Peripheral measurement techniques for the assessment of osteoporosis

Backscatter measurement of cancellous bone using the ultrasound transit time spectroscopy

Recently, ultrasound transit time spectroscopy (UTTS) was proposed as a promising method for bone quantitative ultrasound measurement. Studies have showed that UTTS could estimate the bone volume fraction and other trabecular bone structure in ultrasonic through-transmission measurements. The goal of this study was to explore the feasibility of UTTS to be adapted in ultrasonic backscatter measurement and further evaluate the performance of backscattered ultrasound transit time spectrum (BS-UTTS) in the measurement of cancellous bone density and structure. First, taking ultrasonic attenuation into account, the concept of BS-UTTS was verified on ultrasonic backscatter signals simulated from a set of scatterers with different positions and intensities. Then, in vitro backscatter measurements were performed on 26 bovine cancellous bone specimens. After a logarithmic compression of the BS-UTTS, a linear fitting of the log-compressed BS-UTTS versus ultrasonic propagated distance was performed and the slope and intercept of the fitted line for BS-UTTS were determined. The associations between BS-UTTS parameters and cancellous bone features were analyzed using simple linear regression. The results showed that the BS-UTTS could make an accurate deconvolution of the backscatter signal and predict the position and intensity of the simulated scatterers eliminating phase interference, even the simulated backscatter signal was with a relatively low signal-to-noise ratio. With varied positions and intensities of the scatterers, the slope of the fitted line for the log-compressed BS-UTTS versus ultrasonic propagated distance (i.e., slope of BS-UTTS for short) yield a high agreement (r2 = 99.84%-99.96%) with ultrasonic attenuation in simulated backscatter signal. Compared with the high-density cancellous bone, the low-density specimen showed more abundant backscatter impulse response in the BS-UTTS. The slope of BS-UTTS yield a significant correlation with bone mineral density (r = 0.87; p < 0.001), BV/TV (r = 0.87; p < 0.001), and cancellous bone microstructures (r up to 0.87; p < 0.05). The intercept of BS-UTTS was also significantly correlated with bone densities (r = -0.87; p < 0.001) and trabecular structures (|r|=0.43-0.80; p < 0.05). However, the slope of the BS-UTTS underestimated attenuation when measurements were performed experimentally. In addition, a significant non-linear relationship was observed between the measured attenuation and the attenuation estimated by the slope of the BS-UTTS. This study demonstrated that the UTTS method could be adapted to ultrasonic backscatter measurement of cancellous bone. The derived slope and intercept of BS-UTTS could be used in the measurement of bone density and microstructure. The backscattered ultrasound transit time spectroscopy might have potential in the diagnosis of osteoporosis in the clinic.

Sleep-Disordered Breathing Is Associated with Reduced Mandibular Cortical Width in Children

INTRODUCTION

Evidence from the adult population suggests that sleep-disordered breathing (SDB) (i.e., obstructive sleep apnea [OSA]) is negatively associated with bone mineral density. Whether a similar association exists in children with SDB has not been investigated. Using the mandibular cortical width (MCW) as a proxy for skeletal bone density, we investigated if children at risk of SDB or diagnosed with OSA have a reduced mandibular cortical width compared to children without SDB.

METHODS

Two retrospective cross-sectional studies were performed. The first study included comparison of MCW between 24 children with polysomnographically (PSG) diagnosed OSA and 72 age- and sex-matched control children. The second study included a cohort of children in which SDB was suggested by the Pediatric Sleep Questionnaire (PSQ) ( n = 101). MCW was measured from panoramic radiographs.

RESULTS

Multiple-predictors regression analysis from the first study indicated that in children with a severe form of SDB, as induced by OSA severity, there was a negative association with MCW (β = -0.290, P = 0.049). Moreover, PSG-diagnosed OSA children had thinner MCW (2.9. ± 0.6mm) compared to healthy children (3.5 ± 0.6 mm; P = 0.002). These findings were further supported by the second study illustrating that PSQ total scores were negatively associated with MCW (β = -0.391, P < 0.001).

CONCLUSIONS

Findings suggest that children at risk for or diagnosed with SDB exhibit reduced mandibular cortical width that purportedly may reflect alterations in bone homeostasis.

KNOWLEDGE TRANSFER STATEMENT

We report that sleep-disordered breathing (including its severe form, obstructive sleep apnea) in children is associated with reduced mandibular cortical width. This association might be a direct consequence of reduced bone health to sleep-disordered breathing or a reflection that reduced bone formation underlies the development of sleep-disordered breathing. Our findings suggest that mandibular cortical width can be used as an adjunct diagnostic parameter for the diagnosis of sleep-disordered breathing.

Point-of-Care Phalangeal Bone Mineral Density Measurement Can Reduce the Need of Dual-Energy X-Ray Absorptiometry Scanning in Danish Women at Risk of Fracture

Identifying persons with a high risk of osteoporotic fractures remains a challenge. DXA uptake in women with elevated risk of osteoporosis seems to be depending on distance to scanning facilities. This study aimed to investigate the ability of a small portable scanner in identifying women with reduced bone mineral density (BMD), and to define triage thresholds for pre-selection. Total hip and lumbar spine BMD was measured by dual-energy X-ray absorptiometry and phalangeal BMD by radiographic absorptiometry in 121 Danish women with intermediate or high 10-year fracture probability (aged 61-81 years). Correlation between the two methods was estimated using correlation coefficient (r) and Bland-Altman plots. A moderate correlation between phalangeal BMD versus total hip (r = 0.47) and lumbar spine (r = 0.51), and an AUC on 0.80 was found. The mean difference between phalangeal T score and total hip T score/lumbar spine T score was low, and ranged from -0.26 SD to -0.31 SD depending on site and reference database used for calculation of T scores, but, large variation was seen at an individual level. When applying a triage approach approx. one-third of all DXA scan could be avoided and only 6 % of women in the low-risk group would be false negatives.

Bone densitometry

Dual-energy x-ray absorptiometry (DXA) is the method of choice to measure bone mineral density in elderly patients and others at risk for osteoporosis. Early detection is important because fractures represent an enormous health burden. In this article, the authors discuss the application and interpretation of DXA scans as well as limitations and conditions that can affect results.

Panoramic measures for oral bone mass in detecting osteoporosis: a systematic review and meta-analysis

Different quantitative and qualitative indices calculated on oral panoramic radiographs have been proposed as useful tools to screen for reduced skeletal bone mineral density (BMD). Our aim was to systematically review the literature on linear and qualitative panoramic measures and to assess the accuracy of these indices by performing a meta-analysis of their sensitivity and specificity. The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement was followed. Fifty studies were included in the qualitative appraisal and 19 were considered for meta-analysis. The methodological quality of the retrieved studies, assessed with the QUADAS-2 tool, was on average low. Three indices were reported by most of the studies: mandibular cortical width, panoramic mandibular index, and the Klemetti index. Mandibular cortical width presented with a better accuracy in excluding osteopenia/osteoporosis (specificity), since patients with a cortical width more than 4 mm had a normal BMD in 90% of the cases. Almost all studies used a cutoff of 0.3 for the panoramic mandibular index, resulting in an estimated sensitivity and specificity in detecting reduced BMD, respectively, of 0.723 (SE 0.160; 95% confidence interval [CI], 0.352-0.926) and 0.733 (SE 0.066; 95% CI, 0.587-0.841). The presence of any kind of mandibular cortical erosion gave an estimated sensitivity and specificity in detecting reduced BMD, respectively, of 0.789 (SE 0.031; 95% CI, 0.721-0.843) and 0.562 (SE 0.047; 95% CI, 0.47-0.651) and a sensitivity and specificity in detecting osteoporosis, respectively, of 0.806 (SE 0.105; 95% CI, 0.528-0.9200) and 0.643 (SE 0.109; 95% CI, 0.417-0.820). The mandibular cortical width, panoramic mandibular index, and Klemetti index are overall useful tools that potentially could be used by dentists to screen for low BMD. Their limitations are mainly related to the experience/agreement between different operators and the different image quality and magnification of the panoramic radiographs.

Computed digital absorptiometry for measurement of phalangeal bone mineral mass on a slot-scanning digital radiography system

Computed digital absorptiometry is a low-cost and low-radiation technique for rapid measurement of phalangeal bone mineral mass. We implement and evaluate this technique on a slot-scanning radiography system. Results, based on measurements of excised phalangeal bones, indicate that the technique has potential for use in clinical assessment of osteoporosis.

INTRODUCTION

The current gold standard method for bone assessment in the diagnosis of osteoporosis requires specialised and expensive machines, highly trained personnel to conduct the examination and is available only at specialist centres. The technique, termed dual-energy X-ray absorptiometry (DXA), involves taking a bone mineral density measurement at the femur or lumbar spine. Measurements of bone at peripheral sites such as the phalanges using DXA and other techniques have been shown to have potential use in the diagnosis of osteoporosis. Computed digital absorptiometry (CDA) is a low-cost, low-radiation radiographic technique for assessing phalangeal bone mineral mass. It uses an aluminium step wedge as a calibration device to compute bone mineral mass in units of equivalent aluminium thickness. In this study, we assess the feasibility of using CDA on a slot-scanning radiography system for measuring phalangeal bone mineral mass.

METHODS

We implement and evaluate fully automated computed digital absorptiometry (CDA) of the middle phalanx of the middle finger on a slot-scanning radiography system.

RESULTS

The ash weight of incinerated bones was measured and shown to have a correlation of 0.92 with CDA-derived bone mineral mass. CDA measurements had a coefficient of variation of 0.26%, indicating high precision.

CONCLUSION

We conclude, based on these results, that CDA on a slot-scanning radiography machine may be useful for clinical assessment of osteoporosis.

Premature Adjacent Vertebral Fracture After Vertebroplasty: A Biomechanical Study

BACKGROUND:

There is an increased incidence of fractures in untreated adjacent vertebrae after vertebroplasty.

OBJECTIVE:

To introduce unconstrained 6 degrees of freedom biomechanical testing to investigate whether vertebroplasty lowered the fracture strength of adjacent untreated vertebrae under physiological loading conditions and to describe the observed fracture pattern.

METHODS:

Three-level spinal segments (T10-12 and L1–3) from 6 spines were tested under unconstrained axial compression in which shear forces and torque were minimized using a 6-degrees of freedom robotic arm. Fracture initiation loads and ultimate failure loads of lumbar segments were predicted from the corresponding thoracic segments by assuming constant fracture stress along the spinal column. The predicted values were compared with postvertebroplasty experimental values of the lumbar spine segments. Plain radiographs were taken at 600-N increments to record the developing fracture pattern.

RESULTS:

All 6 vertebroplasty group specimens experienced reductions in fracture strengths ranging from 27.4% to 47.6% with an average decrease of 32.6% (P &lt; .002) and reductions in ultimate failure load ranging from 1.6% to 47.3%, with an average decrease of 34.7% (P &lt; .003) compared with predicted values from the nonvertebroplasty group. In all vertebroplasty group specimens, the superior and inferior endplates of the untreated middle vertebral body (L2) were deflected, whereas 5 of the 6 nonvertebroplasty group specimens did not show any evidence of endplate deflection.

CONCLUSION:

Vertebroplasty altered the load transfer along the anterior spinal column, thereby statistically significantly increasing fracture risk and ultimate failure load of the untreated adjacent vertebrae. The radiographic findings support the endplate deflection fracture mechanism as the cause of adjacent fractures after vertebroplasty.

Characteristics of age-related changes in bone compared between male and female reference Chinese populations in Hong Kong: a pQCT study

There have been few comprehensive studies on the age-related changes in bone mineral density (BMD) and bone structure in Chinese people. Using peripheral quantitative computed tomography (pQCT), we assessed volumetric BMD of both trabecular and cortical bone and their geometry at both radius and tibia in 620 Chinese men and 638 women, aged 20–98 years, in Hong Kong. Cortical BMD did not start declining until after the age of 50 years in women and the age of 60 years in men. In contrast, trabecular BMD declined with age starting from adulthood in both sexes, and the rates of decline accelerated after the age of 50 years only in women. The integral and trabecular bone area expanded with age in older men and women, primarily at the tibia. Cortical bone area decreased significantly in older women, particularly at the tibia, while it decreased only slightly with aging in men. The moment of inertia decreased with age at the radius in older men and women. At the tibia, age-related decline accelerated in older women, but not in older men. It was concluded that trabecularization of bone in response to declining BMD and mechanical loading may be maladaptive by reducing cortical bone area, if periosteal apposition cannot keep pace with it.

Clinical evaluation of a phalangeal bone mineral density assessment system

Because osteoporosis is common and usually managed in primary care, there is a requirement for cheap and convenient methods of measuring bone mineral density (BMD). AccuDEXA (Lone Oak Medical Technologies, Doylestown, PA) is a tabletop dual-energy X-ray absorptiometry (DXA) device that performs BMD measurements of the hand in the middle phalanges of the third finger. The aims of this study were to (1) evaluate the use of AccuDEXA in UK women; (2) investigate the concordance between AccuDEXA T-scores and DXA T-scores for central (spine and hip) sites; (3) investigate the comparative response of AccuDEXA measurements to clinical risk factors for osteoporosis. Measurements of phalangeal and central BMD were performed in 620 women referred by their family doctors for bone densitometry (group 1) and 159 healthy female volunteers (group 2). For 65 women in group 2, aged 39 yr or younger, the mean Z-scores for AccuDEXA and the central sites calculated from US reference ranges were consistent with the expected value of 0, whereas for the 62 group 2 women, aged 50 yr or older, the mean Z-scores for AccuDEXA and the central sites were in the range 0.4-0.7 and were statistically significantly different from 0. In both group 1 and group 2, the AccuDEXA T-scores in older and younger women were systematically higher than those in the central sites by up to 1 unit. Of the 157 women aged 50 yr or older, with osteoporosis, based on their central DXA results, only 34 (22%) had an AccuDEXA T-score less than or equal to -2.5, whereas 76 (48%) had osteopenia and 47 (30%) were normal based on their AccuDEXA T-scores. When assessed by the effect of clinical risk factors on Z-scores, both AccuDEXA and central BMD were affected to a similar extent. We conclude that the conventional World Health Organisation T-score criteria for the diagnosis of osteoporosis should not be applied to AccuDEXA measurements in UK women. Clinical risk factors for low BMD were found to affect AccuDEXA measurements to a similar extent as central BMD measurements. AccuDEXA measurements could, therefore, provide an alternative method for identifying individuals with low bone mass, provided care is taken in interpreting T-scores, perhaps, through the use of device-specific thresholds.

Feasibility of osteoporosis screening by dual-energy radiographic absorptiometry of the phalanx

A new dual-energy radiographic absorptiometry-based technique is presented as a cost-effective method for mass osteoporosis screening. Designed for use in a dental health care setting, we propose a method and device for bone mineral density (BMD) assessment using the middle phalanx of the 3rd digit as our anatomical measurement site. Our 2-staged project includes the development of the prototype to carry out the measurement and the execution of a small pilot study to determine the efficacy of the method and device. Fifty subjects from the general adult population (age range: 25-82 yr), wherein 10 normal subjects (5 females and 5 males) and 40 target group subjects (30 females and 10 males) who were at risk for osteoporosis (as assessed qualitatively through questionnaire responses) were evaluated with our method. The BMD values obtained from the normal and target groups were significantly different (p<0.0001). Phantom measurements to determine the bias and coefficient of variation of the technique yielded values of 1.9% and 7%, respectively. The proposed technique could provide a relatively inexpensive and widely available means for mass osteoporosis screening. Further validation of this method, to include comparison to a gold standard, such as dual-energy X-ray absorptiometry, is warranted.

Reproducibility of metacarpophalangeal bone mass measurements obtained by dual-energy X-ray absorptiometry in healthy volunteers and patients with early arthritis

The prognostic value of measuring hand bone mineral density (BMD) in patients with early arthritis (EA) has been recently assessed. In this work, we evaluate the reproducibility of measuring juxta-articular BMD by dual-energy X-ray absorptiometry (DXA) at the second to fifth metacarpophalangeal (MCP) joints. We obtained whole hand (WH) and MCP joint BMD measurements from 16 healthy subjects and from 22 patients with EA. The coefficient of variation, intraclass correlation coefficient (ICC), and smallest detectable difference (SDD) were calculated. The coefficient of variation ranged from 1.3% to 0.7% at MCP joints and from 1.4% to 0.9% in the WH measurements, respectively. The intra- and interobserver ICC for both WH and MCP joints ranged from 0.97 to 0.99. The SDD at the different anatomical locations analyzed ranged from 0.006 to 0.022 g/cm2 in healthy controls and from 0.005 to 0.010 g/cm2 in EA. Interestingly, patients who fulfilled rheumatoid arthritis criteria showed a lower bone mass than those with undifferentiated arthritis. Therefore, BMD measurements obtained by DXA at MCP joints were reproducible and it might be useful in the study of patients with EA.

Peripheral and central measurements of bone mineral density are equally strongly associated with clinical risk factors for osteoporosis

The aim of this study was to determine whether forearm bone mineral density (BMD) measurements are affected by clinical risk factors for osteoporosis to the same extent as spine and hip BMD. The study population consisted of 1,009 female patients and volunteers, of whom 238 were premenopausal. Women were placed into seven groups according to which clinical risk factor they had (women could be placed in more than one group): (1) atraumatic fracture since the age of 25 years, (2) report of X-ray osteopenia, (3) predisposing medical condition or use of therapy known to affect bone metabolism, (4) premature menopause before the age of 45 years or a history of amenorrhea of longer than 6 months' duration, (5) family history of osteoporosis, (6) body mass index (BMI) <20 kg/m(2), and (7) current smoking habit. Forearm BMD was measured using an Osteometer DTX-200 peripheral dual-energy X-ray absorptiometry scanner, and spine and hip BMD measurements were obtained on a Hologic QDR-4500 scanner. Manufacturers' reference ranges were used to calculate Z scores for the spine and forearm, and the NHANES III reference range was used to calculate Z scores for the hip. Multivariate regression analysis was used to estimate the mean decrease in Z score associated with each clinical risk factor. The Z-score reductions associated with the seven risk factors were similar for forearm and central BMD measurements. For forearm measurements, Z-score decreases associated with a history of atraumatic fracture (-0.25), a medical condition or therapy known to affect bone metabolism (-0.26), premature menopause or history of amenorrhea (-0.30), and BMI <20 kg/m(2) (-0.82) were all statistically significantly different from zero (P < 0.05). With an increasing number of risk factors in each individual, the mean Z score at each measurement site became progressively more negative. In conclusion, clinical risk factors for low BMD affect forearm BMD measurements to a similar extent as central BMD.

A method for the estimation of femoral bone mineral density from variables of ultrasound transmission through the human femur

Quantitative ultrasound (QUS) measurements at peripheral sites can be used to estimate osteoporotic fracture risk. However, measurements at these sites are less suitable to predict bone mineral density (BMD) or fracture risk at the central skeleton. We investigated whether direct QUS measurements at the femur would allow to estimate dual X-ray absorptiometry (DXA) BMD of the total proximal femur with errors comparable to established DXA accuracy errors. Two independent sets of femora were measured in Kiel (6 f, 4 m, age: 55-90) and Paris (19 f, 20 m age: 45-95) using different benchtop systems in the two laboratories. The femora were scanned in transverse transmission mode using focused US transducers of 500 kHz center frequency. The QUS values were averaged over a region similar to the total hip region of dual X-ray absorptiometry (DXA) measurements. BMD was measured using DXA. SOS and BMD correlated significantly (p<0.0001) in both data sets (R2=0.81-0.93). Correlations between BUA and BMD were also significant at p<0.001, but correlation coefficients were lower (R2=0.61-0.75). Residual errors for the estimation of BMD were 8%-10% for SOS as predictor, and 14%-16% for BUA as predictor. The residual error of 8 to 10% for the estimation of BMD from SOS is comparable to variabilities among different DXA femur subregions and accuracy errors of femoral DXA measurements caused by the impact of soft tissue. It is substantially smaller than the errors of 13% for the estimation of total femur BMD from spine BMD, 14% for the estimation of total femur BMD from calcaneus SOS or 16% for the estimation of ash weight from DXA. The results of the study show that SOS is able to predict total BMD with adequate accuracy. If femoral BMD could be obtained in vivo with comparable accuracy, femoral QUS would be suited for the assessment of bone status at one of the main osteoporotic fracture sites.

Renal insufficiency-induced bone loss is associated with an increase in bone size and preservation of strength in rat proximal femur

Chronic renal insufficiency (CRI) results in phosphate retention and secondary hyperparathyroidism, the treatment of which is largely based on the use of calcium salts as phosphate binders. Advanced CRI causes bone fragility, but information about bone geometry and strength in moderate CRI is scarce. We assigned 39 8-week-old male Sprague-Dawley rats to sham-operation (Sham) or 5/6 nephrectomy (NTX). Four weeks later, the rats were randomized to 0.3% calcium (Sham, NTX) or 3.0% calcium diet (Sham + Calcium, NTX + Calcium). After 8 weeks, the animals were sacrificed, plasma samples collected, and femora excised for neck and midshaft analyses: dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and biomechanical testing. The NTX increased plasma urea and PTH 1.6-fold and 3.6-fold, respectively, whereas high calcium intake suppressed PTH to 30% of controls. Total femoral bone mineral content decreased (-6.3%) in the NTX group, while this deleterious effect was reversed by high calcium diet. In the site-specific analysis of the femoral neck, the volumetric bone density (-6.5%) was decreased in the NTX group but not NTX + Calcium group. However, in the nephrectomized rats, there was also a concomitant increase in the cross-sectional area (+15%), and, despite the decrease in bone density, the mechanical strength of the femoral neck was maintained. In the midshaft, NTX decreased cortical volumetric bone density (-1.2%), but similar to the femoral neck, no differences were found in the mechanical strength. In conclusion, a decrease in bone mass in moderate experimental CRI was associated with a concomitant increase in bone size, and maintenance of mechanical competence. Although high calcium diet suppressed plasma PTH to under normal physiological levels, it prevented the CRI-induced loss of bone mass without an adverse influence on bone strength.

Device-specific thresholds to diagnose osteoporosis at the proximal femur: an approach to interpreting peripheral bone measurements in clinical practice

INTRODUCTION

A single T score criterion cannot be universally applied to different peripheral bone measurement devices, since measurements in an identical population result in a tenfold difference in the prevalence of osteoporosis. The use of peripheral devices is increasing in clinical practice, despite the difficulties in interpreting results. We propose the use of two thresholds, which have either 95% sensitivity or 95% specificity, to identify (1) individuals who require treatment or (2) individuals who require no treatment, both based on a peripheral measurement alone, or (3) individuals who require additional central densitometry measurements.

METHODS

We recruited 500 postmenopausal women, 100 premenopausal women and 279 women with proximal femoral, vertebral, distal forearm or proximal humeral fractures. All subjects underwent dual energy X-ray absorptiometry (DXA) measurements of the lumbar spine, total hip and distal forearm, quantitative computed tomography (QCT) of the distal forearm and quantitative ultrasound (QUS) of the heel (four devices), finger (two devices), radius and metatarsal. We identified the threshold for each device that identified women without osteoporosis with the same sensitivity (upper threshold set at 95%) as total hip DXA and women with osteoporosis with the same specificity (lower threshold set at 95%) as total hip DXA. Individuals between the two thresholds required additional examination by central densitometry.

RESULTS

The correlation between devices varied from 0.173 (QUS finger) to 0.686 (DXA forearm) compared with total hip DXA (P<0.0001). The area under the curve (AUC) between devices varied from 0.604 (QUS finger) to 0.896 (DXA forearm) compared with total hip DXA (P<0.0001). In a population-based cohort (prevalence of osteoporosis 9.8%) the threshold approach appropriately identified between 26% (QUS heel) and 68% (DXA forearm) of subjects in whom a treatment decision could be made without additional central DXA with 95% certainty. In a fracture cohort (prevalence of osteoporosis 36%) between 16% (QUS finger) and 37% (QCT forearm) of subjects were appropriately identified.

CONCLUSION

The threshold approach to interpreting peripheral bone measurements enables a substantial number of individuals with either normal bone mineral density (BMD) or osteoporosis to be selected and treated appropriately.

Predicting the risk of fracture at any site in the skeleton: are all bone mineral density measurement sites equally effective?

The ability to assess a patient's risk of fracture is fundamental to the clinical role of bone densitometry. Fracture discrimination is quantified by the relative risk (RR), defined as the increased risk of fracture for a 1 standard deviation decrease in bone mineral density (BMD). The larger the value of RR, the more effective measurements are at identifying patients at risk of fracture. Epidemiological studies show that RR values for predicting the risk of any fracture are approximately the same for all BMD measurement sites. In this study, we show theoretically that this interesting observation is predictable and a consequence of two related observations: (1) that fracture prediction by BMD measurement sites distant from the fracture site is quantitatively explained by the correlation of BMD measurements and (2) that all correlation coefficients between distant BMD sites are comparable, with values in the range r = 0.55-0.65. The first of these conditions (referred to as the correlation hypothesis) is important because it sets a lower limit on the RR values at distant BMD sites on the assumption that measurements at these sites contain no independent information about fracture risk over and above that provided by their correlation with the fracture site BMD. If the correlation hypothesis is true, the present study points to the importance of the correlation coefficient between BMD sites as a key index that is indicative of the ability of different types of measurement to predict fracture risk. If, on the contrary, the correlation hypothesis is not valid, there is scope to improve bone densitometry by further studies to better identify those measurements that do provide independent information about fracture risk and how best to integrate this information with existing techniques to improve decision making.

A list of device-specific thresholds for the clinical interpretation of peripheral x-ray absorptiometry examinations

The UK National Osteoporosis Society (NOS) has recently issued new guidelines on the use of peripheral x-ray absorptiometry (pDXA) devices in managing osteoporosis. The NOS guidelines recommend a triage approach in which patients' bone mineral density (BMD) measurements are interpreted using upper and lower thresholds specific to each type of pDXA device. The thresholds are defined so that patients with osteoporosis at the hip or spine are identified with 90% sensitivity and 90% specificity. Patients with a pDXA result below the lower threshold are likely to have osteoporosis at the hip or spine, patients with a result above the upper threshold are unlikely to have osteoporosis, while those between the two thresholds require a hip and spine BMD examination for a definitive diagnosis. This report presents data from a multicenter study to establish the triage thresholds for a range of pDXA devices in use in the UK. The subjects were white female patients aged 55-70 years who met the normal referral criteria for a BMD examination. For each device, at least 70 women with osteoporosis at the hip or spine and 70 women without osteoporosis were enrolled. All women had hip and spine BMD measurements using axial DXA systems that were interpreted using the National Health and Nutrition Examination Survey (NHANES) reference range for the hip and the manufacturers' reference ranges for the spine. Data are presented for five different devices: the Osteometer DTX-200 (forearm BMD), the Schick AccuDEXA (hand BMD), the GE Lunar PIXI (heel BMD), the Alara MetriScan (hand BMD), and the Demetech Calscan (heel BMD). The clinical measurements were supplemented by theoretical modeling to estimate the age dependence of the triage thresholds and the effect of the correlation coefficient between pDXA and axial BMD on the percentage of women referred for an axial BMD examination. In summary, this study provides thresholds for implementing the new NOS guidelines for managing osteoporosis using pDXA devices. The figures reported apply to postmenopausal white women aged 55-70 years who meet the conventional criteria for a BMD examination. The results confirm that the thresholds are specific to each type of pDXA device and that the NOS triage algorithm requires 40% of women to have an axial DXA examination.

The discriminative ability of peripheral and axial bone measurements to identify proximal femoral, vertebral, distal forearm and proximal humeral fractures: a case control study

Previous studies evaluating peripheral bone measurement devices have often used discontinued technologies, compared single devices, only evaluated a single fracture syndrome or failed to make a comparison with central densitometry, which is currently the gold standard for fracture discrimination. We have used a case control study to evaluate the ability of different peripheral and central bone techniques to discriminate between fracture cases and controls, determine the impact of different measurement sites, evaluate the role of measuring the cortical or trabecular envelopes using quantitative computed tomography (QCT) and determine the impact of using combinations of sites and techniques on fracture discrimination. We recruited postmenopausal women with proximal femoral (n=53), vertebral (n=73), distal forearm (n=78) or proximal humeral (n=75) fractures, and 500 population-based women (age 55-80 years). All subjects had measurements of the spine, total hip and distal forearm with dual-energy X-ray absorptiometry (DXA), distal forearm QCT and quantitative ultrasound (QUS) of the heel (four devices), finger (two devices), radius and metatarsal. The association of each device with fracture was expressed as the age-adjusted standardized odds ratios (sOR) per 1-SD decrease of population variance. The association of bone measurements with fracture was site-specific. We found the hip (sOR up to 3.40) and vertebral (sOR up to 4.67) fractures were more closely associated with central bone measurements than upper limb fractures (sOR 1.96 and 2.05). The performance of heel broadband ultrasound attenuation (sOR 2.09-2.41), heel speed of sound (sOR 1.79-2.28) and peripheral BMD (sOR 2.07 and 2.24) was comparable with total hip (sOR 2.46) and lumbar spine DXA (sOR 2.31) in discriminating all types of osteoporotic fracture. In general, measuring cortical or trabecular envelopes did not increase sOR. However, combining different measurement sites or technologies provided additional information, which was independent of total hip BMD. The ability of different bone measurements to discriminate between fracture cases and controls is device- and site-specific, with additional information obtained by combining measurement sites and technologies.

Age-related changes in cortical bone mass: data from a German female cohort

To describe data from digital radiogrammetry (DXR) in an unselected German female cohort over a wide age range. Using a retrospective study design we analyzed radiographs of the hand from 540 German women (aged 5-96 years) using an automated assessment of cortical thickness, metacarpal index (MCI), and estimated cortical bone mineral density (DXR-BMD) on digitized radiographs. Both hands were radiographed in 97 women. In this group DXR-BMD and cortical thickness were significantly higher in the right metacarpals while there was no significant difference in MCI. To study the association with age we differentiated young (<20 years), middle-aged (20-45 years), and an older patients (>45 years). In young women all parameters increased significantly with age in a linear fashion (r=0.8 for DXR-BMD, r=0.7 for MCI). In those aged 25-45 years DXR-BMD and MCI were highest (peak bone mass). In women aged 45 or older all parameters decreased with age in an almost linear fashion with an annual change ranging from 0.7% to 0.9%. Our results for an unselected German female cohort indicate that DXR is a reliable, widely available osteodensitometric technique based on the refinement of conventional radiogrammetry. These findings are comparable to those from other studies and represent a valid resource for clinical application and for comparisons with other ethnic groups.

Comparison of DXA, QCT and trabecular structure in beta-thalassaemia

Osteopathy, as a major feature of homozygous beta-thalassaemia, is a multifactorial disorder, not fully understood. We studied the lumbar vertebrae of 48 patients using Dual-Energy X-ray Absorptiometry (DXA) and Quantitative Computed Tomography (QCT), and we focused on structural properties, assessed by High Resolution Computed Tomography (HRCT). Bone Mineral Density (BMD) values were expressed as Z-scores and the results were correlated. The effect of age, sex, and type of thalassaemia and hormonal factors on BMD was assessed. We estimated, with HRCT, the cortex integrity and the number and thickness of trabeculae; the latter were classified to a three-grade scale. Our results showed the overall prevalence of osteoporosis to be 44% with DXA and 6% with QCT. Both techniques revealed an inverse correlation between age and BMD, whereas hormonal factors demonstrated associations with QCT and DXA measurements. The correlation coefficient between DXA's BMD and QCT's trabecular BMD was 0.545 (P < 0.001) whereas the corresponding value for Z-scores was r = 0.491 (P < 0.001). The classification of the patients into normal, osteopenic and osteoporotic categories, using QCT's Z, was in better agreement with the assignment based on trabecular number (K = 0.209, P = 0.053) than the classification using DXA's Z (K = 0.145, P = 0.120). Cortex evaluation by HRCT showed discontinuity in 15 patients. Both methods indicate a progression of osteoporosis with age. Hormonal deficiency is associated with thalassaemic osteoporosis whereas the visual estimation of cortex indicates that Thalassaemia Intermedia (TI) patients could be more affected than Thalassaemia Major (TM). Using the trabecular number as an indicator of osteoporosis, it seems that QCT may evaluate osteopathy better than DXA. Since the former has the ability to measure trabecular and cortical BMD separately, it could give early indication of which changes more rapidly and to what degree.

Prediction of density and mechanical properties of human trabecular bone in vitro by using ultrasound transmission and backscattering measurements at 0.2-6.7 MHz frequency range

The ultrasound (US) backscattering method has been introduced as an alternative for the through-transmission measurement of sound attenuation and speed in diagnosis of osteoporosis. Both attenuation and backscattering depend strongly on the US frequency. In this study, 20 human trabecular bone samples were measured in transmission and pulse-echo geometry in vitro. The aim of the study was to find the most sensitive frequency range for the quantitative ultrasound (QUS) analyses. Normalized broadband US attenuation (nBUA), speed of sound (SOS), broadband US backscatter (BUB) and integrated reflection coefficient (IRC) were determined for each sample. The samples were spatially scanned with five pairs of US transducers covering a frequency range of 0.2-6.7 MHz. Furthermore, mechanical properties and density of the same samples were determined. At all frequencies, SOS, BUB and IRC showed statistically significant linear correlations with the mechanical properties or density of human trabecular bone (0.51 < r < 0.82, 0.54 < r < 0.81 and 0.70 < r < 0.85, respectively). In contrast to SOS, IRC and BUB, nBUA showed statistically significant correlations with mechanical parameters or density at the centre frequency of 1 MHz only. Our results suggest that frequencies up to 5 MHz can be useful in QUS analyses for the prediction of bone mechanical properties and density. Since the use of higher frequencies provides better axial and spatial resolution, improved structural analyses may be possible. While extensive attenuation of high frequencies in trabecular bone limits the clinically feasible frequency range, selection of optimal frequency range for in vivo QUS application should be carefully considered.

Limited diagnostic agreement of quantitative sonography of the radius and phalanges with dual-energy x-ray absorptiometry of the spine, femur, and radius for diagnosis of osteoporosis

OBJECTIVE

The aim of our study was to evaluate the diagnostic agreement of quantitative sonography of the radius and proximal phalanx and dual-energy X-ray absorptiometry (DXA) of the radius, lumbar spine, and femoral neck for the detection of osteoporosis.

MATERIALS AND METHODS

In 95 women (mean age, 53 +/- 13 years) and 26 men (mean age, 53 +/- 13 years), DXA measurements of the lumbar spine (posterior-anterior, L1-L4) and the femoral neck, as well as quantitative sonography of the radius and proximal phalanx of the third finger were obtained. The percentage of patients below a given threshold was calculated for each imaging technique. A T score of less than -2.5 indicated presence of osteoporosis. Diagnostic agreement in identifying individuals with osteoporosis was assessed using kappa scores.

RESULTS

Between 14% and 22% of the patients were classified as osteoporotic after DXA of the various regions of interest of the radius, 31% after DXA of the spine, 43% after DXA of the femoral neck, 32% after quantitative sonography of the distal radius, and 34% after quantitative sonography of the phalanx of the third finger. Correlation coefficients between T values for quantitative sonography and those for DXA varied between not significant and 0.54 at the different regions. Kappa analysis showed the diagnostic agreement among quantitative sonography and DXA to be fair to moderate (kappa = 0.38-0.48). The highest agreement was between quantitative sonography of the proximal phalanx of the third finger and DXA of the total radius (kappa 0.48; p < 0.05).

CONCLUSION

Considerable diagnostic disagreement exists between quantitative sonography and DXA of the forearm, as is true for most quantitative techniques in the assessment of skeletal status. The lack of correlation makes quantitative sonography impractical for routine diagnostic use but might characterize different parameters related to bone quality.

Structural properties of the axis studied in cadaveric specimens

Peripheral quantitative computed tomography scans of the axis in 20 fresh cadaveric specimens obtained at autopsy were studied to investigate the internal structural properties of the axis. In all specimens, serial scans were done in three planes. The area of the dens consisted of dense cortical and trabecular bone (Region 1, above the base of the dens) and showed statistically significantly greater peripheral quantitative computed tomography values when compared with the anterior part of the body of the axis (Region 2, below the base of the dens). An age-related progressive decrease of peripheral quantitative computed tomography values was observed, with specimens from subjects younger than 40 years showing statistically significantly greater peripheral quantitative computed tomography values when compared with those from subjects older than 40 years. A small area of trabecular bone with decreased density was found close to the anteroinferior edge of the body of the axis in the specimens from younger subjects. In contrast, a large area of trabecular bone with decreased density extending anteroinferiorly to superoposteriorly to the base of the dens was found in the specimens from older subjects. Based on these findings, we think that dens fracture classification systems and fixation techniques should be reconsidered.

Ability of peripheral DXA measurement to diagnose osteoporosis as assessed by central DXA measurement

In order to evaluate the utility of peripheral measurement of bone mineral density (BMD) in the diagnosis of osteoporosis, we measured BMD at the spine and femoral neck with central dual-energy X-ray absorptiometry (DXA), at phalanx with AccuDXA (Schick) as well as proximal and distal forearm with pDXA (Norland) in 835 women ranging in age from 20 to 85 yr. In receiver operating characteristic (ROC) curves, where a positive case was defined as a T-score < or = -2.5 either on spine or femoral neck, the areas under the curve were not significantly different between sites. At a T-score of -2.5 as determined by each peripheral apparatus, sensitivity and specificity were, respectively, 0.39 and 0.95 for phalanx and 0.75 and 0.85 for proximal forearm whereas they were 0.42 and 0.96 for distal forearm. Using optimal absolute BMD cutoff values improved the results. Sensitivity and specificity were, respectively, 0.79 and 0.83 for phalanx at an absolute BMD value of 0.436 and 0.84 and 0.79 for proximal forearm at a value of 0.703, whereas they were 0.90 and 0.75 for distal forearm at a value of 0.208. Combining the two forearm measurements improves the results slightly. At cutoff values of 0.641 and 0.252, respectively for proximal and distal forearms, sensitivity was 0.83 and specificity was 0.84. Therefore, a peripheral measurement of BMD together with a good clinical evaluation of the osteoporosis risk profile of the patient, can be an interesting tool for the diagnosis of osteoporosis in areas where central DXA is not available.

Bone density measurements in pediatric patients with renal osteodystrophy

Peripheral quantitative computed tomography (pQCT) can selectively measure the densities of cortical and trabecular bone, but there is limited information about its use in patients with renal osteodystrophy. Thus pQCT (Norland XCT-2000, Stratec, Pforzheim, Germany) was performed at the ultradistal radius in 21 patients aged 16+/-3.6 (SD) years on continuous cycling peritoneal dialysis. Trabecular bone density (TBD) was higher in patients, 206+/-16 mg/cm(3), than in controls, 182.7+/-24.8 mg/cm(3) ( P<0.0001), whereas cortical bone density (CBD) was lower in patients, 946.5+/-147.5 mg/cm(3), than in controls, 1,153+/-25.4 mg/cm(3) ( P<0.001). TBD was inversely correlated with age ( r=-0.59, P=0.05), height ( r=-0.59, P<0.01), and weight ( r=-0.51, P<0.05). In contrast, CBD was positively correlated with age ( r=0.53, P<0.05), height ( r=0.56, P<0.05), and weight ( r=0.53, P<0.05). CBD was inversely related to serum alkaline phosphatase ( r=-0.71, P<0.001) and parathyroid hormone levels ( r=-0.50, P<0.05). In patients with adynamic bone, TBD was less, 192+/-9 mg/cm(3), than in those with high-turnover lesions, 215+/-13 mg/cm(3), P<0.001. CBD, however, was lower in patients with high-turnover lesions, 900+/-151 mg/cm(3), than in those with low turnover, 1,022+/-111 mg/cm(3), P<0.05. Compared with controls, in patients with high-turnover lesions, CBD was lower ( P<0.0001) and TBD higher ( P<0.0001). These findings suggest that pQCT may be an additional tool in the assessment of renal osteodystrophy.

Absolute fracture risk varies with bone densitometry technique used. A theoretical and in vivo study of fracture cases

The lack of consensus of how the results of peripheral bone mineral density (BMD) measurements should be interpreted is proving a barrier to the wider use of these devices. One approach is to interpret peripheral measurements using thresholds (so-called equivalent T-scores) defined to have the same absolute fracture risk as a femoral neck T-score of -2.5. For this concept to be valid, the estimates of fracture risk for a population should be the same irrespective of the measurement technique used. We tested this prediction both theoretically and in vivo using data for 63 postmenopausal women with Colles fracture and 191 control subjects. The theoretical analysis showed that if the normal population has a Gaussian BMD distribution and fracture risk varies exponentially with Z-score as exp(-beta Z) then patients who experience a low-trauma fracture have a fracture risk that is larger by a factor exp(beta(2)) compared with the fracture risk of the whole population. Using data from the in vivo study, fracture risk predictions were compared for seven different types of measurement (lumbar spine; femoral neck; total hip BMD; and speed of sound [SOS] at the radius, tibia, phalanx, and metatarsal). When quantitative estimates of fracture risk were made for individual subjects, the average risk of fracture for the Colles group varied between 1.03 times larger (for tibial SOS) and 2.77 times larger (for total hip BMD) than the average fracture risk for the whole population. As predicted by the theoretical study, fracture risk varied according to the odds ratio determined by logistic regression analysis. Therefore, estimates of fracture risk derived for the same group of patients varied almost threefold according to the type of measurement. It was concluded that equating estimates of absolute fracture risk for different types of scan should not be used as the basis of deriving equivalent T-scores for interpreting peripheral measurements.

Comparison of heel ultrasound and finger DXA to central DXA in the detection of osteoporosis. Implications for patient management

The goal of the study was to investigate the potential discordance in patient management when a clinician assumes that a peripheral device is a diagnostic surrogate for central DXA in the detection and treatment of osteoporosis. Over a period of 2 mo, asymptomatic women seeking conventional central DXA evaluation for osteoporosis at a diagnostic imaging center were also evaluated with heel ultrasound and finger DXA peripheral imaging devices. T-Scores of -2.5 or less in screening examinations were used to evaluate the discordance between the two peripheral devices and central DXA in the identification of patients with osteoporosis. Higher T-score cutoffs (>-2.5) were also evaluated. Using central DXA as the standard for comparison, the sensitivity of heel ultrasound for screening cases was 0.34 and specificity was 0.92. For finger DXA, sensitivity was 0.23 and specificity was 0.92. Overall discordance between the peripheral devices and central DXA was 21% (heel) and 23% (finger). Heel ultrasound identified 7 out of every 22 osteoporotic patients diagnosed with central DXA. Finger DXA identified 5 out of every 22 osteoporotic patients. Using lower T-scores for the peripheral devices increased sensitivity but markedly increased discordance with DXA. The peripheral devices we studied cannot be considered equivalent surrogates for central DXA in the screening of asymptomatic women for osteoporosis.

Bone densitometry and the diagnosis of osteoporosis

Over the past decade, bone density scanning has come to be seen as an essential part of the evaluation of patients at risk of osteoporosis. Although dual x-ray absorptiometry (DXA) is the technique most associated with the recent growth in bone densitometry, several innovative devices for performing measurements at sites in the peripheral skeleton are also available. This article examines the question of whether there is any one method or measurement site that performs better than all the others at identifying patients at risk of fracture. Given that it is essential to make greater use of the small, low-cost peripheral devices if the many millions of women most at risk are to be identified and treated, what approaches to the interpretation of bone density scans can be adopted to ensure the greatest degree of consistency among different methods? Finally, does it matter if the imperfect correlation among different types of measurement results in different patients being selected for treatment on the basis of different techniques?

Peripheral or central densitometry: does it matter which technique we use?

Over the past decade, bone density scans have assumed an essential role in the diagnosis of osteoporosis. Although dual X-ray absorptiometry (DXA) scans of the central skeleton remain widely used, a variety of different types of equipment for measuring peripheral sites is now available. However, the poor correlation between different types of measurement and a lack of consensus on how results from peripheral sites should be interpreted have proved a barrier to the more widespread use of these devices. These issues prompt the following questions: Which technique best identifies patients at risk of fracture? What approaches to scan interpretation ensure the closest agreement among different methods? Does it matter if different patients are selected for treatment on the basis of different techniques? The relative risk (RR)of fracture derived from prospective studies is a key parameter for comparing the clinical value of different techniques. Recent reports confirm the advantages of hip bone mineral density compared with peripheral measurements for predicting hip fracture risk, although for fractures at other sites the differences are inconclusive. Using receiver operating characteristic curves, we show that the guidelines adopted for scan interpretation are of crucial importance for ensuring that the information provided is used effectively. The closest agreement among different techniques is achieved by setting thresholds for peripheral devices that target either the same percentage of the population or the same percentage of future fracture cases as femur DXA. Different methods select different groups of individuals from the total pool of patients who will later sustain a fracture, with the most successful technique being the one with the largest RR value. The emphasis placed by many studies on validating new techniques by studying their correlation with DXA may lead to the clinical value of peripheral devices being underestimated when the key datum is the RR value inferred from prospective fracture studies.

Bone mineral measurement of phalanges: comparison of radiographic absorptiometry and area dual X-ray absorptiometry

With a standard, image-intensifier-based, digital radiographic system, high-spatial-resolution images of the hand were acquired for analysis of phalangeal bone mineral density with dual x-ray absorptiometry (DXA). Results with phalangeal DXA had precision of plus or minus 0.67% and accuracy of 4.1% and correlated well with those with radiographic absorptiometry. This phalangeal DXA technique is potentially useful for clinical diagnosis of osteoporosis.

[Estimate of osteoporosis fracture risk with ultrasound bone assessment]

BACKGROUND

Multiple studies suggest that ultrasound measurement of the bone can be a rapid, cheap, and radiation-free alternative to determine the fracture risk. In this paper the ultrasound measurement of the bone was performed among 288 postmenopausal women, and the influence of gynecologic history and factors related to lifestyle on the obtained values was examined.

PATIENTS AND METHODS

One hundred nineteen healthy postmenopausal women and 169 women with previous osteoporotic fractures were included in the study. Both weight and height were determined and a clinical questionnaire was administered to assess factors related to bone mineral density. The values of broadband ultrasound attenuation (BUA) and speed of sound (SOS) were obtained with a contact ultrasound analyzer.

RESULTS

Among women without fractures the mean BUA and SOS values (64.1 [14.9] and 1,601.1 [34.5], respectively) were significantly higher than mean BUA (48.8 [17.3]) and SOS (1,573 [57.8]) values among women with fractures (p < 0.001). Using the logistic regression analysis for predicting fracture risk, the model that suited best was that including BUA (OR = 0.668 [0.544-0.818]), age (OR = 1.102 [1.055-1.151]), age at postmenopause (OR = 0.794 [0.731-0.862]) and height (OR = 0.932 [0.883-0.983]). The area under the curve for this model was 0.871.

CONCLUSIONS

BUA and SOS values are lower among women with osteoporotic fractures. The fracture risk can be predicted by means of a model including the variables BUA, age, postmenopausal age, and height.

Bone loss. Quantitative imaging techniques for assessing bone mass in rheumatoid arthritis

Osteoporosis is associated with low bone mass and microarchitectural deterioration of bone tissue with clinical manifestation of low trauma fractures. Rheumatoid arthritis (RA) is a risk factor due to generalized and articular bone loss. This minireview presents past and current bone mass measurement techniques in RA. These techniques include: plain radiographs, absorptiometry, quantitative computed tomography (QCT) and ultrasound. The most widely used technique is dual x-ray absorptiometry (DXA). RA patients have lower bone mass as compared with normals and substantial bone loss may occur early after the onset of disease. Measurement of bone mineral density (BMD) at the hand using either DXA or ultrasound maybe a useful tool in the management of RA patients.

A new X-ray based osteoporosis screening tool provides accurate and precise assessment of phalanx bone mineral content

Many devices currently available for the assessment of osteoporosis require a significant capital investment, are not portable, and require specially trained operators. The objective of this study was to assess the accuracy and precision of a new tabletop dual-energy computed digital absorptiometry (CDA) device (accuDEXA, Schick Technologies, Long Island City, NY) designed to automatically and instantaneously assess bone mineral content (BMC) and bone mineral density (BMD) of the middle finger. BMC and BMD of 26 cadaveric forearms were measured by dual-energy X-ray absorptiometry, radiographic absorptiometry (RA), and CDA. accuDEXA measurements were repeated five times with and without repositioning on 10 forearms. The portion of the finger evaluated by accuDEXA was then excised, measurements of the specimen were again obtained using the accuDEXA device, and the specimen was incinerated to determine ash weight. BMC assessed by accuDEXA and by RA were strongly correlated with ash weight of the excised phalanx specimens (r2 = 0.94 and r2 = 0.96, respectively). Short-term precision for BMD assessed by the accuDEXA device was 0.9% without repositioning, and 1.8% with repositioning. BMD determined by the accuDEXA device was strongly correlated with BMD of the hand and forearm (r2 = 0.56-0.69). Dual-energy CDA is a new bone densitometry technique that provides rapid, precise, and accurate measurements of the middle phalanx of the third finger. The technique may be useful for widespread testing of osteoporotic patients.

Radiation dose to the patient and operator from a peripheral dual X-ray absorptiometry system

Although peripheral dual X-ray absorptiometry (pDXA) scanners for measuring bone mineral density (BMD) in the forearm are known to produce an exceptionally low radiation dose to the patient, quantitative assessment of patient dose from pDXA procedures is important for reassuring patients about their safety. We have estimated the effective dose of radiation (ICRP-60) to the patient and also the scattered dose to the operator from a forearm BMD examination performed on a DTX-200 pDXA system (Osteometer Meditech, Hoersholm, Denmark). Measurements were performed using thermoluminescent dosimeters (TLD's) attached to the forearm phantom supplied by the manufacturer. The effective dose to a patient was estimated to be 0.1 microSv. At a distance of 1 m from the center of the forearm, the time-averaged scattered dose to the operator assuming scanning five patients per hour was measured to be <0.1 microSv/h. The dose rate over the outside surface of the DTX-200 in line with the primary X-ray beam was measured to be 1.4 microSv/h. These figures compare with a natural background radiation in the United Kingdom of 7 microSv/d. In conclusion the radiation doses from forearm pDXA to both patients and operator were found to be truly trivial.

Radiation exposure in bone mineral density assessment

Osteoporosis is a systematic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue which leads to diminished biomechanical competence of the skeleton and low-trauma or atraumatic fractures. Due to increased awareness of the impact of osteoporosis on the elderly population, the use of bone densitometric techniques is becoming more widespread. Considerable progress has been made in the development of non-invasive methods for the assessment of the skeleton. While DXA and QCT are commonly used techniques, the popularity of other approaches such as RA, SXA and QUS is gaining grounds. QCT has an advantage over the other techniques in its ability to measure the true volumetric density of trabecular or cortical bone. We therefore present an overview of these current techniques for bone mineral density (BMD) measurements. In the second section we discuss the radiation doses incurred in BMD measurements by patients and methods for reducing patient and staff radiation exposure are given. Studies of radiation dose to patient from DXA confirms that patient dose is small (0.08-4.6 muSv) compared to that given by many other investigations involving ionizing radiation. Fan beam technology with increased resolution has resulted in increase patient dose radiation dose (6.7-31 muSv) but this is still relatively small. Carrying vertebral morphometry using DXA also incurs less radiation dose (< 60 muSv) than standard lateral radiographs QCT has radiation dose (25-360 muSv) comparable to simple radiological examination such as chest X-ray but lower than imaging CT. Radiation dose from other techniques such as RA and SXA are in the same order of magnitude as pencil beam DXA. For pencil beam DXA and SXA systems the time average dose to staff from scatter is very low even with the operator sitting as close as 1 m from the patient during measurement. However the scatter dose from fan beam DXA systems is considerable higher and approaches limits set by regulator bodies for occupational exposure.

Role of risk assessment and bone density monitoring in osteoporosis

Osteoporosis and its complications are prevalent medical problems. Of the risk factors for fractures, low bone mass is the best predictor. Measuring bone density in a person with risk factors for osteoporosis can provide important information for both patient and physician when choosing clinical interventions. For patients with the disease it is a way to assess response to drug therapy. Advances in technology have made measuring bone density safer, faster, and more practical than ever. Guidelines addressing when, where, and how the test should be done are useful when deciding how to apply this technology to patient care.

Quantitative diagnostic methods in osteoporosis: a review

During the last two decades there have been major advances in the understanding of pathophysiology and in the diagnosis of osteoporosis. There are now, in addition to standard radiographs, a number of different diagnostic modalities available to doctors for the quantitative assessment of bone mass. These methodologies are having an increasingly important role, not only in the clinical diagnosis, but also in the monitoring of patients with osteoporosis. As the population ages there will be an increasing demand for these services, and radiologists need to be aware of the strength and limitations of the different modalities available.

Diagnosis of osteoporosis in clinical practice

Measurement of bone mineral density is the basis of the diagnosis of osteoporosis. The risk of fracture increases with decreasing bone mineral density, which can be measured using several different techniques. Dual energy x-ray absorptiometry is the most commonly used technique today. A further facility of the new bone densitometry technology is the option for vertebral morphometry. There are errors of accuracy in all bone densitometry techniques and also in the interpretation of the data they provide. Ultrasound of bone may provide new measures of bone fragility. Broadband ultrasound attenuation of the calcaneus predicts the risk of hip fracture in elderly women almost or equally as well as bone densitometry. Ultrasound does not expose to radiation and the equipment is portable. However, bone ultrasound cannot replace bone densitometry. Biochemical bone markers do not differentiate osteoporotic patients from healthy adults. However, they can be useful in deciding on interventions and in monitoring the efficacy of treatment. Their predictive value in individuals suffers from large variability. Biochemistry is widely used in the differential diagnosis of secondary osteoporosis. Suspicion of osteomalacia or an invasive process in the bone marrow are the most common indications for bone biopsy. Finally, although history and physical examination are insufficient in diagnosing primary osteoporosis, they are important in targeting other investigations to exclude secondary forms of osteoporosis.

Applications of bone densitometry for osteoporosis

Over the past decade, growing awareness of the impact of osteoporosis on the elderly population and the availability of new treatments to prevent fractures have stimulated the rapid development of new radiologic techniques to assist in diagnosis. With the ability to perform high precision measurements of bone mineral density (BMD) in the spine and hip, dual X-ray absorptiometry (DXA) is well suited to meet this latter need. However, there is continuing interest in smaller, cheaper systems for assessing the peripheral skeleton that include DXA scanning of the distal forearm and a variety of devices for performing quantitative ultrasound (QUS) measurements on bone. Alongside the new equipment, new guidelines have been developed to assist in the interpretation of bone densitometry studies and, following a report by a World Health Organization working group, osteoporosis is increasingly diagnosed on the basis of the patient's T-score value (difference of BMD from young adult mean normalized to the population SD). For the future, wider provision of bone densitometry services is required to properly target the new treatments now becoming available. Since it is unlikely that conventional DXA can meet these needs, QUS is an attractive alternative, especially because this technique is now proven in its ability to predict fracture risk in the elderly and FDA approval is imminent.

Managing patients with complications of osteoporosis

This article reviews the impact of osteoporosis on quality of life. It defines specific impairments and suggests how best to minimize the impact of osteoporosis on patients' daily lives. Specific issues such as a spinal deformity, limitations on activities of daily living, pain, functionality, social impairment, self esteem, and depression also are addressed. Finally, a multidisciplinary team approach to osteoporosis is advocated.

Peripheral bone mass measurements: current and future perspectives on quantitative ultrasound and peripheral DXA

Although peripheral bone mass measurements have been available for more than a quarter of a century to predict osteoporotic fractures, these studies fell out of favor in the late 1980s and early 1990s as axial measurements replaced appendicular determinations for risk assessment and therapeutic responsiveness. Within the last half decade there has been a resurgence in utilization of peripheral measurements, primarily because of improved technology, enhanced precision, and greater accessibility. There are now nearly 11,000 peripheral densitometers in use around the world with quantitative ultrasound (QUS) of the calcaneus and peripheral densitometry (pDXA) of the wrist or calcaneus the most popular. Three recent prospective studies involving more than 20,000 postmenopausal women have demonstrated that QUS of the calcaneus can predict future fractures as accurately as central measurements of the spine or femur. This has raised the possibility that widespread screening with QUS or pDXA will soon become a reality. In this articles we hypothesize that global utilization of peripheral technology by primary care physicians is an absolutely necessity for the successful identification and treatment of all osteoporotic patients. But despite improvements in the accuracy and precision of these machines, several critical questions remain. In particular the issues which demand further study include: 1. The rate of false negative tests by peripheral instruments; 2. The utilization of appendicular sites to measure therapeutic efficacy of various antiosteoporotic drugs; 3. The timing of follow-up measurements to assess responsiveness; 4. The relationship between fracture risk education and incremental changes in bone mass; 5. The interrelationship between bone density and bone architecture and 6. cost effectiveness of peripheral vs central measurements. Notwithstanding these issues, peripheral scanning by one of several techniques is likely to be at the forefront of screening for osteoporosis risk, not only in specialized clinics but at the "point of care" in primary care offices.

A comparison of a peripheral DXA system with conventional densitometry of the spine and femur

Because of the perceived high cost of dual-energy X-ray absorptiometry (DXA) studies of the spine and femur, there is renewed interest in small, low-cost X-ray devices for scanning the peripheral skeleton. We have compared forearm bone mineral density (BMD) measurements (distal and ultradistal sites) performed on a DTX-200 (Osteometer MediTech, Hoersholm, Denmark) with spine (L1-L4) and femur (femoral neck and total hip sites) scans performed on a QDR-4500 (Hologic, Waltham, MA) in 172 white UK women aged 22-84 yr with a view to establishing differences caused by inconsistent reference ranges and different age-related changes in BMD. All BMDs were expressed as T-scores using the manufacturers' reference ranges for the forearm and spine, and the National Health and Nutrition Examination Survey (NHANES) ranges for the femur. Linear regression between peripheral and axial sites gave correlation coefficients r = 0.71-0.74 and roof mean standard errors (RMSE) 0.88-1.14 in T-score units. Subjects were divided into the following five age groups: <40 yr; 40-49 yr; 50-59 yr; 60-69 yr and >/=70 yr. A large systematic difference between distal and ultradistal T-scores (mean DeltaT = 0.59, SEM = 0.05) was found affecting all age groups. When the mean difference in T-score between each forearm site (distal, ultradistal) and each axial site (spine, femoral neck, total hip) was examined for premenopausal subjects (n = 58) the mean difference between forearm and axial T-score showed a consistent negative offset (DeltaT = -0.41 to -0.48) for the distal forearm site and a consistent positive offset (DeltaT = +0.30 to +0.37) for the ultradistal site. When interpreting results in postmenopausal women, age-related T-score changes in the forearm were in close agreement with the femoral neck region of exterest (ROI), but systematic differences were found between the forearm and the spine and total hip sites. The two forearm and three axial sites were compared to evaluate the number of postmenopausal subjects identified as osteoporotic on the basis of the World Health Organization (WHO) Study Group criteria (T-score <-2.5). Although forearm and spine T-scores identified approximately equal numbers of subjects as osteoporotic (distal 38/114; ultradistal 31/114; spine 30/114), the two femur sites identified fewer subjects as osteoporotic (femoral neck 25/114; total hip 16/114). The number for the total hip site was statistically significantly smaller than the spine and forearm sites.

Bone densitometry: current status and future prospects

Over the past decade, growing awareness of the impact of osteoporosis on the elderly population and the consequent costs of healthcare have stimulated development of new treatments to prevent fractures, together with new imaging technologies to assist in diagnosis. With its ability to perform high-precision measurements of bone mineral density (BMD) in the spine and hip, dual X-ray absorptiometry (DXA) is well suited to meet this latter need. However, there is continuing interest in smaller, less expensive, systems for assessing the peripheral skeleton. These include peripheral DXA scanning of the distal forearm and a variety of devices for performing quantitative ultrasound (QUS) measurements of broad-band ultrasonic attenuation (BUA) and speed of sound (SOS) in bone. Pivotal to all these developments is the demonstration in prospective studies that new technologies can reliably identify patients at risk of osteoporotic fractures. Whether DXA technology can meet the anticipated need for wider provision of diagnostic services is uncertain at present. The likely alternative is bone ultrasound. Although QUS technology is substantially cheaper than DXA and has proved its ability to predict fracture risk in the elderly, it is less precise, there is a lack of appropriate phantoms for quality control and there are doubts about how to interpret results in younger women.