Ablation dynamics during laser interstitial thermal therapy for mesiotemporal epilepsy

<div><p>Introduction</p><p>The recent emergence of laser interstitial thermal therapy (LITT) as a frontline surgical tool in the management of brain tumors and epilepsy is a result of advances in MRI thermal imaging. A limitation to further improving LITT is the diversity of brain tissue thermoablative properties, which hinders our ability to predict LITT treatment-related effects. Utilizing the mesiotemporal lobe as a consistent anatomic model system, the goal of this study was to use intraoperative thermal damage estimate (TDE) maps to study short- and long-term effects of LITT and to identify preoperative variables that could be helpful in predicting tissue responses to thermal energy.</p><p>Methods</p><p>For 30 patients with mesiotemporal epilepsy treated with LITT at a single institution, intraoperative TDE maps and pre-, intra- and post-operative MRIs were co-registered in a common reference space using a deformable atlas. The spatial overlap of TDE maps with manually-traced immediate (post-ablation) and delayed (6-month) ablation zones was measured using the dice similarity coefficient (DSC). Then, motivated by simple heat-transfer models, ablation dynamics were quantified at amygdala and hippocampal head from TDE pixel time series fit by first order linear dynamics, permitting analysis of the thermal time constant (<i>τ</i>). The relationships of these measures to 16 independent variables derived from patient demographics, mesiotemporal anatomy, preoperative imaging characteristics and the surgical procedure were examined.</p><p>Results</p><p>TDE maps closely overlapped immediate ablation borders but were significantly larger than the ablation cavities seen on delayed imaging, particularly at the amygdala and hippocampal head. The TDEs more accurately predicted delayed LITT effects in patients with smaller perihippocampal CSF spaces. Analyses of ablation dynamics from intraoperative TDE videos showed variable patterns of lesion progression after laser activation. Ablations tended to be slower for targets with increased preoperative T2 MRI signal and in close proximity to large, surrounding CSF spaces. In addition, greater laser energy was required to ablate mesial versus lateral mesiotemporal structures, an effect associated with laser trajectory and target contrast-enhanced T1 MRI signal.</p><p>Conclusions</p><p>Patient-specific variations in mesiotemporal anatomy and pathology may influence the thermal coagulation of these tissues. We speculate that by incorporating demographic and imaging data into predictive models we may eventually enhance the accuracy and precision with which LITT is delivered, improving outcomes and accelerating adoption of this novel tool.</p></div

Dynamics of irreversible ablation during mesiotemporal LITT.

<p>(A) Different frames of a sample axial TDE video. The larger image on the right shows a lower magnification view, with the white dashed box highlighting the region used in the left panels. Trajectories were traced from the first frame in each video and the appearance of yellow pixels indicating irreversible ablation was quantified relative to the laser using Matlab Image Processing Toolbox. The blue (lateral) and yellow (mesial) rectangles demonstrate regions of interest used to measure pixel counts on each side of the laser. (B) Time course of total (black), lateral (blue), mesial (yellow), and lateral—mesial (red) pixel counts from the same patient as in G. A, anterior; L, lateral.</p

Preoperative volumetric analyses.

<p>(A) T1 MP-RAGE coronal cut through the hippocampal body for a representative patient. (B) Same image showing manually-traced borders of CSF_Above (light blue) and CSF_Lateral (dark blue) and automatically segmented hippocampal borders (green). (C) 3D model for the same patient showing relationship of CSF structures to amygdala (orange) and hippocampus (green). The red arrow shows the imaging cut used for A & B. (D-F) Same conventions as in A—C for a patient with larger CSF spaces. The white asterisks in E shows the vertical digitation of the hippocampus at its posterior end, which was used as a consistent anatomic landmark for laser position calculations. Scale bar– 5 mm. AC, anterior commissure; MP, midline point; PC, posterior commissure.</p

Overlap of TDE maps with immediate and delayed ablation zone boundaries.

<p>(A-B) Axial and sagittal TDE maps at the end of the LITT procedure for sample Patient 1. The white dashed boxes show the regions highlighted in the panels below. (C-D) Axial and sagittal post ablation contrasted T1 images showing the manually-traced immediate ablation zone (blue) and the boundary of the TDE (yellow) from the same imaging plane. The numbers below the image panels show the DSC values. (E-F) Axial and sagittal T1 MP-RAGE images 6-months after surgery demonstrating the manually-traced delayed ablations (red) and the TDE (yellow). (G-L) Same conventions as A—F but for Patient 2. A, anterior; Del, delayed; Imm, immediate; L, lateral; S, superior; TDE, thermal damage estimate.</p

Relationship of ablation dynamics measures to the independent variables.

<p>Relationship of ablation dynamics measures to the independent variables.</p

Regression coefficients for independent variables with the thermal time constant.

<p>Regression coefficients for independent variables with the thermal time constant.</p

Evaluation of ablation asymmetry.

<p>Evaluation of ablation asymmetry.</p

Proceedings of the Sixth Deep Brain Stimulation Think Tank Modulation of Brain Networks and Application of Advanced Neuroimaging, Neurophysiology, and Optogenetics

© Copyright © 2019 Ramirez-Zamora, Giordano, Boyden, Gradinaru, Gunduz, Starr, Sheth, McIntyre, Fox, Vitek, Vedam-Mai, Akbar, Almeida, Bronte-Stewart, Mayberg, Pouratian, Gittis, Singer, Creed, Lazaro-Munoz, Richardson, Rossi, Cendejas-Zaragoza, D’Haese, Chiong, Gilron, Chizeck, Ko, Baker, Wagenaar, Harel, Deeb, Foote and Okun. The annual deep brain stimulation (DBS) Think Tank aims to create an opportunity for a multidisciplinary discussion in the field of neuromodulation to examine developments, opportunities and challenges in the field. The proceedings of the Sixth Annual Think Tank recapitulate progress in applications of neurotechnology, neurophysiology, and emerging techniques for the treatment of a range of psychiatric and neurological conditions including Parkinson’s disease, essential tremor, Tourette syndrome, epilepsy, cognitive disorders, and addiction. Each section of this overview provides insight about the understanding of neuromodulation for specific disease and discusses current challenges and future directions. This year’s report addresses key issues in implementing advanced neurophysiological techniques, evolving use of novel modulation techniques to deliver DBS, ans improved neuroimaging techniques. The proceedings also offer insights into the new era of brain network neuromodulation and connectomic DBS to define and target dysfunctional brain networks. The proceedings also focused on innovations in applications and understanding of adaptive DBS (closed-loop systems), the use and applications of optogenetics in the field of neurostimulation and the need to develop databases for DBS indications. Finally, updates on neuroethical, legal, social, and policy issues relevant to DBS research are discussed