Tomography

Vol. 3 No. 2 - June 2017

Tomography is a scientific journal for publication of articles in imaging research

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Quantitative Image Quality Comparison of Reduced- and Standard-Dose Dual-Energy Multiphase Chest, Abdomen, and Pelvis CT Mario Buty 1 , Ziyue Xu 1 , Aaron Wu 1 , Mingchen Gao 1 , Chelyse Nelson 1 , Georgios Z. Papadakis 1 , Uygar Teomete 2 , Haydar Celik 1 , Baris Turkbey 1 , Peter Choyke 1 , Daniel J. Mollura 1 , Ulas Bagci 3 , and Les R. Folio 1 1 National Institutes of Health, Radiology and Imaging Sciences Bethesda, Maryland; 2 Bluefield Regional Medical Center, Bluefield, West Virginia; and 3 Center for Research in Computer Vision, University of Central Florida, Orlando, Florida Corresponding Author: Ulas Bagci, PhD Center for Research in Computer Vision, University of Central Florida, Orlando, FL 32816; E-mail: bagci@ucf.edu Key Words: image quality assessment, segmentation, volumetric quantification, texture, intensity- based quantification, quantitative analysis, image analysis Abbreviations: Computed tomography (CT), body mass index (BMI), virtual noncontrast- enhanced (VNC), structural similarity index (SSIM), gradient magnitude similarity deviation (GMSD), Hausdorff distance (HD), weighted spectral distance (WESD), dice similarity coefficient (DSC), Hounsfield unit (HU) We present a new image quality assessment method for determining whether reducing radiation dose im- pairs the image quality of computed tomography (CT) in qualitative and quantitative clinical analyses tasks. In this Institutional Review Board-exempt study, we conducted a review of 50 patients (male, 22; female, 28) who underwent reduced-dose CT scanning on the first follow-up after standard-dose multiphase CT scanning. Scans were for surveillance of von Hippel–Lindau disease (N 5 26) and renal cell carcinoma (N 5 10). We investigated density, morphometric, and structural differences between scans both at tissue (fat, bone) and organ levels (liver, heart, spleen, lung). To quantify structural variations caused by image quality differences, we propose using the following metrics: dice similarity coefficient, structural similarity index, Hausdorff dis- tance, gradient magnitude similarity deviation, and weighted spectral distance. Pearson correlation coeffi- cient and Welch 2-sample t test were used for quantitative comparisons of organ morphometry and to com- pare density distribution of tissue, respectively. For qualitative evaluation, 2-sided Kendall Tau test was used to assess agreement among readers. Both qualitative and quantitative evaluations were designed to examine significance of image differences for clinical tasks. Qualitative judgment served as an overall assessment, whereas detailed quantifications on structural consistency, intensity homogeneity, and texture similarity re- vealed more accurate and global difference estimations. Qualitative and quantitative results indicated no significant image quality degradation. Our study concludes that low(er)-dose CT scans can be routinely used because of no significant loss in quantitative image information compared with standard-dose CT scans. INTRODUCTION Approximately 80 million computed tomography (CT) examina- tions are performed annually in the United States and ;10% are conducted in pediatric patients (1). The use of CT has increased about eightfold since 1980 because of its diagnostic value in patient management (2). Further, ;49% of the US population's collective ionizing radiation dose is caused by exposure ob- tained during diagnostic CT (3). Highly variable radiation expo- sure, varying by as much as a factor of 10 between institutions for comparable scans has raised major concerns regarding the risk of radiation-induced cancer, particularly in pediatric pop- ulations (4, 5). Therefore, reducing radiation exposure is of major importance. Dose reduction was accomplished with team- work, stewardship (6), and a combination of device and case- specific measures such as flat and bowtie filters that reduce X-ray beams at angles deviating from the perpendicular and additional scanning units (7-9). Depending on diagnostic goals, radiation exposure may be reduced through variations in acquisition time, patient size, voltage, section thickness, window, reconstruction algorithms used, and filter kernel (7, 8). Specific body mass index (BMI) guidelines are commonly used in reducing radiation dose so that the dose is increased proportional to the BMI (8, 10-12). Most recent studies on image quality assessment of re- duced-dose CT scans have reported qualitative findings rather than quantitative, or they have focused on image noise and/or spatial resolution as sole indicators of image quality (1, 4, 13-17). Here, we quantitatively analyze the image quality and RESEARCH ARTICLE ABSTRACT © 2017 The Authors. Published by Grapho Publications, LLC This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). ISSN 2379-1381 http://dx.doi.org/10.18383/j.tom.2017.00002 114 TOMOGRAPHY.ORG | VOLUME 3 NUMBER 2 | JUNE 2017

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