Social Media-Based Interventions for Health Behavior Change in Low- and Middle-Income Countries: Systematic Review.

BACKGROUND: Despite the wealth of evidence regarding effective health behavior change techniques using digital interventions to focus on residents of high-income countries, there is limited information of a similar nature for low- and middle-income countries. OBJECTIVE: The aim of this review is to identify and describe the available literature on effective social media-based behavior change interventions within low- and middle-income countries. METHODS: This systematic review was conducted in accordance with the 2009 PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We searched PubMed, Embase, Elsevier, CINAHL, PsycInfo, and Global Index Medicus, and the final search was conducted on April 6, 2021. We excluded studies published before 2000 because of the subject matter. We included studies that evaluated interventions conducted at least partly on a social media platform. RESULTS: We identified 1832 studies, of which 108 (5.89%) passed title-abstract review and were evaluated by full-text review. In all, 30.6% (33/108) were included in the final analysis. Although 22 studies concluded that the social media intervention was effective, only 13 quantified the level of social media engagement, of which, few used theory (n=8) or a conceptual model (n=5) of behavior change. CONCLUSIONS: We identified gaps in the settings of interventions, types and sectors of interventions, length of follow-up, evaluation techniques, use of theoretical and conceptual models, and discussions of the privacy implications of social media use. TRIAL REGISTRATION: PROSPERO CRD42020223572; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=223572.

Development of the place-based Adelante social marketing campaign for prevention of substance use, sexual risk and violence among Latino immigrant youth.

Immigrant Latino youth represent a high-risk subgroup that should be targeted with health promotion efforts. However, there are considerable barriers to engagement in health-related programming. Little is known about the engagement possibilities of social marketing campaigns and digital strategies for traditionally 'hard-to-reach' immigrants, underscoring the importance of testing these techniques with immigrant Latino adolescents. We developed and piloted a place-based social marketing campaign in coordination with the branded, Positive Youth Development-based (PYD) Adelante intervention targeting risk factors for co-occurring youth substance abuse, sexual risk and violence. Building on prior research, we conducted a four-phase formative research process, and planned the Adelante social marketing campaign based on findings from one group interview and ongoing consultation with Adelante staff (n=8) and four focus groups with youth (n=35). Participants identified four overarching campaign themes, and suggested portrayal of resilient, proud youth who achieved goals despite adversity. Youth guided selection of campaign features and engagement strategies, including message/visual content, stylistic elements, and a mixed language approach. We developed a 12-month campaign to be delivered via print ads, multi-platform social media promotion, contests, youth-generated videos, blog posts, and text messaging. We describe the process and outcome of campaign development and make recommendations for future campaigns.

Central arterial stiffness and diastolic dysfunction are associated with insulin resistance and abdominal obesity in young women but polycystic ovary syndrome does not confer additional risk.

STUDY QUESTION: Are arterial stiffness, carotid intima-media thickness and diastolic dysfunction increased in young women with polycystic ovary syndrome (PCOS) independently of the effects of obesity? SUMMARY ANSWER: Insulin resistance and central obesity are associated with subclinical cardiovascular dysfunction in young women, but a diagnosis of PCOS does not appear to confer additional risk at this age. WHAT IS KNOWN ALREADY: Some studies have shown that young women with PCOS may have increased measures of cardiovascular risk, including arterial stiffness, carotid intima-media thickness and myocardial dysfunction. However, it is difficult to establish how much of this risk is due to PCOS per se and how much is due to obesity and insulin resistance, which are common in PCOS and themselves associated with greater vascular risk. STUDY DESIGN, SIZE, DURATION: This cross-sectional study comprised 84 women with PCOS and 95 healthy volunteers, aged 16-45 years. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study was conducted in a university hospital. Subjects underwent a comprehensive assessment of body composition (including computed tomography (CT) assessment of visceral fat; VF), measurements of arterial stiffness (aortic pulse wave velocity; aPWV), common carotid intima-media thickness (ccIMT), diastolic function (longitudinal tissue velocity; e':a') and endocrinological measures. A sample size of 80 in each group gave 80% power for detecting a difference of 0.45 m/s in aPWV or a difference of 0.25 in e':a'. MAIN RESULTS AND THE ROLE OF CHANCE: After adjustment for age and body mass index (BMI), PCOS subjects had a greater insulin response (insulin area under the curve-IAUC) following glucose challenge (adjusted difference [AD] 35 900 pmol min/l, P < 0.001) and higher testosterone (AD 0.57 nmol/l, P < 0.001) and high molecular weight adiponectin than controls (AD 3.01 µg/ml, P = 0.02), but no significant differences in aPWV (AD -0.13 m/s, P = 0.33), ccIMT (AD -0.01 mm, P = 0.13), or e':a' (AD -0.01, P = 0.86) were observed. After adjustment for age, height and central pulse pressure, e':a' and aPWV were associated with logVF and IAUC. ccIMT was not related to logVF. The relationships between e':a' or aPWV and insulin resistance were only partly attenuated by adjusting for logVF. There was no significant relationship between aPWV or e':a' and either testosterone or adiponectin. LIMITATIONS, REASONS FOR CAUTION: The study recruited young women meeting the Rotterdam criteria for PCOS diagnosis; hence our findings may not be generalizable to older patients or those meeting other definitions of the syndrome. Biochemical hyperandrogenism was based solely on measurement of total testosterone. Cases and controls were not matched in advance for age and BMI, although the influence of these variables on the cardiovascular outcome measures was adjusted for. WIDER IMPLICATIONS OF THE FINDINGS: This study shows that central arterial stiffness and diastolic dysfunction are not increased in young women with PCOS, whereas they are associated with both insulin resistance and central obesity. Obesity thus represents the greatest modifiable risk factor for cardiovascular disease in young women with PCOS and lifestyle measures which target weight reduction are critical. STUDY FUNDING/COMPETING INTERESTS: This study received no specific grant support from any funding body. The authors have no conflicts of interest to declare.

Detailed characterisation of circulatory nitric oxide and free radical indices--is there evidence for abnormal cardiovascular homeostasis in young women with polycystic ovary syndrome?

OBJECTIVE: To assess circulating biochemical indices of endothelial function and nitro-oxidative stress in women with polycystic ovary syndrome (PCOS). DESIGN: Case-control study. POPULATION: Seventeen women with PCOS and eighteen age- and body mass index-matched healthy volunteers. METHODS: Nitric oxide (NO) metabolite levels were assessed by chemiluminescence. Electron paramagnetic resonance spectroscopy with spin trapping was used to assess oxidative stress ex vivo and in vitro. Antioxidant capacity was measured using oxygen radical absorbance. MAIN OUTCOME MEASURES: Biochemical indices of endothelial function, including NO metabolites, lipid-derived radicals and antioxidant capacity. RESULTS: Plasma NO metabolites were similar in the two groups (nitrite: 257±116 nmol/l [PCOS], 261±135 nmol/l [controls] P=0.93; nitrate: 27±7 µmol/l [PCOS], 26±6 µmol/l [controls] P=0.89). Alkoxyl free radicals (lipid-derived) were detected as the dominant species, but levels were not different between women with PCOS and controls whether measured directly ex vivo (median 7.2 [range 0.17-16.73]e6 arbitrary units [a.u.] and 7.2 [1.7-11.9]e6 a.u., respectively, P=0.57) or when stimulated in vitro to test radical generation capacity (1.23 [0.3-5.62]e7 a.u. and 1.1 [0.48-15.7]e7 a.u. respectively, P=0.71). In regression analysis, visceral fat area was independently associated with in vitro oxidative potential (ß=0.6, P=0.002). Total plasma antioxidant capacity (94±30% [PCOS], 79±24% [controls], P=0.09) and plasma hydroperoxides (7.5±4 µmol/l [PCOS], 6.7±5 µmol/l [controls], P=0.21) were not different between groups. However, lipophilic antioxidant capacity was lower in women with PCOS compared with controls (92±32 and 125±48%, respectively, P=0.02). CONCLUSIONS: Young overweight women with PCOS display a reduced lipophilic antioxidant capacity compared with healthy volunteers, but no change in circulating free radicals or nitro-oxidative stress.

Quantification of the activity of tritium produced during the routine synthesis of (18)F fluorodeoxyglucose for positron emission tomography.

Gamma emitting radioactive by-products generated during the cyclotron irradiation of (18)O labelled water by protons to produce (18)FDG (fluorodeoxyglucose) for positron emission tomography are well characterised. However, the production of tritium ((3)H) through the (18)O(p,t)(16)O nuclear reaction has not been investigated in detail. The aim of this study was to measure tritium activity produced during a large number of (18)FDG production runs in order to obtain a better perspective on its impact on radioactive waste management, particularly as regards storage and disposal. Tritium was assayed by liquid scintillation counting in recovered (18)O water from 24 separate production runs. The mean (SD) values of activity and activity concentration were 170 (20) kBq and 81 (8) kBq ml(-1) respectively. Both quantities were positively correlated with the activity of (18)F. Tritium was detected in much lower concentration in water used to rinse the target vessel. The activity of tritium is such that it is exempt from regulatory control and may be combined with bulk non-active waste for disposal as Very Low Level Waste. However, variations in the irradiation conditions or the procedures for the collection of recovered water might result in its classification as Low Level Waste, necessitating a more complex disposal regime.

ACTN3 genotypes of Rugby Union players: distribution, power output and body composition.

BACKGROUND AND AIM: To identify the distribution and explore the relationship between ACTN3 genotypes and power and body composition phenotypes. SUBJECTS AND METHODS: Case control and association studies were employed using a homogeneous group of players (n = 102) and a control group (n = 110). Power-related phenotypes were measured using the counter movement jump (CMJ) and body composition phenotypes by dual-energy X-ray absorptiometry (DXA). Statistics used were Pearson's chi-square, ANCOVA, coefficients of correlation and independent t-tests. Genotyping was carried out using polymerase chain reaction followed by enzymatic Ddel digestion. RESULTS: Genotype proportions of players were compared with controls (p = 0.07). No significant genotype differences occurred between forwards or backs (p = 0.822) or within-forwards (p = 0.882) or within-backs (p = 0.07). Relative force and velocity were significantly larger in backs, power significantly greater in forwards; in body composition, all phenotypes were significantly greater in forwards than backs. Correlations between phenotypes were greater for the RX genotype (p = 0.05-0.01). CONCLUSIONS: Relationships between ACTN3 genotypes and power or body composition-related phenotypes were not significant. As fat increased, power-related phenotypes decreased. As body composition increased, power-related phenotypes increased.

ACE ID genotype and leg power in Rugby Union players.

AIM: The present study examined the hypothesis that there were no significant differences between forwards and backs in the elements of leg power between the ID and DD genotypes of the ACE (I/D) gene in developing young adult Rugby Union players. METHODS: Sixty-eight players were recruited to identify the distribution of genotypes between forwards and backs. Fifty-eight players were investigated for leg power. Forwards (n=28) comprised 15 ID and 13 DD genotypes, and backs (n=30) 19 ID and 11 DD genotypes. Leg power was measured on a force platform using a counter movement jump; the parameters of interest were peak and relative force, peak and relative power, displacement and velocity. The three-primer polymerase chain reaction was used to assay the region of interest for I and D variants of the ACE gene. The distribution of genotypes was determined by chi-square and comparisons between forwards and backs made using the independent t-test. RESULTS: No significant differences were identified in the distribution of genotypes between forwards and backs (χ2=2.2, P=0.336). However, significant differences were identified between forwards and backs in a number of components of leg power. Backs had significantly larger values than forwards for relative force (1.50 vs. 1.30 Wt%, P=0.001) and relative power (27.1 vs. 24.3 W.kg-1, P=0.034) for the ID genotype, whereas backs had significantly larger values than forwards for displacement (0.42 vs. 0.38 m, P=0.049) and velocity (2.76 vs. 2.55 m.s.(-1), P=0.007) for the DD genotype. CONCLUSION: The characteristics of leg power identified will enhance the functional requirements of players according to playing position and commitment.

Gamma-ray burst observations by pioneer venus orbiter.

The Pioneer Venus orbiter gamma burst detector is an astrophysics experiment for monitoring cosmic gamma-ray bursts. It is included in this planetary mission to provide a long baseline for accurately locating the sources ofthese bursts in order to identify them with specific astronomical objects. Responses to 14 gammaray burst events were examined; these events were verified from data acquired by other systems. Preliminary locations are proposed for three events, based on data from the Pioneer Venus orbiter, ISEE C, and Vela spacecraft. These locations will be improved, and additional locations will be determined by including in the analyses data from Helios B and the Russian Venera 11, Venera 12, and Prognoz 7 spacecraft.

Can abdominal bioelectrical impedance refine the determination of visceral fat from waist circumference?

Ryo et al (2005 Diabetes Care 28 451-3) reported a new method for measuring the visceral fat area (VFA) by combining abdominal bioelectrical impedance analysis (BIA) with measurement of waist circumference (WC), but very few methodological details were provided. Furthermore, the study did not test the use of WC alone as an indicator of VFA even though others had previously reported a strong correlation. We sought to determine the optimal measurement technique and analysis for measuring VFA by abdominal BIA and WC. 18 volunteers (age 23-64 years) underwent measurement of WC, abdominal impedance (Bodystat 500 four-electrode system) and a single cross-sectional CT scan at the umbilicus. VFA derived using WC(3) and measurements of abdominal impedance from electrode pairs sited at the flank predicted the value of VFA measured by CT with correlation r = 0.904 (p < 0.0001); the optimizing power of WC was 3.3 (r = 0.905). However, the use of WC(1.9) alone, without involving BIA at all, provided a similar correlation (r = 0.923). Our small preliminary study shows that abdominal BIA is potentially a practicable non-invasive technique for measurement of VFA but casts doubt on whether it adds any value to the use of WC alone. Larger studies are now required to test this finding.

Design of a novel digital intervention to promote healthy weight management among postpartum African American women.

BACKGROUND: Excess weight retention among postpartum women is a risk factor for long term obesity, and African American women are at heightened risk. New solutions, including digital technologies and community-based approaches are needed. Digital platforms, like social media, provide opportunity for participant co-creation (i.e., content co-generated by users and investigators) of health messages and may allow for adaptation of evidence-based weight management interventions to reduce participant burden. The BeFAB intervention, a branded, digital weight management program, tests this hypothesis. METHODS: BeFAB content comprises culturally-specific nutrition, physical activity, stress management, health information seeking and related weight management messages and content designed for African American women. The intervention is 12 weeks in duration, delivered through a mobile phone app, and is designed to target specific behavioral predictor beliefs and attitudinal measures (e.g., self-efficacy to achieve weight management goals) based on the culturally-specific content. Use of personal, culturally-specific video-based narratives in the app, and through a secret Facebook group, are included to help model HEAL behaviors and brand BeFAB. Intervention development consisted of iterative formative research steps to engage African American women. The program will be evaluated in a small randomized trial among patients recruited at a clinical facility. CONCLUSIONS: BeFAB applies evidence-based content using a promising digital approach. It is novel in its use of branding, culturally-tailored content, and digital technology for behavior change.Evaluation of BeFAB will contribute to the growing literature on digital health behavior change interventions for weight management.

What community measurements can be used to predict bone disease in patients with COPD?

BACKGROUND: Osteoporosis is common in patients with COPD. Previously we have reported that loss of fat-free mass (FFM), measured by dual X-ray absorptiometry (DXA) is associated with loss of bone mineral density (BMD). In addition, in patients with a low body mass index (BMI) and a low FFM, all had evidence of bone thinning, 50% having osteopenia and 50% osteoporosis. We explored the utility of different anthropometric measures in detecting osteoporosis in a community-based COPD population. METHODS: Patients with confirmed COPD and not on long-term oral corticosteroids (n=58) performed spirometry. They underwent nutritional assessment by skinfold anthropometry, midarm circumference, calculation of both % ideal body weight (IBW) and BMI. All had DXA assessment of BMD. RESULTS: A total of 58 COPD patients had anthropometric measurements taken, with a mean age of 66.8 (SD 8.7) years, 31 (58%) were male, with a forced expiratory volume in 1s (FEV(1)) of 54.17 (20.18)% predicted. Osteoporosis was present at either the hip or lumbar region in 14 patients (24%). The useful anthropometric measurements identifying those with osteoporosis were both % IBW and BMI. The adjusted odds ratio for %IBW was 0.93 (95% confidence interval (CI) 0.87, 0.99), p=0.016 and for BMI: 0.79 (0.64-0.98), p=0.03. The receiver operating characteristics (ROC) score for both was 0.88, indicating a good fit. CONCLUSION: Osteoporosis is common, even in patients with mild airways obstruction. Nutritional assessment, incorporating a calculation of their BMI or %IBW may confer an additional benefit in detecting those at risk of osteoporosis and guide referral for BMD measurement.

Cost effectiveness analysis of using quantitative ultrasound as a selective pre-screen for bone densitometry.

It has been suggested that quantitative ultrasound (QUS) could be used as a selective population pre-screen, to maximise the cost effectiveness of referral for dual energy X-ray absorptiometry (DXA) assessment of bone mineral density (BMD). We set out to examine how such an approach might perform in the assessment of women who were referred by general practitioners for DXA via the open access service in Cardiff. In 115 women aged 40-80 (mean 69) years we used DXA to measure BMD at lumbar spine and hip, and QUS to measure broadband ultrasound attenuation (BUA) in the heel. A bottom-up approach was used to estimate the costs of DXA and QUS. We examined the cost effectiveness of using QUS as a pre-screen, only referring subjects for the more expensive DXA assessment if BUA were less than a pre-determined threshold. The unit costs of pencil-beam DXA and QUS were approximately 44 UK pounds and 16 UK pounds respectively. We identified a BUA threshold of 60 dB/MHz as the most cost effective, and calculated a sensitivity of 81% and specificity of 89% in identifying those subjects whom DXA assessment subsequently identified as having osteoporosis. At the BUA threshold of 60 dB/MHz, pre-screening saved 969 UK pounds at the expense of missing ten women with osteoporosis as diagnosed by DXA. Therefore the cost per additional woman with osteoporosis identified using DXA alone was only 97 UK pounds. QUS assessment does not appear to have a significant cost effective benefit as a pre-screen for DXA in the studied population. A QUS pre-screen would be cost effective only if this investigation could be performed at a substantially lower cost.

Determining true glomerular filtration status in newly presenting type 2 diabetic subjects using age and sex adjustment.

OBJECTIVE: To determine age- and sex-adjusted reference ranges (ASARRs) for glomerular filtration status using data from nondiabetic subjects and to apply these to newly presenting type 2 diabetic subjects. RESEARCH DESIGN AND METHODS: Glomerular filtration rate corrected for body surface area (cGFR) was determined using a radionuclide (51Cr-EDTA) method in 75 non-diabetic subjects (37 men, 38 women) and 219 type 2 diabetic subjects (157 men, 62 women). The 95% constant reference ranges (CRRs) were calculated as mean nondiabetic cGFR+/-1.96 SD. The 95% ASARRs were calculated by Altman's method from the nondiabetic cGFR versus age regression residuals for both male and female subjects. RESULTS: Using Altman's method, the intercepts, but not the gradients, of the cGFR versus age regressions were significantly different between male and female subjects (intercept difference [95% CI] 8.2 [1.3-15.1], gradient difference -0.4 [-1.1 to 0.3]). Fitting a common gradient, 95% ASARRs for normofiltration were found to be from 123.9 - (0.89 X age) to 181.7 - (0.89 x age) for male subjects, and from 116.0 - (0.89 X age) to 173.2 - (0.89 X age) for female subjects. The 95% CRR for normofiltration was 70.2-138.1 ml x min(-1) x (1.73 m)(-2). When applied to the diabetic cGFRs, the CRRs and ASARRs gave, respectively, 17% (37/219) versus 21% (46/219) hyperfiltrators and 83% (181/219) versus 79% (172/219) normofiltrators. Using the ASARRs, 14 normofiltrators (6 men, 8 women) were reclassified as hyperfiltrators (change [n/total n] [95% CI] 8% [14/181] [4-12]), and 5 hyperfiltrators (5 men, 0 women) were reclassified as normofiltrators (change 14% [5/37] [5-30]). CONCLUSIONS: We conclude that age and sex adjustment are essential to assess glomerular filtration status.

The validity of estimating total body fat and fat-free mass from skinfold thickness in adults with growth hormone deficiency.

The regression equations of Durnin and Womersley for estimating total body fat (TBF) and fat-free mass (FFM) from skinfold thickness were validated for adult GH-deficient (GHD) patients by comparing the values of TBF and FFM from the prediction equations with the directly measured values from dual energy x-ray absorptiometry. Twenty-seven male and 24 female patients (aged 21-61 yr) were studied. GHD was isolated in 5 cases and was part of a spectrum of hypopituitarism due to a variety of causes in 46 cases. The mean period of GHD was 6.9 +/- 4.6 yr. All patients were receiving stable replacement therapy. The validation statistics showed no significant differences (P > 0.05) between measured and predicted values of TBF and FFM in either males (24.5 vs. 24.9 and 65.5 vs. 65.8 kg) or females (24.6 vs. 26.3 and 44.7 vs. 43.9 kg). Mean differences were smaller in males (0.4 and 0.2 kg) than females (1.7 and -0.8 kg); they were less than 1% in males and less than 2% in females. Therefore, the Durnin and Womersley equations are suitable for general use with GHD patients. Using TBF (kilograms) from dual energy x-ray absorptiometry as the dependent variable and the log of the sum of skinfold thickness as the independent variable, linear regression equations were formulated to predict TBF in GHD patients. The lowest SE of estimate was 3.8 kg in males and 4.6 kg in females. To determine their general applicability, these equations will need to be cross-validated.

Factors affecting bone density in young adults.

A 14-y follow-up of 581 children who took part in a randomized controlled trial of the effect of a milk supplement on growth of children was conducted to investigate the supplement's effect on adult bone mineral content (BMC) and density (BMD). BMC and BMD of the nondominant forearm were measured by single-photon absorptiometry in 371 subjects (64%) aged 20-23 y, at a proximal site (shaft of radius and ulna) and at a distal site near the wrist. BMCs and BMDs tended to be higher in the intervention group (NS). Cross-sectionally, BMD was positively associated with body weight (P less than 0.01) in both sexes; inversely associated with alcohol consumption (P less than 0.05), and positively with manual occupation (NS) in men; positively associated with current intakes of calcium (P less than 0.05), vitamin D (P less than 0.01), and sports activity during adolescence (P less than 0.01), and inversely with parity (NS) in women. In multiple linear-regression analysis body weight and sports activity during adolescence were stronger determinants of female BMD than was diet.

Effect of recombinant human growth hormone on regional tissue distribution in growth hormone-deficient males.

Dual-energy X-ray absorptiometry was used to analyze the regional tissue distribution of bone mineral mass (BMM), fat mass (FM), and lean tissue mass (LTM) in the arms, trunk, and legs of 23 male growth hormone-deficient (GHD) males. Patients were assigned randomly to treatment (n = 11) and control (n = 12) groups. During the first six months, the treatment group received recombinant growth hormone (rhGH) and the control group placebo. During the second six months, both groups received rhGH. Following treatment there was a trend for BMM to be lost in the arms and legs, with gains at the trunk. Fat mass was lost mainly from the trunk. Proportionally more LTM was distributed to the arms and legs than to the trunk. Treatment was more effective in the first six months than the second. The correlation between the waist-hip ratio and trunk fat was poor, suggesting that its use in patients with GHD may be misleading.

A theoretical analysis of the accuracy of single-energy CT bone-mineral measurements.

A relationship has been derived between the in vivo concentration of calcium hydroxyapatite and the in vitro concentration of K2HPO4 solution in a single-energy quantitative computed tomography (QCT) bone-mineral determination. Under certain simplifying assumptions this relationship is linear. The gradient term has been calculated as a function of scanner effective energy using the measured variation of solvent water density with K2HPO4 concentration; it ranges from 1.17 at 60 keV to 1.21 at 80 keV. The intercept term has been calculated as a function of effective energy, patient age and trabecular bone volume (TBV) by modelling the constituents of whole trabecular bone and using published normal composition data. It varies from about 15 to 25 mg cm-3 at an effective energy of 70 keV and within a TBV range of 5 to 20%. This intercept term may be used as an additive correction which improves the accuracy of single-energy QCT results without significant loss of precision. However, the method is limited by the uncertainties of tissue composition in an individual patient.

Temporal instabilities associated with a planar high purity germanium detector.

Experiments have been performed which show that a grooved planar high purity germanium semiconductor detector may give rise to time variant counting rates in energy regions below prominent spectral peaks. It is postulated that this effect is due to prolonged or incomplete charge collection in the vicinity of the bottom of the groove, and is caused by distortions in the applied electric field in this region. Such effects may lead to changes in the minimum detectable count rate in x-ray fluorescence measurements; these can be reduced by collimating incident photons on the central region of the detector but the resulting reduction in efficiency lowers the overall sensitivity.

Factors affecting the in vivo precision of broad-band ultrasonic attenuation.

The in vivo precision of broad-band ultrasonic attenuation (BUA) was measured in one normal male volunteer over periods of one day and six weeks and in a group of 10 volunteers over a period of two weeks using a Walker Sonix UBA 1001 bone mineral analyser in which the foot is immersed in a water tank. Coefficients of variation ranged from 1-3% and, in general, there was no difference in BUA variance between right and left feet. However, right foot BUA values were consistently greater than those of the left, but there was no difference between mediolateral and lateromedial transmission. The use of preboiled water improved precision and reduced measurement time. In addition, factors affecting BUA precision were investigated in the individual volunteer. Equipment stability and conditions of immersion (immersion time, water depth, water temperature and concentration of a detergent wetting agent) had comparatively little effect on BUA values. On the other hand, the effects of foot positioning were more pronounced: rotation about the long axis of the foot, translation across the water tank and foot movement in the dorsal-plantar direction each contributed a maximum of 1.5-2.0% variation in BUA. However, both rotation about the long axis of the leg and foot movement in the heel-toe direction could change BUA by as much as 9%. It is likely that foot positioning will limit the precision achievable with this technique.

Bone mineral content in normal UK subjects.

Bone mineral content in the lumbar vertebrae and in the shaft of the left radius has been measured in 129 normal British subjects using quantitative computed tomography and single-photon absorptiometry. Significant negative correlations between bone mineral content and age were found at both sites in males and females (p less than 0.001 in all cases). When expressed in g/cm the bone mineral content in the radial shaft showed significant positive correlations with body height and weight in both sexes, but after correction for bone size only a weak correlation with body height in males was found. Spinal trabecular bone mineral content showed no significant correlations with body height or weight in either sex. Comparison of the values obtained with normal data from centres in the USA revealed lower mean values for both radial and spinal bone mineral content in the British subjects. These differences emphasize the importance of using locally derived normal data for comparison with values obtained from patients.