Final answer:
Option A). Conversion from film-screen to CR often involves increasing kVp and adjusting mAs to maintain image quality. Option 1 (4 mAs, 80 kVp) is most likely to correctly convert the technique for CR, while the appropriateness of Option 3 (8 mAs, 70 kVp) is dependent on the CR system's specifications.
Step-by-step explanation:
Adjustments are usually necessary to account for variations in the sensitivities of the film-screen and digital systems when converting the X-ray technique parameters for a knee taken at 4 mAs, 70 kVp using a 400 speed film-screen system to computed radiography (CR). The general idea is to minimize the radiation exposure of the patient while maintaining the same density (brightness) and contrast, although there isn't a conversion formula that is universally accepted.
Option 1 proposes raising the kVp to 80 while keeping the mAs constant, which would typically lead to a lower patient dosage and a faster system. In order to preserve image quality at the same kVp, Option 3 proposes doubling the mAs, which might theoretically make up for the CR system's varying sensitivity. Option 2 entails decreasing the kVp as well as raising the mAs, which may have an impact on the image's contrast that isn't comparable to the film-screen system.
Therefore, out of the options provided, Option 1 is most likely to be correct, but the appropriateness of Option 3 would depend on the specific CR system's sensitivity.