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K G Faulkner

Publications and source records attributed to K G Faulkner.

At least 19 recordsLinked to original sources
PubMed1996

Discrepancies in normative data between Lunar and Hologic DXA systems.

Many studies have shown the high correlation between Lunar and Hologic DXA bone mineral density (BMD) measurements despite differences in absolute calibration. However, in clinical practice, raw BMD values (in g/cm2) are not normally used for assessing skeletal status and fracture risk. Instead, the BMD values are expressed in terms of the number of standard deviations above or below the young normal value (commonly referred to as the T-score). If the normative populations of the various systems are consistent, the standard deviation scores should also be consistent. For this reason, the World Health Organization (WHO) recently established diagnostic criteria for osteoporosis based on T-scores and not BMD. However, few studies have compared the instruments in terms of their standard deviation scores. In this study, we used linear regression to compare T-scores in 83 women at L1-4 and 120 women at the femoral neck obtained on a Lunar DPX and a Hologic QDR-1000/W system. patient BMD and T-score measurements were highly correlated between the two systems (r > 0.95). No clinically significant difference in L1-4 T-scores was seen (less than 0.1 SD). However, linear regression analysis confirmed a systematic difference of 0.9 SD between the femoral neck T-scores. This discrepancy is caused by: (1) differences in the normal populations, and (2) differences in statistical models used to determine the young normal mean and standard deviation. In an attempt to correct the discrepancy, the female young normal mean and standard deviation were recalculated for the femoral neck using published epidemiological data from NHANES and existing DXA cross-calibration equations. The Hologic young normal value (mean +/- SD) was redefined as 0.85 +/- 0.11 g/cm2, while the Lunar value was redefined as 1.00 +/- 0.11 g/cm2. When the femoral neck T-scores for the study population were recalculated on the basis of these new values, the results were equivalent between manufactures, effectively eliminating the discrepancy. However, the revised values should be confirmed by additional measurements in young normal adults.

Absorptiometry, Photon↗
PubMed1996

Determinants of hip axis length in women aged 10-89 years: a twin study.

Hip axis length (HAL), a measure of femoral geometry, has been shown to predict hip fracture in white women over the age of 67 years, independently of bone mineral density at the femoral neck. A cross-sectional study of 304 pairs of female twins [176 monozygous (MZ) and 128 dizygous (DZ)], aged between 10 and 89 years, was performed to examine the influence of age, constitutional, lifestyle, and genetic factors on HAL. HAL was calculated from dual energy X-ray absorptiometry scans of the proximal femur using an automated technique with an Hologic QDR-1000W. Lean mass, fat mass, height, and weight were also measured. Maximum mean HAL was achieved by the age of 15 years. After this age there was no discernible dependency of mean HAL on age. Using within-pair differences, after adjusting for height there were no other independent constitutional or lifestyle predictors. Cross-sectionally, after adjustment for height, MZ and DZ correlations were 0.79 (95% CI: 0.73-0.84) and 0.54 (95% CI: 0.39-0.68), respectively, and independent of age. The MZ correlation exceeded the DZ correlation (p < 0.001). The best-fitting model apportioned 79% (SE 7%) of variation in height-adjusted HAL to additive genetic factors. There was marginal evidence that an environmental influence shared by twins explained 31% (SE 16%) of height-adjusted variance (p = 0.07), in which case the genetic variance was reduced to 51% (SE 15%). Adjustment for height had reduced the magnitude of total variance by 26%, and 95% of this reduction was in the additive genetic component. Applying a previously described theoretical model, approximately 10% of the increased risk of hip fracture associated with a maternal history of hip fracture could be attributed to the genetic factors determining HAL. We conclude that, in women, adult HAL is achieved by midadolescence. After adjustment for height, which is itself largely under genetic influence, other genetic factors appear to play the predominant role in explaining variation in HAL.

Adolescent↗
PubMed1995

Bilateral comparison of femoral bone density and hip axis length from single and fan beam DXA scans.

Dominant/nondominant differences in bone mineral density (BMD) have been observed in the upper extremities. However for the proximal femur, the distinction between dominant and nondominant hips is not clear. The purpose of this study is to evaluate left/right variations in femoral BMD and hip axis length (HAL) in both single beam and fan beam dual x-ray absorptiometry (DXA) scans. A total of 36 women aged 41-76 years (average age 60 +/- 10 years) received single beam and fan beam DXA scans of both proximal femora with a Hologic QDR-2000 scanner. Femoral BMD and hip axis length were determined for each scan. Left/right and single beam/fan beam correlations were determined and differences were evaluated using a two-way analysis of variance. Femoral BMD at corresponding measurement regions in opposing femora were highly correlated (r = 0.81-0.96). No significant left/right differences were detected. At the femoral neck, the mean BMD difference (+/- standard deviation) was 1.5% +/- 4.7% in a single beam mode and -0.6% +/- 6.3% in fan beam mode. Though mean values of femoral BMD were equivalent, the observed individual left/right differences were occasionally large (as high as 26% in the femoral neck). The hip axis length of the left and right hips were highly correlated and statistically equivalent. However, hip axis length using fan beam was significantly larger (7.5%) than the single beam measurement with a larger observed variation. We conclude that measurement of a single proximal femur will usually be sufficient for clinical evaluation of BMD and/or hip axis length.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1995

Quality control of DXA instruments in multicenter trials.

Dual-energy X-ray absorptiometry (DXA) has become the measurement of choice for multicenter trials with bone density endpoints. When performing DXA measurements with several different systems, it is important to implement a quality assurance program to guarantee that any observed density changes are real and not due to machine and/or operator variability. In this study, we present a series of procedures based on phantom measurements designed to monitor DXA instrument stability. Techniques for longitudinal evaluation of machine performance and cross-calibration of instruments are described. These procedures are then demonstrated using quality assurance data collected from a number of different DXA scanners. Together these methods provide a defined approach to instrument quality control. Though based primarily on the use of spinal phantoms, these procedures can be generalized for use in any multicenter DXA study.

Absorptiometry, Photon↗
PubMed1994

Prediction of hip fractures from pelvic radiographs: the study of osteoporotic fractures. The Study of Osteoporotic Fractures Research Group.

To determine whether simple measurements made on conventional radiographs of the hip could predict hip fractures, we obtained pelvic radiographs on 9704 white women age 65 or older. We analyze the radiographs of all 162 women who subsequently suffered a hip fracture and 162 randomly selected women who did not. Adjusting for age, four measurements independently predicted hip fractures: reduced thickness of the femoral shaft cortex (odds ratio 1.7 per standard deviation; 95% confidence interval 1.2, 2.3) and of the femoral neck cortex (1.4 per standard deviation; 1.0, 1.9), reduction in an index of tensile trabeculae (2.0 per unit; 1.4, 2.9), and wider trochanteric region (1.4 per standard deviation; 1.0, 2.0). The combination of these four measurements predicted hip fracture at least as strongly as did measurement of bone density of the femoral neck (areas of the receiver-operating characteristic curve = 0.81 and 0.80, respectively). We conclude that simple measurements made on pelvic radiographs predict hip fractures as well as bone density of the hip.

Absorptiometry, Photon↗
PubMed1994

Automated evaluation of hip axis length for predicting hip fracture.

The hip axis length has been shown in previous studies to be predictive of hip fracture independent of age and femoral bone density. The first studies of hip axis length were performed by manual measurement of dual x-ray absorptiometry (DXA) scan printouts. In this study, an automated analysis procedure is defined using software tools provided by the DXA manufacturer. Manual and automatic hip axis length measurements in 198 women were highly correlated (r = 0.98). Because of scaling factors of the printout, the automatic measurement was 58% longer than the manual value. Precision of the automatic measurement, based upon triplicate DXA scans of 33 women, was 0.07 cm or 0.68%. To define normative data, the hip axis length was measured from femoral DXA scans of 471 female volunteers aged 40-92 scanned on 14 different Hologic QDR-1000 systems. Mean hip axis length was 10.5 cm, with a standard deviation of 0.62 cm. No significant relationship between hip axis length and age was found (r = 0.07, P = 0.15). Based on previously reported odds ratios corrected for femoral bone density, age, height, and weight, an automatic hip axis length measurement of 11.0 cm is associated with a twofold increase in hip fracture risk compared with a woman with an average hip axis length. A hip axis length value of 11.6 cm increases hip fracture risk by a factor of 4 compared with a woman with a normal hip dimension. We conclude that the hip axis length can be easily incorporated into existing DXA hip analysis software in combination with a bone density measurement.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1994

Universal standardization for dual x-ray absorptiometry: patient and phantom cross-calibration results.

The comparison of patient data among different dual x-ray absorptiometry (DXA) scanners is complicated because no universally accepted cross-calibration procedure or standard currently exists. This study was performed under the auspices of the International DXA Standardization Committee to establish appropriate cross-calibration parameters. Posteroanterior (PA) lumbar spine measurements of 100 women, ages 20-80 years (mean 52.6 +/- 16, range of BMD = 0.4-1.6 g/cm2) were obtained on a Norland XR26 Mark II, a Lunar DPX-L, and a Hologic QDR 2000 densitometer using standard procedures (pencil beam mode for all three scanners). Area, BMC, and BMD results from the different scanners were compared for all patients. In addition, the European spine phantom (ESP) and the European spine phantom prototype (ESP prototype), as well as standard phantoms from all three manufacturers, were evaluated on the three systems. To achieve universal scanner calibration, we used the intercept and slope of the patient's correlations and the value of the middle vertebra of the ESP as a reference point in a series of standardization formulas, and we have expressed the results as sBMD (mg/cm2). The correlations of the patients' spinal BMD values were excellent for each of the three scanner pairs. The average absolute difference in patient spinal BMD values (L2-4) between Hologic and Norland was 0.012 g/cm2 (1.3%); it was 0.113 g/cm2 (11.7%) between Hologic and Lunar and 0.118 g/cm2 (12.2%) between Norland and Lunar. The phantoms' regression lines approximated those of the patient regression lines, and the phantoms with only one measurement point were very close to the patients' regression lines. After applying the standardization formulas, the average absolute differences for the 100 patients were 28 mg/cm2 (2.7%) for Hologic/Norland, 23 mg/cm2 (2.2%) for Hologic/Lunar, and 29 mg/cm2 (2.8%) for Norland/Lunar. Average BMD results for the patients before correction were 0.972 mg/cm2 for Hologic, 1.100 g/cm2 for Lunar, and 0.969 g/cm2 for Norland. After correction, sBMD results for patients were 1045 mg/cm2 for Hologic, 1047 mg/cm2 for Lunar, and 1043 mg/cm2 for Norland. The standardization approach as performed in our study provided compatibility of DXA results obtained on different scanners.

Absorptiometry, Photon↗
PubMed1994

Densitometry of the radius using single and dual energy absorptiometry.

Though spinal and femoral measurements are typically preferred for evaluating skeletal density, an abundance of forearm data exists, primarily from single photon absorptiometry (SPA) devices. Most dual X-ray absorptiometry (DXA) scanners are capable of scanning the forearm and provide analysis tools to duplicate conventional SPA measurements. In this study, we have compared the radius density measurements from three commonly available densitometers: a Norland 278 SPA, a Lunar DPX-L, and a Hologic 1000/W. Radius bone mineral density (BMD) on the nondominant forearm was measured in 28 volunteers (21 women and 7 men) aged 24-78, with an average age of 51 +/- 17 years. Values were compared and regression relationships derived at corresponding measurement sites. SPA and DXA BMD values were found to be highly correlated (r = 0.99) with small standard errors (0.014 g/cm2-0.021 g/cm2), though significant absolute differences were observed at most measurement regions. Correlation slopes ranged from 0.85 to 1.04, with intercepts from 0.01 to 0.08 g/cm2. Using the resultant regression equations, SPA BMD values can be converted to DXA values with an expected error of roughly 3%. DXA BMD can also be interconverted between Lunar and Hologic with a similar expected error. In situations where this level of imprecision is acceptable, patient forearm measurements obtained on different systems can be interconverted.

Absorptiometry, Photon↗
PubMed1994

Racial differences in hip axis lengths might explain racial differences in rates of hip fracture. Study of Osteoporotic Fractures Research Group.

Compared with white women, Asian women have about a 40%-50% and blacks a 50%-60% lower risk of hip fracture, but the reason for this racial difference is not known. Women with a shorter hip axis have a lower risk of hip fracture. To test the hypothesis that a shorter hip axis length could account for the lower risk of hip fracture among Asian and black women, we measured hip axis length in 135 Caucasian, 74 Asian and 50 black women. The mean hip axis lengths of Asian and black women were significantly shorter (1.2 and 0.7 standard deviations, respectively) than that of the whites (p < 0.0001). We estimate that, compared with white women, Asians would have a 47% lower risk (95% confidence interval: 32%-63%) and blacks would have a 32% (15%-45%) lower risk of hip fracture because of their shorter hip axis. We conclude that a shorter hip axis length might be a major factor accounting for Asian women's lower risk of hip fracture and might contribute to the lower risk in black women.

Aged↗
PubMed1994

Quantitative ultrasound of the heel: correlation with densitometric measurements at different skeletal sites.

To assess the utility of quantitative ultrasound (QUS) of the heel for osteoporosis screening, we studied a group of 170 early postmenopausal women using both QUS of the heel and dual-energy X-ray absorptiometry (DXA) at the spine, hip, forearm, and whole body. On the basis of the linear regression results between QUS and DXA, a 95% bone mineral density (BMD) estimate confidence range was defined. Correlation coefficients between the QUS measurements and DXA ranged from 0.26 to 0.63. The confidence ranges for the estimated BMD based on a QUS measurement of the heel were large, such that an estimation of skeletal BMD at any of the DXA sites measured was not possible. For example, an estimate of the normative anteroposterior spine BMD (i.e. the T-score or the Z-score) based on a calcaneal ultrasound reading would have an error of +/- 1.9 standard deviations. Results for predicting the normative BMD of the other DXA regions were similar, with expected errors ranging from +/- 1.4 to +/- 2.0 standard deviations. We therefore conclude that QUS is not suited for the screening of early postmenopausal women for low axial or peripheral BMD. However, QUS may have a role as an independent predictor of fracture by measuring skeletal properties in addition to bone density.

Absorptiometry, Photon↗
PubMed1993

Simple measurement of femoral geometry predicts hip fracture: the study of osteoporotic fractures.

Based on engineering principles, geometric measurements of femoral size should be related to femoral strength and the risk for hip fracture. To evaluate whether a simple measurement of femoral geometry is associated with hip fracture risk, we obtained dual x-ray absorptiometry scans of the proximal femur on 8074 white women age 67 or older. During an average of 1.6 years of follow-up, 64 participants suffered hip fractures. In all fracture cases and in a random sample of 134 women who did not subsequently suffer a hip fracture, we measured hip axis length (the distance from greater trochanter to inner pelvic brim), neck width, and the neck/shaft angle on the scan printout, with the observer blinded to subsequent fracture status of the participant. Results were analyzed using multiple logistic models, and odds ratios were determined. After adjustment for age, each standard deviation decrease in femoral neck bone mineral density increased hip fracture risk 2.7-fold (95% confidence interval 1.7, 4.3), and each standard deviation increase in hip axis length nearly doubled the risk of hip fracture (odds ratio = 1.8; 95% CI 1.3, 2.5). The relationship between hip axis length and fracture risk persisted even after adjustment for age, femoral neck density, height, and weight. A longer hip axis length was associated with an increased risk of both femoral neck (OR = 1.9; 95% CI 1.3, 3.0) and trochanteric fractures (1.6; 1.0, 2.4). We found no significant association between the neck width (1.1; 0.8, 1.5) or the neck/shaft angle (1.4; 0.9, 2.2) and risk of hip fracture.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1993

Cross-calibration of DXA equipment: upgrading from a Hologic QDR 1000/W to a QDR 2000.

In this study, the cross-calibration of a fan beam DXA system (Hologic QDR-2000) to a pencil beam scanner from the same manufacturer (Hologic QDR-1000/W) is described. The scanners were calibrated by the manufacturer using the same anthropomorphic spine phantom at installation. To verify consistent machine calibration, a group of 69 female subjects, aged 46-75, had anteroposterior (AP) spine and proximal femur scans on the QDR-1000/W followed by pencil and array scans of the same sites on the QDR-2000 during the same visit. Many of the subjects had bilateral examinations of the proximal femur for a total of 123 hip scans. Pencil and array area, bone mineral content (BMC), and bone mineral density (BMD) from the QDR-2000 were compared with the values obtained on the QDR-1000/W, and linear regression equations were derived for relating the two instruments. At the spine, no differences were found between the QDR-1000/W BMD values and the QDR-2000 array BMD values. A slight difference between pencil beam modes was detected but was not deemed clinically significant. Linear regression models relating the QDR-2000 and QDR-1000/W AP spine BMD measurements showed correlation coefficients greater than 0.99, with slopes of 1.00, intercepts equivalent to zero, and small root mean square errors. Comparisons at the proximal femur showed equivalency at the femoral neck and trochanter regions for the two machines in pencil mode, but slight increases in BMC and BMD at the other femoral sites on the QDR-2000 in both pencil and array mode. Correlation coefficients were 0.97-0.99 for all measurement regions except for Ward's.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1993

Cross-calibration of liquid and solid QCT calibration standards: corrections to the UCSF normative data.

Quantitative computed tomography (QCT) has been shown to be a precise and sensitive method for evaluating spinal bone mineral density (BMD) and skeletal response to aging and therapy. Precise and accurate determination of BMD using QCT requires a calibration standard to compensate for and reduce the effects of beam-hardening artifacts and scanner drift. The first standards were based on dipotassium hydrogen phosphate (K2HPO4) solutions. Recently, several manufacturers have developed stable solid calibration standards based on calcium hydroxyapatite (CHA) in water-equivalent plastic. Due to differences in attenuating properties of the liquid and solid standards, the calibrated BMD values obtained with each system do not agree. In order to compare and interpret the results obtained on both systems, cross-calibration measurements were performed in phantoms and patients using the University of California San Francisco (UCSF) liquid standard and the Image Analysis (IA) solid standard on the UCSF GE 9800 CT scanner. From the phantom measurements, a highly linear relationship was found between the liquid- and solid-calibrated BMD values. No influence on the cross-calibration due to simulated variations in body size or vertebral fat content was seen, though a significant difference in the cross-calibration was observed between scans acquired at 80 and 140 kVp. From the patient measurements, a linear relationship between the liquid (UCSF) and solid (IA) calibrated values was derived for GE 9800 CT scanners at 80 kVp (IA = [1.15 x UCSF] - 7.32).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Quality assurance for bone densitometry research studies: concept and impact.

A concept for quality assurance (QA) in bone densitometry has been developed for clinical multicenter studies. Major elements provided by a coordinating center comprise (1) consulting services and certification of participating centers in the start-up phase of the study, (2) review of scan data acquired on QA standards for cross-calibration and longitudinal assessment of scanner stability, (3) review of selected patient data as well as of problem cases during the study, and (4) comprehensive review and correction of patient results based on QA data after conclusion of the study. Limitations of phantom-based QA data should be acknowledged. Typical problems encountered during research studies and guidelines for solutions are presented. Successful implementation of QA measures may yield substantial enhancement of statistical power. Depending on the study design and the variability of response within patient groups, improvement in precision due to QA measures may reduce the smallest detectable difference between subject groups or, alternatively, sample size by a few to more than 50%, and thus may contribute to a substantial reduction in study cost. Formulae for calculation of the magnitude of these effects are presented. To maximize the net benefit, QA efforts have to be limited to levels that assure reliability of the data at acceptable QA cost. While QA programs at individual clinical sites or for local practitioners may not need to be as extensive as for multicenter clinical trials, awareness of the potential problems and implementation of basic QA measures will help in obtaining high-quality bone densitometry results.

Bone Density↗
PubMed1993

[Osteoporosis diagnosis by broad-band ultrasound attenuation (BUA): its correlation with established measurement procedures of bone densitometry].

Broadband ultrasound attenuation (BUA) measurements of the os calcis of 54 women were correlated to single-energy x-ray absorptiometry (SXA) of the os calcis, dual-energy x-ray absorptiometry (DXA) of the lumbar spine, age and weight. The reproducibility of the BUA measurements was 2.1%. BUA was significantly correlated with SXA (r = 0.7), DXA (r = 0.5) and age (r = 0.6). BUA values ranged from 42 to 117 dB/MHz. Our results confirm BUA's potential as a simple, inexpensive, radiation free, and precise alternative technique for osteoporosis diagnostics of the os calcis. However, the correlation observed with bone mineral density of the spine is too weak to use BUA for predicting the lumbar density status. The ability of BUA to predict the risk of osteoporotic fractures has to be determined directly by assessing the association of BUA and the prevalence or preferably the incidence of fractures.

Absorptiometry, Photon↗