Staging of pelvic lymph nodes in patients with prostate cancer: Usefulness of multiple b value SE-EPI diffusion-weighted imaging on a 3.0 T MR system

Abstract

Purpose: To evaluate the usefulness of diffusion-weighted imaging (DWI) with a multiple b value SE-EPI sequence on a 3.0 T MR scanner for staging of pelvic lymph nodes in patients with prostate cancer candidate to radical prostatectomy and extended pelvic lymph node dissection (PLND). Materials and methods: Institutional review board approval was obtained and written informed consent was taken from all enrolled subjects. A series of 26 patients with pathologically proven prostate cancer (high or intermediate risk according to D’Amico risk groups) scheduled for radical prostatectomy and PLND underwent 3 T MRI before surgery. DWI was performed using an axial respiratory-triggered spin-echo echo-planar sequence with multiple b values (500, 800, 1000, 1500 s/mm2) in all diffusion directions. ADC values were calculated by means of dedicated software fitting the curve obtained from the corresponding ADC for each b value. Fitted ADC measurements were performed at the level of proximal and distal external iliac, internal iliac, and obturator nodal stations bilaterally. Lymph node appearance was also assessed in terms of short axis, long-to-short axis ratio, node contour and intranodal heterogeneity of signal intensity. Results: A total of 173 lymph nodes and 104 nodal stations were evaluated on DWI and pathologically analysed. Mean fitted ADC values were 0.79 ± 0.14 × 10−3 mm2/s for metastatic lymph nodes and 1.13 ± 0.29 × 10−3 mm2/s in non-metastatic ones (P < 0.0001). The cut-off for fitted ADC obtained by ROC curve analysis was 0.91 × 10–3 mm2/s. A two-point-level score was assigned for each qualitative parameter, and the mean grading score was 6.09 ± 0.61 for metastastic lymph nodes and 5.42 ± 0.79 for non-metastatic ones, respectively (P = 0.001). Using a score threshold of 4 for morphological, structural, and dimensional MRI analysis and a cut-­off value of 0.91 × 10–3 mm2/s for fitted ADC measurements of pelvic lymph nodes, per-­station sensitivity, specificity, PPV, NPV and diagnostic accuracy were 100%, 7.9%, 15.6%, 100% and 21.3%, and 84.6%, 89.5%, 57.9%, 97.1% and 88.8%, respectively. Conclusions: 3.0T DWI with a multiple b value SE-EPI sequence may help distinguish benign from malignant pelvic lymph nodes in patients with prostate cancer. Keywords: Diffusion-weighted MR imaging, 3 T system, Lymph nodes, Prostate cancer