Overview of nanoparticle use in cancer imaging.

Current cross-sectional imaging modalities are inaccurate in characterizing nodal metastatic disease because of their use of size and/or morphology as differentiating factors. PET has overcome some of these limitations but it is constrained by its spacial resolution particularly for detecting small nodal metastases. These challenges have led to the development of lymphotropic contrast agents. Ferumoxtran-10 is one such MRI lymphotropic contrast agent that consists of ultrasmall superparamagnetic iron-oxide based nanoparticles targeted at the reticuloendothelial system. After intravenous administration ferumoxtran-10 is phagocytosed by macrophages which then accumulate within benign lymph nodes. Disturbances in lymph flow or in nodal architecture caused by metastases lead to abnormal patterns of accumulation of the particles, which are detectable by MRI. On postcontrast T2- and T2*-weighted MRI benign lymph nodes show a drop in signal intensity and homogenous darkening whereas areas of malignant infiltration show lack of nanoparticle uptake and remain signal-intense. Summary ROC curve analysis for per-lymph-node data showed an overall sensitivity of 88% and overall specificity of 96% for ferumoxtran-10-enhanced MRI. Ferumoxtran-10-enhanced MRI offers higher diagnostic precision than unenhanced MRI and is sensitive and specific for the detection of lymph-node metastases, especially in malignant diseases of the abdomen and pelvis.