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G M Blake

Publications and source records attributed to G M Blake.

At least 91 records · Page 5Linked to original sources
PubMed1994

Dual X-ray absorptiometry of the lumbar spine: the precision of paired anteroposterior/lateral studies.

Supine lateral dual X-ray absorptiometry (DXA) has the potential to provide a sensitive and precise method of measuring changes in trabecular bone mass in the lumbar vertebral bodies. An important reason for the improvement in precision compared with the earlier decubitus lateral technique is the use of baseline compensation, an algorithm which computes the changes in lateral bone mineral density (BMD) using data from both anteroposterior (AP) and lateral scans. This report examines the precision of supine lateral DXA based on scans of 12 female volunteers (age range 21-56 years). Five AP/lateral scan pairs were performed on each subject and precision expressed by the coefficient of variation (CV). For the AP scan the CV for both L1-L4 and L2-L4 BMD was 0.8%. Precision of the L2-L4 lateral vertebral body, mid-vertebral and volumetric BMD parameters with (without) the baseline compensation correction were 1.2% (2.1%), 2.4% (3.0%) and 1.5% (2.5%), respectively. Two methods of performing baseline compensation, referred to as the multiplicative and additive algorithms, were compared and the former shown to give significantly better precision. The precisions of different combinations of lumbar vertebrae for the measurement of lateral vertebral body BMD were compared and the precision for L2-L4 shown to be significantly better than for L3-L4. When individual vertebrae were examined L3 had the best precision although the differences with L2 and L4 were not significant. The study confirmed that supine lateral measurements of vertebral body BMD with baseline compensation give better precision than the decubitus method. The improvement makes it feasible to follow patients longitudinally and may allow the sensitivity of the lateral scan to supersede that of AP measurements.

Absorptiometry, Photon↗
PubMed1994

The ultrasonic assessment of osteopenia as defined by dual X-ray absorptiometry.

Dual X-ray absorptiometry (DXA) studies of bone mineral density (BMD) of the lumbar spine and femoral neck were compared with measurements of broadband ultrasonic attenuation (BUA) and velocity of ultrasound (VOS) in the calcaneus in 300 pre- and postmenopausal women (mean age 53 years). The women were referred for evaluation of possible osteopenia as defined by DXA. The ability of ultrasound measurements to predict osteopenia in women was compared with the ability of lumbar spine and femoral neck DXA scans to predict osteopenia in the hip and spine. A new ultrasound parameter obtained by combining BUA and VOS (combined attenuation and velocity (CAV)) was also evaluated. Linear regression analysis of the three ultrasound parameters and lumbar spine and femoral neck BMD gave weak but statistically significant correlations (r = 0.45-0.54). The correlation between spine and femoral neck BMD was statistically significantly better (r = 0.72). Receiver-operating characteristic (ROC) analysis was used to investigate the sensitivity and specificity of ultrasound measurements in predicting patients with osteopenia. The areas under the ROC curves ranged from 0.64 to 0.75 and ultrasound parameters were shown to be poor at predicting osteopenia as defined by DXA. The ability of lumbar spine and femoral neck DXA measurement to predict osteopenia in the hip and spine, respectively, was statistically significantly better than any of the ultrasound parameters. Ultrasound measurements in the calcaneus did not appear to identify accurately patients with osteopenia defined by DXA measurements of bone density in the axial and appendicular skeleton.

Absorptiometry, Photon↗
PubMed1994

Should broadband ultrasonic attenuation be normalized for the width of the calcaneus?

Broadband ultrasonic attenuation (BUA) is a measure of ultrasound transmission through the calcaneus that is dependent on bone thickness as well as the density of scattering centres. This report examines whether the normalization of BUA (units dB MHz-1) for calcaneal width (nBUA: units dB MHz-1mm-1) improves the discrimination of clinical studies. BUA and calcaneal width were measured in 200 women using a contact ultrasound (CUBA-Research) system and nBUA evaluated by dividing BUA by bone width. 150 subjects were early post-menopausal and the remaining 50 were osteoporotic women with confirmed vertebral crush fracture. The ability of BUA and nBUA to differentiate between the two groups of subjects was compared using receiver operating characteristic (ROC) analysis. The areas (and standard errors) under the ROC curves were 0.878 (0.033) for BUA and 0.910 (0.028) for nBUA. The difference (and standard error) between the areas under the ROC curves was 0.033 (0.026) and was not statistically significant.

Aged↗
PubMed1993

Spine and femur BMD by DXA in patients with varying severity spinal osteoporosis.

Bone mineral density (BMD) at the lumbar spine, femoral neck, trochanteric region, and Ward's triangle was measured using dual-energy X-ray absorptiometry (DXA) in 118 women with osteoporotic vertebral collapse (average age 65 years), divided into four groups according to numbers and SD of vertebral deformation below norms: group 1: -3SD deformations only; group 2: one -4SD deformation; group 3: two-four -4SD deformations; and group 4: 5 or more -4SD deformations. There were no significant differences between the groups. Results were compared with those from 80 premenopausal (average age 32 years, range 20-40 years) and 109 postmenopausal normal women (average age 64, range 60-70 years). Mean BMD in osteoporotic group 1 was lower than premenopausal normal women by 32% at the lumbar spine, 31% femoral neck, 30% trochanteric region, and 44% at Ward's triangle, and postmenopausal controls by 17% lumbar spine, 16% femoral neck, 17% trochanter, and 14% Ward's triangle. There was a clear trend to reduction in mean BMD between osteoporotic groups 1 and 4 at all four measured sites with significant differences at the spine of 0.102 g/cm2 (P < 0.01) and Ward's triangle 0.059 g/cm2 (P < 0.01). When compared with premenopausal controls, there was a reduction in mean BMD between osteoporotic groups 1 and 4 of 10% at the lumbar spine, 7% femoral neck, 8% trochanteric region, and 13% Ward's triangle. Receiver operating characteristic analysis showed no significant differences in diagnostic sensitivities among the four measured sites for vertebral fractures. We conclude from this cross-sectional data that the majority of bone loss in spinal osteoporosis occurs before the onset of fractures.

Absorptiometry, Photon↗
PubMed1993

Measurements of postmenopausal bone loss with a new contact ultrasound system.

Measurements of broadband ultrasonic attenuation (BUA) and velocity of ultrasound through the heel (heel velocity, HV) were performed with a Contact Ultrasonic Bone Analyzer (CUBA-Research model) in 229 women. The subjects consisted of 16 healthy young volunteers (Group 1, mean age 26 years), 170 healthy pre- and postmenopausal women (Group 2, mean age 53 years), and 43 osteoporotic women with radiographically defined vertebral crush fracture (Group 3, mean age 66 years). Subjects in Group 1 had 10 repeated measurements in a study of short-term precision. Women in Groups 2 and 3 also had dual X-ray absorptiometry (DXA) scans to measure lumbar spine and femoral neck bone mineral density (BMD). The BUA and HV measurements for all 229 women showed a significant correlation (r = 0.75, P < 0.001). The precision study on the subjects in Group 1 gave a root mean square coefficient of variation of 6.3% for BUA and 1.04% for HV. Linear regression analysis gave the following relationship between BUA and age for the 170 normal women in Group 2: BUA = 83.6-0.86 (age 40) dB/MHz (r = -0.31, P < 0.001, SEE = 16.3 dB/MHz). The relationship between HV and age was as follows: HV = 1614-2:3 (age 40) m/s (r = -0.33, P < 0.001, SEE = 42 m/s). Multivariate regression analysis showed that in addition to age, years since the menopause was also a significant factor in determining both BUA and HV.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Ultrasonic velocity measurements through the calcaneus: which velocity should be measured?

The assessment of skeletal integrity by the measurement of ultrasonic velocity through the calcaneus has only recently become widely available and is usually made in conjunction with the measurement of broadband ultrasonic attenuation. Using data obtained with a contact ultrasonic bone analyser (CUBA) system, this report examines whether ultrasonic studies of the heel require the measurement of true velocity of sound in the calcaneus (Vbone), or whether heel velocity (Vheel, defined as the mean velocity through bone and soft tissue) or time of flight velocity (Vtof, defined as the mean velocity between the two transducers) are adequate surrogates. The populations selected for study were 15 healthy young women (group 1, mean age 26 years), 231 healthy peri- and postmenopausal women (group 2, mean age 52 years) and 33 osteoporotic women with confirmed vertebral fracture (group 3, mean age 66 years). Precision was studied by performing 10 repeated scans on the subjects in group 1 and duplicate scans on 144 women randomly selected in groups 2 and 3. Precision was expressed as the percentage coefficient of variation (CV). Both precision studies yielded similar results. The precisions (and 5% to 95% ranges) for all groups combined were: Vbone 2.71% (1465-1809 m/s); Vheel, 1.10% (1511-1646 m/s): Vtof, 0.70% (1349-1425 m/s). Although the precision data suggest Vtof should be preferred, when the range of clinical values is taken into account the smaller CV is exactly cancelled by the narrower range.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Total body studies in normal British women using dual energy X-ray absorptiometry.

We report dual energy X-ray absorptiometry (DXA) studies of total body bone mineral and body composition performed in 111 normal caucasian women (aged 42-61). Conventional DXA scans of the lumbar spine and femoral neck were also obtained and each woman completed a detailed questionnaire. Significant correlations were found between total body BMD and BMD in the lumbar spine (r = 0.76) and femoral neck (r = 0.72). We present reference range data for BMD in the total body and in seven subregions of the skeleton. Multiple linear regressions of total body BMD and BMC on weight, height and age showed that the inclusion of height compared with weight and age alone was not statistically significant. The dependence of total body BMD on weight and age was: total body BMD (g cm-2) = 1.043 + 0.0042 x weight (kg) - 0.0039 x age (years) (R = 0.46, SEE = 0.074 g cm2). Body mass derived from DXA scans correlated well with weight measured on scales (r = 0.996, SEE = 0.77 kg). Body composition measurements agreed closely with % body fat estimated from skinfold measurements (r = 0.93), body fat mass estimated from a predictive equation based on weight, height and age (r = 0.91) and % body fat estimated from a predictive equation based on body mass index (r = 0.76). Study precision gave coefficients of variation of 0.6% for total body BMD and 0.7% for % body fat.

Absorptiometry, Photon↗
PubMed1993

Dual X-ray absorptiometry: a comparison between fan beam and pencil beam scans.

The recent introduction of dual X-ray absorptiometry (DXA) systems with fan beam instead of conventional pencil beam scanning geometry represents a significant technical advance in bone densitometry. This report describes phantom and in-vivo studies of the effect of the change in beam configuration on DXA measurements. Fan beam and pencil beam measurements acquired on one of the new generation scanners, the Hologic QDR-2000, were compared with scans performed on an earlier pencil beam model, the Hologic QDR-1000. The variation with height above the scanning table of fan beam measurements of an anthropomorphic spine phantom were: bone mineral content (BMC): -3.1% cm-1; projected area (AREA): -2.8% cm-1; bone mineral density (BMD): -0.2% cm-1. For pencil beam scans the magnitude of height variation was less than 0.1% cm-1. QDR-2000 fan and pencil beam scan results for 20 volunteers correlated closely with QDR-1000 pencil beam data (r = 0.966-0.998). For BMD measurements on the spine and hip, differences between fan and pencil beam data were consistent with the errors expected from measurement precision. For AREA and BMC data, however, larger differences were observed with individual deviations which correlated with body habitus of the subjects. Although the change from pencil to fan beam geometry significantly affected AREA and BMC data, the effect on the clinically more important BMD measurements was negligibly small.

Absorptiometry, Photon↗
PubMed1993

A comparison of reference bone mineral density measurements derived from two sources: referred and population based.

The construction of reference ranges for bone mineral density (BMD) is of importance when defining risk of osteoporosis in an individual. This study examined lumbar spine BMD from two different populations of women aged 40-69 years, both measured by dual X-ray absorptiometry (DXA) using Hologic QDR-1000 machines. Results were compared with the manufacturer's reference range. At one site (Centre 1) women were referred by general practitioners for BMD measurement to aid decisions regarding long term hormone replacement therapy (HRT). At the other (Centre 2), women were drawn from the age/sex register of a London general practice (population 11,000) and invited to attend a screening examination at their local hospital. The BMD for both groups did not differ significantly from the manufacturer's reference range. The BMD at Centre 1 was lower than Centre 2 by 0.0175 g cm-2 but this did not reach significance and after calibration of both DXA machines with a spine phantom the difference in BMD of the two groups was reduced to only 0.0034 g cm-2. Population based sampling carries no advantage over a GP referral based method for the construction of spinal BMD reference ranges. Although local BMD reference ranges may be required for sites outside the spine the comparable results in this study of the two UK reference ranges and those of the USA manufacturer suggest that local reference ranges for lumbar spine BMD using DXA may be unnecessary in the UK.

Absorptiometry, Photon↗
PubMed1992

Measurements of broadband ultrasonic attenuation in the calcaneus in premenopausal and postmenopausal women.

We report a study of broadband ultrasonic attenuation (BUA) in the calcaneus in 248 women. Measurements were performed with a Walker-Sonix UBA-575 ultrasonic bone analyser. The populations studied were 15 healthy young volunteers (group 1, mean age 26 years), 200 healthy pre- and postmenopausal women (group 2, mean age 53 years) and 33 osteoporotic women with vertebral crush fractures (group 3, mean age 66 years). Subjects in group 1 each had 10 repeated measurements of their right heel. Duplicate BUA measurements in the right heel were performed in 96 subjects and bilateral scans in a further 87 women in group 2. The remaining 17 subjects in group 2 and those in group 3 had a single scan of the right heel. All women in groups 2 and 3 had dual X-ray absorptiometry (DXA) scans of the lumbar spine and femoral neck. The precision study on the women in group 1 gave a root mean square (RMS) coefficient of variation (CV) of 4.2%. Individual CV results showed statistically significant differences (range 1.3%-7.6%). Duplicate scans in subjects in group 2 gave a RMS CV of 4.6% while the bilateral measurements showed no significant difference between the two heels. Linear regression analysis gave the following relationship between BUA and age: BUA = 87.1 - 0.76 (Age - 40) dB/MHz (r = -0.31, p less than 0.001, SEE = 14.0 dB/MHz). Multivariate regression analysis showed that, in addition to age, years since the menopause was also a significant factor in predicting BUA.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

The effect of vertebral collapse on spinal bone mineral density measurements in osteoporosis.

Bone mineral density (BMD) of the lumbar spine (L1-L4) was measured using dual-energy x-ray absorptiometry (DXA) in 57 postmenopausal women with spinal osteoporosis aged 50-82 years (average age 64). For each vertebra between L1 and L4, the BMD was compared to age-matched normal population values and a Z score obtained. Twenty three patients had between one and three collapsed vertebrae from L1 to L4. The average Z score for fractured vertebrae was -1.62 but for uncollapsed vertebrae was -2.26 (P less than 0.001). The difference in Z scores obtained for collapsed and uncollapsed vertebrae was greater where only one fracture was present (0.803) compared to two (0.577) or three fractures (0.245). The average increase in density for a fractures vertebra was 0.070 g/cm2. For L1 vertebral fractures alone the average increase in BMD was 0.096 g/cm2, L2 vertebral fractures 0.041 g/cm2, L3 fractures 0.029 g/cm2 and L4 fractures 0.062 g/cm2. It is concluded that as vertebral collapse is not alway detected using DXA and usually causes a rise in BMD, spinal x-rays are necessary to avoid misinterpretation of a falsely elevated BMD in osteoporotic patients, particularly in longitudinal studies or when monitoring therapy, where small changes in BMD are important.

Absorptiometry, Photon↗
PubMed1992

Postmenopausal screening for osteopenia.

Dual energy X-ray absorptiometry (DXA) measurements of bone mineral density (BMD) in the lumbar spine and femoral neck have been performed in 1000 consecutive women aged between 40 and 60 years referred for screening for osteopenia. A detailed history was taken from each woman that included relevant lifestyle parameters and known risk factors for osteoporosis. After exclusions, e.g. because of fractures, corticosteroid or prolonged HRT use, 627 women (mean age 53 years) were considered suitable for further analysis. The mean BMD in the lumbar spine (L1-L4) was 0.946 g/cm2 and in the femoral neck was 0.767 g/cm2. Significant correlations were found between BMD and years after the menopause and weight (range r = 0.20-0.24). However, these parameters are not reliable enough predictors of BMD to be of value in clinical practice. If osteopenia is to be the basis for initiating prophylactic measures against bone loss, then a threshold BMD must be chosen below which treatment will be advised. Since the correlation coefficient between spinal and femoral neck BMD measurements was only 0.64, assessment of any individual requires consideration of both sites. There is as yet no consensus as to the number of women who may require to be treated and we have provided BMD values that identify a range of population sizes (the lowest 20, 30, 40 and 50 percentiles). It should be noted that there was a 16% loss of BMD in the spine and 14% in the femoral neck during the first 5 years after the menopause.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1992

A comparison of three commercially available PET imaging systems.

Three commercial positron emission tomography (PET) imagers were assessed using the same test protocol (Positron Corporation 'Posicam', Siemens Ecat 951/31 and the Scanditronix PC 4096-15WB). A cylindrical phantom and a 'Jaszczak' phantom both filled with 18F were employed to measure sensitivity, slice uniformity, transaxial and axial resolution and cold rod contrast. The spread of results were as follows: sensitivity varied from 2.08 to 3.73 kcps kBq-1 ml-1 (77-138 kcps microCi-1 ml-1); radial resolution on axis (at 17.5 cm) varied from 5.0 to 5.9 mm (6.7-8.1 mm); tangential resolution ranged from 5.4 to 5.8 mm (6.7-8.6 mm); axial resolution ranged from 4.6 to 11.5 mm (6.6-13.6 mm); contrast in the middle of a 30 mm diameter rod varied from 98 to 93% and for a 5 mm rod from 37 to 22%. The performance of all three systems approximated reasonably well to the manufacturers' published specifications. The most significant differences were found to be in sensitivity, axial resolution and deadtime correction and can be explained by the choice of crystal size and crystal/photomultiplier configuration.

Evaluation Studies as Topic↗
PubMed1992

Compliance with hormone replacement therapy (HRT) after screening for post menopausal osteoporosis.

OBJECTIVE: To assess compliance with recommendations for hormone replacement therapy (HRT) in postmenopausal women following screening for osteoporosis. DESIGN: A postal questionnaire sent to women an average of 8 months (range 6-12) following measurement of their bone mineral density (BMD), and recommendations regarding HRT given to the referring general practitioner. SETTING: Referrals from local general practitioners. Mixed social class. SUBJECTS: 400 postmenopausal women aged 40-69 years (average age 52). MAIN OUTCOME MEASURES: Compliance with advice and if failing to comply, reasons for not doing so. RESULTS: Replies were received from 352 women (88%) and 74% of respondents followed advice to start, continue, or refrain from starting or continuing HRT with regard to protecting their skeleton. Those who rejected advice to take HRT mostly had concern over side effects or the efficacy or safety of treatment. Of the women who started HRT 28% subsequently stopped, the principal reasons being withdrawal bleeding and weight gain. Of the women recommended to take HRT, 39% were not taking treatment by 8 months after referral, either because they ignored advice given (22%) or because of side effects (17%). CONCLUSIONS: Screening leads to increased usage of HRT among women at most risk for osteoporosis. However, almost 40% of women with low bone mineral density were not taking HRT 8 months after referral, and therefore until improved compliance has been demonstrated screening cannot be widely recommended.

Aged↗
PubMed1992

Fracture thresholds in osteoporosis: implications for hormone replacement treatment.

The bone mineral densities of the lumbar spine and femoral neck were determined by dual energy chi ray absorptiometry in 110 women aged 40-82 years (average 65 years) with spinal osteoporosis who had had at least one atraumatic vertebral compression fracture and in 1026 normal women aged 40-79 years (average 52 years). The women with osteoporosis showed a significant decrease in bone mineral density (BMD) at the lumbar spine and femoral neck compared with age matched normal women (sixth decade of life -26% spine, -23% femoral neck; seventh decade -26% spine, -16% femoral neck). The fracture threshold, defined as the 90th centile of spinal BMD for women with osteoporosis, was 0.81 g/cm2 at the lumbar spine and 0.656 g/cm2 at the femoral neck. Five per cent of normal women aged 40-49 years, 20% aged 50-59 years, and 45% aged 60-69 years had a BMD below this threshold. To maintain the bones of women above the fracture threshold until the age of 70 years about 50% of postmenopausal women need hormone replacement therapy. However, if the BMD is to be kept above the fracture threshold for a women's lifetime, e.g. until the age of 80-90 years, then most women will need treatment, though for various lengths of time depending on their initial BMD. Measurements of BMD in postmenopausal women currently help in identifying the risk of osteoporotic fractures but in the lifetime assessment of risk in a single subject they may have a more important role in deciding the duration of hormone replacement therapy.

Absorptiometry, Photon↗
PubMed1992

Measurement of forearm bone mineral density in normal women by dual-energy X-ray absorptiometry.

We report the results of forearm measurements, without the use of a water bath, using dual-energy X-ray absorptiometry (DEXA) in 100 normal women aged 29-69 years (average age, 52 years). Studies were performed using the Hologic QDR-1000, with bone mineral density (BMD) measured at three sites in the non-dominant forearm: ultradistal, distal one-third and a region between these two. The precision of the technique was 0.74%, 0.55% and 0.58%, respectively. The normal range for forearm BMD and variation with age was established. BMD was also measured in the lumbar spine (L1-L4) and femoral neck. Linear regression analysis gave a range of correlation coefficients between forearm and axial sites of r = 0.49-0.67. Standard errors of the estimate (SEE) in predicting axial from peripheral measurements gave average values from the three forearm sites of 0.085 g/cm2 for the femoral neck and 0.118 g/cm2 for the spine. Forearm measurements using DEXA can now be reliably performed in air. DEXA produces a high-resolution image, is fast and simple to perform, and enables both cortical and trabecular sites to be examined in one measurement. Forearm and axial measurements can be performed using the same equipment, where centres possess a suitable DEXA system.

Absorptiometry, Photon↗