title: Graphics Processing Unit-Accelerated Nonrigid Registration of MR Images to CT Images During CT-Guided Percutaneous Liver Tumor Ablations.
abstract: OBJECTIVE
  Accuracy and speed are essential for the intraprocedural nonrigid magnetic resonance (MR) to computed tomography (CT) image registration in the assessment of tumor margins during CT-guided liver tumor ablations. Although both accuracy and speed can be improved by limiting the registration to a region of interest (ROI), manual contouring of the ROI prolongs the registration process substantially. To achieve accurate and fast registration without the use of an ROI, we combined a nonrigid registration technique on the basis of volume subdivision with hardware acceleration using a graphics processing unit (GPU). We compared the registration accuracy and processing time of GPU-accelerated volume subdivision-based nonrigid registration technique to the conventional nonrigid B-spline registration technique.
  
  
  METHODS
  Fourteen image data sets of preprocedural MR and intraprocedural CT images for percutaneous CT-guided liver tumor ablations were obtained. Each set of images was registered using the GPU-accelerated volume subdivision technique and the B-spline technique. Manual contouring of ROI was used only for the B-spline technique. Registration accuracies (Dice similarity coefficient [DSC] and 95% Hausdorff distance [HD]) and total processing time including contouring of ROIs and computation were compared using a paired Student t test.
  
  
  RESULTS
  Accuracies of the GPU-accelerated registrations and B-spline registrations, respectively, were 88.3 ± 3.7% versus 89.3 ± 4.9% (P = .41) for DSC and 13.1 ± 5.2 versus 11.4 ± 6.3 mm (P = .15) for HD. Total processing time of the GPU-accelerated registration and B-spline registration techniques was 88 ± 14 versus 557 ± 116 seconds (P < .000000002), respectively; there was no significant difference in computation time despite the difference in the complexity of the algorithms (P = .71).
  
  
  CONCLUSIONS
  The GPU-accelerated volume subdivision technique was as accurate as the B-spline technique and required significantly less processing time. The GPU-accelerated volume subdivision technique may enable the implementation of nonrigid registration into routine clinical practice.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, 75 Francis St, ASB-I L1-050, Boston, MA 02115. Electronic address: tokuda@bwh.harvard.edu.
authors.forename: Junichi
authors.initials: J
authors.lastname: Tokuda
authors.affiliation: IGI Technologies, Inc., Elkridge, Maryland.
authors.forename: William
authors.initials: W
authors.lastname: Plishker
authors.affiliation: Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, 75 Francis St, ASB-I L1-050, Boston, MA 02115.
authors.forename: Meysam
authors.initials: M
authors.lastname: Torabi
authors.affiliation: Department of Neurosurgery, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: Olutayo I
authors.initials: OI
authors.lastname: Olubiyi
authors.affiliation: IGI Technologies, Inc., Elkridge, Maryland.
authors.forename: George
authors.initials: G
authors.lastname: Zaki
authors.affiliation: Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, 75 Francis St, ASB-I L1-050, Boston, MA 02115.
authors.forename: Servet
authors.initials: S
authors.lastname: Tatli
authors.affiliation: Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, 75 Francis St, ASB-I L1-050, Boston, MA 02115.
authors.forename: Stuart G
authors.initials: SG
authors.lastname: Silverman
authors.affiliation: Children's National Medical Center, Washington, DC.
authors.forename: Raj
authors.initials: R
authors.lastname: Shekher
authors.affiliation: Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, 75 Francis St, ASB-I L1-050, Boston, MA 02115.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Hata
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D017115:Catheter Ablation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008099:Liver / Q000000981:diagnostic imaging / Q000473:pathology; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015641:Radiography, Interventional; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
keywords: B-spline; GPU-accelerated image processing; Nonrigid image registration; mutual information