Re: Doppler Jargon
From: Logamuthu Krishnan (logamuthu@gmail.com)
Thu Jun 29 09:24:18 2006
"Inverse Doppler Effect" is found in http://www.physorg.com/news4224.html.
Briefly, "The inverse Doppler effect is not something you can hear, but
understanding it could one day lead to important advances in optics and
communications <http://www.physorg.com/news4224.html#> equipment.
Predicted in the 1940s, the inverse Doppler effect was first observed in
2003 by British researchers Nigel Seddon and Trevor Bearpark using an
experimental magnetic, nonlinear transmission line sketched out by Avenir
Belyantsev and Alexander Kozyrev in 2000. This nonlinear transmission line
is a synthetic structure that allows
electromagnetic<http://www.physorg.com/news4224.html#>waves to
propagate along it in a new fashion.
In the experiment, a pulse of current fed into the line acts as the moving
"siren" or shockwave. It generates a radio frequency (RF) signal but as the
pulse recedes, the spacing between the peaks and troughs in the waves
tighten rather than loosen: the inverse of the Doppler effect. That's just
the opposite of what happens with sound waves when a siren passes you.
Reporting in the May 20 issue of the journal *Physics Review Letters*,
University of Wisconsin-Madison Research Associate Alexander Kozyrev and
Electrical and Computer Engineering
<http://www.physorg.com/news4224.html#>Professor Dan van der Weide
prove how an RF signal moving through this
special transmission line can reverse itself and fall in sync with the
shockwave in order to realize the inverse Doppler effect. They demonstrated
that the shift arises from a complex and remarkable spatial structure of
waves propagating along the line.
Normally consisting of only one spatial period, the considered system
exhibits multiple spatial periods enabled by the periodicity of the
nonlinear transmission line structure. Their explanation may point the way
toward making materials in which this new effect can operate."
"Pseudo-Doppler" is an expression I came across in
http://www.monitoringtimes.com/html/mtramsey.html.
Briefly "Doppler direction finders work on the principle of rotating
antennas - in this case, electronically-switched antennas, thus called
"pseudo-Doppler" since there is no actual physical movement."
As you say rightly, "Multidirectionality" in Doppler equipment is probably
just a sales talk, or isn't it?
I am yet to understand "Directionality-separated" Dopplers; hopefully the
vendor, who put it out in his brochure, would respond to my query.
On 6/29/06, DuBose, Terry <DuboseTerryJ@uams.edu> wrote:
>
> I must admit I do not know what ""Directionality-separated"
> "Multidirectional"" means in the context of Doppler sonography. I did
> find this article, but I do not find useful definitions in it. Hopefully
> someone else can elucidate.
>
> http://www.medicalacupuncture.org/aama_marf/journal/vol16_1/article5.html
>
> "*Functional Multidirectional Transcranial Doppler Sonography
> *The Multi-Dop T System (DWL Electronic Systems GmbH, Sipplin-gen,
> Germany) was used to measure the mean blood flow velocity in different
> cerebral arteries. A 4-MHz (ophthalmic artery), as well as 2-MHz probes
> (posterior cerebral artery, anterior cerebral artery , middle cerebral
> artery) were applied with a specially developed ultrasound probe-holding
> construction.
> Functional Magnetic Resonance Imaging (fMRI) The fMRI investigations were
> performed using a 1.5-T total body system (Intera, Philips Medical
> Systems, Best, Netherlands). The blood oxygen level-dependent contrast
> sensitive images were acquired with a T2-weighted gradient echo sequence
> (single shot planar readout, flip angle 90?, TE 50 ms, FOV 250 mm, matrix 96
> x 96 interpolated at 128 x 128, layer number 30, layer thickness 4 mm). A
> total of 144 volume images were registered continuously in succession, with
> a repetition time of 5 seconds.
>
> The fMRI-study was based on a block design with alternating resting
> conditions for 1 minute and 1 minute of laser needle activation. A total of
> 6 resting and 6 activation intervals were registered. Each fMRI data
> registration required 12 minutes.11,12"
>
> Neither have I heard of "Inverse Doppler Effect and Pseudo-Doppler".
> Pseudo Doppler may be what is called "time-domain correlation (TDC)". TDC
> looks at blood cell aggregates and identifies the change in position in
> time… it does not use the Doppler frequency shift effect which is based upon
> the difference (change) in the frequencies of the incident acoustic beam and
> the frequency of the reflected sound. TDC is more like taking two photos
> exactly one second apart of a moving vehicle and then using the distance
> traveled in one second to calculate the velocity of the vehicle. There is
> a pretty good explanation of TDC here:
>
> http://www.medcyclopaedia.com/library/topics/volume_i/t/time__domain_correlation.aspx
>
> I hope someone else can add to this. Terry
>
> Terry J. DuBose, M.S., RDMS, FSDMS, FAIUM
>
> Associate Professor & Director
> Diagnostic Medical Sonography Program
> University of Arkansas for Medical Sciences, CHRP
> 4301 West Markham St. Mail Slot #563
> Little Rock, Arkansas, 72205 USA
> 501-686-6510
> DuBoseTerryJ@UAMS.edu
> http://www.uams.edu/chrp/sonography/
> http://www.obgyn.net/us/panel/panel.htm
> http://www.io.com/~dubose/
> ---------------------------------------------------------------
> ------------------------------
> ---------------------------------------------------------------
>
> ---------------------------------------------------------------
> *From:* ultrasound@obgyn.net [mailto:ultrasound@obgyn.net] *On Behalf Of *Logamuthu
> Krishnan
> *Sent:* Thursday, June 29, 2006 5:37 AM
> *To:* Multiple recipients of list ULTRASOUND
> *Subject:* Re: Doppler Jargon
>
> Zillion Thanks for a very lucid review.
>
> I am sure many other readers will thank you too.
>
> To pick your brain a bit more -
>
> I have come across some vendor-brochures claiming their product to be
> "Directionality-separated" "Multidirectional" etc., What do you make out of
> this claim of being "Directionality-separated" for what looks like a very
> low level vascular Doppler - too ancient to be a Power Doppler - probably
> just CW! (Vendor name omitted to avoid flaming!). And... What
> is "Multidirectional" as opposed to the mere 2-way "Bi-directional" we know
> of?
>
> Maybe the thread is worth continuing - to throw more *light* on this issue
> - *not heat*, of course!
>
> You must also have heard of Inverse Doppler Effect and Pseudo-Doppler!!
> More will follow! if co-readers chime in!
>
> Prof.K.Loga muthu krishnan.
>
> On 6/29/06, *Terry DuBose* <terrydubose@sbcglobal.net> wrote:
>
> This web site may help.
>
> http://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-html/chapter_01.htm
>
> also this page, scroll down to Doppler:
>
> http://en.wikipedia.org/wiki/Doppler_ultrasound#Doppler_sonography
>
> However, let me see if I can answer briefly. With true Doppler effect,
> the direction of the moving object (blood is a scatter/reflector in the case
> of ultrasound) is in relationship to the transducer. The color displayed
> will be dependent on whether the blood flow is toward the transducer or
> away. With spectral Doppler analysis the same principle applies except flow
> away from the transducer will be below the base line, or above if flow is
> toward the transducer, and displayed as a spectral wave form..
>
> Non-directional "Doppler" is probably not true Doppler (it may be done in
> different ways). It may be called "power Doppler", "amplitude Doppler", or
> something else depending upon the manufacturer. The advantage is it is
> much more sensitive to very slow flow that may not be detected with
> directional Doppler. Another advantage is it will not "alias", which is a
> type of false reading (not really false, but that is the easiest way to
> explain it). The disadvantage is that it does not tell if flow is toward
> the transducer or away.
>
> Range-gating is a software control that allows the machine to look at
> Doppler shift information (spectral only) at a specific point along a
> vector. In this way a specific vessel can be interrogated for flow
> direction and velocity (amount of Doppler frequency shift). Range-gating
> only takes place with pulse-Doppler machines. Continuous Wave (CW) Doppler
> reads all frequency shifts all along the vector, even if it passes through
> two or more vessels.
>
> I hope this helps... it is a very basic explanation. If you ask more
> specific questions, I will try to respond, and am sure others will also.
>
> Terry J DuBose, M.S., RDMS,
>
> UAMS Little Rock, Arkansas
>
> --------------------------------
>
> --------------------------------
>
> --------------------------------
>
> *"Prof.K.Loga muthu krishnan" <logamuthu@gmail.com >* wrote:
>
> I am getting confused with Doppler jargon in recent times - especially
> by brochures from vendors - I need some clarification of two areas -
> 1. Directionality in Doppler - where does it reside? Is it probe-based
> or console-circuitry-based? What is the advantage of a Non-Directional
> Doppler over a Directional Doppler?
> 2.Range-Gating - where does the responsible hardware / software reside -
> in the transducer or in the console?
> I need some physics-based enlightenment. Thanks!
>
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