Characterization of reactively sputtered iron oxide thin films for developing magnetic resonance imaging contrast agents

This paper reports the characterization of reactively sputtered iron oxide thin films for their application in a novel class of top-down engineered contrast agent particles for multispectral magnetic resonance imaging (MRI). Tunable saturation magnetic polarizations (J_S) of iron oxide thin films ranging from approximately 0.05 to 0.2 emu/mg were achieved by adjusting sputtering parameters. The iron oxide thin films were characterized using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and superconducting quantum interference (SQUID) magnetometry to study their chemical compositions, crystalline structures, and magnetic property, respectively. A novel MRI contrast agent was fabricated using the iron oxide deposition parameters to achieve a desired J_S; these particles were subsequently validated using MRI.

INTRODUCTION

The current generation of MRI contrast agents is mainly limited by a lack of multiplexed imaging, relatively low sensitivity, as well as a lack of functional imaging or sensing capability. Categorized by their effect on the image, “positive” contrast agents [1], such as gadolinium chelates, shorten relaxation times and “brighten” the local environments affected by these agents [2], whereas “negative” contrast agents, such as (ultrasmall) superparamagnetic iron oxides (USPIO, SPIO), function largely by shortening relaxation times and “darken” the image [3]. These monochromatic responses are in sharp contrast to the rich, multi-colored palette available with optical imaging contrast agents [4].