The Presence of lymph node metastases in cancer is a key factor for determining prognosis and forming an adequate treatment plan. Determining lymph node status, however, is a challenge. Ferumoxtran-10, an ultrasmall superparamagnetic iron oxide (USPIO) particle has proven to be a valuable contrast agent for detecting lymph node metastases using magnetic resonance imaging (MRI) in various types of cancer (also called nano-MRI). For small lymph node metastases (<5mm) the diagnostic accuracy of this technique does, however, drop substantially. Most of the studies that have been performed with these particles used a 1.5 Tesla or 3 Tesla MRI scanner. The investigators would like to increase the resolution of nano-MRI by using a 7 Tesla scanner, such that the investigators can increase the sensitivity of this technique for small lymph nodes. With this study the investigators would like to validate the results of this technique with pathology in rectal and breast cancer. In these cancer types many patients undergo a surgical lymph node dissection by bulk excision of tissue including the nodes, enabling a node-to-node comparison between MRI and pathology to validate our nano-MRI results . If successful this technique would form a non-invasive alternative to the current lymph node staging techniques such as surgery. Additionally (if metastatic nodes are present), it could complement image guided focal therapies on lymph node metastases such as radiotherapy.