Pottumarthi V. Prasad

Noninvasive Evaluation of Intrarenal Oxygenation With BOLD MRI

BACKGROUNDnThe countercurrent arrangement of capillary blood flow in the medulla of mammalian kidneys generates a gradient of oxygen tension between the renal cortex and the papillary tip that results in a state of relative hypoxia within the renal medulla. Exploration of the pathophysiological implications of medullary hypoxia has been hampered by the absence of a noninvasive technique to estimate intrarenal oxygenation in different zones of the kidney. In the present study, we demonstrate the feasibility of such a method on the basis of blood oxygenation level-dependent (BOLD) MRI, which allows sequential measurements in humans in response to a variety of physiological/ pharmacological stimuli in health and disease.nnnMETHODS AND RESULTSnBOLD MRI measurements were obtained in healthy young human subjects (n = 7), and the effects of three different pharmacological/physiological maneuvers that induce diuresis were studied. Spin-spin relaxation rate, R2*, was measured, which is directly related to the amount of deoxyhemoglobin in blood and in turn to tissue PO2. Furosemide but not acetazolamide (n = 6 each) increased medullary oxygenation (delta R2* = 7.62 Hz; P < .01), consistent with the separate sites of action of these diuretics in the nephron and with previous direct measurements of their effects in anesthetized rats with oxygen microelectrodes. A new finding is that water diuresis improves medullary oxygenation (delta R2* = 6.43 Hz; P < .01) in young human subjects (n = 5).nnnCONCLUSIONSnBOLD MRI can be used to monitor changes in intrarenal oxygenation in humans in a noninvasive fashion.

Noninvasive pulmonary perfusion imaging by STAR-HASTE sequence.

The STAR‐HASTE sequence has been shown to be useful for perfusion imaging in areas that are plagued by magnetic susceptibility artifacts. Pulmonary perfusion imaging with this technique was attempted in this study. Quantitative analysis was also conducted, using an appropriate kinetic model in one subject. In six healthy subjects, gradual enhancement was observed in pulmonary artery to distal lung parenchyma when inflow time was increased. Our initial results suggest that noninvasive evaluation of pulmonary perfusion by magnetic resonance imaging without administration of an exogenous agent is possible. Magn Reson Med 44:808–812, 2000.