Utility of 3 Tesla diffusion-weighted magnetic resonance (DWMR) imaging for the characterisation of small solid renal tumours

Purpose: To determine the utility of apparent diffusion coefficients (ADCs) for the characterisation of small solid renal lesions. Methods and Materials: 26 patients (GFR 30-60 mL/min) with 39 small (1-3 cm) solid renal masses [16 RCCs (10 clear cell types; 6 other types); 18 AMLs (10 fat-containing; 8 minimal-fat) and 5 oncocytomas] were examined on a 3 T system using DW-SS-EPI (b-values 0, 1000 s/mm2). The ADC of the lesions and the ADC of kidney were evaluated. Receiver operator characteristic analysis was performed to evaluate the diagnostic value of ADC for differentiating clear cell RCCs from other type RCCs, AMLs and oncocytomas. Results: The mean ADC of the lesions [1.22\ub1 0.27 28 mm2 /sec (0.76-1.96)] was lower than that of kidney [1.85\ub1 0.12 mm2 /sec (1.38-2.13)] (p< 0.005; Mann-Whitney test). The mean ADC was different between RCCs [1.23\ub1 0.34 mm2 /sec (0.76-1.73)], AMLs [1.07 \ub1 0.1 mm2 /sec (0.85-1.28)] and oncocytomas [1.66\ub1 0.28 mm2 /sec (1.1-1.96)] (p< 0.05, Kruskal-Wallis test). The mean ADC of clear cell RCCs was significantly higher than that of other RCCs [1.46\ub1 0.34 mm2 /sec (1.04-1.73) vs 0.83 \ub1 0.34 (0.76-1.01)] (p< 0.005; Student t-test). There was no significant difference between mean ADC of fat-containing [1.06 \ub10.48 mm2 /sec (0.86-1.28)] and minimal-fat AMLs [1.11 \ub10.33 mm2 /sec (1.04-1.22)] (p=0.46; Student t-test). The best cut-off ADC value for differentiating clear cell RCCs from other RCCs, AMLs and oncocytomas were 1.5,1.12 and 1.73 mm2/sec, respectively. Conclusion: DWI is useful to differentiate benign from malignant small solid renal lesions