EVALUATION OF RENAL-FUNCTION BY DYNAMIC MR-IMAGING - EFFECT OF WATER LOAD

The aim of this study was to investigate the usefulness of magnetic re sonance (MR) imaging in the evaluation of renal function, with particu lar attention to the effects of water load. Ten healthy volunteers und erwent dynamic MR imaging after an injection of gadolinium diethylene- triaminepenta-acetic acid (Gd-DTPA) as a contrast agent to evaluate re nal function by the following four methods:the positive method [longit udinal relaxation time (T1) shortening is the dominant effect],the neg ative method [transverse relaxation time (T2) shortening is the domina nt effect] and two intermediate methods by switching the Gd-DTPA conce ntrations used in the positive and negative methods. A prolonged corti cal peak time and a reduced medullary peak level were observed by the positive method under a dehydrated condition, suggesting that these va riables were slightly influenced by Gd-DTPA concentrated in the medull a. By the negative method, low signals due to T2 (T2 * is the effect ive transverse relaxation time, typically shorter than T2) shortening appeared in the medulla under normal conditions, but these signals wer e unclear when the subject was under an overhydrated condition. These results indicate that water metabolism, in addition to imaging paramet ers and Gd-DTPA dose levels, should be considered when renal function is evaluated by dynamic MR imaging. Analysis of both the pattern of MR images and the time-signal intensity curves may be useful in the eval uation of renal function. The results also indicate that the positive method is preferred when the patient is overhydrated as it allows the evaluation of the local renal kinetic function by recording changes in the regional contrast agent levels.