Catálogo de publicaciones - libros

Fetal magnetocardiography is a non-invasive method to study the fetal heart: the patient (i.e., the mother) is not even touched. A fetal magnetocardiogram (MCG) is the registration of a component of the magnetic field generated by the electrical activity of the fetal heart. Usually the component of the magnetic field that is perpendicular to the maternal abdomen is measured. Fetal MCGs show the typical features that are found in ECGs of adults (i.e. a P-wave, QRS-complex and T-wave). To enable the discrimination between pathological and healthy fetuses, values of the duration of these waveforms are collected in several research groups. These durations can be used as a reference. Measurements show that MCGs of fetuses with severe congenital heart disease have an abnormal shape. Hence, fetal MCGs may be of help in the early intra-uterine detection of congenital heart anomalies and the progress of the disease. Fetal magnetocardiography can also be used to classify fetal arrhythmias.

The fetal MCG is a very weak signal (about 10 tesla) compared with fields that are present in a hospital. The Earth’s magnetic field, for example, is about 5 × 10 tesla. The only magnetic field sensor that is sensitive enough to measure fetal MCGs is a SQUID. This sensor has to be cooled in liquid helium. The vessel containing the helium and the sensor is positioned near the maternal abdomen. At present, fetal MCGs are measured within magnetically shielded rooms in order to avoid disturbing fields. Signal processing techniques, such as filtering and averaging, are used to enhance the signal-to-noise ratio. The electrical activity in the heart gives rise to currents in the fetus and maternal abdomen. These currents also contribute to the fetal MCG. In order to estimate this influence, simulations are carried out and discussed in the last section of this chapter on fetal MCG.

Microwave thermoelastic imaging uses microwave-pulse-induced thermoelastic pressure waves to form planar or tomographic images. Since the generation and detection of thermoelastic pressure waves depends on dielectric permittivity, specific heat, thermal expansion, and acoustic properties of tissue, microwave thermoelastic imaging possesses the characteristic features of a duel-modality imaging system. The unique attributes of the high contrast offered by microwave absorption and the fine spatial resolution furnished by ultrasound, are being explored to provide an imaging modality for noninvasive imaging characterization of tissues, especially for early detection of breast cancer. This chapter describes the research being conducted in developing microwave thermoelastic tomography (MTT) and imaging for medical diagnosis. It discusses the science of thermoelastic wave generation and propagation in biological tissues; the design of prototype microwave thermoelastic tomographic imaging (MTTI) systems; and the reconstruction of tomographic images using filtered-back projection algorithms; as well as the performance of prototype microwave thermoelastic tomographic systems in phantom models and human subjects.

Diffuse optical imaging is a functional medical imaging modality which takes advantage of the relatively low attenuation of near-infrared light to probe the internal optical properties of tissue. The optical properties are affected by parameters related to physiology such as the concentrations of oxy- and deoxyhemoglobin. Instrumentation that is used for optical imaging is generally able to measure changes in the attenuation of light at several wavelengths, and in the case of time- and frequency-domain instrumentation, the time-of-flight of the photons in tissue.

Light propagation in tissue is generally dominated by scattering. Models for photon transport in tissue are generally based on either stochastic approaches or approximations derived from the radiative transfer equation. If a numerical forward model which describes the physical situation with sufficient accuracy exists, inversion methods may be used to determine the internal optical properties based on boundary measurements.

Optical imaging has applications in, e.g., functional brain imaging, breast cancer detection, and muscle imaging. It has the important advantages of transportable instrumentation, relatively high tolerance for external electromagnetic interference, non-invasiveness, and applicability for neonatal studies. The methods are not yet in clinical use, and further research is needed to improve the reliability of the experimental techniques, and the accuracy of the models used.

The usefulness of biotelemetry (remote measurement of biological information) has been recognized in clinical medicine and animal sciences. In biotelemetry, the radio wave has been commonly used as a transmission medium. To answer many new demands for biotelemetry and to overcome various problems of radio telemetry, a technological method called optical biotelemetry has been developed. Using light as a transmission medium, the bandwidth for signal transmission is greatly increased and many EMI problems can be solved. Technical considerations required to realize the optical biotelemetry were presented. On the devices for optical biotelemetry, the wavelength of light, light sources, light detecting elements and the measures for optical noises were discussed. On data transmission, analogue and digital communication, modulation methods, intelligent transmission and multiplexing methods were discussed. To develop an optical biotelemetry technique, we need to know the characteristics of light propagation. The optical characteristics of body surface tissue and the distribution of indirect light in a room were discussed for transcutaneous telemetry and ambulatory telemetry using indirect light, respectively. Two techniques were proposed for multi-channel optical biotelemetry. They were the applications of a pulse-burst method and the spread spectrum method. As concrete examples of optical biotelemetry, some applications of this method to practical use are presented. They are the transcutaneous ECG telemetry, non-contact measurement of body surface displacement, ambulatory telemetry, multi-channel biotelemetry and data transmission between medical equipments. With its promising potential, it is expected that the optical biotelemetry opens new possibilities for further development of biotelemetry.

One of the most conspicuous results of extremely low frequency magnetic field (ELF MF) exposure in animal and human populations has been an effect upon pain behaviours. Pain is a multi-faceted construct having cellular, physiological and psychological domains of action and represents one of the most significant health issues that we deal with on a day to day basis. Our laboratory has been investigating ELF MF effects on pain for over twenty years after it was first noted how magnetic field exposure inhibited morphine induced analgesia. Our mission is to develop effective and efficacious specific pulsed magnetic field designs, initially for the treatment of pain. Although there is a rich body of research in studying animal models, there is a definite lack of well designed studies examining the effects of magnetic fields upon human pain responses. This chapter reviews the historical and current state of magnetic field therapies for the treatment of pain, as well as providing an overview of our current understanding of pain, nociception and the opioid system. We also review some of the current hypothesized mechanism(s) by which time-varying magnetic fields elicit behavioural and physiological responses and how this will provide us with the tools to design specific magnetic field pulses and delivery systems which will be used for chronic and acute pain treatment without the unwanted side-effects often associated with chemical/pharmaceutical therapies. We also hypothesize that the future of magnetic fields and pain therapy lie in the rapid advancement of imaging technologies, such as magnetic resonance imaging (MRI), positron emission tomography (PET), electroencephalography (EEG) and magnetoencephalography (MEG). We advance the concept of image-guided magnetotherapy as the next step in therapeutics oriented bioelectromagnetics research.

There is good experimental evidence for a specific biological interaction with ELF magnetic fields that is functionally dependent on ion cyclotron resonance (ICR) frequencies as derived from ionic charge-to-mass ratios. This evidence is gleaned from studies on an extraordinarily wide variety of biological systems. However, no reasonable underlying theoretical construct has surfaced to explain these results at the microscopic level, and thus the nature of this q/m interaction remains empirical at best. The main difficulty with the various theoretical models that have been advanced is that sustaining ion cyclotron resonance in a biological milieu is highly improbable considering the relatively large damping suffered by ions. Further, in cases where the damping problem may be ameliorated, as for example, in the interior pore of ion channels, there is a large discrepancy between expected cyclotron resonance-mediated ion transit times and observed times, which are faster by a factor of 10. Some, notably Lednev, Blanchard, Binhi, and Zhadin, have attempted to explain the unique charge-to-mass signature using models that do not explicitly involve the classical ICR mechanism, but nevertheless still result in functional dependences on the ion cyclotron resonance frequency. Most recently, del Giudice has suggested replacing Maxwellian statistics when studying bioelectromagnetic interactions at the cellular level with quantum electro-dynamics, claiming that the experimental results support the view that highly ordered coherent domains are involved. Two additional sets of experimental results, both involving conductivity measurements in cell-free systems, have now been reported, first, the discovery by Zhadin that polar amino acids in solution are sensitive to ICR magnetic field exposures, and the second, by Mohri, that a 1 T ICR magnetic signal applied to ultra-pure (18.2 MΩ-cm) water for as little as one minute will result in increased conductivity lasting for days. These findings may shed light on the persistent and controversial reports claiming that the physical properties of water can be altered by relatively weak magnetic field exposures.