title: Ventilation distribution in rats: Part 2--A comparison of electrical impedance tomography and hyperpolarised helium magnetic resonance imaging.
abstract: BACKGROUND
  Hyperpolarised helium MRI (He3 MRI) is a new technique that enables imaging of the air distribution within the lungs. This allows accurate determination of the ventilation distribution in vivo. The technique has the disadvantages of requiring an expensive helium isotope, complex apparatus and moving the patient to a compatible MRI scanner. Electrical impedance tomography (EIT) a non-invasive bedside technique that allows constant monitoring of lung impedance, which is dependent on changes in air space capacity in the lung. We have used He3MRI measurements of ventilation distribution as the gold standard for assessment of EIT.
  
  
  METHODS
  Seven rats were ventilated in supine, prone, left and right lateral position with 70% helium/30% oxygen for EIT measurements and pure helium for He3 MRI. The same ventilator and settings were used for both measurements. Image dimensions, geometric centre and global in homogeneity index were calculated.
  
  
  RESULTS
  EIT images were smaller and of lower resolution and contained less anatomical detail than those from He3 MRI. However, both methods could measure positional induced changes in lung ventilation, as assessed by the geometric centre. The global in homogeneity index were comparable between the techniques.
  
  
  CONCLUSIONS
  EIT is a suitable technique for monitoring ventilation distribution and inhomgeneity as assessed by comparison with He3 MRI.
authors.affiliation: Paediatric Critical Care Research Group, Paediatric Intensive Care Unit, Mater Children's Hospital, South Brisbane, 4101, QLD, Australia. k.dunster@qut.edu.au
authors.forename: Kimble R
authors.initials: KR
authors.lastname: Dunster
authors.forename: Marlies E J
authors.initials: ME
authors.lastname: Friese
authors.forename: John F
authors.initials: JF
authors.lastname: Fraser
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Galloway
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Cowin
authors.forename: Andreas
authors.initials: A
authors.lastname: Schibler
mesh_terms: D000818:Animals; D017097:Electric Impedance; D005260:Female; D006371:Helium; D008279:Magnetic Resonance Imaging; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012121:Respiration, Artificial / Q000379:methods*; D014054:Tomography
chemical_list: D006371:Helium