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Computer assisted diagnosis (CAD) schemes are currently used in the field of musculoskeletal diseases to quantitatively assess vertebral fractures, joint space narrowing, andr erosion. Most systems work semi-automatically, i.e. they are operator dependent in the selection of anatomical landmarks. Fully automatic programs are currently under development. Some CAD products have already been successfully used in clinical trials.

This article is an introduction to dual X-ray absorptiometry (DXA), the most widely used method today for diagnosis of osteoporosis. DXA can be used to assess projective bone mineral density at the lumbar spine, the proximal hip, and the whole body as well as the skeletal periphery at the forearm, the hand, and the heel. The prominent area of application of DXA is the diagnosis and monitoring of osteoporosis and its treatment. Because of its high accuracy, precision, and ability to predict osteoporotic fracture as well as its relatively low cost, DXA has prevailed over alternative methods. This article discusses the underlying X-ray physics and technological aspects, acquisition protocols, quality characteristics, and sources of error and their relevance. It also describes the various skeletal regions accessible to measurement, details on precision, nominal results, usability to predict fracture risk, and results of influential clinical trials.

During the lifetime of Physics in Medicine and Biology, osteoporosis has been recognized as the cause of a major health burden for societies, particularly within developed countries. The health detriment is associated with the consequences of bone fractures and the subsequent increases in morbidity and mortality. Much of the credit for the current availability of means for identifying groups of subjects at risk of fracture and the provision of means for the effective treatment of excessive bone loss can be attributed to the technique of dual photon absorptiometry. In this review, the history of the development of techniques based on the interactions of x- and gamma-rays with bone is considered and the ultimate dominance of x-ray based absorptiometry is described. The advantages and disadvantages of current absorptiometric techniques are presented and the likely future path for bone measurement is outlined.

The risk of osteoporosis and cardiovascular disease increase significantly with age. Because of the long silent latency of these diseases, there is the opportunity for primary prevention before clinical symptoms occur. The newer fan beam dual energy x-ray absorptiometry (DXA) systems can detect vertebral fractures with fast, low dose lateral scans of the vertabrae from T4 to L4 in as little as 10 s. The next generation of DXA imaging technology will image the hip in 3D and is expected to give a more accurate picture of bone density as well as the geometry and underlying strength of a bone. Visualizing abdominal aortic calcifications (AAC) as a part of a standard vertebral fracture assessment exam is a particularly valuable measurement since it is an independent measure of cardiovascular disease risk, including heart attacks and strokes.

We tested the hypothesis that bone mineral density (BMD) and bone mineral content (BMC) in proximal human femur specimens in the upper neck region of interest (ROI) and femoral neck axis length (FNAL) provide a significantly better prediction of femoral bone strength than standard ROIs in vitro. BMD and BMC were measured in 110 proximal femur specimens using a standard dual-energy X-ray absorptiometry (DXA) scanner. The analysis included a new ROI in the upper neck as well as the standard ROIs. FNAL was obtained from the scan images. The specimens' failure-load was measured in a mechanical loading device, simulating a fall on the greater trochanter. For the standard ROIs, correlations between failure-load and BMD ranged from R2 = 0.64 (shaft ROI) to R2 = 0.70, p < 0.001 (femoral neck). Prediction of strength by BMD did not significantly differ from those of BMC (R2 ranging from 0.65 to 0.75, p < 0.001). In the upper neck ROI, for both BMD and BMC correlations with failure-load were higher (R2 = 0.76 and 0.81, respectively; p < 0.001). A lower, yet still significant, correlation was found between FNAL and bone strength (R2 = 0.23, p < 0.001). Normalization of failure-load with respect to FNAL did not significantly increase the correlations with densitometric measures. This study provides in vitro evidence indicating that among the ROIs of the proximal femur the newly defined upper neck ROI provides the best prediction of bone strength. Only a weak association was observed between failure load and FNAL.

Purpose: To determine changes in the number of dual-energy x-ray absorptiometry (DEXA) procedures performed in the United States, as well as changes in the relative number of procedures performed by radiologists and nonradiologists., Methods: The two major Current Procedural Terminology, Fourth Edition, codes for DEXA scans were selected from the national Medicare Part B databases from 1996 through 2002 (the most recent). The total number of scans done on Medicare patients, as well as the percentages performed by radiologists and nonradiologists, were tabulated., Results: In 1996, a total of 501,505 DEXA scans were performed among all Medicare patients. Of these, 30% were performed by radiologists. In 2002, there were 2,195,548 DEXA scans performed among all Medicare patients, of which radiologists performed 45%., Conclusion: Between 1996 and 2002, the number of DEXA scans performed on all Medicare patients increased by more than fourfold. In the same population, the percentage of scans performed by radiologists increased from less than one-third to almost one-half. Consequently, radiologists are steadily gaining market share of this procedure in the Medicare population.

Many inorganic species are now recognized as being essential for life, including many forms of sulfur, phosphate and numerous classes of metal ions. For example, recent progress in the fields of biochemistry and biology has pointed out the critical importance of sulfur in the biosynthesis of vital cofactors and active sites in proteins, and in the complex reaction mechanisms often involved. Special attention has also been drawn to the diverse roles of alkaline (Na(+), K(+)) and alkaline earth (Mg(2+), Ca(2+)) metal ions in mediating the activity of RNA, proteins and many processes in living cells. While the general effect of these ions in biology is mostly understood, information on their detailed role is deficient. Here the application of softer X-ray absorption spectroscopy (XAS) to probe the local structural and electronic environment of such ions within their biological complexes and during physiological reactions is discussed. In addition, the required experimental set-up and the difficulties associated with conducting softer XAS experiments on biological samples are presented.

Here a voice from the past suggests 28 changes that will affect how people study, manage, classify and think about "osteoporoses" today. Those changes depend mainly on two things: (i) "Connecting the dots" between diverse evidence and ideas from many fields and sources in order to find larger "messages" hidden in mountains of often poorly-organized lesser details, (ii) and features of the still-evolving Utah paradigm of skeletal physiology. That paradigm sums contributions from many people who worked in many fields for over 100 years. In one view it is the most important development in skeletal physiology since Rudolf Virchow and others realized approximately 150 years ago that cells provide the basis for human physiology and diseases. This article emphasizes the above messages instead of the details. The messages affect ideas about the nature, pathogenesis, diagnosis, classification, study and management of osteopenias and osteoporoses, as well as some roles of muscle, drugs, hormones, other agents and fatigue damage, in those disorders. Those larger messages also concern how to classify "osteoporosis fractures", how to define bone health, the choice of absorptiometric methods for noninvasive evaluations of bones, osteopenias and muscle strength, and new criteria for selecting patient cohorts for "risk-of-fracture" analyses and in searches for genetic roles in "osteoporoses". Finally, those larger messages identify many new targets for research that should prove unusually useful in clinical and pharmaceutical domains and work.

State-of-the-art techniques for analysing X-ray absorption spectra are reviewed, with an eye to biological applications. Recent attempts to perform full spectral fitting of the XANES energy region and beyond for the purpose of structural analysis have met with encouraging success. The present paper analyses the theoretical motivations behind this success and indicates routes for future improvements. The theoretical background is not entirely new, although the point of view is, and some sections and appendices present material that the Authors believe has never been published before. The aim of this paper is to provide a theoretical analysis that is as self-contained as possible.

Introduction: Osteoporosis and fragility fractures are problems which will increase in significance as the population of the elderly in many countries increases. The availability of bone mineral density (BMD) measurements, which can define osteoporosis, allows the implementation of effective therapeutic interventions to those at risk for fractures before they occur. Because of the increasing at-risk population and the relatively high cost of these measurements and interventions, a case-finding strategy to detecting osteoporosis has been widely recommended. This review highlights the approach to detecting and diagnosing osteoporosis., Methods: A non-systematic review of English-language literature on the diagnosis and assessment of osteoporosis was conducted., Results: Many risk factors have been found to be associated with osteoporosis and fractures. These risk factors may be utilised for case finding in deciding who should be evaluated for osteoporosis. Clinical self-assessment tools have been developed to identify women likely to have low BMD who might be recommended for BMD. Several techniques are available for BMD measurement, but the technique of choice for the diagnosis of osteoporosis is dual-energy X-ray absorptiometry (DXA) measured at the hip. BMD thresholds have been widely used to guide osteoporosis treatment. However, recent research has been directed at using risk factor assessment and self-assessment tools to derive medium-term fracture risk as a guide to therapeutic intervention., Conclusions: Proper selection of individuals for evaluation and treatment for osteoporosis would include risk factor assessment and appropriate BMD measurement to determine the risk of fracture and the need for intervention.

Dual-energy X-ray absorptiometry (DXA) has been recently used for body composition analysis in dialysis patients. It is based on the principle that X-rays passed through various body tissues have different attenuation and, therefore, can be differentiated. By using X-rays at two different energy levels, better tissue differentiation is possible compared with single energy systems. This article will review the evolution of DXA scanners and the role DXA has in assessing body composition in dialysis patients. Overall, this technique has excellent precision and holds promise for use in the serial evaluation of body composition and nutritional evaluation of dialysis patients.

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.

The introduction of new devices demands the assessment of their capabilities in established terms. The accuracy, reproducibility and spatial resolution of in vitro (phantom) osteodensitometric and morphometric measurements of QDR 2000 Plus and EXPERT are presented. Design details of these DXA/MXA-devices are listed and discussed in combination with the data acquired in the test measurements and calculations. The image quality will improve with further software developments. The long-term reproducibility and in vivo reliability remains to be evaluated.

Switching from the Hologic QDR-1000/W to the QDR-2000 DXA densitometer was critically evaluated with regard to cross-calibration and dosimetry. Studies with bone equivalent humanoid spine phantoms and patient studies were done. Fan-beam scanning with the QDR-2000 is problematic because of magnification. Mean phantom bone mineral content (BMC) and bone mineral density (BMD) were moderately but significantly different. Biological variation disguised differences between the two devices in humans, but significant differences were revealed when individual data were analyzed. Longitudinal assessments of BMC and BMD, initiated with QDR-1000/W and continued with the QDR-2000, should employ single-beam mode only and not fan-beam mode--but even if that is done, significant errors can be introduced. The new QDR-2000 should be properly cross-calibrated with the original densitometer, and one should make sure that the same software, phantom, and type of collimator are used. The radiation dose is substantially higher with QDR-2000 (fan-beam and high-resolution array mode) than with QDR-1000/W (pencil-beam mode) and QDR-2000 (pencil-beam mode), and higher than claimed by the manufacturer. The typical radiation dose given by the manufacturer was half the actual radiation dose measured (e.g., for fan-beam scan 62 microSv versus 33 microSv). High-resolution array mode does not improve precision, but augments the radiation dose to the patient.