Bone mineral density measurements in vertebral specimens and phantoms using dual-layer spectral computed tomography

Kai Mei,Ernst J Rummeny,Franz Pfeiffer,Alexander A Fingerle,Benedikt J Schwaiger,Peter B Noël,Thomas Baum,Sebastian Ehn,Jan S Kirschke,Daniela Muenzel,Felix K Kopp,Alexandra S Gersing

doi:10.1038/s41598-017-17855-4

Kai Mei, Ernst J Rummeny + Show 10 more

Open Access

https://doi.org/10.1038/s41598-017-17855-4

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Abstract

To assess whether phantomless calcium-hydroxyapatite (HA) specific bone mineral density (BMD) measurements with dual-layer spectral computed tomography are accurate in phantoms and vertebral specimens. Ex-vivo human vertebrae (n = 13) and a phantom containing different known HA concentrations were placed in a semi-anthropomorphic abdomen phantom with different extension rings simulating different degrees of obesity. Phantomless dual-layer spectral CT was performed at different tube current settings (500, 250, 125 and 50 mAs). HA-specific BMD was derived from spectral-based virtual monoenergetic images at 50 keV and 200 keV. Values were compared to the HA concentrations of the phantoms and conventional qCT measurements using a reference phantom, respectively. Above 125 mAs, errors for phantom measurements ranged between −1.3% to 4.8%, based on spectral information. In vertebral specimens, high correlations were found between BMD values assessed with spectral CT and conventional qCT (r ranging between 0.96 and 0.99; p < 0.001 for all) with different extension rings, and a high agreement was found in Bland Altman plots. Different degrees of obesity did not have a significant influence on measurements (P > 0.05 for all). These results suggest a high validity of HA-specific BMD measurements based on dual-layer spectral CT examinations in setups simulating different degrees of obesity without the need for a reference phantom, thus demonstrating their feasibility in clinical routine.

Highlights

Osteoporosis is estimated to affect 28 million patients in the European Union with increasing prevalence, due to the aging population[1,2]
HA-specific density measurements based on spectral data obtained with a dual-layer spectral CT showed high accuracy when performed on a phantom with different known HA concentrations in scans with radiation exposures comparable to clinical protocols
Phantomless HA-specific spectral bone mineral density (BMD) measurements showed high correlations and good agreement with conventional qCT-based measurements, which are the current standard of reference for assessing volumetric BMD

Summary

Introduction

Osteoporosis is estimated to affect 28 million patients in the European Union with increasing prevalence, due to the aging population[1,2]. Up to 70% of eligible women and far more men do not undergo bone mineral density (BMD) screening with dual-energy x-ray absorptiometry (DXA), the clinical standard[5,6], BMD is a predictor for future fracture risk and all-cause mortaliy[7,8]. While DECT requires the pre-selection of specific dual-energy CT protocols, spectral CT allows for routinely reconstructing spectral information without the use of a specific protocol. Those methods enable the estimation of object composition by exploiting material- and energy-dependent x-ray absorption of various materials. Aims of this study were to (i) validate spectral CT based, HA-specific mineral density quantification with a phantom with known HA densities as reference standard, and (ii) to validate spectral CT based BMD quantification in vertebral specimens with qCT as standard reference; both in a setup with an anthropomorphic phantom simulating different degrees of obesity

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