Low Power MRI Techniques for Neurosurgical Planning and Post-surgical Assessment of Deep Brain Stimulators in Patients with Medically Refractory Parkinson’s Disease or Dystonia

Abstract

Medically refractory Parkinson's or dystonia conditions are often treated with deep brain stimulation (DBS) that are managed with the help of very restricted MRI due to safety concerns. The resulting MR images are often suboptimal but are still considered valuableto assess post-surgical complications as well as electrode placement accuracy. Absorbed radiofrequency power near the DBS electrodes during an MRI could produce tissue burns and,therefore, are subjected to strong conditional guidance from FDA and DBS manufacturers. We developed a comprehensive brain MRI protocol (including T1 MPRAGE, FSET2, DTI and FSE IR with modified refocusing flip angles and stretched RF pulses) for 10 Parkinson's and 5 dystonia patients with implanted electrodes. This included low power 2D and 3D MR pulse sequences that preserved the expected tissue contrast, minimizedsignal artifacts and offered better tissue visualization near electrode edges. Low power images were judged as adequate for stereotactic planning in 12/15 patients while for the rest the neurosurgeons had to resort to additional landmarks. Radiologic diagnostic quality was also equivalent in tissue contrast and pathology detection as compared to high power routine MRI prior to electrode implantation. The white matter fiber tracks in DTI maps were virtually unchanged with minimal interference from the implanted leads.

The restricted SAR protocol: A method to assess MRI coil prototypes in an unconditionally safe manner

“…The high resolution (0.5 × 0.5 × 4.0 mm 3 ) of T 2 *‐weighted images (Figure 4) with a reasonable SNR achievable despite drastic power constraints raises the question of extending the rS protocol to other studies that may require a severe SAR limitation. One can think about its adaptation for the MR exams involving implants 42–44 . Here again, it is essential to consider the high possible localization of the electric field.…”

“…One can think about its adaptation for the MR exams involving implants. [42][43][44] Here again, it is essential to consider the high possible localization of the electric field. In addition to RF energy restriction, safe implant studies include conditions on gradients to avoid additional heating of surrounding tissues, which should be considered separately.…”

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“…Multi-modal approaches hold more promise than advanced applications of single modalities like repeat CT for Hounsfield unit changes [37] or susceptibility MR for micro-hemorrhages [33] or PET/SPECT with new tracer designs. Repetitive minor blast trauma [17] as well as focal surgical procedures as in the placement of neurological shunts or implants [11,12] may act as templates to study effects of controlled, static loads in pre-planned locations to offer useful mechanistic evaluation of mTBI that usually involves dynamic and global loads.…”

“…It is worth noting that analogous to minor brain trauma, when controlled, surgical intervention for placing Deep Brain Stimulation (DBS) electrodes has created increased global cerebral perfusion [11] and have been verified to produce moderately increased MR signal from whole brain tissue even under low Power MRI techniques [12]. Hence the perfusion results after minor head trauma have to be carefully assessed and global insult originating from perhaps oxidative stress model based on whiplash or dynamic blunt load should be taken into account.…”