Re: RBT and Stereo Xrays

[CJMCE@xxxxxxxxxxxxxxxx]

John D. Roll, M.D., Rockford, IL, USA  said:

>I found your discussion of stereo radiography interesting. I have even used 
>this to help an orthopedic surgeon prepare for surgery on a complex pelvic
>fracture.

At the U.S. Naval BioDynamics Laboratories (NBDL) here in New Orleans, they have
been shooting sailors out of ejection seats for about 25 years on a regular
basis. These sailors are Human Research Volunteers (HRVs) generally referred to
as "Lab Rats" (not a slur but a good-natured nickname).  They get strapped into
Impact Accelerators (ejection seats) and withstand 1g to 16g impacts to study
the relation of the human head and neck with respect to the first thorascic 
vertebral element (T-1).  Since it is not possible to surgically implant visible
targets into a person's spine, a method of targeting the T-1 vertebrae was 
devised with non-invasive targets in concert with stereo X-Rays.

With much experimentation, I had their machine shop fabricate an "X-Ray Chair"
that had the exact dimensions and mechanical ajustments as the aluminum seats
used in the accelerators.  The difference was, though, it was made out of
X-Ray transparent plexiglas.  The harness system used on the accelerators was
duplicated with transparent fittings and straps so that the only things that
would appear on the resultant X-Rays was the HRV and my control points (small
lead shot or BBs).

Initial stereo was achieved by simple lateral shifting of the HRV in the chair
in AP views (Anterior-Posterior) - face to the X-Ray source.  Problem with that
was the anterior wall of T-1 was too thin to perceive in stereo - it washed out.
We then rotated the subject 45 degrees and did lateral shifts with success; we
COULD see the anterior wall in stereo!  We then rotated the subject the opposite
direction 45 degrees and got another stereopair successfully.  With that, we 
established a standard procedure to obtain two stereopairs of each HRV which
was then measured and photogrammetrically triangulated to determine the "Body
Anthropometric Coordinate System".

... with my software, of course.  (PC Giant)

Accuracy achieved: +/- 2.7mm in each component X-Y-Z (Variance-Covariance Matrix
used for Eigenvector/Eigenvalue determination).


Clifford J. Mugnier  (cjmce@xxxxxxx)
Topographic Engineering Laboratory
Department of Civil & Environmental Engineering
University of New Orleans
New Orleans, Louisiana  70148
Voice: (504) 286-7095
FAX:         286-5586


------------------------------