Switching from DXA pencil-beam to fan-beam. I: Studies in vitro at four centers

• Published in: Bone (New York, N.Y.) Vol. 15; no. 6; pp. 667 - 670
• Main Authors: Eiken, P., Bärenholdt, O., Jensen, L.Bjørn, Gram, J., Nielsen, S.Pors
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY Elsevier Inc 01.11.1994; Elsevier Science
• Subjects: Absorptiometry, Photon - standards; Biological and medical sciences; Bone densitometry; Bone Density - physiology; Bone mineral content; Bone mineral density; Computer Simulation; Dual x-ray absorptiometry; Humans; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Models, Structural; Osteoarticular system. Muscles; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Reproducibility of Results; Space life sciences; Spine; Spine - physiology; Bone mineral content; Bone mineral density; Dual x-ray absorptiometry; Spine; Bone densitometry; Performance evaluation; Test objet; Biomedical equipment; Radiologic investigation; Fan beam; In vitro; Osteoarticular system; X ray absorption spectrometry; Dual energy; Apparatus; Densitometry; Bone; Comparative study
• ISSN: 8756-3282; 1873-2763
• DOI: 10.1016/8756-3282(94)90315-8

The performance of the Hologic QDR-2000 DXA osteodensitometer was critically evaluated at four centers, using at all four centers one bone equivalent humanoid spine phantom supplied by the manufacturer. Results were compared with results from Hologic QDR-1000/W using that phantom tested at the same centers. It appears that the concept of fan-beam scanning—as used in the QDR-2000: a fan-beam, a linear array detector above the phantom, and an x-ray tube located rather close to the spine below the phantom—creates problems due to the magnification effect of the fan beam. The effect of decreasing the distance between the “vertebrae” of the phantom and the couch are: bone mineral content (BMC) increases by 2.8% per cm, projected area (Area) by 2.8% per cm, and bone mineral density (BMD) is unchanged. When QDR-1000/W is upgraded to QDR-2000, BMD is relatively constant, but there are shifts of BMC and Area which are partly due to the magnification effect of the fanbeam. Replacement of a QDR-1000/W with a QDR-2000 can invalidate longitudinal measurements, even for BMD, unless the proportionality factors of the QDR-2000 are checked and, if necessary, changed. This is true for switching from QDR-1000/W to pencil-beam mode of QDR-2000 or to fanbeam mode of QDR-2000. Even with pencil-beam mode, the long-term precision error with phantoms is higher for QDR-2000 than for QDR-1000/W (for BMD, 0.47% versus 0.35%).