title: Novel MRI contrast development by lock-in suppression.
abstract: OBJECTIVE
  The goal of this study is to develop novel MR contrast by frequency lock-in technique.
  
  
  METHODS
  An electronic feedback device that can control the frequency and bandwidth of the feedback RF field is presented. In this study, the effects of lock-in suppressed imaging are discussed both theoretically and experimentally.
  
  
  RESULTS
  Two important imaging experiments were performed. The first experiment used magnetizations with the same central frequency but different frequency distributions and was compared with MR images obtained with T2 contrast agents. Lock-in suppressed images showed an improvement in contrast relative to the conventional imaging method. The second experiment used magnetizations with small shifts in frequency and a broad frequency distribution. This is helpful for differentiating between small structural variations in biological tissues. The contrast achieved in in vivo tumor imaging using the lock-in suppressed technique provide higher spatial resolutions and discriminate the regimes of necrosis and activation consistent with pathologic results.
  
  
  CONCLUSIONS
  Lock-in suppressed imaging introduces a conceptually new approach to MRI. Heightened sensitivity to underlying susceptibility variations and their relative contribution to total magnetization may thus be achieved to yield new and enhanced contrast.
authors.affiliation: Department of Chemistry and Biochemistry, National Chung Cheng University, Min-Hsiung Township Chiayi, Taiwan.
authors.forename: Yu-Wen
authors.initials: YW
authors.lastname: Chen
authors.forename: Chao-Hsiung
authors.initials: CH
authors.lastname: Hsu
authors.forename: Chou-Hsiung
authors.initials: CH
authors.lastname: Hsu
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Hwang
mesh_terms: D000669:Amplifiers, Electronic; D000818:Animals; D045744:Cell Line, Tumor; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005246:Feedback; D007089:Image Enhancement / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000662:veterinary*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009062:Mouth Neoplasms / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*
keywords: MRI; feedback field; radiation damping; suppression