Introduction: Recent improvements in image resolution of dual-x-ray absorptiometry (DXA) scanners have allowed their use to obtain low-dose images of the thoracolumbar spine for vertebral fracture assessment (VFA), leading to earlier diagnosis and more accurate fracture risk assessment. Assessment of image resolution and contrast are not part of the routine quality assurance protocols recommended by DXA manufacturers for these devices. We assessed whether standard resolution and contrast phantoms designed for conventional radiography could be used to monitor DXA imaging performance. Methods: A standard radiographic line-pair resolution phantom and aluminum step wedge were scanned on a GE-Lunar Prodigy and Hologic Discovery SL in the various scan modes and orientations, using the respective manufactures' VFA acquisition and display software. Vertical and horizontal resolution in line-pairs per millimeter (lp/mm) was assessed from on-screen images of the resolution phantom. Contrast was assessed by simple pass/fail of whether all 11 steps of the wedge could be simultaneously visualized as separate gray levels on the display monitor. Results: Scanner resolutions varied by scanner, scan mode, and line orientation, from a high of 1.5 lp/mm for horizontal lines on PA spine images on the Hologic device, to less than 0.6 lp/mm for the GE-Lunar device. Contrast determination on the Hologic devices was dependent upon phantom positioning within the scan field. Conclusion: Image quality of DXA scanners may be monitored with line-pair and step-wedge phantoms of suitable design, and should be incorporated into routine quality assurance procedures of DXA scanners performing vertebral fracture assessment.
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Faculty Member's Name: Lawrence G. Jankowski, CDT
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