Synthetic apparent diffusion coefficient for high b-value diffusion weighted MRI in Prostate

PurposeIt has been reported that diffusion weighted imaging (DWI) with ultrahigh b-value increases the diagnostic power of prostate cancer. DWI imaging 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 MethodsFifteen patient (7 malignant, 8 benign) with prostate cancer were included in this study retrospectively with the institutional ethical committee approval. All images were acquired at 3T MR scanner. The ADC values were calculated using mono-exponential model. Synthetic ADC (sADC) for higher b-value were 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. ResultsNo 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 lesion (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 (10-3mm2/s). Discussion / ConclusionOur 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 clinician to decide the optimal b-value for prostate lesion identification.