Quantitative Susceptibility Mapping of the Centromedian Nucleus and Indirect Comparison with Alternate Sequences.

INTRODUCTION

Neuromodulation of the thalamic centromedian nucleus (CM) is an established therapy for epilepsy and been applied for pain, Tourette syndrome, and disorders of consciousness. Accurate targeting remains challenging because CM is poorly visualized on conventional MRI sequences, necessitating reliance on indirect targeting approaches. Although advanced MRI sequences, such as magnetization-prepared rapid acquisition of two gradient echoes (MP2RAGE) and white matter null (WMn), have been explored, they fail to reliably delineate the boundary between CM and lateral thalamus, a region associated with optimal stimulation outcomes, particularly in epilepsy. Quantitative susceptibility mapping (QSM) has emerged as a promising technique for differentiating thalamic nuclei based on tissue magnetic susceptibility.

OBJECTIVE

The purpose of this study was to evaluate visualization of CM using QSM, assess contrast between CM and adjacent nuclei, and indirectly compare across WMn and MP2RAGE.

METHODS

This retrospective study included patients with solitary cerebral cavernous malformations, not involving the thalamus, who underwent surveillance MRI including QSM (n=24). WMn sequences were obtained from a separate cohort of patients with epilepsy (n=16). MP2RAGE sequences were acquired from healthy individuals (n=24). All sequences were registered to the MNI152 template space and compared with the Morel histological atlas. Normalized intensity differences, contrast-to-noise ratios (CNR), and signal-to-noise ratios (SNR) were calculated for CM and neighboring nuclei.

RESULTS

On QSM, CM was hypointense to medial and posterior thalamus and hyperintense relative to motor thalamus. Median CNR on QSM (P<0.05) relative to CM was highest for medial pulvinar (median 2.9, interquartile range 1.6-4.7) and ventral lateral thalamus (1.6, 0.6-2.3). Highest overall CNR was seen on WMn for PuM (3.4, 3.0-4.0). SNR on QSM was highest for anterior pulvinar (2.4, 1.1-3.6) and highest overall SNR was on on MP2RAGE for PuA (20.8, 17.3-24.3). In an indirect comparison across independent cohorts, QSM showed greater lateral thalamic contrast than WMn and MP2RAGE, but lower overall SNR.

CONCLUSION

QSM allows visualization of CM including the lateral border poorly seen on other sequences, and may be useful as a complementary sequence for direct targeting of CM.