Predicting ablation zones with multislice volumetric 2-D magnetic resonance thermal imaging

Abstract

Background: High-intensity focused ultrasound (HIFU) serves as a noninvasive stereotactic system for the ablation of brain metastases; however, treatments are limited to simple geometries and energy delivery is limited by the high acoustic attenuation of the calvarium. Minimally-invasive magnetic resonance-guided robotically-assisted (MRgRA) needle-based therapeutic ultrasound (NBTU) using multislice volumetric 2-D magnetic resonance thermal imaging (MRTI) overcomes these limitations and has potential to produce less collateral tissue damage than current methods. Objective: To correlate multislice volumetric 2-D MRTI volumes with histologically confirmed regions of tissue damage in MRgRA NBTU. Methods: Seven swine underwent a total of 8 frontal MRgRA NBTU lesions. MRTI ablation volumes were compared to histologic tissue damage on brain sections stained with 2,3,5-triphenyltetrazolium chloride (TTC). Bland-Altman analyses and correlation trends were used to compare MRTI and TTC ablation volumes. Results: Data from the initial and third swine's ablations were excluded due to sub-optimal tissue staining. For the remaining ablations (n ¼ 6), the limits of agreement between the MRTI and histologic volumes ranged from À0.149 cm 3 to 0.252 cm 3 with a mean difference of 0.052 ± 0.042 cm 3 (11.1%). There was a high correlation between the MRTI and histology volumes (r 2 ¼ 0.831) with a strong linear relationship (r ¼ 0.868). Conclusion:We used a volumetric MRTI technique to accurately track thermal changes during MRgRA NBTU in preparation for human trials. Improved volumetric coverage with MRTI enhanced our delivery of therapy and has far-reaching implications for focused ultrasound in the broader clinical setting.

Intraoperative Ablation Control Based on Real-time Necrosis Monitoring Feedback: Numerical Evaluation

“…For the NF model, the CEM threshold value, CEM th , that divides the ablated and non-ablated status is selected as this is the parameter determining the robustness of the tissue against heat dose. For CEM th , 70 is used as the representing value, P lib as it is utilized in other brain ablation studies [21].…”

State of the Art and Future Opportunities in MRI-Guided Robot-Assisted Surgery and Interventions

“…With regard to design, kinematic redundancy stems from the desire to lock in the instrument's 5-DOF position and orientation and then enable insertion of a cannula, insertion of the instrument, and rotation of the instrument. The full robotic system, as described in detail in [24], was evaluated in a preclinical trial of needle-based therapeutic ultrasound (NBTU) while monitoring thermal dose live with MRTI in seven swines, as described in [25]. The results show strong agreement between MRTI and histology (mean difference in ablation volumes of 0.052 ± 0.042 cm 3 ), further suggesting the ability to effectively use intraoperative MRI to guide ablation volumes using real-time thermal dosimetry from real-time intraoperative MRTI during robotic thermal therapy delivery.…”