title: Non-rigid MR-TRUS image registration for image-guided prostate biopsy using correlation ratio-based mutual information.
abstract: BACKGROUND
  To improve the accuracy of ultrasound-guided biopsy of the prostate, the non-rigid registration of magnetic resonance (MR) images onto transrectal ultrasound (TRUS) images has gained increasing attention. Mutual information (MI) is a widely used similarity criterion in MR-TRUS image registration. However, the use of MI has been challenged because of intensity distortion, noise and down-sampling. Hence, we need to improve the MI measure to get better registration effect.
  
  
  METHODS
  We present a novel two-dimensional non-rigid MR-TRUS registration algorithm that uses correlation ratio-based mutual information (CRMI) as the similarity criterion. CRMI includes a functional mapping of intensity values on the basis of a generalized version of intensity class correspondence. We also analytically acquire the derivative of CRMI with respect to deformation parameters. Furthermore, we propose an improved stochastic gradient descent (ISGD) optimization method based on the Metropolis acceptance criteria to improve the global optimization ability and decrease the registration time.
  
  
  RESULTS
  The performance of the proposed method is tested on synthetic images and 12 pairs of clinical prostate TRUS and MR images. By comparing label map registration frame (LMRF) and conditional mutual information (CMI), the proposed algorithm has a significant improvement in the average values of Hausdorff distance and target registration error. Although the average Dice Similarity coefficient is not significantly better than CMI, it still has a crucial increase over LMRF. The average computation time consumed by the proposed method is similar to LMRF, which is 16 times less than CMI.
  
  
  CONCLUSIONS
  With more accurate matching performance and lower sensitivity to noise and down-sampling, the proposed algorithm of minimizing CRMI by ISGD is more robust and has the potential for use in aligning TRUS and MR images for needle biopsy.
authors.affiliation: Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, 215163, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Lun
authors.initials: L
authors.lastname: Gong
authors.affiliation: Department of Urology, Shanghai Changhai Hospital, Shanghai, 200433, China.
authors.forename: Haifeng
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Electronic Science and Technology, University of Science and Technology of China, Hefei, 230061, China.
authors.forename: Chengtao
authors.initials: C
authors.lastname: Peng
authors.affiliation: Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, 215163, China.
authors.forename: Yakang
authors.initials: Y
authors.lastname: Dai
authors.affiliation: School of Science, Nanjing University of Science and Technology, Nanjing, 210094, China.
authors.forename: Min
authors.initials: M
authors.lastname: Ding
authors.affiliation: Department of Urology, Shanghai Changhai Hospital, Shanghai, 200433, China.
authors.forename: Yinghao
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, 215163, China.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Yang
authors.affiliation: Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, 215163, China. zhengj@sibet.ac.cn.
authors.forename: Jian
authors.initials: J
authors.lastname: Zheng
mesh_terms: D001706:Biopsy / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D011467:Prostate / Q000000981:diagnostic imaging* / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D012007:Rectum; D025321:Surgery, Computer-Assisted / Q000379:methods*; D014463:Ultrasonography
keywords: CRMI; ISGD; Needle biopsy; Non-rigid registration; Prostate