Optimization of computed tomography contrast studies with a new, simple dosing regimen incorporating body size: examination of contrast effects in the thoracoabdominal aorta.

The dosage of contrast agents for computed tomography contrast studies is calculated based on the parameter of actual body weight (ABW) to ensure reproducibility. The use of lean body weight (LBW) and adjustment for physique (lean or obese) improves accuracy. However, this method is complex, because LBW is not a general body parameter and requires a special device to measure. To solve this problem, contrast body weight (CBW), has been proposed as a new and simple parameter that considers physique. CBW is calculated by determining the blood volume ratio based on body height, ABW, and sex and can potentially correct for body size. It can be calculated by entering a formula in a Microsoft Excel sheet. Since CBW can be easily obtained using this general tool, we decided to compare the two body parameters of ABW and CBW. We compared ABW and CBW and demonstrated a higher correlation between CBW-based dosing and the amount of iodine used per body weight than with ABW-based dosing. CBW-based dosing allows correction for body size. This indicates that contrast enhancement over a spectrum of lean or obese examinees can be linearly evaluated. To date, this method has shown good results.

[Contrast enhancement technique in brain 3D-CTA studies: optimizing the amount of contrast medium according to scan time based on TDC].

In three-dimensional CT angiography (3D-CTA), good reproducibility can be obtained by maintaining the maximum CT numbers (HU) at a specified level. However, the correlation between the scan time and the injection time showed that the maximum CT numbers increased and varied due to the additional contrast enhancement effect from recirculation of the injected contrast medium for longer injection times when the dose of iodinated contrast medium per unit time (mgI/s) was maintained at a specified level based on the time-density curve (TDC) of the phantom. The amount of contrast medium employed at our hospital has been optimized based on an iodinated contrast medium dose per unit time providing a contrast enhancement effect of 300 HU in the middle cerebral artery. Using this standard, a TDC phantom was employed to obtain an iodinated contrast medium dose per unit time, permitting equivalent maximum CT values (used as standard values) to be obtained by changing the injection time. A contrast-enhancement technique that accounts for the variation in the scan time was evaluated. Strong correlations were observed between the scan time and the injection time (R2=0.969) and between the injection time and the dose of iodinated contrast medium per unit body weight (R2=0.994). We conclude that adjusting the dose of iodinated contrast medium per unit body weight per unit time according to the scan time permits optimization of the contrast-enhancement technique.

[Overview of cardiac contrast examination using 64-row multislice CT].

ECG-gated multislice CT(MSCT)now supports not only morphological but also functional diagnosis. In order to improve accuracy in the functional analysis of cardiac motion, it is important to depict the endocardial and epicardial contours. The present study was conducted to evaluate a method in which contrast medium and physiological saline solution(saline)are injected simultaneously, and the iodinated contrast medium concentration is varied in a stepwise manner(multi-stage injection)or continuously(cross injection). The results showed that the cross-injection method exhibited small differences in myocardial CT values between the right and left heart and was thought to be effective for automatic region extraction of the cardiac chambers and myocardium. However, cross-injection requires saline and contrast medium to be injected in equal volumes, necessitating a higher injection speed. Therefore, a newly developed trapezoidal cross-injection method was included in the study as an improved method. The results showed that trapezoidal cross injection provided high CT values. The relationship between the patient's body weight and the amount of iodinated contrast medium used also was investigated, and a negative correlation was observed for all three injection methods: multi-stage injection(r=0.63), cross injection(r=0.54), and trapezoidal cross injection(r=0.8). The trapezoidal cross-injection method showed the strongest correlation.

[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.

[Assessment of contrast enhancement using the variable contrast medium injection method in 3D-CTA of the head].

We have reported that, using the bolus-tracking method synchronized with an injector, the injection of contrast medium in a single phase up to 10 sec before the end of the study (referred to as "single-stage injection") or the combination of single-stage injection stopped 15 sec before the end of the study and a physiological saline solution flush (referred to as "saline solution flush") makes it possible to minimize the amount of contrast medium employed in 3D-CTA of the head and neck in a scanning time of approximately 30 sec. If the continuous variable method of contrast medium injection (referred to as "variable injection") can provide the same level of contrast enhancement as that obtained with a single-stage injector for constant-rate injection, it should be possible to eliminate cumbersome study procedures associated with the saline solution flush and to simplify the study protocol. We therefore performed a comparative study to assess the contrast enhancement effect in variable injection. The results showed that variable injection provided almost the same degree of contrast enhancement as single-stage injection + saline solution flush, while permitting the amount of contrast medium to be reduced. It was concluded that variable injection (with a variation parameter of 0.5) is an effective method of improving the contrast enhancement effect and minimizing the amount of contrast medium employed, as compared with the saline solution flush method. Furthermore, it permits the examination procedures to be simplified.

A new method with variable injection parameters in contrast-enhanced CT: a phantom study for evaluating an aortic peak enhancement.

Contrast-enhanced CT employs a standard uniphasic single-injection method (SIM), wherein administration is based on two parameters: the iodine administration rate (mgI/s) and the injection duration (s). However, as the SIM uses a fixed iodine administration rate, only a uniform contrast enhancement can be achieved with this method. The iodine administration rate can be increased only by increasing the iodine dose or shortening the injection duration, and no arbitrary adjustments can be made to the peak enhancement characteristics of the time-enhancement curves (TECs) at the fixed injection parameters used in the SIM. To address this problem, we developed a variable injection method (VIM) with a new parameter, the variation factor (VF), to adjust the TECs. A phantom study with the VIM indicated that arbitrary adjustments to the iodine administration rate could be made without changing the injection duration or increasing the iodine load. In our study, VFs of 0.3 and 0.5, which showed earlier achievement of peak enhancements, showed better temporal separation between arterial vasculature and parenchyma or the venous vasculature than that obtained with the SIM. The higher peak enhancement provided by the VF of 0.3 was also considered to improve the contrast in qualitative diagnostic examinations. A VF of 0.5 increased the duration of the enhancement and was considered to produce stable enhancement of contrast in vascular investigations. The VF is now an essential parameter, and the VIM is useful as a reasonable contrast method that may contribute to both improved visualization and improvement in the accuracy of morphologic diagnosis.

[Evaluation of a contrast examination technique for three-dimensional CT angiography (3DCTA) of the head and craniocervical region].

In three-dimensional CT angiography (3DCTA) studies, we make it a rule to use a CT number monitoring system (SureStart, Toshiba Medical Systems Company) to ensure that contrast-enhanced images are acquired at the optimal timing. However, although SureStart can accurately determine enhancement start timing, it is still possible to inject more contrast medium than necessary because the scan start time is not known with certainty. To address this problem, we conducted investigations to determine the ideal contrast examination technique using SureStart and an injector synchronization system. Our results showed that a CT number of 300 HU in the middle cerebral artery (M1) could be obtained with the injection of contrast medium for a period of 45 s (450 mgI/kg) for the head or for 50 s (450 mgI/kg) for the craniocervical region. This makes it possible to perform contrast studies with greater reproducibility by taking individual variation into consideration. Moreover, it was found that comparable results could be obtained by terminating the injection of contrast medium 15 s before the completion of the study and immediately injecting a physiological saline solution flush, permitting the volume of contrast medium to be further reduced.

[Effects of computed tomography contrast medium factors on contrast enhancement].

The various nonionic iodinated contrast media used in contrast computed tomography (CT) studies differ in terms of their composition, characteristics, and iodine concentration (mgI/ml), as well as the volume injected (ml). Compared with ionic iodinated contrast media, nonionic iodinated contrast media are low-osmolar agents, with different agents having different osmotic pressures. Using a custom-made phantom incorporating a semipermeable membrane, the osmotic flow rate (HU/s) could easily be measured based on the observed increase in CT numbers, and the relationship between the osmotic pressure and the osmotic flow rate could be obtained (r(2)=0.84). In addition, taking the effects of patient size into consideration, the levels of contrast enhancement in the abdominal aorta (AA) and inferior vena cava (IVC) were compared among four types of CT contrast medium. The results showed differences in contrast enhancement in the IVC during the equilibrium phase depending on the type of contrast medium used. It was found that the factors responsible for the differences observed in enhancement in the IVC were the osmotic flow rate and the volume of the blood flow pathways in the circulatory system. It is therefore considered that the reproducibility of contrast enhancement is likely to be reduced in the examination of parenchymal organs, in which scanning must be performed during the equilibrium phase, even if the amount of iodine injected per unit body weight (mgI/kg) is maintained at a specified level.