Optimization of kVp and mAs in contrast and non-contrast CT examinations

JF. Paul

 

Introduction

Lowering radiation exposure during CT examinations increases image noise, with the risk that image quality may be insufficient for diagnostic purposes. A trade-off is necessary between radiation dose reduction and image quality preservation. For any CT scanner, radiation output depends on both the tube current–time product (mAs) and the kilovoltage peak (kVp). In clinical routine, these parameters are often left constant according to a standard protocol. The radiation dose delivered to each patient should ideally be optimized, but how to adapt both kVp and mAs for each patient is not simple. Fortunately, some recent studies and new technical advances can help us choose the best combination (kVp–mAs pair).

Radiation dose decreases linearly with a decrease in mAs and by a power function with a decrease in kVp (approximately kVp2). Appropriate selection of the best values for both these variables is thus crucial, especially in children, but only recently has this topic been studied (e.g. [1]). Optimization of the scanning protocol also requires that the radiologist understand the technical issues involved.

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