  With the recent introduction of CT scanners with large cone angles, wide
coverage detectors now provide a desirable scanning platform for cardiac CT
that allows whole heart imaging in a single rotation. On these scanners, while
half-scan data is strictly sufficient to produce images with the best temporal
resolution, acquiring a full 360 degree rotation worth of data is beneficial
for wide-cone image reconstruction at negligible additional radiation dose.
Applying Model-Based Iterative Reconstruction (MBIR) algorithm to the heart has
shown to yield significant enhancement in image quality for cardiac CT. But
imaging the heart in large cone angle geometry leads to apparently conflicting
data usage considerations. On the one hand, in addition to using the fastest
available scanner rotation speed, a minimal complete data set of 180 degrees
plus the fan angle is typically used to minimize both cardiac and respiratory
motion. On the other hand, a full 360 degree acquisition helps better handle
the challenges of missing frequencies and incomplete projections associated
with wide-cone half-scan data acquisition. In this paper, we develop a
Spatially Adaptive sinogram Weights MBIR algorithm (SAW-MBIR) that is designed
to achieve the benefits of both half and full-scan reconstructions in order to
maximize temporal resolution over the heart region while providing stable
results over the whole volume covered with the wide-area detector.
Spatially-adaptive sinogram weights applied to each projection measurement in
SAW-MBIR are designed to selectively perform backprojection from the full and
half-scan portion of the sinogram based on both projection angle and
reconstructed voxel location. We demonstrate with experimental results of
SAW-MBIR applied to whole-heart cardiac CT clinical data that overall temporal
resolution matches half-scan while full volume image quality is on par with
full-scan MBIR.
