A study of the long-term precision of dual-energy X-ray absorptiometry bone densitometers and implications for the validity of the least-significant-change calculation.
BACKGROUND
Short-term precision is often quoted and used as the most important performance parameter of a dual-energy X-ray absorptiometry (DXA) scanner; however, long-term precision has a more profound impact on patient monitoring. Long-term precision refers to the combination of in-vivo precision errors and long-term equipment stability.


METHODS
To monitor long-term equipment stability, a phantom was designed with four inserts ranging in bone-mineral density from 0.5 to 3.3 g/cm(2). This phantom was used to monitor the equipment stability of four modern fan-beam densitometers, two each from Hologic and GE/Lunar, over a 4-year period. Manufacturer-recommended quality assurance (QA) procedures were performed, and the scanners stayed within manufacturer-specified tolerances throughout the study.


CONCLUSIONS
During the 4-year period, the Hologic scanners were observed to cause clinically insignificant BMD shifts (maximum of 0.34%), whereas the GE/Lunar scanners revealed BMD shifts that were clinically significant (1.5% and 2.1%). As a result, using least-significant-change (LSC) calculations based only on short-term in-vivo precision studies for monitoring patients is not valid for the two GE/Lunar densitometers due to the poorer long-term stability they exhibited.
Hangartner
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TN
BioMedical Imaging Laboratory, Wright State University and Miami Valley Hospital, One Wyoming Street, Dayton, OH 45509, USA. thomas.hangartner@wright.edu
D015502:Absorptiometry, Photon / Q000295:instrumentation* / Q000592:standards; D015519:Bone Density / Q000502:physiology; D002138:Calibration; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods; D019047:Phantoms, Imaging; D010865:Pilot Projects; D015203:Reproducibility of Results; D012984:Software; D013997:Time Factors