QUALITY ASSURANCE IN RADIOGRAPHY WITH EMPHASIS ON LIGHT FIELD X-RAY BEAM ALIGNMENT
Quality Assurance in Radiography with emphasis on light beam/X-ray beam alignment was carried out on X-ray machines of five different hospitals (coded: H1, H2, H3, H4 and H5) in Jos North Local government area of Plateau State, Nigeria. This test was carried out using eight coins having known positions in the collimator light field, two light fields were considered of area 12.5 cm x 12.5 cm and 22.5 cm x 17.5 cm to represent smaller and larger image sizes respectively. The total misalignment, the sum of the vertical and horizontal values were: 2.0, 2.4, 1.0, 3.0 and 1.8 cm for the 22.5 cm x 17.5 cm collimator light field size and 2.1, 2.3, 0.8,2.5 and 1.7 cm for 12.5 cm x 12.5 cm collimator light field size corresponding to H1, H2, H3, H4, and H5 respectively. All the X-ray machines of the five selected hospitals showed satisfactory compliance of X-ray beam / Light field congruency test. However, it was found that significant differences in total misalignment of collimation of the X-ray machines in H3 and H4 between the smaller and the larger image sizes and hence need for collimator adjustment. This shows that the collimator light field is to allow simulation and visualization of the size, shape, and location of the X-ray field and it is important that the light field be approximately congruent to the X-ray field.