(Thursday, 7/16/2020) 10:30 AM - 12:30 PM [Eastern Time (GMT-4)]
Room: Track 4
Purpose: energy CT images can be acquired simultaneously with a dual source dual energy CT (DS-DECT) scanner (Siemens Drive) which can improve both temporal and spatial coincidence compared with sequential DECT. However, one image has a limited FOV (33 cm versus 50 cm) due to design limitations. In this study, we developed a novel method to recover the pixel values outside the smaller FOV for use in dual energy proton stopping power ratio (SPR) calculation.
Methods: DECT at 80 kVp (A_50) and 140 kVp (B_50) were acquired at 50 cm FOV and the 140 kVp image was cropped to 33 cm FOV (B_33) to simulate the limited FOV from a DS-DECT. For each voxel in image A_50 outside the 33 cm FOV, a correspondence to a voxel of similar tissue inside the 33 cm FOV was established. Gradient steepest- descent optimization was used to find matching pairs by minimizing the HU difference, mean square error of two surrounding region of interest ROI and structural similarity (SSIM) index of the two ROIs. The correspondence between voxel pairs in A_50 was then applied onto image B_33 to recover the full FOV. HU differences, linearity and SPR were evaluated by comparison of the recovered image with those from the uncropped image which served as ground truth.
Results: mean relative error for HU number in the expanded region was 0.7%. The relative error of electron density ?, Z and SPR were 2.6%, 2.9%, 5.2% for bone and 0.6%, 0.9%, 0.6% for soft tissue respectively.
Conclusion: proposed method can estimate image information outside the limited FOV for DS-DECT using the larger FOV image. The expansion of the dual energy information from a DS_DECT can be used to calculate SPR for the full 50 cm FOV for patients in proton therapy.
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