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Positive contrast of SPIO‐labeled cells by off‐resonant reconstruction of 3D radial half‐echo bSSFP
Author(s) -
Diwoky Clemens,
Liebmann Daniel,
Neumayer Bernhard,
Reinisch Andreas,
Knoll Florian,
Strunk Dirk,
Stollberger Rudolf
Publication year - 2015
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.3229
Subject(s) - imaging phantom , contrast (vision) , gradient echo , isotropy , nuclear magnetic resonance , robustness (evolution) , materials science , biomedical engineering , magnetic resonance imaging , computer science , physics , chemistry , optics , computer vision , medicine , radiology , biochemistry , gene
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. Copyright © 2014 John Wiley & Sons, Ltd.