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Would transcranial ultrasound have the problem of unwanted hotspots because of reflections and a focusing effect of the curvature of the skull? I would assume t

Would transcranial ultrasound have the problem of unwanted hotspots because of reflections and a focusing effect of the curvature of the skull? I would assume that this could only be done by scanning the head with a MRI, modelling the tissues in detail, simulating the process and then constructing a wave front from many emitters that does what one wants. Ideally all of that in real time as I guess the heating process will change the properties of the treated tissue in a way that would require it.

HorizonXP 7y ago
Precisely. See Ultrasound attenuation coefficient (https://en.wikipedia.org/wiki/Attenuation#Attenuation_coefficient https://en.wikipedia.org/wiki/Attenuation#Attenuation_coeffi...) You'll note that it's measured in dB/(MHz-cm), and that soft tissue is 0.5, while bone is 6.9. Just like light, anytime ultrasound hits an interface, there are reflections and refractions. Furthermore, since bone attenuates ultrasound so much, you have to increase your amplitude greatly (and even more so with higher frequencies) in order to get enough thermal energy to be deposited at your target. If you don't do it right, you can create dangerous hotspots at the bone-tissue interface, and you can also deposit energy where you didn't intend to. Given that ultrasound therapy intends to be more precise than other techniques, you're kind of defeating the purpose! Edit: in response to your edit, yes that's exactly what they do. They create an array of transmitters to be able to precisely target various locations within the skull. It wasn't my area of research, but I'm pretty sure they used them to create interference patterns as well, so many emitters were activated to work in concert to target one area. See this image: https://sunnybrook.ca/uploads/1/_research/about/fus/3-ultrasoundbraindevice.jpg https://sunnybrook.ca/uploads/1/_research/about/fus/3-ultras...
beering 7y ago
Here's an application of ultrasound towards essential tremors that is already being used on people! https://www.usnews.com/news/health-news/articles/2019-11-20/ultrasound-may-ease-common-form-of-hand-tremor https://www.usnews.com/news/health-news/articles/2019-11-20/... Transcranial ultrasound + monitoring via MRI. Requires a rock-solid transmitter clamped on the skull.

HorizonXP 7y ago

Precisely. See Ultrasound attenuation coefficient (https://en.wikipedia.org/wiki/Attenuation#Attenuation_coefficient https://en.wikipedia.org/wiki/Attenuation#Attenuation_coeffi...) You'll note that it's measured in dB/(MHz-cm), and that soft tissue is 0.5, while bone is 6.9. Just like light, anytime ultrasound hits an interface, there are reflections and refractions. Furthermore, since bone attenuates ultrasound so much, you have to increase your amplitude greatly (and even more so with higher frequencies) in order to get enough thermal energy to be deposited at your target. If you don't do it right, you can create dangerous hotspots at the bone-tissue interface, and you can also deposit energy where you didn't intend to. Given that ultrasound therapy intends to be more precise than other techniques, you're kind of defeating the purpose! Edit: in response to your edit, yes that's exactly what they do. They create an array of transmitters to be able to precisely target various locations within the skull. It wasn't my area of research, but I'm pretty sure they used them to create interference patterns as well, so many emitters were activated to work in concert to target one area. See this image: https://sunnybrook.ca/uploads/1/_research/about/fus/3-ultrasoundbraindevice.jpg https://sunnybrook.ca/uploads/1/_research/about/fus/3-ultras...

beering 7y ago

Here's an application of ultrasound towards essential tremors that is already being used on people! https://www.usnews.com/news/health-news/articles/2019-11-20/ultrasound-may-ease-common-form-of-hand-tremor https://www.usnews.com/news/health-news/articles/2019-11-20/... Transcranial ultrasound + monitoring via MRI. Requires a rock-solid transmitter clamped on the skull.