The Effect of a Reconstruction Technique and Heart Rate in the Evaluation of Optimal Trigger Delay Using Multiphase Reconstruction

PURPOSE: To evaluate the mean optimal trigger delays and the difference between the absolute delay and the relative delay as a function of heart rate, using multiphase reconstruction. MATERIALS AND METHODS: A total of 30 patients consecutively underwent a 64-slice MDCT examination. Optimal trigger delays at four planes (the bifurcation of the left main coronary artery, aortic valve, mitral valve and cardiac apex) were measured using multiphase reconstruction based on the absolute and relative delay. For this reason, patients were divided into three groups according to heart rate (group I, = 75 bpm), and the mean optimal trigger delays and the difference between the absolute delay and the relative delay were evaluated at the four planes for each group. RESULTS: The mean optimal trigger delay for the relative delay and absolute delay ranged from 46% to 66% and from 327 to 700 msec, respectively. The differences in the mean optimal trigger delay using the relative and the absolute delay at the four planes were 1% and 4 msec (group I), 3% and 27 msec (group II), and 14% and 46 msec (group III). In group III, the difference of the mean optimal trigger delay based on the relative delay, increased significantly compared to the absolute delay (p = 0.040). CONCLUSION: For the patients analyzed, the results suggest that as the heart rate increased, the mean optimal trigger delays shifted from the mid-diastolic phase to the end-systolic phase and the differences in the mean optimal trigger delay at the four planes were significantly greater for the relative delay.

16-MDCT : A New Modality for Diagnosis of Cardiac Diseases

Since the advent of 16-MDCT in the clinical diagnosis, a paradigm shift is required in the diagnostic algorithm of cardiovascular diseases owing to its revolutionary technical advances. 16-MDCT provides less than 1 mm of high spatial resolution even in z-direction by using detectors with less than 0.75 mm collimation, which in turn allows for volumetric scanning with isotropic 3-dimensional resolution. This high spatial resolution of 16-MDCT enables one to obtain high quality images of the small vessels such as coronary arteries with diameter < 1 mm. For imaging of the heart, scanning with a high temporal resolution is particularly important because of the strong movement during the cardiac cycle. 16-MDCT allows images with a high temporal resolution, less than 250 msec, enough to freeze the cardiac motion. Furthermore, by using ECG information that is recorded simultaneouly with the image acquisition, images synchronized to the specific cardiac phase can either be scanned or post-processed according to the technique of ECG-gating. In order to eliminate the motion artifact from respiratory motion, scanning must be completed within a single breathholding time. By adopting 12~16 detector arrays and less than 0.5 sec of gantry rotation time, imaging of the whole heart with submillimeter spatial resolution can be covered within 20 seconds of breathholding time. Major clinical applications of 16-MDCT in cardiac diseases inlcude detection of coronary stenosis and atherosclerotic plaque, coronary calcium scoring, evaluation of the patients after coronary angioplasty or coronary arterial by-pass graft, assessment of the cardiac valve morphology and function, and ventricular function and perfusion. Among these, currently the most practical area of 16-MDCT application is post-CABG evaluation and the most imporatnt and promising area will be assessment of native coronary arteries for detection of stenotic vessels and for detecting and differentiating atherosclerotic lesions over a spectrum of vulnerable, soft, fibrotic, and calcified plaques. In this review, important technical aspects together with clinical applications of 16-MDCT in diagnosis of cardiovascular diseases will be presented.