Hmmmmmmm,

Interesting speculation on rouleux formation, and the possible
relationship to what appears to be moving blood on the ultrasound image.

>From the dictionary, rouleaux is the plural of rouleau.

Rouleau is a small roll of something, especially a roll of coins,
generally of the same denomination, stacked in a paper wrapper.  Under the
microscope, a blood smear often contains stacks of erythrocytes which look
like a pack of lifesavers candy, with the wrapper missing.  The number of
these is affected by the amount and type of protein in the blood so
patients with abnormal sedimentation rate, newborn babies, smoking
patients, those with IDDM, leukemia and other conditions will have
abnormal numbers of rouleaux.  Sickle Cell disease and AIDS have been
reported to affect then number of rouleaux in opposite directions.  

Two topics dominate the medical literature on rouleau, measurements of
blood viscosity at low shear rates and the scattering of blood by
ultrasound and laser waves.

In the ultrasound literature (Ultrasound in Medicine and Biology V 21 P 
817 and American Heart Journal V 124 p 961) the experiments are often set
up so that the increased scattering can be observed, but the resolutioin
of the system is not sufficient to see the actual individual rouleaux.

Thus, although the idea of "seeing" the blood because of rouleaux is
popular, I will suggest an alternate suggestion.

When examiners used a 45 dB dynamic range for ultrasound imaging, rouleaux
were never reported, now that a dynamic range of 72 dB is common, so are
reports of seeing "smoke" like blood.  This is no surprise, the
echogenicity of blood at 5 MHz is about 55 dB below the brightest echoes
that you might see.  The echogenicity of blood (a rayleigh scatterer)
increases with the frequency to the fourth power, while the echogenicity
of larger structures increases usually by the square for the frequency.

If blood didn't reflect ultrasound (black blood), then no Doppler signals
would be seen.

The speckle pattern that you see in a blood vessel has a spacing about the
same as the speckle pattern in tissue, the pattern in blood is just
dimmer.  This is coherent speckle caused by clusters of erythrocytes.

At normal blood flow velocities of say 30 cm/sec, in 1/30 sec, the
clusters of erythrocytes move 1 cm.  That is the time between images in
"real time" ultrasound imaging.  Thus, each image brings a new speckle
pattern to your eye, unless the blood is stationary.  If the cluster of
erythrocytes sits within the same 2 mm wide sample volume for say .5
seconds, the stable speckle draws your attention and you can see it and
track it.  For this to happen the blood speed must be less than 2 mm/0.5
sec or less than 0.4 mm/sec.  
You can test this theory.  Take a print of "stangant blood with Roleaux"
and another print of "flowing blood without rouleaux"  Is the difference
as great as you noticed with a real time image?  Be sure to keep the gain
settings identical.

Years ago, when Biosound was introducing the Doppler on the 2000, we
witnessed a test in which identical images were made of carotid flow using
the imaging transmitter (12 MHz, 0.1 microsecond burst) vs the Doppler
transmitter (12 MHz, 1.0 microsecond burst).  In the former image, the
blood flow could hrdley be seen, in the latter image, the blood flow
looked like crawling worms.  I think that this difference occurred because
of a difference in coherence of the transmitted ultrasound, and the
associated difference in the size of the Doppler sample volume.

I think that the rouleux hypothesis has been repeated, and taken on a life
of its own, but it has not been proved.

Kirk


On 12 Nov 1996, CARRIE NICKESON wrote:

> WHAT IS ROULEUX FORMATION (? SPLELLING).  WHAT DOES IT MEAN WHEN ITS SEEN ON A
> VENOUS SCAN.
> 
> 
> 
> 
>       CARRIE NICKESON             
> 
>  
>