Geometry and extension of signal voids in MR images induced by aggregations of magnetically labelled cells

Abstract

The ability of magnetic resonance imaging (MRI) to visualize magnetically labelled cells has attracted much attention for revealing cellular events. The present study addressed the geometry and the extension of signal voids in static signal dephasing MRI induced by aggregations of magnetically labelled cells by means of a three-dimensional numerical model. The magnetic field distortions around spherical cell aggregations were treated as equivalent to those of a magnetic dipole. Intravoxel signal dephasing and respective signal voids attributed to these field inhomogeneities were computed. Effects of cell concentration on the signal void in the plane of view were evaluated in terms of dipole magnetization. Signal void characteristics were scrutinized systematically for fundamental sequence parameters including echo time, voxel size and plane-of-view orientation. For all variables examined, significant changes in geometry as well as extension of signal voids were demonstrated. The results are of crucial importance to optimize and interpret MR images with regard to spatial accuracy as well as sensitivity to detect aggregations of labelled cells in vitro or even in vivo. It is anticipated that the dependence of the extension of signal voids on the local magnetization may be valuable for quantifying labelled cells.

Quantitative study of signal decay due to magnetic susceptibility interfaces: MRI simulations and experiments

“…4 that signal loss increases with TE and is greater as pixel size grows. This confirmed previous results [22] and we verified that the signal void increased nearly linearly with TE, as reported by Bos et al [6] who introduced the dephased-volume model, which simplifies the effect of a subvoxel susceptibility deviation to a localized suppression of the signal. The artifact is viewed simply as localized removal of the signal from the vicinity of the object.…”

Discrepancies between the fate of myoblast xenograft in mouse leg muscle and NMR label persistency after loading with Gd-DTPA or SPIOs

“…This makes accurate localization and quantification of SPIO distribution quite difficult to achieve. In some instances, computer simulations and in vitro assessment of the labeled cells prior to injection can help, 38 but quantitation remains generally an unresolved issue.…”

Molecular MRI for sensitive and specific detection of lung metastases

“…www.pnas.org/cgi/doi/10.1073/pnas.1000386107to a macroscopic signal loss similar to that produced by an aggregation of magnetically labeled cells in tissue (33), with a signal decay more likely proportional to the square of the echo time (TE). The long T 2 * of the HP gases in the native lung permit images to be acquired at longer TE than for 1 H MRI, thereby permitting dephasing of a larger surrounding volume of the magnetization.…”