Optimizing MRI based direct visualization of the Subthalamic nucleus on 1.5 T systems Navneet Sharma, Dr. Curtis Sutton Dr. Erich O. Richter

Objectives Determine protocol parameters that enhance visualization of the Subthalamic nucleus (STN) using MRI (1.5T) Check if these parameters need to be changed or not for each individual Compare and contrast the parameter values between normal and Parkinson's patients

DBS research over the years Source: Web of Science

What kind of magnets are we using? Source: Web of Science

Complications Currently the MRI techniques using the 1.5 T magnet only gives a vague outline of the STN’s location localized during the procedure using microelectrode recording RICHTER, ET AL. Determining the position and size of the subthalamic nucleus based on magnetic resonance imaging results in patients with advanced Parkinson disease. J Neurosurg 100:541–546, 2004

Methods T1 volumetric and T2 weighted MRIs were taken from 3 different volunteers Controlled various variables to assess quality of the images ◦ Time Echo (TE) ◦ Time Repetition (TR) ◦ Bandwidth ◦ Slice Thickness 3D reconstructions of the STN were generated using BrainLAB 2.6 software Subsequently, the parameters from the normal MRI scans was compared to those of Parkinson’s patients

Results These values help differentiate Fe containing structures from non-Fe containing structures in the Basal Ganglia *switch to in-patient procedure to accommodate the increased scan time VariableOptimal Value TE144 msec TR4000 msec Bandwidth100 KHz Slice Thickness1 mm NEX2 Scan Time mins* NormalParkinson TR (msec) ± TE (msec) ± 6.3

The reduced TE associated with PD is indicative of increased free iron levels in PD compared to normal This leads to highly neurotoxic states which cause neurodengeneration in the STN Based on literature review, the pars compacta of the SN shows significant increase in free iron accumulation compared to the STN associated with PD. We observed the opposite to be true in our normal controls. Wypijewska, et al Iron and reactive oxygen species activity in parkinsonian substantia nigra Parkinsonism Relat Disord Jun;16(5): Epub 2010 Mar 9.

TE = 108 TE = 126 TE = 153 TE = 144

TR = 3000 TR = 8000TR = 6000 TR = 5000

BW = BW = BW = BW = 62.50

3D recontruction vs Atlas

Conclusion Optimizing the right parameters can help directly visualize the subthalamic and surrounding nuclei with a 1.5T MRI These parameters work equally well for different individuals in normal individuals Further improvements in treatment of PD patients can be achieved through a combinatorial imaging approach Addition of DT images to delineate the white matter shell around the STN T1 based grey-white matter differentiation Future Direction