The two main indications for MRgFUS thermoablation are essential tremor and Parkinson disease. Unilateral ablation of the thalamus in essential tremor and of various brain targets in Parkinson disease has been shown to be efficacious and safe, and to lead to improvements in motor signs, condition-related disability and quality of life4,5,6. In addition, small case series suggest that MRgFUS ablation could be beneficial in people with secondary tremors, focal dystonia or drug-refractory psychiatric conditions7.

However, despite the positive data, several concerns remain in the medical community. The primary concern is that MRgFUS ablation carries the risk of producing irreversible neurological complications. Admittedly, the approach cannot be regarded as a non-invasive therapy. However, the use of real-time MRI thermography and clinical assessment during the gradual production of lesions allows early detection of adverse effects, which enables intraprocedural target correction. Consequently, most adverse events are mild and/or transient, and disabling complications are infrequent8. Another common concern is whether ablation yields long-term benefits. The evidence suggests that an initially effective lesion provides benefit for at least 5 years, even in neurodegenerative conditions such as Parkinson disease7. This finding is consistent with the experience from radiofrequency ablation. The safety of bilateral treatment has also been debated, given past experience with surgical ablation. However, several open-label series, particularly in essential tremor, suggest that the lower invasiveness of MRgFUS would enable bilateral staged approaches in selected patients. Overall, the initial concerns about MRgFUS, although legitimate, are not supported by the evidence.

In its low-intensity modality, focused ultrasound energy delivery combined with an intravenous contrast agent (microbubbles) induces focal and transient blood–brain barrier opening. This approach has been shown to be safe in conditions such as brain gliomas, Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease. The ultimate objective is to introduce chemotherapeutics or drugs that are capable of halting neurodegeneration into the brain. Although this approach is still experimental, enhanced target engagement has been observed in patients with brain metastasis or Alzheimer disease9,10. Other applications such as neuromodulation, histotripsy or sonobiopsy are still in development, but show potential1.