Opportunistic assessment of variations in tissue composition content using chest QCT.

Utilize Quantitative Computed Tomography (QCT) to acquire quantitative parameters of bone, muscle, and adipose tissue in subjects, and subsequently investigate the disparities in these parameters based on classifications of Bone Mineral Density (BMD) and gender. Employ the average values of various parameters at the age of 30 as the baseline to compute the growth rate every five years and analyze the variations in these parameters of different tissues with respect to age and gender. Collect subjects who underwent combined chest CT and QCT scans at our hospital. Following parameters were obtained: volumetric bone mineral density (vBMD) of T12-L2 vertebrae, fat fractions (FF) of liver, pancreas, and paraspinal muscles, the content (including mass and area) of cortical mineral, cancellous mineral, abdominal total adipose tissue, visceral adipose tissue, subcutaneous adipose tissue, splanchnic soft tissue (excluding visceral adipose tissue), paraspinal intramuscular adipose tissue, paraspinal intramuscular muscle tissue at the central level of L2 vertebrae. Based on vBMD, the subjects were categorized into three groups: normal, osteopenia, and osteoporosis group. They were further subgrouped by BMD and gender to compare differences in various parameters. Taking the average values of these parameters at age 30 as the baseline, we calculated the growth rate every five years, observing the age-related changes in these parameters of different tissues in both males and females. Among males, no notable disparities were observed in the splanchnic soft tissue and paraspinal intramuscular muscle content across various vBMD categories, whereas other parameters exhibited significant variations in accordance with vBMD. In females, all parameters, with the exception of liver fat fraction, demonstrated significant changes across different vBMD categories. Males exhibit a higher liver FF, as well as greater content of total adipose tissue, visceral adipose tissue, splanchnic soft tissue, cortical mineral, cancellous mineral, and paraspinal intramuscular muscle compared to females. Conversely, females demonstrate higher muscle FF, paraspinal intramuscular adipose tissue, and subcutaneous adipose tissue content than males. In age-related changes, there is an increase in FF of the liver, pancreas, and paraspinal muscles, accompanied by an augmentation in the content of total adipose tissue, visceral adipose tissue, and paraspinal intramuscular adipose tissue. Conversely, there is a decline in BMD, cortical and trabecular content, as well as in the content of paraspinal intramuscular muscle tissue. The difference lies in the reduction of subcutaneous fat content in males, as opposed to an increase in females. The trend of variations in mass and area within the same tissue does not always align consistently. Furthermore, the content of both cortical and cancellous mineral decreased with age, but cortical mineral loss occurs earlier and faster than cancellous mineral. As vBMD diminishes, muscle content decreases concurrently with an augmentation in fat infiltration. In males, visceral fat infiltration prevails, whereas in females, both muscle loss and fat accumulation are pronounced. The depletion of cortical minerals may transpire earlier and at a quicker rate compared to the loss of cancellous minerals, indicating that clinical attention to osteoporosis cannot ignore changes in the cortical bone.