Statistical analysis. Comparison of GFR in the ischemic kidney between groups (revascularization vs. medical therapy) at each time point will be performed using t-test, repeated measure ANOVA with adjustment of potential confounders, Cox regression model for loss of kidney function as defined above. Sub-group analysis (comparison unilateral vs bilateral stenosis) will be similarly undertaken. ROC curves will be used to determine if the baseline 99mTc DTPA scintiscan-derived indexes can predict the outcome of treatment using the changes in GFR over time as reference. Bland-Altman plot and analysis will be used to compare the estimate of GFR obtained using cystatin using the overall (right and left kidneys) GFR as reference.