title: Regional alveolar partial pressure of oxygen measurement with parallel accelerated hyperpolarized gas MRI.
abstract: OBJECTIVE
  Alveolar oxygen tension (Pao2) is sensitive to the interplay between local ventilation, perfusion, and alveolar-capillary membrane permeability, and thus reflects physiologic heterogeneity of healthy and diseased lung function. Several hyperpolarized helium ((3)He) magnetic resonance imaging (MRI)-based Pao2 mapping techniques have been reported, and considerable effort has gone toward reducing Pao2 measurement error. We present a new Pao2 imaging scheme, using parallel accelerated MRI, which significantly reduces measurement error.
  
  
  METHODS
  The proposed Pao2 mapping scheme was computer-simulated and was tested on both phantoms and five human subjects. Where possible, correspondence between actual local oxygen concentration and derived values was assessed for both bias (deviation from the true mean) and imaging artifact (deviation from the true spatial distribution).
  
  
  RESULTS
  Phantom experiments demonstrated a significantly reduced coefficient of variation using the accelerated scheme. Simulation results support this observation and predict that correspondence between the true spatial distribution and the derived map is always superior using the accelerated scheme, although the improvement becomes less significant as the signal-to-noise ratio increases. Paired measurements in the human subjects, comparing accelerated and fully sampled schemes, show a reduced Pao2 distribution width for 41 of 46 slices.
  
  
  CONCLUSIONS
  In contrast to proton MRI, acceleration of hyperpolarized imaging has no signal-to-noise penalty; its use in Pao2 measurement is therefore always beneficial. Comparison of multiple schemes shows that the benefit arises from a longer time-base during which oxygen-induced depolarization modifies the signal strength. Demonstration of the accelerated technique in human studies shows the feasibility of the method and suggests that measurement error is reduced here as well, particularly at low signal-to-noise levels.
authors.affiliation: Department of Radiology, University of Pennsylvania, 308C Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104. Electronic address: stephen.kadlecek@uphs.upenn.edu.
authors.forename: Stephen
authors.initials: S
authors.lastname: Kadlecek
authors.forename: Hooman
authors.initials: H
authors.lastname: Hamedani
authors.forename: Yinan
authors.initials: Y
authors.lastname: Xu
authors.forename: Kiarash
authors.initials: K
authors.lastname: Emami
authors.forename: Yi
authors.initials: Y
authors.lastname: Xin
authors.forename: Masaru
authors.initials: M
authors.lastname: Ishii
authors.forename: Rahim
authors.initials: R
authors.lastname: Rizi
mesh_terms: D000328:Adult; D003287:Contrast Media / Q000493:pharmacokinetics; D005260:Female; D006371:Helium / Q000493:pharmacokinetics; D006801:Humans; D007554:Isotopes / Q000493:pharmacokinetics; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000378:metabolism*; D019047:Phantoms, Imaging; D011650:Pulmonary Alveoli / Q000378:metabolism* / Q000473:pathology; D029424:Pulmonary Disease, Chronic Obstructive / Q000378:metabolism*; D011659:Pulmonary Gas Exchange; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012907:Smoking / Q000378:metabolism* / Q000473:pathology
chemical_list: D003287:Contrast Media; D007554:Isotopes; D006371:Helium; D010100:Oxygen
keywords: Hyperpolarized MRI; accelerated imaging; alveolar oxygen tension
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