Lesion 3D modeling in transcranial MR-guided focused ultrasound thalamotomy

Transcranial magnetic resonance-guided focused ultrasound (tMRgFUS) allows to perform incisionless thermoablation of deep brain structures. This feature makes it a very useful tool for the treatment of multiple neurological and psychiatric disorders. Currently, feedback of the thermoablation process is based on peak temperature readings assessed on real-time two-dimensional MRI thermometry. However, an accurate methodology relating thermal dosimetry with three-dimensional topography and temporal evolution of the lesion is still to be defined, thus hurdling the establishment of well-defined, evidence-based criteria to perform safe and effective treatments. In here we propose threshold-based thermoablation models to predict the volumetric topography of the lesion (whole lesion and necrotic core) in the short-to-mid-term based on thermal dosimetry estimated from intra-treatment MRI thermometry. To define and validate our models we retrospectively analyzed the data of sixty-three tMRgFUS thalamotomies for treating tremor. We used intra-treatment MRI thermometry to estimate whole-treatment three-dimensional thermal dose maps, defined either as peak temperature reached (T_max) or thermal isoeffective dose (TID). Those maps were thresholded to find the dosimetric level that maximize the agreement (Sorensen-Dice coefficient - SDc) with the boundaries of the whole lesion and its core, assessed on T2w images 1-day (post-24h) and 3-months (post-3M) after treatment. Best predictions were achieved for the whole lesion at post-24h (SDc = 0.71), with T_max /TID over 50.0 °C/90.5 CEM43. The core at post-24h and whole lesion at post-3M lesions reported a similar behavior in terms of shape accuracy (SDc ~0.35), and thermal dose thresholds ~55 °C/4100.0 CEM43. Finally, the optimal levels for post-3M core lesions were 55.5 °C/5800.0 CEM43 (SDc = 0.21). These thermoablation models could contribute to the real-time decision-making process and improve the outcome of tMRgFUS interventions both in terms of safety and efficacy.