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P.zioupos
02-23-1998, 07:18 AM
Dear All
here is a summary of my inquiry on thickness measurements in soft tissue
biomechanics

ORIGINAL MESSAGE: **************************************************

I would like to inquire about the latest techniques in thickness
measurements of soft tissue membranes (fasciae, pericardium, valve
leaflets etc.) especially during deformation.
I am also interested to hear suggestions for methods that can be 1)
non-contacting and 2) independent of the tissue density (which may very
well change during the stretch).
I will try to circulate the answers.

Peter Zioupos, 16 Feb 1998, 15:07
Dept of Materials & Medical Sciences,
Cranfield University,
RMCS Shrivenham, SN6 8LA
United Kingdom
tel:44(0)1793-785932; fax:44(0)1793-785772;
email:zioupos@rmcs.cranfield.ac.uk
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REPLIES
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1) Hi Peter,
I guess you have already read
Lee JM & Langdon SE, J. Biomech. 29(6):829-832, 1996.

Did you see the Jurvelin et. al paper the previous year?
Jurvelin JS, et. al, J Biomech. 28(2):231-235, 1995.

I think ultrasound is going to be the way to go. Mainly
because it can be truly non-contact, allowing one to suspend
the tissue in saline, rather than laying it flat on a glass plate.

Though the transducers and pulser-receiver setup will cost
a bit, it is the high-speed A/D conversion that sends the cost
through the roof. If you can lay your hands on a good storage
oscilloscope, you can hope for about 30micron accuracy with
a 100MHz sampling frequency. [I have not tried this yet.]

The results will however only be as accurate as the estimate of
the speed of sound in the tissue.

-- Santosh Zachariah --
Research Associate, Dept. of Bioengineering
Univ. of Washington, Box 352255, Seattle, WA 98195, USA
ph: (206) 685-3488, fax: (206) 543-6124
zach@limbs.bioeng.washington.edu
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2) Soft tissue thickness can be measured with ultrasound:
See e.g. The effect of prolonged isometrig contractions on muscle
fluid balance by Jensen et al.. Eur. J. Appl Physiol (1994)
69:439-444.

Bente Rona Jensen"
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3) Peter,
You have touched on a very complicated and ongoing problem in
biomechanics. Regarding our work on the pericardium, we tried many
different methods (see work by Michael Lee in particular). We ended up
going back to the old Mitutoyo thickness gauge, with measurements taken
at the same time after the application of load. While low-tech, the
results appear to be consistent. Other methods are:

1 - ultrasound crystals - cumbersome and have tissue density problems as
you have noted.
2 - optical interference - dependent on the properties of the tissue -
not reliable.

Actually, we end up often expressing axial loads in terms of membrane
tensions (f/length), since in many tissue composition varies across the
thickness (e.g. aortic valve).

Michael S. Sacks,Ph.D.
Assistant Professor
Department of Biomedical Engineering
POB 248294
University of Miami
Coral Gables, FL 33124-0621
Voice (305) 284-5434
Fax (305) 284-6494
email: msacks@coeds.eng.miami.edu
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3) Hi Peter:
You may very well already have this, but...a few years ago we took a
hard look
at this problem for bovine pericardium with a variety of techniques.
It's
published in the Journal of Biomechanics 29: 829-832, Lee JM, Langdon
SE,
"Thickness measurement of soft tissue biomaterials" A comparison of five
methods". The Hall effect probe described in there might be useful for
real-
time thickness measurements; however, the issue of tissue compression
would
need to be addressed.

I hope this helps.

Best regards,

J. Michael Lee, Ph.D.
Interim Director, Biomedical Engineering Programme

Associate Professor of Biomaterials (902) 494-6734 (Voice)
Chair, Applied Oral Sciences (902) 494-2527 (FAX)
Dalhousie University
5981 University Avenue jmlee@is.dal.ca
Halifax, Nova Scotia (902) 494-2162 Tissue Mechanics Lab
Canada B3H 3J5 (902) 494-6784 Tissue Structure Lab
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4) We have developed a system to measure weightbearing heel pad
thickness by use of ultrasound.

Keith Rome
SL Physiotherapy
University of teesside
"Keith"
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