Reducing Dose

Increasing kVp

One simple and convenient method of reducing patient skin dose is to operate using a higher peak x-ray tube voltage, such that a more penetrative x-ray beam is used.

Analysis of the wider implications of using this technique in clinical practice is rather complex however. Everything else being equal, the patient skin dose will decrease, however depth dose in the patient will be relatively greater.

Increasing x-ray beam energy also impacts heavily on image quality for a number of reasons. The x-ray subject contrast of iodinated vessels will be decreased, while contrast loss due to scatter will increase.

Increasing beam energy offers a means of reducing patient entrance dose while maintaining detector entrance dose. However, it must be noted that in clinical operation detector DQE will fall as the x-ray beam energy increases.

Overall these various effects will result in a deterioration in the detail signal-to-noise ratio of iodinated vessels and potentially the clinical acceptability of the images. Obviously such issues are compounded when imaging large patients. This technique is more appropriate for fluoroscopy than serial image acquisition.