Reduction of noise in medullary renograms from dynamic MR images

Dynamic magnetic resonance images of the kidney can be used to acquire sepa rate renograms of the cortex and medulla, A high-quality cortical renogram can be determined directly from a region of interest (ROI) placed in the co rtex. Due to partial volume effects, part of the signal from a ROI placed i n the medulla is caused by cortical tissue, By subtracting a fraction of th e cortical signal from the cortico-medullary signal, a purer medullary reno gram can be obtained. A side effect of this subtraction is an increase in n oise level. The noise level increases with larger partial volume fractions. Using a matched image filter, it is possible to exclude those areas from t he ROI that have a high partial volume content, thus reducing the amount of cortical signal that has to be separated from the medullary signal, Noise reductions of up to 50% have been achieved in the medullary renogram, with an average reduction of 23%. (C) 2000 Wiley-Liss, Inc.