IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Jul 2005
Simulation analysis of conduction block in unmyelinated axons induced by high-frequency biphasic electrical currents.
Nerve conduction block induced by high-frequency biphasic electrical currents is analyzed using a lumped circuit model of the unmyelinated axon based on Hodgkin-Huxley equations. Axons of different diameters (5-20 microm) can not be blocked completely when the stimulation frequency is between 2 kHz and 4 kHz. However, when the stimulation frequency is above 4 kHz, all axons can be blocked. ⋯ The stimulation waveform in which the pulsewidth changes with frequency is more effective in blocking nerve conduction than the waveform in which the pulsewidth is fixed. The activation of potassium channels, rather than inactivation of sodium channels, is the possible mechanism underlying the nerve conduction block of the unmyelinated axon. This simulation study further increases our understanding of axonal conduction block induced by high-frequency biphasic currents, and can guide future animal experiments as well as optimize stimulation waveforms that might be used for electrical nerve block in clinical applications.
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IEEE Trans Biomed Eng · Jul 2005
Design and performance issues of RF coils utilized in ultra high field MRI: experimental and numerical evaluations.
In this paper, two TEM resonators were evaluated experimentally and numerically at 8 tesla (T) (340 MHz for 1H imaging). The coils were constructed to be 21.2-cm long (standard) and 11-cm long (a proposed less claustrophobic design). The experimental evaluation was done on a single cadaver using an ultra high field, 8 T, whole-body magnet. ⋯ For head imaging at 8 T, the overall numerical and experimental results demonstrated that when compared to the longer coil, the shorter coil provides superior signal-to-noise ratio, coil sensitivity, and excite field in the biological regions that lie within both of the coils' structures. A study of the RF (excite/receive fields) homogeneity showed variations in the performance of both coils that are mostly dependant on the region of interest and the position of coil with respect to the head. As such, depending on the application, the shorter coil could be effectively utilized.
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IEEE Trans Biomed Eng · Jul 2005
Band-tunable and multiplexed integrated circuits for simultaneous recording and stimulation with microelectrode arrays.
Two thin-film microelectrode arrays with integrated circuitry have been developed for extracellular neural recording in behaving animals. An eight-site probe for simultaneous neural recording and stimulation has been designed that includes on-chip amplifiers that can be individually bypassed, allowing direct access to the iridium sites for electrical stimulation. The on-probe amplifiers have a gain of 38.9 dB, an upper-cutoff frequency of 9.9 kHz, and an input-referred noise of 9.2 microV rms integrated from 100 Hz to 10 kHz. ⋯ Providing gain on this array eliminates the need for bulky headmounted circuitry and reduces motion artifacts. The time-division multiplexing circuitry has crosstalk between consecutive channels of less than 6% at a sample rate of 20 kHz per channel. Amplified, time-division-multiplexed multichannel neural recording allows the large-scale recording of neuronal activity in freely behaving small animals with minimum number of interconnect leads.
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IEEE Trans Biomed Eng · Jul 2005
Clinical TrialApplication of higher order statistics techniques to EMG signals to characterize the motor unit action potential.
The electromyographic (EMG) signal provides information about the performance of muscles and nerves. At any instant, the shape of the muscle signal, motor unit action potential (MUAP), is constant unless there is movement of the position of the electrode or biochemical changes in the muscle due to changes in contraction level. The rate of neuron pulses, whose exact times of occurrence are random in nature, is related to the time duration and force of a muscle contraction. ⋯ In this paper, we report results from applying a cepstrum of bispectrum based system reconstruction algorithm to real wired-EMG (wEMG) and surface-EMG (sEMG) signals to estimate the appearance of MUAPs in the Rectus Femoris and Vastus Lateralis muscles while the muscles are at rest and in six other contraction positions. It is observed that the appearance of MUAPs estimated from any EMG (wEMG or sEMG) signal clearly shows evidence of motor unit recruitment and crosstalk, if any, due to activity in neighboring muscles. It is also found that the shape of MUAPs remains the same on loading.
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IEEE Trans Biomed Eng · Jul 2005
A programmable microsystem using system-on-chip for real-time biotelemetry.
A telemetry microsystem, including multiple sensors, integrated instrumentation and a wireless interface has been implemented. We have employed a methodology akin to that for System-on-Chip microelectronics to design an integrated circuit instrument containing several "intellectual property" blocks that will enable convenient reuse of modules in future projects. The present system was optimized for low-power and included mixed-signal sensor circuits, a programmable digital system, a feedback clock control loop and RF circuits integrated on a 5 mm x 5 mm silicon chip using a 0.6 microm, 3.3 V CMOS process. ⋯ The base station was designed to be adaptive and timing tolerant since the microsystem design was simplified to reduce power consumption and size. The telemetry system was found to have a packet error rate of 10(-3) using an asynchronous simplex link. Trials in animal carcasses were carried out to show that the transmitter was as effective as a conventional RF device whilst consuming less power.