Will,

Micron range bubbles would be pretty tough, because the red blood cells are
6-8 Microns.  Any bubbles smaller than that would be lost in the noise
generated by the blood cells themselves.  (see http://www.wadsworth.org/
chemheme/heme/microscope/rbc.htm)  As a side note, I've imaged myself in 
the lab many times, and noticed that after several drinks, the blood 
cells tend to clump together and you can actually see the clumps come 
through on the machine.  Kind of disconcerting, and convinces you to drink
lots of water after a party ;-)

The resolution limit for ultrasound depends on the wavelength of the
ultrasound wave.  This is determined by its frequency, and the speed of
sound propagation in tissue (~1540 m/s for soft tissue).

For example, a 10Mhz probe would transmit a wavelength of 154 microns
making it difficult to image anything smaller due to diffraction effects.
(Tells you something about the size of those blood clumps I was seeing
doesn't it?)  You can go to higher frequency probes, but the problem is
that the attenuation goes up with the frequency, and pretty soon your
not seeing anything but the air/skin boundary.

The good news is that 154 microns is pretty small.  It's ~.006 inches which
is about the thickness of a piece of paper (well 1.5 pieces of paper).

Anyway, back to your question of how hard it would be to automatically
capture bubble counts from imaging.  I don't know how to do it, but that
doesn't mean that someone else doesn't.  I think you could set up an
_audio_ counter on a laptop with a sound card pretty easily to keep
from having to count the bubbles manually.

Later,

Don W.


William M. Smithers wrote:
> 
> On Tue, 17 Aug 1999, Don W. wrote:
> > Oh yeah, and I spent ~two years designing ultrasound
> > machines for
> > Siemens so I know a little about doppler echocardiography and bubble
> > studies.
> 
> Hi, Don!  Welcome.  Being an EE with various twisted experience myself,
> I've got a question for you.  I've been audio-dopplering myself for a
> couple of years with a 3Mhz obstetric probe.  That's kindof a scary
> thing, as I've come to realize - virtually *all* of the deco
> data (research papers) have used the same device, and
> base their studies on audio bubble-counts.  I figure that's probably
> due to the grad-student agreeable price of an audio unit.
> 
> How hard would it be to construct a device that *precisely* captures
> bubble-counts?  Hell, I figure if they can get pre-natal visual
> imaging down, including user software that measures various
> bone lengths and predicts fetal age, then a system to catch passing
> aeortic bubble counts couldn't be all that tough.  And more importantly,
> what's the resolution of the technology?  I'd really like to detect
> micron range bubbles.
> 
> Regards,
> 
> -Will
--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]