Diffusion-weighted magnetic resonance imaging as a promising technique for detection and follow-up of liver metastases from neuroendocrine tumors: a retrospective and prospective study from the NETTARE task force

Background: A combination of morphological and functional imaging plays a crucial role for neuroendocrine tumors (NETs) management. Diffusion-weighted magnetic resonance imaging (DWI-MRI) is an emerging key imaging technique in the NET field. Aim: to evaluate the diagnostic and prognostic role of DWI-MRI in liver metastases (LMs) from NETs compared with multiparametric MRI and functional imaging with 68Ga-DOTA peptides positron emission tomography (PET)-computed tomography (CT). Methods: This is a monocentric, observational, both retrospective and prospective study including patients with histologically proven diagnosis of gastroenteropancreatic (GEP) NET with LM evaluated with MRI and 68Ga-DOTA peptides PET-CT, performed within 6 months apart at diagnosis or follow-up. We collected clinical, pathological, imaging data including lesions number detected on (a)MRI-gold standard, (b)DWI images, (c)68Ga-DOTA peptides PET-CT. Apparent diffusion coefficient (ADC) was calculated on target lesions. Results: 426 LMs were analyzed from 17 patients (11 males, mean age 57.2 ± 12.6 years) meeting the inclusion criteria (11.8% G1, 64.7% G2, and 23.5% G3); MRI detected a median of 15 (IQR 2.5-40) lesions per patient, DWI 15 (IQR 2.5-36.5) lesions, while PET-CT 6 (IQR 2.5-20) lesions. Non-parametric analyses suggested that DWI had a detection rate comparable to MRI (p = 0.068) and superior to 68Ga-DOTA peptides PET-CT (p = 0.004), whereas mixed-effects modelling accounting for within-patient clustering showed no statistically significant pairwise differences between imaging modalities after multiple-comparison correction. Moderate-to-good consistency in lesion burden estimation across imaging modalities supported the reproducibility of lesion quantification. Correlation analyses suggested MRI lesion load may reflect the aggressiveness of disease. Conclusions: DWI-MRI can be a useful time-saving imaging technique in the diagnosis and follow-up of LMs from NETs, with a potentially favorable cost-effectiveness ratio.