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Deformable MRI to CT Validation Employing Same Day Planning MRI for Surrogate Analysis

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K Padgett

K Padgett1*, R Stoyanova1 , P Johnson1 , J Piper2 , A Javorek2 , N Dogan1 , A Pollack1 , (1) University of Miami School of Medicine, Miami, FL, (2) MIM Software, Inc., Beachwood, OH,


SU-F-BRF-10 Sunday 4:00PM - 6:00PM Room: Ballroom F

Purpose: To compare rigid and deformable registrations of the prostate in the multi-modality setting (diagnostic-MRI to planning-CT) by utilizing a planning-MRI as a surrogate. The surrogate allows for the direct quantitative analysis which can be difficult in the multi-modality domain where intensity mapping differs.

Methods: For ten subjects, T2 fast-spin-echo images were acquired at two different time points, the first several weeks prior to planning (diagnostic-MRI) and the second on the same day in which the planning CT was collected (planning-MRI). Significant effort in patient positioning and bowel/bladder preparation was undertaken to minimize distortion of the prostate in all datasets. The diagnostic-MRI was deformed to the planning-CT utilizing a commercially available deformable registration algorithm synthesized from local registrations. The deformed MRI was then rigidly aligned to the planning MRI which was used as the surrogate for the planning-CT. Agreement between the two MRI datasets was scored using intensity based metrics including Pearson correlation and normalized mutual information, NMI. A local analysis was performed by looking only within the prostate, proximal seminal vesicles, penile bulb and combined areas. A similar method was used to assess a rigid registration between the diagnostic-MRI and planning-CT.

Results: Utilizing the NMI, the deformable registrations were superior to the rigid registrations in 9 of 10 cases demonstrating a 15.94% improvement (p-value < 0.001) within the combined area. The Pearson correlation showed similar results with the deformable registration superior in the same number of cases and demonstrating a 6.97% improvement (p-value <0.011).

Conclusion: Validating deformable multi-modality registrations using spatial intensity based metrics is difficult due to the inherent differences in intensity mapping. This population provides an ideal testing ground for MRI to CT deformable registrations by obviating the need for multi-modality comparisons which are inherently more challenging. Deformable registrations generated in this work significantly outperformed rigid alignments.

Funding Support, Disclosures, and Conflict of Interest: Research reported in this abstract was supported by the NIH National Cancer Institute R21CA153826 "MRI-Guided Radiotherapy and Biomarkers for Prostate Cancer" and Bankhead-Coley Cancer Research Program 10BT-03 "MRI-Guided Radiotherapy and Biomarkers for Prostate Cancer".

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