Reflection Coefficent in Ultrasound scan

[Taylor_1989]

Homework Statement

Discuss the main advantage and disadvantage brought about by a reflection coefficient being very small, and hence highlight the attributes that an ultrasound scanner must have to fully exploit very small boundary reflection.

Homework Equations

The Attempt at a Solution

I am having a issue with this question as in my slides for this module it states that:

''Low levels of reflection from soft tissue boundaries demand that signal detection is sensitive (and this is achievable), but cause most sound energy to be transmitted across the boundary, thus enabling scanning at depth.''

To me the advantage would be to have a increased scanning depth, but I can't understand what is being meant by

'Low levels of reflection from soft tissue boundaries demand that signal detection is sensitive'

Is the with ref to that if the probe is not calibrated correctly then the soft tissue boundaries would not be picked up easily?

The attribute I honestly am not sure on what this is in ref to. I don’t know if it referring to changing the axial or lateral resolution, or the amount of traducer arrays.

edit: I had a thought that if the reflected wave low level then I would need some way of increasing the sensitivity of the probe and I stumbled across as method called 'Time gain compensation' which increase the amplitude on the returning signal, I will research this further but is this what the question I have posed in directing towards?

edit 2: Sorry for the edits, but I am now thinking maybe the question is referring to the scattering effect that happens when ultrasound encounters something smaller that is wavlength i.e rayleigh scattering, then is this not to do with more doppler effect?Could someone point me in the right direction, many thank in advance.

 

[Baluncore]

'Low levels of reflection from soft tissue boundaries demand that signal detection is sensitive'

This is not a doppler or scattering effect so much as the reflection of a wavefront from a curved surface.
Where there is a change in acoustic impedance there is a reflected signal.
Small changes will reflect small amounts of energy so permit more energy to penetrate deeper.
The receiver array and signal processing must be sensitive enough to see the small signals returned from fine detail.
The axial resolution is determined by the bandwidth of the electronics and the data sampling rate, while the lateral resolution is determined by element spacing measured in wavelengths.
Time gain compensation is important as it partly corrects for diminishing energy being returned from distant objects. Most radar or sonar systems exponentially increases the receiver gain with time so as to detect small distant reflections.

 

[Taylor_1989]

Ah okay, that you very much, for the advice.