Diagnosing renal impairments and suggesting treatment strategies for renal impairements such as renal arterial stenosis are hindered by a lack of non-invasive techniques to indicate renal function. MRI provides a non-invasive semi-quantitative measure of renal metabolism in terms of tissue oxygenation, however there are several hinderances. Since the results obtained are semi-quantitative, there is a lack of representation to true tissue oxygenation. Renal anatomy varies so that slice selection becomes critical in order to obtain an accurate representation of the tissue in question (cortex and medulla). Since the kidney receives a substantial amount of blood flow and oxygen in excess of metabolic demands, it is unclear how renal tissue oxygenation is impacted with losses in renal blood flow. Further, the kidney consumes oxygen at different rates in the renal tubules (proximal/ascending loop of Henlel) in order to support the important task of functional reabsorption of sodium. Several key factors are summarized: (a) the anatomical division (cortex / medulla) correspond to the proximal and ascending loop of Henle tubule, (b) certain diuretics are known to deter or inhibit proximal and ascending loop of Henle functional reabsorption of sodium and thus oxygen consumption, (c) it is unclear if increased tissue oxygenation due to clinically relevant proximal and distal loop diuretics will occur or be detectable with MRI, and (d) proximal/distal loss of function is a significant consideration to clinicians when deciding to revascularize the kidney. This project therefore aims to clarify several key factors. The study is designed to determine the tissue oxygenation in the renal cortex and medulla with the application of proximal and distal loop diuretics directly with oxygen electrodes (Specific Aim 1) and indirectly with MRI (Specific Aim 2). Additionally the project proposes to evaluate the MRI field of view and slice determination in conjunction with anatomical details so as to recommend appropriate slice selection (Specific Aim 2). Finally, as a previously study evaluated acute renal arterial stenosis with MRI, the current proposal considers tissue oxygenation measured directly during acute renal arterial stenosis(Specific Aim 3). The successful completion of this project will contribute to the development of criterion improving image acquisition relating renal function and will improve the overall understanding of how the kidney responds to losses in blood flow and in workload. ? ? ?
| Warner, Lizette; Glockner, James F; Woollard, John et al. (2011) Determinations of renal cortical and medullary oxygenation using blood oxygen level-dependent magnetic resonance imaging and selective diuretics. Invest Radiol 46:41-7 |
| Warner, Lizette; Gomez, Sabas I; Bolterman, Rodney et al. (2009) Regional decreases in renal oxygenation during graded acute renal arterial stenosis: a case for renal ischemia. Am J Physiol Regul Integr Comp Physiol 296:R67-71 |
