title: MRI-Guided Stereotactic System for Delivery of Intraspinal Microstimulation.
abstract: METHODS
  Laboratory/animal-based proof of principle study.
  
  
  OBJECTIVE
  To validate the accuracy of a magnetic resonance imaging (MRI)-guided stereotactic system for intraspinal electrode targeting and demonstrate the feasibility of such a system for controlling implantation of intraspinal electrodes.
  
  
  BACKGROUND
  Intraspinal microstimulation (ISMS) is an emerging preclinical therapy, which has shown promise for the restoration of motor function following spinal cord injury. However, targeting inaccuracy associated with existing electrode implantation techniques remains a major barrier preventing clinical translation of ISMS.
  
  
  METHODS
  System accuracy was evaluated using a test phantom comprised of nine target locations. Targeting accuracy was determined by calculating the root mean square error between MRI-generated coordinates and actual frame coordinates required to reach the target positions. System performance was further validated in an anesthetized pig model by performing MRI-guided intraspinal electrode implantation and stimulation followed by computed tomography of electrode location. Finally, system compatibility with a commercially available microelectrode array was demonstrated by implanting the array and applying a selection of stimulation amplitudes that evoked hind limb responses.
  
  
  RESULTS
  The root mean square error between actual frame coordinates and software coordinates, both acquired using the test phantom, was 1.09 ± 0.20 mm. Postoperative computed tomography in the anesthetized pig confirmed spatially accurate electrode placement relative to preoperative MRI. Additionally, MRI-guided delivery of a microwire electrode followed by ISMS evoked repeatable electromyography responses in the biceps femoris muscle. Finally, delivery of a microelectrode array produced repeatable and graded hind limb evoked movements.
  
  
  CONCLUSIONS
  We present a novel frame-based stereotactic system for targeting and delivery of intraspinal instrumentation. This system utilizes MRI guidance to account for variations in anatomy between subjects, thereby improving upon existing ISMS electrode implantation techniques.
  
  
  METHODS
  N/A.
authors.affiliation: Mayo Graduate School.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Grahn
authors.affiliation: Department of Neurologic Surgery.
authors.forename: Stephan J
authors.initials: SJ
authors.lastname: Goerss
authors.affiliation: Department of Neurologic Surgery.|Department of Physiology and Biomedical Engineering.
authors.forename: J Luis
authors.initials: JL
authors.lastname: Lujan
authors.affiliation: Department of Neurologic Surgery.
authors.forename: Grant W
authors.initials: GW
authors.lastname: Mallory
authors.affiliation: Department of Neurologic Surgery.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Kall
authors.affiliation: Department of Neurologic Surgery.
authors.forename: Aldo A
authors.initials: AA
authors.lastname: Mendez
authors.affiliation: Mayo Graduate School.
authors.forename: James K
authors.initials: JK
authors.lastname: Trevathan
authors.affiliation: Department of Radiology.
authors.forename: Joel P
authors.initials: JP
authors.lastname: Felmlee
authors.affiliation: Department of Neurologic Surgery.|Division of Engineering, Mayo Clinic, Rochester, MN.
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Bennet
authors.affiliation: Department of Neurologic Surgery.|Department of Physiology and Biomedical Engineering.
authors.forename: Kendall H
authors.initials: KH
authors.lastname: Lee
mesh_terms: D000818:Animals; D004599:Electric Stimulation Therapy / Q000379:methods*; D004567:Electrodes, Implanted; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008839:Microelectrodes; D013116:Spinal Cord / Q000000981:diagnostic imaging*; D013119:Spinal Cord Injuries / Q000000981:diagnostic imaging / Q000628:therapy; D013238:Stereotaxic Techniques / Q000295:instrumentation; D013552:Swine