title: The use of combined single photon emission computed tomography and X-ray computed tomography to assess the fate of inhaled aerosol.
abstract: BACKGROUND
  Gamma camera imaging is widely used to assess pulmonary aerosol deposition. Conventional planar imaging provides limited information on its regional distribution. In this study, single photon emission computed tomography (SPECT) was used to describe deposition in three dimensions (3D) and combined with X-ray computed tomography (CT) to relate this to lung anatomy. Its performance was compared to planar imaging.
  
  
  METHODS
  Ten SPECT/CT studies were performed on five healthy subjects following carefully controlled inhalation of radioaerosol from a nebulizer, using a variety of inhalation regimes. The 3D spatial distribution was assessed using a central-to-peripheral ratio (C/P) normalized to lung volume and for the right lung was compared to planar C/P analysis. The deposition by airway generation was calculated for each lung and the conducting airways deposition fraction compared to 24-h clearance.
  
  
  RESULTS
  The 3D normalized C/P ratio correlated more closely with 24-h clearance than the 2D ratio for the right lung [coefficient of variation (COV), 9% compared to 15% p < 0.05]. Analysis of regional distribution was possible for both lungs in 3D but not in 2D due to overlap of the stomach on the left lung. The mean conducting airways deposition fraction from SPECT for both lungs was not significantly different from 24-h clearance (COV 18%). Both spatial and generational measures of central deposition were significantly higher for the left than for the right lung.
  
  
  CONCLUSIONS
  Combined SPECT/CT enabled improved analysis of aerosol deposition from gamma camera imaging compared to planar imaging. 3D radionuclide imaging combined with anatomical information from CT and computer analysis is a useful approach for applications requiring regional information on deposition.
authors.affiliation: Department of Medical Physics and Bioengineering, Southampton University Hospitals, NHS Trust, Southampton, United Kingdom. john.fleming@suht.swest.nhs.uk
authors.forename: John
authors.initials: J
authors.lastname: Fleming
authors.forename: Joy
authors.initials: J
authors.lastname: Conway
authors.forename: Caroline
authors.initials: C
authors.lastname: Majoral
authors.forename: Livia
authors.initials: L
authors.lastname: Tossici-Bolt
authors.forename: Ira
authors.initials: I
authors.lastname: Katz
authors.forename: Georges
authors.initials: G
authors.lastname: Caillibotte
authors.forename: Diane
authors.initials: D
authors.lastname: Perchet
authors.forename: Marine
authors.initials: M
authors.lastname: Pichelin
authors.forename: Bernhard
authors.initials: B
authors.lastname: Muellinger
authors.forename: Ted
authors.initials: T
authors.lastname: Martonen
authors.forename: Philipp
authors.initials: P
authors.lastname: Kroneberg
authors.forename: Gabriela
authors.initials: G
authors.lastname: Apiou-Sbirlea
mesh_terms: D000280:Administration, Inhalation; D000293:Adolescent; D000328:Adult; D000336:Aerosols; D000368:Aged; D015902:Gamma Cameras; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009330:Nebulizers and Vaporizers; D010865:Pilot Projects; D013668:Technetium Tc 99m Aggregated Albumin / Q000008:administration & dosage / Q000493:pharmacokinetics*; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
chemical_list: D000336:Aerosols; D013668:Technetium Tc 99m Aggregated Albumin; C083602:technetium Tc 99m nanocolloid