A dynamic approach to identifying desired physiological phases for cardiac imaging using multislice spiral CT.

In this investigation, we describe a quantitative technique to measure coronary motion, which can be correlated with cardiac image quality using multislice computed tomography (MSCT) scanners. MSCT scanners, with subsecond scanning, thin-slice imaging (sub-millimeter) and volume scanning capabilities have paved the way for new clinical applications like noninvasive cardiac imaging. ECG-gated spiral CT using MSCT scanners has made it possible to scan the entire heart in a single breath-hold. The continuous data acquisition makes it possible for multiple phases to be reconstructed from a cardiac cycle. We measure the position and three-dimensional velocities of well-known landmarks along the proximal, mid, and distal regions of the major coronary arteries [left main (LM), left anterior descending (LAD), right coronary artery (RCA), and left circumflex (LCX)] during the cardiac cycle. A dynamic model (called the "delay algorithm") is described which enables us to capture the same physiological phase or "state" of the anatomy during the cardiac cycle as the instantaneous heart rate varies during the spiral scan. The coronary arteries are reconstructed from data obtained during different physiological cardiac phases and we correlate image quality of different parts of the coronary anatomy with phases at which minimum velocities occur. The motion characteristics varied depending on the artery, with the highest motion being observed for RCA. The phases with the lowest mean velocities provided the best visualization. Though more than one phase of relative minimum velocity was observed for each artery, the most consistent image quality was observed during mid-diastole ("diastasis") of the cardiac cycle and was judged to be superior to other reconstructed phases in 92% of the cases. In the process, we also investigated correlation between cardiac arterial states and other measures of motion, such as the left ventricular volume during a cardiac cycle, which earlier has been demonstrated as an example of how anatomic-specific information can be used in a knowledge-based cardiac CT algorithm. Using these estimates in characterizing cardiac motion also provides realistic simulation models for higher heart rates and also in optimizing volume reconstructions for individual segments of the cardiac anatomy.

Reduced partial volume artifacts using spiral computed tomography and an integrating interpolator.

A technique is described for obtaining computed tomography (CT) head images with significantly reduced partial volume artifacts while retaining excellent low contrast resolution. Partial volume artifacts could be reduced by narrowing the collimation and summing thin slices. However, in axial scans, the acquisition and reconstruction time required for generating all the thin slices would prove clinically impractical. In addition, image artifacts could occur due to patient motion during the scans, particularly in trauma cases. In the case of spiral CT, a narrow collimation along with a small pitch can be used to reduce partial volume artifacts. However, the time required to reconstruct and sum the thin slices is still prohibitive. In this paper, we present a spiral technique using an integrating spiral interpolator (ISI) that allows a head study to be performed in less time without the partial volume artifacts normally seen. Using this interpolator, thick slices can be prospectively reconstructed from a spiral scan with a narrow collimation. The slice sensitivity profile for this interpolator was obtained and the full width at half-maximum and full width at tenth-maximum values were compared with both axial and predicted values. Noise values were also measured and compared to axial and theoretical predictions. Using this ISI interpolator, high quality head images were obtained with significantly reduced partial volume artifacts compared to standard axial and spiral scans. Total acquisition time is less than that of standard contiguous axial head scans.