Simulated change in body fatness affects Hologic QDR 4500A whole body and central DXA bone measures.

Changes in body fatness may impact the accuracy of dual energy X-ray absorptiometry (DXA) measures of bone mineral content (BMC) and bone mineral density (BMD). The aim of this study was to determine if DXA can accurately assess BMC and BMD with changes in exogenous fat (lard) placed to simulate weight change. Whole body (WB), lumbar spine (LS), and proximal femur (PF) DXA scans (Hologic QDR 4500A) were performed on 30 elderly (52-83 yr) and 60 young (18-40 yr) individuals (i.e., 45 females and 45 males) of varying body mass index (mean+/-standard deviation: 26.1+/-4.9 kg/m2). When scans were repeated with lard packets (2.54 cm thick, 25.4x17.8 cm, 1 kg), WB BMD decreased 1.1% and 1.6% after chest and thigh packet placement, respectively (p=0.001), PF BMD increased 0.7% (p=0.02) and LS BMD decreased 1.6% (p=0.001) primarily due to a 2.2% reduction in LS BMC (p<0.001). Initial LS BMC and trunk mass were related to error in LS BMC measures due to lard-loading (r=0.64 and 0.45, respectively, p<0.001). We conclude that on average simulated weight change minimally impacts PF bone measures and moderately impacts WB and LS bone measures; however, individual variability in measurement error was noteworthy and may be impacted by body thickness.     

Effect of ascorbic acid on serum lipid levels and depot cholesterol of the baboon (Papio ursinus).

Twelve young male baboons were kept on a diet low in ascorbic acid for 3 months before the experiment. Six animals then received intravenous injections of ascorbic acid 60 mg/kg body mass every third day, while an isotonic saline solution was administered to 6 control animals. The serum ascorbic acid concentration of the animals treated with ascorbic acid levelled off after 9 days, at about 1,1 mg/100 ml. Ascorbic acid treatment resulted in a significant increase (P smaller than 0,005) in serum cholesterol values during the initial stages of treatment, but these returned to normal when the body pool was replenished with ascorbic acid. Ascorbic acid also brought about a significant lowering in serum triglyceride values (P smaller than 0.05). In an acute experiment ascorbic acid caused a 12,7% increase in serum cholesterol level 2 hours after the intravenous injection of ascorbic acid 60 mg/kg body mass. The blood glucose value and serum triglyceride concentration were not affected. The results prove that ascorbic acid treatment causes mobilisation of cholesterol from body depots into the bloodstream.     

The sensitivity of tests to detect in vivo platelet activation induced by the removal of arterial endothelium of the baboon (Papio ursinus)

The relative sensitivities for the various in vivo and in vitro tests for platelet activation are unknown. This was studied in a baboon model where limited and more substantial injury to the vascular endothelium was inflicted. The endothelium of a segment of the right carotid artery was removed with a balloon catheter on day 0 (limited de-endothelialisation), and that of the left carotid artery, abdominal aorta and left femoral artery on day 7 (substantial de-endothelialisation). Eight baboons (Papio ursinus) were used. Baseline tests for platelet activation (platelet volume, platelet density, platelet aggregate ratio, and platelet and plasma levels of platelet factor 4 [PF4] and beta-thromboglobulin [beta-TG]) were performed 7 days before de-endothelialisation and repeated on days 1, 9 and 16. The kinetics of indium-111-labelled platelets were measured after substantial de-endothelialisation. Sham operations were done on 3 animals exactly as in the test, except that the balloon injuries were not inflicted. No influence on the results of the platelet function tests was found. The only test capable of detecting limited injury to the endothelium was the measurement of plasma PF4. The mean platelet life-span (MPLS) shortened, mean platelet density decreased, the circulating platelet aggregate ratio decreased, and plasma levels of PF4 and beta-TG increased (P less than 0.05 in all instances) after the substantial endothelial injury. The mean platelet volume, intraplatelet PF4 and beta-TG, and the in vivo distribution and sites of sequestration of labelled platelets were poor tests for in vivo platelet activation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mitral valve replacement in the baboon (Papio ursinus) and the human with the University of Stellenbosch mitral valve prosthesis

To study the problem of thromboembolism that occurs following the use of prosthetic valves, the mitral valve was replaced in 20 Cape Chagma baboons with the University of Stellenbosch (U.S.B.) mitral valve prosthesis. In the absence of anticoagulants massive thrombus invariably formed on the metal portion of the prosthesis when the latter was left uncovered by material that allows for tissue ingrowth. Smooth, fairly well controlled tissue ingrowth occurred when the prosthetic ring was covered by Dacron velour material. Massive thrombus formation was never encountered although small fibrin thrombi, a potential source of emboli, became loosely attached to the Dacron velour covered prosthetic ring during the first eight post-operative weeks. Thereafter the smooth ingrowth of living tissue into the prosthesis appears capable of preventing thromboembolism. The clinical use of anticoagulants during the initial 3-4 post-operative months is recommended in view of our experimental findings and clinical experience of early embolism that occurred in 3 of 10 patients in whom the U.S.B. Dacron velour covered prosthesis was used in the absence of anticoagulants. This is the first reported study in which a sub-human primate was used to study the problem of thromboembolism associated with prosthetic valve replacement. The baboon can be highly recommended for this purpose.     

Effects of the oral administration of Cannabis sativa (dagga) on chacma baboons (Papio ursinus).

Eighteen adult chacma baboons were fed Cannabis sativa, the plant material being incorporated into their food. They were divided into three equal groups. Group 1 animals were fed on 2% cannabis in food for 4 months, after which 2 animals remained on 2%, 2 were given 4% and 2 6% cannabis in food for the next 4 months. They became mildy apathetic. Five gained weight. Serum glucose, potassium and CO2 values decreased. Neuropathological examination of their brains did not show any significant abnormality. Group 2 animals were fed 10% cannabis for several weeks. They ate less and lost weight, and later became very apathetic. Right temporal biopsies were done in all and in 3 the tissue was analysed for glutamine, glutamate, tryptophan, ammonia and cyclic AMP. No significant change was found. Serum glucose and CO2 levels rose and potassium levels fell. Blood cholesterol values decreased in 3 of the 9 males. Group 3 animals were fed 6% cannabis for 2--4 months. Radio-immunoassay of sera and urine showed the presence of cannabinoids. They became apathetic, and 5 lost weight. Serum glucose and potassium levels (measured in the males) decreased. No neuropathological lesions were found in the brains, apart from an incidental leptomeningitis in 1 animal which died suddenly. The question of cannabis encephalopathy is discussed.     

A multinational study to develop universal standardization of whole-body bone density and composition using GE Healthcare Lunar and Hologic DXA systems

Dual‐energy x‐ray absorptiometry (DXA) is used to assess bone mineral density (BMD) and body composition, but measurements vary among instruments from different manufacturers. We sought to develop cross‐calibration equations for whole‐body bone density and composition derived using GE Healthcare Lunar and Hologic DXA systems. This multinational study recruited 199 adult and pediatric participants from a site in the US (n = 40, ages 6 through 16 years) and one in China (n = 159, ages 5 through 81 years). The mean age of the participants was 44.2 years. Each participant was scanned on both GE Healthcare Lunar and Hologic Discovery or Delphi DXA systems on the same day (US) or within 1 week (China) and all scans were centrally analyzed by a single technologist using GE Healthcare Lunar Encore version 14.0 and Hologic Apex version 3.0. Paired t‐tests were used to test the results differences between the systems. Multiple regression and Deming regressions were used to derive the cross‐conversion equations between the GE Healthcare Lunar and Hologic whole‐body scans. Bone and soft tissue measures were highly correlated between the GE Healthcare Lunar and Hologic and systems, with r ranging from 0.96 percent fat [PFAT] to 0.98 (BMC). Significant differences were found between the two systems, with average absolute differences for PFAT, BMC, and BMD of 1.4%, 176.8 g and 0.013 g/cm², respectively. After cross‐calibration, no significant differences remained between GE Healthcare Lunar measured results and the results converted from Hologic. The equations we derived reduce differences between BMD and body composition as determined by GE Healthcare Lunar and Hologic systems and will facilitate combining study results in clinical or epidemiological studies. © 2012 American Society for Bone and Mineral Research.     

Comparison and Cross-Calibration of DXA Systems: ODX-240 and Sophos L-XRA versus Hologic QDR-4500, for Spinal Bone Mineral Measurement. Translation of a Reference Database

Replacement of dual-energy X-ray densitometry equipment may be necessary in time as a result of upgrading systems or new equipment. The lack of standardization in bone mineral density (BMD) measurements is known. Standardization efforts have been made for several years by the European Union under its organization COMAC-BME (Comité d'Actions Concertés–BioMedical Engineering) and by the International Committee for Standards in Bone Measurement. Cross-calibration is generally considered to be the result of linear regression between the measurements obtained with two densitometers. A major disadvantage of the regression method is the noncompatibility of the two formulae of calibration (Y versus X and X versus Y). In this study we considered cross-calibration in terms of a structural model that produced circular equations when, for example, three systems were cross-calibrated. Cross-calibration in this study was calculated from the measurement of the lumbar BMD of a population of 204 patients, with Hologic QDR-4500, ODX-240 and Sophos L-XRA systems. In vitro accuracy and short-term reproducibility of the three systems were studied. Using the structural calibration equation we transformed a reference database for L2–4 BMD obtained from a population of 983 French females, aged 11–47 years, on an ODX-240 to a reference database for a Hologic QDR-4500. A new young adult reference was obtained and consequently a new evaluation of the T-score for the Hologic QDR-4500. Received: 17 July 1997 / Revised: 9 March 1998     

The presence of α-glucosidase, glycerophosphocholine and carnitine in the epididymis and ejaculate of the vervet monkey (Cercopithecus aethiops) and the Chacma baboon (Papio ursinus)

Summary.  The epididymis is the site of post-testicular sperm maturation in the male genital tract. Studies on human epididymides are hampered by the practical inaccessibility of epididymides of healthy men in their reproductive years. The limited use of laboratory animals therefore seems unavoidable. The objective was to establish baseline values of the epididymal markers α-glucosidase, glycerophosphocholine (GPC) and carnitine in the lumen of the caput, corpus and cauda epididymidis and in the ejaculate of adult male Chacma baboons and vervet monkeys. In both primates, α-glucosidase was found throughout the epididymis and in the ejaculate; values did not vary significantly. In monkeys, the highest concentration of GPC was found in the cauda epididymidis, but smaller amounts were found in the other regions and the ejaculate. In baboons, GPC was absent from the caput, but present in the other regions, including the ejaculate. Carnitine concentrations increased significantly from the caput to the cauda in monkeys and from the caput to the corpus in baboons. With this study, the relative concentration ranges in which these markers are present in the epididymides of these primates have been established. In future studies, changes in concentrations of these substances would probably indicate changes in epididymal function.     

Fundamental evaluation of dual x-ray absorptiometry (DXA) for measurement of bone mineral density in rats

This study was designed to assess the precision and accuracy of newly developed ultra high resolution mode (rat mode) in DXA (Hologic, QDR-1000), determine how body thickness affects measured BMD values and to derive a formula by which BMDs in animals with varying degrees of body thickness can be compared. The long term reproducibility on two phantoms (BMD: 170 and 300 mg/cm²) were under CV 1.0%. The repeated precision in vivo and in vitro lumbar spines and phantoms were within CV 1.5%. Accuracy was evaluated by determining the correlation coefficient between ash weight and tibial BMC. The correlation was excellent (r=0.999, p<0.001) over the ash range of 250–600 mg. Using single regression equations, QDR-1000 BMC values were compared with those obtained by conventional methods. There was a close linear correlation with both SPA (Norland Co., r=0.997) and DCS-600 (Aloka Co., r=0.996) measurements. The effects of body thickness were assessed by immersing phantoms at various water depths. There was a significant linear decrease in BMD, as measured by QDR-1000, with increasing water depth. BMDs in vivo with varying body thickness can be compared with each other by using the following correcting formula: BMD₁=(BMD₂+5.5w+7.6) × 10³/(977-4.8w), where BMD₁=expected BMD of extracted bone (mg/cm²), BMD₂=BMD in vivo (mg/cm²), w=body thickness (cm). There was a significant positive correlation (r=0.996, p<0.001) between calculated BMDs from this equation and the values actually obtained. These results confirm that QDR-1000 rat mode yields data useful for assessing BMD and BMC in small animal bones.     

A comparison of two dual-energy X-ray absorptiometry systems for spinal bone mineral measurement

Summary Two dual-energy X-ray absorptiometry (DEXA) systems—the Hologic QDR-1000 and the Norland XR-26 bone densitometers—were evaluated in terms of precision, accuracy, linearity of response, X-ray exposure, and correlation of in vivo spinal measurements. In vitro precision and accuracy studies were performed using the Hologic anthropomorphic spine phantom; linearity of response was determined with increasing thicknesses of aluminum slabs and concentrations of Tums E-X in a constant-level water bath. Both systems were comparable in precision, achieving coefficients of variation (CVs) of less than 1% in bone mineral content (BMC, g), bone area (cm²), and bone mineral density (BMD, g/cm²). Both were accurate in their determination of BMC, bone area, and BMD with reference to the Hologic spine phantom. Both systems also showed good BMC and BMD linearity of response. Measured X-ray skin surface exposures for the Hologic and the Norland systems were 3.11 and 3.02 mR, respectively. In vivo spinal measurements (n=65) on the systems were highly correlated (BMC: r=0.993, SEE=1.770 g; area: r=0.984, SEE=1.713 cm²; BMD: r=0.990, SEE=0.028 g/cm²). In conclusion, both systems are comparable in terms of precision, accuracy, linearity of response, and exposure efficiency.     

Vertebral Morphometry: Repeat Scan Precision Using the Lunar Expert-XL and the Hologic 4500A. A Study for the “WISDOM” RCT of Hormone Replacement Therapy

On radiation safety grounds there is concern about the morbidity attributable to routine radiographs of the spine for the identification of new fractures in large-scale trials of fracture prevention. However, the role of the potentially safer low-radiation-dose technique of vertebral morphometry performed by third generation dual-energy X-ray absorptiometry equipment requires evaluation for use in clinical trials. We have therefore investigated the short-term inter-scan imprecision as well as the imprecision attributable to different-day analyses by the same operator and differences in analyses by different operators. The volunteer subjects were participants in a pilot study for a randomized controlled trial of hormone replacement therapy (Women”s International Study of long Duration Oestrogen after Menopause, WISDOM). Each subject had two morphometric X-ray analysis scans separated by 2–4 weeks. Exclusions were women with densitometrically defined osteoporosis, as defined by the WHO criterion, and women with a body mass index exceeding 30.9 kg/m². On average, the women were 58.7 years of age and had bone mineral density values in the lumbar spine which were about 0.7 SD units higher than a reference US female age-matched population. Scans were assessed from vertebrae T7 through L4. In the study there were no clinically significant differences in performance between the Hologic QDR 4500A and the Lunar Expert XL equipment. Between-scan imprecision was significantly worse than imprecision attributable to reanalysis of the same scan by a different operator or the same operator after an interval. Vertebral level had an effect on measurement uncertainty, especially at the level of the diaphragm and at T7. Coefficients of variation, expressed as percentages of mean values, were better for absolute height measurements than for height ratios, ranging from 1.75% to 3.40% for the three heights measured on three separate machines and from 2.34% to 4.11% for the two height ratios. These results compared favorably with the equivalent figures from a parallel study of morphometry precision undertaken using standard lateral radiographs of the thoracic and lumbar spine (3.1–3.6% and 3.8–3.9%, respectively). We conclude that in trials of prevention therapy in women (or men) selected for not having osteoporosis, low-dose vertebral morphometry using the Hologic 4500A, the Lunar Expert XL or similar equipment is preferable on safety grounds to the classical technique based on standard radiographs, although conventional radiology may still be required in those with prevalent or incident deformities to exclude causes other than osteoporosis. The place of this low-dose technique in trials performed on patients with osteoporosis requires further study. Received: 29 June 1999 / Accepted: 15 December 1999     

Anteroposterior and lateral spinal DXA for the assessment of vertebral body strength: Comparison with hip and forearm measurement

Spinal bone mineral density (BMD) is traditionally measured by dual-energy X-ray absorptiometry (DXA) in the anteroposterior (AP) projection which includes both the vertebral body and the posterior elements in the measurement. The posterior elements, however, contribute little to the compressive strength of the spine. It has therefore been suggested that spinal BMD measured in the lateral projection, including only the vertebral body in the measurement, might be more appropriate for the prediction of fracture risk. To date little clinical evidence has been presented to support this assumption. To address the issue, we measured vertebral, hip and forearm BMD in situ in 14 human cadavers and remeasured BMD in vitro in excised vertebrae. Lateral spinal measurements were performed in the decubitus position. Fracture force and other bio-mechanical measures were determined for 32 vertebrae in a mechanical testing machine and compared with BMD values in situ and in vitro. Correlations of BMD with vertebral fracture force werer=0.48/0.51 (in situ/in vitro) for the AP spinal measurements,r=0.45/0.71 (in situ/in vitro) for the lateral spinal measurements, andr=0.64 andr=0.53 for total hip and forearm measurements in situ, respectively. Thus, despite an apparent diagnostic advantage in vitro, lateral spinal BMD measurement was not superior to AP measurement when performed in situ. This observation corresponds well with previous clinical findings and is probably due to the larger accuracy error in the lateral than in the AP projection resulting from a lower ratio of bone to soft tissue. The high correlation between hip BMD and vertebral fracture force suggests that hip measurement may prove as useful for vertebral fracture risk assessment as spinal measurement in any projection, especially in the elderly with a high prevalence of degenerative changes in the spine.