Renal functional contrast-enhanced magnetic resonance imaging - Evaluation of a new rapid-clearance blood pool agent (P792) in Sprague-Dawley rats

Objectives: The objective of the present study was to compare P792, a new rapid clearance blood pool agent characterized by negligible interstitial diffusion but unrestricted glomerular filtration, with Gd-DOTA in both qualitative and quantitative aspects of renal functional magnetic resonance imaging. Materials and Methods: Dynamic imaging was performed with a fast T1-weighted gradient-echo sequence on a 1.5-T magnet in 25 Sprague-Dawley rats, after injection of 13 mu mol Gd/kg-1 of P792 (n = 10), 100 (n = 10), or 50 mu mol Gd/kg-1 of Gd-DOTA (n = 5). Signal-time curves from 6 regions of interest (ROIs), including renal parenchyma and contents, were analyzed. Results: Qualitative analysis depicted a typical pattern of temporal enhancement as previously described with extracellular gadolinium chelates, including early and brief enhancement of the aorta, renal vessels and cortex, quickly followed by enhancement of the medulla and then renal pelvis. However, a decrease in signal intensity was noted in the inner medulla and the renal pelvis approximately 90 seconds after bolus injection, being more marked when using the full dose of Gd-DOTA. Curve analysis showed a similar vascular phase within each parenchymal ROI, confirmed by similar upslopes, which ranged from 0.015 +/- 0.007 to 0.019 +/- 0.005. Following this initial phase, T1-enhancement appeared greater and longer within the medulla and renal pelvis, and subsequently in the whole kidney ROI with P792 (time to maximal enhancement (see)/enhancement rate: 85.5 +/- 15.9/3.1 +/- 0.4) as compared with Gd-DOTA full (53.0 +/- 18.9/2.7 +/- 0.3) or half dosage (65.2 +/- 20.1/2.2 +/- 0.2). The subsequent decrease in signal intensity, characterized by a downslope during the minute following maximal enhancement, was faster with Gd-DOTA (0.006 +/- 0.002) as compared either to P792 or half dosage Gd-DOTA (0.003 +/- 0.001). Conclusions: Due to its physicochemical and pharmacokinetic properties, P792 allows the use of a reduced dosage of gadolinium, resulting in less T2(*) effect without compromising T1 enhancement. Thus, P792 appears suitable for renal functional MR imaging.