Unenhanced MRA correctly classified 17 of the 23 renal arteries with > 50 % stenosis and correctly classified 128 of the 138 renal arteries as not having disease ( 50 % stenosis ) to yield a sensitivity of 74 % , specificity of 93 % , and accuracy of 90 % ( ( 2 ) = 0.56 ; p = 0.45 , no statistically significant difference ) .