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Renal masses: characterization with diffusion-weighted MR imaging--a preliminary experience.

PURPOSE
To retrospectively assess the usefulness of apparent diffusion coefficients (ADCs) for characterizing renal masses (ie, viable solid tumors, necrotic or cystic tumor areas, and benign cysts).


MATERIALS AND METHODS
The institutional review board waived the requirement for informed consent for this retrospective HIPAA-compliant study. The data of 25 consecutive patients (15 men, 10 women; age range, 39-75 years) who underwent renal magnetic resonance (MR) imaging, including diffusion-weighted imaging, before nephrectomy were included. Renal MR examinations were performed by using transverse T1-weighted dual-echo in-phase and out-of-phase sequences and transverse and coronal T2-weighted single-shot fast spin-echo sequences. Three-dimensional fat-saturated T1-weighted dynamic gadopentetate dimeglumine-enhanced sequences also were performed. Precontrast single-shot spin-echo echo-planar diffusion-weighted images were obtained with b values of 0, 500, and 1000 sec/mm(2) at 1.5 T. Regions of interest were placed on renal lesions to measure the ADC of whole lesions, enhancing viable soft tissue, and nonenhancing necrotic or cystic areas. The T1 signal characteristics of the renal lesions and necrotic or cystic areas were recorded. The Wilcoxon rank sum test was used to compare the median ADC values of the various types of lesions and areas.


RESULTS
Twenty-six renal tumors were found in the 25 patients. Eight patients were found to have 11 benign cysts. Renal tumors had significantly lower ADCs (median, 189.3 x 10(-5) mm(2)/sec; range, [102.0-262.0] x 10(-5) mm(2)/sec) compared with benign cysts (median, 322.8 x 10(-5) mm(2)/sec; range, [217.0-421.0] x 10(-5) mm(2)/sec; P < .001). Solid enhancing tumors had significantly lower ADCs (median, 162.3 x 10(-5) mm(2)/sec; range, [102.0-284.0] x 10(-5) mm(2)/sec) compared with nonenhancing necrotic or cystic regions (median, 247.7 x 10(-5) mm(2)/sec; range, [85.2-310.0] x 10(-5) mm(2)/sec; P = .007) [corrected]. T1 hyperintense lesions had lower ADCs compared with their hypointense counterparts.


CONCLUSION
The T1 signal characteristics of a renal lesion appear to be related to the ADC of the lesion. ADC may be helpful in characterizing and differentiating renal masses.