Abstract
BackgroundThe first aim of this study was to evaluate the correlation between clinical and physical-technical image quality applied to different strengths of iterative reconstruction in chest CT images using Thiel cadaver acquisitions and Catphan images. The second aim was to determine the potential dose reduction of iterative reconstruction compared to conventional filtered back projection based on different clinical and physical-technical image quality parameters.MethodsClinical image quality was assessed using three Thiel embalmed human cadavers. A Catphan phantom was used to assess physical-technical image quality parameters such as noise, contrast-detail and contrast-to-noise ratio (CNR).Both Catphan and chest Thiel CT images were acquired on a multislice CT scanner at 120 kVp and 0.9 pitch. Six different refmAs settings were applied (12, 30, 60, 90, 120 and 150refmAs) and each scan was reconstructed using filtered back projection (FBP) and iterative reconstruction (SAFIRE) algorithms (1,3 and 5 strengths) using a sharp kernel, resulting in 24 image series. Four radiologists assessed the clinical image quality, using a visual grading analysis (VGA) technique based on the European Quality Criteria for Chest CT.ResultsCorrelation coefficients between clinical and physical-technical image quality varied from 0.88 to 0.92, depending on the selected physical-technical parameter. Depending on the strength of SAFIRE, the potential dose reduction based on noise, CNR and the inverse image quality figure (IQFinv) varied from 14.0 to 67.8 %, 16.0 to 71.5 % and 22.7 to 50.6 % respectively. Potential dose reduction based on clinical image quality varied from 27 to 37.4 %, depending on the strength of SAFIRE.ConclusionOur results demonstrate that noise assessments in a uniform phantom overestimate the potential dose reduction for the SAFIRE IR algorithm. Since the IQFinv based dose reduction is quite consistent with the clinical based dose reduction, an optimised contrast-detail phantom could improve the use of contrast-detail analysis for image quality assessment in chest CT imaging. In conclusion, one should be cautious to evaluate the performance of CT equipment taking into account only physical-technical parameters as noise and CNR, as this might give an incomplete representation of the actual clinical image quality performance.
Highlights
The first aim of this study was to evaluate the correlation between clinical and physical-technical image quality applied to different strengths of iterative reconstruction in chest CT images using Thiel cadaver acquisitions and Catphan images
To evaluate the correlation between clinical and physical-technical image quality, regression curves were plotted for noise, contrast-to-noise ratio (CNR) and IQFinv as a function of visual grading analysis (VGA) scores for the different refmAs settings (Fig. 3)
Potential dose reduction based on clinical image quality varied from 27 to 37.4 % depending on the strength of iterative reconstruction
Summary
The first aim of this study was to evaluate the correlation between clinical and physical-technical image quality applied to different strengths of iterative reconstruction in chest CT images using Thiel cadaver acquisitions and Catphan images. The second aim was to determine the potential dose reduction of iterative reconstruction compared to conventional filtered back projection based on different clinical and physical-technical image quality parameters. A lot of efforts have been made over the last decade to reduce the radiation dose for the patient by introducing new techniques such as automatic tube current modulation, adaptive collimation and iterative reconstruction [3,4,5,6]. Medical physicists assess the image quality in CT using technical phantoms, evaluating parameters as noise, modulation transfer function (MTF), contrast-to-noise ratio (CNR) and/or contrast-detail. As these phantom models are not related to patient anatomy, it is unclear whether this methodology is appropriate to evaluate the clinical image quality. To be able to compare the performance of different CT scanners or to evaluate dose optimisation tools, it is of critical importance that physical-technical image quality based dose optimisation performance is related to the clinical image quality based dose optimisation performance
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have