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Technical Discussions
yuan xu
Student
Texas A&M University, USA, Joined Jan 2000, 4

yuan xu

Student
Texas A&M University,
USA,
Joined Jan 2000
4
02:23 Jun-28-2000
Why I can not image the curve surface in pulse-echo mode?

Dear NDT experts:

I am a graduate student of Biomedical engineering. I am trying to image a muscle with a curved surface(you can just think it is a sphere with a radius of 2cm) buried in fat in pulse-echo mode. I scan the tranducer in one direction and get a 2-D image. The transducer I use is a 1MHz central frequency, 0.6 MHz bandwidth focused transducer, whose active element size is 0.75 inch and focal length is 1 inch. But the image I get is only two parellel lines with the length about 0.5cm , which are perpendicular to the acoustic axis. I just can not get an image of curved surface. Could anyone tell me the reason and how to overcome it?

Thanks!

Best regards

Yuan Xu



    
 
 
Dipl.-Ing. Martin Heinz
Dipl.-Ing. Martin Heinz
09:04 Jun-29-2000
Re: Why I can not image the curve surface in pulse-echo mode?
Dear Yuan Xu,

for answering exactly a breef description of your experimental setup would be helpful:
Is your muscle sample in a water tank, or are you coupling the sound using ultrasonic gel by contact your transducer on the surface? How do you scan exactly (geometrical setup)? How are the dimensions of your sample muscle? If it is very small ( a few millimeters) , you should get problems to "see" your muscle, because 1 MHz is a very low frequency for medical imaging. Although the acoustic impedance of fat and muscle is not very different, thus you won`t get a very big echo.
Remember that on ultrasonic imaging systems the common used frequency is between 3,5 and about 10 MHz, and there although the difference between muscles and fat is difficult to see, because specle and other ultrasonic artefacts are in the range of the echoes obtained by the dividing layers between fat and muscles. For the characterization of tissue differences commonly very high frequencies are used.

Best regards,

Martin Heinz.





    
 
 
Dave Lines
R & D,
Diagnostic Sonar Ltd, United Kingdom, Joined Nov 1998, 8

Dave Lines

R & D,
Diagnostic Sonar Ltd,
United Kingdom,
Joined Nov 1998
8
00:20 Jun-29-2000
Re: Why I can not image the curve surface in pulse-echo mode?
: Dear Yuan Xu,

: for answering exactly a breef description of your experimental setup would be helpful:
: Is your muscle sample in a water tank, or are you coupling the sound using ultrasonic gel by contact your transducer on the surface? How do you scan exactly (geometrical setup)? How are the dimensions of your sample muscle? If it is very small ( a few millimeters) , you should get problems to "see" your muscle, because 1 MHz is a very low frequency for medical imaging. Although the acoustic impedance of fat and muscle is not very different, thus you won`t get a very big echo.
: Remember that on ultrasonic imaging systems the common used frequency is between 3,5 and about 10 MHz, and there although the difference between muscles and fat is difficult to see, because specle and other ultrasonic artefacts are in the range of the echoes obtained by the dividing layers between fat and muscles. For the characterization of tissue differences commonly very high frequencies are used.

: Best regards,

: Martin Heinz.

Martin is correct in pointing out the difference in frequency that you are using. Other points that you will have to consider are the dynamic range of the imagings system that you are using and the number of elements in the active aperture.

Your description matches what was seen in the early days of medical ultrasound when viewing the foetal head. The interface behaves more like a specular reflector rather than a scattering surface. The interface perpendicular to the beam reflects back strongly while those at an angle deflect this strong reflection away from the probe.

The early medical imagers had either bi-stable or linear displays and so did not show the full shape. This effect can be significantly improved by logarithmic compression of the received signal which allows the scattered signals from the curved surface to be presented on the same display. Edge-enhancement is also often used on these scanners & this boosts the response all the way round the curve but the dynamic range of the log amp is still the critical factor.

Another feature of current medical imagers is the use of much larger apertures (the group of elements which contribute to the transmit & receive signal for a given beam). The elements at the edges of the active aperture are able to catch these oblique reflections and so help to fill in much of the curved interface.

Dave Lines


    
 
 
Yuan Xu
Student
Texas A&M University, USA, Joined Jan 2000, 4

Yuan Xu

Student
Texas A&M University,
USA,
Joined Jan 2000
4
09:28 Jul-01-2000
Re: Why I can not image the curve surface in pulse-echo mode?
br>Best Regards


Yuan Xu


-------------
: Dear Yuan Xu,

: for answering exactly a breef description of your experimental setup would be helpful:
: Is your muscle sample in a water tank, or are you coupling the sound using ultrasonic gel by contact your transducer on the surface? How do you scan exactly (geometrical setup)? How are the dimensions of your sample muscle? If it is very small ( a few millimeters) , you should get problems to "see" your muscle, because 1 MHz is a very low frequency for medical imaging. Although the acoustic impedance of fat and muscle is not very different, thus you won`t get a very big echo.
: Remember that on ultrasonic imaging systems the common used frequency is between 3,5 and about 10 MHz, and there although the difference between muscles and fat is difficult to see, because specle and other ultrasonic artefacts are in the range of the echoes obtained by the dividing layers between fat and muscles. For the characterization of tissue differences commonly very high frequencies are used.

: Best regards,

: Martin Heinz.




    
 
 

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