DT imaging is a promising noninvasive technique for functional assessment of renal allografts. FA values in the renal medulla exhibit a good correlation with renal function.

Our results indicate that ASL is a promising technique for nonenhanced quantification of cortical perfusion of renal allografts. Further studies are required to determine the clinical value of ASL for monitoring renal allograft recipients.

The signal of diffusion-weighted imaging of the human kidney differs from the signal in brain examinations due to the different microscopic structure of the tissue. In the kidney, the deviation of the signal behavior of monoexponential characteristics is pronounced. The aim of the study was to analyze whether a mono-or biexponential or a distribution function model fits best to describe diffusion characteristics in the kidney. To determine the best regression, different statistical parameters were utilized: correlation coefficient (R 2 ), Akaike's information criterion, Schwarz criterion, and F-test (F ratio ). Additionally, simulations were performed to analyze the relation between the different models and their dependency on signal noise. Statistical tests showed that the biexponential model describes the signal of diffusion-weighted imaging in the kidney better than the distribution function model. The monoexponential model fits the diffusionweighted imaging data the least but is the most robust against signal noise. From a statistical point of view, diffusion-weighted imaging of the kidney should be modeled biexponentially under the precondition of sufficient signal to noise. Magn Reson Med 64:616-622,

Purpose:To assess the value of arterial spin-labeling (ASL) perfusion magnetic resonance (MR) imaging in the characterization of solid renal masses by using histopathologic findings as the standard of reference. Materials and Methods:This prospective study was compliant with HIPAA and approved by the institutional review board. Informed consent was obtained from all patients before imaging. Fortytwo consecutive patients suspected of having renal masses underwent ASL MR imaging before their routine 1.5-T clinical MR examination. Mean and peak tumor perfusion levels were obtained by one radiologist, who was blinded to the final histologic diagnosis, by using region of interest analysis. Perfusion values were correlated with histopathologic findings by using analysis of variance. A linear correlation model was used to evaluate the relationship between tumor size and perfusion in clear cell renal cell carcinoma (RCC). P , .05 was considered indicative of a statistically significant difference. Results:Histopathologic findings were available in 34 patients (28 men, six women; mean age 6 standard deviation, 60.4 years 6 11.7). The mean perfusion of papillary RCC (27.0 mL/min/100 g 6 15.1) was lower than that of clear cell RCC (171.6 mL/min/100 g 6 61.2, P = .001), chromophobe RCC (152.9 mL/min/100 g 6 80.7, P = .04), unclassified RCC (208.0 mL/min/100 g 6 41.1, P = .001), and oncocytoma (373.9 mL/min/100 g 6 99.2, P , .001). The mean and peak perfusion levels of oncocytoma (373.9 mL/ min/100 g 6 99.2 and 512.3 mL/min/100 g 6 146.0, respectively) were higher than those of papillary RCC (27.0 mL/min/100 g 6 15.1 and 78.2 mL/min/100 g 6 39.7, P , .001 for both), chromophobe RCC (152.9 mL/min/100 g 6 80.7 and 260.9 mL/min/100 g 6 61.9; P , .001 and P = .02, respectively), and unclassified RCC (208.0 mL/ min/100 g 6 41.1 and 273.3 mL/min/100 g 6 83.4; P = .01 and P = .03, respectively). The mean tumor perfusion of oncocytoma was higher than that of clear cell RCC (P , .001). Conclusion:ASL MR imaging enables distinction among different histopathologic diagnoses in renal masses on the basis of their perfusion level. Oncocytomas demonstrate higher perfusion levels than RCCs, and papillary RCCs exhibit lower perfusion levels than other RCC subtypes.q RSNA, 2012