Population-based opportunistic osteoporosis screening: Validation of a fully automated CT tool for assessing longitudinal BMD changes

Abstract

Methods:: The automated BMD tool was retrospectively applied to non-contrast abdominal CT scans in 1603 consecutive asymptomatic adults (mean age, 55.9 years; 770 M/833 F) undergoing longitudinal screening (mean interval, 5.7 years; range, 1.0-12.3 years). The spinal column was automatically segmented, with standardized L1 and L2 anterior trabecular ROI placement. Automated and manual L1 HU values were compared, as were automated supine-prone measures. L1-L2 CT attenuation values were converted to BMD values through a linear regression model. BMD values and changes were assessed according to age and gender.

Results:: Success rate of the automated BMD tool was 99.8 % (four failed cases). Both automated supine vs prone and manual vs automated L1 attenuation measurements showed good agreement. Overall mean annual rate of bone loss was greater in females than males (-2.0% vs -1.0%), but the age-specific rate declined faster in females from age 50 (-2.1%) to age 65 (-0.3%) compared with males (-0.9% to -0.5%). Mean BMD was higher in females than males at age 50 (143.6 vs 135.1 mg cm^-3), but post-menopausal bone loss in females reversed this relationship beyond age 60. By age 70, mean BMD in females and males was 100.8 and 107.7 mg cm^-3 , respectively.

Conclusion:: This robust, fully automated CT BMD tool allows for both individualized and population-based assessment. Mean BMD was lower in men than women aged 50-60, but accelerated post-menopausal bone loss in women resulted in lower values beyond age 60.

Advances in knowledge:: This fully automated tool can be applied to routine abdominal CT scans for prospective or retrospective opportunistic BMD assessment, including change over time. Mean BMD was lower in men compared with women aged 50-60 years, but accelerated bone loss in women during this early post-menopausal period resulted in lower BMD values for women beyond age 60.

Figure 1.

Automated CT BMD tool in asymptomatic 59-year-old male at initial evaluation, evaluated over a 10-year interval. (A) 3D volume-rendered image from the initial CT scan performed in 2007 when the patient was 59 years old shows the relative placement of the automated ROI (green cylinder) within the anterior trabecular space of the L1 vertebral body. (B) Collage of 2D transverse images at the L1 level from CT in 2007 (top row) and 2017 (bottom row). Bone windows (left images) and soft tissue windows (middle images) are shown, as well as placement of the automated ROI (green ovals) with resulting mean HU values (right images). The HU values correspond to an estimated BMD of 186.9 mg cm^–3 in 2006 and 131.6 mg cm^–3 in 2016, reflecting a 30% loss, or annual mean rate of BMD change of −3%/year. Note also the significant interval weight loss. 3D, three-dimensional; BMD, bone mineral density; ROI, region of interest.

Figure 2.

Automated supine vs prone measurements (A), Plot of automated BMD measurement of the supine vs prone CT series (r² = 0.90) (B), Corresponding Bland–Altman plot with 95% limits of agreement. No bias is noted. BMD, bone mineral density.

Figure 3.

Manual vs automated L1 trabecular attenuation measurements in 588 subjects. (A) Plot of manual single-slice ROI and automated volumetric measurements for L1 trabecular attenuation (in HU). (r² = 0.80). (B) Corresponding Bland–Altman plot with 95% limits of agreement. Note that the automated measures are approximately 5 HU higher on average, without bias according to variation of the mean. HU, Hounsfield unit; ROI, region of interest.

Figure 4.

Automated mean BMD values at initial CT according to age and gender. Plots using lines of best fit show that males have lower BMD values on average in the 50–60 age range, whereas females have lower values on average at older ages. The shaded areas around lines correspond to the 95% CIs for the mean BMD values. BMD, bone mineral density.

Figure 5.

Annual rates of BMD change according to age at initial CT and gender. BMD, bone mineral density.