Study for a portable IR sensor to detect the blood temperature during coronary bypass implantation

The objective of this research was to investigate the possibility of using an infrared prototype device for the detection of the blood temperature during a surgical operation for coronary bypass implantation. The correlation between the fluid temperature time behavior and the fluid flow rate was demonstrated. Each blood vessel acts like a thermal wave emitter, so the amount of heat is proportional to the blood flow detected by the IR sensor. The idea was to design a low cost portable device with the advantage that it can be placed near the region of interest. We chose a pyroelectric sensor for its high-quality cost ratio. Because this kind of sensor detects only a variable infrared source, we used an electromechanical chopper for modulating the radiation. It consists of an electronic shutter whose opening speed is controlled by an astable multivibrator. The output signal was analyzed using a dedicated electronic circuit including a bandpass filter and an amplifier; then an acquisition board was employed for capturing and displaying the signal using a PC. Prototype assessment was made with laboratory equipment and in vivo measurements were made during surgical operation on a small pig

Improvement of Magnetic Resonance Imaging at Low Field using a Birdcage Coil

The main goal of this research was to demonstrate the utility of using a transmitter-receiver birdcage coil for magnetic resonance imaging at very low static field (0.18 T). As well known, the SNR decreases with frequency, thus reducing the image quality at very low field. Moreover, we would expect that the birdcage coil Q factor reduces with fre-quency. But, from experimental evidence, we proved that at low frequency (7.66 MHz), the Q factor for a well-designed birdcage coil reverses the trend, reach-ing unexpected high values. It is a prerequisite to use low static magnetic field in microimaging applica-tions for small animals experiments

Quadrature lowpass birdcage coil for low field open MRI scanner

Abstract: The main goal of this research was to demonstrate the utility of using a quadrature birdcage coil in lowpass version for magnetic resonance imaging (MRI) in open scanner at very low static field. When used in horizontal bore MRI systems, the birdcage coil is able to produce circular polarized field using quadrature excitation, thus reaching SNR improvement of 2 as maximum value. The birdcage coil in high-pass version can be employed even in a vertical bore MRI scanner, by combining the sinusoidal and the end-ring resonant modes. In this paper we investigated the lowpass birdcage coil configuration to operate with a vertical bore MRI system, producing two 1B fields components perpendicular to the vertical B0 field. Its implementation is convenient because it requires one half capacitors with respect to the high-pass design. Moreover, at low field the high near-electric field losses, that represent the main disadvantage of the low pass design, can be neglected. Experiments performed on a quadrature birdcage coil prototype mounted on an open MRI scanner, showed that both SNR and homogeneity degree increase with respect to the linear birdcage

Measurement of tissue oxygenation in isolated rat hearts using near infrared spectroscopy

New techniques involving Near Infrared Spectroscopy (NIRS) and imaging are rapidly evolving for a large number of new clinical applications. These techniques, based upon nearinfrared light transmission through biological tissue, aim to monitor the hemoglobin and myoglobin concentration changes due to particular physiological state. Clinical applications regard, for instance, the monitoring of muscles and cerebral oxygenation, functional brain activation studies and heart perfusion research. Recently, some works presented tissue oxygenation studies in beating or arrested isolated porcine hearts. In our work we present the design and realization of a dedicated NIRS system for the myocardial perfusion analysis of isolated, saline solution perfused beating rat hearts; in this case the absence of blood allows for unambiguous measurement of tissue myoglobin oxygenation. The presented prototype is portable, low cost, battery operated and permits the measurement of both oxy and deoxy myoglobin concentration changes during imposed regional or global ischemia and reperfusion

Measurement of tissue oxygenation in isolated rat hearts using near infrared spectroscopy

Radiofrequency (RF) receivers are key components in magnetic resonance imaging (MRI) systems. Birdcage coils are widely used for their ability to achieve high signal-to-noise ratio (SNR), however, when they are used in low field scanners, both the detected signal SNR and the coil quality factor Q decrease with frequency, thus reducing the image quality. In this paper we initially describe the design of a high quality birdcage coil, demonstrating the possibility of obtaining high quality images even using low field scanners (0.18T). To convert the RF signal from the coil into a suitable form for an analog-to-digital (ADC) converter, a classic analog superheterodyne circuit is generally employed. This kind of receiver is simple but also presents many problems for filters and amplifiers design. In this study we implemented a phase-quadrature digital detector system using an alternative technique called undersampling. Our receiver is constituted by a passband filter, an ADC and a DDC (Digital Down Converter) for the frequency translation and filtering to process the signal using a PC. In this work we give all the detailed specifications and hardware design issues for the receiver that is designed to be used in a dedicated scanner guaranteeing top performances with low cost