Comparison of biexponential and monoexponential model of diffusion weighted imaging in evaluation of renal lesions: preliminary experience.

OBJECTIVES

To obtain intravoxel incoherent motion (IVIM) parameters with biexponential analysis of multiple b-value diffusion-weighted imaging (DWI) and compare these parameters to apparent diffusion coefficient (ADC) obtained with monoexponential modeling in their ability to discriminate enhancing from nonenhancing renal lesions.

MATERIALS AND METHODS

Twenty-eight patients were imaged at 1.5 T utilizing contrast-enhanced (CE) magnetic resonance imaging (MRI) and breath-hold DWI using 8 b values (range: 0-800 s/mm(2)). Perfusion fraction (f(p)), tissue diffusivity (D(t)), and pseudo-diffusion coefficient (D(p)) were calculated using segmented biexponential analysis. ADC(total) and ADC(0-400-800) were calculated with monoexponential fitting of the DWI data. f(p), D(t), D(p), ADC(total), and ADC(0-400-800) were compared between enhancing and nonenhancing renal lesions. Receiver operating characteristic analysis was performed for all DWI parameters. f(p) was correlated with percent enhancement.

RESULTS

There were a total of 31 renal lesions (15 enhancing and 16 nonenhancing) in 28 patients on CE-MRI. f(p) of enhancing masses was significantly higher (27.9 vs. 6.1) and D(t) was significantly lower (1.47 vs. 2.40 ×10(-3) mm(2)/s). IVIM parameters f(p) and D(t) demonstrated higher accuracy in differentiating enhancing from nonenhancing renal lesions compared with monoexponential parameters ADC(0-400-800) and ADC(total), with area under the curve of 0.946, 0.896, 0.854, and 0.675, respectively. There was a good correlation between f(p) and percent enhancement (r = 0.7; P < 0.001).

CONCLUSION

IVIM parameters f(p) and D(t) obtained with biexponential fitting of multi-b value DWI have higher accuracy compared with ADC (obtained with monoexponential fit) in discriminating enhancing from nonenhancing renal lesions. Furthermore, f(p) demonstrates good correlation with percent enhancement and can provide information regarding lesion vascularity without the use of exogenous contrast agent.