An assessment of current brain targets for deep brain stimulation surgery with susceptibility-weighted imaging at 7 tesla.

Deep brain stimulation (DBS) surgery is used for the treatment of patients with movement disorders, including Parkinson disease, essential tremor, and dystonia. With the recent US Food and Drug Administration (FDA) approval of DBS for obsessive-compulsive disorder and the likelihood of FDA approval for the treatment of epilepsy, the indications for DBS are rapidly increasing. To date, > 75 000 patients worldwide have undergone DBS surgery, and this number is expected to increase significantly. The success of this surgical procedure is critically dependent on the precise placement of the DBS electrode into the brain target structure of interest. To date, most DBS surgeries have relied on a procedure that involves first an indirect targeting method in which normalized atlas-derived diagrams using set distances from the line connecting the anterior and posterior commissures1,2 are superimposed on a patient's brain magnetic resonance imaging (MRI) scan and approximate distances and coordinates are used for target localization. Indirect targeting can then be modified by anatomic information derived from the particular patient's MRI scan. However, no consensus exists about how best to normalize atlas-derived coordinates to a specific patient's brain3; significant variability exists in the location of thalamic and basal ganglia nuclei in humans4-7; and the target structures are small, measuring < 10 mm in most dimensions.7 All these factors lead to targeting errors in the operating room. Furthermore, current clinical imaging methods are not always sufficiently accurate for placing a DBS electrode and do not allow visualization of nuclei within the thalamus, the division between the lateral and medial segments of globus pallidus (GP) interna (GPi), or even a clear differentiation of the subthalamic nucleus (STN) from the adjacent substantia nigra (SN), distinctions that are critical to optimal electrode placement. As a result, multiple passes with microelectrodes through the brain are performed to refine and confirm the DBS electrode location within the target of interest. Although providing critical information about regional neurophysiology and thus the optimal location for the DBS electrode, these microelectrode recordings carry a risk of hemorrhage and require active patient participation during the procedure. An alternative approach might be surgery based on improving the visualization of the target structure.1,4,8,9 Currently, however, inadequate image resolution and contrast preclude the use of an anatomic imaging-based targeting method for structures as Vim (ventralis intermedius) or for optimally resolving STN from SN. If anatomic imaging-based targeting methods could be improved, the accuracy of target identification on MRI would increase, allowing more accurate selection of the anatomic target. Given recent advances in medical imaging, especially the advent of high-field-strength imaging techniques, our objective was to develop a new approach for the visualization of DBS targets that are FDA approved for the treatment of movement disorders. Using a state-of-the-art high-field (7-T) MRI scanner and capitalizing on the high resolution and enhanced image contrast afforded by high-field MRI, in conjunction with the use of susceptibility-weighted imaging (SWI)10,11 for enhancing MRI contrast, we set out to improve the in vivo detection of DBS target structures. Ultimately, the methods developed here, in addition to improving DBS surgery, will be advantageous for use in a wide range of neurosurgical procedures that could similarly benefit from direct visualization of small, low-contrast brain structures or abnormalities.