Prognostic value of brain tissues’ volumes in patients with essential tremor treated with MRgFUS thalamotomy

MRgFUS Vim thalamotomy is a novel, effective, minimally invasive therapeutic option for patients with essential tremor (ET). Among the selection criteria, some parameters related to the patient's anatomy, such as the skull density ratio (SDR), are well recognized. The role of brain tissue interposed between the target and the ultrasound transducers has never been explored. Therefore, the purpose of our study was to evaluate the correlation and the possible predictive value between brain tissue volumes (grey matter - GM, white matter - WM, and cerebrospinal fluid - CSF) and several treatment-related variables (periprocedural parameters, MRI imaging findings, and the clinical outcome). We analysed data from thirty ET patients previously submitted to MRgFUS thalamotomy. Pre-treatment images were automatically segmented in sopra-tentorial (ST) WM, GM, and CSF using SPM 12. The most significant findings were a positive correlation of the ST-GM with the Accumulated Thermal Dose (ATD) (p 0,001) and a negative correlation of the ATD temperature with ST-CSF and ST-TIV (p 0,001). Ultrasound propagation speed is lower in fluids than brain tissues. Also, WM has an attenuation rate of 1.5 higher than the GM. Therefore, the difference in the ATD may be explained by the different acoustic properties of normal brain tissues interposed between the transducers and the VIM.