Diffusion-weighted MR-imaging for characterization of pelvic lymph nodes in patients with prostate cancer

Objectives Diffusion-weighted magnetic resonance imaging (DWI-MRI) was evaluated as a tool for characterization of pelvic lymph nodes in patients with prostate cancer.

Methods 29 patients with prostate cancer underwent DWI-MRI of the pelvis at 1.5T by a non breath-hold SSEPI sequence with b values of 50, 300 and 600 s/mm² and an additional T2-weighted sequence. 118 lymph nodes (>6 mm) were analyzed by measuring the ADC-value with a polygon region of interest. Feasibility for ADC-measurement was assed by comparing the ADC-value from the automatically created ADC-map (ADC_{MR_unit}) with a manually calculated ACD-value (ADC_calculated) and by using a linear-regression model for comparison with size and standard deviation of the ADC-value. Diagnostic performance was estimated by receiver operator characteristic (ROC) analysis using histological and/or clinical follow-up as standard of reference.

Results ADC_{MR_unit} and ADC_calculated showed a high correlation (r=0.8999) with a mean percentual deviation of 6.33%. There was a highly significant difference between the mean ADC-value (x10^-3mm²/s) of positive (1.07±0.23) vs. negative (1.54±0.25) lymph nodes, even in subgroup analysis for lymph nodes smaller vs. larger than 10mm. ROC-analysis showed a good accuracy of the ADC-value (85.5%; sensitivity:81.1%; specificity:89.1%) for differentiation of malignant versus benign lymph nodes, which was superior to size-based analysis (accuracy:66.1%; p<0.01).

Conclusions DWI-MR is a robust molecular-imaging technique for detection and analysis of pelvic lymph nodes. Moreover, the ADC-value is significantly superior to size criteria to discriminate between benign and malignant lymph nodes.