Assessment of bone densitometry using radiography with a step-wedge phantom: a pilot study of the forearm

Ling Wang; Pengju Huang; Hui Du; Jian Geng; Xinghua Yin; Yandong Liu; Tanuj Puri; Bo He; Liang Lyu; Xiaoguang Cheng; Xieyuan Jiang; Klaus Engelke; Glen M Blake

doi:10.21037/qims-21-842

Assessment of bone densitometry using radiography with a step-wedge phantom: a pilot study of the forearm

Quant Imaging Med Surg. 2022 Jun;12(6):3340-3350. doi: 10.21037/qims-21-842.

Authors

Ling Wang^#^{1

2}, Pengju Huang^#¹, Hui Du^#³, Jian Geng¹, Xinghua Yin³, Yandong Liu¹, Tanuj Puri⁴, Bo He⁵, Liang Lyu², Xiaoguang Cheng¹, Xieyuan Jiang⁶, Klaus Engelke^{7

8}, Glen M Blake⁴

Affiliations

¹ Department of Radiology, Beijing Jishuitan Hospital, Beijing, China.
² Department of Radiology, The First People's Hospital of Yunnan Province, Kunming, China.
³ Department of Orthopedics, Beijing Jishuitan Hospital, Beijing, China.
⁴ School of Biomedical Engineering & Imaging Sciences, King's College London, St Thomas' Hospital, London, UK.
⁵ Department of Radiology, The First Affiliated Hospital of Kunming Medical University, Kunming, China.
⁶ Department of Traumatic Orthopedics, Beijing Jishuitan Hospital, Beijing, China.
⁷ Department of Medicine 3, FAU University Erlangen-Nürnberg and Universitätsklinikum Erlangen, Erlangen, Germany.
⁸ Institute of Medical Physics, University of Erlangen, Erlangen, Germany.

^# Contributed equally.

Abstract

Background: Radiographic absorptiometry (RA) is one of the earliest methods of bone densitometry and has been used to measure the phalanges and metacarpals where soft tissue attenuation is minimal. The aim of this study was to determine whether the technique can be adapted to correct for soft tissue attenuation and measure areal bone mineral density (aBMD) in the forearm.

Methods: A total of 51 patients referred for a clinical spine and hip dual-energy X-ray absorptiometry (DXA) examination and 8 young and middle-aged volunteers were recruited to this study. The first 29 participants (20 women, 9 men, aged 61±14 years) served as the training cohort, and the remaining 30 (20 women, 10 men, aged 55±16 years) comprised the validation cohort. All participants underwent a DXA scan of their non-dominant forearm, and a digital X-ray image of the same arm was acquired with a step phantom. Identical regions of interest (ROIs) in the radius and ulna at the one-third radius site were measured on the X-ray and DXA images, and a soft tissue ROI was measured on X-ray images between the radius and ulna. The X-ray measurements in the training cohort were expressed as equivalent step phantom thickness (Eq. SPT) and used to estimate forearm aBMD using a linear equation calibrated against the DXA scans. Estimates of forearm aBMD made from the digital X-ray images acquired in the validation cohort were compared with the results of the DXA scans.

Results: Digital X-ray estimates of radius and ulna aBMD at the one-third radius site in the validation cohort showed a good correlation with GE-Lunar iDXA scanner measurements (r=0.795; P<0.001). The Bland-Altman plot had a mean bias of -0.002 g/cm² and 95% limits of agreement of -0.185 to +0.181 g/cm².

Conclusions: Digital X-ray estimates of proximal forearm aBMD corrected for soft tissue attenuation correlated with DXA measurements with correlation coefficients comparable to those seen for other peripheral bone densitometry technologies.

Keywords: Radiographic absorptiometry (RA); bone mineral density (BMD); dual-energy X-ray absorptiometry (DXA); forearm.