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Head and neck imaging with MDCT
European Journal of Radiology 45 (2003) S23 /S31 www.elsevier.com/locate/ejrad
Head and neck imaging with MDCT H. Imhof *, Chr. Czerny, A. Dirisamer Univ. Klinik f. Radiodiagnostik/AKH-Vienna, Abtlg. F. Osteologie, Waehringer Guertel 18-20, A-1090 Vienna, Austria Received 7 November 2002; received in revised form 19 December 2002; accepted 20 December 2002
Abstract Multi-slice CT (MDCT) is rapidly becoming the new standard in radiological imaging. Although its advantages in cardiovascular, thoracic and abdominal imaging are evident, the extent of its usefulness for imaging the head and neck has yet to be clarified. Because of the shorter examination time motion artifacts are reduced, phonation-studies are possible. Due to the thin-slicing and nearly isotropic multiplanar reconstruction (MPR) examination in only one plane is necessary, saving both time and radiation exposure. The shorter examination requires the use of higher concentrated contrast medium (400 mg of iodine/ml). The use of such a contrast medium produces a higher degree of contrast enhancement and provides a 5 /10% higher contrast between the surrounding normal and pathological tissue, but is more time critical. MPRs are easily done in any plane within seconds and enables also threedimensional visualization, what helps in the use of minimal invasive therapy, training and teaching and provides a way of handling the hundreds of images acquired during scanning. # 2003 Elsevier Science Ireland Ltd. All rights reserved. Keywords: 4-Row spiral-CT; 16-Row spiral-CT; Head and neck imaging; Protocols
Multi-slice CT (MDCT) is quickly becoming the new standard in radiological imaging. Between 1998 and 2000 during the introduction of MDCT into the clinical routine diagnosis the advantages in cardiovascular-, thoracic- and abdominal-imaging were evident, while the position of MDCT use in head /neck imaging was relatively unclear. The head and neck region presents a difficult anatomy and physiology for imaging. Almost no other anatomical region in the human body needs such a high level of resolution and additional functional information. There are the most dense but also most thin bones in the human body and very delicate soft tissues. All these factors are enormous technical challenges for any CT machine [1].
* Corresponding author. Tel.: /43-1-40400-5803; fax: /43-140400-3777. E-mail address: [email protected] (H. Imhof).
1. Scan protocols With MDCT the examination time is lower than that required with earlier scanners. This reduces the risk of motion artifacts, for example those caused by breathing, swallowing and patient motion. It is also possible to carry out Valsalva- or phonation-studies to visualize the glottis and vocal cords. MDCT allows high-resolution imaging with 0.5 mm slice thickness and multiplanar reconstructions (MPRs) in all planes (nearly isotropic) without loss of detail resolution (Philips DX 8000 maximal variation in the z -axis: S0.69 /0.99 mm). The length of time of contrast medium administration must be reduced, which lowers the volume required and necessitates the use of high-concentration medium (Tables 1 and 2). Usually any abnormality in medical imaging should be visualized in at least two planes*/in the head and neck axial and coronal planes are the most common ones. With earlier CT Scanners two examinations with doubled radiation exposure were necessary. With
0720-048X/02/$ - see front matter # 2003 Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0720-048X(03)00002-0
H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
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Table 1 4-row MDCT scan protocols for the head and neck region mAs kV Temporal bone Facial head Neck Larynx Tumour E-phonation
Section collimation (mm)
Pitch
Rotation time (s) Volume of contrast (ml)
Flow rate (ml/s) Delay (s)
200 160 186
140 2/0.5 140 4/1 120 4/1
1 1 6.0 od./6.0 0.5 6.0 od./6.0 0.5
/ 100 100
/ 2 2
/ 50 50
186 186
120 4/1 120 4/1
6.0 od./6.0 0.75 6.0 od./6.0 0.75
100 100
2 50
50 2
Siemens Somatom Plus 4 VZ; 300 mg of iodine/ml contrast medium.
MDCT these planes can be obtained in a single examination by isotropic reconstruction, saving both time and radiation exposure to the patient. Retakes due to motion artifacts are much rarer than with previous scanners. Overlapping scans, which increase scanning time and radiation are replaced by the possibility of calculating arbitrarily many overlapping images from one MDCT scan without renewed exposure. Standard protocols have been recommended (Tables 1 and 2). kVp is changed on a regular basis and contrast medium is used routinely except for visualizing the temporal bone or the osseous structures of the paranasal sinuses. In the larynx, biphasic application of contrast injection is used, particularly when viewing carcinoma [2,3].
2. Contrast medium
Fig. 1. Density /time curves showing arrival of standard and highconcentration contrast material in the carotid artery after administration at 2 ml/s.
A clinical study was conducted comparing the efficacy of 120 ml of standard contrast medium (Iomeron (R) 300 (300 mg of iodine/ml)) with that of 90 ml of highconcentration contrast medium (Iomeron (R) 400 (400 mg of iodine/ml)) in MDCT of the head and neck. The flow rate for both types of contrast medium was 2 ml/s. With high-concentration contrast material the peak of the density /time curve is reached earlier and is higher, and the slope of the curve is steeper compared with standard contrast medium (Fig. 1). It is important to bear these factors in mind as good contrast enhancement is essential for visualizing structures such as normal soft tissue structures or carcinoma.
The effect of contrast medium concentration was studied in 35 patients with malignant facial tumours. Twenty-six were male (mean age 599/12.3 years) and 9 were female (mean age 689/11.0 years). Eighteen patients were administered standard contrast medium and 17 received high-concentration contrast medium. The absolute tumour density was less different than expected */1099/25 for the Iomeron 300 group and 1129/33 for the Iomeron 400 group. However, there was a high degree of density variation, which was at least 5/10% in the tumour. It is important to examine a large number of individuals in a study such as this to obtain meaningful results.
Table 2 16-row MDCT scan protocols for the head and neck region
Temporal bone Facial head/praeop. Tu Facial head/postop. Tu Facial head/biphasic
mAs kV Section collimation (mm)
Pitch detector area
Rotation time (s)
Volume of contrast (ml)
Flow rate (ml/ Delay s) (s)
200 200
140 4/0.75 120 16/0.75
0.420/4 0.900/16
0.75 0.75
/ 100/120
/ 2
/ 50/60
150
120 16/1.5
0.900/16
0.75
100/120
2
50/60
200
120 16/0.75
0.900/16
0.75
70/50
5/1
70
Philips DX 8000; 300 mg (400 mg) of iodine/ml contrast medium.
H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
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Fig. 2. MDCT images of a 62-year-old male with a large squamous cell carcinoma of the tongue base (arrows) (a , coronal plane; b , axial plane).
MDCT images of head and neck tumours are shown in Figs. 2 /4. Differentiation between normal and abnormal soft tissue, rather than between the surrounding vessels and the tumour, is a major problem. The degree of contrast obtained is low because hypovascular tumours do not rapidly take up much contrast material. In addition, the peak contrast density differs from one tumour to another, so ideally the contrast protocol needs to be tailored to the patient [4,5], fusion of timely different images is advisable. The results of this study show that compared with 120 ml of the standard contrast medium (300 mg iodine), 90 ml of high-concentration contrast medium (400 mg iodine): . produces a greater degree of contrast enhancement density in the tumour . provides 5 /10% higher contrast between the surrounding normal soft tissue and the tumour . is more time critical . fits better to the higher velocity of the most recent 16row MDCT scanners. With 120 ml of standard contrast medium the enhancement is of lower density and lower contrast, but is less time dependent. This protocol is more suitable for slower CT machines. In the near future, a 32/64-row or even flat panel CT machine may become available that can examine a space of 10/20 cm, for example from the nose to the carina, in one sweep in 6 /8 s or less, with a 1 mm slice thickness or less, 30 mm table increment (or even more) and automatic density measurement in regions of interest. This is technically possible with appropriate software, which must be able to adjust the injection rate and
length automatically to achieve homogeneous contrast density in at least two or three different regions (i.e. a tailored MDCT contrast injection). A double-piston injector connected to the CT scanner (and therefore to the software) is essential for these new machines to enable delivery of a high dose of high-concentration contrast medium in a optimized short injection time. Automatic starting and steering of the scanning procedures and contrast injection depending on the acute measured CT-densities in different anatomic regions would improve the diagnostic capabilities enormously. 2.1. Use in head and neck imaging Currently, in the temporal bone, CT is mainly used in the diagnosis and staging of external and middle ear pathologies, while magnetic resonance imaging (MRI) is the preferred imaging method for abnormalities in the inner ear and internal auditory canal. Both congenital and acquired lesions of the middle ear need to be visualized in two planes to rule out dehiscences and to outline the extent of the disease. With MDCT, only one examination in one plane is necessary. The excellently reconstructed images in the other planes allow shortening of the examination time and reduction of the radiation dose. Klingebiel and Bauknecht evaluated virtual otoscopy in comparison to intraoperative correlation in 200 consecutive patients with clinical suspected middle ear disorders. In 95% of all cases the ossicular chain status was correctly evaluated by virtual otoscopy [6]. In blastomas of the facial head (e.g. squamous cell carcinomas of the sinuses) exact delineation of the tumour (T-staging) pre-therapy is absolutely necessary. This minimizes operation time, allows the use of
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H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
Fig. 4. MDCT images of a 53-year-old male with squamous cell carcinoma of the floor of the mouth, lymph node metastasis and destruction of the mandible. The tumour can be clearly seen (arrows), the surrounding tissue is involved and a large lymph node with central necrosis is visible (a , coronal plane; b , axial plane).
Fig. 3. MDCT images of a 60-year-old female with squamous cell carcinoma (trigonum retromandibulare) (arrows) (a , axial plane; b, coronal plane).
minimally invasive procedures with navigation and exact placement of the radiation port, and helps to establish an exact prognosis. In these patients the intravenous application of contrast medium is essential
in order to visualize and delineate the great vessels, nerves, bony structures and soft tissue compartments that may be involved [5,7]. Bruening et al. could show in 58 patients with suspected laryngeal cancer a sensitivity and specificity of 83% in glottic tumours and 96% in subglottic lesions regarding infiltration of the aryepiglottic folds. Regarding infiltration of the anterior part
H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
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Fig. 5. MDCT image of 57-year-old male with squamous cell carcinoma of the larynx. i.v. injection of 100 ml standard contrast medium. The vessels are very well outlined. There is an extensive destruction of the thyroid cartilage on the left side.
of the vocal cords the results were 92 and 88% accordingly [8] (Fig. 5). Mack et al. evaluated the diagnostic potential of MDCT and secondary reconstructions for the work up of pathologies of the paranasal sinuses. He states that axial MDCT and secondary MPR proves as an optimal imaging modality for the evaluations of the paranasal sinuses in 179 patients [9]. Motion artifacts are rare because of the short examination time. Metal artifacts (beam filtering hardening effects) due to prostheses are minimized by reformatted planes and less prominent with 16-row MDCT (Philips DX 8000) due to thinner slices, and new filtering. The short examination needs an absolute exact timing of contrast medium application.
2.2. Lymph node staging The standard technique worldwide for lymph node staging is CT with an injection of intravenous contrast medium, aiming for homogeneous enhancement. A distance of 20/30 cm needs to be covered for a scan beginning at the skull base and ending at the carina. Ideally, CT at high velocity with excellent contrast resolution and detail resolution is needed, but in practice Table 3 Lymph nodes: criteria for malignancy Size ( /6 /7 mm) Configuration (round shape) Morphology (necrosis, infiltration) Number ( /3) Tumour site (e.g. lower part of the skull, likely; near the ethmoid, unlikely) Tumour histology/stage
Fig. 6. MDCT images of the head region showing lymph nodes of normal size, morphology and normal oval shape (arrows) (a , axial plane; b , coronal plane) (reconstruction).
this is often difficult to achieve. The criteria for malignancy in lymph nodes are listed in Table 3 and some example scans are shown in Figs. 6 and 7. As many as 30/40% of lymph nodes of normal size, morphology and shape in patients with head and neck cancer having metastases are not visible using current CT scanning techniques. Lymph nodes are more clearly shown when high-concentration contrast medium is used. Reactive, enlarged lymph nodes pose a particular problem as there is a strong likelihood that they will be identified as false-positives for metastases using the criteria in Table 2. Round lymph nodes are more likely
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H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
Fig. 8. MDCT image (axial plane) of a patient with squamous cell carcinoma of the head and neck visualized. The indicated lymph node (arrow) is round, enlarged and hilar structures are no longer visible, which is suspicious for malignancy.
Fig. 7. MDCT images of the anterior neck region of a patient with squamous cell carcinoma showing normal sized, round shaped lymph nodes with homogeneous enhancement visualized (a , axial plane; b , axial plane after contrast medium application showing marked enhancement).
to have metastases inside. With this suspicion, imaging in at least two planes should be performed. It should be carried out in the plane in which the lymph node diameter is greatest, and isotropic reconstruction should be used. Central necrosis in an enlarged lymph node and infiltration in the neighbouring muscle indicate malignancy with highest probability. MDCT images of lymph nodes are shown in Figs. 8/10. Lymph nodes are often more clearly visible in their size and shape in the vertical or oblique plane rather
than the axial plane, making them amenable to ultrasound imaging (Figs. 10 and 11). Many physicians in Europe use ultrasound rather than CT. Ultrasound has a number of advantages, including the ability to measure the exact size of a lymph node (this depends on its position in a plane, which can be adjusted) and the possibility of immediate fine needle aspiration. The major problem associated with this technique is its subjectivity. In addition, it cannot be used to visualize retropharyngeal lymph nodes [10]. In contrast to ultrasound, MDCT is objective. With MDCT the planes are adjustable so the exact size of a lymph node can be measured. Homogeneous enhancement of the node is possible, allowing the morphology and degree of muscle invasion to be assessed (Fig. 12). The signs of malignancy in lymph nodes that can best be visualized with CT are central necrosis, with an accuracy of 95/100%, and perilymphatic infiltration, with an accuracy of 90%. Size-measurements of the lymph node have only an accuracy of 45% and the configuration (round shape) of less than 40%. As the incidence of micrometastasis exclusively in clinically NO necks with occult metastases is 25%, no imaging technique will ever reach a sensitivity over 75% without loosing high specificity. This statement may change in the future with the availability of new contrast media, such as ultrasmall superparamagnetic iron oxides in MRI and positron emission tomography [10]. 2.3. Special applications of MDCT MPR is used in MDCT for a number First, it enables different planes to be reducing the radiation dose. Second, it can three-dimensional reconstruction (volume
of reasons. visualized, be used for rendering).
H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
Fig. 9. MDCT images of a patient with squamous cell carcinoma of the head and neck visualized. An enlarged lymph node is visible with marked rim-like enhancement and central necrosis and infiltration of neighbouring muscles, which is a strong indicator of malignancy (arrows). (a and b , axial planes in different levels).
three-dimensional reconstruction is carried out routinely at the University Hospital, Vienna, for prosthesis imaging, intraoperative navigation and virtual endoscopy. Virtual endoscopy using colour-coded volume rendering enables visualization of all of the tissue below the tissue surface. As well as facilitating special applications of MDCT, three-dimensional visualization minimizes the operation time, enables the use of minimal invasive surgery, helps with training and teaching, and provides a way of handling the hundreds of images acquired during scanning.
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Fig. 10. MDCT images of a patient with squamous cell carcinoma of the head and neck visualized (a , b/magnified coronal reconstructions). The lymph node is clearly visible (arrows), again showing central necrosis and infiltration of adjacent muscles.
2.4. Dosimetry According to Euratom 97 /43, dose measurements must be reported for all digital imaging processes carried out in Europe. CT-dose index (CTDI) alone is not sufficient for MDCT as they are just phantom measurements. Moreover CTDI measurements are problematic in that different values are quoted by the various organisations or scanner manufacturers, e.g., the Food and Drug Administration in the US and the 100-value in
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H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
Fig. 11. Ultrasound images of (a) enlarged lymph nodes with no invasion; (b) two lymph nodes with metastasis (visible as the enhancement inside the nodes) in thyroid cancer; (c) a lymph node with central necrosis; (d) invasion of the jugularis vein (JV) (J, jugular vein; N, node; C, common carotid artery).
Fig. 12. MDCT image of a 52-year-old male patient with squamous cell carcinoma of the floor of the mouth visualized. The tumour can be seen invading the surrounding tissue (top arrows) and there is a lymph node metastasis with central necrosis (bottom arrows) (a , coronal plane; b , axial plane).
H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
the EU. Measurement and reproduction of standardized CTDI values (as the CTDI-weighted value) and dose length products on an individual basis are absolute requirements [11]. There are currently no automatic dose limitations according to the size and weight or topogram of patients or to the diameter of the scanned region. In MDCT low pitches, thinner slices and a smaller focus all lead to higher radiation doses. When scanning patients of low weight (e.g. children), the lowest kVp possible must be used to minimize the mAs dose. Software that adjusts the dose automatically according to the measured X-ray attenuation is currently under development modulating the tube current according to the anatomic structures. Noise-reducing filters will also become available to aid in radiation dose reduction in the near future [2]. First results with a 16-row MDCT (Philips DX 8000) proved that the recommended dose for sinus-examinations can be lowered by 80% without loss of diagnostic quality. The CTDI value was 25.3 mGy with 130 mAs (recommended by the manufacturer), while it was only 5.1 mGy with 30 mAs in the diagnostic equivalent low dose sinus-examination [11] in patient with chronic sinusitis and 8.4 mGy with 50 mAs in preoperative patients or patients with septum deviation. Very similar results could be found by Damann et al. in 120 patients with chronic sinusitis. Venema developed a dose simulation program, which aims on doses that are as low as reasonable achievable [12,13]. 2.5. Conclusions MDCT has many advantages over single-row CT. It has a high resolution and shorter examination time, acquired data can be subjected to volume rendering and tailored contrast application is possible. However, gains in examination time may be lost in postprocessing and reporting. The radiation dose must be kept low, using what is necessary rather than what is possible, and
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images should be generated with the maximum acceptable level of noise. In head and neck radiology MDCT will become a nonavoidable standard within the next years.
References [1] Reiser MF, Takahashi M, Modic M, Bruening R. Multislice CT. In: In medical radiology/diagnostic imaging. Berlin, Heidelberg, New York: Springer, 2001. [2] Kalender WA, 2000. Computertomographie. Publicis MCD Verlag. [3] Seeram E. Computed tomography. W.B. Saunders, 2001. [4] Mukherji SK, Castelijns JA. Modern head and neck imaging. In: Medical radiology/diagnostic imaging. Berlin, Heidelberg, New York: Springer, 2000. [5] Baum U, Greess H, Lell M, Nomayr A, Lenz M. Imaging of head and neck tumors */methods. Eur J Radiol 2000;33:153 /60. [6] Bruening R, Sturm C, Hong C, Wollenberg B, Schopf U, Becker C, et al. Die Diagnostik der Stadien T1 und T2 des Larynxkarzinoms mit dem Mehrschicht-Spiral-CT. Radiologe 1999;39:939 / 42. [7] Bruneton JN. Applications of sonography in head and neck pathology. In: Medical Radiology/Diagnostic Imaging. Berlin, Springer, 2002. [8] Bruening RD, Ostertag P, Diebold J. Combined use of MultiDetector CT and Multi-planar reconstructions in the preoperative staging of laryngeal cancer RSNA */88. Annual Meeting 2002, 431. [9] Mack MG, Balzer JO, Baghi M, Schafti S, Herzog MD, Vogl TJ. Multislice Spiral CT and secondary reconstruction of the paranasal sinuses RSNA */88. Annual Meeting 2002, 564. [10] Bruneton JN. Applications of sonography in head and neck pathology. In: Medical radiology/diagnostic imaging. Berlin, Heidelberg, New York: Springer, 2002. [11] Imhof H, Schibany N, Ba-Ssalamah A, Czerny C, Hojreh A, Kainberger F, Krestan C, Kudler H, No¨bauer I, Nowotny R. Spiral-CT and radiation dose. Eur J Radiol, in press. [12] Damann F, Momino-Traserra E, Koitschev A, Baumann I, Claussen CD. Dose reduction with single and multi-row spiralCT in paranasal imaging RSNA */88. Annual Meeting 2002, 376. [13] Venema HW. Simulation of CT-scans with a very low dose as a research tool for ALARA studies RSNA */88. Annual Meeting 2002, 592.
Head and neck imaging with MDCT H. Imhof *, Chr. Czerny, A. Dirisamer Univ. Klinik f. Radiodiagnostik/AKH-Vienna, Abtlg. F. Osteologie, Waehringer Guertel 18-20, A-1090 Vienna, Austria Received 7 November 2002; received in revised form 19 December 2002; accepted 20 December 2002
Abstract Multi-slice CT (MDCT) is rapidly becoming the new standard in radiological imaging. Although its advantages in cardiovascular, thoracic and abdominal imaging are evident, the extent of its usefulness for imaging the head and neck has yet to be clarified. Because of the shorter examination time motion artifacts are reduced, phonation-studies are possible. Due to the thin-slicing and nearly isotropic multiplanar reconstruction (MPR) examination in only one plane is necessary, saving both time and radiation exposure. The shorter examination requires the use of higher concentrated contrast medium (400 mg of iodine/ml). The use of such a contrast medium produces a higher degree of contrast enhancement and provides a 5 /10% higher contrast between the surrounding normal and pathological tissue, but is more time critical. MPRs are easily done in any plane within seconds and enables also threedimensional visualization, what helps in the use of minimal invasive therapy, training and teaching and provides a way of handling the hundreds of images acquired during scanning. # 2003 Elsevier Science Ireland Ltd. All rights reserved. Keywords: 4-Row spiral-CT; 16-Row spiral-CT; Head and neck imaging; Protocols
Multi-slice CT (MDCT) is quickly becoming the new standard in radiological imaging. Between 1998 and 2000 during the introduction of MDCT into the clinical routine diagnosis the advantages in cardiovascular-, thoracic- and abdominal-imaging were evident, while the position of MDCT use in head /neck imaging was relatively unclear. The head and neck region presents a difficult anatomy and physiology for imaging. Almost no other anatomical region in the human body needs such a high level of resolution and additional functional information. There are the most dense but also most thin bones in the human body and very delicate soft tissues. All these factors are enormous technical challenges for any CT machine [1].
* Corresponding author. Tel.: /43-1-40400-5803; fax: /43-140400-3777. E-mail address: [email protected] (H. Imhof).
1. Scan protocols With MDCT the examination time is lower than that required with earlier scanners. This reduces the risk of motion artifacts, for example those caused by breathing, swallowing and patient motion. It is also possible to carry out Valsalva- or phonation-studies to visualize the glottis and vocal cords. MDCT allows high-resolution imaging with 0.5 mm slice thickness and multiplanar reconstructions (MPRs) in all planes (nearly isotropic) without loss of detail resolution (Philips DX 8000 maximal variation in the z -axis: S0.69 /0.99 mm). The length of time of contrast medium administration must be reduced, which lowers the volume required and necessitates the use of high-concentration medium (Tables 1 and 2). Usually any abnormality in medical imaging should be visualized in at least two planes*/in the head and neck axial and coronal planes are the most common ones. With earlier CT Scanners two examinations with doubled radiation exposure were necessary. With
0720-048X/02/$ - see front matter # 2003 Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0720-048X(03)00002-0
H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
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Table 1 4-row MDCT scan protocols for the head and neck region mAs kV Temporal bone Facial head Neck Larynx Tumour E-phonation
Section collimation (mm)
Pitch
Rotation time (s) Volume of contrast (ml)
Flow rate (ml/s) Delay (s)
200 160 186
140 2/0.5 140 4/1 120 4/1
1 1 6.0 od./6.0 0.5 6.0 od./6.0 0.5
/ 100 100
/ 2 2
/ 50 50
186 186
120 4/1 120 4/1
6.0 od./6.0 0.75 6.0 od./6.0 0.75
100 100
2 50
50 2
Siemens Somatom Plus 4 VZ; 300 mg of iodine/ml contrast medium.
MDCT these planes can be obtained in a single examination by isotropic reconstruction, saving both time and radiation exposure to the patient. Retakes due to motion artifacts are much rarer than with previous scanners. Overlapping scans, which increase scanning time and radiation are replaced by the possibility of calculating arbitrarily many overlapping images from one MDCT scan without renewed exposure. Standard protocols have been recommended (Tables 1 and 2). kVp is changed on a regular basis and contrast medium is used routinely except for visualizing the temporal bone or the osseous structures of the paranasal sinuses. In the larynx, biphasic application of contrast injection is used, particularly when viewing carcinoma [2,3].
2. Contrast medium
Fig. 1. Density /time curves showing arrival of standard and highconcentration contrast material in the carotid artery after administration at 2 ml/s.
A clinical study was conducted comparing the efficacy of 120 ml of standard contrast medium (Iomeron (R) 300 (300 mg of iodine/ml)) with that of 90 ml of highconcentration contrast medium (Iomeron (R) 400 (400 mg of iodine/ml)) in MDCT of the head and neck. The flow rate for both types of contrast medium was 2 ml/s. With high-concentration contrast material the peak of the density /time curve is reached earlier and is higher, and the slope of the curve is steeper compared with standard contrast medium (Fig. 1). It is important to bear these factors in mind as good contrast enhancement is essential for visualizing structures such as normal soft tissue structures or carcinoma.
The effect of contrast medium concentration was studied in 35 patients with malignant facial tumours. Twenty-six were male (mean age 599/12.3 years) and 9 were female (mean age 689/11.0 years). Eighteen patients were administered standard contrast medium and 17 received high-concentration contrast medium. The absolute tumour density was less different than expected */1099/25 for the Iomeron 300 group and 1129/33 for the Iomeron 400 group. However, there was a high degree of density variation, which was at least 5/10% in the tumour. It is important to examine a large number of individuals in a study such as this to obtain meaningful results.
Table 2 16-row MDCT scan protocols for the head and neck region
Temporal bone Facial head/praeop. Tu Facial head/postop. Tu Facial head/biphasic
mAs kV Section collimation (mm)
Pitch detector area
Rotation time (s)
Volume of contrast (ml)
Flow rate (ml/ Delay s) (s)
200 200
140 4/0.75 120 16/0.75
0.420/4 0.900/16
0.75 0.75
/ 100/120
/ 2
/ 50/60
150
120 16/1.5
0.900/16
0.75
100/120
2
50/60
200
120 16/0.75
0.900/16
0.75
70/50
5/1
70
Philips DX 8000; 300 mg (400 mg) of iodine/ml contrast medium.
H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
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Fig. 2. MDCT images of a 62-year-old male with a large squamous cell carcinoma of the tongue base (arrows) (a , coronal plane; b , axial plane).
MDCT images of head and neck tumours are shown in Figs. 2 /4. Differentiation between normal and abnormal soft tissue, rather than between the surrounding vessels and the tumour, is a major problem. The degree of contrast obtained is low because hypovascular tumours do not rapidly take up much contrast material. In addition, the peak contrast density differs from one tumour to another, so ideally the contrast protocol needs to be tailored to the patient [4,5], fusion of timely different images is advisable. The results of this study show that compared with 120 ml of the standard contrast medium (300 mg iodine), 90 ml of high-concentration contrast medium (400 mg iodine): . produces a greater degree of contrast enhancement density in the tumour . provides 5 /10% higher contrast between the surrounding normal soft tissue and the tumour . is more time critical . fits better to the higher velocity of the most recent 16row MDCT scanners. With 120 ml of standard contrast medium the enhancement is of lower density and lower contrast, but is less time dependent. This protocol is more suitable for slower CT machines. In the near future, a 32/64-row or even flat panel CT machine may become available that can examine a space of 10/20 cm, for example from the nose to the carina, in one sweep in 6 /8 s or less, with a 1 mm slice thickness or less, 30 mm table increment (or even more) and automatic density measurement in regions of interest. This is technically possible with appropriate software, which must be able to adjust the injection rate and
length automatically to achieve homogeneous contrast density in at least two or three different regions (i.e. a tailored MDCT contrast injection). A double-piston injector connected to the CT scanner (and therefore to the software) is essential for these new machines to enable delivery of a high dose of high-concentration contrast medium in a optimized short injection time. Automatic starting and steering of the scanning procedures and contrast injection depending on the acute measured CT-densities in different anatomic regions would improve the diagnostic capabilities enormously. 2.1. Use in head and neck imaging Currently, in the temporal bone, CT is mainly used in the diagnosis and staging of external and middle ear pathologies, while magnetic resonance imaging (MRI) is the preferred imaging method for abnormalities in the inner ear and internal auditory canal. Both congenital and acquired lesions of the middle ear need to be visualized in two planes to rule out dehiscences and to outline the extent of the disease. With MDCT, only one examination in one plane is necessary. The excellently reconstructed images in the other planes allow shortening of the examination time and reduction of the radiation dose. Klingebiel and Bauknecht evaluated virtual otoscopy in comparison to intraoperative correlation in 200 consecutive patients with clinical suspected middle ear disorders. In 95% of all cases the ossicular chain status was correctly evaluated by virtual otoscopy [6]. In blastomas of the facial head (e.g. squamous cell carcinomas of the sinuses) exact delineation of the tumour (T-staging) pre-therapy is absolutely necessary. This minimizes operation time, allows the use of
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H. Imhof et al. / European Journal of Radiology 45 (2003) S23 /S31
Fig. 4. MDCT images of a 53-year-old male with squamous cell carcinoma of the floor of the mouth, lymph node metastasis and destruction of the mandible. The tumour can be clearly seen (arrows), the surrounding tissue is involved and a large lymph node with central necrosis is visible (a , coronal plane; b , axial plane).
Fig. 3. MDCT images of a 60-year-old female with squamous cell carcinoma (trigonum retromandibulare) (arrows) (a , axial plane; b, coronal plane).
minimally invasive procedures with navigation and exact placement of the radiation port, and helps to establish an exact prognosis. In these patients the intravenous application of contrast medium is essential
in order to visualize and delineate the great vessels, nerves, bony structures and soft tissue compartments that may be involved [5,7]. Bruening et al. could show in 58 patients with suspected laryngeal cancer a sensitivity and specificity of 83% in glottic tumours and 96% in subglottic lesions regarding infiltration of the aryepiglottic folds. Regarding infiltration of the anterior part
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Fig. 5. MDCT image of 57-year-old male with squamous cell carcinoma of the larynx. i.v. injection of 100 ml standard contrast medium. The vessels are very well outlined. There is an extensive destruction of the thyroid cartilage on the left side.
of the vocal cords the results were 92 and 88% accordingly [8] (Fig. 5). Mack et al. evaluated the diagnostic potential of MDCT and secondary reconstructions for the work up of pathologies of the paranasal sinuses. He states that axial MDCT and secondary MPR proves as an optimal imaging modality for the evaluations of the paranasal sinuses in 179 patients [9]. Motion artifacts are rare because of the short examination time. Metal artifacts (beam filtering hardening effects) due to prostheses are minimized by reformatted planes and less prominent with 16-row MDCT (Philips DX 8000) due to thinner slices, and new filtering. The short examination needs an absolute exact timing of contrast medium application.
2.2. Lymph node staging The standard technique worldwide for lymph node staging is CT with an injection of intravenous contrast medium, aiming for homogeneous enhancement. A distance of 20/30 cm needs to be covered for a scan beginning at the skull base and ending at the carina. Ideally, CT at high velocity with excellent contrast resolution and detail resolution is needed, but in practice Table 3 Lymph nodes: criteria for malignancy Size ( /6 /7 mm) Configuration (round shape) Morphology (necrosis, infiltration) Number ( /3) Tumour site (e.g. lower part of the skull, likely; near the ethmoid, unlikely) Tumour histology/stage
Fig. 6. MDCT images of the head region showing lymph nodes of normal size, morphology and normal oval shape (arrows) (a , axial plane; b , coronal plane) (reconstruction).
this is often difficult to achieve. The criteria for malignancy in lymph nodes are listed in Table 3 and some example scans are shown in Figs. 6 and 7. As many as 30/40% of lymph nodes of normal size, morphology and shape in patients with head and neck cancer having metastases are not visible using current CT scanning techniques. Lymph nodes are more clearly shown when high-concentration contrast medium is used. Reactive, enlarged lymph nodes pose a particular problem as there is a strong likelihood that they will be identified as false-positives for metastases using the criteria in Table 2. Round lymph nodes are more likely
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Fig. 8. MDCT image (axial plane) of a patient with squamous cell carcinoma of the head and neck visualized. The indicated lymph node (arrow) is round, enlarged and hilar structures are no longer visible, which is suspicious for malignancy.
Fig. 7. MDCT images of the anterior neck region of a patient with squamous cell carcinoma showing normal sized, round shaped lymph nodes with homogeneous enhancement visualized (a , axial plane; b , axial plane after contrast medium application showing marked enhancement).
to have metastases inside. With this suspicion, imaging in at least two planes should be performed. It should be carried out in the plane in which the lymph node diameter is greatest, and isotropic reconstruction should be used. Central necrosis in an enlarged lymph node and infiltration in the neighbouring muscle indicate malignancy with highest probability. MDCT images of lymph nodes are shown in Figs. 8/10. Lymph nodes are often more clearly visible in their size and shape in the vertical or oblique plane rather
than the axial plane, making them amenable to ultrasound imaging (Figs. 10 and 11). Many physicians in Europe use ultrasound rather than CT. Ultrasound has a number of advantages, including the ability to measure the exact size of a lymph node (this depends on its position in a plane, which can be adjusted) and the possibility of immediate fine needle aspiration. The major problem associated with this technique is its subjectivity. In addition, it cannot be used to visualize retropharyngeal lymph nodes [10]. In contrast to ultrasound, MDCT is objective. With MDCT the planes are adjustable so the exact size of a lymph node can be measured. Homogeneous enhancement of the node is possible, allowing the morphology and degree of muscle invasion to be assessed (Fig. 12). The signs of malignancy in lymph nodes that can best be visualized with CT are central necrosis, with an accuracy of 95/100%, and perilymphatic infiltration, with an accuracy of 90%. Size-measurements of the lymph node have only an accuracy of 45% and the configuration (round shape) of less than 40%. As the incidence of micrometastasis exclusively in clinically NO necks with occult metastases is 25%, no imaging technique will ever reach a sensitivity over 75% without loosing high specificity. This statement may change in the future with the availability of new contrast media, such as ultrasmall superparamagnetic iron oxides in MRI and positron emission tomography [10]. 2.3. Special applications of MDCT MPR is used in MDCT for a number First, it enables different planes to be reducing the radiation dose. Second, it can three-dimensional reconstruction (volume
of reasons. visualized, be used for rendering).
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Fig. 9. MDCT images of a patient with squamous cell carcinoma of the head and neck visualized. An enlarged lymph node is visible with marked rim-like enhancement and central necrosis and infiltration of neighbouring muscles, which is a strong indicator of malignancy (arrows). (a and b , axial planes in different levels).
three-dimensional reconstruction is carried out routinely at the University Hospital, Vienna, for prosthesis imaging, intraoperative navigation and virtual endoscopy. Virtual endoscopy using colour-coded volume rendering enables visualization of all of the tissue below the tissue surface. As well as facilitating special applications of MDCT, three-dimensional visualization minimizes the operation time, enables the use of minimal invasive surgery, helps with training and teaching, and provides a way of handling the hundreds of images acquired during scanning.
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Fig. 10. MDCT images of a patient with squamous cell carcinoma of the head and neck visualized (a , b/magnified coronal reconstructions). The lymph node is clearly visible (arrows), again showing central necrosis and infiltration of adjacent muscles.
2.4. Dosimetry According to Euratom 97 /43, dose measurements must be reported for all digital imaging processes carried out in Europe. CT-dose index (CTDI) alone is not sufficient for MDCT as they are just phantom measurements. Moreover CTDI measurements are problematic in that different values are quoted by the various organisations or scanner manufacturers, e.g., the Food and Drug Administration in the US and the 100-value in
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Fig. 11. Ultrasound images of (a) enlarged lymph nodes with no invasion; (b) two lymph nodes with metastasis (visible as the enhancement inside the nodes) in thyroid cancer; (c) a lymph node with central necrosis; (d) invasion of the jugularis vein (JV) (J, jugular vein; N, node; C, common carotid artery).
Fig. 12. MDCT image of a 52-year-old male patient with squamous cell carcinoma of the floor of the mouth visualized. The tumour can be seen invading the surrounding tissue (top arrows) and there is a lymph node metastasis with central necrosis (bottom arrows) (a , coronal plane; b , axial plane).
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the EU. Measurement and reproduction of standardized CTDI values (as the CTDI-weighted value) and dose length products on an individual basis are absolute requirements [11]. There are currently no automatic dose limitations according to the size and weight or topogram of patients or to the diameter of the scanned region. In MDCT low pitches, thinner slices and a smaller focus all lead to higher radiation doses. When scanning patients of low weight (e.g. children), the lowest kVp possible must be used to minimize the mAs dose. Software that adjusts the dose automatically according to the measured X-ray attenuation is currently under development modulating the tube current according to the anatomic structures. Noise-reducing filters will also become available to aid in radiation dose reduction in the near future [2]. First results with a 16-row MDCT (Philips DX 8000) proved that the recommended dose for sinus-examinations can be lowered by 80% without loss of diagnostic quality. The CTDI value was 25.3 mGy with 130 mAs (recommended by the manufacturer), while it was only 5.1 mGy with 30 mAs in the diagnostic equivalent low dose sinus-examination [11] in patient with chronic sinusitis and 8.4 mGy with 50 mAs in preoperative patients or patients with septum deviation. Very similar results could be found by Damann et al. in 120 patients with chronic sinusitis. Venema developed a dose simulation program, which aims on doses that are as low as reasonable achievable [12,13]. 2.5. Conclusions MDCT has many advantages over single-row CT. It has a high resolution and shorter examination time, acquired data can be subjected to volume rendering and tailored contrast application is possible. However, gains in examination time may be lost in postprocessing and reporting. The radiation dose must be kept low, using what is necessary rather than what is possible, and
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images should be generated with the maximum acceptable level of noise. In head and neck radiology MDCT will become a nonavoidable standard within the next years.
References [1] Reiser MF, Takahashi M, Modic M, Bruening R. Multislice CT. In: In medical radiology/diagnostic imaging. Berlin, Heidelberg, New York: Springer, 2001. [2] Kalender WA, 2000. Computertomographie. Publicis MCD Verlag. [3] Seeram E. Computed tomography. W.B. Saunders, 2001. [4] Mukherji SK, Castelijns JA. Modern head and neck imaging. In: Medical radiology/diagnostic imaging. Berlin, Heidelberg, New York: Springer, 2000. [5] Baum U, Greess H, Lell M, Nomayr A, Lenz M. Imaging of head and neck tumors */methods. Eur J Radiol 2000;33:153 /60. [6] Bruening R, Sturm C, Hong C, Wollenberg B, Schopf U, Becker C, et al. Die Diagnostik der Stadien T1 und T2 des Larynxkarzinoms mit dem Mehrschicht-Spiral-CT. Radiologe 1999;39:939 / 42. [7] Bruneton JN. Applications of sonography in head and neck pathology. In: Medical Radiology/Diagnostic Imaging. Berlin, Springer, 2002. [8] Bruening RD, Ostertag P, Diebold J. Combined use of MultiDetector CT and Multi-planar reconstructions in the preoperative staging of laryngeal cancer RSNA */88. Annual Meeting 2002, 431. [9] Mack MG, Balzer JO, Baghi M, Schafti S, Herzog MD, Vogl TJ. Multislice Spiral CT and secondary reconstruction of the paranasal sinuses RSNA */88. Annual Meeting 2002, 564. [10] Bruneton JN. Applications of sonography in head and neck pathology. In: Medical radiology/diagnostic imaging. Berlin, Heidelberg, New York: Springer, 2002. [11] Imhof H, Schibany N, Ba-Ssalamah A, Czerny C, Hojreh A, Kainberger F, Krestan C, Kudler H, No¨bauer I, Nowotny R. Spiral-CT and radiation dose. Eur J Radiol, in press. [12] Damann F, Momino-Traserra E, Koitschev A, Baumann I, Claussen CD. Dose reduction with single and multi-row spiralCT in paranasal imaging RSNA */88. Annual Meeting 2002, 376. [13] Venema HW. Simulation of CT-scans with a very low dose as a research tool for ALARA studies RSNA */88. Annual Meeting 2002, 592.