Under the regulations can the “added” test object used to perform the image contrast test be placed in positions other than on top of the phantom?
It is the intent of the regulation that the test object be placed on top of the phantom in a consistent, and if possible, permanent location in the image area. Consistency in positioning the added test object is necessary to achieve a meaningful operating level density difference between the background of the phantom and the added test object that must not vary by more than +/- 0.05 OD of the established operating level. However, the position of the test object is not specified in the regulations. If a facility believes it beneficial to place the "added" test object in a different position (e.g., adjacent to the phantom), it will have to assure consistent positioning of the "added" test object, as well as provide the additional x-ray attenuation needed to give a background OD equal to that of the phantom.