Positive contrast magnetic resonance imaging of cells labeled with magnetic nanoparticles

TLDR

Superparamagnetic iron‑oxide nanoparticles enable MRI visualization of labeled cells, but the resulting negative contrast from signal dephasing suffers partial‑volume effects. This paper introduces a method for positive‑contrast imaging of labeled cells. Spectrally selective RF pulses excite and refocus off‑resonance water around labeled cells, rendering only adjacent fluid and tissue visible. Experiments in phantom, in vitro, and in vivo settings demonstrate feasibility, with a strong linear correlation (r = 0.87) between cell number and signal. Published in Magn Reson Med 53:999–1005 (2005), © 2005 Wiley‑Liss, Inc.

Abstract

Abstract Contrast agents incorporating superparamagnetic iron‐oxide nanoparticles have shown promise as a means to visualize labeled cells using MRI. Labeled cells cause significant signal dephasing due to the magnetic field inhomogeneity induced in water molecules near the cell. With the resulting signal void as the means for detection, the particles behave as a negative contrast agent, which can suffer from partial‐volume effects. In this paper, a new method is described for imaging labeled cells with positive contrast. Spectrally selective RF pulses are used to excite and refocus the off‐resonance water surrounding the labeled cells so that only the fluid and tissue immediately adjacent to the labeled cells are visible in the image. Phantom, in vitro, and in vivo experiments show the feasibility of the new method. A significant linear correlation ( r = 0.87, P < 0.005) between the estimated number of cells and the signal was observed. Magn Reson Med 53:999–1005, 2005. © 2005 Wiley‐Liss, Inc.