Abstract
Purpose
To assess the dose performance in terms of image quality of filtered back projection (FBP) and two generations of iterative reconstruction (IR) algorithms developed by the most common CT vendors.
Materials and methods
We used four CT systems equipped with a hybrid/statistical IR (H/SIR) and a full/partial/advanced model-based IR (MBIR) algorithms. Acquisitions were performed on an ACR phantom at five dose levels. Raw data were reconstructed using a standard soft tissue kernel for FBP and one iterative level of the two IR algorithm generations. The noise power spectrum (NPS) and the task-based transfer function (TTF) were computed. A detectability index (d′) was computed to model the detection task of a large mass in the liver (large feature; 120 HU and 25-mm diameter) and a small calcification (small feature; 500 HU and 1.5-mm diameter).
Results
With H/SIR, the highest values of d′ for both features were found for Siemens, then for Canon and the lowest values for Philips and GE. For the large feature, potential dose reductions with MBIR compared with H/SIR were − 35% for GE, − 62% for Philips, and − 13% for Siemens; for the small feature, corresponding reductions were − 45%, − 78%, and − 14%, respectively. With the Canon system, a potential dose reduction of − 32% was observed only for the small feature with MBIR compared with the H/SIR algorithm. For the large feature, the dose increased by 100%.
Conclusion
This multivendor comparison of several versions of IR algorithms allowed to compare the different evolution within each vendor. The use of d′ is highly adapted and robust for an optimization process.
Key Points
• The performance of four CT systems was evaluated by using imQuest software to assess noise characteristic, spatial resolution, and lesion detection.
• Two task functions were defined to model the detection task of a large mass in the liver and a small calcification.
• The advantage of task-based image quality assessment for radiologists is that it does not include only complicated metrics, but also clinically meaningful image quality.
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Abbreviations
- CTDI:
-
CT dose index
- CTDIvol :
-
Volume CT dose index
- ESF:
-
Edge-spread function
- FBP:
-
Filtered back projection
- H/SIR:
-
Hybrid or statistical iterative reconstruction
- IR:
-
Iterative reconstruction
- LSF:
-
Line-spread function
- MBIR:
-
Full or advanced or partial model-based iterative reconstruction
- NPS:
-
Noise power spectrum
- TTF:
-
Task-based transfer function
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Acknowledgments
We are deeply grateful to Dr. J. Solomon for support regarding the use of imQuest software. We would like to thank Pr H. Rousseau and Dr. J.M. Teissier for giving us permission to use their measurement results.
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The scientific guarantor of this publication is Jean Paul Beregi.
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Greffier, J., Frandon, J., Larbi, A. et al. CT iterative reconstruction algorithms: a task-based image quality assessment. Eur Radiol 30, 487–500 (2020). https://doi.org/10.1007/s00330-019-06359-6
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DOI: https://doi.org/10.1007/s00330-019-06359-6