Fwd: KVP MEASUREMENT/DEFINITION

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Forwarded message:
From:	joelgray@M3.SPRYNET.COM (Joel E. Gray)
Sender:	medphys@LISTS.WAYNE.EDU (Medical Physics Listserver)
Reply-to:	joelgray@sprynet.com
To:	MEDPHYS@LISTS.WAYNE.EDU (Multiple recipients of list MEDPHYS)
Date: 97-08-26 18:23:42 EDT

Bob,

I did the measurements quite a few years ago-- you get the same contrast
using single phase and three phase generators if you increase the single
phase kVp by 10 kVp.  This results in about the same HVL and the same
dose to the patient also.  (This was necessary since we had both single
and three phase generators and want the films to look the same.)

Caveat-- before the theoretical folks tell me that this can't possible
be true I will add that this works over the typical limited diagnostic
energy range of 60 to 110 or 120 kVp!

            Joel


Joel E. Gray, Ph.D., Consultant
2804 Second Street Southwest, Suite 334
Rochester, Minnesota 55902
U.S.A.

Phone 507-286-8910
Cell Phone 507-269-4247
Fax 507-286-8910
e-mail joelgray@sprynet.com




On Aug 26,  9:39am, Robert G. Zamenhof wrote:
> Subject: KVP MEASUREMENT/DEFINITION
> I am finding this discussion very interesting, because it touches on
> something I have always felt as well: that measuring the kVp is
probably
> the best SIMPLE measure of a complicated parameter that strongly
influences
> both patient dose and image quality (and is, therefore, of critical
> importance in QA).  However, as Bob Kobistek points out it is far from
the
> whole story.  Beam filtration and waveform also affect these
quantities
> (incidentally, Bob, I think that a single-phase 80 kVp waveform
produces
> BETTER contrast than a high-frequency 80 kVp waveform...), so why
don't we
> recalibrate the "kVp" knob in "HVL" or "PENETRATION" units instead?
> True,the HVL would need to be measured using water-equivalent
absorbers
> instead of aluminum; but so what? More applications for solid water!
> Perhaps if that were done, and a correction to the technique charts
were
> made for the differences in absolute output of different tubes, then
indeed
> all x-ray machines might be able to use exactly the same technique
factors
> for given patients.
>
> Yours,
>
> Robert G. Zamenhof, Ph.D.
> Director, Section of Radiological Physics
> Department of Radiology
> Beth Israel Deaconess Medical Center, Harvard Medical School
> 1 Deaconess Road, Boston, MA 02215, U.S.A.
> Tel: (617) 667-0175  Fax: (617) 975-5233  E-Mail: zamenhof@mit.edu or
> rzamenho@bidmc.harvard.edu
> *** "Non iligitimati carborundum est" ***
>-- End of excerpt from Robert G. Zamenhof