Effective energy resolution and scatter rejection in nuclear medicine.

All available imaging devices in nuclear medicine have finite energy resolution. This leads to inclusion of scattered radiation, which in turn degrades the image quality. Different scatter correction schemes therefore try to eliminate the effect of scattered radiation. On the other hand, improvement of the camera's intrinsic energy resolution would reduce the amount of detected scattered radiation as well. A simple model was developed in order to simulate the influence of the energy resolution on the camera response. It is shown that improvement of the energy resolution and scatter correction schemes have a similar effect on the point spread function. On this basis, it is suggested that 'effective energy resolution' be used as a new measure for the effectiveness of scatter correction schemes. As an example, this is done for energy-weighted acquisition (EWA), a scheme wherein each event contributes imaging information according to a real-valued, energy-indexed weighting function.

The pH dependence of SO2 damage to lichens.

In order to determine the influence of the hydrogen-ion concentration on the damage exerted to lichens by sulfur dioxide gas, thalli of the species Hypogymnia physodes and Xanthoria parietina were submerged in buffer solutions of pH 2 to pH 8 and subsequently exposed to SO2 gas. Net photosynthesis was employed as a criterion of vitality.The degree of damage to the lichens after exposure to 4 mg of SO2/m3 air for 14 hrs is dependent on the pH of the buffer solutions. Hypogymnia physodes shows the least damage at pH 7, Xanthoria parietina at pH 5 to pH 7. The degree of damage increases with increasing acidity. After exposure to SO2 gas at pH 3 no apparent photosynthesis is achieved.The different degrees of impairment are due to the fact that the concentration of the toxic products, resulting from the reaction of SO2 and water, is dependent on the pH value.The mere shift of the pH into the strong acid range of pH 3 and pH 2 damages the lichens with Xanthoria parietina being more seriously damaged than Hypogymnia physodes. Basicity, however, is already harmful to the lichens under test in the low range of pH 8. Here Xanthoria parietina is less affected than Hypogymnia physodes.

Statistical analysis of the lichen vegetation of an avenue in freiburg (South-West Germany), with regard to injurious anthropogenous influences.

This paper describes the epiphytic lichen vegetation on maple trees along an 1.1-km avenue leading from the outer suburbs of Freiburg toward the city center. A special aim of this investigation was to examine the variation in the coverage by lichens altogether and by each lichen species as a function of increasing distance from the city. It required very accurate quantitative recording methods, including the "method of hits" and other statistical techniques. The coverage both of total trunk surface and of sectors facing different directions increases with increasing distance from the city. The distribution pattern of SO2 pollution in winter, especially under certain weather conditions, e.g., during winter highs with very high SO2 concentrations, implies a negative correlation between the amount of SO2 pollution and the total percentage of lichen cover. An influence of factors specific to urban climate and traffic emissions is neglegible. The stress caused by increasing immission from outer suburbs towards the city is also indicated by the decline in coverage by the lichens of foliaceous growth form, the increase in coverage by green algae, and the lichens of crustaceous growth form, especially by the resistant Lecanora conizaeoides. The degree of lichen cover changes with exposure. The differences between the four exposure zones may be caused by climatic differences.

CO2-Gaswechsel-Untersuchungen zur SO2-Resistenz von Flechten.

The SO2 resistance of 12 lichen species with different growth forms and taken from different sites was investigated. The thalli were either exposed to different concentrations of SO2 gas (concentration at entry into the cuvette: 0.5; 1.0; 2.0 and 4.0 mg SO2/m3 air) or treated with Na2S2O5 solutions of differing concentration and pH. As a viability criterion the CO2 exchange of the thalli was measured with an infrared gas analyzer before and immediately after SO2 exposure and subsequently at intervals of several weeks. In some cases the chlorophyll content was also determined. 1. Species-specific differences were clearly apparent in the SO2 gas-exposure experiments. The influence of SO2 on net photosynthesis and dark respiration in the most sensitive species was detectable after exposure to 0.5 mg SO2/m3 for 14 h in a fully hydrated state. The photosynthetic intensity of Lobaria pulmonaria was actually irreversibly damaged. In contrast, the most resistant species survived a treatment with 4 mg SO2/m3 for the same length of time with little or no permanent impairment of their CO2 exchange. The reaction of the lichen species investigated to the above treatment allows us to arrange them in decreasing order of resistance: Xanthoria parietina (most resistant), Parmelia scortea, Parmelia acetabulum, Hypogymnia physodes, Parmelia saxatilis, Platismatia glauca, Labaria pumonaria, Parmelia stenophylla, Evernia prunastri. The most sensitive species, Evernia prunastri, is characteristically a fruticose lichen. Lichens with this growth form are known from field studies to be especially sensitive. 2. Examples of the same species (Parmelia saxatilis, Lobaria pulmonaria) can vary in their SO2 resistance according to their growing site. Morphological and anatomical characteristics (thallus and cortex thickness) may cause these differences. 3. The sensitivity of the lichens to SO2 is closely dependent upon their moisture status. When the water potential is lowered the SO2 uptake is reduced and with it the injury. Dried thalli survive high SO2 concentrations in their surroundings without damage. 4. The treatment with Na2S2O5 solutions also brought out species-specific differences in lichen resistance. However, the sequence of decreasing resistance is not the same as that to SO2 gas treatment. Irreversible damage of photosynthesis is not necessarily correlated with destruction of chlorophyll. 5. The damage caused to the lichens by the Na2S2O5 solutions (of the same concentration) is closely dependent upon the pH of the medium. At a low pH the effect is much more pronounced than at a high pH. This can be interpreted as due to the concentration of damaging ions, which changes according to the degree of dissociation of the solution; this is pH dependent. The results are discussed on the basis of Levitt's resistance concept that the total resistance of lichens to SO2 in the air is dependent upon two components, "avoidance" and "tolerance" (see Fig. 15). Resistance to a specific SO2 concentration in the air depends upon how much SO2 is taken up by the thallus, which is conditioned among other things by thallus organization (life form, surface characteristics) and by the degree of hydration of the poikilohydric organism. The toxicity of the SO2 taken up by the lichen can also be reduced; the pH of the thallus and its buffering capacity (dependent among other things upon site and substrate) play a dominant role in this process. In addition to these "avoidance" factors the total resistance of lichens is also dependent upon the plasmatic resistance of sensitive systems to SO2 ("tolerance"). This type of resistance, due to the influence of Na2S2O5 solution, is subject to considerable deviation (for example due to the developmental state of the lichen). The differences in the sequence of resistance for the investigated lichen species in terms of total resistance (SO2 treatment) and plasmatic resistance (Na2S2O5 solution treatment) show the significance of the "avoidance" component for the total resistance of the organisms.In ecological terms the investigation supports the view that lichens are highly sensitive to SO2, even in concentrations which occur due to real immisions. The study also shows the complexity of an ecological interpretation of experimentally determined resistance phenomena.

Detection of hidden regimes in stochastic cyclostationary time series.

Stationary stochastic time series with nonlinear dynamics can feature a probability density function (PDF) with distinct local maxima associated with distinct regimes. For nonstationary time series, on the other hand, such regimes are not necessarily reflected in the shape of the PDF. This occurs when the duration of a regime is too short for the PDF to adjust, and such a regime is called a "hidden" regime. This paper presents an algorithm that allows one to detect hidden regimes in cyclostationary stochastic Markovian time series. The method involves analysis of an appropriately windowed time series, from which the drift and diffusion coefficients of the associated Fokker-Planck equation are estimated. The success of the algorithm is illustrated using synthetic time series with both additive and multiplicative noise.

Temperature changes in deep muscles of humans during upper and lower extremity exercise.

OBJECTIVE: To examine the effect of 15 minutes of upper and lower extremity exercise on raising intramuscular temperature in the triceps surae to 39 degrees C to 45 degrees C (the therapeutic range). DESIGN AND SETTING: Intramuscular temperature was measured 5 cm deep in the triceps surae using a 23-gauge thermistor needle microprobe connected to a monitor. Each subject was tested under 3 conditions: 15 minutes of rest, 15 minutes of jogging on a treadmill, and 15 minutes of handpedaling an upper-body ergometer. Exercise bouts were performed at 70% of each subject's maximum heart rate. SUBJECTS: Six males, either sedentary or recreational athletes (age = 21.3 +/- 2.9 years; ht = 176.8 +/- 6.0 cm; wt = 72.7 +/- 11.6 kg; resting heart rate = 57.8 +/- 6.74 bpm; target heart rate = 156.5 +/- 3.0 bpm), volunteered to participate in this experiment. MEASUREMENTS: Intramuscular temperature was measured at a depth of 5 cm before and after each test condition. RESULTS: Data analyses consisted of analyses of variance with repeated measures and a Tukey post hoc test (P < .05). The results showed a significant temperature increase over baseline after exercise on the treadmill (2.2 degrees C +/- 0.63 degrees C); however, it did not yield temperature increases >/= 39 degrees C. No significant temperature change occurred after exercise on the upper-body ergometer (-0.45 degrees C +/- 0.80 degrees C). CONCLUSIONS: Active exercise increased intramuscular temperature in working muscles but did not affect intramuscular temperature in nonworking muscles. In addition, 15 minutes of jogging on a treadmill at 70% of maximum heart rate was not sufficient to raise intramuscular temperature to 39 degrees C to 45 degrees C.