title: Ultrasound-guided spinal injections: a feasibility study of a guidance system.
abstract: OBJECTIVE
  Facet joint injections of analgesic agents are widely used to treat patients with lower back pain. The current standard-of-care for guiding the injection is fluoroscopy, which exposes the patient and physician to significant radiation. As an alternative, several ultrasound guidance systems have been proposed, but have not become the standard-of-care, mainly because of the difficulty in image interpretation by the anesthesiologist unfamiliar with the complex spinal sonography.
  
  
  METHODS
  We introduce an ultrasound-based navigation system that allows for live 2D ultrasound images augmented with a patient-specific statistical model of the spine and relating this information to the position of the tracked injection needle. The model registration accuracy is assessed on ultrasound data obtained from nine subjects who had prior CT images as the gold standard for the statistical model. The clinical validity of our method is evaluated on four subjects (of an ongoing in vivo study) which underwent facet joint injections.
  
  
  RESULTS
  The statistical model could be registered to the bone structures in the ultrasound volume with an average RMS accuracy of 2.3±0.4 mm. The shape of the individual vertebrae could be estimated from the US volume with an average RMS surface distance error of 1.5±0.4 mm. The facet joints could be identified by the statistical model with an average accuracy of 5.1 ± 1.5 mm.
  
  
  CONCLUSIONS
  The results of this initial feasibility assessment suggest that this ultrasound-based system is capable of providing information sufficient to guide facet joint injections. Further clinical studies are warranted.
authors.affiliation: Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Abtin
authors.initials: A
authors.lastname: Rasoulian
authors.forename: Alexander
authors.initials: A
authors.lastname: Seitel
authors.forename: Jill
authors.initials: J
authors.lastname: Osborn
authors.forename: Samira
authors.initials: S
authors.lastname: Sojoudi
authors.forename: Saman
authors.initials: S
authors.lastname: Nouranian
authors.forename: Victoria A
authors.initials: VA
authors.lastname: Lessoway
authors.forename: Robert N
authors.initials: RN
authors.lastname: Rohling
authors.forename: Purang
authors.initials: P
authors.lastname: Abolmaesumi
mesh_terms: D000368:Aged; D000465:Algorithms; D004867:Equipment Design; D005240:Feasibility Studies; D005260:Female; D005471:Fluoroscopy; D006801:Humans; D007270:Injections, Intra-Articular / Q000379:methods*; D007278:Injections, Spinal / Q000379:methods*; D017116:Low Back Pain / Q000000981:diagnostic imaging* / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009339:Needles; D015203:Reproducibility of Results; D013131:Spine; D014463:Ultrasonography; D021801:Zygapophyseal Joint / Q000000981:diagnostic imaging*