Impact of ROI Size on the Accuracy of Noise Measurement in CT on Computational and ACR Phantoms

Choirul Anam; Pandji Triadyaksa; Ariij Naufal; Zaenal Arifin; Zaenul Muhlisin; Evi Setiawati; Wahyu Setia Budi

doi:10.31661/jbpe.v0i0.2202-1457

Impact of ROI Size on the Accuracy of Noise Measurement in CT on Computational and ACR Phantoms

J Biomed Phys Eng. 2022 Aug 1;12(4):359-368. doi: 10.31661/jbpe.v0i0.2202-1457. eCollection 2022 Aug.

Authors

Choirul Anam¹, Pandji Triadyaksa¹, Ariij Naufal², Zaenal Arifin², Zaenul Muhlisin², Evi Setiawati², Wahyu Setia Budi¹

Affiliations

¹ PhD, Department of Physics, Faculty of Sciences and Mathematics, Diponegoro University, Jl. Prof. Soedarto SH, Tembalang, Semarang 50275, Central Java, Indonesia.
² MSc, Department of Physics, Faculty of Sciences and Mathematics, Diponegoro University, Jl. Prof. Soedarto SH, Tembalang, Semarang 50275, Central Java, Indonesia.

Abstract

Background: The effect of region of interest (ROI) size variation on producing accurate noise levels is not yet studied.

Objective: This study aimed to evaluate the influence of ROI sizes on the accuracy of noise measurement in computed tomography (CT) by using images of a computational and American College of Radiology (ACR) phantoms.

Material and methods: In this experimental study, two phantoms were used, including computational and ACR phantoms. A computational phantom was developed by using Matlab R215a software (Mathworks Inc., Natick, MA Natick, MA) with a homogeneously +100 Hounsfield Unit (HU) value and an added-Gaussian noise with various levels of 5, 10, 25, 50, 75, and 100 HU. The ACR phantom was scanned with a Philips MX-16 slice CT scanner in different slice thicknesses of 1.5, 3, 5, and 7 mm to obtain noise variation. Noise measurement was conducted at the center of the phantom images and four locations close to the edge of the phantom images using different ROI sizes from 3 × 3 to 41 × 41 pixels, with an increased size of 2 × 2 pixels.

Results: The use of a minimum ROI size of 21 × 21 pixels shows noise in the range of ± 5% ground truth noise. The measured noise increases above the ± 5% range if the used ROI is smaller than 21 × 21 pixels.

Conclusion: A minimum acceptable ROI size is required to maintain the accuracy of noise measurement with a size of 21 × 21 pixels.

Keywords: ACR Phantom; Computational Phantom; Diagnostic Imaging; Image Quality; Noise Measurement; Radiologic Phantoms; Tomography, X-Ray Computed; X-Rays.