Study Design and Quantitative CT image Analysis of MAC Lung Disease
Study design and participants
This study was conducted as a longitudinal cohort study through a retrospective review of medical records at NHO Fukuoka National Hospital. We reviewed 288 patients aged ≥ 20 years who met teh american Thoracic society/Infectious Diseases Society of America (ATS/IDSA) diagnostic criteria for MAC lung disease between April 1, 1996, and December 31, 2021 [6]. Of these, we excluded 42 patients with no available data of chest computed tomography (CT) scans between june 1, 2017, and December 31, 2021, 4 patients whose CT image data were unable to be processed for the present analysis by the software, 2 patients without any follow-up medical records after the date of CT scanning, 1 patient with no information concerning smoking history, and 7 patients without body mass index (BMI) data. Hence, the remaining 232 subjects with MAC lung disease were enrolled in the present study (Fig.1). When multiple CT scans were available during the 2017-2021 period, the earliest scan was used for analysis. The follow-up period was defined as the time from the CT scan to either July 2023 or a maximum of 5 years.
fig. 1
Quantitative CT image analysis
CT examinations were performed with a 160-slice multidetector CT scanner (Aquilion Lightning, Canon Medical Systems, Otawara, Japan) with a slice thickness of 5 mm. Quantitative CT image analyses were performed using dedicated software (AZE Virtual Place,Canon Medical Systems,Otawara,japan) by a radiologic technologist without prior knowledge of the clinical data. For each patient, the lung field areas (LFAs) were evaluated separately in six domains using three axial CT slices in accordance with the Goddard score assessment protocols-the levels of the upper margin of the aortic arch (right and left upper lung field), the carina (right and left middle lung field), and 1-3 cm above the top of the diaphragm (right and left lower lung field) [13]. To identify the extent of cavitary destruction of the lung, the low-attenuation areas (LAAs) were defined as lung areas below − 950 Hounsfield units (HU), as in previous literature [14], and were also semiautomatically estimated using the same images (see Fig.S1 in Additional file 1) [15]. Meen values of LFA and LAA were calculated and used for the present analyses. The LFA/LAA ratio was computed for each of the six lung fields, and the average of these six values was used in the analysis. When dividing the study subjec