Application of magnetic iron oxide nanomaterials in tumor imaging

Abstract

The incidence of malignant tumor increases year by year, becoming one of the major diseases affecting the health globally. Early diagnosis is the key to reduce the burden of cancer morbidity and mortality. However, due to inconspicuous characteristics in the early stage of cancer development, and the lack of efficient and accurate diagnostic methods, the early cancer diagnosis is far from satisfied. Iron oxide nanomaterials have shown great potential in cancer diagnosis because of their unique size-dependent properties, surface functionalization feasibility and good biocompatibility. As the only inorganic nanomaterials approved by FDA for clinical use, great progress has been achieved recently for iron oxide nanomaterials in materials design and biomedical applications, especially, being used as novel contrast agents for magnetic resonance imaging (MRI). This review will discuss the application of magnetic iron oxide nanomaterials in cancer diagnosis in recent years. At first, magnetic iron oxide nanomaterials are ideal MRI contrast agents, for the imaging modal (T1, T2 or T1-T2) can be adjusted by the magnetic iron oxide nanomaterials diameters and morphologies. Superparamagnetic iron oxide nanoparticles (diameter >5 nm) are typical MRI T2 contrast agents, while exceedingly small magnetic iron oxide nanoparticles (ES-MIONs, are an efficient and reliable T1 contrast agent. Even T1-T2 dual-modal contrast agents can be obtained by separating T1 contrast agent (paramagnetic shell) and T2 contrast agent (superparamagnetic nanoparticle core) with a non-magnetic silica layer, called artifact filtering nanoparticle imaging agent, AFIA. This dual-mode nanoparticle imaging agent (AFIA) can perform the “AND” logic gate algorithm in the post data processing, displaying areas that only show high MRI contrast differences in both T1 and T2 images, thereby eliminating the pseudo-errors (artifacts) in the original image. That strategy can help clinicians diagnose and evaluate diseases such as early tumors, vascular systems disease and central nervous system disease that are greatly disturbed by artifacts with more efficiency. Secondly, different imaging technologies (MRI, PET, SPECT, X-ray, optical imaging, etc.) have their pros and cons in terms of spatial resolution, sensitivity, penetration ability, and so on and so forth. If multi-modal imaging can be achieved, it will be possible to diagnose tumor more accurately and sensitively. For example, the optical imaging probes are connected to the magnetic iron oxide nanomaterials to obtain MRI-optical dual-mode imaging agents for highly sensitive imaging of sub-millimeter cell clusters. The dual-modality imaging system combining MRI and PET/SPECT can provide high-sensitivity, high-resolution tomographic images, and at the same time obtain biological anatomical structure and biological metabolism information as well. With the quick development in nanomedicine, magnetic nanoparticles-based diagnostics are believed to play vital roles in cancer early diagnosis in the future. Active targeting technology is also an important research field of tumor diagnosis. The combination of bio-active molecules with magnetic iron oxide nanomaterials can increase the active targeting function on the basis of passive target aggregation via EPR effect. It is believed that in the near future, there will be more efficient targeted imaging materials emerging to evaluate and diagnose the basic situation of malignant tumors from multiple layers, making early diagnosis and treatment of cancer possible.