Comparison: IV 1/6 M sodium bicarbonate OR IV 0.9% saline, each isotonic fluid given at the same rate of sodium administration (3.25 ml/Kg over 1 hour pre-contrast, followed by 1.1 ml/Kg/hr for 6 hours for bicarbonate; 3.5 ml/Kg over 1 hour pre-contrast, followed by 1.2 ml/Kg/hr for 6 hours for saline). Total infusion time 7 hours (for both). Maximum rate of fluid permitted is that for a body weight of 110 Kg. Intra-vascular iso- or low-osmolality contrast in the minimal dose needed to complete the required imaging.