The new type of coronary angiography(CAG)that uses 40 mm volumetric computed tomography(VCT)has great potential for cardiac disease. However, it is still necessary to be cognizant of exposure dose. We measured doses of CAG by both VCT and cardiovascular X-ray using a body phantom within 170 glass dosimeters. VCT protocols were 120 kV, 570 mA, and 0.35 sec/rot with and without the dose-reduction features(small cardiac X-ray beam filter and ECG mA modulation). The cardiovascular X-ray protocol was Auto(65 - 77 kV)kV, Auto(41 - 46 mA)mA, 5 sec×11 shots+11 min fluoroscopy(minimum protocol for screening). VCT with and without the dose-reduction features has the same dose distribution, however, the dose-reduction features reduced the amount of dose by about 40-50%. For VCT with those features, measured dose was about 70 mGy in the cardiac area and 60 mGy at the skin of the back, whereas those of cardiovascular X-ray were 10 mGy and 30 mGy. We measured detailed dose distributions and variations in the phantom, and we also demonstrated the possibility of VCT's dose-reduction features. The CT dose was still higher than that of cardiovascular X-ray, however, there were advantages of CT scanning, for instance, information about calcification, soft plaque, and 3D visualization. We think it is important to use both systems with an understanding of their advantages and limitations.
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.
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.
Whole-heart coronary MRA(WHCA)was performed in transaxial and sagittal sections in random order in 10 healthy volunteers to obtain coronal section multiplanar reconstruction(MPR)at an interval of 0.5 mm and thickness of 1 mm for evaluation. Visual evaluation showed sagittal section imaging to be superior to transaxial section imaging in 12 out of a total of 20 regions in the left and right proximal coronary arteries. Sagittal section imaging was found to be superior to transaxial section imaging in evaluation of the hepatic left lobe in all the cases as well as in evaluation of the right peripheral coronary arteries in 8 of 9 cases that could be evaluated. For quantitative evaluation, the difference in brightness between the peripheral adipose tissues(S fat)and the coronary arteries(S coronary)was assigned as CR(S coronary/S fat). Highly comparable results were obtained by quantitative and visual evaluation. Phantom experimentation was performed. The piston of the syringe was substituted for the diaphragm. Ghost artifact caused by movement of the diaphragm and phase return, i.e., the slice phase-encoding direction of the 3D sequence, were the origin of poor images in transaxial section imaging. We thus conclude that sagittal section imaging is useful in WHCA as a 3D sequence.
Heart delayed enhancement magnetic resonance imaging(MRI)is an attempt to obtain intense image contrast using the null-point of normal myocardium, which changes with time. Imaging is generally conducted under breath-hold, but, if the retrospective gating method is used, it is necessary to shorten the imaging time and to fill the center of the k-space with the data in the early phase of imaging. In the present study, we examined free breathing three-dimensional heart delayed enhancement MRI(3D/KING method)using k-space inspired navigator gating(KING). In the 3D/KING, since respiratory artifact decreases by combining with the fat suppression technique and the gating window can be set widely, the imaging time was shortened in comparison with the conventional 3D method. In 3D/KING/isotropic(iso), on the other hand, the respiratory artifact was decreased by transverse imaging. The mean end time of imaging by the 3D/KING method(n=10)and the 3D/KING/iso(n=5)was 3.05±0.69 and 4.59±0.74 minutes, respectively. Moreover, the signal intensity ratio(SIR)of abnormal myocardium versus normal myocardium in the 3D/KING method was low in comparison with that in the breath-hold method. However, the capability to detect lesions was similar, and good images were obtained from the patients showing poor breath-hold. In the 3D/KING/iso, heart delayed enhancement MRI from multiple directions could be conducted in a single imaging by using the image reconstitution method.
Negative product value for coronary artery disease is 98% to 99%. Therefore, the number of unnecessary cardiac catheterization procedures is reduced as the usefulness of CT systems for examination of the coronary arteries improves. In the bolus-tracking method, in which an ROI is placed in the ascending aorta to trigger scanning, scanning may not be performed at the optimal time of contrast enhancement depending on the patient. In addition to identifying the causes of this problem, we have developed a new method in which ROIs are placed in the right ventricle and left atrium to trigger scanning when the concentrations of contrast medium in the right ventricle and left atrium become equal. The two methods were then compared and evaluated. In the scan method, in which an ROI is placed in the ascending aorta, the reason for non-optimal scan timing is considered to be that the time required for contrast medium injected via an antecubital vein to reach the heart varies depending on the individual patient(approximately 3 times the variation of our method)followed by a delay of approximately 5 seconds between the scan trigger time and the actual scan start time. In the scan method in which scanning is triggered when the concentrations of contrast medium in the right ventricle and left atrium become equal, scanning can be performed at the time of peak enhancement regardless of differences in the time required for the injected contrast medium to reach the target region or differences in the injection rate, demonstrating the usefulness of this method.
[Background] Delayed-enhancement MRI is a technique that has significant clinical usefulness, particularly for myocardial viability determination in ischemic heart disease. Delayed enhanced images have been acquired by using the inversion recovery(IR)method. It is necessary for the IR method to select optimal inversion time(TI). Recently, the phase-sensitive inversion recovery(PSIR)method has been developed to detect Gd-DTPA enhanced myocardium. [Purpose]To compare the IR method with the PSIR method by acquiring Gd-DTPA solution phantoms A(0.05 mmol/l)and B(0.04 mmol/l)in various parameters. [Method]Images were acquired using a turbo-fast low angle shot(t-flash)sequence in each method. [Results]The null point of signal intensity(SI)shortened as the flip angle(FA)and segments increased in the IR method. Excess segments also caused the duration of breath holding to be extended. The IR method might cause reversed SI between normal and Gd-DTPA enhanced myocardium if the optimal TI was not carefully selected. On the other hand, PSIR had no problem in obtaining phase-sensitive images that were converted into positive SI keeping inverse longitudinal magnetization. The PSIR method avoided the need to select optimal TI and loss of contrast. [Conclusion]The PSIR method was a useful sequence for delayed-enhancement MRI to detect Gd-DTPA enhanced myocardium.