Radiology - effects of old xray machinery

Author

effects of old xray machinery

Di@bolo

2004-12-29, 7:09 pm

Hi everybody, today I had a spinal chord xray with a very old xray
machine (maybe 20 years old) and for the first time ever I felt on my
skin when the photos were being shot. I could feel the rays coming
through my skin.

Is it normal? Should I worry?

Thank you

Lucio

Rome

Repeating Rifle

2004-12-29, 7:09 pm

in article jQCAd.587666$35.24864208@news4.tin.it, Di@bolo at xxx@xxx.com
wrote on 12/29/04 10:38 AM:

> Hi everybody, today I had a spinal chord xray with a very old xray
> machine (maybe 20 years old) and for the first time ever I felt on my
> skin when the photos were being shot. I could feel the rays coming
> through my skin.
>
> Is it normal? Should I worry?
>
> Thank you
>
> Lucio
>
> Rome

I am not in the medical field. Nevertheless, I doubt what you say can really
be true. I suppose that it is possible that super gross negligence can cause
a sufficient dose to warm the skin.

There was a machine called a Therac used for *therapy* not imaging. IIRC
that should have been about 20 years ago. It had the capability of using
electrons for direct radiation without first converting the energy into
x-rays. In that case, at unfortunate patient did feel the heating from
electrons being stopped in the skin at much higher level than the machine
was supposed deliver.

I have heard of x-ray horror stories. For example, when an x-ray film is
horribly overexposed, instead of finding the cause, the tech just tries
again and usually just gets another overexposure.

If you are really bothered, ask questions including embarassing ones.

My guess is that 20 year old machines using modern film is about as safe as
new ones. Newer machines may use electronic detection rather than real
silver film. Modern machines are not as likely to be well shielded and would
pose more of a risk to the techs than to the patient. Even if modern
detectors are used, there still is a minimum exposure required to get a good
image.

Bill

Cindy

2004-12-29, 7:09 pm

Di@bolo wrote:

> Hi everybody, today I had a spinal chord

That needs a lot of radiation. The thicker the bones, the more
radiation needed.

xray with a very old xray
> machine (maybe 20 years old) and for the first time ever I felt on my
> skin when the photos

You mean "radiographs" not photographs.

> were being shot. I could feel the rays coming
> through my skin.

I suspect what you felt was heat. X-ray production is really an
inefficient procedure because 99% of energy ends up in heat.

> Is it normal? Should I worry?

Let me copy the 12 x-ray properties off from the text book.

"Through his use of the scientific method, Rontgen found that X-rays:

1. Are highly penetrating, invisible rays which are a form of
electromagnetic radiation.

2. Are electrically neutral and therefore not affected by either
electric or magnetic fields.

3. Can be produced over a wide variety of energies and wavelength
(polyenergetic and heterogeneous).

4. Release very small amounts of heat upon passing through matter.

5. Travel in straight lines.

6. Travel at the speed of light, 3 x 10^8 meters per second in a vacuum.

7. Can ionize matter.

8. Cause fluorescence (the emission of light) of certain crystals.

9. Cannot be focused by a lens.

10. Affect photographic film.

11. Produce chemical and biological changes in matter through
ionization and excitation.

12. Produce secondary and scatter radiation."

end of quote.

Before you worry about the x-ray scanning through your body, you should
worry about the diagnosis of your spinal cord.

Ray Laughton

2004-12-29, 7:09 pm

Di@bolo <xxx@xxx.com> wrote:

> Hi everybody, today I had a spinal chord xray with a very old xray
> machine (maybe 20 years old) and for the first time ever I felt on my
> skin when the photos were being shot. I could feel the rays coming
> through my skin.
>
> Is it normal? Should I worry?
>
> Thank you
>
> Lucio
>
> Rome

You're too tense, take a valium..

ray

2004-12-30, 2:08 am

On Wed, 29 Dec 2004 19:57:24 GMT, Repeating Rifle
<salmonegg@sbcglobal.net> wrote:

>My guess is that 20 year old machines using modern film is about as safe as
>new ones. Newer machines may use electronic detection rather than real
>silver film. Modern machines are not as likely to be well shielded and would
>pose more of a risk to the techs than to the patient. Even if modern
>detectors are used, there still is a minimum exposure required to get a good
>image.
>

I have recent experience with old machines and new ones. Our old
orthopaedic office had machines that dated to 1980 (GE & Raytheon).
The machines passed the state inspection (by a radiation physicist)
every time. There was no leakage from the tube.
Our new machines, 3 year old GE Proteus are film/screen (we are going
to convert to CR soon) and basically the difference was a 2/3
reduction in mAs. This is probably owed to the fact that the old units
were single phase, where the new ones are 3 phase high frequency.
Collimation is tight, and accurate. Again the units have passed
initial and annual state radiologic physicist exams. There is no
leakage from the tube housings.
The new machines are a dream to operate, as they are extremely well
balanced (ceiling mounted tube), tube lock buttons are ergonomically
placed, and the control panels require only a few finger contacts on a
touch screen to set technique instead of pressing buttons, or turning
knobs. BTW we routinely show 0 exposure on film badges.

Repeating Rifle

2004-12-30, 2:08 am

in article 0j07t0tuia2l2c4dmoh82fi9j0oltran4j@4ax.com, ZZ at
nospamfromU@hotmail.com wrote on 12/29/04 8:50 PM:

> On Wed, 29 Dec 2004 19:57:24 GMT, Repeating Rifle
> <salmonegg@sbcglobal.net> wrote:
>
>
First, the "Newer" in the second line above should have been "Older".[vbcol=seagreen]
>
> I have recent experience with old machines and new ones. Our old
> orthopaedic office had machines that dated to 1980 (GE & Raytheon).
> The machines passed the state inspection (by a radiation physicist)
> every time. There was no leakage from the tube.
> Our new machines, 3 year old GE Proteus are film/screen (we are going
> to convert to CR soon) and basically the difference was a 2/3
> reduction in mAs. This is probably owed to the fact that the old units
> were single phase, where the new ones are 3 phase high frequency.
> Collimation is tight, and accurate. Again the units have passed
> initial and annual state radiologic physicist exams. There is no
> leakage from the tube housings.
> The new machines are a dream to operate, as they are extremely well
> balanced (ceiling mounted tube), tube lock buttons are ergonomically
> placed, and the control panels require only a few finger contacts on a
> touch screen to set technique instead of pressing buttons, or turning
> knobs. BTW we routinely show 0 exposure on film badges.

What does "CR" mean?

I do not understand how there can be a reduction of the mAs required for an
exposure unless the x-ray tube itself is more efficient or the detector
whether film, CCD, or other detector is more sensitive.

It makes no sense whatsoever for the conversion from single to three-phase
or frequency of conversion to have any effect on the efficiency of x-ray
production. I do understand, however, how such changes can make the
apparatus smaller.

In the very old days, x-ray tubes may have been driven by unfiltered
rectified a-c. Under those circumstances, the hardness of the x-rays would
vary throughout every half cycle pulse thereby exposing a body to softer
x-rays of little use for imaging.

I would be interested in finding out more about the history of x-ray machine
circuitry. In making high voltage radar devices using vacuum tubes, I have
run into problems with soft x-rays getting generated by high voltage
switching tubes and rectifier tubes. When was use of such old technology
ended?

Bill

Kevin France

2004-12-30, 7:08 am

Repeating Rifle <salmonegg@sbcglobal.net> wrote in
news:BDF8DC3C.2E41D%salmonegg@sbcglobal.net:

> What does "CR" mean?

It usually means "computed radiography," using digital image
receptors rather than conventional film.
>
> I do not understand how there can be a reduction of the mAs
> required for an exposure unless the x-ray tube itself is
> more efficient or the detector whether film, CCD, or other
> detector is more sensitive.
>
> It makes no sense whatsoever for the conversion from single
> to three-phase or frequency of conversion to have any
> effect on the efficiency of x-ray production. I do
> understand, however, how such changes can make the
> apparatus smaller.

The phase and waveform has a great deal to do with x-ray
production. Single-phase has 100% "voltage ripple"--it goes
from no voltage up to 100% voltage and then back down again.
The 3-phase, 6-pulse generator has only 14% ripple...the
voltage going to the tube only varies from 86%-100% of the
total voltage available.

There are even better generators in use. Three-phase, 12-
pulse only has 4% ripple (96%-100% of the total voltage in
use), and high-frequency only varies by 1%.

According to Stewart Bushong's "Radiologic Science for
Technologists" textbook (where I got the above figures):

There are many advantages to x-ray tube voltage generated with
less ripple. The principle advantage is the higher radiation
quantity and quality resulting from the more constant voltage
supplied to the x-ray tube. The radiation quantity is higher
because the efficiency of x-ray production is higher when x-
ray tube voltage is high. Stated differently, for any
projectile electron emitted by the x-ray tube filament, more
x-rays are produced when the electron energy (keV) is high
than when it is low.

He continues:

The radiation quality is increased with low voltage ripple
because there are fewer low-energy projectile electrons
passing from cathode to anode to produce low-energy x-rays.
Consequently, the average x-ray energy is increased over that
resulting fromhigh-voltage ripple modes. (both quotes from p.
118).

> In the very old days, x-ray tubes may have been driven by
> unfiltered rectified a-c. Under those circumstances, the
> hardness of the x-rays would vary throughout every half
> cycle pulse thereby exposing a body to softer x-rays of
> little use for imaging.

That's the problem with the single-phase/pulse machine that's
being corrected by the newer machines, I believe. Since with
this older setup a smaller proportion of the photons coming
out of the tube are of usable energy, you have to increase the
mAs to make more of them (and consequently more of the lower-
energy ones, too) to get a usuable radiograph.

Repeating Rifle

2004-12-30, 10:08 pm

in article Xns95CF32061CDE1kfrance0hotmailcom@64.164.98.7, Kevin France at
kfrance0@removeme.hotmail.com wrote on 12/30/04 4:54 AM:

> Repeating Rifle <salmonegg@sbcglobal.net> wrote in
> news:BDF8DC3C.2E41D%salmonegg@sbcglobal.net:
>
>
> It usually means "computed radiography," using digital image
> receptors rather than conventional film.
>
> The phase and waveform has a great deal to do with x-ray
> production. Single-phase has 100% "voltage ripple"--it goes
> from no voltage up to 100% voltage and then back down again.
> The 3-phase, 6-pulse generator has only 14% ripple...the
> voltage going to the tube only varies from 86%-100% of the
> total voltage available.
>
> There are even better generators in use. Three-phase, 12-
> pulse only has 4% ripple (96%-100% of the total voltage in
> use), and high-frequency only varies by 1%.
>
> According to Stewart Bushong's "Radiologic Science for
> Technologists" textbook (where I got the above figures):
>
> There are many advantages to x-ray tube voltage generated with
> less ripple. The principle advantage is the higher radiation
> quantity and quality resulting from the more constant voltage
> supplied to the x-ray tube. The radiation quantity is higher
> because the efficiency of x-ray production is higher when x-
> ray tube voltage is high. Stated differently, for any
> projectile electron emitted by the x-ray tube filament, more
> x-rays are produced when the electron energy (keV) is high
> than when it is low.
>
> He continues:
>
> The radiation quality is increased with low voltage ripple
> because there are fewer low-energy projectile electrons
> passing from cathode to anode to produce low-energy x-rays.
> Consequently, the average x-ray energy is increased over that
> resulting fromhigh-voltage ripple modes. (both quotes from p.
> 118).
>
>
> That's the problem with the single-phase/pulse machine that's
> being corrected by the newer machines, I believe. Since with
> this older setup a smaller proportion of the photons coming
> out of the tube are of usable energy, you have to increase the
> mAs to make more of them (and consequently more of the lower-
> energy ones, too) to get a usuable radiograph.
>

This, I can understand. I had no idea that unfiltered high voltage ws used
to drive x-ray tubes. When did filtering of high voltage become common
practice?

Another problem I can see, even with filtering is that the filter can store
energy and drive the x-ray tube as the filter capacitor discharges. High
voltage switching can take care of that problem. The high frequency
described in the early post will also minimize the amount of stored
electrical energy required by the filter.

Is there a web tutorial that goes over the high points of modern x-ray
equipment?

About 40 years ago, I designed and built a power supply for driving a carbon
dioxide laser at various pulse widths and repetition rates. At that time,
high power high voltage switching with solid state devices was not
economical. I had to use vacuum tube switches. The vacuum tubes acted as
soft x-ray sources. It was only high repetition rates that gave a serious
problem. It was as the high voltage when stray capacitance was charged and
discharged that there was a combination of relatively hign energy electrons
and current that hit the tubes' plates (anodes). With the switching tube
fully on, there was little voltage across it while with the tube fully off,
there was no current. It was only during the transition when x-rays were
produced.

Bill

Repeating Rifle

2005-01-05, 4:07 am