Comparison of pencil-, fan-, and cone-beam dual X-ray absorptiometers for evaluation of bone mineral content in excised rat bone

Correcting fan-beam magnification in clinical densitometry scans of growing subjects

As children grow, body and limb girths increase. For serial densitometric measurements, growth increases the distance between the bone region of interest and X-ray source over time, thereby increasing fan-beam magnification. To isolate bone accrual from magnification error in growing subjects, we developed a correction method based on waist girth, a common anthropometric measure. This correction was applied to dual-energy X-ray absorptiometry output obtained in a cohort of premenarcheal gymnasts and nongymnasts. After correcting for magnification, results for projected area and bone mineral content (BMC) increased by 0.4-1.1% at the lumbar spine and 8-16% at the femoral neck, decreasing areal bone mineral density (aBMD) by 0.4-2.3% at both sites. The effects of magnification correction were similar in magnitude to BMC and aBMD gains previously reported in longitudinal studies of normoactive children. Because of body size differences, the effect of correction for BMC and aBMD was 10-20% greater in nongymnasts than in gymnasts, which increased the observed aBMD differential between gymnasts and nongymnasts. Fan-beam magnification distorts true changes in bone mineral measures in growing premenarcheal girls and, therefore, may obscure additional activity-related changes during growth. Our correction technique may enhance detection of skeletal adaptation, particularly in pediatric populations.

Effects of food abundance, age, and flea infestation on the body condition and immunological variables of a rodent host, and their consequences for flea survival

Temporal variation in body condition and immunological variables of animals that harbor parasites may explain patterns of variation in infestation, as well as parasite impact on the host. We emulated such variability in Sundevall's jirds by manipulating food availability and flea infestation in juveniles and adults and examining how these changes affect survival of fleas on their hosts. Body condition of food-restricted jirds deteriorated, but there was no change in their immunological variables. Adult jirds were in better body condition and had higher immunocompetence than juveniles, however there were no significant effects of flea infestation on any of the variables examined. The main effects of flea infestation were a decrease in the response to phytohaemagglutinin injection, and an increase in the negative effects of food restriction on body mass. Flea survival was higher on juveniles, but fleas did not respond to temporal variability in body condition and immunocompetence of the jirds. We concluded that changes in body condition and immune responses due to growth or variability in food abundance are more important than changes caused by the fleas themselves. Flea infestation is more detrimental to jirds when they are not able to compensate for mass loss through increased food consumption.

Multiphasic Biomaterials: A Concept for Bone Substitutes Developed in the "Pays de la Loire"

This paper reports on the research into multiphase bone substitutes carried out by laboratories from the ‘Pays de la Loire’ region in France. This collaborative research was funded by both the French Government and the Regional Council in the period 2000-2007. Calcium phosphate bioceramics, polymers and combinations have been developed as bone substitutes for various maxillofacial and orthopaedic applications. These bone substitutes should support and regenerate bone tissue and resorb after implantation. In the bone tissue engineering area, they have been combined with autologous bone marrow cells or bioactive factors. The bone substitutes were tested in various animal models mimicking clinical situations or under pathological conditions (osteoporosis). In order to complete our research, the multiphase materials were also evaluated in clinical trials.

Fan-beam densitometry of the growing skeleton: are we measuring what we think we are?

Magnification error in fan-beam densitometers varies with distance from the X-ray source to the bone measured and might obscure bone mineral changes in the growing skeleton. Magnification was examined by scanning aluminum rods of different shapes (square, rectangular, solid round, and hollow round) at four distances above the X-ray source in two orientations, with rods aligned parallel (SI) and perpendicular (ML) to the longitudinal axis of the scanning table. Measured area (cm(2)) decreased linearly with distance above the X-ray source for all rods in the SI orientation (p < 0.005). Measured mineral content (g) decreased linearly with distance but only for SI round rods (p < 0.0001) and for ML hollow round rods (p < 0.005). Area and mineral content decreased 1.6-1.8% per centimeter above the source for round rods. Measured mineral density (g/cm(2)) decreased linearly with distance from the source only for ML hollow round rods (p < 0.005). Variation in area, mineral content, and mineral density measurements was 6.6-6.9%, 6.9-7.5%, and 1.9-2.3%, respectively, for SI round rods. Magnification errors of this magnitude are problematic for clinical studies using fan-beam densitometry. Particularly in pediatric subjects, increases in soft tissue during normal growth could increase a bone's distance from the fan-beam source and result in apparent reductions in area and bone mineral content.

Ex vivo bone mineral density of the wrist: influence of medullar fat

The cone beam technology was recently proposed in a third generation of densitometers (dual photon X-ray absorptiometry, DXA such as the Lexxos densitometer). Because fat is a well-known problem with DXA, we have designed a cadaver study to compare the influence of medullary lipids on the measures performed with the Hologic QDR4500 and the Lexxos. Twenty-three human distal radii were obtained and analyzed in parallel on both densitometers; bone mineral density (BMD) was measured at the distal radius with standard softwares and on a standardized square regions of interest (ROI). Bones were then defatted and a new series of measurement was performed. Bones were then thoroughly dried and a cube was prepared at the distal radius with a banding saw. Trabecular and total bone volumes were measured by microcomputerized tomography. Ash eight was obtained after calcination of the blocks. BMD could be measured on the Lexxos before and after delipidation but this was not possible with the QDR4500. The X-ray image quality was better with the Lexxos. Delipidation had a very significant effect on measurements: after defatting, BMD values were considerably reduced (-49.8 +/- 19.4%). BMD before/after defatting were significantly correlated (r = 0.81, P < 0.0001) but bone mass appeared to reflect 66% of the variance. BMD was significantly correlated with BV/TV after defatting (r = 0.44, P < 0.03) but the correlation improved when cortices were taken into account (r = 0.70, P < 0.0001). Ash weight was significantly correlated with BMD and total bone volume (respectively, r = 0.84, P < 0.0001; r = 0.53, P < 0.03), but not with BV/TV. BMD at the distal radius is influenced by marrow fat and cortical density.

Accuracy and precision of PIXImus densitometry for ex vivo mouse long bones: comparison of technique and software version

Many densitometric studies in mice assess bone mineral density (BMD) at specified regions of interest, often using ex vivo specimens. In the present study, we sought to determine the precision and accuracy of ex vivo densitometry of mouse bones, comparing two software versions and two data acquisition techniques. The newer software allows manual adjustment of the threshold value for bone, improving the ability to analyze bone edges correctly. Root mean square standard deviations were 2-3 mg/cm2, with coefficients of variation ranging between 3% and 5% for femora and humeri and between 6% and 7% for radii. The regression coefficients for bone mineral content as a function of ash mass were near 1 for femora and humeri, but considerably lower for radii. Coefficients of determination were inversely related to bone size, with R2 values exceeding 0.9 at the femur, 0.8 at the humerus, and ranging between 0.3 and 0.6 at the radius. We found that our instrument has a position artifact, with BMD and bone mineral content dependent on the specimen's coordinates in the scanned field. Our findings establish the limitations of ex vivo densitometry with the PIXImus and support our recommendation that investigators seek position artifacts in their instruments.