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    Dear All
    here is a summary of my inquiry on thickness measurements in soft tissue

    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;
    ************************************************** ********************

    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
    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)

    Bente Rona Jensen"
    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
    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.
    published in the Journal of Biomechanics 29: 829-832, Lee JM, Langdon
    "Thickness measurement of soft tissue biomaterials" A comparison of five
    methods". The Hall effect probe described in there might be useful for
    time thickness measurements; however, the issue of tissue compression
    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
    Halifax, Nova Scotia (902) 494-2162 Tissue Mechanics Lab
    Canada B3H 3J5 (902) 494-6784 Tissue Structure Lab
    4) We have developed a system to measure weightbearing heel pad
    thickness by use of ultrasound.

    Keith Rome
    SL Physiotherapy
    University of teesside