Synthetic Apparent Diffusion Coefficient for High b -Value Diffusion-Weighted MRI in Prostate

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Purpose . It has been reported that diffusion-weighted imaging (DWI) with ultrahigh b -value increases the diagnostic power of prostate cancer. DWI with higher b -values is challenging as it commonly suffers from low signal-to-noise ratio (SNR), distortion, and longer scan time. The aim of our study was to develop a technique for quantification of apparent diffusion coefficient (ADC) for higher b -values from lower b -value DW images. Materials and Methods . Fifteen patients (7 malignant and 8 benign) were included in this study retrospectively with the institutional ethical committee approval. All images were acquired at a 3T MR scanner. The ADC values were calculated using a monoexponential model. Synthetic ADC (sADC) for higher b -value was computed using a log-linear model. Contrast ratio (CR) between prostate lesion and normal tissue on synthetic DWI (sDWI) was computed and compared with original DWI and ADC images. Results . No significant difference was observed between actual ADC and sADC for b -2000 in all prostate lesions. However, CR increased significantly ( p = 0.002 , paired t -test) in sDWI as compared to DWI. Malignant lesions showed significantly lower sADC as compared to benign lesions ( p = 0.0116 , independent t -test). Mean (±standard deviation) of sADC of malignant lesions was 0.601 ± 0.06 and for benign lesions was 0.92 ± 0.09 (10 −3 mm 2 /s). Discussion / Conclusion . Our initial investigation suggests that the ADC values corresponding to higher b -value can be computed using log-linear relationship derived from lower b -values ( b ≤ 1000). Our method might help clinicians to decide the optimal b -value for prostate lesion identification.