There is a growing trend in functional neurosurgery toward direct anatomical targeting for deep brain stimulation (DBS). This study describes a method and reports the initial experience placing DBS electrodes under general anesthesia without the use of microelectrode recordings (MER), using a portable head CT scanner to verify accuracy intra-operatively.

Deep brain stimulation (DBS) is an established therapy for Parkinson's disease and tremor. The therapy was first introduced in the late 1980s, and was FDA approved in 1997. Over 100,000 patients have been treated with DBS, and the benefits have been confirmed through multicenter randomized controlled trials.

Traditional DBS is performed with the patient awake. Parkinson's patients are required to be off their Parkinson's medicine during awake DBS, and single-unit cellular recordings are performed to map the intended target. Electrophysiological mapping can require multiple brain penetrations. The surgery can last 4-6 hours. The surgeon uses a local anesthetic to numb the tissue where the incision is made, and mild sedatives are administered to ward off anxiety. The prospect of being awake on the operating table for brain surgery concerns some patients, as does the requirement to be off medicine.

There is growing interest in performing DBS under general anesthesia, whereby targets are selected anatomically (i.e., on MRI) rather than physiologically . So-called "asleep DBS" is performed with the patient under general anesthesia, and uses intraoperative CT imaging both to target and to verify accurate placement of DBS electrodes at the time of surgery. Asleep DBS eliminates the need for the patient to be kept awake and off medicine. The goal of Asleep DBS is to accurately place the electrodes at the target selected by the surgeon preoperatively, and this goal is accomplished through intraoperative imaging. Electrophysiological mapping is not performed.

The Asleep DBS program at Barrow Neurological Institute / SJHMC started in March 2012; the second institution world-wide to adopt the asleep technique developed by Dr. Kim Burchiel. Other institutions have performed asleep DBS within an MRI magnet to visualize the placement of the electrode. The "Burchiel technique" relies upon MRI-CT fusion algorithms to superimpose the leads, seen on CT, on the MRI which was used for planning.

While asleep DBS improves the patient experience, it is incumbent upon us to demonstrate that the functional outcomes are equivalent to those reported for traditional "awake" DBS. Further, despite common use of MRI-CT fusion, which is available on our neuronavigation systems, the evidence supporting this modality comes from the 1990s, primarily from Gamma Knife literature.

This study will include functional outcomes using established metrics for Parkinson's, capturing both motor function (Unified Parkinson's Disease Rating Scale) and quality of life (Parkinson's Disease Questionnaire-39). In addition, follow-up MRI imaging will allow us to verify that the true position of the DBS leads matches where we thought the leads were based on the intraoperative CT scan that was fused to the preoperative MRI. In other words, there is an error in placement that we see at the time of surgery (if we our inaccuracy is over 2 mm, we reposition the DBS lead). There is also an inherent inaccuracy with CT-MRI fusion. If these inaccuracies are compounded such that where we think we are at the time of surgery is far from where we actually are (as seen on the follow-up MRI of the brain), then CT-MRI fusion is not reliable and should not be used to verify lead placement.

Inclusion Criteria:

• Patient's who have undergone DBS surgery under general anesthesia without electrophysiology, utilizing a portable head CT scanner to verify accuracy intra-operatively.

Exclusion Criteria:

• Patient's who have undergone DBS surgery awake, without general anesthesia and with electrophysiology.

Patients will be selected by CPT codes corresponding to bilateral DBS electrode placement placed under general anesthesia with Leksell sterotactic navigation, portable CT and without the use of microelectrode recordings (MER).

Patients who underwent bilateral GPi DBS surgery under general anesthesia

6 months following surgery