Ultrasound Stimulation

Refelcted ultrasound can be used to form a dynamic image of internal structures, enabling diagnosis without invasion. It is commonly used in assessing the well-being of unborn infants and in diagnosing disorders of the heart. Echoes are analysed and presented using real-time computer analysis.

Thanks Crabtree, but how does work the therapeutic ultrasound which is used for stimulating (e.g. tendons)?

Ultrasound can be controlled with shaped/timed pulses and other tricks (pulse inversion and harmonics generation, for example) to relatively precisely focus mechanical energy to an anatomical area of interest.

If you turn up the power enough, you can cause cavitation, break open microbubbles (for drug delivery or imaging contrast, for example), and certainly, a lot of heat.

This is what therapeutic ultrasound is all about. You essentially beam heat deep into tissues that could otherwise be hard to reach with chemical or external physical treatments.

There are some mild electromechanical effects, but mostly it's the heat caused by the cycling of high/low pressure that does the trick.

Even ultrasound imaging equipment can produce enough heat to be uncomfortable, but that's only when things aren't working correctly and some poor engineer gets in trouble. (oops; been there)

Thanks andyhorning, it was really helpfull. Could you give me a tip on pulse inversion and harmonics generation literature? I appreciate your help.

Ultrasound can be focused to break up kidney stones as well. I don't have any specific references for this, it's not my field except to say that I've seen it work.

I used to have some papers online, but I don't anymore. I'm not sure where to point you since it's an awfully specialized, technical field and I don't know how far you want to get into it.

In essence it's simple, though.

Pulse inversion is a term for sending out-of-phase pulses that you'd expect would cancel each other out. But ultrasound is conducted non-linearly, with compression and rarefaction moving at just enough different speeds as to break off into harmonic frequencies.

When the system is properly designed, the most significant harmonic generation occurs in the focal zone. This is very handy for imaging, since you then have a signal that has a higher signal/noise ratio, fewer sidelobe artifacts, etc.

Therapeutically, it just means that there's a lot of thermo-mechanical stuff going on there.

Well andyhorning, I would like to go as far as I can... I am not a specialist in this subject and I am trying to understand if a therapeutic ultrasound can be designed to acquire images as well when required and, how to calculate the rate of heat production during its use. I appreciate your help.

Leo

I have a tough time imagining ultrasound as mechanical energy in that they use frequencies in the region of 4 MHz which to me are radio frequencies. I will have to ask my wife though. She is the ultrasound technologist in the family.

Bill