The development of an effective method for staging liver fibrosis has always been a hot topic of research in the field of liver fibrosis. In this paper, PEGylated ultrafine superparamagnetic iron oxide nanocrystals (SPIO@PEG) were developed for T₁–T₂ dual-modal contrast-enhanced magnetic resonance imaging (MRI) and combined with Matrix Laboratory (MATLAB)-based image fusion for staging liver fibrosis in the rat model. Firstly, SPIO@PEG was synthesized and characterized with physical and biological properties as a T₁–T₂ dual-mode MRI contrast agent. Secondly, in the subsequent MR imaging of liver fibrosis in rats in vivo, conventional T₁ and T₂-weighted imaging, and T₁ and T₂ mapping of the liver pre- and post-intravenous administration of SPIO@PEG were systematically collected and analyzed. Thirdly, by creative design, we fused the T₁ and T₂ mapping images by MATLAB and quantitively measured each rat's hepatic fibrosis positive pixel ratio (PPR). SPIO@PEG was proved to have an ultrafine core size (4.01 ± 0.16 nm), satisfactory biosafety and T₁–T₂ dual-mode contrast effects under a 3.0 T MR scanner (r₂/r₁ = 3.51). According to the image fusion results, the SPIO@PEG contrast-enhanced PPR shows significant differences among different stages of liver fibrosis (P < 0.05). The combination of T₁–T₂ dual-modal SPIO@PEG and MATLAB-based image fusion technology could be a promising method for diagnosing and staging liver fibrosis in the rat model. PPR could also be used as a non-invasive biomarker to diagnose and discriminate the stages of liver fibrosis.