Fwd: Off-focus radiation

[Ccja@aol.com]

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Forwarded message:
From:	upmedphy@FRONTIERNET.NET (Douglas Pfeiffer, MS)
Sender:	medphys@LISTS.WAYNE.EDU (Medical Physics Listserver)
Reply-to:	MEDPHYS@LISTS.WAYNE.EDU (Medical Physics Mailing List)
To:	MEDPHYS@LISTS.WAYNE.EDU (Multiple recipients of list MEDPHYS)
Date: 97-07-06 16:06:25 EDT

One of our clients has been having a bad time with off-focus radiation. They
had been complaining about poor
image quality since the room was installed and called us in to help
(acceptance testing was done in house).
The complaints were mainly of poor contrast and inconsistent techniques
(almost always much less than other
similar rooms).

All indicators pointed to off-focus radiation, and we saw some clinical
images that pretty much clinched it.
Once the problem was identified, they inspected the other rooms more closely.
Four of six radiographic units
exhibited the problem to one degree or another, including one new Continental
room that was installed just a
few weeks before (which we did do acceptance testing on, but we did not look
specifically for this problem).
Generally, the older units were better than the newer ones.

I had seen this phenomenon several years ago on a Toshiba Neuro-Angio unit,
at acceptance testing. The problem
was solved by having the vendor put in a collimating cone at the x-ray tube
exit port.

The Continental engineer acknowledged the problem and swapped collimators, to
no avail. He said that the
collimataor blades are being made thinner and thinner and that is the root of
the problem. The vendor of the
first room has not yet acknowedged off-focus radiation as the cause of poor
image quality.

How much experience do other physicists have with off-focus radiation? How
often is it exibited strongly enough
to be of clinical concern? What else can we do? I would welcome any advice on
how to get this resolved.


Douglas Pfeiffer, M.S., D.A.B.R.
Upstate Medical Physics