Ultrasmall superparamagnetic iron oxide enhanced MR imaging for lymph node metastases

The presence of a lymph node metastasis is one of the most important factors influencing therapeutic planning and prognosis in patients with malignancy. For example, a single nodal metastasis approximately halves the survival rate in patients with head and neck cancer, regardless of the location or size of the primary tumor. Currently used imaging techniques such as CT or conventional MRI are unreliable in detecting involved nodes accurately. There are few new techniques that have proven to be of value in nodal staging, and one such technique is ultrasmall superparamagnetic iron oxide (USPIO) contrast agents for MRI. Administered intravenously, USPIO are phagocytosed by macrophages within lymph nodes. Homogeneous uptake of iron oxide particles in normal lymph node shortens the T2 and T2*, turning these nodes dark on post contrast images whereas malignant nodes, lacking the normal physiologic uptake, remain hyperintense on T2- and T2*-weighted images. These differences in signal intensity between normal and metastatic nodes are easily detected visually, leading to high sensitivity and specificity regardless of size or morphological features.This article will review the physiologic properties of USPIO, the technical considerations for imaging using USPIO agent, the results of various clinical trials, and other experimental agents, as well asthe future directions.