New reconstruction algorithm for stack artifact reduction in breathing-adaptive four-dimensional computed tomography

Even with new adaptive four-dimensional computed tomography (4DCT) techniques, artifacts can still occur with strong irregular breathing amplitudes. A new image reconstruction algorithm, currently available for cardiac CT, was tested on 4DCT data for its performance to reduce stack artifacts and thus improve anatomical correctness.

The 'ZeeFree' algorithm employs a deformable image registration during reconstruction to reduce remaining stack artifacts. Its performance was evaluated using data of 20 irregular breathing ('challenging group') and 10 randomly selected ('verification group') patients with tumors in the thorax. Using a 5-score-scale, image quality in terms of stack artifacts was rated by three physicians and three physicists. Statistical significance was assessed using the Wilcoxon signed-rank test for the mean ratings and the Chi-square test for anatomical correctness.

Expert scoring revealed that 88.3% of the amplitude-based ZeeFree reconstructions showed (almost) no artifacts (rated with ≥ 4) compared to 66.8% of the standard reconstruction. With phase-based binning, 70.0% of the ZeeFree and 23.3% of standard were rated with a score ≥ 4. Mean scores were 4.1 and 4.0 for amplitude- and phase-based binning with ZeeFree and 3.4 and 2.5 for standard reconstruction, respectively. Differences were significant (p < 0.001). 91.1% (ZeeFree) and 41.1% (standard) were rated as anatomically correct. Again, differences were significant (p < 0.001).

This study demonstrated a statistically significant reduction of stack artifacts, resulting in improved anatomical correctness when ZeeFree was applied to 4DCTs. The algorithm was not observed to introduce new artifacts on already artifact-free images.