Objective: To assure the X-ray field is aligned with the light field produced by the light and mirror in the collimator assembly.
Field alignment test tool
24 X 30 cm cassette
lead letters A, C, F (anode, cathode and front)
- Position the X ray tube 100 cm from the cassette on the table top.
- Place the test tool and lead letters on the cassette. Align the central ray with the middle of the test tool.
3. Pre-expose the entire cassette using 50 kV and 1 mAs with the test tool in place (this will allow for the entire shadow of the tool to be seen)
4. Adjust the collimation to line up with the rectangle in the middle of the tool.
5. Take another exposure with the same technical factors used above.
6. Process and evaluate your results.
- 1. What are the recommendations in SC 35 for accuracy of light/X-ray field alignment? (include the section number in your response)
SC 35 p. 25 (2.5.2 # 9) Radiation Field and Light Field Alignment–The beam limiting device must incorporate an X-ray field indicator which uses light to visually define the X-ray field so that the limits of the X-ray field are visible under the ambient lighting condition in an X-ray room. When the X-ray beam axis is perpendicular to the image receptor plane, the separation between the perimeter of the visually defined field and that of the X-ray field does not exceed 2% of the focal spot to image receptor distance.
- 2. Is the x-ray field and light field you tested congruent? (explain)
A IR is placed perpendicular to the beam central axis at the Isocenter and test tool on top of that. The difference between the edges of the light and radiation fields checked on monitor. The size of the radiation field is compared to the light field size. I wanted to find possible movement of the light source of collimator. By visual examination I found that light filed and radiation field are congruent to within 2% of the SID, and over time the mirror end other mechanism did not have improper performance.
- 3. Does this equipment meet the SC35 standards?
The equipment meets the SC35 standards, because according to SC35,: “When the X-ray beam axis is perpendicular to the image receptor plane, the separation between the perimeter of the visually defined field and that of the X-ray field does not exceed 2% of the focal spot to image receptor distance.”