The measurement of the depth of a point source of a radioisotope from gamma ray spectra.

The spectrum of the scattered radiation from a 'point' source of 99Tcm located within a slab of tissue-like material has been studied with a 19-phototube gamma camera, a 7.5 cm x 7.5 cm sodium iodide detector and a Ge(Li) counter. Both backscatter and forward scattered radiation contribute to the spectra observed; 'infinite' backscatter is achieved at a thickness of 8 cm. The scattered radiation can be used to estimate the thickness of the overlying material. The scatter from 133Xe and 51Cr was also measured. The depth of a source could usually be determined to within a few millimetres from the proportion of scatter in the spectrum; it was more accurate with the 51Cr (320 keV) than with the lower-energy photopeaks of the other two isotopes. The variation in the spectrum as the source moved across the field of the gamma camera was recorded.     

Simulation of small-angle x-ray scattering from collagen fibrils and comparison with experimental patterns

Simulation of small-angle x-ray scattering from collagen in healthy and cancerous breast tissue may reveal detailed information on the structural changes in collagen. Collagen fibril is modelled as a cylinder with axially periodic step-function electron density, and packing is approximated by placing the cylinders in small hexagonal bundles. The intensity from a bundle is calculated by summing analytical scattering amplitudes from the cylinders, and intensities from several bundles with varying lattice constants are averaged. Comparisons with more complex models are made to estimate the robustness of the model. The oscillations in the equatorial direction are not significantly affected by added complexity. The relative intensities of the Bragg peaks in the meridional direction can be tuned by modifying the axial electron density distribution. Tests with different fibril radius distributions show that the average radius can be determined with an accuracy of +/-0.5 nm but that the shape of the radius distribution cannot be accurately determined from the scattering patterns. The effect of multiple scattering and the detector point-spread function (PSF) is considered, and the PSF may make a significant contribution to the final slope of the scattering pattern. Comparisons with observed scattering indicate that the model is basically correct at the supra-molecular level.     

X-ray and neutron small-angle scattering of random coil polymer solutions

Small-angle scattering curves of random coil polymer solutions are calculated from the general scattering theory of solutions by making use of a previous calculation of the Yvon-Born-Green integral equation for the radial distribution function of the solute polymer molecules. The calculated scattering function is a monotonously decreasing function of the scattering angle at low polymer concentration, and it has a minimum and a maximum at high concentration, where the polymer interaction is repulsive. For large scattering angle, the reciprocal values of the scattering function increase almost linearly with sin²(θ/2), where θ is the scattering angle. This calculated result is in qualitative agreement with recent experimental results of X-ray and neutron small-angle scatterings of polymer solutions.     

A facility for in vivo measurement of kidney and liver cadmium by neutron capture prompt gamma ray analysis

An in vivo method for the determination of Cd levels in human kidney and liver has been developed. The method allows detection of absolute quantities of Cd in the left kidney and Cd concentration in the liver. The limit of detection of cadmium is 2.5 mg for the left kidney and 1.8 microgram/g (wet weight) for the liver, for a localized dose of 670 mrem. The effects of patient positioning, organ geometry and liver-kidney interference on the measurement have been investigated using an Alderson phantom.     

Study of nanoscale structures in hydrated biomaterials using small-angle neutron scattering

Distribution of water in three classes of biomedically relevant and degradable polymers was investigated using small-angle neutron scattering. In semicrystalline polymers, such as poly(lactic acid) and poly(glycolic acid), water was found to diffuse preferentially into the non-crystalline regions. In amorphous polymers, such as poly(d,l-lactic acid) and poly(lactic-co-glycolic acid), the scattering after 7 days of incubation was attributed to water in microvoids that form following the hydrolytic degradation of the polymer. In amorphous copolymers containing hydrophobic segments (desaminotyrosyl-tyrosine ethyl ester) and hydrophilic blocks (poly(ethylene glycol) (PEG)), a sequence of distinct regimes of hydration were observed: homogeneous distribution (～10 Å length scales) at <13 wt.% PEG (～1 water per EG), clusters of hydrated domains (～50 Å radius) separated at 24 wt.% PEG (1–2 water per EG), uniformly distributed hydrated domains at 41 wt.% PEG (～4 water per EG) and phase inversion at >50 wt.% PEG (>6 water per EG). Increasing the PEG content increased the number of these domains with only a small decrease in distance between the domains. These discrete domains appeared to coalesce to form submicron droplets at ～60 °C, above the melting temperature of crystalline PEG. The significance of such observations on the evolution of micrometer-size channels that form during hydrolytic erosion is discussed.     

Measurement of small-angle photon scattering for some breast tissues and tissue substitute materials

For photon energies encountered in diagnostic radiology the shape of the scattering distributions for low-atomic-number media exhibits peaks in intensity close to the forward direction that are not predicted by conventional theoretical models. The positions and shapes of the peaks depend upon the interatomic and intermolecular configurations of the scatterers. The phenomenon is of particular interest because of its relevance to the understanding and modelling of x-ray imaging processes and the possibility that the peaking may be characteristic of tissue type. In the present study, peaks in the forward scattering distributions have been demonstrated for 19 samples of breast tissue and three tissue substitute materials using a position-sensitive photon detector and a 60 kVp x-ray source. Prominent features were observed for all samples investigated. Large differences were found in the shapes of the distributions between adipose and fibroglandular tissues and only small differences were found between carcinomas and fibroglandular tissues.     

Nuclear resonant scattering of gamma rays--a new technique for in vivo measurement of body iron stores.

A technique for the measurement of body iron utilising nuclear resonant scattering of gamma rays has been developed. 847 keV photons emitted from a gaseous 56MnCl2 source are resonantly scattered from 56Fe present in the body. Measurement is made using large volume Ge(Li) detectors. The spatial uniformity of activation, the sensitivity of the detection system and the limits of detection have been investigated. Measurements were made on a liver phantom. The resonance scattering technique permits determination of normal levels of Fe in the liver with a radiation dose of 2 rem.     

Computed radiography as a gamma ray detector--dose response and applications

Computed radiography (CR) can be used for imaging the spatial distribution of photon emissions from radionuclides. Its wide dynamic range and good response to medium energy gamma rays reduces the need for long exposure times. Measurements of small doses can be performed without having to pre-sensitize the computed radiography plates via an x-ray exposure, as required with screen-film systems. Cassette-based Agfa MD30 and Kodak GP25 CR plates were used in applications involving the detection of gamma ray emissions from technetium-99m and iodine-131. Cassette entrance doses as small as 1 microGy (140 keV gamma rays) produce noisy images, but the images are suitable for applications such as the detection of breaks in radiation protection barriers. A consequence of the gamma ray sensitivity of CR plates is the possibility that some nuclear medicine patients may fog their x-rays if the x-ray is taken soon after their radiopharmaceutical injection. The investigation showed that such fogging is likely to be diffuse.     

The structure of rice dwarf virus determined by small-angle neutron scattering measurements

The structure of rice dwarf virus (RDV) has been investigated by small-angle neutron-scattering measurements using the contrast variation method. The contrast match point gave an RNA content of about 20% by weight. The value of the neutron intensity scattered at zero angle in water divided by the virus concentration yielded a particle weight of 65.2 x 10(6). The data suggest that the viral RNA is located at radii 相似文献   

Quantification of vertical-fiber defect in cattle hide by small-angle light scattering.

Vertical-fiber defect (VFD), an abnormal arrangement of collagen fibers in hides of certain cattle breeds, is still not fully understood. Prior work has been limited to subjective histological examinations from hide biopsies. A device using small angle light scattering (SALS) was used to quantify the collagen fiber orientation of sections taken from hide biopsies. Sections were chosen from the Hereford cattle breed and classified by conventional observation as belonging to either the normal, intermediate, or vertical phenotypes. The vertical fibers occur only in the upper reticular dermis, with the fibers in the lower reticular dermis lying parallel to the plane of the hide in all phenotypes. By SALS the vertical phenotype was found to be significantly different from the normal phenotype, whilst the intermediate phenotype was found to be structurally indistinguishable from the vertical one. No evidence was found for the existence of other phenotypes.     

Observation of the conformation and structure of some liquid-crystal polymers by small-angle neutron scattering

The conformation of the backbone and the structure of the mesogenic groups of some liquidcrystal polymethacrylates and polysiloxanes were determined by small- and low-angle scattering of neutrons. A strong magnetic field aligned the mesomorphic monodomains. For most samples and phases the polymer backbone adopts an oblate shape versus the mesogenic director. The observation of several diffuse spots together with Bragg peaks allows to propose models for the structure of these samples.     

Quantitative measurement of airborne allergens from dust mites, dogs, and cats using an ion-charging device

BACKGROUND: Increasing evidence suggests that children raised with an animal(s) in the house have a decreased risk of becoming sensitized. However, it is not clear whether this phenomenon is related to airborne exposure. OBJECTIVE: To estimate airborne exposure to animal dander and dust mite allergens using a device that can sample large volumes of air silently. METHODS: The device, which uses an ion-charging technique to move air and to collect particles, was run at 1.7 m3/min for 24 h in 44 homes with and without animals. The allergen collected was measured by ELISA for Fel d 1, Can f 1, Der p 1, and Der f 1. RESULTS : Airborne Fel d 1 was present in all homes with a cat (n=27). The quantities measured, i.e. 0.5-20 microg in 24 h, represent 0.01-0.3 microg Fel d 1 inhaled/day at normal breathing rates (20 L/h). Values for houses without a cat were 0.01-0.05 microg inhaled/day. Airborne Fel d 1 correlated significantly with floor Fel d 1 (r=0.58, P<0.001). Results for Can f 1 were similar in houses with a dog, but this allergen was only detected airborne in two houses without a dog. Neither Der p 1 nor Der f 1 (i.e. <0.01 microg) was detected, which represents < or =1 ng inhaled/day during normal domestic activity. During disturbance airborne mite was detected with both the ion-charging device and a filter run in parallel. For cat and mite allergens there was a close correlation between the two techniques (r=0.84, P<0.001). CONCLUSION: Exposure to cat or dog allergen airborne in homes with an animal can be up to 100 times higher than exposure to mite allergen. The results are in keeping with a model where immunological tolerance to animal dander allergens results from high exposure.     

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.     

Experimental comparison of high-density scintillators for EMCCD-based gamma ray imaging

Detection of x-rays and gamma rays with high spatial resolution can be achieved with scintillators that are optically coupled to electron-multiplying charge-coupled devices (EMCCDs). These can be operated at typical frame rates of 50 Hz with low noise. In such a set-up, scintillation light within each frame is integrated after which the frame is analyzed for the presence of scintillation events. This method allows for the use of scintillator materials with relatively long decay times of a few milliseconds, not previously considered for use in photon-counting gamma cameras, opening up an unexplored range of dense scintillators. In this paper, we test CdWO? and transparent polycrystalline ceramics of Lu?O?:Eu and (Gd,Lu)?O?:Eu as alternatives to currently used CsI:Tl in order to improve the performance of EMCCD-based gamma cameras. The tested scintillators were selected for their significantly larger cross-sections at 140 keV ((99m)Tc) compared to CsI:Tl combined with moderate to good light yield. A performance comparison based on gamma camera spatial and energy resolution was done with all tested scintillators having equal (66%) interaction probability at 140 keV. CdWO?, Lu?O?:Eu and (Gd,Lu)?O?:Eu all result in a significantly improved spatial resolution over CsI:Tl, albeit at the cost of reduced energy resolution. Lu?O?:Eu transparent ceramic gives the best spatial resolution: 65 μm full-width-at-half-maximum (FWHM) compared to 147 μm FWHM for CsI:Tl. In conclusion, these 'slow' dense scintillators open up new possibilities for improving the spatial resolution of EMCCD-based scintillation cameras.     

Investigations of the crystallization of polyethylene by means of simultaneous small-angle and wide-angle X-ray scattering

The isothermal crystallization of linear polyethylene fractions was studied by means of simultaneous measurements of wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) employing synchrotron radiation. From WAXS the overall degree of crystallinity x_c was determined. From SAXS, the scattering power Q was evaluated and compared with several different models for the crystallizing system. When the scattering arises solely from the supermolecular structures, such as spherulites, Q is proportional to x_s·x_cL·(1 ? x_cL), where x_s is the fraction of material transformed into such structures and x_cL is the degree of crystallinity within these structures. By comparing x_c with Q it was possible to separate the primary and secondary crystallization and to show that secondary crystallization takes place within the lamellar stacks where the crystals become thicker and the amorphous layers become thinner. The process of recrystallization during annealing of crystalline samples was studied in the same way. Other models were treated in a similar manner.