title: Joint registration of ultrasound, CT and a shape+pose statistical model of the lumbar spine for guiding anesthesia.
abstract: OBJECTIVE
  Facet joint injections and epidural needle insertions are widely used for spine anesthesia. Accurate needle placement is important for effective therapy delivery and avoiding complications arising from damage of soft tissue and nerves. Needle guidance is usually performed by fluoroscopy or palpation, resulting in radiation exposure and multiple needle re-insertions. Several ultrasound (US)-based approaches have been proposed but have not found wide acceptance in clinical routine. This is mainly due to difficulties in interpretation of the complex spinal anatomy in US, which leads to clinicians' lack of confidence in relying only on information derived from US for needle guidance.
  
  
  METHODS
  We introduce a multimodal joint registration technique that takes advantage of easy-to-interpret preprocedure computed topography (CT) scans of the lumbar spine to concurrently register a shape+pose model to the intraprocedure 3D US. Common shape coefficients are assumed between two modalities, while pose coefficients are specific to each modality.
  
  
  RESULTS
  The joint method was evaluated on patient data consisting of ten pairs of US and CT scans of the lumbar spine. It was successfully applied in all cases and yielded an RMS shape error of 2.1 mm compared to the CT ground truth. The joint registration technique was compared to a previously proposed method of statistical model to US registration Rasoulian et al. (Information processing in computer-assisted interventions. Springer, Berlin, pp 51-60, 2013). The joint framework improved registration accuracy to US in 7 out of 17 visible vertebrae, belonging to four patients. In the remaining cases, the two methods were equally accurate.
  
  
  CONCLUSIONS
  The joint registration allows visualization and augmentation of important anatomy in both the US and CT domain and improves the registration accuracy in both modalities. Observing the patient-specific model in the CT domain allows the clinicians to assess the local registration accuracy qualitatively, which is likely to increase their confidence in using the US model for deriving needle guidance decisions.
authors.affiliation: Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada. delaramb@ece.ubc.ca.
authors.forename: Delaram
authors.initials: D
authors.lastname: Behnami
authors.affiliation: Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Alexander
authors.initials: A
authors.lastname: Seitel
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.affiliation: Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Emran Mohammad Abu
authors.initials: EM
authors.lastname: Anas
authors.affiliation: Department of Ultrasound, Women's Hospital, Vancouver, BC, Canada.
authors.forename: Victoria
authors.initials: V
authors.lastname: Lessoway
authors.affiliation: Department of Anesthesia, St. Paul's Hospital, Vancouver, BC, Canada.
authors.forename: Jill
authors.initials: J
authors.lastname: Osborn
authors.affiliation: Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada.|Department of Mechanical Engineering, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: Rohling
authors.affiliation: Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Purang
authors.initials: P
authors.lastname: Abolmaesumi
mesh_terms: D000758:Anesthesia; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007270:Injections, Intra-Articular / Q000379:methods*; D007278:Injections, Spinal / Q000379:methods*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D015233:Models, Statistical; D064847:Multimodal Imaging / Q000379:methods; D009339:Needles; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014463:Ultrasonography / Q000379:methods*
keywords: Guidance; Joint registration; Multi-vertebrae model; Spinal ultrasound; Statistical shape+pose model