Bone mineral density measures in longitudinal studies: The choice of phantom is crucial for quality assessment. The Tromsø study, a population-based study

Abstract

Determination of change in bone mineral density (BMD) requires high-precision densitometry techniques. The purpose of the study is to investigate to what degree different densitometer phantoms reflect observed changes in human BMD and to investigate to what degree fluctuations in densitometers' measurement level influence bone loss estimates. Densitometer influence was assessed using the aluminum forearm phantom (AFP) provided by the manufacturer, the European forearm phantom (EFP) of semi-anthropomorphic calcium-hydroxyapatite, and repeated population measurements on different densitometer combinations. The mean follow-up time was 6.4 years (SD 0.6). Measured population bone loss varied from 4.6%/year to 3.2%/year, depending on densitometer combinations. These variations could not be explained by differences in sex, age, height, weight and baseline BMD. They were predicted by EFP measurements, but not AFP measurements. The EFP measurements indicate that X-ray tube replacement changed the densitometers' measurement level in one of three instances, whereas "wear and tear" did not. We used the EFP data for adjustment of the densitometers' measurement levels. After adjustment, the overall crude bone loss was reduced from 4.14% to 3.92%. Mean annual loss was reduced from 0.64% or 0.61%. We conclude that densitometer performance might influence the accuracy of bone loss estimates. Changes in performance are not detected by aluminum phantoms. Quality control of BMD measurements in longitudinal studies should be performed with anthropomorphic calcium-hydroxyapatite phantoms in order to detect possible differences between the participating densitometers' measurement levels.

Leisure time physical activity and risk of non-vertebral fracture in men and women aged 55 years and older: the Tromsø Study

“…The mean in vitro precision error for the SXA devices was 0.9% when using the European Forearm Phantom [31].…”

“…Two different single X-ray absorptiometric (SXA) devices (DTX-100, Osteometer MediTech, Inc., Hawthorne, CA, USA) were used to measure aBMD of the distal and ultradistal forearm, as described elsewhere [31]. The non-dominant arm was measured except when it was considered ineligible.…”

“…Throughout the study, all densitometers underwent daily phantom measurements to secure stability [31]. In a recent validation study, the short-term in vivo precision error for the Lunar Prodigy was 1.7% and 1.2%…”

Solid anthropomorphic infant whole-body DXA phantom: design, evaluation, and multisite testing

“…Phantoms are necessary for system calibration, precision testing, quality control (QC), cross-calibration, and stability evaluation, all of which are necessary for reliable instrument performance (11,12). For bone studies, for example, Emaus et al (13) found that not only was the accuracy of bone loss estimates affected by densitometer performance, but that a calibration phantom itself could influence the quality of the results. DXA measurement results are also highly dependent on the manufacturer (14).…”

“…Long-term stability of research instruments must be documented. Semianthropomorphic phantoms mimic in vivo results better than their nonanthropomorphic counterparts do (13). Any phantoms used for cross-calibration studies must be sturdy and easily transported (21).…”