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Deformable Registration of Post-Implant MRI to Intra-Operative Ultrasound Images for Permanent Prostate Brachytherapy Treatment Assessment


Y Le

Y Le*, J Lee, A Robinson, D Song, Johns Hopkins University, Baltimore, MD

SU-C-WAB-6 Sunday 1:00PM - 1:55PM Room: Wabash Ballroom

Purpose:
Transrectal-ultrasound (TRUS) is the most common image modality used in permanent prostate brachytherapy (PPI), while MRI images can provide additional anatomical information. Our goals were to develop a novel method to register post-implant MRI to intra-operative ultrasound (US) images and demonstrate its potential usage for retrospective implant assessment.

Methods:
TRUS images of prostate and non-isocentric C-arm fluoroscopy (FL) images are captured intraoperatively right after implant. The reconstructed 3D seed cloud from FL images (seeds_FL) will be used as a bridge to register post MRI to US images. The Registration of Ultrasound and Fluoroscopy (RUF) images is done by an intensity-based point to volume algorithm. The day-one post CT and T2-MRI images are co-registered and the 3D seed cloud is segmented from CT (seeds_CT). The iterative-closest-point algorithm is used to compute rigid transformation between seeds_FL and seed_CT. MRI can be transferred to FL coordinate using registration of two seed clouds and then to US coordinate using RUF registration. A thin-plate-spline algorithm is used to deform the MRI contours and images according to deformation of two seed clouds.
To demonstrate this registration method, post MRI images from ten patients were registered to US images. The prostate contours were compared between post US and MRI. The planning needle interferences with critical structure like neurovascular bundles (NVB) were investigated.

Results:
After registration, center of mass of both prostate and urethra were within 3mm between two contour sets. The anterior boundaries of prostate were often overestimated in post US contours. When planning needles were superimposed over contours, there were about 3-4 needles passing through or in close vicinity of NVB in all patients.

Conclusion:
A novel method to register post-implant MRI to intra-operative US images was developed and demonstrated in evaluating accuracy of intra-operative US contours and accessing needle passages to NVB during PPI.

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