Automatic Exposure Control in CT
AEC is analogous to acquisition timing in general radiography. The user determines the image quality requirements (as regards noise or the contrast-to-noise ratio), and the CT system determines the right tube current–time product. In practice, Automatic Exposure Control in CT is relatively straightforward for the system to deliver the desired image quality, once that has been defined. However, Automatic Exposure Control in CT can be quite difficult to achieve agreement on the image quality requirement for the various CT examination types and patient age groups.
In defining the required image quality, the user needs to remember that pretty pictures are not needed for all diagnostic tasks, but, rather, a choice can be made between low noise and a low dose, depending on the diagnostic task. The CT system will then adjust the tube current during the gantry rotation, during movement along the z-axis, or during movement in all three dimensions, according to the patient’s body habitus and the user’s image quality requirements. Thus, we differentiate between the modulation of the tube current to achieve a defined image quality, and the prescription of the desired image quality by the user. Together these tasks are referred to as Automatic Exposure Control in CT .
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