Re: stereo x-rays at NSA

[P3D Clifford J. Mugnier <CJMCE@xxxxxxxxxxxxxxxx>]

I did about a hundred or so people in the early nineties with stereo
X-rays, each person getting two stereopair (2 shots tilted to the left, 2
shots tilted to the right) in order to get convergent (4-ray solutions) of
a particular point on the anterior (front) surface of the T-1 vetebral
element (first thoracic vertebrae).  The stuff was for an analytical
photogrammetric analysis of people (male and female sailors) for
ejection-seat testing at the National (then Naval) Bio Dynamics Laboratory
(NBDL) here in New Orleans.

For a guy used to doing stereo aerial photo stuff for topographic mapping,
this was really, really weird stuff to look at in stereo.

Anyway, the opposite tilts were at about 15 degrees each, and were not
viewable in the convergent case, but each tilt was done with a pair,
laterally separated so that a left-tilted pair was easily viewable in
stereo.  Points were identified in stereo (marked and measured) for the
left-tilted pair, and then the same for the right-tilted pair.  Results
yielded X-Y-Z positions inside the body cavity with accuracies typically
0.1 to 0.2 mm in all three components.

The lab is now part of the University of New Orleans

Cliff Mugnier
----------
> From: P3D Peter Abrahams <telscope@xxxxxxxxxx>
> To: Multiple recipients of list <photo-3d@xxxxxxxxxxxxxxxxxxxxxxxx>
> Subject: stereo x-rays at NSA
> Date: Tuesday, 29 July, 1997 2:40 PM
> 
> Concerning the stereo x-rays at NSA,
> 
> >The images had a relatively high percentage of areas that weren't
expressed
> >equally in both left and right views.
> 
> Yes, if I get a chance to do these again, I will decrease the disparity
> between R & L.  The x-ray techs tilt the gun maybe 5 degrees to the R of
> vertical and 5 to the left to make a stereo pair, a really radical
amount,
> the subject is only about two feet away.  Probably this is because they
are
> trying to locate the z axis placement of some tumor or bullet, and will
> strain their eyes a little to do this if necessary.  It's particularly
> noticeable because you're seeing the front & the back surfaces.  The
> simpler shells, with a clean spiral form, needed this 
> disparity, but the images of the complex shells had lots of areas that
were
> white on one side and black on the other, creating a rivalry.    If the
> right side has an area of exposure (black) & the left is white, then the
> thickness of the shell that the x rays passed through is different by
that
> amount, thin on the right and thick on the left.
> 
> _______________________________________
> Peter Abrahams   telscope@xxxxxxxxxx
> the history of the telescope, the microscope,
>     and the prism binocular


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