Neuronavigation-guided histotripsy of the brain on cadavers: a feasibility study

Sang Won Choi

Objective: Typical brain surgery involves a neuronavigation guidance system that uses pre-treatment computed tomography (CT) and/or magnetic resonance imaging (MRI) scans to guide neurosurgeons to perform accurate operations. Neuronavigation system uses CT & MRI images to track neurosurgical tools and the patient head in real-time, providing the surgeons with visual feedback during critical operations. However, traditional neurosurgery operation involves drilling through the skull and healthy brain tissues to get to the tissue of interest, making this a highly risky and invasive procedure.

Histotripsy is a non-invasive ultrasound surgical technique. This means histotripsy can precisely eliminate unwanted tissues in the brain (ex: tumors or hemorrhage) without drilling through the skull and healthy brain tissue. To demonstrate that histotripsy can safely treat brain tissues in human patients, we treated fresh cadavers guided by a neuronavigation system and evaluated its targeting accuracy.

Methods: We acquired whole-body cadavers within 96 hours of death, acquired CT and MR images, and treated with a histotripsy transducer. The cadavers and the histotripsy transducer location were co-localized by the neuronavigation system. After post-treatment MRI, the brain was extracted and fixed for gross morphology evaluation and histology. The overview of the workflow is presented in Figure 1

Results: Pre and post-treatment MRI images of one of the cadavers treated are shown (Figure 2). Apparent Diffusion Coefficient (ADC) images best show the histotripsy homogenized region. Diffusion images capture the random Brownian motions of water molecules, and this is perfect for histotripsy because histotripsy renders tissues into liquid homogenates. Treated tissue will move around more freely than untreated solid tissue, and therefore increase diffusion signals in MRI. 

This study is ongoing and therefore the accuracy of the neuronavigation guided transcranial histotripsy setup is not presented here.

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Figure 1. Neuronavigation guided histotripsy workflow. 1) CT and MRI were acquired of the cadaver, 2) uploaded to neuronavigation system (Medtronic, Stealth 7) and coregistered to the cadaver. Then using the locations of the cadaver and histotripsy transducer focus given by the neuronavigation system, 3b) CT-based aberration correction was uploaded to 3a) histotripsy array to regain lost pressure. After treatment, 4) accuracy was evaluated by comparing the post-treatment MRI to pre.

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Figure 2. Apparent Diffusion Coefficient (ADC) images of one of the cadavers. The histotripsy lesion is pointed by red arrows and can be seen on the 2nd row. We non-invasively put a 1cm3 cubic hole in the thalamus.