WHAT IS THE NEPHROGRAM

One of the oldest questions in radiology, ''what is the nephrogram?'', has been approached in a novel manner using dynamic bolus contrast enhanced computed tomography to monitor the arrival and distribution of contrast agent in the normal kidney. A modification of a mathematical technique first developed for applications in positron emission tomography has been used to analyse the data. It is concluded that the blood pool contribution to the nephrogram is greater in the first minutes after rapid bolus contrast injection than generally supposed and that the ''immediate'' nephrogram is a predominantly blood pool contrast phenomenon.