Computerised Microtomography : Non-invasive imaging and analysis of biological samples, with special reference to monitoring development of osteoporosis in small animals

The use of Computerised microtomography (CμT) in biomedical research is well established, with most applications developed at synchrotron facilities. The possibility to non-invasively monitor morphological changes in biological samples, makes it an attractive technique in biomedicine. However, high absorbed doses and long examination times are a disadvantage that limits the possibilities of performing longitudinal examinations. The aim of this work was to optimise CmT using conventional X-ray tubes for applications in non-destructive material testing and for skeleton research in small animals (rat). A calculational model of the imaging system was developed and used to optimise the relation between image quality, expressed as the signal-to-noise ratio (SNR) in detecting a contrasting detail, and imaging time in material testing. The model was modified to optimise the relation between the SNR in detecting a trabecular detail in cancelleous bone and the mean absorbed dose in spongiosa and skin for (rat) tibia and femur. Gastrectomized Sprague-Dawley rats were used to initiate osteoporotic changes. In order to detect differences in between gastrectomized rats and controls, spatial resolutions of 150 mm or better were needed. The minimum absorbed doses in femur spongiosa at SNR = 5 were 1mGy - 700 mGy at spatial resolutions from 100 mm to10 mm. In femur skin, the corresponding minimum absorbed doses were 2 mGy - 2000 mGy. Corresponding values for tibia were 0.3 mGy - 300 mGy for both spongiosa and skin (spatial resolution of 100 mm to10 mm). Taking 0.5 Gy as the tolerance limit for the spongiosa dose, longitudinal studies with six repeated examinations will be possible at a spatial resolution of 25 mm in femur and 17 examinations in tibia

Computerised Microtomography : Non-invasive imaging and analysis of biological samples, with special reference to monitoring development of osteoporosis in small animals

The use of Computerised microtomography (CμT) in biomedical research is well established, with most applications developed at synchrotron facilities. The possibility to non-invasively monitor morphological changes in biological samples, makes it an attractive technique in biomedicine. However, high absorbed doses and long examination times are a disadvantage that limits the possibilities of performing longitudinal examinations. The aim of this work was to optimise CmT using conventional X-ray tubes for applications in non-destructive material testing and for skeleton research in small animals (rat). A calculational model of the imaging system was developed and used to optimise the relation between image quality, expressed as the signal-to-noise ratio (SNR) in detecting a contrasting detail, and imaging time in material testing. The model was modified to optimise the relation between the SNR in detecting a trabecular detail in cancelleous bone and the mean absorbed dose in spongiosa and skin for (rat) tibia and femur. Gastrectomized Sprague-Dawley rats were used to initiate osteoporotic changes. In order to detect differences in between gastrectomized rats and controls, spatial resolutions of 150 mm or better were needed. The minimum absorbed doses in femur spongiosa at SNR = 5 were 1mGy - 700 mGy at spatial resolutions from 100 mm to10 mm. In femur skin, the corresponding minimum absorbed doses were 2 mGy - 2000 mGy. Corresponding values for tibia were 0.3 mGy - 300 mGy for both spongiosa and skin (spatial resolution of 100 mm to10 mm). Taking 0.5 Gy as the tolerance limit for the spongiosa dose, longitudinal studies with six repeated examinations will be possible at a spatial resolution of 25 mm in femur and 17 examinations in tibia

Across conceptual models and practices : workplace learning in higher vocational education in Sweden and Finland

Godkänd; 2004; 20061120 (kirhon

Prólogo: El dilema perpetuo

Absolute energy spectra [1/(keV·mAs·sr)] for an industrial micro focal X-ray source has been measured under working conditions, using a Compton scattering spectrometer. The energy spectra were measured as a function of tube potential (30 – 190 kV for every 10th kV) at maximum tube charge of 8 W for the minimum focus (~5 μm diameter). Target material was tungsten. The spectra were measured for a highly focused fresh focal spot. Neither focal spot wear (age) nor defocusing of the focal spot was considered. The measured spectra were compared to simulated spectra for the same source supplied by the X-ray source manufacturer. It was found that the measured spectra have slightly different energy distributions with a lower mean energy even though their emitted number of photons were similar. The energy calibration was shown to be accurate compared to the energy resolution, Dhu=0.5 keV, used

Absolute energy spectra for an industrial micro focal X-ray source under working conditions measured with a Comptonscattering spectrometer : full spectra data

Absolute energy spectra [1/(keV·mAs·sr)] for an industrial micro focal X-ray source has been measured under working conditions, using a Compton scattering spectrometer. The energy spectra were measured as a function of tube potential (30 – 190 kV for every 10th kV) at maximum tube charge of 8 W for the minimum focus (~5 μm diameter). Target material was tungsten. The spectra were measured for a highly focused fresh focal spot. Neither focal spot wear (age) nor defocusing of the focal spot was considered. The measured spectra were compared to simulated spectra for the same source supplied by the X-ray source manufacturer. It was found that the measured spectra have slightly different energy distributions with a lower mean energy even though their emitted number of photons were similar. The energy calibration was shown to be accurate compared to the energy resolution, Dhu=0.5 keV, used

Boosting the Performance of Shared Memory Multiprocessors

Shared memory multiprocessors make it practical to convert sequential programs to parallel ones in a variety of applications. An emerging class of shared memory multiprocessors are nonuniform memory access machines with private caches and a cache coherence protocol. Proposed hardware optimizations to CC-NUMA machines can shorten the time processors lose because of cache misses and invalidations. The authors look at cost-performance trade-offs for each of four proposed optimizations: release consistency, adaptive sequential prefetching, migratory sharing detection, and hybrid update/invalidate with a write cache. The four optimizations differ with respect to which application features they attack, what hardware resources they require, and what constraints they impose on the application software. The authors measured the degree of performance improvement using the four optimizations in isolation and in combination, looking at the trade-offs in hardware and programming complexities. Although one combination of the proposed optimizations (prefetching and migratory sharing detection) can boost a sequentially consistent machine to perform as well as a machine with release consistency, release consistency models offer significant performance improvements across a broad application domain at little extra complexity in the machine design. Moreover, a combination of sequential prefetching and hybrid update/invalidate with a write cache cuts the execution time of a sequentially consistent machine by half with fairly modest changes to the second-level cache and the cache protocol. The authors expect that designers will begin to turn more to the release consistency model