97 (Figs 1,2). Many researchers Protein Tyrosine Kinase inhibitor are attempting to determine whether anatomical lesions are functionally significant using MRI, MD-CTA (multi detector system) and DU. The most widely used ultrasonographic parameter to assess the functional significance of RAS is the resistive index (RI). The RI can be calculated from a spectral Doppler and is defined as 1 – (minimum diastolic velocity divided by maximum systolic velocity) × 100. Radermacher et al.21 have shown that in patients
with at least 50% stenosis in at least one renal artery RI values above 80 are highly sensitive and specific to identifying patients in whom angioplasty or surgery will not improve renal function, blood pressure or kidney survival. However, a potential source of bias in this study is that revascularization was considered only in patients with ≥50% stenosis on duplex ultrasound. In clinical practice, the assessment of the functional significance of RAS with CT is performed by measuring morphological parameters such as cortical thickness and area, medullary length and area22,23 and by analysis of renal time
attenuation curves after contrast injection as a measure of renal perfusion. Monier-Vehier et al.23 found a mean cortical thickness of 6.6 mm in post-stenotic kidneys and 7.9 mm in normal contralateral kidneys. A cortical thickness threshold of 8 mm identified significant RAS with a sensitivity of 73% and specificity of 93%. Further work by the same group demonstrated that renal length and cortical Chorioepithelioma thickness see more increased 6 months after angioplasty for atherosclerotic RAS.24 The drawback of CT assessment is the additional contrast and radiation dose. There are several functional parameters such as renal perfusion, glomerular filtration rate, tubular concentration and transit, diffusion and oxygenation that can be assessed using MRI.25,26 Prince et al.27 have demonstrated that the defacing artefact due to turbulent flow distal to RAS as measured with 3D phase contrast MRA is correlated
with the presence of haemodynamically significant stenosis. Haemodynamic significance was defined as a decrease in serum creatinine level of 30 µmol/L or a reduction in the number of medications required for blood pressure control after renal artery PTA or surgery. In addition, the study showed that the ischaemic kidney length and mean parenchymal thickness were reduced in unilateral haemodynamically significant lesions. Schoenberg et al.28,29 demonstrated that the post-gadolinium two-dimensional cine phase contrast flow measurements profile had a sensitivity of 90% and specificity of 94% for the presence of haemodynamically significant stenosis. Characteristic changes in significant RAS include delay and complete loss of the early systolic peak. Binkert et al.