[Method for determining scan timing based on analysis of formation process of the time-density curve]

[Usefulness of Trapezoidal Cross-injection in Aortic 3D-CTA]

PURPOSE

This study aimed to compare the contrast effects of administration via the subclavian vein, the superior vena cava and right ventricular venous tract, and the aorta in three-dimensional computed tomography angiography (3D-CTA) using one-step injection and trapezoidal cross-injection.

METHOD

The subjects were 56 patients who underwent aortic 3D-CTA. In the one-step injection method, a 30-second injection of contrast medium was followed by saline injected at the same rate as the 30-ml contrast medium. In the trapezoidal cross-injection method, after injecting the contrast agent for 15 seconds, a variable mixture of the contrast agent and saline was injected for 15 seconds, followed by 20 ml saline injected at the same rate as the initial contrast agent injection. CT values were measured in the subclavian vein, superior vena cava, right ventricle, and aorta.

RESULT

A significant difference was found in the subclavian vein and right ventricle, with the trapezoidal cross-injection method showing a lower CT value than the one-step injection method (p<0.01). There were no significant differences in the CT values in the superior vena cava and the aorta.

CONCLUSION

The trapezoidal cross-injection method for aortic 3D-CTA produced lower CT values in venous pathways than those via the one-step injection method, but no changes were observed in the aortic CT values. These results suggest that the trapezoidal cross-injection method is useful in aortic 3D-CTA.

Cardiac output obtained from test bolus injections as a factor in contrast injection rate revision of following coronary CT angiography

BACKGROUND

Optimal contrast enhancement is crucial for the detection of coronary artery stenoses and atherosclerotic changes in coronary CT angiography (CTA).

PURPOSE

To demonstrate the feasibility of using the cardiac output (CO) obtained from the test bolus injection data-set (COtest) as a factor in contrast injection rate revision of the following coronary CTA.

MATERIAL AND METHODS

The test bolus injection data-sets of 52 consecutive coronary CTAs were examined. COtest was calculated from the test bolus data-set. Aortic peak enhancement (APE) was measured on the following coronary CTA. We simulated the APE at a fixed contrast injection rate of 4 mL/s (simAPE) in each patient.

RESULTS

The ranges of COtest and simAPE were 2.82-7.56 L/min and 194-527 Hounsfield Units, respectively. There was a significant negative correlation (R = -0.802, P < 0.001) between simAPE and COtest.

CONCLUSION

COtest can be used for injection rate revision on coronary CTA.

[Noninvasive assessment of coronary artery with substantial contrast volume reduction using 320-detector row computed tomography: a feasibility study]

The recently introduced 320-detector row computed tomography (320-row CT) allows very fast volumetric acquisition of the entire heart. Because the total amount of contrast agent required for CT coronary angiography (CTCA) depends directly on the acquisition time, 320-row CTCA would substantially reduce the contrast agent dose. The objective of this retrospective study was to evaluate the feasibility of contrast volume reduction on 320-row CTCA compared with 64-detector row CTCA (64-row CTCA). We retrospectively reviewed consecutive 320- and 64-row CTCA data (16 eligible cases for each; administrated contrast volume, 20-24 ml for the former and 50-65 ml for latter) from a homogeneous patient population (age ≤ 81, body weight ≤ 67 kg, and heart rate ≤ 69 bpm). The two types of CTCA data were compared with respect to the successful rate of adequate intravascular contrast enhancement defined as the number of segments with attenuations of more than 250 HU divided by total number of coronary segments evaluated. Our dataset provided mean intravascular attenuation values of 320 and 404 HU on the 320- and 64-row CTCA, respectively. Although the attenuation values were statistically lower for the 320-row CTCA (P < 0.001), there was no significant difference in the successful rates of adequate intravascular contrast enhancement (rate of 0.98 for each; P > 0.05). We therefore conclude that 320-row CTCA is a feasible method of diagnostic imaging and is superior to 64-row CTCA because it uses less of the contrast medium.

[Development of test bolus tracking method and usefulness in coronary CT angiography]

The test bolus tracking (TBT) method is a new injection method of contrast medium that we developed. The TBT method is an injection technique that continuously performs the test bolus injection and the main bolus injection, such that the best acquisition of scan timing and the improvement of examination efficiency can be expected. We compared the TBT method and the test injection method by coronary CT angiography. The results demonstrated that the contrast enhancement of the coronary arteries was high and the variation of the CT value was also small in the TBT method. When the scan timing expected by the TI method and the TBT method were compared, it was different of two seconds or more by the case with 43%. However, the variation of CT value was small for the TBT method in these cases. Therefore, the TBT method is a very useful method for CCTA.

[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.

[Estimation of aortic time-enhancement curve in pharmacokinetic analysis: dynamic study by multi-detector row computed tomography]

This paper presents an introduction to the development of software that provides a physiologic model of contrast medium enhancement by incorporating available physiologic data and contrast medium pharmacokinetics to predict an organ-specific aortic time-enhancement curve(TEC)in computed tomography(CT)with various contrast medium injection protocols in patients of various heights, weights, cardiac output levels, and so on. The physiologic model of contrast medium enhancement was composed of six compartments for early contrast enhancement pharmacokinetics. Contrast medium is injected via the antecubital vein and distributed to the right side of the heart, the pulmonary compartment, the left side of the heart, and the aorta. It then circulates back to the right side of the heart via the systemic circulation. A computer-based, compartmental model of the aortic system was generated using human physiologic parameters and six differential equations to describe the transport of contrast medium. Aortic TEC generated by the computer-based physiologic model of contrast medium enhancement showed validity and agreement with clinical data and findings published previously. A computer-based physiologic model that may help predict organ-specific CT contrast medium enhancement for different injection protocols was developed. Such a physiologic model may have multiple clinical applications.