Reference Information for Facilities - the STEP Test
The following guidance is designed to help a facility or a group of facilities set up a processor performance testing process similar to FDA’s STEP test. Facilities may use this procedure to check whether they are consistently processing their mammography film according to the manufacturer’s recommendations.
Identification of a Standard Reference Film Processor
First, a processor must be identified which is known to be operating according to the film manufacturer's recommendations. The local film representative may be able to assist in the identification of such a processor.
Sensitometer, Densitometer and Film
Since there currently is no national standard for light sensitometry, any 21-step commercial light sensitometer is adequate. The film used for the test should be the same film used clinically for mammography. The comparison between the Standard Reference Film Processor and the tested processor should use the same sensitometer, densitometer and the same test film obtained from the same box.
To calculate processing speed, determine the speed density. Speed density is the density equal to the base plus fog density plus 1.00. A sensitometric step number (speed step) corresponding to the speed density is interpolated from the sensitometric curve of the film.
Processing Speed is then calculated using the following formula:
Processing Speed = 100 x 10(Sr – So) x 0.15
Speed density = 1.0 + (B+F)
S = speed step, the sensitometer step number corresponding to the speed density,
So = Observed speed step for the tested processor, and
Sr = Reference speed step when the film is processed according to the film manufacturer's recommendations.
If there is no difference between So and Sr, then the processing speed is 100 for standard processing. Extended cycle processing speed is measured relative to standard cycle processing, and the appropriate processing speed is in the 130 – 140 range. STEP action limits are based on a 20% difference in processing speed, and corresponds to a nominal 2.2 degree Celsius (4.0 degree Fahrenheit) developer temperature difference. For a more detailed discussion, please refer to the article by Suleiman et. al., "Automatic Film Processing: Analysis of 9 Years of Observations" (Radiology 1992; 185:25-28).
If you follow the guidance above and you don’t see an improvement, contact your medical physicist or FDA’s Facility Hotline (1-800-838-7715) for further assistance.