title: Efficient imaging of midbrain nuclei using inverse double-echo steady-state acquisition.
abstract: OBJECTIVE
  Imaging of midbrain nuclei using T2- or T2*-weighted MRI often entails long echo time, leading to long scan time. In this study, an inverse double-echo steady-state (iDESS) technique is proposed for efficiently depicting midbrain nuclei.
  
  
  METHODS
  Thirteen healthy subjects participated in this study. iDESS was performed along with two sets of T2*-weighted spoiled gradient-echo images (SPGR1, with scan time identical to iDESS and SPGR2, using clinical scanning parameters as a reference standard) for comparison. Generation of iDESS composite images combining two echo signals was optimized for maximal contrast-to-noise ratio (CNR) between the red nuclei and surrounding tissues. Signal-to-noise ratios (SNRs) were calculated from the occipital lobe. Comparison was also made using phase-enhanced images as in standard susceptibility-weighted imaging (SWI).
  
  
  RESULTS
  The iDESS images present significantly higher SNR efficiency (171.3) than SPGR1 (158.7, p = 0.013) and SPGR2 (95.5, p < 10(-8)). iDESS CNR efficiency (19.2) is also significantly greater than SPGR1 (6.9, p < 10(-6)) and SPGR2 (14.3, p = 0.0016). Compared with DESS, iDESS provides further advantage on enhanced phase information and hence improved contrast on SWI-processed images.
  
  
  CONCLUSIONS
  iDESS efficiently depicts midbrain nuclei with improved CNR efficiency, increased SNR efficiency, and reduced scan time and is less prone to susceptibility signal loss from air-tissue interfaces.
authors.affiliation: Department of Computer Science and Information Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan and Institute of Medical Informatics, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan.
authors.forename: Ming-Long
authors.initials: ML
authors.lastname: Wu
authors.affiliation: Brain Imaging and Analysis Center, Duke University Medical Center, 2424 Erwin Road, Suite 501, Durham, North Carolina 27705 and Department of Diagnostic Radiology, The University of Hong Kong, Room 406, Block K, Queen Mary Hospital, Pok Fu Lam Road, Hong Kong.
authors.forename: Hing-Chiu
authors.initials: HC
authors.lastname: Chang
authors.affiliation: Department of Computer Science and Information Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan and Institute of Medical Informatics, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan.
authors.forename: Tzu-Cheng
authors.initials: TC
authors.lastname: Chao
authors.affiliation: Brain Imaging and Analysis Center, Duke University Medical Center, 2424 Erwin Road, Suite 501, Durham, North Carolina 27705.
authors.forename: Nan-Kuei
authors.initials: NK
authors.lastname: Chen
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008636:Mesencephalon / Q000033:anatomy & histology*; D009778:Occipital Lobe / Q000033:anatomy & histology; D055815:Young Adult