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Replies to request for ultra sound info

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  • Replies to request for ultra sound info

    Several weeks ago I requested information on ultra sound measuring systems.
    Despite accidently neglecting to mention our specific application, I received
    many replies which I have attached below. Thanks to everyone who responded.

    Deborah King
    Biomechanics Lab
    Penn State University

    ================================================== ===
    I just finished a sabattical at the universityof Bern where I used a
    Toshiba Tosbee ultrasound unit to document and survey the abdominal wall.
    It is a very versatile unit with good calibration routines for distance
    measurements. Don't know the cost over here though. Incidentally do you
    know of Peter Cavanaughs e-mail address, thanks, Stu McGill

    The is a German company marketing an ultra-sound based
    motion analysis system if that is what you are looking for.
    The address is as follows:

    Zebris Medizintechnik
    Grabenstr. 17
    88316 Isny (Allgaeu)

    phone: (01149 for Germany) 7562 - 4221
    sorry, I don`t have a fax number.

    You should contact Mr. Brunner.

    While the SAC device is quite accurate, beware of systems that use speakers
    as sources. Even with fairly sophicticated electronics and signal
    processing, wave jumping occurs, which can throw the systems off by 1 or
    more wavelengths of the sound that is being used. This is the case with an
    Israili system (forget the name), that is a hybrid IR/sonic device.

    Also beware of ambient noise suceptability, and use in drafty areas where
    the spead of sound may fluctuate between the speed measurment apparatus and
    the sensor array.

    There is a system called Signal/RTS. This system runs on a DOS PC and can
    handle a sample rate of up to 250KHz.

    For more information please contact:

    Engineering Design
    43 Newton Street
    Belmont, MA 02178
    Tel: 617-484-3520
    Fax: 617-484-6559

    We have made extensive use of SAC digitizers (the older
    GP8-3D) over the past five years to record the posture of
    automobile drivers in laboratory vehicle mockups. We have
    written our own software, the latest in LabVIEW, to communicate
    with the digitizer and handle data acquisition, calibration,
    transformation, etc.

    We have found that we can repeatedly digitize a point within
    the target volume with a standard deviation of about 1 mm.
    Measurements of known lengths (e.g., 200 mm) within the volume
    are also routinely accurate to within 1 mm. Since we are
    recording the location of palpated body landmarks, this
    accuracy and precision are considerably better than our
    ability to locate those landmarks.

    Important limitations:
    1. Throughput. Because the system relies on sound travel
    times to determine location, sequential emitters cannot be
    fired closer together in time than the maximum amount of time
    it could take for the sound to reach all of the microphones.
    In practice, the minimum time spacing is usually longer,
    because of ...
    2. Echo. When we have used the system in smaller
    laboratories, echo from the walls and other hard surfaces has
    caused erroneous readings, particularly when using high
    sequential sampling rates. We have instituted software checks
    to eliminate potentially spurious data arising from echo
    effects and have used acoustic baffles to reduce echo.
    3. Sequential measurement. The principle of measurement is such
    that multiple body landmarks are recorded sequentially rather
    than simultaneously, as is the case with video or film-based
    systems. For quasi static or relatively slow motions, this is
    not a problem, but for faster motions it could be.
    4. Measurement volume. The spacing of the microphone array
    determines both the measurement volume and the accuracy of
    measurement within that volume. We use square arrays of about
    600 mm on a side. Slant ranges to three microphones are
    required to locate the emitter, if the emitter can be assumed
    to be on one side of the microphone array. This spacing gives a
    measurement volume of about 1 m^3. If larger spacing is used,
    the volume goes up but the accuracy goes down. We have used
    two arrays side-by-side to expand the sampling volume, and
    switched data acquisition between them as needed.

    Ulrich Raschke and others at the University of Michigan Center
    for Ergonomics have developed an ultrasonic system that allows
    for a much larger digitization envelope, and includes
    algorithms for using the redundant information from multiple,
    arbitrarily positioned microphones to reduce error. He'll
    probably respond to your post. If not, you can contact him at

    I worked with an SAC GP-8 3D sonic digitizer at Columbia Unviersity
    for three years. It had numerous problems but some advantages as well.
    If given the choice, I would not use an sonic digitizer for human or
    animal work however.

    First, as you may know, active markers emit a spark which creates an
    acoustic signal. Recievers mounted in a fixed arrangement detect
    the acoustic signal, and the time between generation and reception
    provides a measure of distance. The sparking of the emitters was
    a little distressing to subjects, especially at first. In any case,
    you can not place the emitter directly on the surface of the skin
    or the emitter will not spark properly.

    Second, we had lots of problems with reflections. The signal from
    the emitters would bounce off of the table, the subject, the light,
    and who knows what else. We found that we had to completely cover
    the walls and ceiling of our 6x6x8 ft room with acoustical foam to
    dampen the reflections, and even then we had substantial problems.
    On some days we had to throw out up to half of all trials because
    they included a reflection.

    Next, the sampling rate was quite slow, 100 Hz maximum divided by the
    number of emitters in use. That meant we could only use 5 emitters
    at a time if we wanted to have any chance of capturing the frequency
    range of human movement. Moreover, we achieved this sampling rate
    only after purchasing a speeded up version of the ROM chip from SAC
    and doing substantial reprogramming of the interface between the
    digitizer and the computer. This speed is more dependent on the
    digitizer than on the computer. Recall that sound moves relatively

    Next, the calibration process was difficult, though it is relatively
    permanent. We found it nearly impossible to square the receivers
    accurately enough to insure that the entire workspace was
    measured in the same manner. As a result, we ended up doing an
    extensive regression analysis on data collected systematically
    throughout the workspace and then adjusting all subsequent data based
    on those results. On the other hand, once we finished with this
    process, the system was very stable over a two year period and reliable
    to within .3mm.

    Next, we used the system for measuring arm movements. We had it running
    for 10 seconds at a time, for up to 500 trials within a session and
    probably ran up to 200 sessions over the two year period. We found that
    emitters burned out periodically and we had to be careful that we always
    had extras on hand. They were not particularly cheap either (about $40?),
    and some were defective to begin with. Also, replacing emitters during
    an experimental session was sometimes a real hassle.

    Finally, on the down-side, we found the device driver to be very badly
    written. I can't give you the details on that because my colleague,
    Ted Wright, did the work of re-writing it. I can say it was very
    inefficiently written, used lots of goto loops. Also, the digitizer
    was designed so that the computer could not query it in any way to
    discover its current state. As a result, the driver had to be written
    to reset the device periodically, so that we could insure it was in
    a known state. We had some lengthy discussions with Science Accessories
    about this and suggested some changes for subsequent versions. Perhaps
    they've cleaned up that side of things.

    On the up side, it was GREAT to have a device that digitized automatically,
    and with which you could generate on-line feedback in real time. The
    GP-8 3D system is about least expensive means I know to do that. Despite
    these problems, we did use it to collect a substantial amount of very
    useful kinematic data.

    we have a GP-12 in the lab and a collegue of mine is working with
    it. It seem that the system is very unreliable and unaccurate. I don't
    know if this due to the instrument or to the fact that it is not optimally
    configured by us. For sure forget to use with success as is out of the
    Try to contact this company:
    Logitech, Inc.
    6505 Kaiser Drive
    Fremont, CA 94555
    Logitech faxback phone # 1-800-245-0000
    sale information 1-800-231-7717
    Technical support hotline 1-510-795-8100
    General Fax (510) 792-8901
    Developer relations 1-510-713-5338

    Their products include 3D ultrosonic head tracker and 3D mouse.

    I would like to know what you want to measure? What freqency do you want?
    What type of scanning (A-scan, B-scan or C-scan). We have two companies
    in Denmark making ultrasound equipment (B&K Medical and Cortex Technology).
    I am by myself working with ultrasound (High freqency 20MHz) and
    Ultrasound Microscopy (up to 1GHz). My Ph.D. thesis is biomechanics of
    wall mechanics by ultrasound (elasticity ).
    I will be in USA from Feb 16 to March 4. Do you know SPIE Medical
    Imaging95 in San Diego. I will be there.

    I have used several sonic digitizers from Science Accesories Corporation.
    They are quite reliable and easy to install for laboratory work. My only
    concerns are:
    1) occasional obstructions (sonic shadowing),
    2) variations due to temperature and humidity,
    3) jitter due to background noise, and
    4) variations due to air currents caused by large rapid motions.

    You may wish to investigate electromagnetic trackers (Polhemus, Bird) if
    your workspace does not include large metallic objects.


    Thanks again to everyone who replied. Your responses were very helpful.