In the analog screen-film detector paradigm, the fixed speed of the detector requires that the exposure be correct, otherwise the response of the film optical density in the processed image is either too light (underexposure) or too dark (overexposure). A phenomenon known as 'dose creep' can occur based on the visible negative impact that underexposure can have on image appearance, and lack of perceived negative impact when the patient is overexposed but with beautiful electronic images. In some cases, a three to five times overexposure or more can happen, without any complaints from anyone. Unfortunately, the patient in this situation has received needless radiation exposure, often without the knowledge of anyone involved in the acquisition or reading of the case. Except for extreme overexposures, images that are produced are usually of excellent radiographic quality with high contrast resolution sensitivity and low quantum mottle, due to the ability of the digital detector system to rescale the high signals to a grayscale range optimized for viewing on a soft copy monitor or hard copy film.

At least in this situation the underexposure is easy to recognize based upon the appearance of the image.Ī more problematic situation occurs with detector overexposure caused by inappropriately high radiographic technique factors, resulting in needless patient dose. This causes the low contrast resolution sensitivity to be compromised, and often necessitates a retake. If the detector is underexposed due to inadequate radiographic technique factors, even though the image can be amplified and rescaled to present a good grayscale rendition, the quantum mottle in the image is likewise amplified, resulting in a noisy and grainy image. An 'appropriate' patient dose is that required to provide a resultant image of 'acceptable' image quality necessary to confidently make an accurate differential diagnosis. The wide exposure latitude of digital radiography devices can result in a wide range of patient doses, from extremely low to extremely high.

Predicting Bone Fracture in Metastatic Breast Cancer Lesions.

Cerebral Blood Perfusion Studies on Rats.Technique: Current Exposure Time Product (mAs).University Radiology Associates (Physicians' Private Practice).

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