Evaluation of Apparent Noise on CT Images Using Moving Average Filters

This study aims to devise a simple method for evaluating the magnitude of texture noise (apparent noise) observed on computed tomography (CT) images scanned at a low radiation dose and reconstructed using iterative reconstruction (IR) and deep learning reconstruction (DLR) algorithms, and to evaluat...

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Bibliographic Details
Published in:Journal of digital imaging 2022-02, Vol.35 (1), p.77-85
Main Authors: Fujii, Keisuke, Nomura, Keiichi, Imai, Kuniharu, Muramatsu, Yoshihisa, Tsushima, So, Ota, Hiroyuki
Format: Article
Language:English
Subjects:
Algorithms
Computed tomography
Curve fitting
Deep learning
Filters
Frequency dependence
Humans
Image contrast
Image filters
Image reconstruction
Imaging
Iterative methods
Machine learning
Mean
Medical imaging
Medicine
Medicine & Public Health
Noise
Phantoms, Imaging
Radiation
Radiation Dosage
Radiographic Image Interpretation, Computer-Assisted - methods
Radiology
Texture
Tomography, X-Ray Computed - methods
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Summary:This study aims to devise a simple method for evaluating the magnitude of texture noise (apparent noise) observed on computed tomography (CT) images scanned at a low radiation dose and reconstructed using iterative reconstruction (IR) and deep learning reconstruction (DLR) algorithms, and to evaluate the apparent noise in CT images reconstructed using the filtered back projection (FBP), IR, and two types of DLR (AiCE Body and AiCE Body Sharp) algorithms. We set a square region of interest (ROI) on CT images of standard- and obese-sized low-contrast phantoms, slid different-sized moving average filters in the ROI vertically and horizontally in steps of 1 pixel, and calculated the standard deviation (SD) of the mean CT values for each filter size. The SD of the mean CT values was fitted with a curve inversely proportional to the filter size, and an apparent noise index was determined from the curve-fitting formula. The apparent noise index of AiCE Body Sharp images for a given mAs value was approximately 58, 23, and 18% lower than that of the FBP, AIDR 3D, and AiCE Body images, respectively. The apparent noise index was considered to reflect noise power spectrum values at lower spatial frequency. Moreover, the apparent noise index was inversely proportional to the square roots of the mAs values. Thus, the apparent noise index could be a useful indicator to quantify and compare texture noise on CT images obtained with different scan parameters and reconstruction algorithms.
ISSN:0897-1889
1618-727X
DOI:10.1007/s10278-021-00531-5