Optimal b value in diffusion-weighted imaging for differentiation of abdominal lesions.

PURPOSE

To explore the optimal b value in diffusion-weighted imaging (DWI) for differentiation of benign and malignant abdominal lesions.

MATERIALS AND METHODS

A total of 108 consecutive patients (age 60 ± 12.5 years) with 127 pathologically confirmed diagnoses of abdominal lesions were included. Single-shot echoplanar imaging (SH-EPI) DWI (1.5T) with seven b values and eight apparent diffusion coefficient (ADC) maps were obtained. The lesions were analyzed visually on DWI and ADC maps for benignity/malignity using a 5-point scale and by measuring the ADC values and ADC lesion/normal parenchyma ADC ratio. ROC analysis was used to evaluate the diagnostic accuracy of ADC for differentiating between benign and malignant lesions. Pathology results were the reference standard.

RESULTS

Differentiation between malignant and benign lesions using visual scoring was successful at b values of 600 or higher (sensitivities, specificities, and accuracies were 100/93.8/92.5, 84.7/82.6/80.4, and 94.4/89.7/88.1, respectively, for b600, 800, and 1000). The mean ADC values of malignant lesions were significantly lower than those of benign lesions for all b-value combinations except b0 and 50 s/mm(2) (P = 0.032 for b0 and 50 s/mm(2) , P = 0.000 for other b values). The best b-value combination was 0 and 600 s/mm(2) and multiple b2. The lesion/normal parenchymal ADC ratio for b600, b1000, and multiple b2 better distinguished between benign and malignant lesions.

CONCLUSION

In DWI, the optimal b value is 600 s/mm(2) ; multiple b values of 600 s/mm(2) and higher are recommended to differentiate between benign and malignant abdominal lesions. The lesion ADC/normal parenchyma ADC ratio is more accurate than using lesion ADC only.