Panographic Dental X-Ray Surveys

["Michael P. Grissom" <MIKEG%SLACVM.bitnet@vmd.cso.uiuc.edu>]

1.  Since the commentary to this point has included where is the best
place to put a specific vendor's detector, I would suggest that like
the radiology technologist, the typical X-Ray surveyor doesn't really
have enough time to REALLY determine the cumulate, depth, partial body,
or any other kind of dose from Panographic dental X-Ray machines.

2.  I have used the MDH 6 cc chamber as a relative indicator of
exposure from a given unit by taping it on the chin rest.  In general,
by doing so for every machine surveyed, you at least get a relative
exposure number for a complete scan.

3.  Are there differences between machines?  You bet there are.  In the
bidirectional machines, the exposure can be different counter-clockwise
from that clockwise (very consistently).  Relative outputs can vary,
but not very much for a machine that has been installed for some time
and is showing good "behavior" with annual follow-up sureys (or once
every two years, normally satisfactory for dental units).  I did see
one machine (a new installation by a non-U.S. vendor) where the
relative exposure for a single pass exceeded the average for the
machines in my customer population by more than 10 times!!  In that
case, I had the vendor return and re-examine the installation (and
they replaced the unit, and properly bolted it to the floor--which
had also not been done with the original unit leading to interesting
irregularities in the "orbital" path using a test film).  I suspect
in that case the normally "pulsed" mode of firing the tube had
somehow turned into continuous firing of the tube, hence greatly
enhanced exposure.

3.  Anyway, you can determine things about panograph functionality
without making it a several hour research project or a DENT type
exercise!

----------------------------------------------------------------------
The opions expressed above are those of the author alone and do not
not represent those of the Stanford University or the US Department
of Energy.
----------------------------------------------------------------------