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Gastrointestinal Imaging |
1 From the Department of Radiology, Kumamoto University School of Medicine, 1-1-1 Honjo, Kumamoto, 860-0811, Japan (Y.Y., Y.K., M.T.); the Department of Radiology, Kurume University School of Medicine, Japan (M.U., N.H.); and the Department of Radiology, Osaka Medical College, Japan (T.S., I.N.). Received July 27, 1999; revision requested August 30; revision received December 16; accepted December 21. Address correspondence to Y.Y. (e-mail: yama@kaiju.medic.kumamoto-u.ac.jp).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: A prospective randomized study of helical CT of the abdomen was performed by using different doses of intravenous contrast material in 221 patients (mean body weight, 57.3 kg) who were assigned randomly to three groups receiving 1.5, 2.0, or 2.5 mL/kg or a fixed dose of 100 mL of iopamidol 300. The degree of enhancement was scored visually. The CT numbers (HU) of the aorta, portal vein, liver, and pancreas were obtained at three levels of the abdomen.
RESULTS: In arterial enhancement, the 2.0 mL/kg, 2.5 mL/kg, and fixed-dose groups were significantly better than the 1.5 mL/kg group, but there was no significant difference among the 2.0 mL/kg, 2.5 mL/kg, or fixed-dose groups. The degree of enhancement of the liver, pancreas, and portal vein increased with larger doses. At visual analysis, hepatic parenchymal enhancement was graded as good or excellent in 64% of the 1.5 mL/kg, 85% of the 2.0 mL/kg, 94% of the 2.5 mL/kg, and 65% of the fixed-dose groups.
CONCLUSION: When dose was tailored to patient weight, the use of 2.0–2.5 mL/kg of intravenous contrast material produced better results than did 1.5 mL/kg or a fixed dose. Arterial enhancement did not differ among the 2.0 mL/kg, 2.5 mL/kg, or fixed-dose groups.
Index terms: Abdomen, CT, 70.12112, 70.12115 • Aorta, CT, 981.12912, 981.12915 • Computed tomography (CT), comparative studies, 70.12112, 70.12115 • Computed tomography (CT), contrast media, 70.12112, 70.12115 • Liver, CT, 761.12112, 761.12115 • Pancreas, CT, 770.12112, 770.12115 • Portal vein, CT, 957.12912, 957.12915
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Excluding disease states that alter circulation, such as congestive heart failure, the most important patient-related factor is body weight (1–6). Previous investigations have provided information about the way in which some of these factors affect hepatic or pancreatic contrast enhancement, an important determinant of tumor conspicuity. The volume of intravenous contrast material used (1,2) and the rate of injection (1–3,5) are both directly related to maximum hepatic enhancement, whereas patient weight is related inversely to it (6,7). It also has been shown that mean hepatic enhancement increases with an increased volume of contrast material in the same patients (8). At higher injection rates, pancreatic and hepatic enhancement were achieved faster and increased (9,10). Certain guidelines have been proposed for use of intravenous contrast materials, but the dose of contrast material is subject to considerable variation and still is determined mainly empirically.
Despite experimental data that indicate an inverse relationship between hepatic contrast enhancement at CT and patient weight (6), most radiologists administer a uniform dose of intravenous contrast material in all patients undergoing abdominal CT, regardless of patient size. In the interest of performing high-quality studies that optimize detection of abdominal lesions while minimizing cost, a more tailored approach to intravenous administration of contrast material is desirable.
The purpose of our study was to evaluate systematically the optimal dose of intravenous contrast material in the abdomen for the aorta, portal vein, liver, and pancreas, with the aim of developing a tailored approach to intravenous contrast material use depending on patient weight for helical CT of the abdomen.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Patients were examined initially by means of ultrasonography or underwent CT examinations as follow-up studies. Patients who had renal failure (serum creatine level of more than 2 mg/dL [152 µmol/L]), congestive heart failure, respiratory failure, hepatic failure, poor general condition, or contraindication for iodinated contrast material were excluded from the study. Patients younger than 15 years or older than 76 years were not included.
This study was performed within the routine clinical standards of our hospitals, and the patients were recruited consecutively. The Declaration of Helsinki principles were followed. Informed consent for study protocol and dose of intravenous contrast material was obtained from all the patients before the CT examinations.
CT Protocol
All patients received iopamidol with an iodine concentration of 300 mg/mL (Iopamiron; Nihon Schering, Osaka, Japan). The rate of intravenous injection of contrast material was set at 3.0 mL/sec with an automatic power injector for all examinations. Patients were assigned randomly to one of three approximately equal groups receiving 1.5, 2.0, or 2.5 mL of contrast material per kilogram of body weight or a fixed dose of 100 mL of contrast material. On the basis of the results of a pilot study (Yamashita Y, unpublished data, 1998), a fixed scan delay of 30 seconds was chosen for the arterial phase; 70 (1.5 mL/kg), 75 (2.0 mL/kg and fixed dose), or 80 (2.5 mL/kg) seconds was chosen for the portal venous phase; and 200 (1.5 mL/kg), 210 (2.0 mL/kg and fixed dose), or 220 (2.5 mL/kg) seconds for the equilibrium phase.
CT was performed by using one of three helical CT units (HiSpeed Advantage, GE Medical Systems, Milwaukee, Wis; Proseed, GE Yokogawa Medical Systems, Tokyo, Japan; or X-Vigor, Toshiba Medical, Tokyo, Japan). The variation in CT numbers among the three CT units was corrected by scanning the same phantom (GE Medical Systems). For scans obtained during the arterial phase, parameters were 7-mm collimation, pitch of l.5, 7-mm reconstruction interval, and 220-mA tube current. A softening algorithm was used to smooth image noise. For scans obtained during the portal venous phase, parameters were 7-mm collimation, pitch of 1.5, 7-mm reconstruction interval, and 280–320-mA tube current (mean, 290 mA). For scans obtained during the equilibrium phase, nonhelical scans with 7-mm collimation were used to reduce the tube load. The tube current was 280–320 mA (mean, 290 mA). A standard algorithm was used for image display. All sets of helical scans were obtained cephalocaudally.
After data acquisition, the resultant attenuations (HU) of the abdominal aorta, the hepatic parenchyma, the portal vein, and the pancreas were measured before and after administration of contrast material by using a circular region-of-interest cursor. In all patients, attenuation measurement was determined at three levels, and maximum CT numbers were measured from each phase of the scan after the start of administration of the bolus. An attempt was made to place the regions of interest in approximately the same location on each section and to maintain a constant region-of-interest area of approximately 2 cm2. The regions of interest were placed by the attending radiologists at their respective institutions.
Visible blood vessels, bile ducts, and possible hepatic or pancreatic lesions were excluded from the region-of-interest measurements in the liver and pancreas to reduce partial volume effects. The contrast enhancement was calculated for each contrast-enhanced section as the maximal difference in CT numbers of nonenhanced and contrast-enhanced scans. Maximum CT numbers of the aorta, portal vein, liver, and pancreas were obtained. In all patients, hepatic attenuation was determined in three different hepatic segments—right lobe, medial segment, and left lobe of the liver—on each CT section, and mean attenuation was calculated. We considered maximum hepatic enhancement greater than 50 HU to be adequate.
Visual Analysis
Three experienced radiologists (Y.Y., M.U., T.S.) from each of the three institutions involved in the study qualitatively assessed the degree of arterial, portal venous, hepatic parenchymal, and pancreatic enhancement on all the CT images obtained in the 221 patients. The three radiologists performed the assessment independently and had no prior knowledge of the injection protocol used.
All images were printed by using a window level of 50 HU and a width of 280 HU. We visually scored the degree of hepatic and pancreatic enhancement and vascular enhancement as follows: excellent, contrast enhancement provided optimal information to make a radiologic diagnosis; good, contrast enhancement provided adequate information to make a radiologic diagnosis; fair, contrast enhancement provided acceptable information to make a radiologic diagnosis, but image quality was unsatisfactory; poor, contrast enhancement did not provide adequate information to make a radiologic diagnosis; or no, no enhancement.
Statistics
The quantitative results of the different protocol groups were compared by using one-way analysis of variance. When the overall differences were statistically significant, post hoc analysis was performed by means of the Bonferroni adjustment. The visual analyses for the different protocol groups were compared by using the Kruskal-Wallis test. If there was a statistically significant difference among all the groups, pairwise comparisons were performed by means of the Mann-Whitney U test. Statistical significance was set at .05.
To assess the interobserver variability in visual analyses, weighted 
statistics were used to measure the degree of agreement among the three observers. A value greater than 0 was considered to indicate positive correlation. Values up to 0.40 were considered to indicate positive but poor correlation; values of 0.41–0.75, good correlation; and values greater than 0.75, excellent correlation.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Vessel enhancement.—Aortic attenuation during the arterial phase was greater than that during the portal venous phase or equilibrium phase. Mean aortic attenuation in the 1.5 mL/kg group was significantly smaller than that in the 2.0 mL/kg, 2.5 mL/kg, or fixed-dose group during the arterial phase (P < .05). However, there was no difference among the 2.0 mL/kg, 2.5 mL/kg, and fixed-dose groups (Fig 3).
For each dose of intravenous contrast material tested, enhancement of the portal vein during the portal venous phase was greater than that during the arterial phase or equilibrium phase. The difference in portal venous attenuation among the four groups was statistically significant (P < .01) during the portal venous phase. The enhancement in the 2.5 mL/kg group was significantly better than that in the other groups, followed by the 2.0 mL/kg, fixed-dose, and 1.5 mL/kg groups (P < .01) (Fig 4).
Visual Assessment
The results of visual assessment of the organ and vascular enhancement in the four groups are summarized in Tables 2–5. The agreement for the degree of enhancement for the arterial system ( = 0.53), portal venous system ( = 0.55), and hepatic parenchyma ( = 0.48) showed good correlation, but that for the pancreas indicated positive but poor correlation ( = 0.23).
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Depiction of arterial enhancement was judged to be excellent in more than 90% of patients in the 2.5 mL/kg, 2.0 mL/kg, and fixed-dose groups, which was better than that seen in the 1.5 mL/kg group. In the portal vein, the 2.5 mL/kg group showed better results than did the other groups. Excellent depiction was seen in 68% of patients in the 2.5 mL/kg group, 46% in the 2.0 mL/kg group, 11% in the 1.5 mL/kg group, and 19% in the fixed-dose group. In an overall assessment, 53 (98%), 51 (94%), 45 (80%), and 45 (79%) images were judged as good or excellent in the 2.5, 2.0, and 1.5 mL/kg and fixed-dose groups, respectively.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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In detecting the majority of metastatic tumors, adequate enhancement of hepatic parenchyma is of the utmost importance. The magnitude of hepatic enhancement is, however, determined by a combination of several factors. The most important technique-related factors include the dose (ie, volume and concentration) of intravenous contrast material (14–17) and the rate of injection of contrast material (15).
At a given injection rate, the magnitude of peak hepatic contrast enhancement increases linearly with the dose of iodine administered (14–17). As to the minimum volume of intravenous contrast material required for helical CT of the liver, investigations to date have been somewhat contradictory. Results of the series by Brink et al (11) indicate adequate enhancement with doses of 26–36 g of iodine, whereas Freeny et al (18) caution that substantial reduction of hepatic contrast occurs at doses of 30–32 g of iodine (mean body weight, 70.2 kg). Similarly, Berland and Lee (2) believe that 45 g of iodine is required for adequate hepatic enhancement. Walkey (19) suggested that a minimum enhancement of 50 HU is necessary to ensure adequate conspicuity of low-attenuation hepatic lesions. As indicated by Brink et al (11), administration protocols for intravenous contrast material need to achieve maximum hepatic CT numbers of more than 50 HU.
In our study, the group that received 2.5 mL/kg of iopamidol 300 had the highest percentage of patients (87% [47 of 54]) with maximum hepatic CT numbers of more than 50 HU. In our visual analysis, adequate hepatic parenchymal enhancement was achieved in more than 90% of the study population in the 2.5 mg/mL group and 85% in the 2.0 mg/mL group. In the group that received a fixed dose of 100 mL (30 g for a mean body weight of 58.1 kg), the mean enhancement was 45.2 HU, and adequate enhancement of the liver was not attained in more than 20% of the study population.
Adequate enhancement of the pancreatic parenchyma is important in the diagnosis of pancreatic diseases (10,20). In a recent article by Kim et al (10), a higher dose (2.0 vs 1.5 mL/kg) and a faster injection rate (5.0 vs 3.0 mL/sec) increased pancreatic enhancement. This result appears to be somewhat different from ours. In our study, when intravenous contrast material was administered at a flow rate of 3.0 mL/sec, we found that the degree of contrast enhancement did not increase proportionally with an increase in the dose of intravenous contrast material.
Although pancreatic enhancement in the 1.5 mL/kg group was inferior to that in the other groups that received higher doses, as was seen in the report by Kim et al (10), there were no significant differences among the 2.0 mL/kg, 2.5 mL/kg, and fixed-dose groups. This is probably because, since the arterial supply to the pancreas arises from large arteries in the abdomen, the peak contrast enhancement of the pancreas follows shortly after the peak contrast enhancement of the abdominal aorta. At a certain level, both aortic and pancreatic enhancement increase are minimal at a higher dose of contrast material administered at a constant injection rate.
An optimal amount of intravenous contrast material is important to enable discrimination between normal structures, such as vessels, and pathologic processes, such as soft-tissue masses or lymph node enlargement. We found that adequate arterial enhancement was attained in the majority of patients when the contrast material was administered intravenously at a rate of 3.0 mL/sec. In the portal vein, excellent depiction required a larger dose of intravenous contrast material, preferably 2.5 mL/kg. This observation is consistent with the results of a pharmacokinetic analysis proposed by Bae et al (20).
The arterial phase with a scanning delay of 30 seconds and a volume of intravenous contrast material of 100 mL or 1.5 mL/kg was suboptimal in approximately of 10%–20% of the patients. In the images obtained during the arterial phase, the increase in volume of intravenous contrast material to 2.0 mL/kg led to a reduction in the number of suboptimal CT images obtained during the arterial phase. However, the increase in volume to 2.5 mL/kg did not substantially improve arterial enhancement. This is probably because the degree of maximum enhancement in the arterial system is close to maximum with 2.0 mL/kg when an injection rate of 3.0 mL/sec is used. A more rapid injection rate may result in superior arterial enhancement.
Prefilled syringes are more commonly used in the clinical field in some countries because of their convenience or for sanitary reasons. In such instances, the dose of contrast material tends to be fixed in the majority of institutions. Among radiologists in Japan, an empiric dose of 100 mL of contrast material (300 mg of iodine per milliliter) is used most commonly for helical CT of the abdomen. When we used this dose for all the patients, enhancement of the liver was judged to be inappropriate in approximately 30% of the patient population (mean body weight, 57.3 kg) in our study. This was fully expected, because the mean dose was calculated to be 1.7 mL/kg, which is between our 1.5 and 2.0 mL/kg protocols. Therefore, several types of prefilled syringes should be available in CT rooms to administer the optimal dose of intravenous contrast material properly.
There are several potential limitations of our study design. First, we used a fixed scanning delay for all patients. Although the scanning delay was selected on the basis of the results of a pilot study (Yamashita Y, unpublished data, 1998) together with our experience of more than 5 years with helical CT, it may not have been optimal. We may not have attained the peak enhancement for each organ. Furthermore, a fixed scanning delay cannot take into account the individually variable transit time of contrast material. This may be essential for helical CT during the short arterial phase of approximately 10 seconds. Measurement of multiple sections may compensate somewhat for this limitation.
Second, although we excluded patients with severe hepatic dysfunction, the patient population in our study consisted of a large number of patients with chronic hepatic diseases, conditions that may result in alteration of the degree of hepatic parenchymal enhancement.
Third, our fixed dose of iopamidol 300 appears to be inadequate for Western people. However, most of the patients in our study weighed less than 60.0 kg (mean, 58.1 kg), and 100 mL is used most frequently in Japanese hospitals, so we chose this dose as the predetermined dose. The results should be more obvious in a Western population with a higher mean body weight of 70.0 kg or more.
Finally, although comparison between empiric dose and enhancement on the basis of weight should be performed in the same group of patients to avoid wide interpatient variations in organ and vessel enhancement, we did not compare this in this study. Instead, we collected a relatively large number of patients to overcome the variation among patients, which was supported by a careful statistical study design.
In conclusion, when dose was tailored to patient weight, the use of 2.0–2.5 mL/kg of intravenous contrast material produced better results than did 1.5 mL/kg or a fixed dose of 100 mL. Neither arterial nor pancreatic enhancement differed among the 2.0 mL/kg, 2.5 mL/kg, or fixed-dose groups when intravenous contrast material was administered at a rate of 3.0 mL/sec. Inadequate enhancement of the hepatic parenchyma was seen occasionally when we used a fixed dose in the patient population in our study. We believe that the dose of intravenous contrast material should be tailored according to patient weight to achieve adequate contrast enhancement in the majority of patients.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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1.5 cm) malignant hepatic neoplasms. AJR Am J Roentgenol 1995; 164:879-884.This article has been cited by other articles:
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