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At least 1,153 records · Page 64Linked to original sources
PubMed1997

Lung density for assessment of hydration status in hemodialysis patients using the computed tomographic densitometry technique.

The density of the lung reflects the total mass of fluid, air, and dry lung tissue per unit volume of the lung. Lung density can be measured by evaluation of attenuation of an electron beam with computed tomography (CT). This technique has been shown to be sufficiently reliable and sensitive to distinguish normal from abnormal lung water. The aim of this study was to find out whether lung density properly reflects the hydration status in hemodialysis patients in comparison with other standard methods. Fourteen hemodialysis patients, with an ultrafiltration ranging from 0.3 to 4.5 liters per session, underwent CT measurements of lung density, ultrasonographic measurements of the diameter of the inferior vena cava after quiet expiration (IVCe) and quiet inspiration (IVCi), and measurements of the hematocrit and plasma levels of the biochemical hydration markers cyclic guanosine monophosphate (cGMP) and atrial natriuretic peptide (ANP). These measurements were performed before and 3.5 to 4 hours after termination of dialysis. Quantitative estimates of lung density were obtained within pixels with CT numbers ranging between -1000 and -100 Hounsfield Units (HU), and compared with normal data from 18 normal controls. In normal controls, the lung density ranged from -800 to -730 HU. In hemodialysis patients, lung density was significantly higher than normal before dialysis (-678 +/- 96 HU, P < 0.01) and significantly decreased after dialysis (-706 +/- 92 HU, P < 0.05), indicating a decrease in fluid content of the lung. The density was normalized in 5 patients. A significant correlation was found between lung density and IVCe both before and after dialysis (r = 0.8, P < 0.01 for both). Change in density was significantly correlated to amount of ultrafiltration (r = 0.67, P < 0.01) and percent change in blood volume (r = 0.63, P < 0.05), indicating that lung density is greatly affected by changes in the extracellular fluid volume, mainly the intravascular volume. In conclusion, lung water reflects the hydration status in hemodialysis patients and can be monitored by measuring the lung density by CT. Accordingly, normalization of lung density can help to achieve a proper dry weight in these patients.

Adult↗
PubMed2003

Precision of bone densitometry measurements: when is change true change and does it vary across bone density values?

The precision error of the bone densitometer is used to interpret significant change in bone mineral density (BMD) in serial studies. The precision error can be expressed as standard deviation (SD) or coefficient of variation (CV). The aims of this study are to determine the precision error over a range of BMD values and to demonstrate the application of the precision error in clinical practice. A bone phantom was used consisting of a perspex block with eight compartments containing varying amounts of hydroxyapatite powder to simulate a range of bone densities. The block was scanned 21 times and manual regions placed over each compartment to measure the BMD in each compartment. There were no significant differences in the variances or SD for all eight compartments, that is, over the range of BMD normally encountered in clinical practice. However, the calculated CV show a progressive fall in values as the BMD rises. Therefore, the SD should be used to calculate significant BMD change. In a practise with quality control procedures in place to detect calibration drift and with appropriately trained personnel, a change of approximately 0.05 g/cm2 is generally regarded as being a significant change at a 95% confidence level.

Absorptiometry, Photon↗
PubMed2001

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.

Absorptiometry, Photon↗
PubMed1976

[Mineral content of bone in long-standing diabetes: densitometry of "diabetic osteopathy" (author's transl)].

Using 125I-photon absorption, skeletal mineral content was measured in 57 diabetics requiring insulin. Average age was 33 years, mean duration of diabetes 19 years. Abnormally reduced mineral content was detected in ten of 21 males and 11 of 36 women. This finding is interpreted as being a late complication of diabetes. Pathological fractures were not seen and there were very few complaints referable to the skeletal system.

Adolescent↗
PubMed1976

[Coronary flow measurements, using cine densitometry. Results using a multiple detector method. I. Normal flow values in healthy and stenosed coronary arteries during rest (author's transl)].

Coronary blood flow was measured by a cine densitometric method using a newly developed system incorporating computer data analysis. The first results concerning front and wave velocity of a selectively injected contrast bolus are reported. Average absolute flow volumes in the right coronary artery are 114 ml. per minute, in the left coronary artery, 88 ml per minute (RIVA = 52 ml/min., RC = ml/min.). There is good agreement with the results of dye dilution and isotope wash out techniques, but the latter are more complicated and less easily reproduced and therefore less suitable for routine use. The results are critically evaluated.

Absorptiometry, Photon↗
PubMed1978

[Coronary flow measurements with cine densitometry. II. Quantitative determinations of flow velocities and flow volumes through severe coronary stenoses during rest (author's transl)].

The normal flow values through healthy or moderately narrowed coronary arteries, which had been determined by a new method of cine radiography, together with a computer, were published in this Journal in 1976. In the present paper we report the results of further studies of flow velocity and flow volume through high-grade coronary artery stenosis of severity III and III--IV. Compared with the results obtained on normal and mildly stenosed arteries, measurements at rest through severely stenosed coronaries showed an almost constant flow. The first results on aorto-coronary vein graft measurement are described.

Absorptiometry, Photon↗
PubMed1979

[Computer tomographic densitometry of human blood. The effect of absorption by parenchymatous organs and effusions (author's transl)].

In vitro measurements of human blood with varying haemoglobin and plasma concentrations have shown a linear relationship between haemoglobin concentrations and attenuation values. A change of haemoglobin content of 1 g/100 ml. blood produced and equivalent density change of 1.5 HU. Attenuation of normal blood is between 55 to 75 HU, that of plasma about 33 HU. Transudates with a protein concentration of less than 5 g/100 ml. show an attenuation value of less than 26 HU. It is therefore possible to indicate the presence of effusions by computer tomography. The effect of the composition of the blood on the attenuation produced by parenchymatous organs is discussed. It is concluded that attenuation values of organs is not seriously affected by even severe haematological changes.

Absorptiometry, Photon↗
PubMed2005

[Analysis of the static pressure volume curve of the lung in experimentally induced pulmonary damage by CT-densitometry].

PURPOSE: To study quantitative changes of lung density distributions when recording in- and expiratory static pressure-volume curves by single slice computed tomography (CT). MATERIALS AND METHODS: Static in- and expiratory pressure volume curves (0 to 1000 ml, increments of 100 ml) were obtained in random order in 10 pigs after induction of lung damage by saline lavage. Simultaneously, CT acquisitions (slice thickness 1 mm, temporal increment 2 s) were performed in a single slice (3 cm below the carina). In each CT image lung segmentation and planimetry of defined density ranges were achieved. The lung density ranges were defined as: hyperinflated (-1024 to -910 HU), normal aerated (-910 to -600 HU), poorly aerated (-600 to -300 HU), and non aerated (-300 to 200 HU) lung. Fractional areas of defined density ranges in percentage of total lung area were compared to recorded volume increments and airway pressures (atmospheric pressure, lower inflection point (LIP), LIP*0.5, LIP*1.5, peak airway pressure) of in- and expiratory pressure-volume curves. RESULTS: Quantitative analysis of defined density ranges showed no differences between in- and expiratory pressure-volume curves. The amount of poorly aerated lung decreased and normal aerated lung increased constantly when airway pressure and volume were increased during inspiratory pressure-volume curves and vice versa during expiratory pressure-volume loops. CONCLUSION: Recruitment and derecruitment of lung atelectasis during registration of static in- and expiratory pressure-volume loops occurred constantly, but not in a stepwise manner. CT was shown to be an appropriate method to analyse these recruitment process.

Absorptiometry, Photon↗
PubMed1992

[Use of computer-assisted image analysis for the detection of immunohistochemical receptor status in breast cancer. Immunohistochemical densitometry receptor analysis--IRDA].

A method for the evaluation of the immunohistochemical staining score of steroid receptors in breast cancer using computer-based image analysis is presented. The optical density of tumour cell nuclei was measured using kryostat sections and, using a control section as reference, an objective threshold for specific staining was defined. In intensively stained sections, a good correlation with visual scoring was achieved, but in 9 out of 16 sections, which were regarded as receptor-negative by visual scoring, a specific receptor-positive staining was demonstrated by image analysis. Next to the percentage of positive cells (PP) and the mean staining intensity (SI), a histogram of the receptor concentration in positive nuclei was calculated. The method allows, besides an objective evaluation and documentation, an exact definition of a threshold for specific receptor measurement and furthermore shows the pattern of receptor concentration in the tumour cell nuclei. Hence, the method could contribute towards a more widespread use of immunohistochemical receptor analysis.

Breast↗
PubMed1993

[Stress fractures of the navicular bone--biomechanical and densitometry studies].

One of the most important pathogenetic mechanisms regarding stress fractures of the navicular bone lies in the hyperpronation movement of the foot. For recording the impacts of the pronation movement on the talonavicular joint, stress and pressure experiments are carried out and the radii of curvature as well as the bone density are measured. The stress experiments show a rotation movement of the talar head in a medioplantar direction of about 20 degrees. The radii of curvature of the articulating joint surfaces do not differ to a great extent. A possible incongruency in the joint therefore has to be attributed to the rotation movement of the talus during pronation of the foot. The pressure experiments show a very irregular distribution of pressure in the joint presenting a lateral and medial pressure maximum. Fractures preferably occur in the area in between these maxima. Areas of high subchondral bone density in the densitometric results are found in the central part of the talar head as well as in the medial part of the navicular bone. Within the functional adaptation the distribution of bone density expresses the rotation movement of the talus during pronation of the foot.

Absorptiometry, Photon↗
PubMed1992

[Structure of the palmar plate of the proximal interphalangeal joint with reference to the typical injury pattern in hyperextension trauma of the finger. A morphometric, densitometry and histologic study].

The palmar plates of the PIP of the fingers are examined in 43 hands. Apart from macroscopic morphometric studies special attention is paid to the density of bone in the areas of insertion, measured with the help of a computerized image analysing system. Especially the distal area of insertion in the basis of the medial phalanx shows a low density of bone. The consequent low adaptation to stress explains clinical findings, describing most frequent osseous ruptures of the palmar plates in case of hyperextension injuries to the fingers. The fibrous structure of the palmar plate is studied in histological sections. A palmar layer of transversally running collagenous fibres, as well as a medial layer of diagonally and a dorsal layer of longitudinally running fibres can be differentiated. The distal area of the palmar plate mostly consists of transversal, the proximal area of longitudinal collagenous fibres. Therefore a hyperextension stress, hitting the fibres in a right angle distally, cannot be neutralized sufficiently. This result is closely linked to clinical observations describing mostly distal ruptures of the palmar plate in spite of its proximal region being of weaker structure.

Athletic Injuries↗
PubMed1994

[Diagnostic value and interpretation of imaging bone densitometry based on quantitative CT].

Quantitative CT of the axial skeleton (aQCT) may serve as an example of the evaluation and interpretation of bone densitometric data as it is the only state-of-the-art technique with valid longitudinal observations. The value of bone density measurements in interindividual cross sections refers to a grading derived from a representative reference population and provides an evaluation of fracture risk. The presence and rate of any bone loss can only be evaluated in an intraindividual longitudinal follow-up. Adequate follow-up for trabecular bone requires at least 3 to 5 years intervals to discriminate between different loss rates. Bone losses induced by steroid therapy or immobilisation may have faster kinetics apparent within months; bone density increase due to hormone substitution may be significant after one to two years. Morphological data allow critical evaluation of the quantitative measurements, eliminating false values and differentiating between rarefying and destructive osteopenia.

Absorptiometry, Photon↗
PubMed1993

[Native radiologic staging of osteoporosis--CT densitometry of lumbar vertebral spongiosa. A correlation study].

Lumbar spine radiographs in 47 patients with manifest or clinically suspected osteoporosis were evaluated, using a staging system, and correlated to quantitative computed tomography (QCT) of lumbar vertebrae. The accuracy of osteoporosis assessment, obtained with plain film analysis, was 60%, the sensitivity 67%, the specificity 56%. Statistical correlation showed high standard deviation of each of the QCT-mean values according to the respective stage groups, and altogether poor linear correlation between increasing morphological stages of osteoporosis and decreasing QCT-values. As our results show plain film differentiation of normal from reduced trabecular bone mineral content is unreliable, even by use of a staging system. The diagnostic value of spine radiographs therefore remains limited to demonstration of advanced osteoporotic changes.

Absorptiometry, Photon↗