If Automatic Exposure Control (AEC) is used at an SID of 72" instead of 40", what will the outcome be for the image?

When Automatic Exposure Control (AEC) is used, the system measures the amount of radiation passing through the patient to determine the appropriate time for exposure. The important factor to consider in the change of source-to-image distance (SID) from 40 inches to 72 inches is how it affects the intensity of the X-ray beam reaching the image receptor.

As the distance from the X-ray source to the image receptor increases, the intensity of the radiation decreases according to the inverse square law. This means that at a greater distance, the amount of radiation hitting the detector is less, which could lead to underexposure if the AEC is not adjusted or properly compensatory factors are not considered.

However, in this scenario, when AEC is used effectively at a longer SID, the system detects the lower intensity of radiation and compensates by extending the exposure time to achieve the necessary dose to produce a properly exposed image. Therefore, the automatic adjustment mechanism of AEC enables it to provide the correct exposure even at the increased distance.

This compensation capability means that the image taken at the 72-inch SID would remain properly exposed, as the AEC adapts to ensure that the total exposure is appropriate despite the increased distance from the source.