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.