MRA resolution continues to improve with the use of faster gradients and parallel imaging techniques (Fig. 22). However, a really exciting area of development involves the contribution of functional information to enable more comprehensive assessments of renal physiology in individual patients and individual kidneys. MR spectroscopy, quantitative perfusion imaging and oxygen saturation may add information to help answer the question of which patients with renal artery stenosis will benefit from renal revascularization. MR spec-troscopy takes advantage of the unique spin resonance of common organic molecules to determine their relative concentration in tissue. It can be applied to hydrogen protons as well as to isotopes of sodium, phosphorus, carbon and a host of other atoms. Blood oxygen saturation determinations based upon T2 shifts in whole blood which corre-
spond to the hemoglobin oxidation status may also be useful. Ischemic organs tend to extract more oxygen which results in decreased oxygen saturation in the venous blood coming from the organ. However, these and all of the other functional methods require further study to determine their relative importance for predicting hemodynami-cally significant stenosis and the potential benefit of revasculization.
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