European Radiology

, Volume 24, Issue 6, pp 1239–1250

Optimal image reconstruction for detection and characterization of small pulmonary nodules during low-dose CT

  • SayedMasoud Hashemi
  • Hatem Mehrez
  • Richard S. C. Cobbold
  • Narinder S. Paul

DOI: 10.1007/s00330-014-3142-9

Cite this article as:
Hashemi, S., Mehrez, H., Cobbold, R.S.C. et al. Eur Radiol (2014) 24: 1239. doi:10.1007/s00330-014-3142-9



To optimize the slice thickness/overlap parameters for image reconstruction and to study the effect of iterative reconstruction (IR) on detectability and characterization of small non-calcified pulmonary nodules during low-dose thoracic CT.

Materials and methods

Data was obtained from computer simulations, phantom, and patient CTs. Simulations and phantom CTs were performed with 9 nodules (5, 8, and 10 mm with 100, −630, and −800 HU). Patient data were based on 11 ground glass opacities (GGO) and 9 solid nodules. For each analysis the nodules were reconstructed with filtered back projection and IR algorithms using 10 different combinations of slice thickness/overlap (0.5–5 mm). The attenuation (CT#) and the contrast to noise ratio (CNR) were measured. Spearman’s coefficient was used to correlate the error in CT# measurements and slice thickness. Paired Student’s t test was used to measure the significance of the errors.


CNR measurements: CNR increases with increasing slice thickness/overlap for large nodules and peaks at 4.0/2.0 mm for smaller ones. Use of IR increases the CNR of GGOs by 60 %.

CT# measurements: Increasing slice thickness/overlap above 3.0/1.5 mm results in decreased CT# measurement accuracy.


Optimal detection of small pulmonary nodules requires slice thickness/overlap of 4.0/2.0 mm. Slice thickness/overlap of 2.0/2.0 mm is required for optimal nodule characterization. IR improves conspicuity of small ground glass nodules through a significant increase in nodule CNR.

Key Points

• Slice thickness/overlap affects the accuracy of pulmonary nodule detection and characterization.

• Slice thickness ≥3 mm increases the risk of misclassifying small nodules.

• Optimal nodule detection during low-dose CT requires 4.0/2.0-mm reconstructions.

• Optimal nodule characterization during low-dose CT requires 2.0/2.0-mm reconstructions.

• Iterative reconstruction improves the CNR of ground glass nodules by 60 %.


Computed tomographyPulmonary nodule detectionUltra-low-dose reconstructionPulmonary nodule characterizationImage reconstruction

Copyright information

© European Society of Radiology 2014

Authors and Affiliations

  • SayedMasoud Hashemi
    • 1
  • Hatem Mehrez
    • 2
  • Richard S. C. Cobbold
    • 3
  • Narinder S. Paul
    • 4
  1. 1.Institute of Biomaterial and Biomedical EngineeringUniversity of TorontoTorontoCanada
  2. 2.Toshiba of Canada LtdMarkhamCanada
  3. 3.Institute of Biomaterial and Biomedical EngineeringUniversity of TorontoTorontoCanada
  4. 4.Medical Imaging, Toronto General HospitalUniversity Health NetworkTorontoCanada