Abstract
Hip axis length (HAL) has been reported as an independent risk factor for hip fracture. DEXA machines using fan beam techniques have become increasingly available. Errors in calculated hip axis length may be expected because of different degrees of magnification by the fan beam. The magnitude of this error on measurement of hip geometry was studied, using an anthropomorphic femur phantom with both fan beam (Lunar Expert and Hologic QDR-2000) and pencil beam (Lunar DPXL) densitometers. The clinical relevance of these findings was also examined using patient measurements of buttock soft tissue thickness.
Femoral neck axis length (FNAL), which correlates well with HAL, was used as a measurement of hip geometry. There was a linear increase or decrease of FNAL with increasing distance of the phantom above the scanning table, when measured with the Lunar Expert or Hologic QDR-2000, respectively. There was no significant difference in FNAL at different heights using the pencil beam densitometer. The maximal difference in buttock soft tissue thickness in 30 women studied was 8.7 cm. From the equations, derived from the phantom studies, this difference would result in an 8.2% (1.4 SD) increase, or an 11.4% (1.9 SD) decrease in FNAL in the largest woman as compared with the smallest woman when measured using the Lunar Expert or Hologic QDR-2000, respectively.
We conclude that there may be unpredictable degrees of magnification of FNAL in vivo, caused by differences in buttock thickness, when measured using a fan beam densitometers. Until these problems are resolved. FNAL, or related parameters of femoral geometry, should be measured using pencil beam instruments.
Similar content being viewed by others
References
Faulkner KG, Cummings SR, Black D, Palermo L, Gluer CC, Genant HK (1993) Simple measurement of femoral geometry predicts hip fracture: the study of osteoporotic fractures. J Bone Miner Res 8: 1211–1217
Kuiper JW, Slis HW, van Daele P, Pols HAP (1995) A comparison of femoral geometry measurements using DXA and conventional radiography. Osteoporosis Int 5: S101
Fukunaga M, Tomomitsu T, Ono S, Otsuka N, Nagai K, Morita K, Imai H, Miyake M, Katagiri M (1992) Determination of vertebral bone mineral density with new dual energy X-ray absorptiometry using multiple detectors: fundamental studies. Radiation Med 10: 39–43
Faulkner KG, Gluer CC, Estilo M, Genant HK (1993) Cross-calibration of DXA equipment: upgrading from a Hologic QDR 1000/W to a QDR 2000. Calcif Tissue Int 52: 79–84
Finkelstein JS, Butler JP, Cleary RL, Neer RM (1994) Comparison of four methods for cross-calibrating dual-energy X-ray absorptiometers to eliminate systematic errors when upgrading equipment. J Bone Miner Res 9: 1945–1952
Franck H, Munz M, Scherrer M (1995) Evaluation of dual energy X-ray absorptiometry bone mineral measurement comparison of a single-beam and fan-beam design: the effect of osteophytic calcification on spinal bone mineral density. Calcif Tissue Int 56: 192–195
Faulkner KG, Genant HK, McClung M (1995) Bilateral comparison of femoral bone density and hip axis length from single and fan beam DEXA scans. Calcif Tissue Int 56: 26–31
Blake GM, Parker JC, Buxton FM, Fogelman I (1993) Dual x-ray absorptiometry: a comparison between fan beam and pencil beam scans. Brit J Radiol 66: 902–906
Eiken P, Kolthoff N, Barenholdt O, Hermansen F, Pors Nielson S (1994) Switching from DXA pencil-beam to fan-beam. II: studies in vitro at four centers. Bone 15: 667–670
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Pocock, N.A., Noakes, K.A., Majerovic, Y. et al. Magnification error of femoral geometry using fan beam densitometers. Calcif Tissue Int 60, 8–10 (1997). https://doi.org/10.1007/s002239900177
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/s002239900177