Quinnipiac University Diagnostic ImagingRS 240L Lab #3

Radiographic Density- Manipulating mA and Exposure Time

Name: Karen Finn

Objective: To demonstrate the effects of various exposure factors on radiographic density.

Equipment Used

The equipment that was used during this lab was the portable x-ray, a phantom elbow, a 14 by 17 Konica CR plate (100 RSI image receptor), AL step wedge, and the dark room, which included the processor with the feed tray.

Procedure: The first step in this lab was to place the extremity cassette on the x-ray table. Then the elbow phantom was placed on the cassette. Next, the AL step wedge was placed perpendicular to the elbow phantom and the SID was set to 40 inches. The central ray was properly centered to the phantom and the elbow was collimated. 58 kVp and 6.3 mAs were set for the technical factors. The film was then exposed and the film was labeled as image 1. Next another radiograph was taken but the technical factors were set as 58 kVp and 12 mAs. The film was then exposed and the film was labeled as image 2. Radiograph number three was taken with the kVp adjusted to compensate for the increase in mA, which provided a comparable density to the first image. For radiograph 3, the kVp was set to 47 and the mAs was kept at 12. The film was then exposed and the film was labeled as image 3.

Results / Discussion / Questions

1. Radiograph 1 and 3 look similar because in order to maintain density if the mAs is doubled the kVp is decreased by 15%, which was done for radiograph 3 so they look similar. Radiograph 2 is denser because the mAs was doubled but the kVp remained the same so it was denser than radiograph 1 and 3.

2. Radiograph 1 and 3 looked similar in density. Radiograph 2 was denser because the mAs was doubled but the kVp remained the same. This is because as mAs is increased then the radiographic density on the film is increased/darker.

3. As mA is increased the density is increased. If the mA is doubled in order to maintain density, the exposure time should be deceased by 15%. As mA is doubled, the number of electrons able to cross the tube also doubles so the exposure time needs to be reduced. Increasing kVp will cause an increase in the speed and energy of the electrons applied across the x-ray tube. Therefore, the penetrability of the photon increases, as does the quantity (the intensity, # of photons, the density) and also gives a decreased contrast.

4. In order to maintain density, if the mA is doubled then the kVp should decrease 15%.

5. If the mA remains the same and the exposure time is increased the radiographic density will increase. If exposure time remains the same and mA is halved then the film will be lighter.

6. The step wedge was placed perpendicular to the elbow phantom due to the geometry of the angled anode target, the radiation intensity is greater on the cathode side.