Digital subtraction angiography: principles and pitfalls of image improvement techniques

Abstract

Since the original digital subtraction angiography (DSA) systems were introduced in the late 1970s, some important advances in imaging technology have occurred. As a result, a variety of methods of improving DSA quality have been either proposed or implemented. This has created some confusion among radiologists who must make decisions regarding purchase and use of such systems, but who generally lack the physics or engineering background needed to properly evaluate them. Perhaps as a result, one can note that many recent publications on DSA fail to describe the technical factors or equipment specifications used in performing procedures, even though the very purpose of these studies is to assess the efficacy of DSA as an imaging method.First, we will review some of the basic principles applicable to all television (TV) and DSA imaging techniques; second, we will discuss the various methods of improving image quality (some already established, others under development) and point out some of their associated pitfalls. These image improvement methods include frame integration, sequential video scanning, video camera modifications, the use of larger image intensifiers and matrices, reregistration, hybrid subtraction, recursive filtration, matched filtration, DSA tomography, and edge enhancement. The discussion will primarily emphasize acquisition and processing of serial-mode images at 1-10 frames/sec, the type of imaging generally used by radiologists for noncardiac applications. Image storage technology will not be addressed here, nor will cardiac imaging, which is often performed at real-time frame rates (30 frames/ sec) and presents a somewhat different set of problems. Basic PrinciplesThe front-end components for video fluoroscopy include the x-ray tube,

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