1,721,027 research outputs found
Bone Densitometry: Science and Practice
No full textDual-energy X-ray absorptiometry (DXA) scans to measure bone mineral density (BMD) at the spine and hip have an important role in the evaluation of individuals at risk of sustaining an osteoporosis-related fracture and in helping clinicians advise patients about the appropriate use of anti-fracture treatment. Compared with alternative bone densitometry techniques, hip and spine DXA examinations have a number of advantages that include a consensus that BMD results should be interpreted using the World Health Organization (WHO) T-score definition of osteoporosis, a proven ability to predict fracture risk, proven effectiveness at targeting anti-fracture therapies, and the ability to monitor response to treatment. This review discusses the evidence for these and other clinical aspects of DXA scanning. Particular attention is paid to the new WHO FRAX® algorithm, which uses clinical risk factors in combination with a hip DXA scan to predict a patient's 10-year risk of experiencing an osteoporotic fracture. We review the recently published clinical guidelines that incorporate the FRAX fracture risk assessment tool in decisions about patient treatment and discuss the reasons why a quantitative evaluation of fracture risk should become the standard approach to the clinical interpretation of DXA examinations in postmenopausal women and older men
Skeletal Tracer Kinetics: Science and Practice
No full textQuantitative bone scan imaging has a useful role in studies of the pathophysiology of metabolic bone disease and the response of patients to treatment. The advantage of nuclear medicine imaging as a way of studying bone remodelling is that it offers a unique way of measuring bone turnover both for the whole skeleton and in selected localised regions of interest (ROI). This chapter reviews methods of quantifying <sup>99m</sup>Tc-MDP and <sup>18</sup>F-fluoride skeletal tracer kinetics by combining imaging data with blood sampling to measure bone plasma clearance. For studies using <sup>99m</sup>Tc-MDP, we describe three methods of measuring whole-skeleton plasma clearance (K <inf>bone</inf>): (1) The area-under-the-curve (AUC) method based on taking six blood samples between 5 min and 4 h and measuring the plasma concentration of free <sup>99m</sup>Tc-MDP by ultrafiltration. The AUC method requires a simultaneous measurement of glomerular filtration rate (GFR) using <sup>51</sup>Cr-EDTA as a co-tracer. (2) The modified Brenner method, which measures K <inf>bone</inf> by drawing a soft tissue ROI over the adductor muscles and plotting the soft tissue counts at 1, 2, 3 and 4 h against the AUC values at the corresponding time points. (3) The Patlak method based on combining gamma camera measurements of whole-body retention with plasma data and finding K <inf>bone</inf> from the slope of the Patlak plot fitted to the 2, 3 and 4 h data points. Unlike the first two methods, the Patlak plot can also be used to measure regional values of K <inf>bone</inf> for any chosen ROI. Studies of <sup>18</sup>F-fluoride skeletal tracer kinetics are performed using a 60-min dynamic positron emission tomography (PET) scan with measurement of the input function by either direct arterial sampling or using an image-derived input function from the heart, aorta or femoral artery and can be used to measure the net plasma clearance to the bone mineral compartment (K <inf>i</inf> ) at either the spine, hip or humerus. Further studies are required comparing radionuclide measurements with the gold standard of bone biopsy. Nuclear medicine measurements of bone turnover have an established role as a research technique, and there is a need for further studies to examine their role in assessing the pathophysiology of metabolic bone diseases, such as osteoporosis, Paget's disease and renal osteodystrophy, and better understanding the effects of new pharmaceutical treatments at various sites throughout the skeleton.</p
Assessment of tibolone as hormone replacement therapy in the postmenopausal woman
No full textFull text is available to authenticated members of The University of Auckland only.When ovarian failure occurs, oestrogen deficiency may produce a multitude of symptoms and affect many organ systems of the body. A number of women seek medical attention during the climacteric period for relief of menopausal acute symptoms, the most common being hot flushes. However the longterm consequences of oestrogen failure, namely osteoporosis and cardiovascular disease risk, not only have an effect on a woman's general health, but also on her longevity. The evidence suggests that hormone replacement therapy is beneficial both for the relief of the acute problems and the prevention of the longterm sequelae.
Osteoporosis is associated with significant morbidity and mortality, but if it is to be prevented then oestrogen therapy should ideally be commenced perimenopausally and continued for 10 years. Compliance with conventional hormone replacement therapy is poor as there are a significant incidence of side-effects and women do not tolerate monthly bleeding at such an age. The development of non-bleeding forms of hormone replacement therapy will hopefully see greater compliance amongst postmenopausal women.
Tibolone is a synthetic steroid with weak oestrogenic, progestagenic and androgenic properties. It has been shown by previous investigators that it relieves symptoms of oestrogen deficiency. The main aim of this thesis is to address the effect of tibolone on the skeleton, but the genital tract, cardiovascular effects and symptomatology are also investigated.
This is a non-randomised prospective study of 100 normal postmenopausal women, 50 women took tibolone 2.5mg daily and over two years they were compared with 50 women who were matched for months since menopause.
It has been shown that after 2 years treatment with tibolone (n=46) at a dose of 2.5mg daily there was a significant increase in bone mass as measured by dual energy X-ray absorptiometry (DXA) in the lumbar spine of 3% (p< 0.001) and in the neck of femur of 2.5% (p< 0.05) whereas in the control group (n=45) bone loss occurred (spine -3%, p < 0.001; femur - 2.5%, p < 0.001).In the tibolone group the urinary hydroxyproline/creatinine and calcium/creatinine ratios decreased (p < 0.01; p < 0.001) while the serum gla and alkaline phosphatase also decreased (p < 0.01, p < 0.001 respectively) supporting a decrease in skeletal metabolism.
Tibolone, when given in the early postmenopausal years suppresses skeletal metabolism and prevents bone loss in both spine and femur. Tibolone therefore has a potentially important longterm role in the reduction of the incidence of osteoporotic fractures, particularly in view of the compliance that "bleedfree" therapy will encourage
Skeletal scintigraphy and quantitative tracer studies in metabolic bone disease
Get PDFBone scan imaging with the current bone seeking radiopharmaceuticals, the technetium-99m labelled diphosphonates, has dramatically improved our ability to evaluate skeletal pathology. In this thesis, chapter 1 presents a review of the history of bone scanning, summarises present concepts as to the mechanism of uptake of bone seeking agents and briefly illustrates the role of bone scanning in clinical practice. In chapter 2 the applications of bone scan imaging and quantitative tracer techniques derived from the bone scan in the detection of metabolic bone disease are discussed. Since skeletal uptake of Tc-99m diphosphonate depends upon skeletal metabolism one might expect that the bone scan would be of considerable value in the assessment of metabolic bone disease. However in these disorders the whole skeleton is often diffusely involved by the metabolic process and simple visual inspection of the scan image may not reveal the uniformly increased uptake of tracer. Certain patterns of bone scan abnormality have, however, been reported in patients with primary hyperparathyroidism and renal osteo-dystrophy; the present studies extend these observations and introduce the concept of "metabolic features" which are often recognisable in conditions with generalised increased bone turnover. As an aid to systematic recognition of these features on a given bone scan image a semi-quantitative scoring system, the metabolic index, was introduced. The metabolic index allowed differentiation between various groups of patients with metabolic disorders and a control population. In addition, in a bone scan study of patients with acromegaly, it was found that the metabolic index correlated well with disease activity as measured by serum growth hormone levels. The metabolic index was, however, found to be a relatively insensitive means of identifying disease in individual patients. Patients with increased bone turnover will have an absolute increase in skeletal uptake of tracer. As a means of quantitating this uptake the use of bone to soft-tissue ratios derived from the bone scan image by computer was critically evaluated. The technique was shown to be observer dependent and again found to be of limited value due to the large overlap of patient results with those from control subjects. In chapter 3 the use of bone scan imaging in metabolic bone disease has been compared with radiology. Despite the difficulties mentioned above the metabolic index was employed, and the bone scan found to be the more sensitive investigation in primary hyperparathyroidism, renal osteodystrophy and osteomalacia. In osteoporosis, however, the bone scan was often unable to identify disease and radiology remains the investigation of choice. In a further study comparing bone scanning and radiology in Paget's disease, the bone scan was found to be clearly the more sensitive investigation. As a result of the work described in chapter 2 it became apparent that a sensitive means of quantitating absolute bone uptake of tracer could be of diagnostic value. In chapter 4 a promising new quantitative technique is described in which the 24-hour whole-body retention of Tc-99m diphosphonate (WBR) is measured using a shadow-shield whole-body monitor. At 24 hours after injection, diphosphonate has reached a stable equilibrium in bone reflecting skeletal metabolic activity, while tracer in the soft-tissues of the body has been largely excreted via the urinary tract. It was found that this technique provided a sensitive means of detecting patients with primary hyperparathyroidism, osteomalacia, renal osteodystrophy and Paget's disease and that in these conditions all the results from individual patients lay outside the control range. In further studies the WBR technique was shown to be highly reproducible and not subject to any significant technical errors
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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