A Voxel-Based Assessment of Noise Properties in Computed Tomography Imaging with the ASiR-V and ASiR Iterative Reconstruction Algorithms

Patrizio Barca,Antonio Claudio Traino,Daniela Marfisi,Stefano Diciotti,Marco Giannelli,Chiara Marzi,Sabino Cozza

doi:10.3390/app11146561

Abstract

Given the inherent characteristics of nonlinearity and nonstationarity of iterative reconstruction algorithms in computed tomography (CT) imaging, this study aimed to perform, for the first time, a voxel-based characterization of noise properties in CT imaging with the ASiR-V and ASiR algorithms as compared with conventional filtered back projection (FBP). Multiple repeated scans of the Catphan-504 phantom were carried out. CT images were reconstructed using FBP and ASiR/ASiR-V with different blending levels of reconstruction (20%, 40%, 60%, 80%, 100%). Noise maps and their nonuniformity index (NUI) were obtained according to the approach proposed by the report of AAPM TG-233. For the homogeneous CTP486 module, ASiR-V/ASiR allowed a noise reduction of up to 63.7%/52.9% relative to FBP. While the noise reduction values of ASiR-V-/ASiR-reconstructed images ranged up to 33.8%/39.9% and 31.2%/35.5% for air and Teflon contrast objects, respectively, these values were approximately 60%/50% for other contrast objects (PMP, LDPE, polystyrene, acrylic, Delrin). Moreover, for all contrast objects but air and Teflon, ASiR-V showed a greater noise reduction potential than ASiR when the blending level was ≥40%. While noise maps of the homogenous CTP486 module showed only a slight spatial variation of noise (NUI < 5.2%) for all reconstruction algorithms, the NUI values of iterative-reconstructed images of the nonhomogeneous CTP404 module increased nonlinearly with blending level and were 19%/15% and 6.7% for pure ASiR-V/ASiR and FBP, respectively. Overall, these results confirm the potential of ASiR-V and ASiR in reducing noise as compared with conventional FBP, suggesting, however, that the use of pure ASiR-V or ASiR might be suboptimal for specific clinical applications.

Highlights

IntroductionGiven that computed tomography (CT) examinations are the major source of population exposure to ionizing radiation in industrialized countries [9,10], many strategies have been implemented to keep patient dose as low as reasonably achievable while maintaining a good diagnostic image quality [11]
N-filtered backprojection (FBP) and N-ASiR/N-ASiR-V maps of the CTP486 homogeneous module and CTP404 module with contrast objects are shown in Figures 1 and 2, respectively
PDN-ASiR and PDN-ASiR-V maps of the CTP486 homogeneous module and CTP404 module with contrast objects are displayed in Figures 3 and 4, respectively

Summary

Introduction

Given that CT examinations are the major source of population exposure to ionizing radiation in industrialized countries [9,10], many strategies have been implemented to keep patient dose as low as reasonably achievable while maintaining a good diagnostic image quality [11]. In this regard, acquisition-related approaches, such as tube current modulation (both in the axial and longitudinal planes), appropriate selection of tube voltage according to patient size, table motion, and gantry rotation speed optimization have been successfully adopted on modern CT scanners [11,12,13]. For each specific IR algorithm, a comprehensive characterization of the noise properties and quality of reconstructed CT images is recommended to adequately assess its dose reduction potential and usefulness

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Discussion

Conclusion