16.6 Angiography and Digital Subtraction Angiography
One important problem in diagnostic radiology is to image portions of the vascular tree. Angiography can confirm the existence of and locate narrowing (stenosis), weakening and bulging of the vessel wall (aneurysm), congenital malformationsof vessels, and the like. This is done by injecting a contrast material containing iodine into an artery. If the images are recorded digitally, it is possible to subtract one without the contrast medium from one with contrast and see the vessels more clearly (Fig. 16.23).
|Figure 16.23 in Intermediate Physics for Medicine and Biology. Digital subtraction angiography. (a) Brain image with contrast material. (b) Image without contrast material. (c) The difference image. Anterior view of the right internal carotid artery. Photograph courtesy of Richard Geise, Department of Radiology, University of Minnesota.|
Within weeks of Roentgen’s discovery of the x-ray in 1895, Haschek and Lindenthal performed post-mortem arteriography in a hand. For the next 60 years, radiology in general and angiography in particular were largely limited to using film as a means for permanent recording of x-ray images. Recently, new technical developments in television, digital electronics, and image intensifier design have improved the electronic recording of images, and have caused renewed interest in the techniques of intravenous angiocardiography and arteriography originally described by Castellanos et al. [and] Robb and Steinberg.
Prior to 1970, applications involving the subtraction of unprocessed video information stored on analog discs or tape were common. These methods were adequate for augmentation of arterial injection techniques but were not sensitive enough to be used in conjunction with intravenous injection of contrast media. However, techniques capable of imaging the small contrast levels produced after an intravenous injection of contrast media were reported by Ort et al. and Kelcz et al. In combination with analog storage devices, these investigators used both time and K-edge energy subtraction methods for iodine imaging. In spite of their greater sensitivity, the poor reliability of those analog systems made them unsuitable for clinical use and lead to the design of the University of Wisconsin digital video image processor. Over the next five years, this processor was used by a number of investigators for a variety of energy and time subtraction studies both in animals and humans…
Mistretta is now professor emeritus in the Department of Radiology at the University of Wisconsin, where he has been doing medical imaging research since 1971. Students will benefit from his advice for young medical physicists presented in a spotlight article from the University of Wisconsin.
Choose a career and position that you enjoy and that you are eager to go to every day. Pick a career that makes a difference in the world and hopefully helps people. When you get old some day and start becoming aware of your mortality, it really helps to look back and say “I did my best and I helped make the world a little better place”. As medical physicists we have an excellent chance of making this come true.
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