Effect of duration of contrast material injection on peak enhancement times and values of the aorta, main portal vein, and liver at dynamic MDCT with the dose of contrast medium tailored to patient weight
Introduction
Optimization of contrast enhancement has become crucial with the introduction of multidetector-row helical computed tomography (MDCT), given the shorter image acquisition time compared with that of single-row detector helical CT. Many abdominal CT applications require intravenous administration of contrast medium to enhance lesion conspicuity, and proper selection of acquisition timing is critical to optimize contrast medium enhancement. Technical factors for the administration of contrast material generally include dose (volume of injected contrast material for a given concentration), injection rate, and scan delay time.1 Recent studies have shown that the dose should be tailored according to the patient's weight to achieve adequate enhancement, particularly for the liver.1, 2, 3, 4, 5, 6, 7 There are two methods for administering an optimal dose of contrast material tailored for individual patients: injecting the contrast material at a fixed rate in all patients, which is the method commonly used at present; and injecting the contrast material for a fixed duration. For both methods, it is important to predict the enhancement pattern of the aorta, liver, and main portal vein to permit an optimal imaging protocol with proper scan delays to be determined.7
Recently, Awai et al.7 showed that the temporal scan window for peak aortic enhancement was more uniform with an injection protocol with fixed injection durations of 25 and 35 s than with a fixed injection rate of 4 ml/s. They also stated that the fixed injection duration method could reduce variations in aortic peak enhancement values.7 In earlier studies, Bae et al.8 reported that the time to the peak in aortic enhancement corresponded to the sum of the injection duration and the bolus transfer time from the injection site to the aorta, and that for hepatic enhancement corresponded to the sum of injection duration and the time to reach the distribution equilibrium.8, 9
Although Awai et al. showed that an injection protocol with a fixed injection duration might be effective in providing more uniform scan timing and enhancement,1, 7 to our knowledge, no comprehensive data are available on the correlation of peak enhancement times and values with different duration times; information that would be crucial for establishing the optimal parameters for contrast-enhanced hepatic CT. Therefore, the aim of the present study was to investigate the effect of different injection duration times on the peak enhancement times and values of the aorta, main portal vein, and liver.
Section snippets
Subjects
Between January 2002 and May 2002, 75 patients (39 men, 36 women; mean age 48.7 years, range 25–71 years) with a previous history of resected pelvic malignancies who underwent contrast-enhanced abdominal CT for the evaluation of local recurrence or distant metastases were prospectively enrolled. Surgical resections for the primary pelvic malignancies in all patients had been performed at least 24 months (range 25–75 months; mean 41 months) before the present study. No patients showed any
Results
Mean ages and weights of the patients in each group and gender distributions are summarized in Table 1. One-way ANOVA revealed no significant intergroup differences in patient age (p = 0.98), patient weight (p = 0.33), or gender distribution (p = 0.86).
Scatter diagrams demonstrating the relationship between patient weight and peak enhancement values and times of aorta, main portal vein, and liver showed no statistically significant correlations between patient weight and delay to peak enhancement or
Discussion
Awai et al.1, 7 recently showed that variations in aortic peak times and aortic peak enhancement values can be reduced by using an injection protocol in which a volume of contrast material tailored to the patient dose is administered intravenously with a fixed injection duration. In earlier studies, Bae et al.8, 9 showed that the time from the initiation of the injection to the peak aortic enhancement is closely associated with injection duration. It appears from these studies that fixed
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