Question

Is the visual appearance of an image a reliable indicator of overexposure? Why/why not ? How could this negatively affect the patient?

-How images suffer from a loss of diagnostic quality due to excessive exposure? Explain.

(Radiologic question)

Answer 1

Solution:

Yes, the visual appearance of an image is a reliable indicator of overexposure when using conventional film-screen radiography technique. The noise level in the film-screen radiography is determined primarily by the receptor sensitivity (or speed). That is determined by the design characteristics of the intensifying screens and film used.
When using a film-screen receptor the exposure must be set to match the sensitivity of the receptor or the results will be either and underexposed (light film) or overexposed (dark film) image. Therefore, all acceptable films, from an exposure and contrast perspective, will be produced with a receptor exposure that is determined by the sensitivity characteristic of the receptor. The noise level can only be changed by changing the receptor, typically by changing the film to one with a different sensitivity (speed).

In film-screen radiography it is important that appropriate exposure and technique factors be used for imaging process. An optimum (correct) exposure is one that produces an image with an acceptable noise level without unnecessary or excessive exposure to the patient. In radiographic systems display, along with the image, and indication of the amount of exposure used to form the image. The sensitivity, "S" factor is used to indicate the effect sensitivity (speed) used by the system for that specific image. A high S factor (=1000) indicated the image was formed with a low exposure and excessive noise would be expected. A low S factor (=50) indicates and unnecessarily high exposure of radiation to the patient was used. The image quality is good because of the low noise but the patient was subjected to unnecessary exposure and this is a negative effect to the patient.

Images suffer from a loss of diagnostic quality due to excessive exposure because of low sensitivity of the receptor and high quantum noise. Radiographs recorded on film with deviation from the optimum exposure resulted in under-exposed (light) or over exposed (dark) films.