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Re: Doppler JargonFrom: DuBose, Terry (DuboseTerryJ@uams.edu)Thu Jun 29 08:57:03 2006
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.htm l "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_cor relation.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/ch apter_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 --------------------------------
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-- -------------------------------- "Prof.K.Loga muthu krishnan" <logamuthu@gmail.com > wrote:
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