Lateral Dual Energy Radiography: A New Method for Measuring Vertebral Bone Density

Dual energy radiography (DER) is a new technique for non-invasive measurement of vertebral bone mineral density, which because of its high precision (1%), is particularly suitable for prospective analyses of time-related changes in bone mass. However, we recently found that DER is less sensitive to demineralization of trabecular bone than quantitative computed tomography (QCT). Since the compact bone of the posterior vertebral elements are included in the standard anterior-posterior DER (APDER), but not in QCT measurements, changes in trabecular bone mass attending the early phases of the osteoporotic process go undetected with the APDER technique due to the preponderance of cortical mass. Lateral-view DER (LDER), however, would minimize the contribution of vertebral compact bone as well as intra-abdominal calcifications to the trabecular component. To determine the in vivo short-term precision of the LDER method, we obtained three measurements in 18 healthy women, aged 23 to 76, during a four-week period. In addition, both APDER and LDER measurements were obtained in 53 healthy women, aged 23 to 80. The coefficient of variation for LDER was 2.87. LDER density values accounted for a higher percentage of the variance of bone mass measurements with age (47%) than APDER (23%). Moreover, LDER declined significantly with age in both premenopausal (r = −0.42,  p  < 0.05) and postmenopausal women (r = −0.50,  p  < 0.005), whereas the age-related changes in APDER values failed to reach statistical significance in either group. The rate of bone loss with age in the premenopausal group was 0.45% per year with LDER, and 0.10% per year with APDER. Postmenopausal women showed a 0.78% loss of bone mass per year with LDER and 0.47% per year with APDER. The correlation between APDER and LDER was significant (r = 0.78,  p  < 0.01). The accumulated data indicate that LDER may be a more appropriate technique than APDER for detecting the initial loss of vertebral trabecular bone that characterizes early subclinical osteoporotic syndrome.