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At least 811 records · Page 45Linked to original sources
PubMed1979

Bone densitometry using computed tomography. Part I: selective determination of trabecular bone density and other bone mineral parameters. Normal values in children and adults.

Gamma-ray computed tomography (gamma-ray CT), using a special purpose scanner, enables in-vivo quantitative analysis of bone mineralization. Trabecular bone density (TBD), the relative amount of compact bone (bone density, BD) and the total absorption (TA) for a cross-section of the radius are determined from measurements of local linear absorption coefficients. A preliminary study of normal children (n = 49) and adults (n = 34) indicated that TBD is independent of age and sex in the age range 4 to 40 years. DB remains constant throughout childhood but increases after puberty in both women and men. TA is higher for adults than for children, and also higher for men than for women. A correlation between TA and parameters relating to body size indicates a relationship between body weight and bone mass.

Adolescent↗
PubMed2002

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.

Aged↗
PubMed1988

Computerised densitometry of red-free retinal photographs correlated with automatic perimetry.

An image analyser installed in a 16 bit personal computer was used to measure grey levels in red free photographs of normal and glaucomatous eyes. Regional photographic image intensity and density were correlated with Humphrey Field Analyser results for corresponding areas of visual field. Two methods for standardising photographic exposure by histogram equalisation and slide were compared in two groups of eyes from 13 subjects. For histogram equalisation, r2 varied from 0.16 to 0.29 for linear fits in temporal retinal quadrants. For the histogram slide, r2 varied between 0.19 to 0.45 for linear fits. Similar results were found for mean histogram equalised image intensity versus Humphrey Field Analyser global indices: Mean Deviation, (r2 = 0.27) and Pattern Standard Deviation, (r2 = 0.37). For histogram equalised image data, resistant line analysis showed a linear goodness of fit of 0.92 and for histogram slide goodness of fit was 0.97 for upper and 0.87 for lower temporal quadrants.

Color↗
PubMed1975

Cardiac output determinations with ear piece densitometry.

The results of cardiac output determinations by a dye dilution technique were compared using (a) a dichromatic earpiece which was calibrated as a flow-through cuvette, but also permitted automatic computing by virtue of a pressure capsule, and (b) an ordinary flow-through densitometer. Eleven subjects, some with cardio-pulmonary disease, were investigated. Cardiac outputs were systematically overestimated when automatically computed. The results obtained by manual calculation with the ear-piece corresponded more nearly with those derived from the flow-through cuvette, but still with a deviation from the identity line and with a residual standard deviation of 0.8 l/min. Double determinations had a residual standard deviation of 0.7 l/min. Despite its ease of handling, an earpiece densitometer seems to be too unreliable to be suitable for routine use.

Adult↗
PubMed1997

Image analysis of the duodenal endocrine cells in mice with particular regard to optical densitometry.

The endocrine cells in the murine proximal duodenum have been investigated by means of immunohistochemistry and computerized image analysis. Five endocrine cell types were identified, namely secretin-, gastric inhibitory polypeptide (GIP)-, gastrin-CCK-, somatostatin- and serotonin immunoreactive cells. The number of endocrine cells/mm3 epithelial cells was estimated and the cell secretory index (CSI) for different endocrine cell types was determined. Furthermore, the optical density of the cellular immunoreactivity and the immunoreactive area in the cell were determined and an index, cell immunoreactivity content was estimated as the optical density multiplied by the immunoreactive area. It has been suggested that the use of this index might better reflect the cellular peptide/amine content than does the CSI. Serotonin-immunoreactive cells were the predominant endocrine cell type, followed by gastrin/CCK-immunoreactive cells. The numbers of secretin-, GIP- and somatostatin immunoreactive cells were almost identical. All endocrine cell types were present both in crypts and in villi, but were, more numerous in the crypts, except for secretin which was more frequent in the villi.

Animals↗
PubMed1986

Methods and application of bone densitometry in clinical diagnosis.

With the awareness of osteoporosis as a major health problem for an aging population, there is great interest in early recognition and treatment of abnormal bone loss. Effective prevention of bone loss has to occur prior to the occurrence of irreparable damage. Standard radiographic procedures are not sensitive enough for the task. Therefore, a number of alternative procedures to estimate bone loss have been developed over the years, ranging from efforts to quantitate information obtained from radiographic images to sophisticated procedures such as neutron activation analysis or procedures based on the Compton scatter phenomenon. Only two procedures, photon absorptiometry and computed tomography (CT), have emerged as applicable for routine clinical use. In photon absorptiometry the entire bone mineral (cortical and trabecular bone) of a specific skeletal site is measured. CT allows measuring of bone mineral of trabecular or cortical bone alone. Normally, bone mass reaches a maximum in the third decade and then continuously declines. This age-related bone loss is greater in women in whom an accelerated rate of loss occurs at the menopause. When bone density reaches a critical fracture threshold, skeletal fractures occur (spine, hip, and distal long bones). The age at which this critical fracture threshold is reached depends on the maximal bone mass achieved in early adulthood and the rate of loss with increasing age. With the exception of NaF, present-day therapeutic efforts only retard or prevent bone loss but do not significantly add bone mineral to the skeleton. Recognition of high-risk groups and early treatment are therefore required. Absorptiometry, and probably in the future CT, also permit the measuring of bone mineral at sites of fracture with sufficient accuracy and precision to allow an early detection of lower than normal (for age and sex) bone mass, estimating fracture risk, and monitoring of the rate of bone loss by repeated measurements. An operational diagnosis of osteoporosis based on fracture risk has also been attempted from bone mineral measurements. And last, the effect of a drug regimen used to prevent or decrease bone loss can be monitored with these procedures.

Bone and Bones↗
PubMed1987

Mineral content of upper tibia assessed by dual photon densitometry.

Bone mineral content (BMC, g/cm) and bone mineral density (BMD, g/cm2) of the proximal tibia were determined by dual photon absorptiometry (DPA). Measurements just distal to the subchondral plates of the tibia condyles, where the bone structure is predominantly trabecular, proved to give the most consistent results. The precision of BMC measurements in this region, expressed as the coefficient of variation, was 1.1 per cent and of BMD measurements 2.5 per cent. In a cross-sectional study on 63 normal women and men, BMC and BMD showed a decrease with age at a rate of about 8 and 9 per cent per decade, respectively, in women, but not in men. In normal women, BMC of proximal tibia was correlated with BMC of lumbar spine, femoral neck, and femoral shaft, as well as with body weight and height. DPA may be useful in the study of bone reactions, such as in patients undergoing arthroplasty of the knee.

Adolescent↗