MR Contrast in Mouse Lymph Nodes with Subcutaneous Administration of Iron Oxide Particles: Size Dependency

Abstract

Purpose: We investigated the spatiotemporal changes in signal in draining lymph nodes of mice to ascertain the size-dependent eŠects of variously sized particles of iron oxide used to enhance magnetic resonance (MR) lymphography.Materials and Methods: We injected iron oxide particles of 50-, 100-, 200-, or 1,000-nm diameter into the footpads of individual mice and obtained sequential MR images of the popliteal and inguinal lymph nodes with 11.7 tesla up to 6 weeks after particle administration.Results: Up to 30 min after administration of particles smaller than 100 nm, we observed a marked reduction in signal in the popliteal node that spread from the periphery atˆrst observation toward the center of the node in subsequent measurements and persisted up to 6 weeks. In contrast, 1,000-nm particles caused dot-like areas of hypointensity in the popliteal lymph node, primarily in the inner portion, that appeared after 2 days. In the inguinal lymph nodes, signal changes occurred after 2 days for 50-and 100-nm particles and after one week for 1,000-nm particles. For 1,000-nm particles, areas of hypointensity were visible in the inner portion and not the periphery of the inguinal lymph node up to 6 weeks. In this study, we demonstrate the strong dependence of MR imaging contrast in draining lymph nodes on the size of the particle-shaped contrast agents injected subcutaneously. Particle size represented passive and active targeting eŠects, so micron-sized particles produced delayed enhancement.Conclusion: Choosing the size of iron oxide particles for MR imaging contrast depends on the objective of observation, such as identifying the morphology or migration of immune cells in the lymph node.

From cartoon to real time MRI: in vivo monitoring of phagocyte migration in mouse brain

“…To overcome inherent limitations in the signal to noise ratio (SNR) of conventional in vivo MRI, a stronger magnetic field can be applied. In addition, super-paramagnetic nanoparticles of iron oxide (SPIO), a contrast agent for MRI, improves MRI contrast to noise ratio (CNR) and detectability in the stronger magnetic fields by shortening the T 2 /T 2 * relaxation time, further advancing MRI application in cell imaging and tracking789. Combining high-magnetic-field strength with high-sensitivity radio-frequency (RF) coils and optimal contrast agents enables the visualisation of cell populations and molecular events in vivo in both animals and humans910.…”

Comparison of three magnetic nanoparticle tracers for sentinel lymph node biopsy in an in vivo porcine model

“…The purpose of these studies was to optimize tracer uptake in the SLNs to facilitate preoperative localization with MRI, rather than intraoperative detection. Mori et al 30 used 50 nm, 100 nm, 200 nm, and 1,000 nm-sized particles and concluded that particles of 200 nm and larger are not suitable in view of lack of uptake within 24 hours. Iida et al 28 compared the performance of 4 nm, 8 nm, and 20 nm citrate-coated nanoparticles and concluded that the 20 nm particles were best retained in the SLNs and accumulated in the highest concentration.…”

“…[28][29][30] Tracers with particle sizes ranging from 4 to 1,000 nm were used in these studies. The purpose of these studies was to optimize tracer uptake in the SLNs to facilitate preoperative localization with MRI, rather than intraoperative detection.…”

Image alignment for single-cell imaging of macrophage in the mouse brain using 11.7T MRI

“…Mori et al developed a novel method for monitoring single cell dynamics of macrophages using a high tesla magnetic resonance imaging (MRl) system [3] [4]. It acquires time series sectional macrophage images with contrast using 11.7 T MRI.…”