81. Doppler Flow-meter and combined methodsrename
yaboiemil's version from 2016-02-14 21:56
Section1. 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
|Fd||Doppler Frequency Shift|
|v||Velocity of moving Boundary|
|c||Speed of propagation of ultrasound in a given medium|
|alpha||Angle between ultrasound beam and direction of moving structure|
3. 2 different techniques are employed in Doppler Diagnostic Methods:
|CWD||Continuous Wave Doppler||Superficial Vessels|
|PWD||Pulse Wave Doppler||Deep 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
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.
|The Doppler Principle||A shift in frequency between an incident ray and a reflected ray, when the medium is moving|
|Blueshift||The medium is moving towards you, the returned frequency is faster|
|Redshift||The medium is moving away from you, the returned frequency is slower|
|Duplex Method||2D Scan + Doppler Method for Velocity|
|Triplex Method||2D Scan + Doppler Method for Velocity + Colour Flow Mapping|
|Colour Flow mapping red||Blood Flows towards you|
|Colour Flow mapping blue||Blood Flows away from you|