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UVMFLOWNET  February 2014

UVMFLOWNET February 2014

Subject:

Re: Terminology - rouleaux

From:

Registered Vascular Solutions <[log in to unmask]>

Reply-To:

UVM Flownet <[log in to unmask]>

Date:

Thu, 13 Feb 2014 11:23:00 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (88 lines)

Kirk that was awesome!

Sent from my iPhone

> On Feb 13, 2014, at 11:08 AM, Kirk W Beach <[log in to unmask]> wrote:
> 
> 
> 
> Good Point Steve,
> 
> Resolution means that you can see two objects close to each other as separate and count them.
> Imagine headlights (2) coming toward you.  Even if you can see the light, you might not be able to tell the difference between a car (2) and a motor cycle (1) if the distance is great or your vision is blurred.
> We see "stars" by eye, but we can not resolve "double stars" without a wide aperture telescope.
> 
> Generally, you cannot resolve objects closer than the wavelength with light or ultrasound.
> 1 MHz US; wavelength = 1.5 mm = 1500 microns, (and if you consider the path is folded, because of a reflection) then the depth resolution might be 750 microns).  So, you can measure Intima-Media Thickness of around 1 mm or so, because IMT measurement uses depth resolution.
> But in the lateral direction, when the width of the transducer (numeric aperture) is also important, then the resolution is 10 times larger (10 times poorer). So, at 1 MHz, lateral resolution is near 5 or 10 mm.
> 
> for 2 MHz US wavelength = 750 microns
> for 5 MHz US wavelength = 300 microns
> for 20 MHz US wavelength = 75 microns.
> So, the estimate of 40 micron resolution is optimistic.
> 
> The "smoke" that you see is speckle, which you can see in light if you use a LASER, which is coherent.
> Shine a LASER on paper, and you will see speckles that move if you move your head, and if you dilate your eye pupils, then the speckle dots move closer together.
> Ultrasound imaging is always coherent so we can always see speckle.
> The spacing of speckle depends on the wavelength, so if you compare an ultrasound image taken with 3 MHz ultrasound to an image taken with 6 MHz ultrasound, the speckle spacing with the 6 MHz ultrasound will be half of the spacing with 3 MHz ultrasound.
> ATL (Advanced Technology Laboratories now called Philips) introduced High Definition Imaging (HDI) which combined images taken at 4.5 MHz, 5 MHz and 6 MHz (I'm guessing at the frequencies).  Echoes from structure were identical, so they aligned and were enhanced, but speckle spots from the three frequencies were in different locations, so the spaces between speckles of 4.5 MHz were filled in by the speckles from the 5 MHz and 6 MHz and the speckle was suppressed.  That made solid tissue look smoother.  All of the ultrasound companies adopted this method.
> 
> In blood, the average spacing of erythrocytes is about 5 microns (5,000,000 RBC per microliter) so erythrocytes are spaced at close to their diameter (8 microns), the extra volume (for blood plasma) comes because they are only 2 microns thick. Each cluster of erythrocytes in liquid blood has a characteristic speckle brightness. This speckle brightness changes with angle and location of the erythrocytes at random.  The cluster volume is the size of the resolution of the ultrasound system (around half a mm long and a couple of mm wide), so a typical cluster of erythrocytes in 4 cumm = 4 microliters will have 20,000,000 erythrocytes.  If the erythrocytes move much compared to the wavelength of ultrasound, their contribution to speckle is changed.  Venous blood velocity is around 2 cm/s or less.
> The frame rate of ultrasound is near 25 frames per second (in Europe, 30 FPS in the US), or 40 milliseconds per frame.  In 40 milliseconds, the erythrocytes will move 0.8 mm, which is near the wavelength of 2 MHz ultrasound.  So, if flow is much slower than that, the erythrocytes will move only a fraction of a wavelength between frames and the speckle won't change much between frames.  If the ultrasound system averages each pixel in image between frames which will enhance non-moving or slow moving speckle spots, then slowly moving speckles will be enhanced and fast moving speckles will be suppressed.
> 
> SOOO, the "smoke" appearance is enhanced by slow moving blood, using lower frequency ultrasound (which preserves speckle for larger between frame motions of erythocytes) while averaging the image between frames, Higher ultrasound frame rates (like imaging at 100 fps and then combining 4 images together to yield 25 fps) (this gives the erythrocytes less time to move between acquired images), using "narrrow band" ultrasound (not combining images from different frequencies (HDI); combining different frequencies will suppress speckle).
> 
> Here is an experiment to try.
> Image a vessel and try to get the "smoke" appearance aligning the scanhead with the "key" cephalad.  Repeat the image with the scanhead "flipped" so that you have the same plane, but the "key" is now caudad.  In most instruments, with the "key" cephalad, the image will be acquired with the scanlines proceeding from cephalad to caudad at a sweep speed of 100 cm/s (vely close to arterial blood speed), in the direction of arterial flow and opposite to the direction of venous flow.  When the key is caudad, the scanlines proceed from caudad to cephalad, now the scanlines proceed in the direction of venous flow.
> You might be able to change the sweep speed by changing the frame rate.
> 
> Please post on flownet if you see a difference in the image with the two alternate scanhead locations.
> 
> Thanks Kirk
> 
>> On Wed, 5 Feb 2014, Steven Knight wrote:
>> 
>> A single erythrocyte is approximately 8 microns in diameter, below the resolution of conventional ultrasound. For whatever reason (reduced shear, proteins, hypercoagulability?),
>> when blood flows slowly, erythrocytes tend to aggregate or clump together (rouleaux). And by clump I don’t mean permanently. When that clump is greater than about 40 microns it is
>> big enough to be resolved as a discrete echo with conventional ultrasound. New transducers allow us to routinely image with higher frequencies (therefore shorter wavelengths) so
>> we are more likely to resolve these “clumps”. In other words, it’s not we have and epidemic of patients with rouleaux or smoke. It’s that our technology has changed and flow is
>> more likely to look smoky when the conditions are suitable for aggregation/clumping.
>>  
>> ~S
>>  
>> Steve Knight BSc RVT RDCS
>> Senior Vascular Technologist
>> [log in to unmask]
>>  
>> Beth Israel Deaconess Medical Center
>> CardioVascular Institute
>> Division of Vascular and Endovascular Surgery
>>  
>> 110 Francis Street
>> Boston, MA 02215
>>  
>> (617) 632-9962 Phone
>> (617) 632-7977 Fax
>> www.bidmc.org
>>  
>> BIDMC logo
>>  
>> From: UVM Flownet [mailto:[log in to unmask]] On Behalf Of S Ewing
>> Sent: Tuesday, February 04, 2014 12:08 AM
>> To: [log in to unmask]
>> Subject: Terminology
>>  
>> What it the term used to describe the highly viscous  appearing venous  flow ? In echo it was called smoke.  Thanks in advance.  Sharen Ewing ,BS RVT RDCS.
>> To unsubscribe or search other topics on UVM Flownet link to: http://list.uvm.edu/archives/uvmflownet.html
>> ___________________________________________________________________________________________________________________________________________________________________________________
>> This message is intended for the use of the person(s) to whom it may be addressed. It may contain information that is privileged, confidential, or otherwise protected from
>> disclosure under applicable law. If you are not the intended recipient, any dissemination, distribution, copying, or use of this information is prohibited. If you have received
>> this message in error, please permanently delete it and immediately notify the sender. Thank you.
>> To unsubscribe or search other topics on UVM Flownet link to: http://list.uvm.edu/archives/uvmflownet.html
> 
> To unsubscribe or search other topics on UVM Flownet link to:
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