Proceedings Article | 13 March 2007
KEYWORDS: Reconstruction algorithms, Image segmentation, Algorithm development, Heart, Beam propagation method, Computed tomography, Detection and tracking algorithms, X-ray computed tomography, CT reconstruction, Time metrology
In order to obtain motion-compensated reconstructions of calcified coronary plaques in cardiac CT, the dynamic
trajectory of the plaque must be known rather accurately. The purpose of this study is to evaluate whether
the dynamic trajectories of a plaque extracted from reconstructions provided by a previously developed tracking
algorithm can be used for obtaining motion-compensated reconstructions of this plaque. A single projection
dataset of the modified FORBILD phantom containing a calcified plaque undergoing continuous periodic motion
was acquired with a gantry rotation time of 0.4 s and a heart rate of 90 bpm. Three sets of phase-correlated 4D
ROI images centered on the calcified plaque (labeled G1, G2, and G3) were obtained from this dataset by varying
the numbers of data segments used for cardiac gating (N = 1, 2, 3) during the reconstruction steps of the tracking
algorithm. Dynamic trajectories from each of these datasets were calculated from edge-based segmentations of
these datasets. When compared to the true trajectory (labeled T), root-mean-square (RMS) values of position
for trajectories G1, G2, and G3 were 1.473 mm, 1.166 mm, and 0.736 mm, respectively. Trajectories G1, G2, G3,
and T then were used to obtain motion-compensated reconstructions MC1, MC2, MC3, and MCT, respectively,
at 6.25 ms time intervals over 2 cardiac cycles. The areas (number of pixels) of the plaque then were measured
at all time intervals for each set of reconstructions. When compared against areas obtained for MCT, RMS
values of areas for reconstructions MC1, MC2, and MC3 were 26.888, 12.384, and 4.837, respectively. On visual
inspection, MC3 also exhibited the least motion artifacts at most time intervals.
