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Optimal image reconstruction for detection and characterization of small pulmonary nodules during low-dose CT
Authors:SayedMasoud Hashemi  Hatem Mehrez  Richard S. C. Cobbold  Narinder S. Paul
Affiliation:1. Institute of Biomaterial and Biomedical Engineering, University of Toronto, Room RS-420A, 164 College Street, Toronto, ON, Canada, M5S 3G9
2. Toshiba of Canada Ltd, 191 McNabb Street, Markham, ON, Canada, L3R-8H2
3. Institute of Biomaterial and Biomedical Engineering, University of Toronto, Room MB-316A,164 College Street, Toronto, ON, Canada, M5S 3G9
4. Medical Imaging, Toronto General Hospital, University Health Network, NCSB-1C562, 585 University Avenue, Toronto, ON, Canada, M5G 2 N2
Abstract:

Objectives

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.

Results

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.

Conclusion

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 %.
Keywords:
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