Intravenous urography with low-osmolality contrast agents: theoretical considerations and clinical findings.

There are theoretical reasons for expecting some aspects of image quality in intravenous urography to be modified when low-osmolality, rather than conventional, contrast agents are used. The clinical findings in urography using two of these, the non-ionic agents iohexol (Omnipaque 350, Nyegaard) and iopamidol (Niopam 370, Bracco/Merck), are compared with those using sodium iothalamate (Conray 420, May & Baker Ltd), and are discussed against this theoretical background. The best nephrogram obtained with the new agents often occurred later than with the conventional agent, but quantitative differences in its density were explicable on a total iodine dose basis. The pyelographic density obtained with the new agents was significantly greater than with the conventional agent without any evidence, when abdominal compression was used, of the predicted associated poor distension of the collecting system.