Compensating collimator for digital subtraction angiography.

Adequate visualization of vascular structures in digital subtraction angiography requires that the radiographic density across the field of interest be as uniform as possible. Only in this way can the total image be recorded without exceeding the dynamic range of the camera system. In practice, both careful collimation of the primary beam as well as the addition of considerable bolus material around the patient, particularly in the neck area, have been required to achieve reasonably uniform transmission. We recently installed a digital system on an angiographic C-arm that has the disadvantage of having an iris-type collimator. This caused particular trouble when imaging the neck because of the required field size and shape. Digitally controlled beam attenuators are under development but are not yet commercially available [1 ]. We have had considerable success in using the collimator as pictured in figure 1 A.