Evaluation of Intrarenal Oxygenation at 3.0 T Using 3-Dimensional Multiple Gradient-Recalled Echo Sequence

Abstract

Objective-The objective of this study was to validate quantitation of R 2 * and ΔR 2 * measurements obtained with a 3-dimensional (3-D) multiple gradient-recalled echo (mGRE) sequence for evaluating intrarenal oxygenation in humans.Materials and Methods-Validation was accomplished (1) by comparing R 2 * values with previously established 2-D techniques (n = 5, mean age = 33.6 years) and (2) by measuring change in ΔR 2 * after furosemide (20 mg intravenously) administration (n = 5, mean age = 22 years). Additional pre-and postfurosemide scans were done at 1.5 T for comparison purposes.Results-R 2 * measurements with the 3-D technique showed good agreement with the 2-D techniques. The baseline medullary R 2 * at 3.0 T was about twice the value found at 1.5 T. Furosemide-induced change in R 2 * was observed within 5 minutes after administration.Conclusions-R 2 * measurements with 3-D mGRE were comparable with those reported using 2-D techniques. The 3-D implementation facilitates observation of temporal changes in the medullary oxygenation without compromising spatial coverage. Keywords kidney; BOLD MRI; 3-D mGRE; oxygenation; 3.0 T The renal medulla operates at low oxygenation levels (renal medullary hypoxia) making it more susceptible to mild reductions in blood flow. 1-3 Renal medullary hypoxia is thought to play a role in the pathogenesis and/or progression of acute renal failure, 4-6 hypertension, 7,8 and diabetic nephropathy. 9,10 Blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) has been used to evaluate intrarenal oxygenation levels noninvasively in humans under normal conditions and during physiological and pharmacologic maneuvers at field strengths of 1.5 T 10-14 and most recently at 3.0 T. 15 To date, all BOLD MRI applied to the human kidney for functional evaluation have used single-shot echo planar (EPI) 13 or 2-dimensional (2-D) breathhold multiple gradient-recalled echo (mGRE) techniques. 14 Despite the advantage of faster acquisition times, the singleshot EPI technique suffers from limitations such as having high sensitivity to susceptibility Copyright © 2006 NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript differences, which can lead to signal loss, image distortions, and increased blurring resulting from T 2 * decay during data acquisition. 14 The 2-D mGRE technique, although efficacious in terms of R 2 * mapping, requires multiple acquisitions to achieve adequate spatial coverage, typically a breathhold for each slice acquisition. In this study, we validated the quantitation of R 2 * and ΔR 2 * using a 3-D implementation of mGRE to perform intrarenal oxygenation studies. R 2 * measurements obtained by the 3-D technique were compared with measurements acquired with the 2-D sequence used in previous studies. Changes in R 2 * (ΔR 2 *) after administration of furosemide were also compared against previous reports.Furosemide is a loop diuretic that has been shown to improve medullary oxygenation, presumably because it selectively decreases ox...

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