Non-invasive write · writes
High-intensity focused ultrasound (HIFU) ablation is non-invasive neurosurgery: a transducer array sends ultrasound through the skull and concentrates it on a small target inside the brain. What it writes is heat: the focus warms until the tissue coagulates, which destroys it permanently. What it reads is tissue temperature by MR thermometry, used to watch the target heat and the lesion form; this is a measure of temperature, not of brain activity. The skull's uneven acoustics distort the focusing.
High-intensity focused ultrasound (HIFU) ablation is a non-invasive neurosurgical procedure that destroys a targeted volume of brain tissue by heat. A hemispherical transducer array with hundreds to more than a thousand elements, each driven with its own phase and amplitude, sends ultrasound through the skull and concentrates it on a focus inside the brain; spreading the energy over the skull surface reduces local heating of scalp and bone. Absorbed acoustic energy heats the focus until the tissue coagulates, which destroys it permanently. In the MR-guided form (MRgFUS), real-time MRI identifies the target and MR thermometry records tissue temperature and lesion formation; the measured quantity is temperature, not neural activity. In one treatment practice, sonications aim for a maximum of about 60 °C at the hotspot centre, and a thermal dose of 240 cumulative equivalent minutes at 43 °C (CEM43) marks tissue assumed to be ablated, with 17 CEM43 giving an estimated 50% probability of necrosis. In one reported thalamotomy, acoustic energy was raised gradually under MR thermometry, with clinical safety and tremor evaluation after each sonication and target repositioning, before the ablative sonication. The skull's heterogeneous acoustics distort the energy deposition, shift the focus and lower the thermal gain. Low-intensity ultrasound is a different technique: it can modulate neurons without destroying tissue.
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