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to perform complete selective extraction, due to the requirement for manual selection and data extraction. Thus, accurate measurement depends on the selection criteria as well as the operating ability of the measurer. Moreover, 1-mm slices were used in previous studies21), whereas 0.5-mm slices were used in this study. We believe that manual selection and use of 0.5-mm slices enabled better evaluations; furthermore, in contrast to the previous study21), we have described the operation procedure and selection criteria in detail to make measurement easier to reproduce. Fluctuations in intraclass and interrater correlations are likely to be due to differences in manually selected areas. We believe that this difference will be smaller if the technical training and operating procedures are standardized.Although it remains uncertain whether the volume measured using the workstation Attractive Medical Image Processor software application, reflects the true volume of the diaphragm, other researchers have already confirmed that the volume of some organs measured on CT was the same as the actual volume. For example, in 1979, Heymsfield et al27). were the first to accurately measure liver, kidney, and spleen volumes and masses using computerized axial tomography. The authors showed that this method was accurate by comparing the estimated and actual weights obtained at autopsy. The determination of liver volume on CT is now widely used in the field of liver surgery28) and transplantation29). In 2002, Surusuk et al30). suggested that Heymsfield’s method27) is also reliable for the volumetric analysis of liver segments. Therefore, the diaphragm volume assessment in this study could have clinical value. However, this study was limited by its small sample size and retrospective nature. Consequently, the results were not sufficient to show the clinical usefulness of 3D-CT assessment of the diaphragm volume in comparison to that with a current refer-ence imaging method, such as sonography. In previous studies, conventional fluoroscopy, ultrasound, and magnetic resonance imaging (MRI) have been used to evaluate diaphragmatic functionality31, 32). B- and M-mode ultrasound can easily diagnose diaphragmatic dysfunction and compare changes during the follow-up period33), as well as provide real-time evaluation. It is often the 488imaging modality of choice and is a suitable bedside procedure. However, ultrasound is limited by oper-ator dependency33, 34) and cannot be used to eval-uate the total diaphragm volume. Several studies have shown that it is possible to evaluate diaphragm morphology and function using MRI35, 36). MRI is a radiation-free technique that can provide static or dynamic evaluations, with the benefit of a wider field of view and more detailed soft tissue characterization37). However, MRI, like ultrasound, cannot be used to evaluate the total diaphragm volume. Furthermore, the wide use of MRI is restricted by its limited availability, difficult scheduling, difficult patient preparation, and high costs38). Because of its wider availability, CT scans are more commonly used as frontline imaging tests than MRI scans36). The present method also allows for the full use of existing CT data. The CT data used in this study were not initially collected to evaluate the diaphragm; rather, the CT data were obtained preoperatively. As existing CT data can be used, the problem of radiation exposure is reduced. As the conditions of the study subjects were limited, the postoperative diaphragm volume could not be measured in this study; however, changes in the diaphragm volume can be examined using existing CT data before and after surgery. Diaphragm volume measurements on 3D-CT can be expected to best combine the benefits of MRI and ultrasound and provide the most comprehensive assessment of the major inspi-ratory muscles.In this study, the ICCs between the two observers using different workstation software were high for diaphragm volume measurements on 3D-CT. We considered the use of only echography to measure muscle thickness as insufficient for evaluating the diaphragm. Rather, we expect the present measure-ment method for evaluating the morphology and muscle volume of the diaphragm to be more useful when determining the timing of postoperative extubation. Diaphragmatic assessment is also commonly used in other areas of research such as in sarcopenia, physical development, and aging, where various situations and conditions can affect the ability of the diaphragm muscles to generate force. Although the diaphragm muscles can signifi-cantly weaken with age, leading to dysfunction, it is unclear whether there are any specific correla-