title: Frameless deep brain stimulation using intraoperative O-arm technology. Clinical article.
abstract: OBJECTIVE
  Correct lead location in the desired target has been proven to be a strong influential factor for good clinical outcome in deep brain stimulation (DBS) surgery. Commonly, a surgeon's first reliable assessment of such location is made on postoperative imaging. While intraoperative CT (iCT) and intraoperative MR imaging have been previously described, the authors present a series of frameless DBS procedures using O-arm iCT.
  
  
  METHODS
  Twelve consecutive patients with 15 leads underwent frameless DBS placement using electrophysiological testing and O-arm iCT. Initial target coordinates were made using standard indirect and direct assessment. Microelectrode recording (MER) with kinesthetic responses was performed, followed by microstimulation to evaluate the side-effect profile. Intraoperative 3D CT acquisitions obtained between each MER pass and after final lead placement were fused with the preoperative MR image to verify intended MER movements around the target area and to identify the final lead location. Tip coordinates from the initial plan, final intended target, and actual lead location on iCT were later compared with the lead location on postoperative MR imaging, and euclidean distances were calculated. The amount of radiation exposure during each procedure was calculated and compared with the estimated radiation exposure if iCT was not performed.
  
  
  RESULTS
  The mean euclidean distances between the coordinates for the initial plan, final intended target, and actual lead on iCT compared with the lead coordinates on postoperative MR imaging were 3.04 ± 1.45 mm (p = 0.0001), 2.62 ± 1.50 mm (p = 0.0001), and 1.52 ± 1.78 mm (p = 0.0052), respectively. The authors obtained good merging error during image fusion, and postoperative brain shift was minimal. The actual radiation exposure from iCT was invariably less than estimates of exposure using standard lateral fluoroscopy and anteroposterior radiographs (p < 0.0001).
  
  
  CONCLUSIONS
  O-arm iCT may be useful in frameless DBS surgery to approximate microelectrode or lead locations intraoperatively. Intraoperative CT, however, may not replace fundamental DBS surgical techniques such as electrophysiological testing in movement disorder surgery. Despite the lack of evidence for brain shift from the procedure, iCT-measured coordinates were statistically different from those obtained postoperatively, probably indicating image merging inaccuracy and the difficulties in accurately denoting lead location. Therefore, electrophysiological testing may truly be the only means of precisely knowing the location in 3D space intraoperatively. While iCT may provide clues to electrode or lead location during the procedure, its true utility may be in DBS procedures targeting areas where electrophysiology is less useful. The use of iCT appears to reduce radiation exposure compared with the authors' traditional frameless technique.
authors.affiliation: Department of Neurosurgery, Rush University Medical Center, Chicago, Illinois, USA. Adam_Smith@rush.edu
authors.forename: Adam P
authors.initials: AP
authors.lastname: Smith
authors.forename: Roy A E
authors.initials: RA
authors.lastname: Bakay
mesh_terms: D000328:Adult; D000368:Aged; D046690:Deep Brain Stimulation / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008839:Microelectrodes; D008875:Middle Aged; D038361:Neuronavigation / Q000379:methods*; D010300:Parkinson Disease / Q000628:therapy; D011184:Postoperative Period; D016634:Radiosurgery / Q000379:methods*; D020531:Subthalamic Nucleus / Q000601:surgery*; D014202:Tremor / Q000628:therapy