Adjustment of scan delay for bolus tracking with cardiothoracic ratio of CT scout image for hepatic artery phase of hepatic dynamic CT.

This study aimed to determine the scan delay for bolus tracking in the hepatic artery phase (HAP) of hepatic dynamic computed tomography (CT) using the cardiothoracic ratio (CTR) from CT scout images. We retrospectively studied 188 patients who underwent hepatic dynamic CT, 24 of whom had scan delays adjusted for CTR. The contrast enhancement of the abdominal aorta, portal vein, hepatic vein, and hepatic parenchyma was calculated for HAP. The adequacy of the scan timing for HAP was assessed using three classifications: early, appropriate, or late. The effect of HAP on scan timing adequacy was determined using multivariate logistic regression analysis, and the optimal cutoff value of CTR was evaluated using receiver operating characteristic analysis. The trigger times for bolus tracking (odds ratio: 1.58) and CTR (odds ratio: 1.23) were significantly affected by the appropriate scan timing of the HAP. The optimal cutoff value of CTR was 59.3%. The scan timing of HAP with a scan delay of 15 s was 14% of early and 86% of appropriate, and the proportion of early in CTR ≥ 60% (early, 52%; appropriate, 48%) was higher than that in CTR < 60% (early, 6%; appropriate, 94%). Adjusting the scan delay to 20 s in CTR ≥ 60% increased the proportion of appropriate (early, 4%; appropriate, 96%). The CTR of a CT scout image is an effective index for determining the scan delay for bolus tracking. Adjusting the scan delay by CTR can provide appropriate HAP images in more patients. Trial registration number: R-080; date of registration: 9 March 2023, retrospectively registered.

Improvement in arterial enhancement using diluted injection of contrast medium in CT angiography.

BACKGROUND: Arterial enhancement after contrast injection affects the quality of computed tomography angiography (CTA) images. PURPOSE: To evaluate whether the dilution of contrast medium (CM) for CTA increases arterial enhancement after the adjustment of iodine concentration as per the patient's body weight (BW). MATERIAL AND METHODS: We retrospectively studied 700 patients who underwent coronary CTA. The first 350 consecutive patients underwent standard CTA with a fixed iodine concentration, whereas the remaining 350 underwent CTA with a diluted CM injection. All patients were classified into three groups according to their BW (<55, 55-65, and 66-73 kg). The mean and proportion of contrast enhancements (CEs) in the ascending aorta of ≥350 Hounsfield units (HUs) (CE350) were compared between the standard CTA and diluted CM injection and among the BW groups. The associations between BW and CE were analyzed using linear regression. RESULTS: Receiving diluted CM increased the mean CE in the <55-kg group (403.4 ± 55.4 HU vs. 382.8 ± 59.3 HU; P < 0.01) but not in the groups with heavier BW. The proportion of patients with CE350 increased with BW (<55 kg = 71%, 55-65 kg = 84%, and 66-73 kg = 91%) and increased after dilution (86%, 93%, and 96%, respectively). After CM dilution, the correlation between BW and CE among patients undergoing CTA decreased from 0.37 to 0.22 (P < 0.05). CONCLUSION: CM dilution for CTA improves arterial enhancement.

Split-bolus injection protocol with optimized timings of contrast medium injection and CT scanning for 3D CT angio-venography before laparoscopic gastrectomy.

PURPOSE: To propose an optimization method of contrast medium injection for the split-bolus protocol based on the contrast medium pharmacokinetics and investigate the utility of the optimized split-bolus protocol in 3D CT angio-venography for laparoscopic gastrectomy. MATERIALS AND METHODS: A pharmacokinetic relationship between injection duration and time to the peak enhancement was taken into account in the protocol design. The first 20 consecutive patients underwent a multi-phase scan with a single-bolus injection (single-bolus protocol), and the next 20 underwent the proposed split-bolus protocol. CT attenuations of the arteries and veins and dose-length products (DLPs) were compared between the two protocols. Two radiologists visually assessed arterial and venous depictions and the misregistrations. RESULTS: Mean arterial CT attenuations were not significantly different between the two protocols. Though mean venous CT attenuations for the split-bolus protocol were 7-11% lower than those of the single-bolus protocol, they were visually evaluated as similar. The mean DLP of the split-bolus protocol was 46% lower than that of the single-bolus protocol. Misregistration between the arteries and veins occurred 35-80% during the single-bolus protocol, but was not indicated in the split-bolus protocol. CONCLUSION: The split-bolus protocol with optimized timing was more effective for providing improved image quality with reduced radiation dose compared with the single-bolus protocol in 3D CT angio-venography for laparoscopic gastrectomy.

[Effect of Tube Voltage on Contrast Enhancement and Contrast Medium Dose in Abdominal Contrast-enhanced Computed Tomography].

The purpose of this study was to investigate the effect of tube voltage on relationship between a patient's body weight and contrast enhancement in abdominal contrast-enhanced computed tomography (CT). Five phantoms with diameters ranging from 19.2 to 30.6 cm, including syringes filled with iodine solution diluted to different concentrations, were used to compare the effects at tube voltages of 80, 100, and 120 kVp. Furthermore, for clinical study, 300 patients who underwent abdominal contrast-enhanced CT examinations were enrolled and enhancements of aorta and hepatic parenchyma in arterial phase and equilibrium phase were compared at 80, 100, and 120 kVp using a contrast medium administration proportional to the body weight. The contrast enhancement was decreased with increase in phantom size because of the beam-hardening effect, and however, the decrease was less at low tube voltages of 80 and 100 kVp (lowest at 80 kVp), demonstrating the beam-hardening effect was reduced at low tube voltages. The enhancements of aorta and hepatic parenchyma indicated tended to increase in patients with a heavy body weight, and this trend was stronger at 80 and 100 kVp (80 kVp>100 kVp). Therefore, it was indicated that the problem of excessive contrast enhancement in patients with a high body weight was prominent at low tube voltages because the beam-hardening effect in patients with a heavy body weight was weaken by low tube voltages.

[Assessment of the effects of administering a saline solution flush after contrast medium injection using different injection durations and flush methods].

The purpose of administering a saline solution flush after contrast medium injection is to more effectively utilize the contrast medium remaining in the vessels from the subclavian vein to the superior vena cava. In order to investigate the effects of administering a saline solution flush after a contrast medium injection, we evaluated the effects of various contrast medium injection durations and injection methods on the time-density curve (TDC) using a custom-made TDC measurement phantom. The TDC was found to have a biphasic appearance, showing a rapid increase after the arrival of contrast medium in the target region followed by a slower increase from an inflection point at 25 s after the start of contrast medium injection, reflecting the differences in circulatory dynamics for each duration. The results showed that the effect of saline solution flush was allowed the differences by contrast medium duration at the inflection point. Specifically, when the saline solution flush was administered before the inflection point, the CT number was increased, and when it was administered after the inflection point, contrast enhancement was prolonged. With regard to the method in which the saline solution flush is administered before the inflection point, it was found that injecting a mixture of contrast medium and saline solution before the saline solution flush reduced the degree of inflection of the TDC, resulting in a more stable TDC.

[Evaluation of the variable-speed injection method for three-dimensional CT angiography of the trunk].

In three-dimensional CT angiography (3DCTA) studies, the CT values within blood vessels ideally should be uniform because the reproducibility and detectability of the morphological characteristics of blood vessels change depending on the threshold value selected. The time-density curve (TDC) therefore should be maintained at a certain level. However, conventional contrast medium injectors have a fixed injection speed, and the injection speed must therefore be changed in a stepwise manner. This means that it is not possible to maintain the TDC precisely. However, recent advances in the performance capabilities of contrast medium injectors allow the injection speed to be changed continuously with a user-selectable injection-speed ratio, permitting studies to be performed using the so-called "variable-speed injection method". We have conducted studies using this new method to determine the optimal injection speed ratio that permits the TDC to be maintained at the desired level. Our results showed that an injection-speed ratio of 0.5 permits the TDC to be maintained at the optimal level, improving the reproducibility and detectability of blood vessel morphology in 3DCTA studies. In addition, when contrast medium injection was terminated at a time point > or =50% of the preset contrast medium injection time, the mean CT value was not adversely affected (i.e., was not significantly reduced), making it possible to reduce the amount of contrast medium administered to the patient.