First published online October 12, 2006
British Journal of Radiology (2007) 80, 231-234
© 2007 British Institute of Radiology
doi: 10.1259/bjr/60407135
Usefulness of saline pushing in reduction of contrast material dose in abdominal CT: evaluation of time–density curve for the aorta, portal vein and liver
F Tatsugami, MD
M Matsuki, MD
Y Inada, MD
G Nakai, MD
M Tanikake, MD
S Yoshikawa, RT
and
I Narabayashi, MD
Department of Radiology, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki City, Osaka 569-8686, Japan
Correspondence: Fuminari Tatsugami, MD, Department of Radiology, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki City, Osaka 569-8686, Japan. E-mail: sa104{at}rg8.50-net.ne.jp
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Abstract
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The effects of saline pushing after contrast material injection were investigated as well as the possibility for this technique to reduce contrast material doses in liver CT examinations. 52 patients were divided randomly into three groups: 100 ml of contrast material (300 mg I ml–1) only (A; n = 19), 100 ml of contrast material pushed with 50 ml of saline solution (B; n = 17), and 85 ml of contrast material pushed with 50 ml of saline solution (C; n = 16). Single-level images were obtained at the level of the main portal vein after the initiation of contrast material injection. There were no significant differences in the mean peak enhancement values (PE) and the mean time to peak enhancement values (TPE) of the aorta between the three groups. The mean PE of the portal vein in group B increased 21 HU over that in group A (p<0.05), and there was no significant difference between groups A and C. The mean PE of the liver in group B increased 7 HU over that in group A (p<0.05), and there was no significant difference between groups A and C. The mean TPE of the portal vein was shorter by 4 s (p<0.05), and that of the liver was shorter by 5 s (p<0.05) in group C compared with those in group A. In conclusion, saline pushing increases the enhancement values of the portal vein and liver, and allows a contrast material dose reduction of 15 ml without decreasing hepatic and vascular enhancement at adequate scan timing.
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Introduction
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In thoracic CT examinations, it is reported that saline pushing of contrast material remaining in the injector tubing, peripheral veins, superior vena cava and right heart after the administration of contrast material leads to an increase in enhancement values of the pulmonary arteries and the thoracic aorta [1, 2]. However, only a few studies have evaluated the effect of saline pushing in abdominal CT examinations [3–7]. In this study, the objectives were to investigate the effect of saline pushing after contrast material injection and the possibility for this technique to reduce contrast material doses in liver CT examinations based on time–density curves.
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Materials and methods
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Patients
This study was performed according to the principles of the Declaration of Helsinki and approved by our institutional review board. Informed consent was obtained from all patients before the CT examination. Initially, 78 patients with malignancies who were referred for abdominal multidetector (MD) CT to evaluate liver metastasis were recruited consecutively in this study. However, patients who had congestive heart failure, renal failure and conditions that could affect hepatic arterial and portal venous flow (extensive hepatic tumour involvement, cirrhosis, portal vein thrombosis, compression or invasion of hepatic artery or portal vein), were excluded. The purpose of this study was explained to the patients. Specifically, that radiation levels would be increased 25–30%, and that this study would not interfere with clinical examinations. 16 patients who did not consent to the purpose of this study were excluded.
The final study group consisted of 52 patients (25 men, 27 women) who were 41–78 years old (mean 59.9 years) and weighed 40–73 kg (mean, 56.9 kg). The patients were divided randomly into three groups and received only 100 ml of non-ionic iodinated contrast material (Iomeprol, Iomeron 300 mg I ml–1, Eisai, Tokyo, Japan) (group A; n = 19), 100 ml of contrast material (300 mg I ml–1) with 50 mL of saline solution (group B; n = 17), or 85 ml of contrast material (300 mg I ml–1) with 50 ml of saline solution (group C; n = 16) (Table 1
).
CT scanning
The CT scanner was a 16 MDCT, Aquilion multi-scanner (Toshiba Corporation Medical Systems, Tokyo, Japan). Initially, a scout image of the upper abdomen was obtained, which was used to map the longitudinal field of view of the helical scan. With reference to the scout image, pre-contrast helical scans of the liver (approximately 200 mm including the entire liver) were obtained at a voltage of 120 kV, a tube current of 300 mA, 0.5 s/rotation, 4x3 mm detector configuration and a beam pitch of 0.938. Next, a 20 gauge intravenous injection catheter (Termo, Tokyo, Japan) was inserted into the antecubital vein. A dual shot injector (Nemoto Kyorindo, Tokyo, Japan) was prepared, and a syringe filled with either 100 ml or 85 ml of contrast material was set up. When using saline pushing, another syringe with 50 ml of saline solution was set up and a Y-adapter tube with a no return valve was used to connect the two syringes. On the basis of the unenhanced images, the middle section of the main trunk of the portal vein was determined. The contrast material and saline solution were injected at a rate of 5 ml s–1. Saline solution was injected immediately after the contrast material was completely administered. In this examination, we selected an injection rate of 5 ml s–1 for an application of the three-dimensional (3D) CT arteriography and portography [8–13]. Single-level dynamic CT images were obtained at this level every 3 s from 0 s to 90 s after the initiation of intravenous contrast material injection. This examination was performed with a voltage of 120 kV, a tube current of 40 mA, 0.5 s/rotation. After this examination, the entire liver CT examination was performed with a voltage of 120 kV, a tube current of 300 mA, 0.5 s/rotation and a beam pitch of 0.938.
Methods of evaluation
CT attenuation values for the aorta, main portal vein and liver parenchyma were measured using a circular region of interest (ROI) cursor on the 31 scans obtained (Figure 1). In the liver parenchyma, ROIs were measured in three separate areas including both the left and right lobes, and the results were averaged. Vessels and artefacts were carefully excluded from the ROI measurements. The enhancement value at each time point was calculated as the difference between the unenhanced and contrast-enhanced images of the aorta, portal vein and liver parenchyma. The mean enhancement values for the aorta, portal vein and liver parenchyma at each time point for each group were plotted on graphs as functions of time (time–density curves). Enhancement parameters consisted of the mean peak enhancement values (PE) and the mean time to peak enhancement values (TPE) of the aorta, portal vein and liver parenchyma. All of these measurements were performed by one radiologist who was blind to the injection technique.
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Figure 1. CT attenuation values for the aorta(dotted line), main portal vein (thin line) and liver parenchyma (thick line) are measured using a circular region of interest (ROI) cursor on the 31 scans obtained.
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Statistical analyses
Patients' ages and body weights were compared between the three groups by one-way analysis of variance (ANOVA). The quantitative results for the three groups were compared using the Kruskal–Wallis test, and pairwise comparisons of groups were performed using the Mann–Whitney U test. All the data were expressed as means±SD, and differences were considered to be statistically significant at p<0.05.
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Results
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There was no statistically significant difference in age or body weight between the three groups (p>0.05). The mean PE and the mean TPE of the aorta, portal vein and liver parenchyma are shown in Tables 2 and 3. The time–density curves of the aorta, portal vein and liver parenchyma are shown in graphs (Figures 2–4).
Aortic enhancement
The mean PE of the aorta in group B was greater by 21.6 HU than that of group A, and was greater by 6.0 HU than that of group C; however, there was no significant difference between the three groups (p = 0.773). There was no significant difference in the mean TPE of the aorta between the three groups (p = 0.198).
Main portal vein enhancement
The mean PE of the portal vein in group B was significantly greater than that in group A, and there was no significant difference between groups A and C (p = 0.783) and between groups B and C (p = 0.136). The mean TPE of the portal vein in group C was significantly shorter than those in groups A and B, and there was no significant difference between groups A and B (p = 0.55).
Hepatic enhancement
The mean PE of the liver parenchyma in group B was significantly greater than those in groups A and C, and there was no significant difference between groups A and C (p = 0.581). The mean TPE of the liver parenchyma in group C was significantly shorter than those in groups A and B, and there was no significant difference between groups A and B (p = 0.937).
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Discussion
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In fast MDCT scanning, a substantial amount of contrast material remains in the injector tubing, peripheral veins, superior vena cava and right heart. Therefore, the technique of pushing the remaining contrast material by a saline solution after the complete administration of contrast material was developed. In thoracic CT examinations, it is reported that the saline pushing technique increases the enhancement values of the pulmonary arteries and thoracic aorta, and permits a reduction of contrast material volume, which leads to reduced perivenous artefacts in the superior vena cava [1, 2]. However, only a few studies have evaluated the effect of saline pushing in abdominal CT examinations [3–7]. Previously, it was reported that the saline pushing technique can improve the enhancement values of the portal vein in the portal venous inflow phase, but there was almost no increase in the enhancement values of the liver parenchyma in the hepatic phase 80 s after the beginning of the contrast material injection [5, 6]. Dorio et al. [3] reported that using 100 ml of contrast material pushed with 50 ml of saline solution resulted in no significant difference in the enhancement value of the liver parenchyma compared with using 150 ml of contrast material only. In that study, scanning was started when the liver parenchyma was enhanced by 50 HU more than the baseline using an automated bolus-tracking technology and the scanning start time ranged from 30 s to 97 s with a mean of 56 s. It was then considered for the hepatic phase that 80 s after the beginning of the contrast material injection may be too late in evaluating the enhancement of the liver parenchyma. In this study, we performed a single-level dynamic scanning at the level of the main portal vein after the initiation of contrast material injection, and measured the CT attenuation values of the aorta, main portal vein and liver parenchyma.
Initially, the effect of saline pushing after injecting contrast material on hepatic and vascular enhancement and the adequate scanning timing for the arterial, portal venous and hepatic phase were examined. Subsequently, the possibility of this technique was examined for reducing contrast material doses with saline pushing in liver examinations.
Initially, both of the mean PEs of the portal vein and liver parenchyma increased significantly using saline pushing. It was considered that the increase of the enhancement values in the aorta and splenic artery by saline pushing chiefly led to an increase in the enhancement values of the splenic vein, portal vein and liver parenchyma [5]. The mean TPE of the liver parenchyma was about 56 s, which is consistent with the results in Dorio's report. These results indicated that a saline pushing technique can contribute to improving 3D CT arteriography and portography as well as the enhancement values of the liver parenchyma. We therefore considered that a saline pushing technique can be helpful in the detection of metastatic liver tumour and a vascular evaluation before interventional procedures or surgery for liver tumour or liver transplantation. In the future, we must clinically review whether the diagnostic sensitivity of metastatic liver tumours increases by using 100 ml of contrast material with 50 ml of saline solution, and whether the diagnostic sensitivity of metastatic liver tumours using 85 ml of contrast material with 50 ml of saline solution is similar to that using 100 ml of contrast material alone.
Second, there were no significant differences in the mean PE of the aorta, portal vein and liver parenchyma between groups using 100 ml of contrast material only and 85 ml of contrast material with saline pushing. This indicated that the saline pushing allows a contrast material dose reduction of 15 ml without decreasing hepatic and vascular enhancement. However, in using 85 ml of contrast material with saline pushing, the scanning delay time of the portal vein was shorter by 4 s and that of the liver shorter by 5 s compared with that for 100 ml of contrast material injection only. Using a saline pushing technique is cost-effective; if contrast material is priced strictly by volume in Japan, we can save $18 per patient, which corresponds to 15 ml of non-ionic iodinated contrast material (Iomeprol, Iomeron 300 mg I ml–1).
In conclusion, saline pushing increases the enhancement values of the portal vein and liver without moving the mean time to peak enhancement, and allows a contrast material dose reduction of 15 ml without decreasing hepatic and vascular enhancement at adequate scan timing.
Received for publication May 8, 2006.
Revision received July 14, 2006.
Accepted for publication August 15, 2006.
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References
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Abstract
Introduction
