1. There is a wavelength and penetration depth trade off. For better accuracy you need smaller wavelengths (i.e. higher frequencies) but at higher frequencies ultrasound pressure gets absorbed at a higher rate, making it challenging to get the required pressure levels deeper into tissue.
2. Ultrasound focus can deflect as it travels in tissue (tissue is a non-linear material and multiple tissue types impacts wave propagation). The deeper you try to focus, the more likely that there is a deflection; thus your focus point won’t be exactly where you were planning.
We are more than a decade away from knowing if Histosonics technology will actually be a meaningful treatment modality. It definitely is 'cool' in that there is no incision. However, whenever you deliver ultrasound energy from outside of the body, accuracy goes down; you are also limited by anatomy in the path of the ultrasound (e.g. going through the rib cage with ultrasound is not trivial). Folks I have spoken to who have bought these units say they are only allowed to use them if the tumor is superficial (i.e. near the skin). On top of that patient motion due to breathing definitely causes inaccuracies and complications. One doctor said it's an expensive paperweight (but it does bring patients in who ask for it).
Also, the clinical efficacy is not fully understood. Researchers are most excited by an enhanced abscopal effect (i.e. natural immune response), but that's not a proven phenomenon. Finally, it is really expensive (~$1.5M) so it will be difficult to scale outside of research hospitals and cancer centers. Of course, I don't want to be too negative. It's a win for patients when they have more options.
Full disclosure: I am co-founder of Current Surgical, where we are developing a minimally invasive system based on miniaturized focused ultrasound to achieve precise thermal ablation (not cavitation). Our device can both see and destroy tissue from the same sensors, we can achieve millimeter accuracy. And because the technology can be integrated into any number of surgical tools (needle, catheter, etc) we can potentially reach any anatomy.
1. There is a wavelength and penetration depth trade off. For better accuracy you need smaller wavelengths (i.e. higher frequencies) but at higher frequencies ultrasound pressure gets absorbed at a higher rate, making it challenging to get the required pressure levels deeper into tissue.
2. Ultrasound focus can deflect as it travels in tissue (tissue is a non-linear material and multiple tissue types impacts wave propagation). The deeper you try to focus, the more likely that there is a deflection; thus your focus point won’t be exactly where you were planning.