Subthalamic nucleus deep brain stimulator placement using high-field interventional magnetic resonance imaging and a skull-mounted aiming device: technique and application accuracy

Abstract

Object: The authors discuss their method for placement of deep brain stimulation (DBS) electrodes using interventional MR (iMR) imaging and report on the accuracy of the technique, its initial clinical efficacy, and associated complications in a consecutive series of subthalamic nucleus (STN) DBS implants to treat Parkinson disease (PD).

Methods: A skull-mounted aiming device (Medtronic NexFrame) was used in conjunction with real-time MR imaging (Philips Intera 1.5T). Preoperative imaging, DBS implantation, and postimplantation MR imaging were integrated into a single procedure performed with the patient in a state of general anesthesia. Accuracy of implantation was assessed using 2 types of measurements: the "radial error," defined as the scalar distance between the location of the intended target and the actual location of the guidance sheath in the axial plane 4 mm inferior to the commissures, and the "tip error," defined as the vector distance between the expected anterior commissure-posterior commissure (AC-PC) coordinates of the permanent DBS lead tip and the actual AC-PC coordinates of the lead tip. Clinical outcome was assessed using the Unified Parkinson's Disease Rating Scale part III (UPDRS III), in the off-medication state.

Results: Twenty-nine patients with PD underwent iMR imaging-guided placement of 53 DBS electrodes into the STN. The mean (+/- SD) radial error was 1.2 +/- 0.65 mm, and the mean absolute tip error was 2.2 +/- 0.92 mm. The tip error was significantly smaller than for STN DBS electrodes implanted using traditional frame-based stereotaxy (3.1 +/- 1.41 mm). Eighty-seven percent of leads were placed with a single brain penetration. No hematomas were visible on MR images. Two device infections occurred early in the series. In bilaterally implanted patients, the mean improvement on the UPDRS III at 9 months postimplantation was 60%.

Conclusions: The authors' technical approach to placement of DBS electrodes adapts the procedure to a standard configuration 1.5-T diagnostic MR imaging scanner in a radiology suite. This method simplifies DBS implantation by eliminating the use of the traditional stereotactic frame and the subsequent requirement for registration of the brain in stereotactic space and the need for physiological recording and patient cooperation. This method has improved accuracy compared with that of anatomical guidance using standard frame-based stereotaxy in conjunction with preoperative MR imaging.

Fig. 1

Intraoperative photograph showing the position of the patient’s head in an MR-compatible headholder with placement of radiofrequency surface coils. The connection between the endotracheal tube and ventilator is led through the anterior coil. The posterior coil, placed under the headholder, is hidden under a towel.

Fig. 2

Magnetic resonance images showing the method of trajectory planning using reformatted oblique slices passing through the target, angled to exclude the lateral ventricle (MR protocol 1). A: First step. On a coronal plane passing through the target, an oblique sagittal plane is defined (white line) that avoids the lateral ventricle. B: Second step. The oblique sagittal plane selected in panel A is constructed on the MR console, and a safe trajectory (black line) to the target is planned.

Fig. 3

Intraoperative photographs demonstrating surgical draping and trajectory guides. A: Patient’s head is shown at the back of the MR bore, with a sterile drape. B: Trajectory guides with alignment stems are shown. C: Trajectory guides with multilumen insert and peel-away sheath prior to advancing the sheath into the brain. The flexible radiofrequency receiving coils are covered with sterile blue towels.

Fig. 4

Axial MR image used to define the target in the dorsolateral STN (black arrow indicates right STN; MR protocol 3).

Fig. 5

Coronal MR image used to define the coordinates of the pivot points for the trajectory guides, prior to aligning the alignment stem (MR protocol 4).

Fig. 6

Rapid acquisition oblique coronal (A) and sagittal (B) images passing through the target and pivot point after the trajectory guide has been aligned (MR protocol 5). Black arrows show the predicted trajectory of the DBS lead.

Fig. 7

A and B: Axial T2-weighted MR images obtained 4 mm below the commissures, showing sheath and ceramic stylet assembly at target (MR protocol 3). Close up (B) showing the stylets in the target region, with the desired targets indicated by the centers of the white circles. The right lead has a radial error of 0.5 mm in the medial direction. The left lead has a radial error of 0.2 mm in the lateral direction.

Fig. 8

Final lead location as assessed on T1-weighted volumetric MR images. A: Axial image at 4 mm inferior to the commissures. B: Reformatted oblique image in the sagittal plane along the lead trajectory (MR protocol 8).

Fig. 9

Bar graph showing the distribution of lead tip errors (3D or vector error) in STN DBS placed using iMR imaging versus frame-based stereotaxy. Comparison data are from Starr et al., 2002.