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Dear Larry,

Nice to hear from you.

Although diagnostic ultrasound is "safe", diagnostic ultrasound does exert 
a force on tissue that is proportional to the ultrasound power, and the 
attenuation of the tissue.  In pulsed-Doppler TCD, the transmit burst is 
often 10 microseconds long (compared to 0.2 microseconds for B-mode) with 
a pulse-repetition frequency of 2.5 KHz (a pulse every 400 microseconds. 
So, the effect is like knocking on the clot every 400 microseconds.  This 
probably squeezes the clot like a sponge, 2,500 times per second.  Of 
course, if bubbles are present, the effect is larger, both because the 
bubbles are compliant and because the bubbles are reflectors, so the 
radiation force is greater.
This "sponge" effect causes mechanic fatigue on the clot as well as 
provide the "sponge" effect of enhancing the flow of thrombolytic agents 
into the clot by convection, which is faster than diffusion if the clot is 
static.

As an expert in obstetrics, you know that a fetus will "hear" an 
ultrasound examination, not because the fetal ear can hear 3 MHz 
ultrasound (they don't "hear" CW Doppler fetal monitors) but because the 
radiation force of the pulsed ultrasound bursts, at a 5 KHz PRF for 
Doppler or at a 30 Hz frame rate for 2-D B-mode imaging, knocks on the 
oval window of the coclea (and probably even on the hair cells in the 
coclea) to allow the fetus the "hear" the ultrasound PRF, which is within 
their hearing range.

With High Intensity Focussed Ultrasound (HIFU) therapy, at 2,000 Watts 
per square centimeter, the radiation pressure can be larger than the blood 
pressure, and can really push things around.

Kirk

On Wed, 29 Mar 2006, Larry Waldroup wrote:

> Hi Flownetters,
> Would like to get your opinion on the rather startling claims by Dr. Paul Syme of Edinburgh concerning use of TCD as therapy for small vessel stroke.  The videos that he provides seem convincing to me, but then I am not a vascular expert -- so would like to get feedback on this one.  Real -- or not?  Has anyone else seen miracle cures following TCD?  Is this old hat and I'm just out of touch, or is it really as new and exciting as I think it is?  Your comments would be much appreciated.  Links are in the lead story on the SonoWorld home page at http://www.sonoworld.com
> Best regards
> larry
>
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