A wide range of patient exposure occurs in diagnostic radiology. For example, the entrance skin exposure (ESE) for an x-ray of a hand is only a few mR; however, ESE’s in fluoroscopy may be several thousand mR. This wide range of exposures is expected and hardly surprising. What is surprising is that even for the same routine procedure and for the same average size adult, exposures may vary substantially between healing arts facilities throughout the United States.
As an example, for an AP Abdomen of a 23 cm. adult, ESE’s range from 21 mR to 2575 mR with a average value of 366 mR! Some of the variation can be attributed to a difference in the clinical criteria of what is considered an acceptable film image by the medical professional reviewing the x-ray film. This criteria will effect the decision on what film imaging system is used and what technique factors are employed for a particular procedure. However, another contributing factor in the observed variation in patient exposure can be attributed to the use of sub optimal imaging equipment, poor choice of technique factors and/or incorrect film processing procedures.
Factors Affecting ESE
ESE is affected by kVp, voltage wave form, total filtration, mAs, source to image receptor distance (SID), patient thickness, relative speed of the film/screen, processing parameters and individual preferences of the Medical professional. However, from a practical point of view, there are essentially three things a facility can do to substantially reduce patient exposure in routine diagnostic x-ray procedures. They are:
- make sure processing is done according to film manufacturer’s recommendations;
- use the highest available kVp; and,
- use the fastest film/screen procedures system consistent with clinical objectives.
Steps to Reduce ESE
If, in your facility’s opinion, the ESE to your patients is excessive and you would like to reduce it, then:
- Review Film Image Quality: Can you increase the kVp by 8 to 10 units and/or choose a smaller mAs (make the overall film density lighter)? Do you need to use a grid? Is the grid ratio appropriate?
- Review Film Processing Procedures: If your facility is routinely "under processing" films, you are having to choose technique factors that require larger ESE to obtain images of acceptable film density. "Under processing" can occur because of low developer temperature, too short a development time, or improper replenishment rates. Ask your service representative or film supplier to check this out. Review the elements of your processor quality assurance program.
- Evaluate the Imaging System: How does the relative speed index of your film/screen system compare with other systems that are currently available? If your screens are old and worn, consider replacing them with a faster screen. Sometimes, you can increase the relative speed of the film/screen system simply by choosing another film. Talk to your film supplier.