Howard S. Barden

Performance evaluation of a dual-energy X-ray bone densitometer

SummaryWe tested a dual-energy bone densitometer (LUNAR DPX) that uses a stable x-ray generator and a K-edge filter to achieve the two energy levels. A conventional scintillation detector in pulse-counting mode was used together with a gain stabilizer. The densitometer normally performs spine and femur scans in about 6 minutes and 3 minutes, respectively, with adequate spatial resolution (1.2×1.2mm). Total body scans take either 10 minutes or 20 minutes. The long-term (6 months, n=195) precision of repeat measurement on an 18-cm thick spine phantom was 0.6% at the medium speed. Precision errorin vivo was about 0.6, 0.9 and 1.5% for spine scans (L2-L4) at slow, medium and fast speeds, while the error was 1.2 and 1.5 to 2.0%, respectively, for femur scans at slow and medium speed. The precision of total body bone density was 0.5%in vitro andin vivo. The response to increasing amounts of calcium hydroxyapatite was linear (r=0.99). The densitometer accurately indicated (within 1%) the actual amount of hydroxyapatite after correction for physiological amounts of marrow fat. The measured area corresponded exactly (within 0.5%) to that of known annuli and to the radiographic area of spine phantoms. There was no significant effect of tissue thickness on mass, area, or areal density (BMD) between 10 and 24cm of water. The BMD values for both spine and femurin vivo correlated highly (r=0.98, SEE=.03 g/cm2) with those obtained using conventional153Gd DPA. Similarly, total body BMD correlated highly (r=0.96, SEE=.02g/cm2) with DPA results.

Bone mineral density in women with breast cancer treated with adjuvant tamoxifen for at least two years

SummaryWhile in limited animal studies tamoxifen is reported to protect against loss of bone mineral, data in humans are lacking. We measured bone mineral density (BMD) using single photon absorptiometry at the radius and dual photon absorptiometry at the lumbar spine in breast cancer patients treated with chemotherapy at our institution. In this group, 37 women were not treated with tamoxifen (NT) and 48 women were treated with tamoxifen (T) for at least two years. Younger age, greater weight and height, premenopausal status, and shorter time since menopause were found to be significant predictors of greater BMD. Tamoxifen-treated women had been postmenopausal for more years (p = 0.012). Regression analyses used to adjust for differences in risk of bone loss did not reveal significant differences in BMD between the two groups of women. For the postmenopausal women (27 NT and 34 T subjects), the adjusted mean BMD (g/cm2) at the spine was 1.11 (NT), 1.11 (T) (p = 0.93); and at the radius 0.63 (NT), 0.62 (T) (p = 0.30). This limited retrospective study suggests that tamoxifen does not have ‘anti-estrogenic’ effects on BMD.

Interrelationships among bone densitometry sites in normal young women.

Interrelations among skeletal sites were examined in a population of up to 300 normal young white women aged 20-40 years. Measurements were done on the radius shaft, ultradistal radius, and ultradistal ulna using single-photon absorptiometry (SPA) and on the lumbar spine, proximal humerus, and proximal femur using dual-photon-absorptiometry (DPA). Because of the narrow range of intrapopulation variance in these normal young women, the intercorrelations among skeletal sites were not very high; the average correlation (r) was 0.43 for bone mineral content (BMC) and 0.45 for bone mineral density (BMD). The results at any one site predicted values at other sites with a standard error of estimate (SEE) of approximately 11% for BMD and 17% for BMC. Even in this relatively homogeneous sample, measurements at a single skeletal site could not be extrapolated to indicate skeletal status at other sites. BMC, and to a lesser extent BMD, were influenced by body size much as has been observed in both men and postmenopausal women. Bone results are preferably expressed as BMD, because (a) intrapopulation variability is lower (10% versus 15% for the lumbar spine), (b) intercorrelations among skeletal sites, and even among adjacent vertebrae, are higher for BMD, and (c) the influence of body size on BMD is lower (the average r for weight and BMD was 0.26 versus 0.33 for BMC).

Bilateral Measurement of Femoral Bone Mineral Density

Both femora were measured on 61 normal adults using dual X-ray absorptiometry (DXA). In a subset of 31 subjects, each femur was scanned once using the conventional leg-positioning device supplied with the densitometer, and once using a new positioning device and software that allowed both legs to be measured simultaneously. In another subgroup (n = 30), subjects were measured three times using the new dual-femur approach to better assess precision error. The data were analyzed for differences owing to the different positioning devices and for differences between right and left sides. The correlation between results with the old and new positioners was high (r > 0.99, standard error of the estimate [SEE] = 0.01-0.02 g/cm(2)). There was no significant difference in the average bone mineral density (BMD) values between the old and new positioner. The precision errors for each femur alone with the dual-femur approach were similar to those reported for the single-femur scans (1 to 2%), but the precision errors for the combined femora were reduced by 30% as expected. The correlation between right and left sides was high (r = 0.94-0.96), and the SEE in predicting one side from the other was moderate for total, trochanteric, and femoral neck BMD (0.05, 0. 05, and 0.06 g/cm(2), respectively). These SEE equate to about 0.5 standard deviation in terms of T-score. Differences in many individual cases between the right and left sides were significantly greater than the precision error. The new dual-femur software and leg positioner allows rapid measurement and analysis of both femora, thereby eliminating the uncertainty between sides.

Bone Densitometry for Diagnosis and Monitoring Osteoporosis

Conclusions Bone densitometry is used in over 1000 institutions in the United States to aid in diagnosis of bone disease and to monitor bone changes with disease and therapy. The leading method (DPA) has a low radiation dose (1 mrem) and modest cost (

Bone densitometry in infants

125/scan) compared with the QCT alternative (1000 mrem and

The costs and benefits of screening for PKU in Wisconsin.

250). These methods are generally considered to be essential to basic clinical management (3, 19). Insurers have used the controversy about “screening” in a normal population without symptoms to avoid payment for medically indicated densitometry in patients with symptoms. The Southern California Bone Club has provided a guideline for medical use (Table VII). Responsible application of any densitometric method can enhance clinical control; this is particularly the case for the new x-ray absorptiometry approach that allows rapid and precise assessments hitherto impossible.

Body Composition by Dual-Photon Absorptiometry and Dual-Energy X-Ray Absorptiometry

Bone mineral mass and density can be measured noninvasively by various absorptiometric procedures. Two methods, dual-photon absorptiometry (DPA) and quantitative computed tomography, have widespread application in adults but only limited use in children. One method, single-photon absorptiometry (SPA), has been used extensively in adults and children and has been modified for use in infants. The radius shaft has been used for most research on infants. However, the difficulty of using older SPA methods on this small bone (4 to 7 mm width) has led a few investigators to measure the shaft of the humerus. The typical precision of measurement in a newborn is about 5% with the use of computerized rectilinear scanners for the radius; older linear scanners have a precision error of 5% to 10% on the humerus. Linear scanners cannot measure precisely the radius in individual neonates. The SPA scans typically take about 5 minutes. The DPA technique using 153Gd has been modified for use on smaller animals (5 to 10 kg monkeys and dogs), but it has not been used on infants because DPA scans take 20 minutes. New methods using x-ray absorptiometry allow rapid (1 minute), precise (1%) measurements in the perinate. The need for a soft tissue bolus is eliminated, and both the axial and peripheral skeletons can be measured with dual-energy x-ray absorptiometry. Ultrasonic measurements do not yet offer adequate precision in the neonate, given the limited biologic range of values.

Automated assessment of exclusion criteria for DXA lumbar spine scans.

Abstract A comprehensive benefit‐cost analysis of the screening program to detect newborns with PKU in Wisconsin is presented. Classic PKU is a genetic disorder which, if undetected and untreated during the first few weeks of life, generally results in mental retardation and a variety of other abnormal conditions. Monetary costs of the detection and treatment program were compared with the projected benefits (avoided costs) that result from the prevention of the mental retardation associated with the disorder. Future costs and benefits were determined using a 4 per cent, 7 per cent, and 10 per cent rate of discount. Net benefits (benefits‐costs) for detecting and treating one individual with PKU were

The costs and benefits of screening for congenital hypothyroidism in Wisconsin

208,000 (