title: Software-based PET-MR image coregistration: combined PET-MRI for the rest of us!
abstract: BACKGROUND
  With the introduction of hybrid positron emission tomography/magnetic resonance imaging (PET/MRI), a new imaging option to acquire multimodality images with complementary anatomical and functional information has become available. Compared with hybrid PET/computed tomography (CT), hybrid PET/MRI is capable of providing superior anatomical detail while removing the radiation exposure associated with CT. The early adoption of hybrid PET/MRI, however, has been limited.
  
  
  OBJECTIVE
  To provide a viable alternative to the hybrid PET/MRI hardware by validating a software-based solution for PET-MR image coregistration.
  
  
  METHODS
  A fully automated, graphics processing unit-accelerated 3-D deformable image registration technique was used to align PET (acquired as PET/CT) and MR image pairs of 17 patients (age range: 10 months-21 years, mean: 10 years) who underwent PET/CT and body MRI (chest, abdomen or pelvis), which were performed within a 28-day (mean: 10.5 days) interval. MRI data for most of these cases included single-station post-contrast axial T1-weighted images. Following registration, maximum standardized uptake value (SUVmax) values observed in coregistered PET (cPET) and the original PET were compared for 82 volumes of interest. In addition, we calculated the target registration error as a measure of the quality of image coregistration, and evaluated the algorithm's performance in the context of interexpert variability.
  
  
  RESULTS
  The coregistration execution time averaged 97±45 s. The overall relative SUVmax difference was 7% between cPET-MRI and PET/CT. The average target registration error was 10.7±6.6 mm, which compared favorably with the typical voxel size (diagonal distance) of 8.0 mm (typical resolution: 0.66 mm × 0.66 mm × 8 mm) for MRI and 6.1 mm (typical resolution: 3.65 mm × 3.65 mm × 3.27 mm) for PET. The variability in landmark identification did not show statistically significant differences between the algorithm and a typical expert.
  
  
  CONCLUSIONS
  We have presented a software-based solution that achieves the many benefits of hybrid PET/MRI scanners without actually needing one. The method proved to be accurate and potentially clinically useful.
authors.affiliation: Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Health System, 111 Michigan Ave. NW, Washington, DC, 20010, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Robertson
authors.affiliation: Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Health System, 111 Michigan Ave. NW, Washington, DC, 20010, USA.
authors.forename: Xinyang
authors.initials: X
authors.lastname: Liu
authors.affiliation: IGI Technologies, Inc., College Park, MD, USA.
authors.forename: William
authors.initials: W
authors.lastname: Plishker
authors.affiliation: IGI Technologies, Inc., College Park, MD, USA.
authors.forename: George F
authors.initials: GF
authors.lastname: Zaki
authors.affiliation: Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Health System, 111 Michigan Ave. NW, Washington, DC, 20010, USA.
authors.forename: Pranav K
authors.initials: PK
authors.lastname: Vyas
authors.affiliation: Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Health System, 111 Michigan Ave. NW, Washington, DC, 20010, USA.
authors.forename: Nabile M
authors.initials: NM
authors.lastname: Safdar
authors.affiliation: Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Health System, 111 Michigan Ave. NW, Washington, DC, 20010, USA. rshekhar@childrensnational.org.|IGI Technologies, Inc., College Park, MD, USA. rshekhar@childrensnational.org.
authors.forename: Raj
authors.initials: R
authors.lastname: Shekhar
mesh_terms: D000293:Adolescent; D000465:Algorithms; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007223:Infant; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D012189:Retrospective Studies; D012984:Software; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: Children; Deformable image registration; Image coregistration; Image fusion; Positron emission tomography; Positron emission tomography/magnetic resonance imaging