title: MR image overlay guidance: system evaluation for preclinical use.
abstract: OBJECTIVE
  A clinical augmented reality guidance system was developed for MRI-guided musculoskeletal interventions Magnetic Resonance Image Overlay System (MR-IOS). The purpose of this study was to assess MRI compatibility, system accuracy, technical efficacy, and operator performance of the MR-IOS.
  
  
  METHODS
  The impact of the MR-IOS on the MR environment was assessed by measuring image quality with signal-to-noise ratio (SNR) and signal intensity uniformity with the system in various on/off states. The system accuracy was assessed with an in-room preclinical experiment by performing 62 needle insertions on a spine phantom by an expert operator measuring entry, depth, angle, and target errors. Technical efficacy and operator performance were tested in laboratory by running an experiment with 40 novice operators (20 using freehand technique versus 20 MR-IOS-guided) with each operator inserting 10 needles into a geometric phantom. Technical efficacy was measured by comparing the success rates of needle insertions between the two operator groups. Operator performance was assessed by comparing total procedure times, total needle path distance, presumed tissue damage, and speed of individual insertions between the two operator groups.
  
  
  RESULTS
  The MR-IOS maximally altered SNR by 2% with no perceptible change in image quality or uniformity. Accuracy assessment showed mean entry error of 1.6 ± 0.6 mm, depth error of 0.7 ± 0.5 mm, angle error of 1.5 ± 1.1°, and target error of 1.9 ± 0.8 mm. Technical efficacy showed a statistically significant difference (p = 0.031) between success rates (freehand 35.0% vs. MR-IOS 80.95%). Operator performance showed: mean total procedure time of 40.3 ± 4.4 (s) for freehand and 37.0 ± 3.7 (s) for MR-IOS (p = 0.584), needle path distances of 152.6 ± 15.0 mm for freehand and 116.9 ± 8.7 mm for MR-IOS (p = 0.074), presumed tissue damage of 7,417.2 ± 955.6 mm(2) for freehand and 6062.2 ± 678.5 mm(2) for MR-IOS (p = 0.347), and speed of insertion 5.9 ± 0.4 mm/s for freehand and 4.3 ± 0.3 mm/s for MR-IOS (p = 0.003).
  
  
  CONCLUSIONS
  The MR-IOS is compatible within a clinical MR imaging environment, accurate for needle placement, technically efficacious, and improves operator performance over the unassisted insertion technique. The MR-IOS was found to be suitable for further testing in a clinical setting.
authors.affiliation: Department of Mechanical and Materials Engineering, Queen's University, Kingston, ON, Canada. paweena@jhu.edu
authors.forename: Paweena
authors.initials: P
authors.lastname: U-Thainual
authors.forename: Jan
authors.initials: J
authors.lastname: Fritz
authors.forename: Choladawan
authors.initials: C
authors.lastname: Moonjaita
authors.forename: Tamas
authors.initials: T
authors.lastname: Ungi
authors.forename: Aaron
authors.initials: A
authors.lastname: Flammang
authors.forename: John A
authors.initials: JA
authors.lastname: Carrino
authors.forename: Gabor
authors.initials: G
authors.lastname: Fichtinger
authors.forename: Iulian
authors.initials: I
authors.lastname: Iordachita
mesh_terms: D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D007278:Injections, Spinal / Q000295:instrumentation*; D053783:Magnetic Resonance Imaging, Interventional / Q000295:instrumentation*; D008954:Models, Biological; D019637:Orthopedic Procedures / Q000295:instrumentation*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio