On the (Non‐)equivalency of monopolar and bipolar settings for deep brain stimulation fMRI studies of Parkinson's disease patients

Abstract

Background The majority of Parkinson's disease patients with deep brain stimulation (DBS) use a monopolar configuration, which presents challenges for EEG and MRI studies. The literature reports algorithms to convert monopolar to bipolar settings. Purpose/Hypothesis To assess brain responses of Parkinson's disease patients implanted with DBS during fMRI studies using their clinical and presumed equivalent settings using a published conversion recipe. Study Type Prospective. Subjects Thirteen DBS patients. Field Strength/Sequence 1.5T and 3T, fMRI using gradient echo‐planar imaging. Assessment Patients underwent 30/30sec ON/OFF DBS fMRI scans using monopolar and bipolar settings. To convert to a bipolar setting, the negative contact used for the monopolar configuration remained constant and the adjacent dorsal contact was rendered positive, while increasing the voltage by 30%. fMRI activation/deactivation maps and motor Unified Parkinson's Disease Rating Scale (UPDRS‐III) scores were compared for patients in both configurations. Statistical Tests T‐tests were used to compare UPDRS scores and volumes of tissue activated (VTA) diameters in monopolar and bipolar configurations. Results The patterns of fMRI activation in the monopolar and bipolar configurations were generally different. The thalamus, pallidum, and visual cortices exhibited higher activation using the patient's clinical settings than the presumed equivalent settings. VTA diameters were lower (7 mm vs. 6.3 mm, P = 0.047) and UPDRS scores were generally higher in the bipolar (33.2 ± 16) than in the monopolar configuration (28.3 ± 17.4), without reaching statistical significance (P > 0.05). Data Conclusion Monopolar and bipolar configurations result in different patterns of brain activation while using a previously published monopolar–bipolar conversion algorithm. Clinical benefits may be achieved with varying patterns of brain responses. Blind conversion from one to the other should be avoided for purposes of understanding the mechanisms of DBS. Level of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018.

The effect of device configuration and patient’s body composition on image artifact and RF heating of deep brain stimulation devices during MRI at 1.5T and 3T

“…Such off-label studies have relied on in-home safety assessments mostly performed in ASTM-like Phantoms (i.e., the box shaped phantom filled with a single material), and with limited number of DBS device configurations (12,13). This oversimplified approach to MRI safety assessment is concerning for two reasons.…”

Functional MRI Safety and Artifacts during Deep Brain Stimulation: Experience in 102 Patients

“…Experiments in phantoms have yielded inconsistent results with regard to safe MRI of DBS; this is due in part to the heterogeneous and continually evolving DBS and MRI hardware (21,22). Notably, recent phantom studies have demonstrated an acceptable temperature rise at the electrodes when using 3-T MRI and a body transmit coil (15,19,23).…”

RF heating of deep brain stimulation implants in open‐bore vertical MRI systems: A simulation study with realistic device configurations

“…The majority of DBS patients who need MRI for clinical assessment have fully implanted devices. MRI of fully implanted DBS systems is also highly desired to perform functional studies that investigate changes in patterns of brain activation as a function of stimulation parameters …”

“…In the next stage, an IPG is implanted in the chest and leads are connected to the IPG via subcutaneous extensions (Figure 1 fully implanted DBS systems is also highly desired to perform functional studies that investigate changes in patterns of brain activation as a function of stimulation parameters. 20,21 To account for major clinically relevant DBS configurations, we simulated 1 representative patient of each category. Secondary use of imaging data for simulation and modeling was approved by the ethics review board of Northwestern University and by the Institutional Review Board at Albany Medical College.…”