Positive contrast of SPIO-labeled cells by off-resonant reconstruction of 3D radial half-echo bSSFP.
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.
Institute of Medical Engineering, Graz University of Technology, Graz, Austria; BioTechMed-Graz, Graz, Austria.
Clemens
C
Diwoky
Daniel
D
Liebmann
Bernhard
B
Neumayer
Andreas
A
Reinisch
Florian
F
Knoll
Dirk
D
Strunk
Rudolf
R
Stollberger
D000818:Animals; D003198:Computer Simulation; D003287:Contrast Media; D003911:Dextrans / Q000378:metabolism*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007279:Injections, Subcutaneous; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D051379:Mice; D019047:Phantoms, Imaging; D012815:Signal Processing, Computer-Assisted; D013194:Staining and Labeling
D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; C065507:ferumoxides
3D radial half-echo sampling; bSSFP; off-resonant reconstruction; positive contrast; stem cell tracking