Abstract

Molecular imaging is a multidisciplinary field that enables the in vivo, non-invasive visualization, characterization, and quantitative assessment of pathological and physiological processes at the cellular and molecular levels without compromising structural integrity. Preclinical molecular imaging technologies developed in laboratory settings serve as a strategic bridge in translational medicine by facilitating the investigation of disease mechanisms in small animal models, evaluating the pharmacokinetic behavior of novel therapeutic agents, and accelerating drug discovery and development processes. Unlike conventional approaches, these technologies allow longitudinal monitoring of the same experimental animal over time, thereby enhancing the robustness of biological data and contributing significantly to research in oncology, neuroscience, and cardiology. In this review, the main imaging modalities widely used in preclinical research are discussed in detail. These include micro-computed tomography (μCT) and micro-magnetic resonance imaging (μMRI), which provide high-resolution anatomical detail; micro-positron emission tomography (μPET) and micro-single-photon emission CT (μSPECT), which offer highly sensitive metabolic and molecular information; as well as optical imaging techniques based on bioluminescence and fluorescence, together with micro-ultrasound systems. Optical imaging approaches, particularly bioluminescence and fluorescence-based methods, are widely utilized in preclinical studies due to their non-ionizing nature, relatively low cost, and high experimental throughput.

Recent advances in detector technology have led to the emergence of digital preclinical PET and SPECT systems, which provide improved signal-to-noise ratio, higher count sensitivity, and enhanced quantitative accuracy compared with conventional photomultiplier tube-based systems. Furthermore, hybrid imaging configurations such as μPET/μCT and μPET/μMRI, combined with artificial intelligence-assisted image reconstruction algorithms and targeted smart contrast agents, have significantly expanded the performance limits of these modalities. Overall, preclinical imaging systems represent an indispensable component of the translational research pipeline, and ongoing integration of digital technologies is expected to further advance spatial resolution, sensitivity, and quantitative imaging capabilities in the future.