Quantitative ultrasound imaging of the calcaneus: precision and variations during a 120-Day bed rest.
This study reports on the precision and variation of quantitative ultrasound (US) parameters [broadband ultrasonic attenuation (BUA) or slope of the frequency-dependent attenuation in dB/MHz and speed of sound (SOS m/second)] after 120 days of continuous bed rest in six normal male volunteers. Quantitative US was measured at the calcaneus using a new US bone imaging scanner. The measurements were carried out on both heels at approximately 2-week intervals. The short-term precision was 0.31% for SOS and 2.8% for BUA. The long-term precision was 0.58% for SOS, 4.7% for BUA. A significant decrease of SOS values of -26 m/second (P < 0.0001) for the right heel and -17 m/second (P < 0.05) for the left heel was found at the group level. In terms of percentage change this represents -1.7% for the right heel and -1.1% for the left heel. These percentage decrements were 3.5-5.5 times that of the short-term precision and 2-3 times that of the long-term precision of the technique. At the individual level, the decrease of SOS was statistically significant (P < 0.05) or marginally significant (P < 0.1) for four out of 6 subjects. For 2 other subjects, similar trends were observed, but without reaching statistical significance. BUA did not change significantly during follow-up. These results are consistent with previous findings on changes of ultrasonic properties from the calcaneus during aging, pregnancy, or therapy, showing that calcaneus SOS is a valuable index of bone loss. These preliminary data suggest that prolonged exposure to simulated weightlessness may lead to a lower SOS, which then could be used for the follow-up of bone demineralization occurring during long-term space flights.
Laugier
P
P
Laboratoire d'Imagerie Paramétrique UMR 7623, 15 Rue de l'Ecole de Médecine 75006 Paris, France.
Novikov
V
V
Elmann-Larsen
B
B
Berger
G
G
D000328:Adult; D001510:Bed Rest; D015519:Bone Density; D016723:Bone Remodeling / Q000502:physiology*; D002111:Calcaneus / Q000000981:diagnostic imaging*; D006801:Humans; D007103:Immobilization / Q000502:physiology*; D008137:Longitudinal Studies; D008297:Male; D015203:Reproducibility of Results; D014463:Ultrasonography / Q000295:instrumentation