Understanding the basic concepts of CO2 angiography

The diagnostic quality of carbon dioxide angiography depends both on optimal setting of radiological aspects (X-ray emission and image post-processing) and on the mechanical behavior of the injected gas bubbles. The gas behavior differs in large cavities (d>12 mm), medium sized vessels (d>6 mm), and small diameter vessels (d<6mm): to optimize the result the operator has to adapt his action to the physical rules governing the phenomenon in the particular situation. In most cases, it is impossible to fill a vessel completely with gas, and to obtain an adequate angiogram, the gas volume and injection pressure must be properly selected, patient’s position must be adjusted and radiological image optimization algorithms, like Digital Subtraction Angiography (DSA) and stacking, must be applied. In this optimization process, the cultural and practical intervention of a medical physicist is fundamental. Obtaining a good quality CO2 angiogram is not only a matter of medical operator experience or radiological system performance, but involves matching a wide knowledge of medical physics to particular pathophysiological conditions and to unusual measurement tests. Most medical physicists are used to dealing mainly with radiological problems, and other physical aspects are considered beyond their interest. In CO2 angiography, non-radiological aspects strongly interfere with radiological issues and an optimal result can only be obtained by tackling the two simultaneously.