Quantitative computed tomography precision and accuracy for long-term follow-up of bone mineral density measurements: a five year in vitro assessment.

The purpose of this work was to test the long-term precision of quantitative computed tomography (QCT) on a CT scanner partly used for the measurement of bone mineral density (BMD). A spine phantom (ESP), which simulates three lumbar vertebrae (Li, i = 2-4) with given mineral densities of 50, 100, and 200 mg hydroxyapatite equivalents (HAP)/cm(3), respectively, was measured periodically over more than 5 yr on a Elscint-Marconi CT-Twin scanner. A total of 80 measurements were taken. The measured BMDi values were 48.4 +/- 1.2, 101.3 +/- 1.1, and 212.6 +/- 1.7 mg HAP/cm3, respectively (coefficient of variation [CV%] = 2.4, 1.1, and 0.8), and they were linearly correlated with the given density values (r > 0.99). The mean BMD value of the three simulated vertebrae was 120.8 +/- 1.1 mg HAP/cms(3) (CV% = 0.9), a value that corresponds to the mean lumbar BMD value in normal 65-yr-old women. We concluded that QCT is a precise and accurate method for long-term follow-up of BMD assessment in the population affected by osteoporosis.

Bone mineral content and soft-tissue assessment in limb segments by dual-energy X-ray absorptiometry: optimal scan speed and pixel size.

The aim of this study was to define the best scanning parameters to assess bone mineral content (BMC) and bone mineral density (BMD) in specific dual-energy X-ray absorptiometry (DXA) applications, such as those encountered in orthopedics for the measurements of the peripheral skeleton. To simulate soft tissues and bones in a limb, we used simple phantoms made with plastic bottles (500 mL and 1500 mL) filled with tap water and cylinders of hydroxyapatite (HAP) powder set in a polymer at various concentrations (range, 0.150-1.500 g HAP/cm3). Data obtained from 204 measurements of these phantoms with different scanning speeds and pixel sizes showed that the best compromise for obtaining precise measurements in the shortest scan time was a scanning speed of 50 mm/s and a pixel size of 1.5 mm x 1.5 mm.

Estimation of stature and length of limb segments in children and adolescents from whole-body dual-energy X-ray absorptiometry scans.

BACKGROUND: Anthropometric standards vary among different populations, and renewal of these reference values is necessary. OBJECTIVE: To produce formulae for the assessment of limb segment lengths. MATERIALS AND METHODS: Whole-body dual-energy X-ray absorptiometry scans of 413 Caucasian children and adolescents (170 boys, 243 girls) aged from 6 to 18 years were retrospectively analysed. Body height and the lengths of four long bones (humerus, radius, femur and tibia) were measured. The validity (concurrent validity) and reproducibility (intraobserver reliability) of the measurement technique were tested. RESULTS: High linear correlations (r > 0.9) were found between the mentioned five longitudinal measures. Corresponding linear regression equations for the most important relationships were derived. The tests of validity and reproducibility revealed a good degree of precision of the applied technique. CONCLUSION: The reference formulae obtained from the analysis of whole-body DEXA scans will be useful for anthropologists, and forensic and nutrition specialists, as well as for prosthetists and paediatric orthopaedic surgeons.

Bone mineral content and body composition in overweight children and adolescents.

The aim of this study was to analyze the bone mineral content (BMC) of the skeleton and the body composition in lean and fat masses in a population of young overweight subjects, before diet or medical intervention. A total of 496 white youths (298 females, 198 males) were studied. Their body mass index (BMI) values were 29.2+/-5.5 kg/m2 in females and 28.3+/-5.1 kg/m2 in males, corresponding to relative weights (wts) [actual wt, W, divided by the mean wt normal for height (ht), Wi] of 1.55+/-0.24 and 1.53+/-0.24, respectively. Whole-body dual-energy x-ray absorptiometry (DXA) scans were performed (Norland XR36 DXA system) to obtain the total BMC (BMCt), lean tissue mass (LTMt) and fat mass (FMt), as well as the values of the corresponding parameters in arms (a), legs (l), and abdomen (ab). The measured data were compared with theoretical values calculated for Wi. The differences with reference values in LTMt and FMt were sex dependent, and the accretion in FMt, greater in males than in females, yielded a similar FMt/LTMt ratio in both sexes. The wt corresponding to the BMC of the bearing skeleton, lower than the actual wt by about 20%, seemed a reasonable first step to consider in the wt management of these youths.

Skeletal and total body volumes of human fetuses: assessment of reference data by spiral CT.

OBJECTIVE: To define reference data for skeletal and total body volumes of normal human fetuses. MATERIALS AND METHODS: Spiral CT was used to assess the skeletal and total body volumes of 31 normal human stillborn infants with gestational age (GA) and body weight (BW) ranging from 14 to 41.5 weeks and 22 to 3,760 g, respectively. CT scans (slice thickness 2.7 mm, pitch 0.7) were performed within the first 24 h after delivery. Precise bone and soft-tissue windows were defined from analysis of the density along the diaphysis of the fetal long bones and from the measurement of a phantom that mimics soft tissues. Lengths and volumes were obtained from 3D reconstructions. The femur lengths measured from CT images (FLct) were compared with those provided by US studies (FLus). RESULTS: Significant correlations ( r>0.9) were found between BW, measured volumes of the entire skeleton or head, long-bone lengths, biparietal diameter and GA. Strong linear correlations ( r>0.98) were observed between FLct and FLus. CONCLUSIONS: Skeletal and total body volume values obtained using spiral CT were significantly correlated with fetal biometric measurements. These data could complement those obtained in obstetric investigations with US.