A Monte Carlo study of the timing resolution of BaF2 forTOF PET

A Monte Carlo study of the timing resolution of small BaF₂ crystals for time-of-flight (TOF) positron emission tomography (PET) is presented. The interaction of 511-keV gammas, the emission and transport of ultraviolet light in the crystal, and the pulse formation in the photomultiplier are simulated. The individual contributions to the timing resolution and the overall effect are calculated and compared to experimental measurements. It is found that for small crystal lengths the choice of photomultiplier can have strong effect on the resolution     

Prediction of laser action properties of organic dyes from their structure and the polarization characteristics of their electronic transitions

Effects of substitution by auxochromic groups on the electronic spectra of aromatic compounds are discussed. Depending on the location and direction of the singlet-singlet (S-S) relative to the triplet-triplet (T-T) oscillators within the molecular frame, substitution by an auxochromic group may cause T-T absorption bands to move into or out of the fluorescence region, or they may be left unchanged. Predictions can thus be made of potential dye laser materials based on substitutional effects on the spectral properties of aromatic compounds. The predictions are incorporated in a graph that presents possible arrangements of low-energy SS oscillators relative to a T-T oscillator located in the fluorescence region of the aromatic compound. Depending on short- or long-axis substitution, the red shifts of the S-S and T-T absorption bands result in two promising constellations (structures) for low T-T absorption over the fluorescence region. The laser action properties of coumarin and some of its derivatives are discussed.     

Design and development of a multimedia database for emergency telemedicine

Recent studies conclude that early and specialised pre-hospital patient management contributes to emergency cases survival. Recent developments in telecommunication and medical informatics by means of telemedicine can be extremely useful to accomplish such tasks in a cost-effective manner. Along that direction, we have designed a portable device for emergency telemedicine. This device is able to telematically "bring" the expert doctor at the emergency site, have him perform an accurate diagnosis, and subsequently direct the Emergency Medical Technicians on how to treat the patient until he arrives to the hospital. The need for storing and archiving all data being interchanged during the telemedicine sessions is very crucial for clinical, legal and administrative purposes. For this, we have developed a multimedia database able to store and manage the data collected by the AMBULANCE system. The database was equipped with a user-friendly graphical interface to enable use from computer naive users. Furthermore, the database has the possibility to display, in an standard way, ECG's, X-ray, CT and MRI images. The application is password protected with a three-level hierarchy access for users with different privileges. The scope of this application is to enhance the capabilities of the doctor on duty for a more precise and prompt diagnosis. The application has the ability to store audio files related to each emergency case and still images of the scene. Finally, this database can become a useful multimedia tool which will work together with the AMBULANCE portable device, the HIS and the PACS of the hospital. The system has been validated in selected non-critical cases and proved to be functional and successful in enhancing the ability of the doctor's on duty for prompt and accurate diagnosis and specialised pre-hospital treatment.     

Spectroscopy and molecular structure of efficient laser dyes: vibronic spin-orbit interactions in heterocyclics

Some characteristics of selected laser dyes are reviewed, and the effect of heterocyclic atom substitutions on triplet (pi, pi*) transitions is studied experimentally. Specifically, the intensities (oscillator strengths f) of the lowest-energy singlet-singlet (S-S) and triplet-triplet (T-T) transitions of anthracene and some of its heterocyclic analogs were measured. It is shown that this type of substitution of carbon atoms by heteroatoms results in a considerable reduction of intensity of T-T transitions. This observation is important to laser dye technology. The effect is explained by the existence of an efficient vibronic coupling mechanism between (n, pi*) and (pi, pi*) triplet states in heteroatom molecules. Some general guidelines for how to find efficient laser dyes are proposed.     

A high position resolution X-ray detector: an "Edge on" illuminated capillary plate combined with a gas amplification structure

We have developed and successfully tested a prototype of a new high position resolution hybrid X-ray detector. It contains a thin-wall lead glass capillary plate converter of X-rays combined with a microgap parallel-plate avalanche chamber operating in various gas mixtures at 1 atm. The operation of these converters was studied in a wide range of X-ray energies (from 6 to 60 keV) at incident angles varying from 0-90/spl deg/. The detection efficiency, depending on the geometry, photon's energy, incident angle and the mode of operation was between 5-30% in single step mode and up to 50% in a multi-layered combination. Depending on the capillary's geometry, the position resolution achieved was between 50-250 /spl mu/m in digital form and was practically independent of the photon's energy or gas mixture. The usual lead glass capillary plates operated without noticeable charging up effects at counting rates of 50 Hz/mm/sup 2/ and hydrogen treated capillaries-up to 10/sup 5/ Hz/mm/sup 2/. The developed detector has several important potential advantages over the exciting X-ray detectors and may open new possibilities for medical imaging, for example in mammography, portal imaging, radiography (including security devices), as well as many other applications.     

Laser Action from a 2,6,8-Position Trisubstituted 1,3,5,7-Tetramethylpyrromethene-BF(2) Complex: Part 3

Some laser action properties of a new Pyrromethene-BF(2) complex, 1, 3, 5, 7-tetramethyl-8-ethyl-2, 6-dicyanopyrromethene-BF(2) complex are reported. This laser dye exhibits laser action in the green-yellow portion of the spectrum, and its laser action efficiency was ~350% higher compared with Coumarin 545. Exceptional photostability of the new laser dye was observed when a mixture of 1, 4-dioxane:heptane ratio of 1:4 was used as the solvent. Further, it is suggested that dye lasers can be upscaled to high average power output when surface-emitting laser diode arrays are used as pump (excitation) sources.     

Fuzzy neural network-based texture analysis of ultrasonic images

The efficacy of a novel fuzzy neural network classifier for the characterization of ultrasonic liver images based on texture analysis techniques is investigated. Classification features are extracted with the use of image texture analysis techniques such as fractal dimension texture analysis, spatial gray-level dependence matrices, gray-level difference statistics, gray-level run-length statistics, and first-order gray-level parameters. These features are fed to a neural network classifier based on geometrical fuzzy sets. Starting from the construction of the Voronoi diagram of the training patterns, an aggregation of Voronoi regions is performed, leading to the identification of larger regions belonging exclusively to one of the pattern classes. The resulting scheme is a constructive algorithm that defines fuzzy clusters of patterns. Based on observations concerning the grade of membership of the training patterns to the created regions, decision probabilities are computed through which the final classification is performed