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Abulaiti ABUDUREZAKE, Terumasa MORITA, Takuya MORI, Atsushi AMANOObjectives: The aim of this study was to measure the diaphragm volume using three-dimensional computed tomography (3D-CT) and verify its validity.Design: This was a retrospective study of existing samples.Methods: Participants comprised five male patients, aged 65-70 years, who underwent preoperative chest CT (with a slice thickness of 0.5 mm) before coronary artery bypass surgery. The diaphragm was selectively extracted using a workstation to reconstruct a stereoscopic image, and the total muscle volume was measured. To confirm the accuracy and reproducibility of diaphragm muscle volume measurements on CT, all cases were measured three times by two observers, and intraclass correlation coefficients (ICCs) and interobserver correlations were determined.Results: Observers #1 and #2 reported an average diaphragm volume of 256.7±33 cm3 and 259.3±36 cm3, respectively. The ICC analyses yielded Cronbach’s alphas of 0.992 and 0.981 from both observers, and the interobserver correlation was 0.991. The ICC of a single measurement and the average measurement was 0.984 (95% confidence interval: 0.998-0.884) and 0.992 (95% confidence interval: 0.999-0.939), respectively.Conclusions: To our knowledge, this study is the first to standardize the method for measuring the total diaphragm volume and examine the reproducibility and validity of the new method. The diaphragm could be selectively extracted and reconstructed. Measurement of the total diaphragm muscle volume using a workstation to reconstruct a stereoscopic image is feasible and highly reproducible. This technique can be reliably employed to evaluate diaphragm volume, thickness, and morphology.Key words: diaphragm, diaphragm volume, respiratory muscles, three-dimensional computed tomography, workstationJuntendo Medical Journal2022. 68(5), 481-490Original ArticlesIntroductionThe diaphragm is the main muscle involved in functions during breathing1). respiration, and Understanding its anatomy is important for surgical treatment. Furthermore, an accurate evaluation of respiratory function during surgery performed under general anesthesia is an absolute condition for safely performing intraoperative and postoper-ative management and directly affects the surgical outcome, especially in thoracic surgery with thora-cotomy2, 3). Mechanical ventilation (MV) is neces-Department of Cardiovascular Surgery, Juntendo University Graduate School of Medicine, Tokyo, JapanCorresponding author: Abulaiti AbudurezakeDepartment of Cardiovascular Surgery, Juntendo University Graduate School of Medicine2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, JapanTEL: +81-3-5802-1080　FAX: +81-3-3815-5228　E-mail: abudoure@juntendo.ac.jp〔Received　Feb. 16, 2022〕〔Accepted　Jun. 16, 2022〕J-STAGE Advance published date: Sep. 9, 2022Copyright © 2022 The Juntendo Medical Society. This is an open access article distributed under the terms of Creative Commons Attribution License (CC BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original source is properly credited. doi: 10.14789/jmj.JMJ22-0006-OAsary during surgery, as well as after surgery in the intensive care unit (ICU)4-6). Multiple studies have suggested that MV has a significant effect on the respiratory system, especially the respiratory muscles7, 8). In animal experiments, inactivity of the diaphragm on MV and passive ventilation lasting for more than 18 hours induced atrophy in the muscle fibers of the diaphragm7, 9). This is also the case for the human diaphragm; MV for 18-69 hours resulted in significant atrophy of the human diaphragm muscle fibers10). A clinical study that measured muscle thickness using echography 481Validity of Diaphragm Volume Measurements Using Three-Dimensional Computed Tomography