Can diffusion-weighted imaging be used in the examination of peritoneal fluids?

Introduction
The aetiology of free fluid detected in the abdomen can be investigated with magnetic resonance imaging (MRI). The aim of this study is to investigate the effectiveness of diffusion-weighted images (DWI) and apparent diffusion coefficient (ADC) values in the evaluation of abdominopelvic fluids.

Material and methods
Patients with abdominopelvic fluid detected on MRI of the lower abdomen were included in this retrospective, single-centre study. Paracentesis and fluid analysis was performed in these patients. The average ADC values in fluids were measured by a radiologist. A cut-off value was determined, and the specificity, sensitivity, negative predictive value (NPV), and positive predictive values (PPV) were calculated. Intra-observer agreement was investigated.

Results
The study comprised 41 (33 female) patients, and their mean age was 48 ± 4.02 years. The ADC values in infective fluids were significantly higher than in non-infective fluids (p < 0.001). The cut-off value used was 2.95 × 10-3 mm²/s. According to this threshold value, sensitivity in distinguishing non-infective from infective fluids was 88%, specificity was 93.8%, PPV was 95.7%, and NPV was 83.3%. Intra-observer agreement was strong in ADC values (κ = 0.699) (p < 0.001).

Conclusions
We concluded that the ADC value is a non-invasive, reliable, reproducible imaging parameter that can be useful in the evaluation and characterization of abdominal fluids.