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Published online before print September 21, 2007, 10.1148/radiol.2452061749
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(Radiology 2007;245:475-482.)
© RSNA, 2007

Gastrointestinal Imaging

Pancreas: Patient Body Weight–tailored Contrast Material Injection Protocol versus Fixed Dose Protocol at Dynamic CT1

Yumi Yanaga, MD, Kazuo Awai, MD, Yoshiharu Nakayama, MD, Takeshi Nakaura, MD, Yoshitaka Tamura, MD, Masahiro Hatemura, RT, and Yasuyuki Yamashita, MD

1 From the Department of Diagnostic Radiology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan (Y. Yanaga, K.A., Y.N., T.N., Y. Yamashita); and Department of Radiology, Kumamoto University Hospital, Kumamoto, Japan (Y.T., M.H.). Received October 10, 2006; revision requested December 7; revision received February 20, 2007; accepted March 20; final version accepted May 7. Address correspondence to Y. Yanaga.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Purpose: To prospectively compare the effect of a protocol with a fixed contrast material injection dose and one with a dose tailored to patient body weight on pancreatic enhancement at dynamic computed tomography (CT) of the pancreas.

Materials and Methods: This study was approved by the institutional review board, and patients gave informed consent. Seventy-eight patients suspected of having pancreatic tumor were randomly assigned to one of two protocols (39 patients in each protocol). In protocol 1, a fixed contrast material dose (120 mL of iohexol 300) was delivered at an injection rate of 4.0 mL/sec; in protocol 2, a dose tailored to the patient's body weight (2.0 mL/kg) was injected over the course of 30 seconds. Scans were started 25, 45 (pancreatic parenchymal phase [PPP]), and 70 (portal venous phase [PVP]) seconds after the initiation of contrast material injection. Pancreatic enhancement during the PPP and hepatic enhancement during the PVP were compared by using the Student t test in patients whose body weight was less than 60 kg (group A) or 60 kg or greater (group B). A radiologist who was blinded to the injection protocol used measured the CT number of each organ.

Results: With protocol 1, mean pancreatic enhancement during the PPP was 94.1 HU in group A and 76.1 HU in group B; the difference was statistically significant (P = .02). With protocol 2, mean pancreatic enhancement was 89.5 HU in group A and 84.7 HU in group B; there was no significant difference (P = .45). Mean hepatic enhancement with protocol 1 during the PVP was 59.6 HU in group A and 48.5 HU in group B (P < .01); with protocol 2, it was 55.4 HU in group A and 58.3 HU in group B. The difference was not statistically significant (P = .34).

Conclusion: The dose protocol tailored to the patient's body weight yielded satisfactory pancreatic and hepatic enhancement irrespective of patient weight.

© RSNA, 2007


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Because multidetector computed tomography (CT) offers high volumetric coverage, speed, and spatial resolution, it is now widely used for the acquisition of reliable images for the diagnosis and follow-up of pancreatic tumors. Some pancreatic dynamic CT studies (1–5) have emphasized the importance of the pancreatic parenchymal phase (PPP) that occurs 40–70 seconds after the start of contrast material injection at a rate of 3.0 mL/sec (2,3). Maximum pancreatic enhancement can be obtained during the PPP (2–4), and the detection of pancreatic cancer is maximized during the PPP because the cancer is hypoattenuated compared with the surrounding pancreatic parenchyma. The PPP is also useful for evaluating tumor invasion into the peripancreatic arteries and portal vein because these vessels are intensively enhanced during the PPP (1–4,6,7).

Technique-related factors for contrast enhancement at pancreatic dynamic CT include the scan delay time after the start of contrast material injection (1–4), the dose (8,9) and concentration of contrast material (8,10), the injection rate (injection duration) (9,11), and the use of a saline flush after contrast material administration (12,13). In most of these examination protocols, the contrast material dose is fixed (1–4,6,7,11,14), although some investigators have tailored the contrast material dose to patient body weight (8,9,15).

Because the feeding arteries for the pancreas are the branches derived from the abdominal aorta, pancreatic enhancement is presumed to be almost parallel to that of the abdominal aorta. Aortic enhancement is associated with the contrast material dose per body weight (15). Therefore, protocols in which a fixed contrast material dose is used may yield insufficient aortic enhancement in heavy patients. Thus, the purpose of our study was to prospectively compare the effect of a protocol with a fixed contrast material injection dose and one with a contrast material dose tailored to the patient's body weight on pancreatic enhancement at dynamic CT of the pancreas.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Our study was approved by our institutional review board; informed consent was obtained from all patients.

Patients
Between July 2005 and April 2006, we enrolled 78 patients (39 men and 39 women; age range, 23–91 years; mean age, 66.4 years) in this prospective study. Inclusion criteria were (a) suspicion of pancreatic tumors at ultrasonography (US) or elevated tumor marker levels (CA19-9, DUPAN-2, or elastase-1) and (b) absence of renal failure (serum creatinine level > 1.5 mg/dL [132 µmol/L]) or the absence of a contraindication to iodinated contrast material. All enrolled patients satisfied both criteria. The final diagnosis was intraductal papillary mucinous neoplasm in 10 patients, pancreatic carcinoma in 38 patients, islet cell tumor in five patients, mucinous cystic adenoma in one patient, serous cystadenoma in one patient, and pancreatic cyst in seven patients; 16 patients were proved to be without pancreatic lesions. The diagnosis in five patients with intraductal papillary mucinous neoplasm; 30 patients with pancreatic carcinoma; and all patients with islet cell tumor, mucinous cystic adenoma, and serous cystadenoma was based on pathologic findings at definitive surgery. The diagnosis in the remaining five patients with intraductal papillary mucinous neoplasm was made on the basis of both follow-up CT results and blood chemistry evaluation. The diagnosis in eight patients with pancreatic carcinoma, all patients with pancreatic cysts, and all patients without pancreatic disease was determined by means of follow-up with US, CT, or magnetic resonance imaging and blood chemistry evaluation. In these patients, follow-up ranged from 6 to 14 months (mean follow-up, 11 months).

The patients were randomly assigned to one of two protocols. In protocol 1, a fixed contrast material dose was used, and in protocol 2, the contrast material dose was tailored to the patient's weight. Thirty-nine of the 78 patients were assigned to protocol 1, and 39 were assigned to protocol 2. In the protocol 1 group, there were 18 men and 21 women aged 23–91 years (mean, 64.5 years) and weighing 40–88 kg (mean, 56.8 kg). Twenty-six patients weighed less than 60 kg (group A), and 13 weighed 60 kg or greater (group B). In the protocol 2 group, there were 21 men and 18 women aged 46–85 years (mean, 68.2 years) and weighing 37–74 kg (mean, 55.0 kg). Twenty-two patients weighed less than 60 kg (group A), and 17 weighed 60 kg or greater (group B). We measured the body weight of each patient just before the CT examinations. There was no statistically significant difference in the distribution of age (P = .21, two-tailed Student t test), sex (P = .33, {chi}2 test), and body weight between the two protocols (P = .33, two-tailed Student t test).

Contrast Material Injection Protocols
The contrast material used was iohexol (Omnipaque; Daiichi Pharmaceutical, Tokyo, Japan), which contained 300 mg iodine per milliliter. In all patients, the contrast material was administered with a mechanical power injector (Dual Shot; Nemoto-Kyorindo, Tokyo, Japan) through a 20-gauge cannula inserted into an antecubital vein. Patients in the protocol 1 group received a total of 36 g of iodine (120 mL of contrast material at 300 mg of iodine per milliliter). Patients in the protocol 2 group received a contrast material dose that was tailored to their body weight; they received 600 mg of iodine per kilogram (2.0 mL of contrast material per kilogram of body weight). Yamashita et al (15) reported that when dose was tailored to patient weight, the use of 2.0 or 2.5 mL/kg intravenous contrast material produced better results for abdominal dynamic CT than did the use of 1.5 mL/kg contrast material. According to this report, we adopted the 2.0 mL/kg contrast dose, which was tailored to patient weight.

Because the average body weight in the Japanese population is approximately 60 kg (16), patients weighing 60 kg received 36 g of iodine, a concentration identical to that used in protocol 1. In all patients, the contrast material was injected over 30 seconds. Therefore, the injection rate was a constant 4 mL/sec with protocol 1; in protocol 2, the injection rate varied from 2.5 mL/sec (37 kg) to 4.9 mL/sec (80 kg). After contrast material injection, all patients were injected with 30 mL of saline solution delivered at the same rate as the contrast material.

Scanning Protocol
All patients were scanned by using a 40-detector CT scanner (Brilliance-40; Philips Medical Systems, Cleveland, Ohio). Imaging parameters were as follows: rotation time, 0.5 second; detector collimation, 40 x 1.5 mm; helical pitch, 0.7; gantry rotation time, 0.5 second; reconstructed section thickness and interval, 3.0 mm; tube voltage, 120 kV; and tube current–time product, 300 mAs. Image reconstruction was in a 25–35-cm display field of view, depending on the patient's physique. All scans began at the top of the liver and went through to the lower pole of the kidney in a cephalocaudal direction. Patients were instructed to hold their breath, with tidal inspiration during scanning. Unenhanced and three-phase contrast material–enhanced helical scans of the whole liver were obtained. In both protocols, first-, second-, and third-phase scanning was started 25, 45, and 70 seconds, respectively, after the inception of contrast material injection; the phases corresponded to the arterial phase, the PPP, and the portal venous phase (PVP), respectively. The scans were the same as those acquired with pancreatic dynamic CT in our routine clinical practice.

Quantitative Assessment
All numeric data are presented as means ± standard deviations. Because the PPP reportedly provides the best tumor contrast and good enhancement of the peripancreatic arteries and portal vein and the PVP is adequate for the detection of liver metastases (3,17), we measured the enhancement values of the pancreas, celiac artery, and portal vein during the PPP and those of the liver during the PVP. We also determined the enhancement of the celiac artery during the arterial phase. For each protocol, we compared the mean enhancement values of the pancreas, celiac artery, liver, and portal vein obtained in the two body weight groups (ie, patients weighing less than 60 kg [group A] and those weighing 60 kg or greater [group B]).

The enhancement values during the PPP and PVP were measured by placing manually defined regions of interest (ROIs) on the pancreas, liver, celiac artery, and portal vein. These procedures were performed by a board-certified radiologist (Y. Yanaga, with 10 years of experience in abdominal CT). She was blinded to the specific protocol used and to the patient group.

In the pancreas, attenuation was measured in the head, body, and tail, and all attenuation values were averaged. An attempt was made to maintain a constant ROI area of approximately 50 mm2. The actual ROI area ranged from 30 to 60 mm2. Visible blood vessels, the pancreatic duct, tumor, cystic lesions, calcification, and artifacts were carefully excluded from ROI measurements in the pancreatic parenchyma. Contrast enhancement (in Hounsfield units) of the pancreatic parenchyma during the PPP was calculated as the absolute difference between the attenuation values of the pancreas on unenhanced scans and those obtained during the PPP.

To measure enhancement of the celiac artery, an attempt was made to maintain a constant ROI area of approximately 15 mm2. The actual ROI area ranged from 12 to 17 mm2. Enhancement of the celiac artery in the arterial phase and PPP was calculated as the absolute difference between the attenuation values of the celiac artery on unenhanced scans and those on scans obtained during the aortic phase or PPP.

Liver attenuation was measured in three areas—the left lobe and the anterior and posterior segments of the right lobe—on images obtained at the level of the main portal vein; all attenuation values were averaged. An attempt was made to maintain a constant ROI area of approximately 150 mm2. The actual ROI area ranged from 80 to 200 mm2. Visible blood vessels, bile ducts, and artifacts were carefully excluded from ROI measurements in the hepatic parenchyma. Contrast enhancement in the hepatic parenchyma during the PVP was calculated as the absolute difference between the attenuation values of the liver on unenhanced scans and those obtained during the PVP.

We also measured the attenuation values of the main portal vein during the PPP. We attempted to maintain a constant ROI area of approximately 50 mm2; the actual ROI area ranged from 40 to 60 mm2. Contrast enhancement in the main portal vein during the PPP was calculated as the absolute difference between the attenuation values of the main portal vein on unenhanced scans and those obtained during the PPP.

Qualitative Assessment
Two board-certified radiologists (K.A. and Y.N., with 20 and 12 years of experience, respectively) independently performed visual evaluation of the quality of pancreatic enhancement. They specialized in body imaging, read abdominal CT scans on a regular basis, and were blinded to the contrast material protocol used.

We prepared a four-point imaging scale to grade image quality (Fig 1), as follows: grade 1 indicated poor quality (no pancreatic enhancement); grade 2, fair quality (despite slight pancreatic enhancement, the image was diagnostically inadequate); grade 3, adequate quality; and grade 4, excellent quality. If the readers disagreed about the quality of enhancement, images were reevaluated for consensus.


Figure 1A
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  		Figure 1a: Examples of visual grading of pancreatic enhancement. Transverse CT scans at level of pancreatic body and tail in (a) 62-year-old woman with pancreatic cancer, (b) 41-year-old man who was proved to be without pancreatic lesions, and (c) 72-year-old man with pancreatic head cancer that caused dilatation of main pancreatic duct. Image in a was classified as grade 2 (despite slight pancreatic enhancement, image is diagnostically inadequate), image in b was classified as grade 3 (adequate), and image in c was classified as grade 4 (excellent).

 

Figure 1B
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  		Figure 1b: Examples of visual grading of pancreatic enhancement. Transverse CT scans at level of pancreatic body and tail in (a) 62-year-old woman with pancreatic cancer, (b) 41-year-old man who was proved to be without pancreatic lesions, and (c) 72-year-old man with pancreatic head cancer that caused dilatation of main pancreatic duct. Image in a was classified as grade 2 (despite slight pancreatic enhancement, image is diagnostically inadequate), image in b was classified as grade 3 (adequate), and image in c was classified as grade 4 (excellent).

 

Figure 1C
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  		Figure 1c: Examples of visual grading of pancreatic enhancement. Transverse CT scans at level of pancreatic body and tail in (a) 62-year-old woman with pancreatic cancer, (b) 41-year-old man who was proved to be without pancreatic lesions, and (c) 72-year-old man with pancreatic head cancer that caused dilatation of main pancreatic duct. Image in a was classified as grade 2 (despite slight pancreatic enhancement, image is diagnostically inadequate), image in b was classified as grade 3 (adequate), and image in c was classified as grade 4 (excellent).

 
Statistical Analysis
We used the two-tailed Student t test to evaluate differences between protocols 1 and 2 with respect to pancreatic enhancement during the PPP and to assess differences in the enhancement of the pancreas, celiac artery, liver, and portal vein in the two body weight groups with the two different protocols. The Mann-Whitney U test was used to compare the quality of images obtained in the two body weight groups with the different protocols. Furthermore, we performed a generalized estimating equation analysis (18) to evaluate the enhancement of the celiac artery because we measured it during both the arterial phase and PPP, and enhancement of the celiac artery during these two phases may correlate. Generalized estimating equation analysis, in particular, was focused on the effect of patient body weight on the enhancement of the celiac artery and was performed for protocols 1 and 2 independently.

The sample size was obtained as follows: The primary variable was pancreatic enhancement during the PPP, and anticipated effect size d (difference of means divided by standard deviation) was estimated as 1.3 as a result of the preliminary study conducted before this study. The sample size was based on a two-tailed t test with a significance level of .05 and a power level of 0.90. The required sample size was 13 in each weight group, for a total of 26 patients.

To assess the degree of observer agreement for the quality of depiction of pancreatic enhancement, we used the Cohen {kappa} coefficient. The scale for the {kappa} coefficients for interobserver agreement was as follows: {kappa} less than 0.20 indicated poor agreement; {kappa} between 0.21 and 0.40, fair agreement; {kappa} between 0.41 and 0.60, moderate agreement; {kappa} between 0.61 and 0.80, substantial agreement; and {kappa} between 0.81 and 1.00, almost perfect agreement.

Statistical analyses were performed with a software package (SPSS, version 15.0; SPSS, Chicago, Ill). For all statistical analyses, a P value of less than .05 was considered to indicate a statistically significant difference. Sample size was calculated with statistical software (Sample Power, version 2.0; SPSS).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Pancreatic Enhancement during PPP
The mean pancreatic enhancement for all patients was 89.0 HU ± 24.4 with protocol 1 and 87.2 HU ± 19.1 with protocol 2; the difference was not statistically significant (P = .54). With protocol 1, the mean pancreatic enhancement was 94.1 HU ± 24.3 (range, 61.3–140.7 HU) for group A patients and 76.1 HU ± 19.0 (range, 35.3–109.3 HU) for group B patients (Fig 2); the difference was statistically significant (P = .02). With protocol 2, the mean pancreatic enhancement was 89.5 HU ± 19.4 (range, 51.3–138.7 HU) for group A patients and 84.7 HU ± 19.5 (range, 37.3–110.3 HU) for group B patients (Fig 2); the difference was not statistically significant (P = .45).


Figure 2
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  		Figure 2: Bar graph shows enhancement of pancreas during PPP. With protocol 1, mean pancreatic enhancement in patients with body weight of 60 kg or greater (group B) was significantly lower than that in patients weighing less than 60 kg (group A) (P = .02). With protocol 2, there was no significant difference between the two weight groups (P = .45). Error bars show standard deviations.

 
Enhancement of Celiac Artery during Arterial Phase and PPP
During the arterial phase, the mean enhancement with protocol 1 was 283.9 HU ± 56.2 (range, 207.3–395.5 HU) in group A and 235.3 HU ± 29.6 (range, 190.1–294.4 HU) in group B (Fig 3); the difference was statistically significant (P < .01). With protocol 2, the mean enhancement during the arterial phase was 268.0 HU ± 59.0 (range, 155.6–372.4 HU) for group A and 291.1 HU ± 31.0 (range, 251.5–367.5 HU) for group B; the difference was not statistically significant (P = .21).


Figure 3A
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  		Figure 3a: Bar graphs show enhancement of celiac artery during (a) arterial phase and (b) PPP. (a) In arterial phase, with protocol 1, mean enhancement was significantly lower in patients with body weight of 60 kg or greater (group B) than in those weighing less than 60 kg (group A) (P < .01). With protocol 2, there was no statistically significant difference between the two weight groups (P = .21). (b) In PPP, irrespective of the protocol used, there was no significant difference between the two weight groups (protocol 1, P = .64; protocol 2, P = .59). Error bars show standard deviations.

 

Figure 3B
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  		Figure 3b: Bar graphs show enhancement of celiac artery during (a) arterial phase and (b) PPP. (a) In arterial phase, with protocol 1, mean enhancement was significantly lower in patients with body weight of 60 kg or greater (group B) than in those weighing less than 60 kg (group A) (P < .01). With protocol 2, there was no statistically significant difference between the two weight groups (P = .21). (b) In PPP, irrespective of the protocol used, there was no significant difference between the two weight groups (protocol 1, P = .64; protocol 2, P = .59). Error bars show standard deviations.

 
During the PPP, the mean enhancement with protocol 1 was 188.1 HU ± 90.0 (range, 94.8–420.7 HU) in group A and 168.8 HU ± 81.4 (range, 99.7–396.8 HU) in group B (Fig 3); the difference was not statistically significant (P = .64). Likewise, there was no significant difference with protocol 2; enhancement was 189.0 HU ± 76.5 (range, 109.9–384.0 HU) in group A and 204.1 HU ± 89.0 (range, 117.7–396.1 HU) in group B (P = .59).

In the analysis of the effect of patient body weight on the enhancement of the celiac artery, as determined with generalized estimating equation analysis, there was a statistically significant correlation between aortic enhancement and patient body weight with both protocol 1 and protocol 2 (P < .01 and P < .01, respectively).

Hepatic Enhancement during PVP
The mean hepatic enhancement for all patients during the PVP was 55.9 HU ± 12.3 with protocol 1 and 56.7 HU ± 9.5 with protocol 2; the difference was not statistically significant (P = .75). With protocol 1, the mean hepatic enhancement was 59.6 HU ± 12.8 (range, 45.3–93.0 HU) in group A and 48.5 HU ± 6.8 (range, 39.0–59.3 HU) in group B (Fig 4). The difference was statistically significant (P < .01). With protocol 2, the mean hepatic enhancement was 55.4 HU ± 10.5 (range, 36.7–79.0 HU) in group A and 58.3 HU ± 7.9 (range, 46.7–76.3 HU) in group B; the difference was not statistically significant (P = .34).


Figure 4
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  		Figure 4: Bar graph shows hepatic enhancement during PVP. With protocol 1, mean hepatic enhancement was significantly higher in patients weighing less than 60 kg (group A) than in those weighing 60 kg or greater (group B) (P < .01). With protocol 2, there was no significant difference between the two weight groups (P = .34). Error bars show standard deviations.

 
Portal Venous Enhancement during PPP
The mean portal venous enhancement for all patients during the PPP was 120.4 HU ± 21.8 with protocol 1 and 124.5 HU ± 14.4 with protocol 2; the difference was not statistically significant (P = .32). With protocol 1, the mean portal venous enhancement was 193.8 HU ± 46.9 (range, 50.7–282.7 HU) in group A and 139.9 HU ± 34.8 (range, 88.7–206.0 HU) in group B (Fig 5); the difference was statistically significant (P < .01). With protocol 2, the mean portal venous enhancement was 180.4 HU ± 31.4 (range, 117.7–269.0 HU) in group A and 168.6 HU ± 29.8 (range, 111.7–221.0 HU) in group B; the difference was not statistically significant (P = .24).


Figure 5
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  		Figure 5: Bar graph shows enhancement of portal vein during PPP. With protocol 1, mean enhancement of the portal vein was significantly higher in patients weighing less than 60 kg (group A) than in those weighing 60 kg or greater (group B) (P < .01). With protocol 2, there was no significant difference between the two weight groups (P = .24). Error bars show standard deviations.

 
Qualitative Assessment
With protocol 1, 21 of the 26 images (81%) from group A were graded as excellent; the remaining five images were graded as adequate (Table 1). Eight of the 13 images (62%) obtained in group B showed good enhancement. With protocol 1, pancreatic enhancement was significantly better in patients weighing less than 60 kg (group A) than in heavier patients (P < .01). With protocol 2, there was no statistically significant difference between the two body weight groups; the images in 19 of the 22 group A patients (86%) and 13 of the 17 group B patients (76%) showed excellent pancreatic enhancement (P = .43). There was good interobserver agreement with regard to the quality of depiction of pancreatic enhancement ({kappa} = 0.69). The population means for grades 4 and 3 were 129.6 HU ± 23.0 and 99.0 HU ± 21.4, respectively (Table 2). Because only two images were classified as grade 2 and none of the scans were categorized as poor, we did not calculate these values for this set of images.


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  		Table 1. Results of Visual Analysis of Contrast Enhancement of Pancreas during PPP

 

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  		Table 2. Estimated Population Mean and 95% Confidence Interval of Pancreatic Enhancement during PPP according to Image Grade

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
With the fixed contrast material dose protocol (protocol 1), pancreatic enhancement during the PPP was significantly worse in the heavier patients (body weight of 60 kg or greater, group B) than in the lighter patients (body weight of less than 60 kg, group A). Conversely, there was no significant difference between the two weight groups with the protocol in which contrast material dose was tailored to patient weight (protocol 2). Qualitative evaluation of the images indicated that among the lighter weight groups (group A), the readers judged 81% of the images acquired with protocol 1 and 86% of those obtained with protocol 2 to show excellent pancreatic enhancement. Conversely, in the heavier weight groups (group B), only 23% of scans in the protocol 1 group were graded as excellent, although 76% of scans in the protocol 2 group were graded as excellent. This suggests that, at dynamic CT of the pancreas, fixed dose protocols do not yield diagnostically satisfactory pancreatic enhancement in heavier patients, whereas weight-adjusted protocols do.

With protocol 2 (contrast material dose, 2.0 mL/kg), the mean pancreatic enhancement during the PPP for all patients was 87.1 HU. Others have reported mean pancreatic enhancement to be 84.0–93.6 HU when a fixed dose of 140–150 mL was injected at 4.0–5.0 mL/sec (11,19). Direct comparison of their results with our results is difficult because the attenuation value of organs is affected by the effective tube voltage of the CT equipment used, even if the blood iodine concentration is similar (20,21). Our results, however, suggest that a weight-tailored contrast material injection protocol (eg, 2.0 mL/kg) yields pancreatic enhancement similar to that achieved with protocols in which a fixed contrast material dose of 140–150 mL is used.

Our findings suggest that protocol 2 yields better enhancement of the celiac artery during the arterial phase in patients of greater body weight. Therefore, the body weight–tailored contrast material dose protocol is preferable in this group for CT angiography of the peripancreatic arteries (22).

The mean hepatic enhancement during the PVP exceeded 50 HU in all patients in the protocol 2 group and in lighter patients in the protocol 1 group. In the heavier patient group, protocol 1 yielded lower enhancement (48.5 HU). Walkey (23) suggested that enhancement of 50 HU was the lowest threshold for the visualization of hepatic lesions with low attenuation. Similarly, Brink et al (24) reported 50 HU during the PVP as the minimum enhancement value required of contrast material injection protocols used with hepatic dynamic CT. On the basis of these considerations, we suggest that the weight-tailored contrast material injection protocol be used to ensure sufficient hepatic enhancement at dynamic CT—especially in heavier patients.

With protocol 1, we injected 120 mL of contrast material, a dose lower than that used by others (140–150 mL) (2–4,6,7,11,19,25), because the mean weight of Japanese patients, at around 60 kg (16), is lower than the body weight of patients in those studies. In our study, the contrast material dose delivered in group A with protocol 1 was approximately 2.0 mL/kg, set to correspond with the per-kilogram dose used with protocol 2. We are aware that, although appropriate in Japanese patients, injection doses of 120 mL may be too low in Westerners.

We delivered a saline flush after the administration of contrast material. Schoellnast et al (13) reported that a saline flush statistically significantly improved enhancement of the liver, pancreas, portal vein, and abdominal aorta at contrast-enhanced abdominal multidetector CT. It is possible that a contrast material dose of 2.0 mL/kg may be too low unless contrast material administration is followed by a saline flush.

In protocol 1, the contrast material (120 mL) was delivered at 4.0 mL/sec, resulting in a 30-second delivery time; in protocol 2, the injection duration was fixed at 30 seconds. The prevalent method for contrast material delivery at pancreatic dynamic CT is to choose a fixed injection rate. Awai et al (26) reported that variations in aortic peak times and aortic peak enhancement values were reduced with injection protocols that employed fixed duration times and adjusted the contrast material dose to patient weight. Because the feeding arteries to the pancreas are branches derived from the abdominal aorta, enhancement of the pancreas and the abdominal aorta can be expected to occur almost simultaneously. We postulate that injection protocols with doses tailored to patient weight and a fixed injection duration may help reduce variations in pancreatic enhancement.

In protocol 1, we used a fixed contrast material dose at an injection rate of 4.0 mL/sec. We consider that the faster injection rate may increase the risk of extravasation of contrast material, although previous investigators (27) reported that there was no extravasation of contrast material or occurrence of any systemic disorders with use of injections with a high flow rate of 8 mL/sec.

There were some potential limitations in our study. First, because the weight range and mean body weight of our study population are smaller than those of Westerners, the applicability of our results to populations of greater body weight must be verified. Second, although our results suggest that it may be possible to reduce variations in pancreatic enhancement by using injection protocols that tailor the contrast material dose to the patient's weight and use a fixed injection duration, the optimum injection duration remains to be determined.

In conclusion, our results suggest that CT protocols that deliver a contrast material dose tailored to patient weight at a fixed injection duration yield satisfactory pancreatic enhancement in patients of different body weights.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 


   IMPLICATION FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
References
 


   FOOTNOTES
 

Abbreviations: PPP = pancreatic parenchymal phase • PVP = portal venous phase • ROI = region of interest

Author contributions: Guarantors of integrity of entire study, Y. Yanaga, Y. Yamashita; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, Y. Yanaga; clinical studies, Y.N., T.N., Y.T., M.H.; statistical analysis, K.A.; and manuscript editing, Y. Yanaga, K.A., Y. Yamashita.

Authors stated no financial relationship to disclose.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 

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