Quality control in bone densitometry

Bone densitometry is a biological measurement which must comply to the usual rules of quality control. Calibration phantoms are available and must be regularly measured. Results may be interpreted by visual inspection or by estimating drift percentage. Different calculation methods have been proposed. A rigorous procedure is required when replacing densitometry devices. Simple and regular controls can assure the reliability of the technique.     

Linearity and accuracy errors in bone densitometry

This investigation was undertaken to quantify accuracy errors and identify possible linearity errors in dual energy X-ray absorptiometry (DXA) of bone, based on studies of commercially available bone densitometers for planar densitometry. The following was found in a combination of in vitro phantom studies and in vivo investigations of human volunteers: (1) Pronounced differences between the instruments when measuring vertebral size and contours of the projected bone regions. (2) Falsely low bone mineral content (BMC in terms of g) in cases of low nominal bone mass, due to the fact that edge regions were omitted by the calculation software of some devices. (3) An increase in the projected bone area secondary to an increase in nominal bone mass with some instruments. (4) Clinically and statistically significant errors of accuracy of BMC and to a lesser extent bone mineral density (BMD). (5) Substantial linearity errors with some osteodensitometers for BMC, a phenomenon that reduces the usefulness of this parameter. It is concluded that DXA devices are affected by a combination of accuracy errors and linearity errors, some more than others, and that linearity errors influence their ability to monitor change in BMC and to a lesser extent in BMD, making system intercomparison difficult.     

Current methods and advances in bone densitometry

Bone mass is the primary, although not the only, determinant of fracture. Over the past few years a number of noninvasive techniques have been developed to more sensitively quantitate bone mass. These include single and dual photon absorptiometry (SPA and DPA), single and dual X-ray absorptiometry (SXA and DXA) and quantitative computed tomography (QCT). While differing in anatomic sites measured and in their estimates of precision, accuracy, and fracture discrimination, all of these methods provide clinically useful measurements of skeletal status. It is the intent of this review to discuss the pros and cons of these techniques and to present the new applications of ultrasound (US) and magnetic resonance (MRI) in the detection and management of osteoporosis. Correspondence to: G. Guglielmi     

Different approaches to bone densitometry.

From 1990 to 2000, several effective new treatments were introduced for the prevention of osteoporotic fractures; these treatments were proven effective in large, international, clinical trials. At the same time, there was rapid technologic innovation, with the introduction of new radiologic methods for the noninvasive assessment of patients' bone density status. These developments led to the publication of guidelines for the clinical use of bone densitometry that include criteria for the referral of patients for investigation as well as recommendations for intervention thresholds for the initiation of preventive treatment of osteoporosis. Dual-energy x-ray absorptiometry scanning of the spine and hip remains the technique of choice for bone densitometry studies, although there is now a wider appreciation of the need for smaller, cheaper devices for scanning the peripheral skeleton if the millions of women most at risk of a fragility fracture are to be identified and treated. This article reviews these developments, concentrating in particular on the advantages and disadvantages of the different types of equipment available for performing bone densitometry investigations, the guidelines for the referral of patients, and the principles for the interpretation of the scan findings.     

Bone scintigraphy and densitometry in symptomatic haemodialysis bone disease

Bone scintigraphy and densitometry (iodine-125 photon absorptiometry) were performed in eight patients with symptomatic haemodialysis bone disease. The bone scintiscan showed either hot spots or hyperactivity as a feature of metabolic bone disease. The bone density (BMC/W) was reduced, but could not be distinguished from the degree of demineralisation found in asymptomatic patients on longterm haemodialysis. Therefore, bone density measurements require critical interpretation. Complementary bone scintigraphy should be used in symptomatic haemodialysis bone disease for assessing the extent of the disease.     

Monitoring treatment for osteoporosis by using bone densitometry

In recent years, the range of treatments available for patients with osteoporosis has greatly increased. A decade ago, the only proven therapy was estrogen, but today the choices include bisphosphonates, selective estrogen-receptor modulators, calcitonin, and parathyroid hormone. Clinical trials involving bone mineral density (BMD) scans of the spine and femur have had an important role in the evaluation of these new therapies. In particular, the efficacy of treatments has now been verified in large studies powered to show reductions in fracture risk. In contrast with the use of BMD scans in research studies, their value for monitoring response to treatment in individual patients is less certain. In many cases, the increases in BMD are too small to reliably distinguish between true changes and measurement error. However, experience with estrogen and bisphosphonates suggests that these treatments have a beneficial effect on bone in most patients. Follow-up scans for patients taking these agents are therefore of limited value, apart from offering reassurance to the patient and the doctor. However, when new therapies are first introduced, follow-up scans have a useful role in building up the physician's experience and confidence.     

Rat lumbar vertebrae bone densitometry using multidetector CT

Peripheral quantitative CT (pQCT) is the main method of bone mineral density (BMD) measurement in small animals. However, pQCT is usually only available in specialized centers, while clinical multidetector computed tomography (MDCT) is much more widely available. This study investigated the feasibility of using clinical 64-slice MDCT for measuring the BMD of rat lumbar vertebrae. The lumbar vertebrae of 18 7-month-old female Sprague-Dawley rats were studied. Two MDCT protocols (General Electric LightSpeed), comprising single 2.5-mm and continuous 0.625-mm acquisitions, and a single pQCT protocol (Scanco Densiscan 2000), comprising 1-mm acquisitions, were performed. The following comparisons were carried out: 2.5-mm MDCT densitometry versus 0.625-mm MDCT densitometry; 0.625-mm MDCT densitometry compared to pQCT densitometry; same day repeatability of 0.625-mm MDCT densitometry; longitudinal repeatability of 0.625-mm MDCT densitometry on day 0 and day 28 and longitudinal 0.625-mm MDCT densitometry in ovariectomized rats on day 0 and day 28. Comparisons were made using intra-class correlation coefficient (ICC). Examination time per animal was 5 min for MDCT and 30 min for pQCT. Acquisitions of 2.5-mm MDCT had a larger coefficient of variation (CoV) than 0.625-mm acquisitions. MDCT densitometry had good agreement with pQCT densitometry (ICC = 0.85). Same-day MDCT densitometry with 0.625-mm acquisitions had a small CoV (1.61%). MDCT densitometry of non-ovariectomized animals at 28 days showed no BMD change, while MDCT densitometry of ovariectomized animals showed a 13.7 +/- 6.7% BMD reduction at 28 days. Clinical MDCT can reliably and accurately measure rat lumbar vertebral BMD and is much faster than pQCT.     

Predictors of patient education by bone densitometry technologists

OBJECTIVE: This study investigated which factors predict the likelihood of densitometry technologists counseling their patients about osteoporosis prevention. METHOD: Predictors of osteoporosis prevention patient education by bone densitometry technologists were analyzed in a sample of 417 radiologic technologists with ARRT advanced certification in bone densitometry and 158 densitometry technologists, none of whom were ARRT certified in bone densitometry. RESULTS: The regression model accounted for 41% of the variation in reports of bone health counseling. Densitometry technologists with high internal motivation and low personal barriers reported educating their patients about osteoporosis prevention. CONCLUSION: Recommendations for increasing bone health promotion include increasing personal interest through sensitivity training, expanding delivery by promoting models for clinical implementation and creating educational opportunities to strengthen counseling skills.     

Current and innovative methods for noninvasive bone densitometry

This article summarizes a variety of noninvasive techniques for measuring bone density in the clinical setting. Although dual-energy x-ray absorptiometry and quantitative computed tomography are currently the most widely used methods, older techniques such as radiogrammetry and single-photon absorptiometry continue to have research applications, and experimental approaches such as compton scattering and proton activation analysis may be important in the future. The evaluation of bone mass measurement underscores continuing progress in our understanding of bone metabolism and biomechanics, and has provided valuable insight into improvements in the therapy of osteoporosis and other forms of metabolic bone disease.     

Digital bone densitometry. A routine method for evaluating and monitoring bone mineralization

Digitalized bone densitometry is a simple technique for studying bone mineralization which can be performed during the radiological examination. Digitalized bone densitometry was used to estimate the bone mineral content of the third lumbar vertebra in 30 women and 16 men, the neck of the femur in 27 women and 20 men and the second metacarpal in 27 women and 17 men. The results were compared to the data provided by conventional methods. The appearance of the curves, the index of accuracy and reproducibility of the method suggest that it can be used to detect and monitor bone mineralization of patients for a moderate cost.     

Role of photon absorption densitometry of the bone in uremic osteodystrophy

The aim of this investigation is to evaluate the role of bone photonic densitometry in uremic osteodystrophy. Bone mineral content (BMC) and bone density (BD) have been measured in 80 hemodialyzed patients by double photonic emission densitometry. Photonic densitometry shows an higher sensibility to quantitative changes in bone mineral content than metacarpal index (IM). Photonic densitometry is unable to differentiate osteoporosis from osteomalacia; this differential diagnosis can be obtained by radiological analysis: low BD and low IM means osteoporosis, low BD and resorptive changes in cortical bone means osteomalacia and/or hyperparathyroidism. Photonic densitometry is particularly suitable for uremic osteodystrophy follow-up because of its easy repetitiveness and innocuousness and for its close correlation with iPTH variations.     

Osteoporosis. Current techniques and recent developments in quantitative bone densitometry

Knowledge about the proper use and interpretation of bone densitometry studies and an understanding of appropriate medical interventions are not universal among physicians, nor are instrumentation and technical performance of bone density studies of uniformly high quality. Indeed, this deficiency of medical and technical expertise is the principal deterrent to widespread implementation of our recommended clinical applications at this time. Nonetheless, given the current impetus to disseminate information about osteoporosis, to make newer instrumentation more readily available, and to limit the cost of these techniques, we anticipate that our recommendations may soon become standard medical practice.