Contrast media tonicity. Part I. Effects upon IV-DSA time-concentration curve peak and width: experimental studies

Prior to the formation of an intravenous digital subtraction angiography (IV-DSA) image, contrast medium passes through the lesser circulation and is diluted by the blood volume of the heart and lungs. If the contrast medium alone influences central blood volume or cardiac output, the shape of the resultant time-concentration curve may be degraded. To the extent that contrast medium tonicity reduces curve peak or increases width, image quality for mask mode IV-DSA will suffer. To quantify the effect of contrast medium tonicity upon curve shape, contrast medium (1) at increasing iodine concentration and increasing osmolality and (2) at constant iodine concentration and increasing osmolality was injected into the right atria of mongrel dogs. In both experiments, increasing osmolality was associated with an increase in central blood volume (CBV) and cardiac output. With an increase in CBV, curve peak fell. With an increase in both CBV and cardiac output, curve width was not influenced by increasing osmolality. The effect of osmolality upon CBV was highly variable; in these experiments CBV was influenced more by subject-to-subject variability. However, on the average, higher tonicity contrast media produced curves with lower peaks. These studies suggest that isotonic contrast medium does not increase CBV and that isotonic contrast medium is preferable to hypertonic contrast medium for IV-DSA image formation.