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At least 757 records · Page 42Linked to original sources
PubMed1983

[Densitometry and fetal superficial cell count in the amniotic fluid for the determination of fetal lung maturity].

It was shown that a spectrophotometric investigation of the amniotic fluid for the determination of fetal lung maturity can be achieved with a photometer of the wave length 644 nm (CD) and 623 nm (HG) in conjunction with a count of superficial cells. In a small number of investigations the combination of spectrophotometry and fetal cell count is a sufficiently accurate method to determine fetal lung maturity.

Amniotic Fluid↗
PubMed1991

[Lens changes following pneumatic retinopexy: preliminary results of linear densitometry image analysis of Scheimpflug photographs two months after operation].

The small degree of morbidity and a better postoperative visual acuity are the advantages of pneumatic retinopexy in comparison to encircling procedures in the treatment of retinal detachment. The injection of air or gas into the vitreous cavity can theoretically induce a cataract postoperatively. Two months after pneumatic retinopexy (SF6-gas) Scheimpflug photography and microdensitometric evaluation of the negative were performed on 22 pairs of phacic eyes showing changes in the transparency of the lens. The deterioration of transparency in the operated eye was small but higher than that of the non-operated eye. Due to the short follow up period no prognosis is possible as to the future lens transparency changes.

Cataract↗
PubMed1955

Electron densitometry of stained virus particles.

Methods are described for determining the relative mass of particles in electron microscope specimens through the measurement of photographic densities in recorded images. These methods were applied to a quantitative study of the amounts of electron stains that could be associated with the particles of tomato bushy stunt virus (BSV) and tobacco mosaic virus (TMV). In the pH range above 2 where the viruses are stable, the amount of stain absorbed is too small to produce adequate contrast in the electron microscope. Maximum stain absorption was achieved at pH about 1 where with several reagents and combinations of reagents the mass of BSV could be increased to about four times that of the unstained particles. Optimum results were obtained with phosphotungstic acid alone or in combination with Pt, Th, or La ions. Since the pH conditions for high stain absorption are normally destructive, morphology is satisfactorily preserved only when the phosphotungstic acid is applied in concentrations of 10 per cent or greater or when the use of destructive reagents is preceded by a preliminary fixation under mild conditions. Maximum staining of TMV increased the mass of the particles to about two times that of the unstained. Estimates of the mass of heavily stained BSV particles indicate that their density is 3.3 gm./cm.(3) The high internal hydration of BSV probably accounts for the greater stain absorption and penetration compared to those of TMV which has very low or zero internal hydration. Anomalous images resulting from the use of electron stains are shown and discussed.

Coloring Agents↗
PubMed1955

The variation in the corpuscular hemoglobin concentration in the human red cell, as measured by densitometry.

This paper deals with measurement of the hemoglobin concentration in individual human red cells, the concentration being measured as a function of the optical density, at 5461 A, of the central part of the cell in its spherical form. A number of technical difficulties, principally concerned with the effects of focus, have been met with, and these are described in detail. The results show that the coefficient of variation of the hemoglobin concentration is relatively small (about 5.5 per cent) in the case of fresh human red cells in ACD solution, that the coefficient of variation is almost doubled when the red cells have been stored for 6 weeks at 4 degrees C. or when heparin is used as an anticoagulant instead of ACD solution, but that the average hemoglobin concentration is substantially the same in all three cases. The increase in the coefficient of variation found when the red cells have been stored or when heparin is used is probably due to volume changes, some cells shrinking while others swell.

Citric Acid↗
PubMed1979

Compton scatter densitometry in cancellous bone.

A single-source low-energy Compton densitometer has been used to investigate the effects of multiple scattering on density determinations. The relative electron density and mass density were determined in samples of known density, and in samples of human cancellous bone tissue. The influence of sample diameter on the measured relative electron density of known samples was investigated. The measured value was strongly dependent on the diameter and the density range of the sample. The bias inherent in the density determination which is attributable to multiple scattering and attenuation in human femoral bone was evaluated, and a correction for these effects is suggested for clinical measurements.

Bone and Bones↗
PubMed2004

High resolution MR based polymer dosimetry versus film densitometry: a systematic study based on the modulation transfer function approach.

Precise methods of modem radiation therapy such as intensity modulated radiotherapy (IMRT), brachytherapy (BT) and high LET irradiation allow for high dose localization in volumes of a few mm3. However, most dosimetry methods-ionization chambers, TLD arrangements or silicon detectors, for example-are not capable of detecting sub-mm dose variations or do not allow for simple dose imaging. Magnetic resonance based polymer dosimetry (MRPD) appears to be well suited to three-dimensional high resolution relative dosimetry but the spatial resolution based on a systematic modulation transfer function (MTF) approach has not yet been investigated. We offer a theoretical construct for addressing the spatial resolution in different dose imaging systems, i.e. the dose modulation transfer function (DMTF) approach, an experimental realization of this concept with a phantom and quantitative comparisons between two dosimetric systems: polymer gel and film dosimetry. Polymer gel samples were irradiated by Co-60 photons through an absorber grid which is characterized by periodic structures of different spatial period (a), the smallest one at width of a/2 = 280 microm. The modulation in dose under the grid is visualized via calibrated, high resolution, parameter-selective (T2) and dose images based on multi-echo MR imaging. The DMTF is obtained from the modulation depth of the spin-spin relaxation time (T2) after calibration. Voxel sizes below 0.04 mm3 could be achieved, which are significantly smaller than those reported in MR based dose imaging on polymer gels elsewhere, using a powerful gradient system and a highly sensitive small birdcage resonator on a whole-body 3T MR scanner. Dose modulations at 22% of maximum dose amplitude could be observed at about 2 line pairs per mm. The polymer DMTF results are compared to those of a typical clinical film-scanner system. This study demonstrates that MR based gel dosimetry at 200 microm pixel resolution might even be superior, with reference to relative spatial resolution, to the results of a standard film-scanner system offering a nominal scan resolution of 200 microm.

Calibration↗
PubMed1994

Body composition in white adults by dual-energy x-ray absorptiometry, densitometry, and total body water.

Percent body fat (%BF) and fat-free mass (FFM) were determined in 151 adults from the Fels Longitudinal Study by total body scans with a Lunar DPX (DXA), by underwater weighing and residual lung volume with a two-compartment model using body density (Dens), and total body water (TBW) using deuterium dilution. For the DPX, the medium scan mode ensures precision up to 100 kg body wt and for a ratio of weight to stature < or = 0.7214. Because of these specifications, 15% (n = 23) of the original sample of 151 were excluded. Results for 78 women and 50 men are presented. %BFTBW was significantly (P < 0.05) less than %BFDens in women (mean difference 2.7 +/- 4.2%) and %BFDXA in men (mean difference 2.2 +/- 4.3%). No other significant intermethod differences were observed for %BF and FFM estimates. Pairwise regressions showed the lowest SEEs for %BFDens regressed vs %BFDXA (2.3% for men, 3.2% for women) and for FFMDens vs FFMDXA (2.2 kg for men, 1.9 kg for women). For each sex, reliability analyses and limits of agreement for body composition estimates showed less agreement between TBW and either Dens and DXA than between Dens and DXA.

Absorptiometry, Photon↗
PubMed1996

Predicting body composition by densitometry from simple anthropometric measurements.

New equations have been developed to predict body fat (percent BF) calculated from body density measured by underwater weighing from simple anthropometric measurements, using stepwise-multiple-regression analysis in 63 men and 84 women. Log10 sum of four skinfold thickness explained 80.1% (SE = 3.8) of variance of percent BF in men and 76.4% (SE = 4.6) in women. Alternative equations using limb lengths instead of height may be valuable for epidemiologic and clinical work, with particular advantages for the chair- or bed bound, for whom no previous predictive equations existed. Five equations combining triceps-skinfold thickness with other anthropometric measurements explained > 80% (men) and 77% (women) of variance. The most powerful prediction was from waist circumference and triceps-skinfold thickness, which explained 86.6% (SE = 3.2) of variance of percent BF in men and 79.0% (SE = 4.0) in women. Percent BF for men = 0.353 waist (cm) + 0.756 triceps (mm) + 0.235 age (y) - 26.4; for women = 0.232 waist (cm) + 0.657 triceps (mm) + 0.215 age (y) - 5.5. The equations were tested in a separately studied validation sample of 146 men and 238 women aged 18-83 y. Skinfold-thickness measurements continued to give good predictions of mean body density, but with significant bias at extremes of body fat and age. The most robust prediction with the least bias was from waist circumference adjusted for age. Percent BF for men = 0.567 waist (cm) + 0.101 age (y) - 31.8; and for women = 0.439 waist (cm) + 0.221 age (y) - 9.4.

Adipose Tissue↗
PubMed1975

Preparation of superior thin-layer chromatograms for quantitative in situ densitometry by nonequilibrated development. I. Trisulfapyrimidines: sulfadiazine, sulfamerazine, and sulfamethazine.

A method of obtaining controlled nonequilibrated horizontal plate development by employing a developing system open to room atmosphere is described and compared with other plate-developing techniques. Nonequilibrated plate development produced spot configurations with the precise physical outline and densitometric distribution needed for optical scanning.

Chromatography, Thin Layer↗
PubMedDate not supplied

Measurement of percent oxyhemoglobin by optical densitometry in perfluorocarbon supplemented blood.

A new generation of perfluorocarbon emulsions is being clinically evaluated as erythrocyte substitutes. However, the effect of perfluorocarbon emulsions on optical densitometric measurements of percent oxyhemoglobin (%O2Hb) has not been fully characterized. The purpose of this study is to quantify the effect of blood perfluorochemical concentration and hematocrit (Hct) on %O2Hb measurements. The authors hypothesize that perfluorocarbon emulsions affect the accuracy of %O2Hb measurements, and that the effect of perfluorochemical concentration and Hct on these measurements can be mathematically described. Porcine blood was used in this experiment. Blood with a Hct of 18% or 9% was mixed with a perfluorocarbon emulsion (Oxygent [AF0142]; Alliance Pharmaceutical Corporation, San Diego, CA). The concentrations tested were 0 g (Group I; n = 69 measurements for a Hct of 18%, and n = 35 measurements for a Hct of 9%), 0.73 g (Group II; n = 47 at 18%, n = 33 at 9%), 1.45 g (Group III; n = 46 at 18%, n = 30 at 9%), and 2.90 g (Group IV; n = 45 at 18%, n = 31 at 9%) of perfluorochemical per deciliter of blood (g PFC/dl). A tonometer was used to establish a range of oxygen tensions within each group while maintaining physiologic pH and PCO2. Error in %O2Hb measurements increases with higher perfluorochemical concentrations and lower Hct values. These errors in %O2Hb measurements are predictable; as such, an equation for correcting %O2Hb measurements in perfluorocarbon supplemented blood can be generated.

Animals↗
PubMed1985

Parathyroid adenomas and hyperplasia. Dual radionuclide scintigraphy and bone densitometry studies.

Dual radionuclide imaging of the neck (Tc-99m pertechnetate and TI-201 thallous chloride) was performed in 22 patients with chemical evidence of hyperparathyroidism (elevated blood calcium and parathormone [PTH] levels). Of these, 19 of 22 had localization of a TI-201 "excess" area on radiothallium-radiotechnetium subtraction images. In 13 patients who have had operative confirmation at this writing, the dual radionuclide imaging was positive in 12 (12/13 = 92.3%). One patient had two parathyroid adenomas, both of which were seen on the images; thus, overall detection was 13 out of 14 or 92.8%. The parathyroid adenomas visualized weighed from 0.06 to 3.0 g; the one not detected weighed 0.25 g. In three patients with parathyroid hyperplasia secondary to renal disease, the subtraction imaging detected eight of 12 glands (66.7%). The forearm bone mineral content and bone density were determined in eight patients with parathyroid adenomas; results were abnormally low in five of these eight. One of the three patients with secondary hyperparathyroidism had an abnormally low radial bone mass. The combination of dual radionuclide imaging and radial bone mass determination may present a useful approach in both localizing abnormal parathyroid tissue and in examining its functional consequences.

Adenoma↗