OSL and TL techniques combined in a beryllium oxide detector to evaluate simultaneously accumulated and single doses.

Optically stimulated luminescence (OSL) and thermoluminescence (TL) are similar techniques widely used in radiation dosimetry. The main difference between these techniques is the stimulus to induce luminescence emission: TL technique uses thermal stimulation, whereas OSL uses optical stimulation. One of the main intrinsic characteristics of the OSL technique is the possibility of reading several times the dosimetric materials with a negligible loss of signal. In the case of BeO, recent studies have shown that TL stimulation up to 250°C does not affect its OSL signal. Taking the advantages of dosimetric characteristics of BeO combined with both techniques, in this study, we demonstrated the possibility of measuring accumulated and single doses in the same BeO-based detector in order to use it to improve individual monitoring of radiation workers exposed to X-ray or gamma-ray fields. Single doses were measured using TL technique by heating the detector up to 250°C, whereas accumulated doses were estimated using OSL technique in the same detector in a relatively short time of optical stimulation. The detectors were exposed to two energies: 28keV X-rays and 1.25MeV Co-60 gamma rays. The doses estimated by OSL and TL of BeO (Thermalox 995) were compared with those obtained with LiF (TLD-100) and recorded with a calibrated ionization chamber. The results indicate that combined OSL and TL signals of BeO detectors can provide additional information of accumulated dose, with additional exploration of the advantages of both techniques, such as speed in readouts with OSL, and double-check the doses using TL and OSL intensities from BeO.

A reconfigurable arbitrary waveform generator using PWM modulation for ultrasound research.

BACKGROUND: In ultrasound imaging systems, the digital transmit beamformer is a critical module that generates accurate control over several transmission parameters. However, such transmit front-end module is not typically accessible to ultrasound researchers. To overcome this difficulty, we have been developing a compact and fully programmable digital transmit system using the pulse-width modulation (PWM) technique for generating simultaneous arbitrary waveforms, specifically designed for research purposes. METHODS: In this paper we present a reconfigurable arbitrary waveform generator (RAWG) for ultrasound research applications that exploits a high frequency PWM scheme implemented in a low-cost FPGA, taking advantage of its flexibility and parallel processing capability for independent controlling of multiple transmission parameters. The 8-channel platform consists of a FPGA-based development board including an USB 2.0 interface and an arbitrary waveform generator board with eight MD2130 beamformer source drivers for individual control of waveform, amplitude apodization, phase angle and time delay trigger. RESULTS: To evaluate the efficiency of our system, we used equivalent RC loads (1 kΩ and 220 pF) to produce arbitrary excitation waveforms with the Gaussian and Tukey profiles. The PWM carrier frequency was set at 160 MHz featuring high resolution while keeping a minimum time delay of 3.125 ns between pulses to enable the acoustic beam to be focused and/or steered electronically. Preliminary experimental results show that the RAWG can produce complex arbitrary pulses with amplitude over 100 Vpp and central frequency up to 20 MHz with satisfactory linearity of the amplitude apodization, as well as focusing phase adjustment capability with angular resolution of 7.5°. CONCLUSIONS: The initial results of this study showed that the proposed research system is suitable for generating simultaneous arbitrary waveforms, providing extensive user control with direct digital access to the various transmission parameters needed to explore alternative ultrasound transmission techniques.

Avaliação da fadiga muscular pela mecanomiografia durante a aplicação de um protocolo de EENM / Muscle fatigue assessment by mechanomyography during application of NMES protocol

Contextualização: A estimulação elétrica neuromuscular (EENM) é uma técnica bastante utilizada na área da reabilitação em fisioterapia, porém a instalação da fadiga ocorre de maneira mais rápida se comparada à contração voluntária. Na prática clínica, torna-se necessário monitorar a fadiga muscular em protocolos de EENM, visando adequar os parâmetros da corrente elétrica e prolongar o tempo de estimulação. OBJETIVOS: O objetivo deste estudo foi utilizar a mecanomiografia como meio de avaliação da fadiga muscular periférica durante a aplicação de um protocolo de EENM. MÉTODOS: Um sistema de aquisição de sinais mecanomiográficos (MMG) e um protocolo experimental foram desenvolvidos. Durante os ensaios in vivo com 10 voluntários, foram realizados testes de contração voluntária máxima (CVM) para extensão do joelho. Realizou-se uma fase de potencialização com contrações dinâmicas produzidas por EENM a 10 por cento da CVM (100 Hz, 400 µm) no músculo quadríceps femoral, e o protocolo de EENM propriamente dito ocorreu a 30 por cento da CVM (50 Hz, 400 µm). Simultaneamente, foram adquiridos os sinais de MMG RMS (amplitude) e MMG MPF (frequência) do músculo reto femoral e de torque (amplitude) para a extensão do joelho. RESULTADOS: A linha de tendência da MMG RMS foi descendente, indicando que a MMG RMS relaciona-se à amplitude do torque. Porém, a MMG MPF não teve uma boa correlação com o torque para este protocolo de EENM. CONCLUSÕES: A MMG pode ser aplicada simultaneamente à EENM, pois não ocorre interferência elétrica, e pode ser utilizada na realização de movimentos funcionais na contração muscular gerada por EENM. Artigo registrado no Australian New Zealand Clinical Trials Registry (ANZCTR) sob o número ACTRN12609000866202.

Background: Neuromuscular electrical stimulation (NMES) is a widely used technique for rehabilitation in physical therapy, however it causes muscle fatigue more rapidly than does voluntary contraction. In clinical practice, it becomes necessary to monitor muscle fatigue during NMES protocols to adjust the parameters of electrical current stimulation and, thus, increase stimulation time. OBJECTIVES: The aim of this study is to use mechanomyography (MMG) as a means of evaluating peripheral muscle fatigue during the execution of an NMES protocol. METHODS: An MMG signal acquisition system and an experimental protocol were developed. During in vivo tests, 10 participants performed maximal voluntary contractions (MVCs) for knee extension. A maximization phase was conducted with dynamic contractions generated by NMES at 10 percent of MVC (100 Hz, 400 µs) on the quadriceps muscle, and the main NMES protocol occurred at 30 percent of MVC (50 Hz, 400 µs). Simultaneously, MMG RMS (amplitude) and MMG MPF (frequency) signals of the rectus femoris and the knee extension torque were acquired. RESULTS: The tendency line of the MMG RMS was descendant, indicating that MMG RMS correlates with torque amplitude. However, MMG MPF did not show a significant correlation with torque for the present NMES protocol. CONCLUSIONS: MMG is a technique that can be simultaneously applied to NMES because there is no electrical interference and it can be used during functional movements in the NMES-generated muscle contraction. Article registered in the Australian New Zealand Clinical Trials Registry (ANZCTR) under the number ACTRN12609000866202.

Broadband ultrasound attenuation in the calcaneal region: a comparative study of single-position versus scanning systems.

This work describes a system developed to measure the broadband ultrasound attenuation (BUA) in the calcaneal region. The patient's calcanei were inspected using a microcomputer-controlled X-Y axis displacement unit with two 500-kHz, central-frequency, ultrasound transducers. The transducers facing each other are submerged in a small water tank with a support for the patient's foot between them. The system allows data to be collected from a single position or by scanning the calcaneal region to obtain a BUA map. Tests were carried out on 201 patients (110 using the single-position method, and 91 using the scanning method). The results were compared with those of densitometry tests performed using the dual energy X-ray absorptiometry (DEXA) technique (single position: r=0.50; P<0.0001; scanner: r=0.75; P<0.0001). It was concluded that the single position method is more susceptible to errors due to the difficulty in positioning the transducers relative to the calcaneus. The scanning method provides better results and can be used to screen patients before referring them for DEXA.