Attenuation characteristics and application of gadolinium-DTPA in fast helical computed tomography

RATIONALE AND OBJECTIVES. The computed tomography (CT) attenuation characteristics of gadolinium (Gd)-DTPA have been analyzed both in vitro and in vivo to evaluate the possibility of its substitution for iodine in patients with contraindications for iodine utilization. METHODS. In vitro attenuation values of Gd-DTPA were measured relative to those of iodine under variation of concentration, voltage, preattenuation, and beam hardening. In vivo iodine attenuation values were obtained for different injection rates (3.0 mL/second and 4.5 mL/second) to calculate the attenuation values of 0.5 molar Gd-DTPA to be expected in vivo by the help of the previously obtained attenuation-concentration curves. Subsequently, CT enhancement after an injection of 0.3 mmol/kg body weight Gd-DTPA was evaluated in five patients with contraindications for iodine administration. RESULTS. The injection of a 0.7 molar Gd-DTPA solution at a flow rate of 4.5 mL/second was calculated to be equivalent to that of 2.36 molar iodine at a flow rate of 3 mL/second. Sufficient enhancement for diagnosis of dissections/aneurysms of arterial vessels could be achieved. Both arterial and venous cervical or thoracic vessels could be enhanced to 100 Hounsfield units with a bolus injection. In contrast to the thyroid gland, the parenchyma of the liver and the kidney was not sufficiently enhanced. CONCLUSIONS. Gadolinium-DTPA is more effective than iodine in x-ray attenuation; however, its present concentration of 0.5 molar and permitted dose of 0.3 mmol/kg body weight are insufficient to provide parenchymal enhancement with CT. The visualization of arterial vessels appears possible with gadolinium enhanced CT but requires optimal timing and fast scanning capabilities.