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Self‐refocused spatial‐spectral pulse for positive contrast imaging of cells labeled with SPIO nanoparticles
Author(s) -
Balchandani Priti,
Yamada Mayumi,
Pauly John,
Yang Phillip,
Spielman Daniel
Publication year - 2009
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21973
Subject(s) - imaging phantom , pulse (music) , materials science , nuclear magnetic resonance , spins , contrast (vision) , magnetic resonance imaging , pulse sequence , optics , biomedical engineering , physics , medicine , radiology , detector
MRI has been used extensively to noninvasively track the location of cells labeled with superparamagnetic iron‐oxide nanoparticles (SPIOs) in vivo. Typically, SPIOs are employed as a negative contrast agent which makes it difficult to differentiate labeled cells from extraneous sources of inhomogeneity and actual voids in the image. As a result, several novel approaches have been put forth to obtain positive contrast from SPIOs. One technique proposed by Cunningham et al. utilizes spectrally selective pulses to excite and refocus spins in the vicinity of the SPIOs. Although the frequency selectivity of this technique provides effective positive contrast, the lack of slice selectivity results in interfering signal from sources of off‐resonance outside the slice of interest. We have developed a self‐refocused spatial‐spectral (SR‐SPSP) pulse to achieve slice‐selective spin‐echo imaging of off‐resonant spins. Using a self‐refocused pulse affords flexibility in echo‐time selection since the spin echo may be placed at any time after the end of the pulse. The spatial selectivity achieved by the SR‐SPSP RF pulse eliminates background signal from out‐of‐slice regions and reduces the on‐resonant water suppression requirements. Phantom and in vivo data demonstrate that positive contrast and slice‐selectivity are achieved using this novel RF pulse. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.