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

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 = 6), the limits of agreement between the MRTI and histologic volumes ranged from -0.149 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) = 0.831) with a strong linear relationship (r = 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.

Automated summary

In this study, it was demonstrated through experiments on pigs that using multislice volumetric 2-D magnetic resonance thermal imaging can accurately track thermal changes during MRgRA NBTU, preparing for human trials and improving therapy delivery. The enhanced volumetric coverage with MRTI has significant implications for focused ultrasound in clinical settings.