A new test object for evaluating resolu- tion in serial angiography.

Abstract

Recent advances have led to increasing emphasis on angiography of vessels 0.3 mm or less in diameter (1–3). Unfortunately, there are many problems peculiar to roentgenography of small objects; e.g., vessels appear as much as 0.4 mm larger than their true size in conventional angiography and may be distorted in shape (4, 5). Roentgenographic interpretation is complicated by these effects, so their quantitative evaluation isof clinical importance. In our studies we developed test “vessels” of calibrated sizes, filled with typical contrast media such as Renografin-60. These devices have been used in three ways: to compare potential resolution of alternative technics, to verify resolution actually achieved in practice; and to study distortion effects. Because the preparation of these test objects presented several unexpected problems, we shall discuss their design and construction in some detail. I. Basic Design Considerations Because of considerable scatter in abdominal and cerebral angiographic studies, we simulated tissue with water in plastic tanks (Fig. 1). The test objects consisted of Renografin-60-filled tubes in paraffin blocks. A. Test Object Materials: In conventional and enlargement angiography, the photon spectra of the exit beams range roughly from 33–85 and :33–110 keV, respectively. This consideration dominates the choice of test object materials. For an accurate simulation of the true situation, we used a conventional radiographic contrast agent: Renografin-60. This is a 60 per cent aqueous solution of an iodinated methylglucaminc derivative with chemical stabilizers. Its x-ray attenuation contrast in tissue is essentially the same as that of 0.29 g iodine element per milliliter solution in water since its other chemical elements are essentially water-equivalent in the energy range involved. Other materials considered were inorganic aqueous solutions and metal wires. Most inorganic iodine or barium compounds have limited solubility, as well as other disadvantages. Salts are also generally low in solubility, except for barium iodide which is soluble but costly. Metal wires offer obvious fabrication advantages. However, they match the attenuation of 0.3 g of iodine/ml poorly for both density and atomic number reasons (Fig. 2); hence, they were excluded in this rather demanding application. We excluded various plastic and rubber tissue substitutes for practical reasons, although such materials could be considered as possible alternatives in future developments. It is evident from Figure 2, however, that the substitution of paraffin for water does not significantly alter Renografin-60 subject contrast in the photon range of major interest (above 33 keV).