Quantification of renal perfusion and function on a voxel‐by‐voxel basis: A feasibility study

Abstract

The feasibility of a voxel-by-voxel deconvolution analysis of T 1 -weighted DCE data in the human kidney and its potential for obtaining quantification of perfusion and filtration was investigated. Measurements were performed on 14 normal humans and 1 transplant at 1.5 T using a Turboflash sequence. Signal time-courses were converted to tracer concentrations and deconvolved with an aorta AIF. Parametric maps of relative renal blood flow (rRBF), relative renal volume of distribution (rRVD), relative mean transit time (rMTT), and whole cortex extraction fraction (E) were obtained from the impulse response functions. For the normals average cortical rRBF, rRVD, rMTT, and E were 1.6 mL/min/mL (SD 0.8), 0.4 mL/mL (SD 0.1), 17s (SD 7), and 22.6% (SD 6.1), respectively. A gradual voxelwise rRBF increase is found from the center of two infarction zones toward the edges. Voxel IRFs showed more detail on the nefron substructure than ROI IRFs. In conclusion, quantitative voxelwise perfusion mapping based on deconvolved T 1 -DCE renal data is feasible, but absolute quantification requires inflow correction. rRBF maps and quantitative values are sufficiently sensitive to detect perfusion abnormality in pathologic areas, but further research is necessary to separate perfusion from extraction and to characterize the different compartments of the nephron on the ( Key words: renal; T-weighted; perfusion; deconvolution; quantificationDynamic contrast enhanced MRI is a promising noninvasive method for imaging renal perfusion and function (1-5), since it avoids the use of ionizing radiation and combines high temporal and spatial resolution. Moreover, Gd-DTPA is very well tolerated, not nephrotoxic, and has properties comparable to the radioisotopic 99mTc-DTPA (6,7). Tissue perfusion imaging with dynamic Gd-DTPA enhanced MRI therefore offers the potential for obtaining important information about organ viability, anatomy, and function in the normal as well as in the compromised kidney.Experiments with a rabbit model (1) have shown that Gd-DTPA enhanced bolus tracking and a deconvolution analysis of ROI signals permit quantitative measures of perfusion and filtration, independent of the effect of the shape and size of the bolus. On the other hand, results obtained with an intravascular contrast agent have shown that a pixel-by-pixel approach to perfusion quantification can be a useful tool for distinguishing normality from renal artery stenosis in dogs as well as humans (2,3).In this study we investigate the combination of both approaches: a pixel-by-pixel deconvolution analysis in the human kidney, using Gd-DTPA enhanced bolus tracking. We investigate the quality of the resulting parametric maps, evaluate to what extent they represent perfusion and extraction, and assess the potential of the technique for obtaining reliable quantification of renal blood flow and a measure of filtration. We also investigate the possibility of obtaining other parameters like the tracers' volume of distribution and mean transit time. Our first results...

Renal Relevant Radiology

“…Ultrasmall paramagnetic iron oxide (USPIO) particles and gadolinium-chelates have been used as contrast agents for renal hemodynamic assessments (2,3). USPIO particles, tens of nanometers in diameter, remain initially intravascular and are eliminated from the blood pool by the reticuloendothelial system.…”

Detection of Local Recurrence with 3-Tesla MRI After Radical Prostatectomy: A Useful Method for Radiation Treatment Planning?

“…DCE and T2-weighted images were also taken into account for differential diagnosis between nodules and artifacts such as clips or bowel movements. Contrast enhancement curves were analyzed with a model-free deconvolution analysis as described elsewhere (40,41,44). The arterial input function was measured in a plane with clear delineation of the common femoral artery at arrival of contrast agent.…”

“…We assumed that with 3-T MRI protocols (40)(41)(42), detection of local recurrence after radical prostatectomy is feasible at early stages when the PSA value is still below 1 ng/ml. Accurate detection would further reduce geographical miss and most probably enhance therapeutic ratio, by dose escalation to small residual volumes (18) …”

Comparison of Gd‐DTPA and Gd‐BOPTA for studying renal perfusion and filtration

“…The increased relaxivity may cause T1-saturation and T2*-interference effects, which potentially affect calculation of perfusion parameters (17). Generally, there is no consensus on the ideal dose of contrast agent to be administered for MR renography; however, it is generally accepted that it should be performed with a dose between 0.025 and 0.05 mmol/kg (18).…”