title: Semiautomatic nonrigid registration for the prostate and pelvic MR volumes.
abstract: OBJECTIVE
  Three-dimensional (3D) nonrigid image registration for potential applications in prostate cancer treatment and interventional magnetic resonance (iMRI) imaging-guided therapies were investigated.
  
  
  METHODS
  An almost fully automated 3D nonrigid registration algorithm using mutual information and a thin plate spline (TPS) transformation for MR images of the prostate and pelvis were created and evaluated. In the first step, an automatic rigid body registration with special features was used to capture the global transformation. In the second step, local feature points (FPs) were registered using mutual information. An operator entered only five FPs located at the prostate center, left and right hip joints, and left and right distal femurs. The program automatically determined and optimized other FPs at the external pelvic skin surface and along the femurs. More than 600 control points were used to establish a TPS transformation for deformation of the pelvic region and prostate. Ten volume pairs were acquired from three volunteers in the diagnostic (supine) and treatment positions (supine with legs raised).
  
  
  RESULTS
  Various visualization techniques showed that warping rectified the significant pelvic misalignment by the rigid-body method. Gray-value measures of registration quality, including mutual information, correlation coefficient, and intensity difference, all improved with warping. The distance between prostate 3D centroids was 0.7 +/- 0.2 mm after warping compared with 4.9 +/- 3.4 mm with rigid-body registration.
  
  
  CONCLUSIONS
  Semiautomatic nonrigid registration works better than rigid-body registration when patient position is changed greatly between acquisitions. It could be a useful tool for many applications in the management of prostate.
authors.affiliation: Department of Radiology, Case Western Reserve University and University Hospitals of Cleveland, 11100 Euclid Avenue, Cleveland, OH 44106, USA. baowei.fei@case.edu
authors.forename: Baowei
authors.initials: B
authors.lastname: Fei
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Duerk
authors.forename: D Bruce
authors.initials: DB
authors.lastname: Sodee
authors.forename: David L
authors.initials: DL
authors.lastname: Wilson
mesh_terms: D000465:Algorithms; D005269:Femur / Q000473:pathology; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010388:Pelvis / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000628:therapy