Help needed with some medical physics terminology

[dermite]

hi there,
i found the following information on Dux College regarding Doppler Ultrasound and didnt understand it at all.
Can someone help me?

The Doppler Effect is the apparent change in frequency of a wave due to relative motion between the source and the observer. It is used in ultrasound to measure blood flow or the movement in the body.

An ultrasound pulse is directed into the body and some of the ultrasound I reflected off blood cells in the blood. If the blood cells are moving towards the transducer then they will experience the ultrasound at a higher frequency than was emitted from the transducer and hence ‘Doppler-shift’ will occur. However, when the blood cells reflect these sound waves they will act as a source of ultrasound that is moving relative to the transducer, i.e. they will also be moving into the waves they reflect. Hence ‘Doppler-shift’ will occur again. Therefore the transducer will pick up a reflected intensity much greater than the emitted intensity and by calculating the Doppler-shift the speed of the blood can be calculated.

Similarly blood cells moving away from the transducer will cause the reflected frequency to be less than the transmitted frequency. The amount of Doppler-shift also depends on the angle at which the ultrasound strikes the blood and hence this must be considered when calculating blood flow. Pulsed beams of ultrasound rather than a continuous stream are used to reduce scattering from tissues encountered when blood flow deep in the body is being tested.

High blood flow can indicate such as high blood pressure and blockage or narrowing of arteries while a low blood flow can indicate leaks around faulty heart valves.

thanks in adv.

[StormyAngel]

Hiya,
I can't promise I understand what this is saying perfectly, but i think i got most of it, so i should be able to explain!
What part of it don't you understand? There's quite a lot of information there.
First off, are you familiar with the Doppler effect?

(I'm new here. This is my first comment! )

[S200]

-snip-

The Doppler Effect is the apparent change in frequency of a wave due to relative motion between the source and the observer. It is used in ultrasound to measure blood flow or the movement in the body.

An ultrasound pulse is directed into the body and some of the ultrasound I reflected off blood cells in the blood. If the blood cells are moving towards the transducer then they will experience the ultrasound at a higher frequency than was emitted from the transducer and hence ‘Doppler-shift’ will occur. However, when the blood cells reflect these sound waves they will act as a source of ultrasound that is moving relative to the transducer, i.e. they will also be moving into the waves they reflect. Hence ‘Doppler-shift’ will occur again. Therefore the transducer will pick up a reflected intensity much greater than the emitted intensity and by calculating the Doppler-shift the speed of the blood can be calculated.

Similarly blood cells moving away from the transducer will cause the reflected frequency to be less than the transmitted frequency. The amount of Doppler-shift also depends on the angle at which the ultrasound strikes the blood and hence this must be considered when calculating blood flow. Pulsed beams of ultrasound rather than a continuous stream are used to reduce scattering from tissues encountered when blood flow deep in the body is being tested.

High blood flow can indicate such as high blood pressure and blockage or narrowing of arteries while a low blood flow can indicate leaks around faulty heart valves.

thanks in adv.

Hey Dermite...
Sorry, I kinda just addressed the first part. The second is mainly vice-versa.
As Stormy said, how familiar are you with the Doppler effect? Pitch/Frequency changes?
Assuming you know it, I'll move on. Also assuming you know how an ultrasound machine works...

So the ultrasound goes through and hits the blood cell. Assuming the blood cell is moving towards the transducer already, Doppler-shift will occur, and the sound pulse travelling back to the transducer will be a higher frequency. Then there is the complication... Other sound waves sent out by the transducer might be influenced\interfered by this reflected and different frequency wave.  So basically, the machine has to factor out these errors whilst still correctly computing how fast the blood cell contacted was in fact moving towards the transducer.

That's what I get out of it, but others may understand different...

(I'm new here. This is my first comment! )

Welcome aboard StormyAngel!