CrossOvers, What's the Correct Procedure
Users may need instructions for performing a crossover. Radiologists, radiologist technicians, and physicists should all know how to do this. No manufacturer is able to produce all batches of film with exactly the same speed, contrast, D-Max, Base+Fog, etc. From one batch to the next there will typically be some small shifts in the emulsion's reaction to exposure and processing. A crossover is performed to identify and compensate for these small inconsistencies. The Fall issue (1998) of "Mammography Matters" (Volume 5, Issue 4), includes a concise article by Orhan H. Suleiman, Ph.D., Chief Radiation Programs Branch, Division of Mammography Quality and Radiation Programs. In brief, Dr. Suleiman reminds us that crossovers are NOT performed to solve processor problems; rather the processor must be in control before a crossover is performed. Take a few minutes to visit the link and download a copy of this paper.Begin the procedure by preparing a set of films as follows:1. Expose and process 5 old and 5 new films on the same day.For Example:2. Select a channel not normally used for daily processing.
3. Read the first (1st) film from the older emulsion.
4. Record the calculated Base+Fog, Speed Index, and Contrast Index.
5. Repeat with the remaining four (4) films.
6. Manually average the recorded values.
| Film # | Base+Fog | S. Index | C. Index (Old Film Emulsion) |
| 1 | 0.19 | 1.27 | 3.22 |
| 2 | 0.20 | 1.29 | 3.18 |
| 3 | 0.19 | 1.26 | 3.24 |
| 4 | 0.18 | 1.28 | 3.17 |
| 5 | 0.20 | 1.26 | 3.17 |
| Avg | 0.19 | 1.27 | 3.20 |
7. Repeat steps 3 through 6 with the newer emulsion.For Example:
| Film # | Base+Fog | S. Index | C. Index (New Film Emulsion) |
| 1 | 0.21 | 1.31 | 3.31 |
| 2 | 0.21 | 1.33 | 3.29 |
| 3 | 0.22 | 1.35 | 3.27 |
| 4 | 0.20 | 1.33 | 3.30 |
| 5 | 0.21 | 1.34 | 3.25 |
| Avg | 0.21 | 1.33 | 3.28 |
8. For the Base+Fog, Speed and Contrast Indices, subtract the Old from the New and record the differences.9. Select the channel which is being modified.
10. Replace the AUTO Aims with MANUAL Aims for Base+Fog, Speed, and Contrast.
New Aim = Old Aim + (New Average - Old Average)
Base+Fog = Old Aim + (0.19 - 0.21)
S. Index = Old Aim + (1.33 - 1.27)
C. Index = Old Aim + (3.28 - 3.20)
