81. Doppler Flow-meter and combined methods

yaboiemil's version from 2016-02-14 21:56


1. The Doppler Principle is that there is a frequency shift between a signal that is
reflected from a medium moving towards you (faster freq, blueshift) and a medium
moving away from you (slower freq, redshift)
2. The measuring and imaging of moving structures is based on this principle.

Equation to determine Doppler Frequency Shift



Question Answer
FdDoppler Frequency Shift
vVelocity of moving Boundary
cSpeed of propagation of ultrasound in a given medium
alphaAngle between ultrasound beam and direction of moving structure


3. 2 different techniques are employed in Doppler Diagnostic Methods:


AcronymMethodExamination possible
CWDContinuous Wave DopplerSuperficial Vessels
PWDPulse Wave DopplerDeep Vessels


4. CWD makes use of 2 transducers, a TRANSMITTING and a RECEIVING.
5. PWD can also give information on the position of a structure.
6. Added Methods such as Colour Flow Mapping and 2D scans can be combined for
better diagnoses.
7. 2D Scans can be first used to identify the position of a vessel, before velocity is measured.
8. Colour Flow mapping is a process used to image the direction of blood in a vessel. Red
Towards, Blue Away.


Question Answer
The Doppler PrincipleA shift in frequency between an incident ray and a reflected ray, when the medium is moving
BlueshiftThe medium is moving towards you, the returned frequency is faster
RedshiftThe medium is moving away from you, the returned frequency is slower
Duplex Method2D Scan + Doppler Method for Velocity
Triplex Method2D Scan + Doppler Method for Velocity + Colour Flow Mapping
Colour Flow mapping redBlood Flows towards you
Colour Flow mapping blueBlood Flows away from you