Impact of a novel exponential weighted 4DCT reconstruction algorithm
Morris ED, Kim JP, Klahr P, and Glide-Hurst CK. Impact of a novel exponential weighted 4DCT reconstruction algorithm. J Appl Clin Med Phys 2018; Nov;19(6):217-225.
Journal of applied clinical medical physics
PURPOSE: This work characterizes a novel exponential 4DCT reconstruction algorithm (EXPO), in phantom and patient, to determine its impact on image quality as compared to the standard cosine-squared weighted 4DCT reconstruction.
METHODS: A motion platform translated objects in the superior-inferior (S-I) direction at varied breathing rates (8-20 bpm) and couch pitches (0.06-0.1) to evaluate interplay between parameters. Ten-phase 4DCTs were acquired and data were reconstructed with cosine squared and EXPO weighting. To quantify the magnitude of image blur, objects were translated in the anterior-posterior (A-P) and S-I directions for full-width half maximum (FWHM) analysis between both 4DCT algorithms and a static case. 4DCT sinogram data for 10 patients were retrospectively reconstructed using both weighting factors. Image subtractions elucidated intensity and boundary differences. Subjective image quality grading (presence of image artifacts, noise, spatial resolution (i.e., lung/liver boundary sharpness), and overall image quality) was conducted yielding 200 evaluations.
RESULTS: After taking static object size into account, the FWHM of EXPO reconstructions in the A-P direction was 3.3 ± 1.7 mm (range: 0-4.9) as compared to cosine squared 9.8 ± 4.0 mm (range: 2.6-14.4). The FWHM of objects translated in the S-I direction reconstructed with EXPO agreed better with the static FWHM than the cosine-squared reconstructions. Slower breathing periods, faster couch pitches, and intermediate 4DCT phases had the largest reductions of blurring with EXPO. 18 of 60 comparisons of artifacts were improved with EXPO reconstruction, whereas no appreciable changes were observed in image quality scores. In 18 of 20 cases, EXPO provided sharper images although the reduced projections also increased baseline noise.
CONCLUSION: Exponential weighted 4DCT offers potential for reducing image blur (i.e., improving image sharpness) in 4DCT with a tendency to reduce artifacts. Future work will involve evaluating the impact on treatment planning including delineation ability and dose calculation.
Medical Subject Headings
Abdominal Neoplasms; Algorithms; Breast Neoplasms; Female; Follow-Up Studies; Four-Dimensional Computed Tomography; Humans; Image Processing, Computer-Assisted; Lung Neoplasms; Movement; Organs at Risk; Phantoms, Imaging; Prognosis; Radiometry; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy, Intensity-Modulated; Respiration; Retrospective Studies