurysms were <5 mm in size. Table 1 summarizes the frequency of aneurysms according to sac size measured on 2D DSA and 3D DSA. View of the Aneurysm Neck
There was a statistically significant difference between 2D and 3D DSA in the capability to delineate the necks of the aneurysms, with better delineation seen on 3D DSA (P < .0005). Three-dimensional DSA was able to clearly delineate the necks of all the aneurysms except one. The same aneurysm was also not well visualized on standard 2D DSA or on the additional acquisitions. The reason for the poor neck visualization was that the aneurysm arose between or straddled across a bifurcation in the distal left middle cerebral artery branches (Fig 3). Table 2 summarizes the delineation of aneurysm necks on 2D DSA and 3D DSA. Diameter of the Aneurysm Neck
The neck diameter could be measured in 31 aneurysms on 2D DSA and 43 aneurysms on 3D DSA. The neck of a fusiform aneurysm located in the anterior communicating artery could not be measured on either 2D or 3D DSA. The diameters of the aneurysm necks were significantly larger (P = .02) on 3D DSA, averaging 3.0 mm, than on 2D DSA, averaging 2.6 mm. Comparing 3D DSA to 2D DSA, aneurysm neck diameters were found to be larger in 22 aneurysms (71%), similar in three (10%), and smaller in six (19%). The largest difference was 2.5 mm, measured in a patient with a bilobar anterior communicating artery aneurysm (Fig 4). 703
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Figure 2. Two-dimensional digital subtraction angiography (DSA) of the left internal carotid artery (ICA) in an anteroposterior (AP) projection (a) did not show any aneurysm. However, the AP (b) and oblique AP (c) projections on three-dimensional DSA showed an aneurysm (open white arrow) arising from the intracavernous part of the left ICA.
TABLE 1. Frequency of Aneurysms According to Sac Size Measured on 2D DSA and 3D DSA 2D DSA
3D DSA
Size Category (mm)
n
%
n
%
1–5 5–10 10–15 15–20 20–25 Total
26 10 3 1 1 41
63.4 24.4 7.3 2.4 2.4 100.0
31 10 1 1 1 44
70.5 22.7 2.3 2.3 2.3 100.0
DSA, digital subtraction angiography; 3D, three-dimensional; 2D, two-dimensional.
(P < .0005 for total 2D DSA total vs 3D DSA, P = .011 for additional views on 2D DSA vs 3D DSA). We also found that the DAP for total 2D DSA (mean, 2797.29 mGym2; maximum, 6428.20 mGym2) was slightly larger than that for 3D DSA (mean, 2632.23 mGym2; maximum, 4666.20 mGym2). However, this difference was not statistically significant. On the other hand, the DAP for 3D DSA was significantly larger (P < .0005) than the DAP for additional views on 2D DSA (mean, 1053.57 mGym2; maximum, 2911.4 mGym2). Significantly (P < .0005) more contrast was used for total 2D acquisitions (mean, 59.46 mL; maximum, 130 mL) and additional views (mean, 33.00 mL; maximum, 90 mL) compared to 3D DSA (mean, 21.1 mL; maximum, 36 mL).
Relationship of the Aneurysm to Surrounding Vessels
Procedural Time
There was a statistically significant difference between 3D DSA and 2D DSA in the capability to delineate aneurysms from the surrounding vessels (P < .0005). On 3D DSA, the relationship of the surrounding vessels to the aneurysm was well delineated for all aneurysms. However, on standard conventional 2D digital subtraction angiographic views, only one aneurysm could be clearly delineated from the surrounding arteries. Using additional 2D views, 23 of the 41 aneurysms became well delineated, but 17 remained obscured by overlying vessels.
The times needed to perform total 2D DSA (mean, 189.2 seconds; maximum, 1345 seconds) and additional views on 2D DSA (mean, 163.10 seconds; maximum, 1325 seconds) were longer than for 3D DSA (mean, 101.7 seconds; maximum, 110 seconds). The difference was statistically significant (P = .028) for total 2D DSA compared to 3D DSA but was not statistically significant for additional views on 2D DSA compared to 3D DSA.
Radiation Dose and Contrast Media Volume
The ESDs for total 2D DSA (mean, 287.14 mGy; maximum, 882.6 mGy) and for additional views on 2D DSA (mean, 173.31 mGy; maximum, 607.60 mGy) significantly exceeded the ESD for 3D DSA (mean, 93.25 mGy; maximum, 165.20 mGy). The differences in ESDs between the two study protocols were statistically significant 704
DISCUSSION In this study, we considered 3D DSA to be the relative ‘‘reference standard’’ compared to 2D DSA. This is because previous studies have stated that there is substantial benefit of the former technique, especially in aneurysm detection, depiction of aneurysm shape, neck location, and relationship to parent artery (1,2,4). The overall incidence of aneurysm detection from spontaneous subarachnoid hemorrhage in our study was 88.6%, which is within the range of previous studies
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Figure 3. Two-dimensional digital subtraction angiography of the left internal carotid artery in an anteroposterior acquisition (a) and oblique projection (b) showing an aneurysm arising from the distal middle cerebral artery, with the neck straddled between a bifurcation (open black arrow). The threedimensional digital subtraction angiographic manipulated image (c) of the same vessel also could not clearly delineate the aneurysm’s neck (open white arrow) from the bifurcation.
TABLE 2. Delineation of Aneurysm Necks on 2D DSA and 3D DSA 2D DSA
3D DSA
Neck View
n
%
n
%
Not well delineated Well delineated Well delineated in additional view Total
19 1 21
46.34 2.44 51.22
1 43 NA
2.27 97.73 NA
41
100.00
44
100.00
NA, not applicable.
(6,7). The average sizes of aneurysms in our study were 5.5 mm on 2D DSA and 5.3 mm on 3D DSA, similar to a study done in Germany (8). Almost all the aneurysms in our study arose from the anterior circulation, in particular the distal ICA, anterior communicating artery, and posterior communicating artery. The recent adoption of 3D rotational angiography has enabled better understanding and discussion of complex intracranial vascular anatomy surrounding aneurysms among interventionists, neuroradiologists, and neurosurgeons (9,10). In addition, patients and their relatives can also be shown the manipulation of SSD images in the explanation of the aneurysm, methods of treatment, and the risks of endovascular therapy. This can promote better understanding of the intracranial vascular anatomy so that patients can be better informed in the decision-making process. Our results show that the main benefit of 3D DSA in neuroradiology is the 3D visualization of complex anatomic vascular patterns, especially aneurysms in difficult locations, complex configurations (multilobulation), and obscurity of the aneurysm neck in standard projections. The visualization of the neck and delineation from surrounding vascular
structures are vastly improved on 3D DSA compared to 2D DSA. This benefits both interventionists and neurosurgeons in terms of improved visualization of aneurysms to their parent vessels and surrounding vascular structure and planning safe treatment. In particular, these benefits enable a more informed decision on whether an aneurysm is better suited for coil placement or surgical clipping. More important, in endovascular treatment, knowledge of detailed anatomy can help in selecting the shape of the coil, configuration of the aneurysm, accurate neck localization, and angiographic working position during coil placement and deployment (11). As documented in previous studies (2,12), our data also show that there is a greater tendency to detect aneurysms on 3D DSA compared to 2D DSA. In our case, this is especially true for aneurysms <4 mm in size. In the standard 2D digital subtraction angiographic projections, these small aneurysms are often obscured by surrounding vessels. In contrast, the multiplanar capability of 3D DSA enables the vessels to be virtually rotated out of the view of small aneurysms, resulting in a higher confidence level for detecting small aneurysms. If 3D DSA were not performed, patients with undetected aneurysms would fall into the angiographically negative subarachnoid hemorrhage group and would routinely be subjected to further investigations and possibly surgical exploration. We used 3D SSD to detect, localize, and measure aneurysm size and the aneurysm neck. Display of aneurysms on 3D SSD involves the selection of a threshold of Hounsfield units (HUs), above which the contrast density within the artery is shaded. Although the threshold of HUs is predetermined by a preset, it may also be changed manually to optimize vessel visualization. The threshold of HUs selected may affect the size of the measured aneurysm, whereby lower a HU threshold may artificially make vessels appear larger and vice versa. Another 3D data set display technique is 705
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Figure 4. Two-dimensional (2D) (a) and three-dimensional (3D) (b) digital subtraction angiographic images showing a bilobar aneurysm arising from the anterior communicating artery. The neck diameter measured smaller on 2D digital subtraction angiography (open black arrow) than on 3D digital subtraction angiography (open white arrow).
maximum-intensity projections (1,4,5). However, maximum-intensity projections are less superior at displaying the morphologic characteristics of aneurysms, although they have similar detection and neck visualization rates to SSD (4). We found that there was no significant difference between the two protocols in the size of the aneurysm sac. This is in contrast to a study done by Kawashima et al (12), who found that aneurysm size was larger on 3D DSA than on 2D DSA. However, we did find a significant difference in the sizes of the aneurysm necks. The sizes of aneurysm necks that could be measured on 2D DSA tended to be smaller compared to 3D DSA. Brijinkji et al have also reported larger measurement of aneurysm neck on 3D SSD than on 2D DSA that led them to suggest that 3D DSA may be inferior to 2D DSA for triage of aneurysms to or from endovascular therapy. However they acknowledged that results may be affected by the type of equipment used to obtain the 3D DSA and the threshold values selected to analyze the 3D SSD images. Also, their study which regarded 2D DSA as the relative ‘reference standard’, did not show if the discrepancy in neck size between the 2 techniques would necessarily alter patient’s management (13). While we agree that neck size is an important factor when deciding between surgical and endovascular therapy, there are also other considerations that would impact clinical decision such as location of aneurysm, degree of angle between the sac and the parent artery, configuration of aneurysm sac, and relationship of the neck from surrounding vessel. These other factors are shown to be better evaluated by 3D DSA than 2D DSA (2,4,11,14). In trying to explain the discrepancy in neck diameters between the two techniques, we offer these contributing factors. First, the angle of rotation may have some effect on the reconstruction and measurement of the neck. Second, the mathematical algorithm used to display the aneurysm may not have been optimized to display the angle of the aneurysm neck. Third, the aneurysm neck, usually being of smaller structure and caliber than the aneurysm, is more affected by 706
the HU threshold selected for the display of SSD images. A phenomenon related to the angle of rotation beam is also known to affect aneurysm neck measurement in 3D images. However, this phenomenon, known as pseudostenosis, causes the aneurysm neck to measure smaller on 3D DSA than on 2D DSA (15). Because of these conflicting findings, further investigation, such as correlation with surgical or endovascular findings, should be undertaken. We noted that 2D DSA resulted in a statistically significant higher ESD compared to 3D DSA. In terms of biologic effect, this means that there is a lower risk for developing deterministic effects, such as skin erythema and cataracts, with 3D DSA compared to 2D DSA. The maximum ESD for 2D DSA recorded in our patients was almost 1 Gy. Fortunately, none of our patients reported any deterministic effect. This may be because the radiation was not consistently concentrated on a single particular area during the procedure. Our results indicate that the risk for deterministic effects on patients would be greatly reduced if 3D DSA were to replace the acquisition of additional views on 2D DSA. The DAP value or stochastic risk of 3D DSA was lower compared to that of total 2D DSA but higher compared to that of additional views on 2D DSA. A previous study also found higher stochastic risk for 3D DSA compared to additional views on 2D DSA (16). The main consideration for stochastic risk is in children and young adults, as the risk for developing malignancy increases in this age group. The DAP is the product of the incident dose and x-ray field area, which are totaled over the entire field of view. For 2D DSA, the fluoroscopic field of view was manually collimated to just within the skull boundary. In contrast, for 3D rotational angiography, the field of view extended beyond the skull margin because of the standard rotational beam. As a result, the cumulated DAP for 3D DSA will be larger than the corresponding DAP for 2D DSA, thus overestimating the patient’s exposed area as well as the risk for stochastic effects.
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We found a significant reduction of contrast use on 3D DSA compared to 2D DSA. This is not surprising, as a single rotational angiographic acquisition requires only a single contrast injection of 18 mL, while 2D DSA necessitates multiple contrast injections because of the multiple projections. The contrast volume reduction would not only provide cost effectiveness but would also be very beneficial in children (16–18). It is also more time saving to perform 3D DSA instead of additional projections on 2D DSA, with an average saving of 1 minute. This time saving is important, especially in critical patients, in whom angiographic procedure time needs to be as short as possible. However, depending on the hardware, 3D DSA reconstruction involves additional time for data transfer and image processing. With more technological advancement in the future, this duration will be reduced. It is important to note that because of the necessity of mask images, both 2D DSA and 3D DSA are susceptible to small motion artifacts. Motion or registration artifacts are a known limitation of subtraction studies. Although this may not affect overall image quality, it may still influence the measurement of size, especially on 3D DSA. Apart from diagnosing and characterizing aneurysms, there are other uses of 3D rotation. Three-dimensional rotation can be used without subtraction for on-table evaluation of postprocedural complications (eg, intracranial hematoma, intraventricular hemorrhage, hydrocephalus, and brain edema), without the need to transfer to a computed tomographic scan (19). In the setting of aneurysm clipping, 3D DSA can also show more aneurysm remnant than 2D DSA (20). Neurosurgeons can also use the information from 3D DSA for guidance of aneurysm surgery (21). CONCLUSIONS In the investigation of intracranial aneurysm, we showed that 3D DSA is better than 2D DSA for delineation of aneurysm from surrounding vessels and visualization of the aneurysm neck. 3D DSA also detects more aneurysms, especially small aneurysms, with significantly lower radiation dose, lesser contrast usage and shorter procedural time than 2D DSA. However, there is a tendency for the aneurysm neck to be measured wider on 3D DSA than in 2D DSA. We recommend that in the investigation of intracranial aneurysm, 3D DSA should be performed following acquisition of standard 2D DSA projections. Additional 2D DSA views are only performed in working projections (derived from 3D DSA) that best depict the neck, for further analysis of the neck size.
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REFERENCES 1. Hochmuth A, Spetzger U, Schumacher M. Comparison of threedimensional rotational angiography with digital subtraction angiography in the assessment of ruptured cerebral aneurysms. AJNR Am J Neuroradiol 2002; 23:1199–1205. 2. van Rooij WJ, Sprengers ME, de Gast AN, et al. 3D rotational angiography: the new gold standard in the detection of additional intracranial aneurysms. AJNR Am J Neuroradiol 2008; 29:976–979. 3. White PM, Teasdale EM, Wardlaw JM, et al. Intracranial aneurysms: CT angiography and MR angiography for detection prospective blinded comparison in a large patient cohort. Radiology 2001; 219:739–749. 4. Sugahara T, Korogi Y, Nakashima K, et al. Comparison of 2D and 3D digital subtraction angiography in evaluation of intracranial aneurysms. AJNR Am J Neuroradiol 2002; 23:1545–1552. 5. Abe T, Hirohata M, Tanaka N, et al. Clinical benefits of rotational 3D angiography in endovascular treatment of ruptured cerebral aneurysm. AJNR Am J Neuroradiol 2002; 23:686–688. 6. Kim BJ, Park KJ, Shin IY, et al. Clinical analysis of spontaneous subarachnoid hemorrhage with negative angiography. Korean J Cerebrovasc Surg 2009; 11:5–11. 7. Suarez JI, Tarr RW, Selman WR. Aneurysmal subarachnoid hemorrhage. N Engl J Med 2006; 354:387–396. 8. Beck J, Rohde S, Berkefeld J, et al. Size and location of ruptured and unruptured intracranial aneurysms measured by 3-dimensional rotational angiography. Surg Neurol 2006; 65:18–25. 9. Tanoue S, Kiyosue H, Kenai H, et al. Three-dimensional reconstructed images after rotational angiography in the evaluation of intracranial aneurysms: surgical correlation. Neurosurgery 2000; 47:866–871. ~o-Duque CH, Guardia-Mas E, de Juan-Delago M, et al. Pre-embo10. Castan lization study of ruptured cerebral aneurysm with rotational and 3D reconstruction angiography. Int Cong Ser 2002; 1247:39–52. 11. Anxionnat R, Bracard S, Ducrocq X, et al. Intracranial aneurysms: clinical value of 3D digital subtraction angiography in the therapeutic decision and endovascular treatment. Radiology 2001; 218:799–808. 12. Kawashima M, Kitahara T, Soma K, et al. Three-dimensional digital subtraction angiography vs two-dimensional digital subtraction angiography for detection of ruptured intracranial aneurysms: a study of 86 aneurysms. Neurol India 2005; 53:287–289. 13. Brinjikji W, Cloft H, Lanzino G, et al. Comparison of 2D digital subtraction angiography and 3D rotational angiography in the evaluation of dome-toneck ratio. AJNR Am J Neuroradiol 2009; 30:831–834. 14. Cognard C, Weill A, Castaings L, et al. Intracranial berry aneurysms: angiographic and clinical results after endovascular treatment. Radiology 1998; 206:499–510. 15. Hirai T, Korogi Y, Ono K, et al. Pseudostenosis phenomenon at volumerendered three-dimensional digital angiography of intracranial arteries: frequency, location, and effect on image evaluation. Radiology 2004; 232:882–887. 16. Racadio JM, Fricke BL, Jones BV, et al. Three-dimensional rotational angiography of neurovascular lesions in pediatric patients. AJR Am J Roentgenol 2006; 186:75–84. 17. Schueler BA, Kallmes DF, Cloft HJ. 3D cerebral angiography: radiation dose comparison with digital subtraction angiography. AJNR Am J Neuroradiol 2005; 26:1898–1901. 18. Bridcut RR, Murphy E, Workman A, et al. Patient dose from 3D rotational neurovascular studies. Br J Radiol 2007; 80:362–366. 19. Brzegowy P, Urbanik A, Popiela TJ. Application 3D DSA and angiographic CT in interventional neuroradiology. Przegl Lek 2010; 67:300–305. 20. Ahn SS, Kim YD. Three-dimensional digital subtraction angiographic evaluation of aneurysm remnants after clip placement. J Korean Neurosurg Soc 2010; 47:185–190. 21. Raabe A, Beck J, Rohde S, et al. Three-dimensional rotational angiography guidance for aneurysm surgery. J Neurosurg 2006; 105:406–411.
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erebral aneurysm is a potentially life threatening disorder, which may result in spontaneous subarachnoid hemorrhage and is further complicated by hydrocephalus, vasospasm, and brain infarction. Apart from localizing the aneurysm, the aim of imaging is to measure the size and neck of the aneurysm, as well as determine the relationship of the aneurysm to the surrounding vessels. Imaging a cerebral aneurysm can be done using several imaging methods, with the noninvasive techniques being computed tomographic angiography and magnetic resonance angiography. The introduction of three-dimensional (3D) reconstruction of the rotational angiographic images has given reviewers the advantage of viewing the vascular anatomy in
Acad Radiol 2012; 19:701–707 From the Department of Biomedical Imaging, University Malaya Medical Centre, 59100 Kuala Lumpur, Malaysia (S.C.W., O.N., K.A.A.K.); and the Faculty of Medicine, University Malaya Research Imaging Centre, University Malaya, Kuala Lumpur, Malaysia (N.R.). Received October 25, 2011; accepted February 16, 2012. Address correspondence to: O.N. e-mail: [email protected] ªAUR, 2012 doi:10.1016/j.acra.2012.02.012
any angle and plane, thus making it useful for viewing small aneurysms or aneurysms in areas of arterial branching that may be missed on two-dimensional (2D) angiography. Hochmuth et al (1) reported that compared to biplanar digital subtraction angiography (DSA), 3D rotational angiography allows more accurate depiction of anatomic details that are essential in planning surgical and endovascular treatment for intracranial aneurysms in terms of improving the delineation of aneurysmal neck (71%), the parent vessel (45%), and the relationship to adjacent vessels (50%). In addition, 3D DSA allows the detection of more aneurysms, especially small aneurysms (<3 mm), which are not detected on DSA (1–3). With regard to radiation dose, 3D DSA can also reduce the number of exposures compared to 2D DSA, not only to determine the working projection for therapy but also for procedures (1,4,5). However, unlike in previous studies in which only the standard projections of 2D DSA were compared to 3D DSA, in this study, we included additional 2D digital subtraction angiographic views in the evaluation and comparison. In this study, we aimed to confirm the beneficiary role of 3D DSA in the diagnosis and characterization of cerebral aneurysms and to demonstrate the overall reductions of cost, 701
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time, and radiation dose. This is especially important in a developing nation where resources are scarce, so that procuring expensive equipment must be justified with clear benefits in terms of cost and time savings. MATERIALS AND METHODS Study Design
This was a cross-sectional study including 35 patients who underwent angiography for suspected intracranial aneurysm from August 2008 to November 2009. The patients presented with clinical histories of headache, vomiting, dizziness, neck pain, altered sensorium, and diplopia, with computed tomography showing subarachnoid hemorrhages. The study was carried out with the approval of the hospital’s medical ethics committee. Written informed consent was obtained from patients when possible or from close relatives for patients unfit to give consent. Angiography
All patients were imaged using a Siemens angiographic unit (Axiom-Artis VB30E; Siemens Healthcare, Erlangen, Germany). The C-arm system used was a single-plane AXIOM Artis dFa C-Arm Angiography System (Siemens Healthcare). Image acquisition was performed using a dynamic flat-panel detector system with a 48-cm diagonal entrance plane, producing an image with a 1024 1024 matrix. Ultravist 300 mg I/mL (Schering AG, Berlin, Germany) was used for both 2D DSA and rotational angiography. All catheterizations were performed with femoral artery access. Standard 4-Fr or 5-Fr diagnostic catheters were used to cannulate the intracranial arteries and to perform the angiographic examination. In the first phase of the study (2D DSA), selective angiography of both internal carotid arteries (ICA) and vertebral arteries was performed in the Towne’s, lateral, and oblique views (standard projections). If an aneurysm was detected, additional projections were performed until the aneurysm neck was satisfactorily demonstrated. Following 2D DSA, the second phase of the study (3D rotational DSA) was performed on the vessel that showed or was suspected of having the aneurysm, regardless of the findings on 2D DSA. Precontrast data acquisition was performed with 200 of C-arm rotation, at a total rotation time of 5 seconds at 30 frames/s. This resulted in a C-arm speed of 40 /s. A total of 266 images were produced. The angiography arm then was returned to its initial position, after which a postcontrast rotation, taking another 5 seconds, was performed in the same manner. The images from the contrasted rotational angiogram were subtracted from its equivalent mask per scanner protocol, resulting in rotational digital subtraction angiographic images.
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a multimodality workstation (Leonardo; Siemens Healthcare), on which 3D surface shaded displays (SSDs) of the cerebral vascular supply were reconstructed from the rotational digital subtraction angiographic source data. The 2D digital subtraction angiographic images were reviewed first, followed by the 3D digital subtraction angiographic images. The parameters analyzed were aneurysm detection, aneurysm sac size, aneurysm neck delineation, aneurysm neck diameter, and relationship of the aneurysm to surrounding arteries. Measurement was performed using the built-in automated isocenter calibration system available on the Siemens angiographic unit. A neuroradiologist and an interventional radiologist, each with 8 years of experience, reviewed the images independently. The results were reviewed, and the final decision in case of any discrepancy was reached by consensus between the two reviewers. Measurement of Radiation Dose
The parameters measured were entrance surface dose (ESD), which is the radiation dose to skin at the entrance point of the radiation beam, and total dose-area product (DAP). Both parameters were calculated using the built-in electronic dose-measuring chamber available on the C-arm system. The radiation doses for total 2D DSA (standard and additional views) and for additional views on 2D DSA (only additional views) were measured and compared to the measured 3D DSA radiation dose. Measurement of Contrast Volume
The contrast volumes used for total (standard and additional views) 2D DSA and for additional views on 2D DSA (only additional views) were recorded and compared to the contrast volume used for 3D DSA. Measurement of Procedural Time
Procedural time for 2D DSA was calculated from the time taken to perform the first acquisition until the last acquisition, including additional views. As for 3D DSA, procedural time started from the setup position of the mask rotation until the end of 3D computer subtraction. Statistical Analysis
Statistical analysis of differences between the two techniques in aneurysm sac diameter, neck diameter, radiation dose, contrast volume and procedural time were performed using Mann-Whitney U tests. The difference in aneurysm neck delineation and the relationship of the aneurysm to surrounding vessels was determined using Wilcoxon’s test. Statistical significance for all analyses was taken as P < .05.
Image Analysis
RESULTS
The 2D digital subtraction angiographic images and rotational digital subtraction angiographic raw data were transferred to
Four patients (three men, one woman) had no aneurysms detected on either 2D DSA or 3D DSA. There were 22
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Figure 1. Two-dimensional (2D) digital subtraction angiographic image from lateral acquisition of left internal carotid artery (ICA) run (a) showing a large aneurysm (open black arrow) arising from the supraclinoid part of the left ICA. There was another smaller aneurysm (open white arrows) detected on three-dimensional digital subtraction angiographic lateral (b) and oblique lateral (c) views, close to the large aneurysm, which was not seen on 2D digital subtraction angiography.
women and 13 men recruited in our study, for a ratio of about 2:1. The age range was 16 to 71 years, with a mean age of 50.5 13.5 years. Aneurysm Detection
Forty-four aneurysms were detected on 3D DSA, while 41 aneurysms were detected on 2D DSA, for a false-negative detection rate of three of 44 (6.8%) for 2D DSA. The three aneurysms that were not detected on 2D DSA measured <3 mm in size; one was obscured by a larger aneurysm (Fig 1), and two were hidden by bends in the intracavernous portion of the ICA (Fig 2). Number, Sites and Sizes of Aneurysms
The majority of patients had single aneurysms (26 patients [83.9%] on 2D DSA and 25 patients [80.6%] on 3D DSA). Four patients (12.9%) and three patients (9.7%) had two aneurysms on 2D and 3D DSA, respectively. Two patients (6.5%) had three aneurysms detected only on 3D DSA. The largest number of aneurysms detected in a patient on 2D and 3D DSA was seven, in a patient with hypertension who had undergone renal transplantation. The patient had five aneurysms measuring <5 mm and two aneurysms measuring 5 to 10 mm. Most of the aneurysms were found to arise from the ICA (25%), followed by the anterior communicating artery (23%) and posterior communicating artery (23%). Only one aneurysm originated from the basilar artery. The largest aneurysm measured in our study was a left supraclinoid ICA aneurysm, measuring 23.1 mm on 2D DSA and 22.9 cm on 3D DSA in a patient with hypertension. The smallest aneurysm on 2D DSA measured 1.5 mm but measured 1.1 mm in 3D DSA. Twenty-four aneurysms (58.5%) were found to be larger on 3D DSA than on 2D DSA. Four aneurysms (9.8%) had the same measurements
with both techniques, while 13 of 41 aneurysms measured smaller on 3D DSA than on 2D DSA. However, these differences were not statistically significant. The majority of aneurysms were <5 mm in size. Table 1 summarizes the frequency of aneurysms according to sac size measured on 2D DSA and 3D DSA. View of the Aneurysm Neck
There was a statistically significant difference between 2D and 3D DSA in the capability to delineate the necks of the aneurysms, with better delineation seen on 3D DSA (P < .0005). Three-dimensional DSA was able to clearly delineate the necks of all the aneurysms except one. The same aneurysm was also not well visualized on standard 2D DSA or on the additional acquisitions. The reason for the poor neck visualization was that the aneurysm arose between or straddled across a bifurcation in the distal left middle cerebral artery branches (Fig 3). Table 2 summarizes the delineation of aneurysm necks on 2D DSA and 3D DSA. Diameter of the Aneurysm Neck
The neck diameter could be measured in 31 aneurysms on 2D DSA and 43 aneurysms on 3D DSA. The neck of a fusiform aneurysm located in the anterior communicating artery could not be measured on either 2D or 3D DSA. The diameters of the aneurysm necks were significantly larger (P = .02) on 3D DSA, averaging 3.0 mm, than on 2D DSA, averaging 2.6 mm. Comparing 3D DSA to 2D DSA, aneurysm neck diameters were found to be larger in 22 aneurysms (71%), similar in three (10%), and smaller in six (19%). The largest difference was 2.5 mm, measured in a patient with a bilobar anterior communicating artery aneurysm (Fig 4). 703
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Figure 2. Two-dimensional digital subtraction angiography (DSA) of the left internal carotid artery (ICA) in an anteroposterior (AP) projection (a) did not show any aneurysm. However, the AP (b) and oblique AP (c) projections on three-dimensional DSA showed an aneurysm (open white arrow) arising from the intracavernous part of the left ICA.
TABLE 1. Frequency of Aneurysms According to Sac Size Measured on 2D DSA and 3D DSA 2D DSA
3D DSA
Size Category (mm)
n
%
n
%
1–5 5–10 10–15 15–20 20–25 Total
26 10 3 1 1 41
63.4 24.4 7.3 2.4 2.4 100.0
31 10 1 1 1 44
70.5 22.7 2.3 2.3 2.3 100.0
DSA, digital subtraction angiography; 3D, three-dimensional; 2D, two-dimensional.
(P < .0005 for total 2D DSA total vs 3D DSA, P = .011 for additional views on 2D DSA vs 3D DSA). We also found that the DAP for total 2D DSA (mean, 2797.29 mGym2; maximum, 6428.20 mGym2) was slightly larger than that for 3D DSA (mean, 2632.23 mGym2; maximum, 4666.20 mGym2). However, this difference was not statistically significant. On the other hand, the DAP for 3D DSA was significantly larger (P < .0005) than the DAP for additional views on 2D DSA (mean, 1053.57 mGym2; maximum, 2911.4 mGym2). Significantly (P < .0005) more contrast was used for total 2D acquisitions (mean, 59.46 mL; maximum, 130 mL) and additional views (mean, 33.00 mL; maximum, 90 mL) compared to 3D DSA (mean, 21.1 mL; maximum, 36 mL).
Relationship of the Aneurysm to Surrounding Vessels
Procedural Time
There was a statistically significant difference between 3D DSA and 2D DSA in the capability to delineate aneurysms from the surrounding vessels (P < .0005). On 3D DSA, the relationship of the surrounding vessels to the aneurysm was well delineated for all aneurysms. However, on standard conventional 2D digital subtraction angiographic views, only one aneurysm could be clearly delineated from the surrounding arteries. Using additional 2D views, 23 of the 41 aneurysms became well delineated, but 17 remained obscured by overlying vessels.
The times needed to perform total 2D DSA (mean, 189.2 seconds; maximum, 1345 seconds) and additional views on 2D DSA (mean, 163.10 seconds; maximum, 1325 seconds) were longer than for 3D DSA (mean, 101.7 seconds; maximum, 110 seconds). The difference was statistically significant (P = .028) for total 2D DSA compared to 3D DSA but was not statistically significant for additional views on 2D DSA compared to 3D DSA.
Radiation Dose and Contrast Media Volume
The ESDs for total 2D DSA (mean, 287.14 mGy; maximum, 882.6 mGy) and for additional views on 2D DSA (mean, 173.31 mGy; maximum, 607.60 mGy) significantly exceeded the ESD for 3D DSA (mean, 93.25 mGy; maximum, 165.20 mGy). The differences in ESDs between the two study protocols were statistically significant 704
DISCUSSION In this study, we considered 3D DSA to be the relative ‘‘reference standard’’ compared to 2D DSA. This is because previous studies have stated that there is substantial benefit of the former technique, especially in aneurysm detection, depiction of aneurysm shape, neck location, and relationship to parent artery (1,2,4). The overall incidence of aneurysm detection from spontaneous subarachnoid hemorrhage in our study was 88.6%, which is within the range of previous studies
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Figure 3. Two-dimensional digital subtraction angiography of the left internal carotid artery in an anteroposterior acquisition (a) and oblique projection (b) showing an aneurysm arising from the distal middle cerebral artery, with the neck straddled between a bifurcation (open black arrow). The threedimensional digital subtraction angiographic manipulated image (c) of the same vessel also could not clearly delineate the aneurysm’s neck (open white arrow) from the bifurcation.
TABLE 2. Delineation of Aneurysm Necks on 2D DSA and 3D DSA 2D DSA
3D DSA
Neck View
n
%
n
%
Not well delineated Well delineated Well delineated in additional view Total
19 1 21
46.34 2.44 51.22
1 43 NA
2.27 97.73 NA
41
100.00
44
100.00
NA, not applicable.
(6,7). The average sizes of aneurysms in our study were 5.5 mm on 2D DSA and 5.3 mm on 3D DSA, similar to a study done in Germany (8). Almost all the aneurysms in our study arose from the anterior circulation, in particular the distal ICA, anterior communicating artery, and posterior communicating artery. The recent adoption of 3D rotational angiography has enabled better understanding and discussion of complex intracranial vascular anatomy surrounding aneurysms among interventionists, neuroradiologists, and neurosurgeons (9,10). In addition, patients and their relatives can also be shown the manipulation of SSD images in the explanation of the aneurysm, methods of treatment, and the risks of endovascular therapy. This can promote better understanding of the intracranial vascular anatomy so that patients can be better informed in the decision-making process. Our results show that the main benefit of 3D DSA in neuroradiology is the 3D visualization of complex anatomic vascular patterns, especially aneurysms in difficult locations, complex configurations (multilobulation), and obscurity of the aneurysm neck in standard projections. The visualization of the neck and delineation from surrounding vascular
structures are vastly improved on 3D DSA compared to 2D DSA. This benefits both interventionists and neurosurgeons in terms of improved visualization of aneurysms to their parent vessels and surrounding vascular structure and planning safe treatment. In particular, these benefits enable a more informed decision on whether an aneurysm is better suited for coil placement or surgical clipping. More important, in endovascular treatment, knowledge of detailed anatomy can help in selecting the shape of the coil, configuration of the aneurysm, accurate neck localization, and angiographic working position during coil placement and deployment (11). As documented in previous studies (2,12), our data also show that there is a greater tendency to detect aneurysms on 3D DSA compared to 2D DSA. In our case, this is especially true for aneurysms <4 mm in size. In the standard 2D digital subtraction angiographic projections, these small aneurysms are often obscured by surrounding vessels. In contrast, the multiplanar capability of 3D DSA enables the vessels to be virtually rotated out of the view of small aneurysms, resulting in a higher confidence level for detecting small aneurysms. If 3D DSA were not performed, patients with undetected aneurysms would fall into the angiographically negative subarachnoid hemorrhage group and would routinely be subjected to further investigations and possibly surgical exploration. We used 3D SSD to detect, localize, and measure aneurysm size and the aneurysm neck. Display of aneurysms on 3D SSD involves the selection of a threshold of Hounsfield units (HUs), above which the contrast density within the artery is shaded. Although the threshold of HUs is predetermined by a preset, it may also be changed manually to optimize vessel visualization. The threshold of HUs selected may affect the size of the measured aneurysm, whereby lower a HU threshold may artificially make vessels appear larger and vice versa. Another 3D data set display technique is 705
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Figure 4. Two-dimensional (2D) (a) and three-dimensional (3D) (b) digital subtraction angiographic images showing a bilobar aneurysm arising from the anterior communicating artery. The neck diameter measured smaller on 2D digital subtraction angiography (open black arrow) than on 3D digital subtraction angiography (open white arrow).
maximum-intensity projections (1,4,5). However, maximum-intensity projections are less superior at displaying the morphologic characteristics of aneurysms, although they have similar detection and neck visualization rates to SSD (4). We found that there was no significant difference between the two protocols in the size of the aneurysm sac. This is in contrast to a study done by Kawashima et al (12), who found that aneurysm size was larger on 3D DSA than on 2D DSA. However, we did find a significant difference in the sizes of the aneurysm necks. The sizes of aneurysm necks that could be measured on 2D DSA tended to be smaller compared to 3D DSA. Brijinkji et al have also reported larger measurement of aneurysm neck on 3D SSD than on 2D DSA that led them to suggest that 3D DSA may be inferior to 2D DSA for triage of aneurysms to or from endovascular therapy. However they acknowledged that results may be affected by the type of equipment used to obtain the 3D DSA and the threshold values selected to analyze the 3D SSD images. Also, their study which regarded 2D DSA as the relative ‘reference standard’, did not show if the discrepancy in neck size between the 2 techniques would necessarily alter patient’s management (13). While we agree that neck size is an important factor when deciding between surgical and endovascular therapy, there are also other considerations that would impact clinical decision such as location of aneurysm, degree of angle between the sac and the parent artery, configuration of aneurysm sac, and relationship of the neck from surrounding vessel. These other factors are shown to be better evaluated by 3D DSA than 2D DSA (2,4,11,14). In trying to explain the discrepancy in neck diameters between the two techniques, we offer these contributing factors. First, the angle of rotation may have some effect on the reconstruction and measurement of the neck. Second, the mathematical algorithm used to display the aneurysm may not have been optimized to display the angle of the aneurysm neck. Third, the aneurysm neck, usually being of smaller structure and caliber than the aneurysm, is more affected by 706
the HU threshold selected for the display of SSD images. A phenomenon related to the angle of rotation beam is also known to affect aneurysm neck measurement in 3D images. However, this phenomenon, known as pseudostenosis, causes the aneurysm neck to measure smaller on 3D DSA than on 2D DSA (15). Because of these conflicting findings, further investigation, such as correlation with surgical or endovascular findings, should be undertaken. We noted that 2D DSA resulted in a statistically significant higher ESD compared to 3D DSA. In terms of biologic effect, this means that there is a lower risk for developing deterministic effects, such as skin erythema and cataracts, with 3D DSA compared to 2D DSA. The maximum ESD for 2D DSA recorded in our patients was almost 1 Gy. Fortunately, none of our patients reported any deterministic effect. This may be because the radiation was not consistently concentrated on a single particular area during the procedure. Our results indicate that the risk for deterministic effects on patients would be greatly reduced if 3D DSA were to replace the acquisition of additional views on 2D DSA. The DAP value or stochastic risk of 3D DSA was lower compared to that of total 2D DSA but higher compared to that of additional views on 2D DSA. A previous study also found higher stochastic risk for 3D DSA compared to additional views on 2D DSA (16). The main consideration for stochastic risk is in children and young adults, as the risk for developing malignancy increases in this age group. The DAP is the product of the incident dose and x-ray field area, which are totaled over the entire field of view. For 2D DSA, the fluoroscopic field of view was manually collimated to just within the skull boundary. In contrast, for 3D rotational angiography, the field of view extended beyond the skull margin because of the standard rotational beam. As a result, the cumulated DAP for 3D DSA will be larger than the corresponding DAP for 2D DSA, thus overestimating the patient’s exposed area as well as the risk for stochastic effects.
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We found a significant reduction of contrast use on 3D DSA compared to 2D DSA. This is not surprising, as a single rotational angiographic acquisition requires only a single contrast injection of 18 mL, while 2D DSA necessitates multiple contrast injections because of the multiple projections. The contrast volume reduction would not only provide cost effectiveness but would also be very beneficial in children (16–18). It is also more time saving to perform 3D DSA instead of additional projections on 2D DSA, with an average saving of 1 minute. This time saving is important, especially in critical patients, in whom angiographic procedure time needs to be as short as possible. However, depending on the hardware, 3D DSA reconstruction involves additional time for data transfer and image processing. With more technological advancement in the future, this duration will be reduced. It is important to note that because of the necessity of mask images, both 2D DSA and 3D DSA are susceptible to small motion artifacts. Motion or registration artifacts are a known limitation of subtraction studies. Although this may not affect overall image quality, it may still influence the measurement of size, especially on 3D DSA. Apart from diagnosing and characterizing aneurysms, there are other uses of 3D rotation. Three-dimensional rotation can be used without subtraction for on-table evaluation of postprocedural complications (eg, intracranial hematoma, intraventricular hemorrhage, hydrocephalus, and brain edema), without the need to transfer to a computed tomographic scan (19). In the setting of aneurysm clipping, 3D DSA can also show more aneurysm remnant than 2D DSA (20). Neurosurgeons can also use the information from 3D DSA for guidance of aneurysm surgery (21). CONCLUSIONS In the investigation of intracranial aneurysm, we showed that 3D DSA is better than 2D DSA for delineation of aneurysm from surrounding vessels and visualization of the aneurysm neck. 3D DSA also detects more aneurysms, especially small aneurysms, with significantly lower radiation dose, lesser contrast usage and shorter procedural time than 2D DSA. However, there is a tendency for the aneurysm neck to be measured wider on 3D DSA than in 2D DSA. We recommend that in the investigation of intracranial aneurysm, 3D DSA should be performed following acquisition of standard 2D DSA projections. Additional 2D DSA views are only performed in working projections (derived from 3D DSA) that best depict the neck, for further analysis of the neck size.
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