Frameless deep brain stimulation using intraoperative O-arm technology

Clinical article

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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.


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.


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).


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.

Abbreviations used in this paper: ALARA = as low as reasonably achievable; AP = anteroposterior; cZI = caudal zona incerta; DBS = deep brain stimulation; GPi = internal globus pallidus; iCT = intraoperative CT; iMR = intraoperative MR; MER = microelectrode recording; MS = multiple sclerosis; PD = Parkinson disease; STN = subthalamic nucleus; Vim = ventralis intermedius nucleus.

Article Information

Address correspondence to: Adam P. Smith, M.D., Department of Neurosurgery, Rush University Medical Center, 1725 West Harrison Avenue, Suite 1115, Chicago, Illinois 60612. email:

Please include this information when citing this paper: published online April 15, 2011; DOI: 10.3171/2011.3.JNS101642.

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Operating room setup demonstrating position of O-arm and planning station in relation to the patient. Electrophysiology equipment is out of the picture on the opposite side of the patient caudal to the operative field.

  • View in gallery

    Preoperative StealthStation views showing the intended target based on indirect and direct planning. These coordinates are later compared with the coordinates of the actual lead on postoperative MR imaging, and the euclidean distance is calculated.

  • View in gallery

    StealthStation views showing the final location of planned target after electrophysiological testing. The yellow trajectory is the initial intended target based on preoperative planning, but microelectrode recording and microstimulation suggested that the final target should be anterior and medial as shown by the purple trajectory. These final planned coordinates are later compared with the coordinates of the actual lead on postoperative MR imaging, and the euclidean distance is calculated. Of note, these final planned coordinates are not necessarily the actual coordinates of the moved microelectrode. These coordinates are calculated by the distance moved from the preoperative intended target based on set distances on the microdrive.

  • View in gallery

    StealthStation views showing final lead coordinates on the merged iCT. These iCT coordinates are later compared with the coordinates of the actual lead on postoperative MR imaging, and the euclidean distance is calculated. The yellow trajectory is the initial intended target based on preoperative planning, the purple trajectory is the final planned target after electrophysiological testing, and the red trajectory marks the lead itself on iCT. Of note, the red trajectory is extrapolated by centering its tip in the iCT artifact (tip of the actual lead).

  • View in gallery

    Intraoperative AP radiographs of frame-based procedures. Left: Lead in the GPi. Right: Bilateral leads in the STN. Note the more lateral entry point on the skull for the GPi lead, making the frameless techniques less desirable than for the STN target.

  • View in gallery

    Postoperative CT scan (left) and MR image (right) obtained after a bilateral procedure, showing no pneumocephalus or brain shift. This was a consistent finding in our series.

  • View in gallery

    StealthStation view used to confirm the merge of the preoperative MR imaging (right half) and preoperative CT (left half). We achieved extremely low merging error in our series.


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