MR contrast agents in lymph node imaging

The detection of tumor metastases in lymph nodes is clinically important for tumor staging and therapy planning in cancer patients. However, differentiating between malignant and benign lymph nodes is still a problem because current imaging modalities rely only on the size and shape of the lymph nodes. Thus, small metastases in normal-sized lymph nodes can be missed, and it is difficult to differentiate enlarged nodes (benign hyperplasia versus malignant disease). Therefore, a specific lymphotropic contrast agent is needed to obtain a high contrast between functional and metastatic tissue. Contrast-enhanced MR lymphography is a noninvasive method for the analysis of the lymphatic system after interstitial (intracutaneous or subcutaneous) or intravenous application of contrast media. Interstitial MR lymphography using extracellular, liposomal, polymeric, lipophilic or particulate contrast agents results in high accumulation in regional lymph nodes. The systemic administration of a lymphotropic contrast medium is needed to address each individual lymph node. Ultrasmall superparamagnetic iron oxide particles are in late-stage clinical development for this indication, but they take 24h to show sufficient contrast. Recently, a gadolinium-type contrast agent (Gadofluorine M) was described that detected lymph node metastases within 60 min of intravenous injection.