Evaluation of 4D CT acquisition methods designed to reduce artifacts

Abstract

Four-dimensional computed tomography (4D CT) is used to account for respiratory motion in radiation treatment planning, but artifacts resulting from the acquisition and postprocessing limit its accuracy. We investigated the efficacy of three experimental 4D CT acquisition methods to reduce artifacts in a prospective institutional review board approved study. Eighteen thoracic patients scheduled to undergo radiation therapy received standard clinical 4D CT scans followed by each of the alternative 4D CT acquisitions: 1) data oversampling, 2) beam gating with breathing irregularities, and 3) rescanning the clinical acquisition acquired during irregular breathing. Relative values of a validated correlation-based artifact metric (CM) determined the best acquisition method per patient. Each 4D CT was processed by an extended phase sorting approach that optimizes the quantitative artifact metric (CM sorting). The clinical acquisitions were also postprocessed by phase sorting for artifact comparison of our current clinical implementation with the experimental methods. The oversampling acquisition achieved the lowest artifact presence among all acquisitions, achieving a 27% reduction from the current clinical 4D CT implementation (95% confidence interval = 34–20). The rescan method presented a significantly higher artifact presence from the clinical acquisition (37%; p < 0.002), the gating acquisition (26%; p < 0.005), and the oversampling acquisition (31%; p < 0.001), while the data lacked evidence of a significant difference between the clinical, gating, and oversampling methods. The oversampling acquisition reduced artifact presence from the current clinical 4D CT implementation to the largest degree and provided the simplest and most reproducible implementation. The rescan acquisition increased artifact presence significantly, compared to all acquisitions, and suffered from combination of data from independent scans over which large internal anatomic shifts occurred.

Reduction of breathing irregularity-related motion artifacts in low-pitch spiral 4D CT by optimized projection binning

“…Their approach is, however, limited to the specific challenges of 4D CBCT and especially the presence of streaking artifacts due to projection undersampling; the respective objective function to be minimized can therefore not directly be transferred to standard 4D CT reconstruction and artifacts. Similar thoughts and promising results can, nevertheless, also be found in the context of ciné 4D CT image sorting [20]; the respective work forms the basis of our implementation. Thus, with the design of the two steps of our approach for reduction of breathing irregularity-related 4D CT motion artifacts being motivated by recent developments in the context of 4D CT imaging, we present a novel combination thereof and describe their adaptation to low-pitch spiral 4D CT.…”

“…From a methodical perspective, the present study in parts builds on respective work in the field of ciné 4D CT [20], but represents the first attempt to transfer and adapt related concepts to low-pitch spiral 4D CT – and further contains the first comprehensive evaluation thereof.…”

“…Addressing violations of A2 in the context of ciné 4D CT imaging, Castillo et al suggested integrating a dissimilarity measure between axial image segments acquired at spatially adjacent couch positions and the minimization of the measure into 4D CT formation [20]. Their presented workflow is, however, dependent on principles of ciné 4D CT imaging, i. e. a consecutive acquisition and reconstruction of a series of image segments for fixed couch positions, breathing signal-based assignment of respiratory states to already reconstructed image segments, and the assembly of the image segments of a similar breathing state but different couch positions.…”

Tumor motion in lung cancers: An overview of four-dimensional radiotherapy treatment of lung cancers

“…To the other group belongs the slow CT scan (4 s per slice in axial mode), prospective gated CT scan (images at only 1 phase with longer acquisition times that are 4 to 5 times longer than conventional scans), and 4D CT scan (three-dimensional [3D] scans at multiple phases), all of which require some kind of modification to the scanner's hardware or its software or both. [9] In one of these methods, called retrospective 4D gated CT, at every position of interest along the patient's long axis, multiple images are obtained spanning the entire breathing cycle. Each image is tagged with the phase information of the breathing cycle it belongs to.…”

The dosimetric effect of electron density overrides in 3DCRT Lung SBRT for a range of lung tumor dimensions

“…The most common technique for managing temporal tumor variation is four‐dimensional imaging, including respiration‐correlated 4‐Dimensional CT (4DCT) scanning, however, this can result in motion artifacts . Artifacts can be caused by irregular breathing traces, for example, coughing or patient motion during the scanning process …”