title: Hyperpolarized 3He MR imaging of the lung: effect of subject immobilization on the occurrence of ventilation defects.
abstract: OBJECTIVE
  To investigate immobilization-induced ventilation defects when performing hyperpolarized (3)He (H(3)He) magnetic resonance imaging (MRI) of the lung.
  
  
  METHODS
  Twelve healthy subjects underwent MRI of the lungs after inhalation of H(3)He gas at three time points: 1) immediately after having been positioned supine on the MRI scanner table, 2) at 45 minutes while remaining supine, 3) and immediately thereafter after having turned prone. All image sets were reviewed in random order by three independent, blinded readers who recorded number, location, and size of H(3)He ventilation defects. Scores were averaged for each time point and comparisons were made to determine change in number, location, and size of ventilation defects with time and positioning of the subject in the scanner.
  
  
  RESULTS
  At baseline supine, there were small numbers of defects in the dependent (posterior) and nondependent (anterior) portions of the lung (P = .625). At 45 minutes, there was a significant increase in the mean number of ventilation defects/slice (VDS) for the dependent (P = .005) and a decrease for the nondependent lung portions (P = .021). After subjects turned prone, mean VDS for posterior defects decreased significantly (P = .011), whereas those for anterior defects increased (P = .010). Most defects were less than 3 cm in diameter.
  
  
  CONCLUSIONS
  It was found that immobilization of the subject for an extended period led to increased number of H(3)He ventilation defects in the dependent portions of the lung. Therefore, after a subject is positioned in the scanner, H(3)He MR imaging should be performed quickly to avoid the occurrence of the immobilization-induced ventilation defects and possible overestimation of disease.
authors.affiliation: Center for In-vivo Hyperpolarized Gas MR Imaging, Department of Radiology, Box 801339, University of Virginia School of Medicine, Charlottesville, VA 22908, USA. jfm4q@virginia.edu
authors.forename: Jaime
authors.initials: J
authors.lastname: Mata
authors.forename: Talissa
authors.initials: T
authors.lastname: Altes
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Knake
authors.forename: John
authors.initials: J
authors.lastname: Mugler
authors.forename: James
authors.initials: J
authors.lastname: Brookeman
authors.forename: Eduard
authors.initials: E
authors.lastname: de Lange
mesh_terms: D000280:Administration, Inhalation; D000328:Adult; D005260:Female; D006371:Helium; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007103:Immobilization; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011187:Posture; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology*
chemical_list: D006371:Helium