Biomedical subjects

I Leichter

Publications and source records attributed to I Leichter.

44 records · Page 3Linked to original sources

PubMed1981

The effect of age and sex on bone density, bone mineral content and cortical index.

The density of cancellous bone in the nondominant radius of healthy subjects has been observed by the Compton scattering method as a function of age and sex. The average density for males is higher than for females. In males the density does not change up to the age of 80 years, while in females the density decreases beginning at age 50. A significant decrease in the bone mineral content of the distal radius is observed at earlier ages as measured by the Cameron-Sorenson technique. The average value of the cortical index of the third metacarpal shows some difference between the sexes over the age of 50, the index in males being higher than in the females. Between 30 and 50 years the female cortical index is greater than in the males. Little correlation was found among the three parameters studied, suggesting that they measure different phases of the pathophysiological processes involved in aging bone.

Adult↗

PubMed1980

The effective attenuation coefficient of soft tissue in the presence of Compton scattering from bone: experiments on models.

Calibration methods are investigated for the determination of bone density by the Compton scattering method. The scattered radiation from materials of different densities and dimensions is measured for this purpose. A function for the dependence of the intensity on these parameters is derived and compared with the experimental results. The influence of the surrounding soft tissue is studied by simulation experiments with water. It is found that the 'effective attenuation coefficient' of water for the incident and scattered radiation depends on the thickness of the surrounding water layer itself, as well as on the density of the scattering material. The implications of these findings for the evaluation of bone density measurements are discussed.

Bone and Bones↗

PubMed1977

The early detection of osteoporosis by Compton gamma ray spectroscopy.

The density of the distal end of the radius is one of the parameters used to determine the presence and degree of osteoporosis in patients. In this work the bone density has been determined by measuring the intensity of the Compton scattered photons, since this is proportional to the absolute density of the scatterer, in materials for which Z/A is constant. A collimated beam from a 500 mCi 137Cs source was used and the intensity of the scattered radiation measured at an angle of 90 degrees. The exact point of measurement was determined by a two-dimensional scanning technique. A plastic water phantom was used to calculate the correction needed for absorption and backscatter by the surrounding tissue. Bone density was measured by this method in 50 subjects. A good correlation was found between density of the radius and the degree of morphological change in the vertebrae. In a number of cases a low bone density was discovered without signs of osteoporosis in the spine. These findings were considered indicative of early osteoporotic change, not definable by routine X-ray techniques. This technique may be of value in the follow-up of patients and in controlling the effect of various treatment schedules.

Aged↗

PubMedDate not supplied

Characterization of tissue via coherent-to-Compton scattering ratio: sensitivity considerations.

It is known that the ratio (R) of the detected coherent and Compton scattered photons from bone can be used in order to determine its mineral density. This technique utilizes the dependence of the coherent scattering on the effective atomic number (Z) of the scattering medium. It is generally accepted that a small scatter angle is preferred in order to ensure adequate counting statistics by favoring the detection of more coherent photons. Moreover, it has been assumed that a change in the scatter angle does not affect the sensitivity of the measurement. Our theoretical calculations for 60-keV photons and for the range of Z that corresponds to trabecular bone, indicate that increasing the scatter angle results in a stronger power dependence of the measured ratio on Z. This implies that by increasing the scatter angle, smaller changes in the mineral density can be detected, thus improving the sensitivity of the measurement. This effect was investigated experimentally by using a collimated beam of 59.54-keV photons from Am-241 (44.4 GBq) and a collimated intrinsic germanium detector. Solutions of K2HPO4 with different concentrations were used in order to simulate trabecular bone. The scatter spectra were recorded for all solutions at six scatter angles between 37 degrees and 98 degrees and the value of R was computed for each spectrum. The sensitivity of the measurement, evaluated from these experiments increased, with the increase of the scatter angle.

Americium↗

PubMedDate not supplied

The effect of the momentum transfer on the sensitivity of a photon scattering method for the characterization of tissues.

The ratio of coherent to Compton photon scattered by a tissue-like material depends on its effective atomic number. This ratio can, therefore, be used for the in vivo characterization of tissues. The intrinsic sensitivity of this measurement is defined as the change in the coherent-to-Compton ratio for a given change in the atomic number. The effect of the scatter angle on the sensitivity has already been described by us in a paper recently submitted to this journal. In this study, the dependence of the sensitivity on the energy of the incident photons is investigated in two ways. The first approach is quasitheoretical and is based on computations of the cross sections of the coherent and Compton scattering for various energies. The second approach is experimental and it involves the measurement of the scatter ratio from a series of K2HPO4 solutions for three primary photon energies: 60, 81, and 140 keV. The combined effect of both the photon energy and the scatter angle on the sensitivity can be described by a single parameter which is the momentum transfer. It is concluded that for the limited range of the atomic numbers which apply to trabecular bone (8 less than or equal to Z less than or equal to 11) the momentum transfer reflects completely the effect of the scatter angle and photon energy on the sensitivity.

Elementary Particles↗

PubMedDate not supplied

Quantitative assessment of bone mineral by photon scattering: accuracy and precision considerations.

A method to determine the bone mineral density of the calcaneum has been reported earlier by our laboratory. In this method, the calcaneum is irradiated by a 60-keV photon beam from 241Am source and both the coherent and Compton scattered photons are detected by a high-purity Ge detector. The bone mineral density is determined by measuring the ratio of coherent-to-Compton scattered photons. The accuracy and the precision (in vitro) of the method are reported in this paper. The accuracy was determined to be 5%. This was obtained by comparing the bone mineral density values of cadaver calcanea measured directly by Archimedes' volume displacement method with the values measured by the scattering method. The precision was determined to be 3% by measuring the bone mineral density of a calibration phantom intermittently over a ten-month period by the scattering method.

Bone and Bones↗

PubMedDate not supplied

Quantitative assessment of bone mineral by photon scattering: calibration considerations.

The ratio of the coherent-to-Compton photons scattered from bone can be used to measure its mineral density. Conversion of this ratio (R) to bone mineral density (BMD) requires calibration using bone simulating phantoms. The widely used aqueous solution of K2HPO4 proved unsatisfactory for calibration purposes when using the coherent-to-Compton technique. These solutions differ markedly in their scatter spectra and composition from trabecular bone. In this study a new and more realistic series of phantoms is proposed which simulates well the trabecular bone of the calcaneum. These phantoms are made of bone ash suspended in white petrolatum in varying concentrations. A calibration curve has been established using these phantoms with a range of BMD values of 0 to 347 mg/cm3. The scatter spectra, and range of R values and BMD of these phantoms are in very good agreement with those of real trabecular bone. A measuring device has been built for the determination of the BMD of the calcaneum by using the established calibration curve.

Biophysical Phenomena↗

PubMedDate not supplied

Progressive bone loss during long-term home total parenteral nutrition.

Metabolic bone disease occurs in patients receiving prolonged home total parenteral nutrition (HTPN). We studied bone-mass status in 10 patients (seven males, three females, age 19-66 years) who had been receiving HTPN for 0 to 67 months (mean 24 months), mostly for short-bowel syndrome. Four patients had spinal osteoporosis on radiograms. The density of various bone components at the wrist was measured noninvasively using a novel technique based on Compton scattering effect. The density of the cancellous and cortical bone was decreased in nine and six patients, respectively. During a follow-up period of up to 19 months, a further significant decrease in the density of both bone components was found. We conclude that prolonged HTPN is associated with an ongoing bone diminution, affecting mainly the cancellous bone.

Adult↗