Ultra-small superparamagnetic iron oxide contrast agents for lymph node staging of high-risk prostate cancer

Abstract

Ultrasmall superparamagnetic particles of iron oxide (USPIOs) imaged with magnetic resonance imaging (MRI) have been proposed as an experimental method for visualizing lymph node (LN) metastases. The method does not require ionizing radiation, yet can detect small nodes that are involved with metastases. USPIOs are naturally taken up by macrophages that deposit in the normal LN creating a low signal region in normal areas; areas within the node that do not show this loss of signal are likely involved by tumor although there can be other causes (fibrosis or inflammation). However, the lack of approved USPIOs that are clinically available hinders adoption and larger studies. The proposed indications for USPIO MRI, including specific compounds and imaging methods are discussed.

Keywords: Ultrasmall superparamagnetic particles of iron oxide (USPIO); lymph node (LN); magnetic resonance imaging (MRI); prostate cancer.

Figure 1

Ferumoxytol enhanced MR Lymphography findings of benign hyperplastic lymph nodes. (A-D) Pre-administration of ferumoxytol; (E-H) 24 hours post-administration images. (A,E) T2-weighted images; (B,F) T2* axial images; (C,G) diffusion-weighted images; (D,H) T2* spectral pre-saturation with inversion recovery (SPIR) images. A 57-year-old male with T3 high-grade papillary urothelial carcinoma. Two enlarged lymph nodes were seen, one in the right inguinal chain (arrow) and one in the right iliac chain (arrowhead). After administration of Ferumoxytol a signal diffuse signal loss is seen in these lymph nodes indicating benign hyperplasia, later seen on biopsy.

Figure 2

Ferumoxytol enhanced MR Lymphography findings of metastatic lymph nodes. (A-C) Pre-administration of ferumoxytol; (D-F) 24 hours post-administration images. (A,D) T2* axial images; (B,E) diffusion-weighted images; (C,F) T2* spectral pre-saturation with inversion recovery (SPIR) images. A 43-year-old male with Gleason 5+5 cancer, previously treated with radical prostatectomy and external beam radiotherapy. Enlarged paraortic lymph nodes were seen (arrowheads). After administration of Ferumoxytol, these lymph nodes retain their signal indicating metastasis.