Published online before print May 9, 2002, 10.1148/radiol.2241010894
(Radiology 2002;224:171-176.)
© RSNA, 2002
Single-Bolus Technique for Spiral CT of Laryngopharyngeal Squamous Cell Carcinoma: Comparison of Different Contrast Material Volumes, Flow Rates, and Start Delays1
Marc Keberle, MD,
Alexander Tschammler, MD and
Dietbert Hahn, MD
1 From the Department of Radiology, University of Würzburg, Josef-Schneider-Strasse 2, 97080 Würzburg, Germany. Received May 7, 2001; revision requested June 22; revision received October 1; accepted December 18. Address correspondence to M.K. (e-mail: marc.keberle@mail.uni-wuerzburg.de).
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ABSTRACT
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PURPOSE: To evaluate different contrast material volumes, flow rates, and start delays for contrast material enhancement of neck structures and squamous cell carcinoma to determine the most effective examination protocol.
MATERIALS AND METHODS: Seventy patients with squamous cell carcinoma were prospectively randomized into four groups for examination with different protocols (125 mL of contrast material administered at a flow rate of 2.5 mL/sec, 100 mL at 2.0 mL/sec, 90 mL at 1.5 mL/sec, or 70 mL at 1.0 mL/sec). Dynamic series were performed on the tumors and relevant anatomic structures to obtain time-attenuation curves. The protocols were compared (analysis of variance and Tukey-Kramer tests) with regard to time and level of maximum tumor enhancement and carotid arterial enhancement of more than 150 HU. One selected protocol was tested in 30 additional routine examinations with start delays of 40 seconds (for laryngeal and/or hypopharyngeal tumors, 3-mm collimation) and 45 seconds (for oropharyngeal tumors, 5-mm collimation).
RESULTS: Except for the 70-mL bolus administered at 1.0 mL/sec, the other protocols performed similarly well, yielding comparable maximum tumor enhancement at 52 seconds and later. In spite of a smaller volume of 90 mL, due to the prolonged flow time at 1.5 mL/sec, carotid arterial enhancement of more than 150 HU was prolonged (when compared with that in 100- or 125-mL protocols). As a result of these circumstances, injection of 90 mL at 1.5 mL/sec was considered more effective, providing no significant differences in tumor (P = .39) or carotid arterial (P = .52) enhancement between routine examinations and dynamic series.
CONCLUSION: A single bolus of 90 mL administered at 1.5 mL/sec appears to be the most desirable protocol for contrast enhancement.
© RSNA, 2002
Index terms: Computed tomography (CT), helical, 272.12115 • Larynx, CT, 271.12112, 271.12113, 271.12114 • Larynx, neoplasms, 2718.373 • Pharynx, CT, 272.12112, 272.12113, 272.12114 • Pharynx, neoplasms, 272.373
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INTRODUCTION
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Computed tomography (CT) is a widely accepted diagnostic tool for the staging of laryngeal, hypopharyngeal, and oropharyngeal malignancies. However, data on contrast material volumes (60–200 mL), flow rates (0.5–3.0 mL/sec), and start delays (20–90 seconds) vary to a large extent (1-12). Furthermore, there appears to be no consensus about how many boli of contrast material are to be given (single bolus, bolus followed by fast infusion, or two boluses) (Table 1). This can all be explained by the two main goals of this study: (a) detection of pathologically enlarged lymph nodes, requiring adequate contrast material enhancement of neck vessels (for N staging), and (b) exact delineation of the primary tumor (for T staging and volume determinations) (1–16). During preliminary tests, however, we noted that spiral CT performed with a single-bolus technique may accomplish both goals during a diagnostic window of approximately 25 seconds, when vessel opacification is still good (>150 HU) and tumor enhancement is already at a maximum. It is important to determine the most efficient protocol (contrast material volume, flow rate, and start delay) for further improvement of single-bolus CT. The purpose of our study was to evaluate different contrast material volumes, flow rates, and start delays for enhancement of neck structures and squamous cell carcinoma to determine the most effective examination protocol.
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MATERIALS AND METHODS
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Dynamic Series
During a 9-month period, we examined 70 consecutive patients (17 women and 53 men; median age, 60 years; age range, 44–80 years) referred for spiral CT of the neck for tumor staging. In all patients, the histologic diagnosis (from primary surgery [n = 48] or endoscopic biopsy [n = 22]) was squamous cell carcinoma. Our CT findings completely matched these histologic results. The tumors were located in the oral cavity (n = 16), oropharynx (n = 22), hypopharynx (n = 10), supraglottic larynx (n = 12), and glottic larynx (n = 10). CT-based staging yielded nine T1, 22 T2, 17 T3, and 22 T4 tumors.
Twenty patients were randomly assigned to receive 125 mL of the intravenous contrast agent iomeprol (Imeron 300; Byk Gulden, Konstanz, Germany) at a flow rate of 2.5 mL/sec, 20 received 100 mL at 2.0 mL/sec, and 20 received 90 mL at 1.5 mL/sec; the remaining 10 patients were randomly assigned to receive 70 mL at 1.0 mL/sec. We found no significant differences between these groups regarding age (one-way analysis of variance [ANOVA], P = .38) or sex (Table 2). The study was performed according to the ethical standards of the institutional committee on human experimentation, and informed consent was obtained from all patients.
All CT examinations were performed with a spiral CT scanner (Somatom Plus 4; Siemens, Erlangen, Germany). Prior to contrast material administration, a representative nonenhanced scan that showed most of the tumor was obtained. At a delay of 10 seconds after the start of injection, a dynamic series (with 6-second intervals from the beginning of one scan to the beginning of the next scan) was initiated (5-mm collimation; 140 kV; 189 mA; 1.5-second rotation time). The dynamic series was stopped after 15 images were obtained (94 seconds after the start of injection).
On every image (of one dynamic series), attenuation measurements were obtained by placing a constant-sized circular region of interest in the same region in the center of the tumor, the boundary of the tumor, the muscle (sternocleidomastoid and/or pterygoid), and the carotid arteries. In each patient, the size of the region of interest chosen for attenuation measurement was as large as possible but at least 3 mm in diameter. Only homogeneously enhancing parts of the tumors were selected for measurement. To reduce bias, these measurements were repeated at a different location within the tumor (or within the contralateral muscle or artery) by the same person (M.K.). Time-attenuation curves based on the mean attenuations of the tumor boundary, tumor center, muscle, and carotid arteries were obtained. We defined the diagnostic window as the time that carotid arterial opacification of more than 150 HU overlapped the time of maximum enhancement of the tumor boundary. Carotid arterial opacification of more than 150 HU was regarded as sufficient for good delineation between lymph nodes and neck vessels (1). Means of the SDs of the attenuations measured during the diagnostic window (52–76 seconds after the start of injection) were calculated for all aforementioned neck structures and all protocols. To find statistical differences between protocols regarding tumor boundary, tumor center, and muscle at 52, 58, 64, and 70 seconds after the start of injection, two-way ANOVA and Tukey-Kramer tests were performed; regarding enhancement of the carotid artery, one-way ANOVA and Tukey-Kramer tests were performed at the essential time point of 70 seconds after the start of injection.
Routine Examinations
On the basis of the highest level of maximum tumor enhancement, the longest duration of the diagnostic window, and the required contrast material volume, the most effective protocol was used in 30 additional patients who consecutively and routinely underwent examination for tumor staging (140 kV; rotation time, 1.0 second; caudocranial scan direction starting at the thoracic inlet; two different angulations for a lower and upper spiral volume; pitch, 1.5). To remain within the diagnostic window, tumors of the larynx and hypopharynx, which require a smaller collimation of 3 mm within the lower spiral volume, were scanned at a start delay of 40 seconds (274 mA); the rest of the tumors were scanned with a collimation of 5 mm (291 mA) at a start delay of 45 seconds.
There were eight women and 22 men (median age, 58 years; age range, 32–85 years) with tumors of the oral cavity (n = 5), oropharynx (n = 9), hypopharynx (n = 5), supraglottic larynx (n = 7), and glottic larynx (n = 4). At endoscopic biopsy, all tumors proved to be squamous cell carcinoma (two T1, 10 T2, 11 T3, and seven T4 tumors). First, we verified that all tumors were scanned during the diagnostic window. Then, on representative images of each tumor, attenuation measurements of the tumor boundary were obtained as described (within a region of interest of only enhancing tumor parts) and compared with the time-attenuation curve (± SD) for the protocol used during the dynamic series. Moreover, on all images obtained during one examination, attenuation values of the carotid artery were obtained to find any differences between lower and upper spiral volumes. For the upper spiral volume, a carotid arterial opacification of more than 100 HU was considered sufficient. To find statistical differences between routine examinations and dynamic series of the most effective protocol, an unpaired t test was used (regarding enhancement in the tumor boundary and maximum enhancement in the carotid artery).
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RESULTS
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Enhancement of the Carotid Artery
Contrast material injections of 125 mL at 2.5 mL/sec and 100 mL at 2.0 mL/sec resulted in similar curves, with a fast increase, a strong peaklike enhancement (of >230 HU at 52 seconds), and a rapid decrease (Fig 1). The curves reached 150 HU after 75 seconds for 100 mL and 78 seconds for 125 mL. When the point estimate ± SD is considered (Table 3), enhancement is below 150 HU at 70 seconds for both protocols (and at 64 seconds for 100 mL).
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Figure 1. Time-attenuation curves obtained in the carotid artery. Contrast material injections of 125 mL at 2.5 mL/sec and 100 mL at 2.0 mL/sec resulted in more peaked curves, and injections of 90 mL at 1.5 mL/sec and 70 mL at 1.0 mL/sec resulted in more level curves. A volume of 90 mL administered at 1.5 mL/sec appears to provide a reliably long enhancement that is well over 150 HU.
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Injection of 90 mL at 1.5 mL/sec resulted in a curve that increased less rapidly, had a more level enhancement of approximately 190 HU between 40 and 70 seconds, and decreased to 150 HU at 78 seconds. Also, considering the point estimate ± SD (Table 3), enhancement was not below 150 HU at 64 or 70 seconds for this protocol.
Injection of 70 mL at 1.0 mL/sec resulted in a curve that increased even less steeply, reached a level of approximately 160 HU between 52 and 76 seconds, and decreased to 150 HU at 79 seconds. When the point estimate ± SD was taken into account, the attenuation values included those below 150 HU at all times. Moreover, three of 10 individual enhancements were below 150 HU, as opposed to those in the other protocols. For that reason, we stopped using this protocol after 10 patients.
In summary, injections of 125 mL at 2.5 mL/sec and 100 mL at 2.0 mL/sec resulted in more peaked curves, and injections of 90 mL at 1.5 mL/sec and 70 mL at 1.0 mL/sec resulted in more level curves. Also taking account of the point estimate ± SD, in contrast with the other protocols, injection of 90 mL at 1.5 mL/sec provided a delayed enhancement of the carotid artery well over 150 HU until 70 seconds.
Tumor Enhancement
At maximum enhancement, attenuation values in the tumor center were approximately 10 HU lower than those in the tumor boundary, regardless of the protocol (Fig 2). Tumor enhancement was lower after injection of 70 mL at 1.0 mL/sec (in the tumor center, P < .05 at 58, 64, and 70 seconds after the start of injection, as compared with that in the other three protocols), whereas the curves of all three other protocols were not significantly different (P > .05, regarding all possible combinations between the protocols during the diagnostic window), reaching a maximum level of approximately 90 HU at 52 seconds in the tumor boundary (compare also Fig 3). For the tumor boundary, the results of ANOVA were P = .08, .12, .66, and .62 at 52, 58, 64, and 70 seconds, respectively; for the tumor center, the results of ANOVA were P = .03, .02, .02, and .03 at 52, 58, 64, and 70 seconds, respectively.
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Figure 2a. (a) Time-attenuation curves obtained in the tumor boundary. Except for injection of 70 mL at 1.0 mL/sec, the three other protocols yielded comparable curves that reached maximum enhancement after approximately 52 seconds. (b) Time-attenuation curves obtained in the tumor center. Regardless of protocol, maximum enhancement was approximately 10 HU lower than that of the tumor boundary in a.
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Figure 2b. (a) Time-attenuation curves obtained in the tumor boundary. Except for injection of 70 mL at 1.0 mL/sec, the three other protocols yielded comparable curves that reached maximum enhancement after approximately 52 seconds. (b) Time-attenuation curves obtained in the tumor center. Regardless of protocol, maximum enhancement was approximately 10 HU lower than that of the tumor boundary in a.
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Figure 3a. (a-d) Transverse CT images show tumor enhancement (large arrowheads) achieved by using different protocols (a, 125 mL at 2.5 mL/sec; b, 100 mL at 2.0 mL/sec; c, 90 mL at 1.5 mL/sec; and d, 70 mL at 1.0 mL/sec) 64 seconds after the start of injection. Note the difference in carotid arterial enhancement (small arrowheads in a). The attenuation values (in Hounsfield units) measured in the common carotid artery (CCA), tumor boundary (TB), and tumor center (TC) are as follows: 125 mL: CCA = 247, TB = 103, TC = 94; 100 mL: CCA = 230, TB = 92, TC = 92; 90 mL: CCA = 178, TB = 99, TC = 85; and 70 mL: CCA = 131, TB = 68, TC = 67. The regions of interest were omitted from the figures to better depict contrast enhancement.
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Figure 3b. (a-d) Transverse CT images show tumor enhancement (large arrowheads) achieved by using different protocols (a, 125 mL at 2.5 mL/sec; b, 100 mL at 2.0 mL/sec; c, 90 mL at 1.5 mL/sec; and d, 70 mL at 1.0 mL/sec) 64 seconds after the start of injection. Note the difference in carotid arterial enhancement (small arrowheads in a). The attenuation values (in Hounsfield units) measured in the common carotid artery (CCA), tumor boundary (TB), and tumor center (TC) are as follows: 125 mL: CCA = 247, TB = 103, TC = 94; 100 mL: CCA = 230, TB = 92, TC = 92; 90 mL: CCA = 178, TB = 99, TC = 85; and 70 mL: CCA = 131, TB = 68, TC = 67. The regions of interest were omitted from the figures to better depict contrast enhancement.
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Figure 3c. (a-d) Transverse CT images show tumor enhancement (large arrowheads) achieved by using different protocols (a, 125 mL at 2.5 mL/sec; b, 100 mL at 2.0 mL/sec; c, 90 mL at 1.5 mL/sec; and d, 70 mL at 1.0 mL/sec) 64 seconds after the start of injection. Note the difference in carotid arterial enhancement (small arrowheads in a). The attenuation values (in Hounsfield units) measured in the common carotid artery (CCA), tumor boundary (TB), and tumor center (TC) are as follows: 125 mL: CCA = 247, TB = 103, TC = 94; 100 mL: CCA = 230, TB = 92, TC = 92; 90 mL: CCA = 178, TB = 99, TC = 85; and 70 mL: CCA = 131, TB = 68, TC = 67. The regions of interest were omitted from the figures to better depict contrast enhancement.
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Figure 3d. (a-d) Transverse CT images show tumor enhancement (large arrowheads) achieved by using different protocols (a, 125 mL at 2.5 mL/sec; b, 100 mL at 2.0 mL/sec; c, 90 mL at 1.5 mL/sec; and d, 70 mL at 1.0 mL/sec) 64 seconds after the start of injection. Note the difference in carotid arterial enhancement (small arrowheads in a). The attenuation values (in Hounsfield units) measured in the common carotid artery (CCA), tumor boundary (TB), and tumor center (TC) are as follows: 125 mL: CCA = 247, TB = 103, TC = 94; 100 mL: CCA = 230, TB = 92, TC = 92; 90 mL: CCA = 178, TB = 99, TC = 85; and 70 mL: CCA = 131, TB = 68, TC = 67. The regions of interest were omitted from the figures to better depict contrast enhancement.
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In summary, maximum enhancement of the tumor was reached at 52 seconds and later. The largest volume tested (125 mL) did not further increase tumor enhancement when compared with 100 and 90 mL; however, the smallest volume (70 mL) resulted in a temporarily significantly lower enhancement.
Enhancement of Muscle and Time-Attenuation Curves
Figure 4 reveals comparable curves for muscle, showing a slight increase of attenuation values, regardless of the protocol, with no significant differences between 125 mL at 2.5 mL/sec, 100 mL at 2.0 mL/sec, and 90 mL at 1.5 mL/sec (P > .05, regarding all possible combinations between these protocols during the diagnostic window). Again, attenuation values after injection of 70 mL at 1.0 mL/sec were lower than those of the other protocols (P < .05 at 52 seconds, as compared with 90 mL at 1.5 mL/sec or 100 mL at 2.0 mL/sec; P < .05 at 70 seconds, as compared with 100 mL at 2.0 mL/sec). The results of ANOVA were P = .02, .07, .10, and .04 at 52, 58, 64, and 70 seconds, respectively.
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Figure 4a. (a) Time-attenuation curves obtained in muscle. Except for injection of 70 mL at 1.0 mL/sec, the other three protocols yielded comparable curves. (b) Time-contrast curves for tumor boundary versus muscle. All protocols yielded comparable curves, reaching maximum enhancement after approximately 52 seconds.
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Figure 4b. (a) Time-attenuation curves obtained in muscle. Except for injection of 70 mL at 1.0 mL/sec, the other three protocols yielded comparable curves. (b) Time-contrast curves for tumor boundary versus muscle. All protocols yielded comparable curves, reaching maximum enhancement after approximately 52 seconds.
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Thus, time-contrast curves between tumor boundary and muscle for all four protocols were similar, masking the difference in absolute enhancements between the 70-mL protocol and the others (Fig 4). However, as shown for the enhancement of tumors in Figure 2, Figure 4 reveals that there is also a maximum level of enhancement after 52 seconds, regardless of the protocol.
Diagnostic Window
All protocols resulted in comparable diagnostic windows between 52 and 75–79 seconds (Fig 1). However, when considering the point estimate ± SD for the enhancements measured in the carotid artery and the tumor boundary (Table 3), Figure 5 shows that injection of 90 mL at 1.5 mL/sec provided the longest diagnostic window—between 52 and 73 seconds (with highly significant differences in carotid arterial enhancement at 70 seconds after the start of injection between 90 mL at 1.5 mL/sec and 125 mL at 2.5 mL/sec [P < .01], 100 mL at 2.0 mL/sec [P < .01], or 70 mL at 1.0 mL/sec [P < .01]; ANOVA, P < .01).
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Figure 5. Time-attenuation curves beginning at 52 seconds for the time of maximum enhancement in the tumor boundary. Curves show the mean carotid arterial enhancements after subtraction of SDs. As a consequence, the points of intersection of the curves with the 150-HU line (dotted line) reveal the duration of the SD-corrected diagnostic windows: approximately 68 seconds for 125 mL at 2.5 mL/sec, 63 seconds for 100 mL at 2.0 mL/sec, and 73 seconds for 90 mL at 1.5 mL/sec. Injection of 70 mL at 1.0 mL/sec lacks such a SD-corrected diagnostic window because all respective attenuation values are below 150 HU.
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Routine Examinations
For routine examinations, injection of 90 mL at 1.5 mL/sec was chosen for the following reasons: Because of a longer flow time of 60 seconds, a volume of 90 mL at 1.5 mL/sec yielded delayed vascular enhancement (>150 HU), resulting in a prolonged diagnostic window in spite of the relatively small volume, as compared with the 125-mL protocol. Moreover, tumor enhancement was not inferior when compared with injections of 100 or 125 mL. By using a collimation of 3 mm and a start delay of 40 seconds for all laryngeal and hypopharyngeal tumors or a collimation of 5 mm and a start delay of 45 seconds for tumors of the oropharynx and oral cavity, almost all individual attenuation values of the tumor boundary were within 1 SD above or below the mean attenuation curve obtained from the dynamic series (P = .39) (Fig 6). Moreover, all tumors were scanned 51–69 seconds after the start of injection (within the diagnostic window) (Fig 7).
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Figure 6. Graph shows attenuation values (in Hounsfield units) measured in the tumor boundary during routine CT of the neck (90 mL at 1.5 mL/sec). All values were acquired 51-69 seconds after the start of injection. They corresponded predominantly with the mean attenuation values (± SD) obtained from the dynamic series (solid lines), except for in one almost isoattenuating tumor. Symbols represent individual patients.
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Figure 7a. Transverse CT images show enhancement of neck structures during the (a) lower and (b) upper spiral of a routine examination (90 mL at 1.5 mL/sec with a start delay of 40 seconds). a shows a well-delineated hypopharyngeal tumor (90 HU in the tumor boundary 62 seconds after the start of injection; large arrowhead) and excellent enhancement of the carotid arteries (194 HU; small arrowheads). b shows adequate enhancement of the internal carotid arteries (116 HU at 107 seconds after the start of injection; arrowheads).
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Figure 7b. Transverse CT images show enhancement of neck structures during the (a) lower and (b) upper spiral of a routine examination (90 mL at 1.5 mL/sec with a start delay of 40 seconds). a shows a well-delineated hypopharyngeal tumor (90 HU in the tumor boundary 62 seconds after the start of injection; large arrowhead) and excellent enhancement of the carotid arteries (194 HU; small arrowheads). b shows adequate enhancement of the internal carotid arteries (116 HU at 107 seconds after the start of injection; arrowheads).
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The mean attenuation of the carotid artery was 173 HU ± 20 (range, 150–208 HU) at the beginning of the lower spiral volume on the most caudal image of the common carotid arteries, mean attenuation was 198 HU ± 18 (range, 162–230 HU) in the middle of the lower spiral volume (P = .52 as compared with the dynamic series), and mean attenuation was 160 HU ± 16 (range, 111–188 HU) on the most cranial image of the lower spiral volume, showing the internal carotid arteries at the level of the mastoid bones. On the most caudal image of the upper spiral volume (gap between lower and upper spiral volume, 30–41 seconds), the mean attenuation of the internal carotid arteries was 121 HU ± 19 (range, 97–147 HU), and on the most cranial image, the mean attenuation was 118 HU ± 17 (range, 93–136 HU) (Fig 7).
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DISCUSSION
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With regard to flow rate and volume of the intravenous contrast material, four different protocols were compared (125 mL at 2.5 mL/sec, 100 mL at 2.0 mL/sec, 90 mL at 1.5 mL/sec, and 70 mL at 1.0 mL/sec). Injections of 125 mL at 2.5 mL/sec and 100 mL at 2.0 mL/sec were characterized by a relatively large volume and fast flow. Both protocols yielded an enhancement of the carotid artery of more than 230 HU, which is actually not necessary for differentiation from lymph nodes. Furthermore, both curves decreased quickly, and, when considering the point estimate ± SD, were already below 150 HU at 70 seconds (at 64 seconds, even, for 100 mL at 2.0 mL/sec). Because squamous cell carcinomas enhance late, a comparison with lower volumes, such as 90 or 70 mL, only makes sense if flow rates are reduced accordingly (to 1.5 or 1.0 mL/sec, respectively) so the flow time, which should be a minimum of 50 seconds for long vascular enhancement, is not affected (12). As a result of this comparison, we expected reduced tumor and vascular enhancement, and, thus, a shorter diagnostic window. However, a reduction of volume and flow rate to 90 mL at 1.5 mL/sec does not appear to have substantially influenced the goals of this study (ie, strong tumor enhancement and carotid arterial enhancement of more than 150 HU). Moreover, an increase of flow time to 60 seconds (by using 90 mL at 1.5 mL/sec) provided constant attenuation values of approximately 190 HU during an even slightly prolonged diagnostic window (if the point estimate ± SD is considered). However, a further reduction of flow rate (ie, 1.0 mL/sec) and/or volume (ie, 70 mL) resulted in a significant decrease of vessel and tumor enhancement, and, thus, unacceptable image quality.
Analysis of images from 30 routine examinations confirmed that injection of 90 mL at 1.5 mL/sec reliably provides excellent tumor enhancement and good vessel enhancement in a typical patient population with primary neck tumors, regardless of differences in age and sex. Although this protocol was not specifically tested in patients with cardiovascular disorders, we speculate that a start delay of 50 seconds or more (instead of 40 or 45 seconds) might yield similar results in this subset of patients; the same applies to a faster data acquisition (ie, with multidetector scanners). Instead, in the case of thinner collimation, less pitch, and/or increased rotation time, the start delay has to be reduced accordingly. In general, however, automatic bolus tracking, such as that used with abdominal CT, does not appear to be beneficial in CT of neck malignancies, mainly because an additional early arterial phase would not support detection and/or differentiation, as is the case with carcinomas of the liver, pancreas, or kidney.
A former comparison of sequential and spiral CT of laryngopharyngeal carcinoma yielded comparable results (17). In that study, 200 and 150 mL were used for sequential and spiral CT, respectively (both at 2.0 mL/sec with a start delay of 70 seconds). Although not directly proven, it can be assumed that the capacity of squamous cell carcinoma to enhance is limited, even if large volumes of contrast material are administered. In this regard, the results of our study show that spiral CT can yield excellent image quality by using only 90 mL of intravenous contrast material. Thus, because of the smaller volumes of contrast material needed, spiral CT should be favored in the future.
Although not evaluated in the present study, comparably rare nasopharyngeal carcinoma should be examined by using a protocol different from the one presented here, because nasopharyngeal carcinoma is visualized in the upper spiral volume. The delay caused by the different angulation required for the upper spiral volume may eventually decrease tumor enhancement, although some tumors remain enhanced for more than 2 minutes after the end of contrast material injection or may even enhance more over time, up to a limit.
In the present study, we have not taken into account protocols with a two-phase application of contrast material, such as that used by several other groups. This might be considered a limitation. However, Figure 2 appears to reveal that a maximum level of tumor enhancement is already reached at approximately 52 seconds, although peak enhancements in the carotid artery are reached later—between 52 and 76 seconds, depending on the protocol. Thus, although not directly compared with injection of 90 mL at 1.5 mL/sec, a substantial further increase of tumor enhancement cannot be expected by using a two-phase application of contrast material (eg, 80 mL at 1.5 mL/sec followed by 70 mL at 0.3 mL/sec [6])—only prolonged enhancement of major neck vessels needed for slower sequential CT examinations.
In conclusion, the results of this study show that spiral CT of laryngeal, hypopharyngeal, and oropharyngeal malignancies performed with a single bolus of 90 mL can yield excellent tumor enhancement in combination with good vessel enhancement if a flow rate of 1.5 mL/sec is used.
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FOOTNOTES
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Abbreviation: ANOVA = analysis of variance
Author contributions: Guarantor of integrity of entire study, M.K.; study concepts and design, M.K., A.T.; literature research, M.K.; clinical studies, M.K.; data acquisition and analysis/interpretation, M.K.; statistical analysis, M.K.; manuscript preparation and definition of intellectual content, M.K.; manuscript editing, M.K., A.T. D.H.; manuscript revision/review and final version approval, A.T. D.H.
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