title: Comparison of CT-derived ventilation maps with deposition patterns of inhaled microspheres in rats.
abstract: OBJECTIVE
  Computer models for inhalation toxicology and drug-aerosol delivery studies rely on ventilation pattern inputs for predictions of particle deposition and vapor uptake. However, changes in lung mechanics due to disease can impact airflow dynamics and model results. It has been demonstrated that non-invasive, in vivo, 4DCT imaging (3D imaging at multiple time points in the breathing cycle) can be used to map heterogeneities in ventilation patterns under healthy and disease conditions. The purpose of this study was to validate ventilation patterns measured from CT imaging by exposing the same rats to an aerosol of fluorescent microspheres (FMS) and examining particle deposition patterns using cryomicrotome imaging.
  
  
  METHODS
  Six male Sprague-Dawley rats were intratracheally instilled with elastase to a single lobe to induce a heterogeneous disease. After four weeks, rats were imaged over the breathing cycle by CT then immediately exposed to an aerosol of ∼ 1 μm FMS for ∼ 5 minutes. After the exposure, the lungs were excised and prepared for cryomicrotome imaging, where a 3D image of FMS deposition was acquired using serial sectioning. Cryomicrotome images were spatially registered to match the live CT images to facilitate direct quantitative comparisons of FMS signal intensity with the CT-based ventilation maps.
  
  
  RESULTS
  Comparisons of fractional ventilation in contiguous, non-overlapping, 3D regions between CT-based ventilation maps and FMS images showed strong correlations in fractional ventilation (r = 0.888, p < 0.0001).
  
  
  CONCLUSIONS
  We conclude that ventilation maps derived from CT imaging are predictive of the 1 μm aerosol deposition used in ventilation-perfusion heterogeneity inhalation studies.
authors.affiliation: 1Health Impacts and Exposure Science, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Jacob
authors.forename: Wayne J
authors.initials: WJ
authors.lastname: Lamm
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Einstein
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Krueger
authors.forename: Robb W
authors.initials: RW
authors.lastname: Glenny
authors.forename: Richard A
authors.initials: RA
authors.lastname: Corley
mesh_terms: D000280:Administration, Inhalation; D000336:Aerosols / Q000378:metabolism*; D000818:Animals; D021621:Imaging, Three-Dimensional / Q000379:methods; D008168:Lung / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000502:physiology; D008297:Male; D008863:Microspheres; D012123:Pulmonary Ventilation / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D000336:Aerosols
keywords: CT imaging; animal models; fluorescent microspheres; lung; particle deposition; ventilation