title: Attenuation correction for lung SPECT: evidence of need and validation of an attenuation map derived from the emission data.
abstract: OBJECTIVE
  The aim of our study was to investigate the importance of attenuation correction (AC) in reconstructed and reprojected images on lung SPECT studies.
  
  
  METHODS
  Simulation studies were undertaken to evaluate the influence of AC on defect-to-normal ratios (D/N), to demonstrate the influence of errors in the correction map values and to detect lung boundaries used for AC. The use of a synthetic map (SM) for AC of the clinical data was also evaluated and the results compared with those obtained with data derived from CT (CTM). Additionally, the role of AC in reprojected SPECT data was assessed and level of noise on the 'planar-like' images was measured.
  
  
  RESULTS
  Phantom studies showed that AC markedly affects the D/N ratio. However, variations in micro values typical of those found in clinical studies resulted in relatively small changes in results. Eroded and dilated conditions did not cause any significant effect on D/N. The level of noise in the reprojected images is reduced in comparison with real planar data. Clinical SPECT/CT data reconstructed with AC using CTM and SM showed an excellent correlation between the two methods.
  
  
  CONCLUSIONS
  AC improves D/N in lung SPECT studies, thus potentially enhancing the diagnostic capability of the method. The use of a synthetic map for AC is feasible, avoiding the need for an additional procedure and the increased radiation dose involved. Planar-like images generated from reprojected SPECT data are well matched to normal planar images provided AC is performed and attenuation included in the reprojection.
authors.affiliation: University School of Medical Technology, Montevideo, Uruguay. marga.nr@gmail.com
authors.forename: Margarita
authors.initials: M
authors.lastname: Núñez
authors.forename: Vineet
authors.initials: V
authors.lastname: Prakash
authors.forename: Ricardo
authors.initials: R
authors.lastname: Vila
authors.forename: Fernando
authors.initials: F
authors.lastname: Mut
authors.forename: Omar
authors.initials: O
authors.lastname: Alonso
authors.forename: Brian F
authors.initials: BF
authors.lastname: Hutton
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional; D008168:Lung / Q000098:blood supply / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*