Digital angiography: The implementation of computer technology for cardiovascular imaging

Digital Angiography: Technology Jonathan The Implementation of Computer for Cardiovascular Imaging Tobis, Orhan Nalcioglu, T HERE HAVE BEEN significant improve- ments in computer technology over the past five years that have resulted in dramatic clinical applications of digital angiography.lm3 Although digital angiography was initially developed as a means for obtaining intravenous first-pass angio- grams, it has proven to be most beneficial as an adjunct to invasive cardiac catheterization. One reason for this rapid development is the com- puter’s unique capacities to manipulate images and obtain functional information about blood flow, iodine contrast density, and ventricular performance.4” In the area of cardiovascular diagnosis, digital angiography has been used to obtain left ventriculograms with a lower dose ( I2 mL) of iodinated contrast media than is used during standard film-based angiography. This permits multiple left ventriculograms to be per- formed, which, in turn, facilitates the perfor- mance of interventional studies such as atria1 pacing to assess the functional significance of coronary artery stenosis. During selective coro- nary angiography, digital acquisition of the images has been shown to yield diagnostic infor- mation equal to cineangiography using 35 mm film.’ In addition, the digital format provides immediate access to enhance the coronary images through computer processing techniques such as edge sharpening, contrast amplification, and fourfold image magnification. Computer software programs are also readily applied to facilitate quantitation of coronary lesions either by edge detection or videodensitometric analysis. Computer processing of selective coronary angio- grams has also been used to study the relative appearance time of iodinated contrast as a mea- sure of coronary flow reserve across stenotic vessels.* An exciting application of digital angi- ography has been the development of digital roadmapping, which uses computer processing to provide a continual image of the coronary anat- omy to act as a guide during angioplasty.’ As advances in computer technology improve and the speed of acquisition and storage of data increases, the medical applications of this science will continue to have profound effects. This Progress in Cardiovascular Diseases, Vol XXVIII, No 3 (November/December), and Walter Henry review will describe these recent innovations in the application of computers to cardiovascular imaging. CAPABILITIES Digitization OF DIGITAL PROCESSING Process Computers are typically used to process radio- logic images by transforming the continuous black and white gradations of an x-ray picture into a matrix in which the shade of gray in each small segment of the image is assigned a number that corresponds to the intensity of x-ray absorp- tion in that small image segment.” Instead of recording the x-ray image on radiographic film, the x-rays that penetrate the body and strike the image intensifier are transformed by a television camera into a television image as is commonly performed during fluoroscopy.” Each television frame is created by a rapidly moving electron beam that traces out 512 horizontal lines from the top to the bottom of the image. This television or video image is described as an analog image because there is a continuous change in electric voltage along each horizontal line corresponding to the varying light intensity across the image. Digital image-processing computers take this analog video image and convert it or digitize it into a series of binary numbers that can be utilized by the computer for manipulating the image. Each television frame is digitized by breaking up each of the 512 horizontal lines in the image into 5 12 bins. This process establishes the x--v coordinates of each bin (also referred to as a picture element or pixel) in the new com- puter image. In a 512 x 512 matrix, there are From the Division of Cardiology, University of California, Irvine, Medical Center, IO1 City Dr South, Orange. Calif Supported in part by grants from the American Heart Association, California A@iliate. and by grant No. RO I-HL31440-01 from the National Institutes of Health. Address reprint requests to Jonathan Tobis. MD, Division of Cardiology, University of California. Irvine, Medical Center, 101 City Dr South. Orange CA 92468. d I985 by Grune & Stratton, Inc. pp 195-212