Abdomen: angiography with 16-detector CT--comparison of image quality and radiation dose between studies with 0.625-mm and those with 1.25-mm collimation.

PURPOSE: To prospectively compare image quality and volume computed tomographic (CT) dose index (CTDI(vol)) of 16-detector CT angiograms of the abdomen acquired with 0.625-mm collimation with those of images acquired with 1.25-mm collimation. MATERIALS AND METHODS: This study had institutional review board approval, and informed consent was obtained from all patients. Dual-phase contrast material-enhanced CT was performed in 78 patients (48 men and 30 women; age, 34-91 years; mean age, 64.8 years) by using a 16-detector CT scanner. Patients were prospectively randomized into two equal-sized groups: those who underwent CT with 0.625-mm collimation and nonoverlapped reconstruction and those who underwent CT with 1.25-mm collimation and 50% overlapped reconstruction. Scan acquisition time was 7.5 seconds in both groups. CTDI(vol) was recorded. Arterial phase volume-rendered, arterial phase multiplanar reformatted, and portal venous phase multiplanar reformatted CT angiograms were generated. Qualitative assessment was performed for image quality and for depiction of splanchnic, intercostal, and lumbar arteries and veins. The unpaired t test was used for statistical comparison. RESULTS: On the arterial phase CT angiograms, there was no difference between the two collimation groups for the depiction of proximal splanchnic arteries, while the dorsal pancreatic, intercostal, and lumbar arteries and some peripheral splanchnic arterial branches were better delineated on CT scans obtained with 0.625-mm collimation than on scans obtained with 1.25-mm collimation (P < .05). Regarding the portal venous phase CT angiograms, no difference between the two groups was found in most veins, except the right adrenal vein (P = .003). Image quality was superior for 1.25-mm collimation (P < .001). CTDI(vol) values were positively correlated with patient body weight (r = 0.34, P < .001) but had no correlation with collimation size (P = .24). CONCLUSION: Scanning with 1.25-mm collimation seems adequate for a routine CT angiography examination of most arteries and veins at 16-detector CT, while scanning with 0.625-mm collimation facilitates improved delineation of fine vessels. CTDI(vol) values correlate positively with body weight but have no correlation with collimation size.

Abdominal multidetector CT in patients with varying body fat percentages: estimation of optimal contrast material dose.

PURPOSE: To determine if contrast material dose for abdominal multidetector computed tomography (CT), as determined by using body weight (BW), overestimates the amount of contrast material required in heavier patients. MATERIALS AND METHODS: Institutional review committee approval and patients' written informed consent were obtained. CT images of the abdomen were obtained by using 2 mL per kilogram of BW of intravenous contrast material (300 mg/mL iodine) injected at 4 mL/sec in 161 consecutive patients (age range, 28-90 years; mean age, 63 years; 95 men, 66 women). CT scans were initiated 45 and 150 seconds after aortic enhancement increased by 50 HU. The patients were divided into low (37-54 kg) and high (55-75 kg) BW groups. The DeltaHU/I, where DeltaHU is change in CT number and I is iodine dose in grams, and adjusted maximum hepatic enhancement (DeltaHU/[I/kg]) were assessed for correlation with BW, body mass index (BMI), and body fat percentage (BFP) by using linear regression. RESULTS: DeltaHU/I correlated (P < .001) inversely with BW in the aorta (r = -0.78) and liver (r = -0.80) and with BMI in the aorta (r = -0.59) and liver (r = -0.61) on portal venous phase images. Regression formula for the low BW group was DeltaHU/I = 4.1 - .044 x BW (P < .001) and for the high BW group was DeltaHU/I = 2.7 - .017 x BW (P < .001), suggesting that the amount of contrast material required with increased BW is less in the high BW group. Adjusted maximum hepatic enhancement directly correlated with BFP (r = 0.25, P < .01). CONCLUSION: Excessive contrast material may inadvertently be given in heavier patients when the dose is determined by patient BW. Contrast material dose may need to be tailored in individual patients by using BFP.

[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.

[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.

[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.

[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.

Simulation of aortic peak enhancement on MDCT using a contrast material flow phantom: feasibility study.

OBJECTIVE: The objective of our study was to develop a flow phantom simulating aortic peak enhancement after the injection of contrast material on CT and to investigate the validity of the flow phantom by comparing the time-enhancement curves obtained for the flow phantom and humans. MATERIALS AND METHODS: We developed a flow phantom simulating the enhancement pattern of the aorta after the injection of contrast material. In protocols 1, 2, and 3 of the phantom study, 90, 102, and 150 mL of iohexol, respectively, was administered over 35 sec. In protocol 4, 102 mL of iohexol was administered over 25 sec. In phantom protocols 1', 2', and 3', the dose and contrast injection duration were the same as in protocols 1, 2, and 3; however, saline (10 mL) was injected during the 20 sec after contrast delivery. In the human study, 20 patients were randomized into four groups: Groups A, B, and C received 1.5, 1.7, and 2.5 mL of iohexol per kilogram of body weight, respectively, over 35 sec; and group D received 1.7 mL/kg over 25 sec. In patient groups A, B, C, and D, phantom protocols 1, 2, 3, and 4 were used, respectively. Single-level serial CT scans were obtained using a 16-MDCT scanner on the simulated and real aortas after the injection of contrast material. Time-enhancement curves of simulated and real aortas were generated, and aortic peak times and aortic peak enhancement values were calculated. RESULTS: Aortic peak enhancement and aortic peak times in protocols 1-4 and 1'-3' of the phantom study were 2-8% larger and 6-18% longer, respectively, than in the corresponding patient study. The shape of the time-enhancement curves before aortic peak time in protocols 1-3 and 1'-3' of the phantom study closely resembled that of the corresponding patient study. After the aortic peak time, the shape of time-enhancement curves in protocols 1, 2, and 3 of the phantom study was different from the corresponding patient study; however, it was similar in phantom protocols 1'-3' and the corresponding patient study. In all four phantom protocols, the difference between maximal and minimal aortic peak enhancement was less than the SD of the corresponding patient study. CONCLUSION: The level of peak aortic enhancement and the time to peak aortic enhancement were similar in the phantom and human studies when we used our different contrast injection protocols for MDCT.