Per-Lesion Assessment of Individual MRI Sequences and 68Ga-DOTATATE PET in Neuroendocrine Liver Metastases

Objectives: To explore magnetic resonance imaging (MRI) and gallium-68 (68Ga)-DOTATATE positron emission tomography (PET) performance in the assessment of neuroendocrine liver metastases (NELMs) on a per-lesion basis, with particular attention to the contribution of individual MRI sequences and assessment of other factors that might influence their detection. Materials and methods: This observational retrospective study included patients with histologically confirmed neuroendocrine tumors who underwent both contrast-enhanced MRI and 68Ga-DOTATATE PET within 12 weeks between August 2017 and December 2023. Three readers in consensus assessed individual MRI sequences [diffusion-weighted imaging (DWI), dynamic contrast-enhanced imaging (DCE), and hepatobiliary phase (HBP) imaging when available], entire MRI data set, and PET in random order. The reference standard was histopathology or follow-up imaging. Diagnostic performance metrics were calculated using generalized estimating equations with Bonferroni correction. Correlations were assessed using Pearson correlation coefficients. Results: A total of 1249 lesions, comprising 1050 metastases, were analyzed in 60 patients (mean age: 64.9±11.5 years; 56.7% male). Compared with PET, MRI demonstrated superior sensitivity (93% vs. 59%, P<0.001) and accuracy (93% vs. 63%, P<0.001), with DWI and HBP providing the highest sensitivity (89% and 92%). Size-stratified analysis showed that MRI outperformed PET, particularly for metastases <5 mm (81.6% vs. 19.7%) and 5 to 10 mm (96.1% vs. 61.8%) (P<0.001). Arterial enhancement and portal venous washout were present in 67.8% and 23.7% of metastases, respectively, with only portal venous washout showing size dependence (11.9% in <5 mm to 55.6% in >20 mm lesions, P<0.01). PET-negative metastases were smaller than PET-positives (5.0 vs. 8.0 mm, P=0.001), with lesion size correlating with maximum standardized uptake values and normalized uptake ratios (r=0.54 to 0.59, P<0.001). Conclusions: MRI outperformed 68Ga-DOTATATE PET in detecting NELMs, with DWI and HBP providing particularly high sensitivity for small metastases.