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X-RAY TECHNICAL PROBLEMS

Generally we realize that we have a problem in radiology because our film results are not what we expected.  Determining the cause is not so simple because there are various factors to obtaining an acceptable film.  We need a good source of radiation that is consistent and linear from ma station to ma station.  We need an acceptable screen film combination with suitable cassettes that are new enough to enjoy good screen film contact coupled with screens of a sufficient quality to provide an acceptable level of detail (some imported screens have very poor inherent detail, but they are cheap to buy).   Finally we need a darkroom room and processing facility that ensures routine quality processing.  The darkroom must be light tight, shielded from scatter radiation, and use a safelight that does not fog your film (not all "safelights" are safe...sounds like a good title for an article).  Of all of the above, most of the complaints relating to film quality come from processing.  Chemistry must be maintained fresh and at the proper temperature and concentration.  Routine processor cleaning is essential. 

Before you try to establish a technique chart or try to solve a processing problem for your facility it is important to do the following:

1.    Have your x-ray machine completely calibrated by your x-ray service company.  It is important that kV and mR output be linear and as accurate as possible.

2.  Have your film processor cleaned and loaded with fresh chemistry.  Use developer starter in the upper developer tank as denoted by the chemical supplier.

Problem:  "We have to take several films before we get an "acceptable" one."  Maybe this is our most common complaint.  This can obviously be caused by a malfunctioning x-ray machine or one that is out of calibration;  however it can also be caused by many other factors, including mixed cassettes or film types or other forms of "pilot error".  USUALLY THE X-RAY MACHINE ITSELF IS NOT THE PROBLEM!  The cumulative errors in processing can exceed the allowable variance and accuracy of a modern x-ray.  "Modern" x-ray machines are designed with the extensive use of digital electronics.  An MR meter can verify the radiation output of the x-ray machine.  But, having said that, a calibrated x-ray no more guarantees acceptable images than a well tuned race car guarantees winning a race...but it helps!   I once drove several hundred miles to a facility that convinced us they had an x-ray problem and their only problem was using three different brands (and therefore speeds) of film (yes, I had asked but was assured they always used the same film).  This turned into a rather expensive lesson.  The different types of film were unnoticed in the darkroom but certainly caused a lack of consistency on the results.  This type of problem is more common that you would imagine, so before you call for service verify that the cassettes and screens and film are exactly the same.  Another facility had 3 technique charts posted and different technicians used different techniques.  The results varied.  Finally, make sure that your processor is working correctly and heating the developer to the desired temperature (approximately 95 degrees F or whatever your processor service suggests).  Temperature is generally determined by the chemical maker and not the film processor manufacturer although 95F generally works for clinical processors and chemistry made by Simon, White Mountain, Kodak and DuPont.   Do not attempt to use 3M manual chemistry (or anyone's manual chemistry for dip tanks for that matter) in an automatic film processor.  Neither you or the processor will like the results. Processing varies considerably during the general 3 to 4 week cycle of servicing.  Densities will be much darker with fresh chemistry in the upper (processing) tank than 2 or 3 weeks later.   You may have to increase Mas by from 25% to 100 % to compensate for depleted chemistry.

Problem:    "Our x-ray machine is not working because when we take a film it comes out clear".  This is a typical opening comment which we hear on a typical service phone call.  Generally the problem is 80% darkroom (depleted developer) and no more than 20% real x-ray failures.  As easy way to tell if your tube is generating x-rays is to open a cassette on the table, adjust the collimator so that the beam covers a screen and turn out the room lights.  Stand where you can observe the screen and make an exposure of 20 mAs (100ma at .2 sec) and 80 kV.  This will test your small focus filament.   Your screen will phosphoresce a blue or green light upon exposure if your tube is generating x-rays.  Duplicate the procedure on the 200ma or 300ma (large focus).   If the screen illuminates your x-ray is working.  If one works and the other does not, you may have a defective tube or a bad high tension cable.  Contact your x-ray service department for further analysis.  If your x-ray is firing, then the imaging problem is elsewhere and probably can be traced to the darkroom. (Using the above technique also precludes the embarrassing situation of calling for service when one of the staff accidentally left the collimator shutters closed).

Problem:  "Our x-ray machine is producing too much scatter"When I asked the technologist why they believed this to be the case, the response was that when collimating down they could see some image beyond the collimator shutters.  The "problem" was getting worse.  In reality this is exactly what we would expect from scatter radiation.  It is a function of the patient and technique not the tube and generator.  Some fast screen film combinations are more sensitive and will also show the effects of scatter more readily than a slow combination. To eliminate such effects, always use a lead rubber divider to split a view on a film;  never use the collimator alone.  In addition wear aprons and gloves if working at the table (this is general procedure for veterinary use) if you cannot be behind the barrier.

Problem:  "Our x-ray machine will not fire on any ma setting".  When I asked if they had a bucky (everyone always answers yes whether a true bucky as opposed to a grid cabinet exists or not) and was the bucky switch ON or OFF, the response was "the bucky is on".  Realizing the facility was a veterinary hospital and that they did not have a bucky but indeed had a grid cabinet, I suggested they turn the switch to OFF and try again.  The system works fine.  Some installers will remember to jumper out he bucky switch with grid cabinets when possible.  Some systems cannot be jumped and so the switch must be left in the BUCKY OFF position for the x-ray to expose.

Problem:  "Our x-ray machine fires intermittently". Most of the time it is fine but occasionally we get a clear film."  Indeed this can be a problem with the x-ray and require a service call.  Often, however, there is nothing wrong with the x-ray, but a misunderstanding of how the footswitch and exposure system function.  Footswitches are designed to press and hold while they expose.   If a tech momentarily attempts to make an exposure, the circuitry will prevent an exposure.  This is by design.  A simple test is to open a cassette under an open collimator with the collimator light off and the room lights out so that a dim room is presented.  Actual x-rays will cause the screen to phosphoresce and put out a light during the exposure.  By using the tip of the footswitch and holding the switch closed, you can verify that the x-ray indeed is working correctly.  If it still misfires with the footswitch totally compressed, then a service call is in order.  We have a moderately high percentage of these calls where we cannot find anything wrong with the x-ray.  With service rates in excess of $150 per hour (and much higher in certain areas), we believe it is worth the time to investigate before you call for a technician. This problem can also be caused by corroded wire terminals or loose connections, but are generally repeatable and would probably show using the above footswitch test.

Problem:  "Our collimator shutters will not open to allow full coverage of a 14 x 17 film."  Generally this would be a collimator problem, but we had a recent service call where our service technician found the tube had been lowered to approximately a 24" SID instead of the usual 40" SID.  Raising the tube solved the problem.   (This is really too basic to teach and shouldn't deserve comment). I bet they saw some grid cutoff too. Incidentally, SID is measured from the focal spot of the tube (not the exit port face plate) to the film plane (cassette).  Forty inches is typically used because most of the fixed grids are focused at 40".  Accordingly the collimators are generally calibrated at 40".  You could decide to use 36" and due to the inverse square law, the effective power of your 300ma x-ray would be increased almost 20%.  This is derived from the ratio of 40" squared (1600) to 36" squared (1296).

Last updated 12/03/08 

Last Updated 3/03/2014

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