title: Deformable registration of trans-rectal ultrasound (TRUS) and magnetic resonance imaging (MRI) for focal prostate brachytherapy.
abstract: OBJECTIVE
  Focal therapy in low-risk prostate cancer may provide the best balance between cancer control and quality of life preservation. As a minimally invasive approach performed under TRUS guidance, brachytherapy is an appealing framework for focal therapy. However, the contrast in TRUS images is generally insufficient to distinguish the target lesion from normal prostate tissue. MRI usually offers a much better contrast between the lesion and surrounding tissues. Registration between TRUS and MRI may therefore significantly improve lesion targeting capability in focal prostate brachytherapy. In this paper, we present a deformable registration framework for the accurate fusion of TRUS and MRI prostate volumes under large deformations arising from dissimilarities in diameter, shape and orientation between endorectal coils and TRUS probes.
  
  
  METHODS
  Following pose correction by a RANSAC implementation of the ICP algorithm, TRUS and MRI Prostate contour points are represented by a 3D extension of the shape-context descriptor and matched by the Hungarian algorithm. Eventually, a smooth free-form warping is computed by fitting a 3D B-spline mesh to the set of matched points.
  
  
  RESULTS
  Quantitative validation of the registration accuracy is provided on a retrospective set of ten real cases, using as landmarks either brachytherapy seeds (six cases) or external beam radiotherapy fiducials (four cases) implanted and visible in both modalities. The average registration error between the landmarks was 2.49 and 3.20 mm, for the brachytherapy and external beam sets, respectively, that is less than the MRI voxels' long axis length ([Formula: see text]). The overall average registration error (for brachytherapy and external beam datasets together) was 2.56 mm.
  
  
  CONCLUSIONS
  The proposed method provides a promising framework for TRUS-MRI registration in focal prostate brachytherapy.
authors.affiliation: Diagnostic Imaging Institute, Sheba Medical Center, Ramat Gan, Israel. arnmayer@gmail.com.|Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel. arnmayer@gmail.com.
authors.forename: Arnaldo
authors.initials: A
authors.lastname: Mayer
authors.affiliation: Diagnostic Imaging Institute, Sheba Medical Center, Ramat Gan, Israel.
authors.forename: Adi
authors.initials: A
authors.lastname: Zholkover
authors.affiliation: Diagnostic Imaging Institute, Sheba Medical Center, Ramat Gan, Israel.|Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel.
authors.forename: Orith
authors.initials: O
authors.lastname: Portnoy
authors.affiliation: Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel.|Department of Urology, Sheba Medical Center, Ramat Gan, Israel.
authors.forename: Gil
authors.initials: G
authors.lastname: Raviv
authors.affiliation: Diagnostic Imaging Institute, Sheba Medical Center, Ramat Gan, Israel.|Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel.
authors.forename: Eli
authors.initials: E
authors.lastname: Konen
authors.affiliation: Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel.|Department of Radiation Oncology, Sheba Medical Center, Ramat Gan, Israel.
authors.forename: Zvi
authors.initials: Z
authors.lastname: Symon
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000379:methods; D019160:Endosonography / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D012007:Rectum; D012189:Retrospective Studies
keywords: Brachytherapy; Deformable image registration; Focal therapy; Image-guided prostate surgery; TRUS–MRI fusion