✓ The cerebrospinal fluid (CSF) flow rates in 12 patients with symptoms suggestive of CSF shunt obstruction were measured with magnetic resonance (MR) phase imaging. The shunts were imaged over the skull, just distal to any reservoir, using a curved surface coil. Images perpendicular to the direction of flow were made on a 1.5-tesla clinical unit with a flow-sensitive pulse sequence. The patients' ages ranged from 2 months to 28 years. All patients had ancillary investigations to determine the functional status of the shunt. No flow was detected in seven patients with blocked shunts. Flow rates between 3 and 40 cc/hr were found in three patients with functioning shunts. Two patients, one with a blocked shunt and one with a functioning shunt, could not be imaged due to motion artifact. Magnetic resonance phase imaging is a promising technique in the determination of CSF shunt obstruction.
James M. Drake, Alastair J. Martin, and R. Mark Henkleman
Vibhor Krishna and Mojgan Hodaie
Walter A. Hall, Haiying Liu, Alastair J. Martin, Robert E. MAxwell, and Charles L. Truwit
Object. The authors describe their initial results obtained using a skull-mounted trajectory guide for intraoperative magnetic resonance (MR) imaging—guided brain biopsy sampling. The device was used in conjunction with a new methodology known as prospective stereotaxis for surgical trajectory alignment.
Methods. Between January 1999 and March 2000, 38 patients underwent 40 brain biopsy procedures in which prospective stereotaxis was performed with the trajectory guide in a short-bore 1.5-tesla MR imager. In most cases, orthogonal T2-weighted half-Fourier acquisition single-shot turbo spin—echo (HASTE) images were used to determine the desired trajectory and align the device. The surgical trajectory was defined as a line connecting three points: the target, pivot, and alignment stem points. In all cases, surgical specimens were submitted for frozen section and pathological examination. Postoperative turbofluid-attenuated inversion-recovery and gradient-echo images were obtained to exclude the presence of hemorrhage. Trajectory determination and alignment was simple and efficient, requiring less than 5 minutes. Confirmatory HASTE images were obtained along the biopsy needle as it was being advanced or after reaching the target. All biopsy procedures yielded diagnostic tissue. One patient with a lesion near the motor strip experienced a transient hemiparesis of the hand related to passage of the biopsy needle, and another sustained a fatal postoperative myocardial infarction. No patient suffered a clinically significant or radiologically visible hemorrhage.
Conclusions. In combination with prospective stereotaxis, the trajectory guide provided a safe and accurate way to perform brain biopsy procedures.
Melanie A. Morrison, Anthony T. Lee, Alastair J. Martin, Cameron Dietiker, Ethan G. Brown, and Doris D. Wang
Direct visualization of the ventral intermediate nucleus (VIM) of the thalamus on standard MRI sequences remains elusive. Therefore, deep brain stimulation (DBS) surgery for essential tremor (ET) indirectly targets the VIM using atlas-derived consensus coordinates and requires awake intraoperative testing to confirm clinical benefits. The objective of this study was to evaluate the utility of proton density (PD)–weighted MRI and tractography of the intersecting dentato-rubro-thalamic tract (DRTT) for direct “intersectional” targeting of the VIM in ET.
DBS targets were selected by identifying the VIM on PD-weighted images relative to the DRTT in 2 patients with ET. Tremor reduction was confirmed with intraoperative clinical testing. Intended target coordinates based on the direct intersectional targeting technique were compared with consensus coordinates obtained with indirect targeting. Pre- and postoperative tremor scores were assessed using the Fahn-Tolosa-Marin tremor rating scale (TRS).
Planned DBS coordinates based on direct versus indirect targeting of the VIM differed in both the anteroposterior (range 0 to 2.3) and lateral (range −0.7 to 1) directions. For 1 patient, indirect targeting—without PD-weighted visualization of the VIM and DRTT—would have likely resulted in suboptimal electrode placement within the VIM. At the 3-month follow-up, both patients demonstrated significant improvement in tremor symptoms subjectively and according to the TRS (case 1: 68%, case 2: 72%).
Direct intersectional targeting of the VIM using PD-weighted imaging and DRTT tractography is a feasible method for DBS placement in patients with ET. These advanced targeting techniques can supplement awake intraoperative testing or be used independently in asleep cases to improve surgical efficiency and confidence.
Alastair J. Martin, Paul S. Larson, Nathan Ziman, Nadja Levesque, Monica Volz, Jill L. Ostrem, and Philip A. Starr
The objective of this study was to assess the incidence of postoperative hardware infection following interventional (i)MRI–guided implantation of deep brain stimulation (DBS) electrodes in a diagnostic MRI scanner.
A diagnostic 1.5-T MRI scanner was used over a 10-year period to implant DBS electrodes for movement disorders. The MRI suite did not meet operating room standards with respect to airflow and air filtration but was prepared and used with conventional sterile procedures by an experienced surgical team. Deep brain stimulation leads were implanted while the patient was in the magnet, and patients returned 1–3 weeks later to undergo placement of the implantable pulse generator (IPG) and extender wire in a conventional operating room. Surgical site infections requiring the removal of part or all of the DBS system within 6 months of implantation were scored as postoperative hardware infections in a prospective database.
During the 10-year study period, the authors performed 164 iMRI-guided surgical procedures in which 272 electrodes were implanted. Patients ranged in age from 7 to 78 years, and an overall infection rate of 3.6% was found. Bacterial cultures indicated Staphylococcus epidermis (3 cases), methicillin-susceptible Staphylococcus aureus (2 cases), or Propionibacterium sp. (1 case). A change in sterile practice occurred after the first 10 patients, leading to a reduction in the infection rate to 2.6% (4 cases in 154 procedures) over the remainder of the procedures. Of the 4 infections in this patient subset, all occurred at the IPG site.
Interventional MRI–guided DBS implantation can be performed in a diagnostic MRI suite with an infection risk comparable to that reported for traditional surgical placement techniques provided that sterile procedures, similar to those used in a regular operating room, are practiced.
Deep brain stimulation for Parkinson disease
Andres M. Lozano
Philip A. Starr, Alastair J. Martin, Jill L. Ostrem, Pekka Talke, Nadja Levesque, and Paul S. Larson
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).
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.
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%.
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.
Michael E. Ivan, Jay Yarlagadda, Akriti P. Saxena, Alastair J. Martin, Philip A. Starr, W. Keith Sootsman, and Paul S. Larson
Brain shift during minimally invasive, bur hole–based procedures such as deep brain stimulation (DBS) electrode implantation and stereotactic brain biopsy is not well characterized or understood. We examine shift in various regions of the brain during a novel paradigm of DBS electrode implantation using interventional imaging throughout the procedure with high-field interventional MRI.
Serial MR images were obtained and analyzed using a 1.5-T magnet prior to, during, and after the placement of DBS electrodes via frontal bur holes in 44 procedures. Three-dimensional coordinates in MR space of unique superficial and deep brain structures were recorded, and the magnitude, direction, and rate of shift were calculated. Measurements were recorded to the nearest 0.1 mm.
Shift ranged from 0.0 to 10.1 mm throughout all structures in the brain. The greatest shift was seen in the frontal lobe, followed by the temporal and occipital lobes. Shift was also observed in deep structures such as the anterior and posterior commissures and basal ganglia; shift in the pallidum and subthalamic region ipsilateral to the bur hole averaged 0.6 mm, with 9% of patients having over 2 mm of shift in deep brain structures. Small amounts of shift were observed during all procedures; however, the initial degree of shift and its direction were unpredictable.
Brain shift is continual and unpredictable and can render traditional stereotactic targeting based on preoperative imaging inaccurate even in deep brain structures such as those used for DBS.
Jill L. Ostrem, Nathan Ziman, Nicholas B. Galifianakis, Philip A. Starr, Marta San Luciano, Maya Katz, Caroline A. Racine, Alastair J. Martin, Leslie C. Markun, and Paul S. Larson
The ClearPoint real-time interventional MRI-guided methodology for deep brain stimulation (DBS) lead placement may offer advantages to frame-based approaches and allow accurate implantation under general anesthesia. In this study, the authors assessed the safety and efficacy of DBS in Parkinson’s disease (PD) using this surgical method.
This was a prospective single-center study of bilateral DBS therapy in patients with advanced PD and motor fluctuations. Symptom severity was evaluated at baseline and 12 months postimplantation using the change in Unified Parkinson’s Disease Rating Scale (UPDRS) Part III “off” medication score as the primary outcome variable.
Twenty-six PD patients (15 men and 11 women) were enrolled from 2010 to 2013. Twenty patients were followed for 12 months (16 with a subthalamic nucleus target and 4 with an internal globus pallidus target). The mean UPDRS Part III “off” medication score improved from 40.75 ± 10.9 to 24.35 ± 8.8 (p = 0.001). “On” medication time without troublesome dyskinesia increased 5.2 ± 2.6 hours per day (p = 0.0002). UPDRS Parts II and IV, total UPDRS score, and dyskinesia rating scale “on” medication scores also significantly improved (p < 0.01). The mean levodopa equivalent daily dose decreased from 1072.5 ± 392 mg to 828.25 ± 492 mg (p = 0.046). No significant cognitive or mood declines were observed. A single brain penetration was used for placement of all leads, and the mean targeting error was 0.6 ± 0.3 mm. There were 3 serious adverse events (1 DBS hardware-related infection, 1 lead fracture, and 1 unrelated death).
DBS leads placed using the ClearPoint interventional real-time MRI-guided method resulted in highly accurate lead placement and outcomes comparable to those seen with frame-based approaches.
Philip A. Starr, Leslie C. Markun, Paul S. Larson, Monica M. Volz, Alastair J. Martin, and Jill L. Ostrem
The placement of deep brain stimulation (DBS) leads in adults is traditionally performed using physiological confirmation of lead location in the awake patient. Most children are unable to tolerate awake surgery, which poses a challenge for intraoperative confirmation of lead location. The authors have developed an interventional MRI (iMRI)–guided procedure to allow for real-time anatomical imaging, with the goal of achieving very accurate lead placement in patients who are under general anesthesia.
Six pediatric patients with primary dystonia were prospectively enrolled. Patients were candidates for surgery if they had marked disability and medical therapy had been ineffective. Five patients had the DYT1 mutation, and mean age at surgery was 11.0 ± 2.8 years. Patients underwent bilateral globus pallidus internus (GPi, n = 5) or sub-thalamic nucleus (STN, n = 1) DBS. The leads were implanted using a novel skull-mounted aiming device in conjunction with dedicated software (ClearPoint system), used within a 1.5-T diagnostic MRI unit in a radiology suite, without physiological testing. The Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) was used at baseline, 6 months, and 12 months postoperatively. Further measures included lead placement accuracy, quality of life, adverse events, and stimulation settings.
A single brain penetration was used for placement of all 12 leads. The mean difference (± SD) between the intended target location and the actual lead location, in the axial plane passing through the intended target, was 0.6 ± 0.5 mm, and the mean surgical time (leads only) was 190 ± 26 minutes. The mean percent improvement in the BFMDRS movement scores was 86.1% ± 12.5% at 6 months (n = 6, p = 0.028) and 87.6% ± 19.2% at 12 months (p = 0.028). The mean stimulation settings at 12 months were 3.0 V, 83 μsec, 135 Hz for GPi DBS, and 2.1 V, 60 μsec, 145 Hz for STN DBS). There were no serious adverse events.
Interventional MRI–guided DBS using the ClearPoint system was extremely accurate, provided real-time confirmation of DBS placement, and could be used in any diagnostic MRI suite. Clinical outcomes for pediatric dystonia are comparable with the best reported results using traditional frame-based stereotaxy. Clinical trial registration no.: NCT00792532 (ClinicalTrials.gov).