Medicine:Transcranial focused ultrasound

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Transcranial focused ultrasound
Other namestFUS; Transcranial focused ultrasound stimulation
SpecialtyPsychiatry, neurology

Transcranial focused ultrasound (tFUS), also known as transcranial ultrasound stimulation (TUS) or low-intensity focused ultrasound (LIFU), is a form of focused ultrasound (FUS) which is being investigated for the potential non-invasive treatment of psychiatric and neurological disorders.[1][2][3] It has also been used as a tool to investigate causal effects of tFUS targeting subcortical brain structures in humans.[4] It differs from other non-invasive brain stimulation methods such as magnetic (transcranial magnetic stimulation or TMS) and electrical (transcranial direct-current stimulation or tDCS) in that it has higher spatial resolution and precision (millimetric) and is able to reach deep brain structures.[1][3] Depending on the parameters, tFUS can inhibit, stimulate, and even ablate brain tissue.[1] Only a handful of clinical studies of tFUS for psychiatric conditions have been conducted as of 2024.[3]

Safety

The International consortium for Transcranial Ultrasound Stimulation Safety and Standards (ITRUSST) was formed in 2021[5], with the purpose of working towards the safe, effective and replicable application of transcranial ultrasonic stimulation for non-invasive neuromodulation in humans.[6] In 2025, ITRUSST published a consensus on biophysical safety with a number of safety considerations for thermal and mechanical risks during tFUS.[7] Based on the currently available regulations for other biomedical ultrasound devices, such as diagnostic ultrasound, the consensus proposes exposure levels under which the thermal and mechanical risks of TUS are considered nonsignificant. In order to estimate these exposure levels, software packages for numerical simulations of acoustic fields are often used.[8]

As a Neuromodulation Tool

At lower acoustic intensities, generally below the FDA's 510(k) limit for diagnostic ultrasound of a Mechanical Index (MI) less than 1.9,[9] tFUS can provide a neuromodulatory effect without causing permanent tissue damage. While the exact nature of tFUS neuromodulation is not completely understood, at least three mechanisms probably act in consort to produce the effects, all of which implicate the neuronal membrane.[10]

  1. Acoustic cavitation, the formation and subsequent implosion of bubbles in the membrane, may transiently disrupt its insulation or capacitance.[11] However, since ultrasound neuromodulation has been described at intensities below those thought to cause cavitation, it is also possible that simple mechanical deformation of the membrane, mediated by the acoustic radiation force, causes the same effects.[12]
  2. Fluctuations in neural activity have been correlated to local temperature differences of less than 0.1C in the brain,[13] providing a plausible mechanism in heating induced by the absorption of ultrasound energy interacting with tissue. Temperature increases may also increase mobility of lipid rafts and enzymes in the neuronal membrane.
  3. Mechanosensitive ion channels in the neuronal membrane may react to the ordered mechanical deformation of ultrasound waves. Piezo1 has been shown to react to ultrasound stimulation in vitro.[14]

Applications of tFUS neuromodulation in clinical practice may include treatment of essential tremor,[15] treatment-resistant major depressive disorder (MDD),[16] post-stroke chronic pain,[17] epilepsy,[18] obsessive-compulsive disorder (OCD),[19] and anxiety.[20]

References

  1. ↑ 1.0 1.1 1.2 "Transcranial Focused Ultrasound (tFUS) and Transcranial Unfocused Ultrasound (tUS) Neuromodulation: From Theoretical Principles to Stimulation Practices". Front Neurol 10. 2019. doi:10.3389/fneur.2019.00549. PMID 31244747. 
  2. ↑ "Clinical Intervention Using Focused Ultrasound (FUS) Stimulation of the Brain in Diverse Neurological Disorders". Front Neurol 13. 2022. doi:10.3389/fneur.2022.880814. PMID 35614924. 
  3. ↑ 3.0 3.1 3.2 "Transcranial Focused Ultrasound Neuromodulation in Psychiatry: Main Characteristics, Current Evidence, and Future Directions". Brain Sci 14 (11): 1095. October 2024. doi:10.3390/brainsci14111095. PMID 39595858. 
  4. ↑ Yaakub, Siti N.; Eraifej, John; Bault, Nadège; Lojkiewiez, Mathilde; Bellec, Elouan; Roberts, Jamie; Philip, Noah S.; Divanbeighi Zand, Amir Puyan et al. (2025-11-27). "Non-invasive ultrasonic neuromodulation of the human nucleus accumbens impacts reward sensitivity" (in en). Nature Communications 16 (1): 10192. doi:10.1038/s41467-025-65080-9. ISSN 2041-1723. PMC 12660320. https://www.nature.com/articles/s41467-025-65080-9. 
  5. ↑ "ITRUSST Group Launched for Transcranial Focused Ultrasound Safety and Standards" (in en). https://brainbox-neuro.com/news/2021/itrusst-group-launched-for-transcranial-focused-ultrasound-safety-and-standards. 
  6. ↑ "About Us - ITRUSST - International Transcranial Ultrasonic Stimulation Safety and Standards" (in en). https://www.itrusst.com/about-us. 
  7. ↑ Aubry, Jean-François; Attali, David; Schafer, Mark E.; Fouragnan, Elsa; Caskey, Charles F.; Chen, Robert; Darmani, Ghazaleh; Bubrick, Ellen J. et al. (2025-11-01). "ITRUSST consensus on biophysical safety for transcranial ultrasound stimulation". Brain Stimulation 18 (6): 1896–1905. doi:10.1016/j.brs.2025.10.007. ISSN 1935-861X. PMC 12644226. https://www.sciencedirect.com/science/article/pii/S1935861X25003535. 
  8. ↑ Murphy, Keith R.; Nandi, Tulika; Kop, Benjamin; Osada, Takahiro; Lueckel, Maximilian; N’Djin, W. Apoutou; Caulfield, Kevin A.; Fomenko, Anton et al. (2025-03-01). "A practical guide to transcranial ultrasonic stimulation from the IFCN-endorsed ITRUSST consortium". Clinical Neurophysiology 171: 192–226. doi:10.1016/j.clinph.2025.01.004. ISSN 1388-2457. https://www.sciencedirect.com/science/article/pii/S1388245725000148. 
  9. ↑ "Marketing Clearance of Diagnostic Ultrasound Systems and Transducers Guidance for Industry and Food and Drug Administration Staff". https://www.fda.gov/media/71100/download. 
  10. ↑ Darmani, G.; Bergmann, T. O.; Butts Pauly, K.; Caskey, C. F.; de Lecea, L.; Fomenko, A.; Fouragnan, E.; Legon, W. et al. (2022-03-01). "Non-invasive transcranial ultrasound stimulation for neuromodulation". Clinical Neurophysiology 135: 51–73. doi:10.1016/j.clinph.2021.12.010. ISSN 1388-2457. PMID 35033772. https://www.sciencedirect.com/science/article/pii/S1388245721008920. 
  11. ↑ Plaksin, Michael; Kimmel, Eitan; Shoham, Shy (May 2016). "Cell-Type-Selective Effects of Intramembrane Cavitation as a Unifying Theoretical Framework for Ultrasonic Neuromodulation" (in en). eNeuro 3 (3): ENEURO.0136–15.2016. doi:10.1523/ENEURO.0136-15.2016. ISSN 2373-2822. PMID 27390775. 
  12. ↑ Menz, Mike D.; Ye, Patrick; Firouzi, Kamyar; Nikoozadeh, Amin; Pauly, Kim Butts; Khuri-Yakub, Pierre; Baccus, Stephen A. (2019-08-07). "Radiation Force as a Physical Mechanism for Ultrasonic Neurostimulation of the Ex Vivo Retina" (in en). Journal of Neuroscience 39 (32): 6251–6264. doi:10.1523/JNEUROSCI.2394-18.2019. ISSN 0270-6474. PMID 31196935. PMC 6687898. https://www.jneurosci.org/content/39/32/6251. 
  13. ↑ Owen, Scott F.; Liu, Max H.; Kreitzer, Anatol C. (July 2019). "Thermal constraints on in vivo optogenetic manipulations" (in en). Nature Neuroscience 22 (7): 1061–1065. doi:10.1038/s41593-019-0422-3. ISSN 1546-1726. PMID 31209378. 
  14. ↑ Prieto, Martin Loynaz; Firouzi, Kamyar; Khuri-Yakub, Butrus T.; Maduke, Merritt (June 2018). "Activation of Piezo1 but Not NaV1.2 Channels by Ultrasound at 43 MHz" (in en). Ultrasound in Medicine & Biology 44 (6): 1217–1232. doi:10.1016/j.ultrasmedbio.2017.12.020. PMID 29525457. 
  15. ↑ Deveney, Chloe; Surya, Jean-Rama; Haroon, Jonathan M.; Mahdavi, Kennedy D.; Hoffman, Katelyn R.; Enemuo, Kevin C.; Jordan, Kaya G.; Becerra, Sergio A. et al. (2025-01-01). "Update on Ongoing Open Label Trial of Focused Ultrasound for Essential Tremor" (in English). Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation 18 (1): 446–447. doi:10.1016/j.brs.2024.12.683. ISSN 1935-861X. https://www.brainstimjrnl.com/article/S1935-861X(24)00878-7/fulltext. 
  16. ↑ Oh, Jooyoung; Ryu, Jin Sun; Kim, Junhyung; Kim, Soojeong; Jeong, Hyu Seok; Kim, Kyung Ran; Kim, Hyun-Chul; Yoo, Seung-Schik et al. (August 2024). "Effect of Low-Intensity Transcranial Focused Ultrasound Stimulation in Patients With Major Depressive Disorder: A Randomized, Double-Blind, Sham-Controlled Clinical Trial". Psychiatry Investigation 21 (8): 885–896. doi:10.30773/pi.2024.0016. ISSN 1738-3684. PMID 39111747. 
  17. ↑ He, Sijin; Luo, Kaixuan; Li, Xiang; Duan, Jiajia; Ding, Lei; Chen, Moxian; Xu, Xuan; Sun, Xianghua et al. (2025). "A clinical case report on transcranial low-intensity focused ultrasound neuromodulation for central post-stroke pain". Frontiers in Neuroscience 19. doi:10.3389/fnins.2025.1686623. ISSN 1662-4548. PMID 41278189. 
  18. ↑ Bubrick, Ellen J.; McDannold, Nathan J.; Orozco, Janet; Mariano, Timothy Y.; Rigolo, Laura; Golby, Alexandra J.; Tie, Yanmei; White, P. Jason (2024-01-01). "Transcranial ultrasound neuromodulation for epilepsy: A pilot safety trial" (in English). Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation 17 (1): 7–9. doi:10.1016/j.brs.2023.11.013. ISSN 1935-861X. PMID 38070706. https://www.brainstimjrnl.com/article/S1935-861X(23)01956-3/fulltext. 
  19. ↑ Germann, Jürgen; Elias, Gavin J B; Neudorfer, Clemens; Boutet, Alexandre; Chow, Clement T; Wong, Emily H Y; Parmar, Roohie; Gouveia, Flavia Venetucci et al. (2021-12-16). "Potential optimization of focused ultrasound capsulotomy for obsessive compulsive disorder" (in en). Brain 144 (11): 3529–3540. doi:10.1093/brain/awab232. ISSN 0006-8950. PMID 34145884. https://academic.oup.com/brain/article/144/11/3529/6305828. 
  20. ↑ Chou, Tina; Deckersbach, Thilo; Guerin, Bastien; Wong, Karianne Sretavan; Borron, Benjamin M.; Kanabar, Anish; Hayden, Ashley N.; Long, Marina P. et al. (2024-03-01). "Transcranial focused ultrasound of the amygdala modulates fear network activation and connectivity" (in English). Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation 17 (2): 312–320. doi:10.1016/j.brs.2024.03.004. ISSN 1935-861X. PMID 38447773. https://www.brainstimjrnl.com/article/S1935-861X(24)00040-8/fulltext. 



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