title: Controlling diffusion of 3He by buffer gases: a structural contrast agent in lung MRI.
abstract: OBJECTIVE
  To study the influence of admixing inert buffer gases to laser-polarized (3)He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution.
  
  
  METHODS
  The diffusion coefficient of (3)He was altered by admixing buffer gases of various molecular weights ((4)He, N(2), and SF(6)). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laser-polarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments.
  
  
  RESULTS
  Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted and was experimentally validated. Images acquired under such conditions revealed improved resolution. The nature and concentration of the admixed gas defines a structural threshold for the observed apparent diffusion coefficient (ADC) as demonstrated with diffusion-weighted MRI on a pig's lung flooded with suitable gas mixtures.
  
  
  CONCLUSIONS
  A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. Their molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this enables images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion.
authors.affiliation: Max Planck-Institute for Polymer Research, Mainz, Germany.
authors.forename: Rodolfo H
authors.initials: RH
authors.lastname: Acosta
authors.forename: Peter
authors.initials: P
authors.lastname: Blümler
authors.forename: Luis
authors.initials: L
authors.lastname: Agulles-Pedrós
authors.forename: Andreas E
authors.initials: AE
authors.lastname: Morbach
authors.forename: Jörg
authors.initials: J
authors.lastname: Schmiedeskamp
authors.forename: Annette
authors.initials: A
authors.lastname: Herweling
authors.forename: Ursula
authors.initials: U
authors.lastname: Wolf
authors.forename: Alexander
authors.initials: A
authors.lastname: Scholz
authors.forename: Wolfgang G
authors.initials: WG
authors.lastname: Schreiber
authors.forename: Werner
authors.initials: W
authors.lastname: Heil
authors.forename: Manfred
authors.initials: M
authors.lastname: Thelen
authors.forename: Hans-Wolfgang
authors.initials: HW
authors.lastname: Spiess
mesh_terms: D003287:Contrast Media / Q000737:chemistry*; D038524:Diffusion Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D005740:Gases / Q000737:chemistry; D006371:Helium / Q000737:chemistry*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007554:Isotopes / Q000737:chemistry; D008168:Lung / Q000033:anatomy & histology* / Q000737:chemistry*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D005740:Gases; D007554:Isotopes; D006371:Helium