Ultra-high field magnetic resonance imaging of the basal ganglia and related structures.

Birgit R Plantinga,Yasin Temel,Alard Roebroeck,Bart M Ter Haar Romenij,Dimo Ivanov,Kã¢Mil Uludaäÿ,Mark L Kuijf

doi:10.3389/fnhum.2014.00876

Abstract

Deep brain stimulation is a treatment for Parkinson's disease and other related disorders, involving the surgical placement of electrodes in the deeply situated basal ganglia or thalamic structures. Good clinical outcome requires accurate targeting. However, due to limited visibility of the target structures on routine clinical MR images, direct targeting of structures can be challenging. Non-clinical MR scanners with ultra-high magnetic field (7T or higher) have the potential to improve the quality of these images. This technology report provides an overview of the current possibilities of visualizing deep brain stimulation targets and their related structures with the aid of ultra-high field MRI. Reviewed studies showed improved resolution, contrast- and signal-to-noise ratios at ultra-high field. Sequences sensitive to magnetic susceptibility such as T2* and susceptibility weighted imaging and their maps in general showed the best visualization of target structures, including a separation between the subthalamic nucleus and the substantia nigra, the lamina pallidi medialis and lamina pallidi incompleta within the globus pallidus and substructures of the thalamus, including the ventral intermediate nucleus (Vim). This shows that the visibility, identification, and even subdivision of the small deep brain stimulation targets benefit from increased field strength. Although ultra-high field MR imaging is associated with increased risk of geometrical distortions, it has been shown that these distortions can be avoided or corrected to the extent where the effects are limited. The availability of ultra-high field MR scanners for humans seems to provide opportunities for a more accurate targeting for deep brain stimulation in patients with Parkinson's disease and related disorders.

Highlights

The basal ganglia are a group of nuclei deep in the brain, which play an important role in specific motor, limbic, and associative processes (Temel et al, 2005)
Several sequences have been investigated for the visualization of basal ganglia structures at clinical field strengths, deep brain stimulation (DBS) structures such as the motor part of the STN, and certain regions within the thalamus, such as the ventrolateral nuclei, need to be displayed more distinctively in order to rely on these images solely for targeting
Accurate visualization of deep-brain structures is important to improve our understanding of their anatomy, connectivity and function, and for improved surgical targeting for DBS in movement and psychiatric disorders

Summary

INTRODUCTION

The basal ganglia are a group of nuclei deep in the brain, which play an important role in specific motor, limbic, and associative processes (Temel et al, 2005). The SNR increases close to linearly with field strength, which offers the option to scan with higher spatial resolution (Vaughan et al, 2001) and/or CNR in a shorter time (Duyn, 2012) This makes ultra-high field MRI especially beneficial for detailed imaging of structures with altered magnetic susceptibility, such as the basal ganglia, myelin, and blood, which is important for ultra-high field high-resolution fMRI imaging. Several sequences have been investigated for the visualization of basal ganglia structures at clinical field strengths, DBS structures such as the motor part of the STN, and certain regions within the thalamus, such as the ventrolateral nuclei, need to be displayed more distinctively in order to rely on these images solely for targeting. Seven pathways could be successfully identified: the nigrostriatal, nigropallidal, nigrothalamic, Line number Study Subject Field strength (T) Sequence 2D or 3D Contrast Orientation Matrix size Nr slices Resolution (mm or mm3) Slice thickness (mm) TR (ms) TE (ms) TI (ms) Flip angle (deg) Receiver bandwidth (Hz/pixel) Partial Fourier along phase and slice encoding direction (%) PIAF b-value (s/mm2) Nr diffusion directions Number of coil receive channels Gradient field strength (mT/m) Time (min:sec)

SPACE – T2w

Findings

DISCUSSION

LIMITATIONS

CONCLUSION