Luis F. Requicha Ferreira

The performance of the GPSC/MSGC hybrid detector with argon-xenon gas mixtures

The performance for x-ray spectrometry of neon-xenon gas proportional scintillation counters using a CsI-coated microstrip plate in direct contact with the scintillation gas as a VUV photosensor is investigated for different neon-xenon mixtures. At best operation conditions, the detector gain can reach values about 50% higher than those achieved with pure xenon filling. The highest gains and the best energy resolutions are achieved for xenon contents around 40%. However, the achieved energy resolutions are similar to those achieved with pure xenon. As in pure xenon and argon-xenon mixture gas-fillings, the detector performance is limited by optical positive feedback resulting from additional scintillation produced in the electron avalanche processes around the MSP-anodes. Best energy resolutions are achieved for positive feedback gains in the range of 1.1 to 1.2. The performance achieved with neon-xenon mixtures is inferior to that achieved with argon-xenon mixtures.

Programmable Test Bench for Hemodynamic Studies

The non-invasive assessment of hemodynamic parameters has been a permanent challenge posed to the scientific community. The literature shows many contributions to this quest expressed as algorithms dedicated to revealing some of its characteristics and as new probes or electronics, featuring some enhanced instrumental capability that can improve their insight.

Optically Isolated Current Source

This work addresses two different issues associated with the design voltage controlled current sources (VCSS): galvanic isolation between the load and the control voltage and loss of performance due to operational amplifier common mode rejection ratio (CMRR) degradation with frequency.

GEM Operation in High-Pressure

Tetrafluoromethane (CF4) combined with Helium-3 is widely used as the filling gas for neutron detectors. CF4 is generally known as an efficient gas for proton and tritium stopping, as well as a medium with low gamma sensitivity. Filling pressures above 2.5 bar are needed to achieve detector position resolutions below 1 mm. In this work, we have studied the performance of a single-GEM operating in CF4 in the pressure range of 1.0 to 2.5 bar and shown that it is possible to achieve gains one order of magnitude higher than what is needed for thermal neutron detection. Charge gains of 1.6 times 104 and 400 are reached at pressures of 1.0 and 2.5 bar, respectively, indicating good properties for this purpose. In opposition to gases with higher scintillation efficiency such as xenon, GEM scintillation readout with VUV-sensitive avalanche photodiodes results in gains that are less than one order of magnitude higher than those obtained with charge readout, delivering similar energy resolutions.

{\rm CF}_{4}

The main motivation of this work was to provide a valid contribution for the assessment of the cardiovascular condition by the analysis of several Arterial Pressure Waveform (APW) parameters collected by a new non-invasive device. Three sets of recordings for the carotid pressure waveform at left and right carotid arteries were performed, under standardized conditions, in 20 volunteers by three trained operators. The mean of the inter-operator differences were higher for the right artery, comparatively to the left artery. In this case, an Augmentation Index (AIx) value of -2.31 ± 7.29 % and a Systolic Wave Transit Time (SWTT) value of -12.94 ± 31.46 ms were observed, which are higher than the left measurements, 0.94 ± 7.52 % and -2.96 ± 22.67 ms, respectively. Intra-operator differences were calculated for each of the three sets of measurements and showed good reproducibility. The pulse-by-pulse variability analysis gives very good markers for the Left Ventricular Ejection Time (LVET), Dicrotic Wave Amplitude (DWA), Reflection Wave Amplitude (RWA), Coefficient of Variation (CV) < 10 %, and satisfactory values for the AIx (CV< 30 %). The SWTT and Reflected Wave Transit Time (RWTT) also presented satisfactory results (10 % < CV < 30 %). Results demonstrated the reproducibility of the parameter, being a simple and non-invasive device, that can be used to assess central hemodynamics.

: Studies of Charge and Scintillation Properties

In gaseous neutron detectors, tetrafluoromethane (CF4) combined with Helium-3 is generally known as an efficient gas for proton and tritium stopping, as well as a medium with low gamma sensitivity and is widely used as the filling gas for neutron detectors. Previous work has demonstrated that GEMs did not deliver gains high enough to be useful for neutron detection. In this work, we have studied the performance of a single-GEM operating in CF4 in the pressure range of 1.0 to 2.5 bar and shown that it is possible to achieve gains one order of magnitude higher than what is needed for neutron detection. Charge gains of 1.6 × 104 and 400 are reached at pressures of 1.0 and 2.5 bar, respectively, indicating good properties for this purpose. In opposition to gases with higher scintillation efficiency such as xenon, GEM scintillation readout with VUV-sensitive avalanche photodiodes results in gains that are less than one order of magnitude higher than those obtained with charge readout, delivering similar energy resolutions.

Assessment of the Pulse Wave Variability for a New Non-invasive Device

The present work focuses an experimental and theoretical approach to non-invasive cardiovascular (CV) system monitoring. The CV diseases are currently one of the leading causes of death in the developed countries. The development of early diagnostic tools contributes for the early identification of important markers in the CV development. A piezoelectric (PZ) probe to arterial pressure waveform (APW) monitoring at peripheral arteries, such as carotid artery was developed. A dedicated test bench capable of emulating the main CV dynamic properties was developed, providing an interesting tool to carry out the preliminary tests. The PZ probe output signal suffers additional processing to original waveform recovering. The deconvolution method was used for this purpose. Algorithms to waveform delineation were developed, based on the wavelet transform and probability density function (PDF). The AIx was calculated for each one of the developed algorithms. These methods were comparatively evaluated with the reference value from the synthesis procedure. The probes performance was assessed using realistic simulation based on exponential pulses and in in vivo data acquisitions, Results demonstrate that the developed probe exhibits a good performance with maximum errors less than 0.5% in the AIx determination.

GEM operation in CF 4 : Studies of charge and scintillation properties

Two new laser Doppler flowmeter prototypes are herein validated with Monte Carlo simulations paired with measurements. The first prototype is a multi-wavelength laser Doppler flowmeter with different spaced detection fibres that will add depth discrimination capabilities to laser Doppler flowmetry skin monitoring. The other prototype is a self-mixing based laser Doppler flowmeter for brain perfusion estimation. Monte Carlo simulations in a phantom consisting of moving fluid as well as in a skin model are proposed for the first prototype validation. We obtain a good correlation between simulations and measurements. For the second prototype validation, Monte Carlo simulations are carried out on a rat brain model. We show that the mean measurement depth in the rat brain with our probe is 0.15 mm. This positioning is tested in vivo where it is shown that the probe monitors the blood flow changes.