Diffusion-weighted MRI in prostatic lesions: Diagnostic performance of normalized ADC using normal peripheral prostatic zone as a reference

Abstract

Aim of study: Evaluate the potential value of the normal peripheral zone as a reference organ to normalize prostatic lesion apparent diffusion coefficient (ADC) to improve its evaluation of prostatic lesions. Patients and methods: This prospective study included 38 patients with clinical suspicion of cancer prostate (increased PSA levels (>4 ng/ml, hard prostate in digital rectal examination) and who are scheduled to undergo a TRUS-guided biopsy. Conventional and DW-MRI was done and ADC was calculated. The normalized ADC value was calculated by dividing the ADC of lesion by ADC of reference site (healthy peripheral zone). DWI-MRI results were compared to the results of biopsy. Comparison of ADCs and nADCs of benign and malignant lesions was done. Receiver operating characteristics (ROC) curve analysis was done. Results: The patients were classified by histopathology into non-malignant group (16 patients) and malignant group (22 patients). Significant negative correlation between ADC and normalized ADC (nADC) and malignancy was detected. There was no significant difference between the mean ADC of peripheral health prostatic zones (PZ) between benign and malignant cases (2.221 ± 0.356 versus 1.99 ± 0.538x10−3 mm2/sec, p = 0.144).There was significant difference between the mean ADC and mean nADC in benign and malignant lesions (1.049 ± 0.217 versus 0.659 ± 0.221x10−3 mm2/sec, p < 0.001) and (0.475 ± 0.055 versus 0.328 ± 0.044, p < 0.001) respectively.There was significant higher diagnostic performance of nADC than ADC with ADC Cut-off value 0.75 × 10−3 mm2/sec and nADC cut-off value 0.39 could significantly differentiate between benign and malignant lesion with sensitivity, specificity, PPV,NPV of 86.36,75,82.61 and 80% respectively, p < 0.0001 for ADC and 95.45, 93.75, 95.45 and 93.75%, p < 0.0001 for nADC. Conclusion: diagnostic performance of nADC using normal peripheral zone is higher than ADC in discrimination between cancerous and non-cancerous lesions of the prostate. Keywords: Prostate, Diffusion weighted image (DWI), MRI, Cancer, ADC