Effect of Heart Rate on CT Angiography Using the Enhanced Cardiac Model of the 4D NCAT
W. Paul Segars, K. Taguchi, G.S.K. Fung, E.K. Fishman, and B.M.W. Tsui
Fig. 1: Enhanced cardiac model based on the gated MSCT data.
We investigate the effect of heart rate on the quality of coronary artery images obtained using multi-slice computed tomography (MSCT) with the purpose of finding the optimal time resolution for data acquisition.
METHODS AND MATERIALS:
Fig. 2: Reduction in plaque contrast measured using three different heart rates (60, 90, and 120 bpm) and data acquisition windows (100, 175, and 250ms).
We used the 4D NCAT phantom, a computer model of the normal human anatomy and cardiac and respiratory motions developed in our laboratory. In this work, we updated the cardiac model to include a more detailed anatomy and physiology based on high-resolution clinical gated MSCT data. To demonstrate its utility in high-resolution dynamic CT imaging research, the enhanced 4D NCAT was then used in a pilot simulation study to investigate the effect of heart rate on CT angiography. The 4D NCAT was used to simulate patients with different heart rates (60-120 beats/minute) and with various cardiac plaques of known size and location within the coronary arteries. For each simulated patient, MSCT projection data was generated with data acquisition windows ranging from 100 to 250 ms centered within the quiet phase (mid-diastole) of the heart using an analytical CT projection algorithm. CT images were reconstructed from the projection data, and the contrast of the plaques was then measured to assess the effect of heart rate and to determine the optimal time resolution required for each case.
The enhanced cardiac model (Fig. 1) was found to illustrate the smooth contracting and twisting motion of the heart. The chamber volumes followed the normal pattern for the beating heart. The total myocardial mass was found to be conserved. From the pilot simulation study using this enhanced model, the contrast of the plaques was found to decrease with increasing heart rate and longer data acquisition windows, Fig. 2. The effect was the most dramatic for plaques located in the right coronary artery (RCA) due to the increased motion of this arterial branch during mid-diastole. The contrast of an RCA plaque was found to be reduced by more than 40% even at the shortest data acquisition window of 100 ms. Imaging during mid-diastole may not be optimal for the RCA as has been indicated in other studies.
The 4D NCAT phantom with its enhanced model for the cardiac motion provides a valuable tool to investigate the optimization of CT cardiac applications. Parameters such as the heart rate and motion and the location and size of cardiac plaques are all under user control thus providing a gold standard from which to evaluate and improve imaging techniques and methods. From our pilot simulation study using the phantom, we conclude that heart rate is an important determinant of image quality and artifact generation in MSCT imaging of the coronary arteries. It was found to contribute significantly to blurring and artifacts in MSCT images. Our results indicate the importance of optimizing the data acquisition window with regard to heart rate and plaque location for improved CT images at a reduced patient dose.
NIH Research Grant RO1EB001838