Positive contrast of SPIO‐labeled cells by off‐resonant reconstruction of 3D radial half‐echo bSSFP

Abstract

This article describes a new acquisition and reconstruction concept for positive contrast imaging of cells labeled with superparamagnetic iron oxides (SPIOs). Overcoming the limitations of a negative contrast representation as gained with gradient echo and fully balanced steady state (bSSFP), the proposed method delivers a spatially localized contrast with high cellular sensitivity not accomplished by other positive contrast methods. Employing a 3D radial bSSFP pulse sequence with half-echo sampling, positive cellular contrast is gained by adding artificial global frequency offsets to each half-echo before image reconstruction. The new contrast regime is highlighted with numerical intravoxel simulations including the point-spread function for 3D half-echo acquisitions. Furthermore, the new method is validated on the basis of in vitro cell phantom measurements on a clinical MRI platform, where the measured contrast-to-noise ratio (CNR) of the new approach exceeds even the negative contrast of bSSFP. Finally, an in vivo proof of principle study based on a mouse model with a clear depiction of labeled cells within a subcutaneous cell islet containing a cell density as low as 7 cells/mm(3) is presented. The resultant isotropic images show robustness to motion and a high CNR, in addition to an enhanced specificity due to the positive contrast of SPIO-labeled cells.

Ultrashort echo time magnetic resonance fingerprinting (UTE‐MRF) for simultaneous quantification of long and ultrashort T2 tissues

“…The excitation time would be halved with hard pulse volume excitation in 3D. 56,57 To speed up the acquisition further, effective 3D k-space sampling could be used. 58 As part of the future implementation of UTE-MRF techniques, we will adapt the preceding and other methods to accelerate the process.…”

Dextran-coated superparamagnetic iron oxide nanoparticles for magnetic resonance imaging: evaluation of size-dependent imaging properties, storage stability and safety

“…This allows an increase in MRI sensitivity almost to the cellular level and enables their use for in vivo cell visualization and tracking. [10][11][12] Until now, three SPION-based agents have been clinically approved as intravascular contrast agents for MRI, namely, ferumoxide (trade names: Feridex, Endorem), ferucarbotran (trade name: Resovist), and ferumoxtran-10 (trade name: Sinerem). These contrast agents were in the clinical use for diagnostic applications such as imaging of lymph nodes, intestine, liver, and the cardiovascular system.…”

Non-immunogenic dextran-coated superparamagnetic iron oxide nanoparticles: a biocompatible, size-tunable contrast agent for magnetic resonance imaging

“…2,3 Having strong T 2 and T 2 * effects in MRI, SPION/USPIO can be detected even at very low concentrations, allowing an increase of MRI sensitivity almost to the cellular level. 4,5 Consequently, SPION-labeling was shown to enable in vivo tracking of mononuclear cells, 6 as well as the real-time visualization of intra-arterial stem cell delivery to target…”