Evaluation of a digital subtraction angiography unit

The operating characteristics of a digital subtraction angiography unit were evaluated. Measurements included image intensifier and system linearity, uniformity, quantum and system noise, and iodine contrast. Various approaches to noise measurement were analyzed and tested, leading to the following conclusions: the video level should be maximized; changes in signal-to-noise ratio (SNR) due to changes in x-ray exposure do not necessarily reflect changes in quantum SNR alone, due to dependence of video levels on x-ray exposure; an understanding of the separate contributions of quantum and video SNRs to the total SNR guides proper selection of variables to minimize patient dose and x-ray tube heat loading.