title: Selective magnetic resonance imaging of magnetic nanoparticles by acoustically induced rotary saturation.
abstract: OBJECTIVE
  The goal of this study was to introduce a new method to selectively detect iron oxide contrast agents using an acoustic wave to perturb the spin-locked water signal in the vicinity of the magnetic particles. The acoustic drive can be modulated externally to turn the effect on and off, allowing sensitive and quantitative statistical comparison and removal of confounding image background variations.
  
  
  METHODS
  We demonstrated the effect in spin-locking experiments using piezoelectric actuators to generate vibrational displacements of iron oxide samples. We observed a resonant behavior of the signal changes with respect to the acoustic frequency where iron oxide is present. We characterized the effect as a function of actuator displacement and contrast agent concentration.
  
  
  RESULTS
  The resonant effect allowed us to generate block-design "modulation response maps" indicating the contrast agent's location, as well as positive contrast images with suppressed background signal. We found that the acoustically induced rotary saturation (AIRS) effect stayed approximately constant across acoustic frequency and behaved monotonically over actuator displacement and contrast agent concentration.
  
  
  CONCLUSIONS
  AIRS is a promising method capable of using acoustic vibrations to modulate the contrast from iron oxide nanoparticles and thus perform selective detection of the contrast agents, potentially enabling more accurate visualization of contrast agents in clinical and research settings.
authors.affiliation: Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.|Harvard-MIT Division of Health Sciences Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhu
authors.affiliation: Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Witzel
authors.affiliation: David H Koch Institute for Integrative Cancer Research, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Shan
authors.initials: S
authors.lastname: Jiang
authors.affiliation: Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.
authors.forename: Susie Y
authors.initials: SY
authors.lastname: Huang
authors.affiliation: Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.|Department of Meridian & Acupuncture, Collaborating Center for Traditional Medicine, East-West Medical Research Institute and School of Korean Medicine, Kyung Hee University, Seoul, Republic of Korea.|Harvard-MIT Division of Health Sciences Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Rosen
authors.affiliation: Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA.|Harvard-MIT Division of Health Sciences Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Wald
mesh_terms: D003287:Contrast Media / Q000737:chemistry / Q000528:radiation effects; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles / Q000737:chemistry / Q000528:radiation effects* / Q000648:ultrastructure*; D057054:Molecular Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012399:Rotation; D012680:Sensitivity and Specificity; D013016:Sound
chemical_list: D003287:Contrast Media; D058185:Magnetite Nanoparticles
keywords: MR contrast agent; contrast mechanism; molecular imaging; positive contrast/spin-lock