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The thylakoids of Rhodopseudomonas viridis have been studied by freeze-fracturing whole cells. Depending on growth conditions and treatment before freezing, three different types of particle arrangements in the photosynthetic membrane are reported: a random arrangement, an isometric (quadratic) lattice arrangement with a lattice constant of 12.5 ± 0.8 nm, and a hexagonal lattice arrangement with a lattice constant of 12.5 ± 0.8 nm. [ABSTRACT FROM AUTHOR]

X-ray diffraction experiments with stacks of wet, oriented bacterial thylacoids were performed. The main result is the determination of the electrondensity profile, which is the projection of the electrondensity of the membrane stack onto the stacking axis. Our evaluation procedure takes into account statistical deviations of the quasi-crystalline arrangement of membranes in the stack, differences between the electrondensities in the interthylacoid space and the thylacoid lumen, the statistical distribution of the stack lengths and differences between the mean electrondensity of the stacks and the surrounding medium. Electronmicroscopical determination of parameters describing the statistical lattice deviations in freeze fractured specimens, prepared in the same way as for X-ray diffraction, showed that the influence of membrane undulations can be neglected. They also provided information concerning the validity of the model assumption of lattice deviations of the second kind [27]. The procedure for evaluation which we describe also yielded an absolute calibrated electrondensity scale for the final structure. This profile enabled to be determined the distribution of the membrane components with respect to their position along the stacking axis to be estimated. [ABSTRACT FROM AUTHOR]

Bone density has been assessed during and after radiotherapy of metastases of the spine using quantitative computed tomography (QCT) in 19 patients with osteolytic vertebral lesions. All patients underwent external photon radiation with a total dose of 40 Gy over a period of 4 weeks. Measurements of vertebral mineral density were performed at the beginning, at the end, and 3 months after radiotherapy. In 13 patients with osteolytic metastases, radiotherapy achieved complete release of pain; it was unsuccessful in the remaining 6 patients. Immediately after successful radiotherapy, osteolytic metastases showed a decrease of bone density of 24.7% followed by an increase of 60.6% 3 months later. Normal bone surrounding the osteolysis showed an increase of density at the end and 3 months after radiotherapy. QCT has proved to be a helpful tool in assessing successful radiotherapy of metastases of the spine. [ABSTRACT FROM AUTHOR]

To estimate subchondral mineralisation patterns which represent the long-term loading history of individual joints, a method has been developed employing computed tomography (CT) which permits repeated examination of living joints. The method was tested on 5 knee, 3 sacroiliac, 3 ankle and 5 shoulder joints and then investigated with X-ray densitometry. A CT absorptiometric presentation and maps of the area distribution of the subchondral bone density areas were derived using an image analyser. Comparison of the results from both X-ray densitometry and CT-absorptiometry revealed almost identical pictures of distribution of the subchondral bone density. The method may be used to examine subchondral mineralisation as a measure of the mechanical adaptability of joints in the living subject. [ABSTRACT FROM AUTHOR]