Radiographic Technique

1. 15% rule: If you increase the Kvp by 15% you must reduce the mAs by 50% to retain isodensity. With a 15% decrease in KvP you must double the mAs.

2. 100 mA or less = small focal spot. Greater than 100 mA = large focal spot.

3. If you are using a moving grid, you will require an exposure time greater than .1 sec.

4. During breathing cycle studies use times greater than 1 full second.

5. Distance has no effect on KvP.

6. Regarding mAs:

1. Increase distance from 40 to 60 = double the mAs needed.

2. Increase from 40 to 72 = 3.3 times the original mAs needed.

7. Longer distances:

1. Decrease magnification

2. Decrease patient dose

3. Increase time of exposure

Category: Radiology Notes