Abstract: A signal/noise ratio optimization tuning system, which can be used for tuning receiver antennas in Magnetic Resonance Imaging receiver systems, has a switch-controlled noise source means that is weakly coupled to the receiver antenna. The switch-controlled noise source switches a noise source between higher and lower power states at a predetermined frequency. A noise power meter means, which is synchronized to the switch-controlled noise source means, measures outputs of the receiver antenna. The noise power meter means measures the outputs of the receiver antenna when the noise source is switched between higher and lower power states and computes a ratio of the receiver antenna output with the noise source in the higher power state to the receiver antenna output with the noise source in the lower power state to obtain a noise power ratio. The tuning adjustment means is varied to maximize this noise power ratio.

Abstract: A carrier rejection circuit for improving carrier rejection in a balanced modulator includes balun transformers, connected to the carrier signal port and the modulated signal port, which reduces parasitic carrier leakage by reducing the average voltages at the ports, offset adjustment circuitry, connected to the modulating signal port, which applies an adjustable offset voltage to the modulating signal to reduce in-phase parasitic carrier leakage and carrier leakage caused by offset voltage at the modulating port, and a reactance network, connected between the carrier signal port and the modulated signal port, for reducing quadrature-phase parasitic carrier leakage.

Abstract: A lowpass filter with improved D.C. offset characteristics is disclosed. The lowpass filter includes an adjustable amplifier, an offset detecting circuit for producing an offset signal proportional to the D.C. offset between the voltage from the adjustable amplifier and the voltage to the lowpass filter, and a feedback circuit for producing a feedback signal in response to the offset signal which controls the adjustable amplifier to reduce the D.C. offset.

Abstract: An MRI signal processing apparatus is disclosed which provides a low noise output signal for use in a multi-coil MRI system, wherein each sensing coil provides an input signal to the MRI signal processing apparatus.

Abstract: Yarn is guided along a linear path through a light beam which is directed toward a photoelectric detector. Non-uniformities in the surface texture of the yarn cause the intensity of the light received by the detector to fluctuate rapidly as long as the yarn is moving. If the yarn stops moving as a result of breakage, the intensity of the light remains constant, and the detector produces an electrical signal indicative of the breakage.

Abstract: A communication system for transmitting data between a transmitting platform and a receiving platform, having two equal lengths of leaky coaxial cable forming the transmitting antenna which is located on the transmitting platform and the receive antenna is located on the receiving platform. The two equal lengths of leaky coaxial cable form a circle wherein one end of each of the equal lengths is a feedpoint for inputting data and the other end of each of the two equal lengths is terminated with a resistor to ground. The receive antenna is maintained a predetermined distance from the plane of the transmitting antenna.

Abstract: An RF coil system, used for a magnetic resonance imaging apparatus and adapted to perform at least one of application of an excitation high-frequency magnetic field and detection of magnetic resonance signals, comprises a plurality of coil elements arranged at regularly spaced intervals without overlap therebetween, an RF circuit for putting at least one of the coil elements into an operative state or an inoperative state, a neutralizing circuit for neutralizing inductive coupling between the coil elements, a tuning circuit for tuning at least one of the coil elements to a given frequency, an adder circuit for adding an output signal of the tuning circuit and conductors for electrically connecting the coil elements, the RF circuit, the neutralizing circuit and the adder circuit.

Abstract: A communication system for transmitting data between a transmitting platform and a receiving platform moving relative to each other. A circular strip-line transmission line forms the transmitting antenna located on the transmitting platform and a short segment of strip-line, similar in width to the circular strip-line, forms the receive antenna located on the receiving platform. The strip-line transmission line has at least two feedpoints for inputting data and at least two termination points that are terminated with a resistor to ground. The receive antenna is mounted close to the transmitting antenna.

Abstract: A feedback circuit for a magnetic resonance imaging (MRI) or spectroscopy device comprising a resonant circuit, including an MRI receiver antenna, for generating output voltages in response to nuclear magnetic resonance magnetization signals received by the antenna; an amplifier, coupled to the resonant circuit, for amplifying the output voltages; a resistive feedback path from an output of the amplifier to the resonant circuit, the feedback path carrying a first feedback current; and a capacitive current divider having a tap point to which the first feedback path is connected, for diverting a first portion of the feedback current away from the resonant circuit and for directing a second portion of the first feedback current to the resonant circuit. The Q value of the feedback circuit may be decreased without degrading the signal to noise ratio in order to obtain a sufficient bandwidth for receiving the nuclear magnetic resonance magnetization signals.

Abstract: A coil system for a magnetic resonance imaging (MRI) system includes a plurality of adjacent surface coils for sensing magnetization in a patient. Switches are provided for enabling selected ones of the plurality of coils to output electrical signals. A signal combiner combines the electrical signals from the selected coils into an output signal for further processing. Coupling cancellation networks are provided between adjacent ones of the plurality of coils for cancelling electrical coupling existing therebetween.

Abstract: In a quadrature antenna coil assembly of a magnetic resonance imaging system, the antenna coil assembly having a first receiver coil and a second receiver coil and having external coupling between the first and second receiver coils, a coupling cancellation network has a first set of terminals connected across the first receiver coil, a second set of terminals connected across the second receiver coil, and circuitry, connected between the first and second terminal sets, for generating additional coupling between the first and second receiver coils in opposite polarity and equal magnitude to the external coupling to cancel the external coupling.

Abstract: A variable-transconductance four-quadrant Gilbert-type modulator comprises a differential-transconductance amplifier, a fixed current source, a current sensing resistor, variable-transconductance circuitry, and feedback circuitry. The feedback circuitry is operatively connected to the differential-transconductance amplifier and to the current sensing resistor to receive the modulation voltage signal and to cause the voltage across the current sensing resistor to follow the voltage of the modulation voltage signal thereby causing the differential output current of the differential-transconductance amplifier to be directly proportional to the voltage on its input port thereby improving the linearity of the modulator. Also provided is an isolation output amplifier on the modulated output of the modulator to improve isolation between the carrier input signal and the modulated output.

Abstract: A quadrature antenna for magnetic resonance imaging systems is provided which includes first and second channels, each of these channels comprising a coil pair. Each of the four coils comprising the antenna is elliptical in shape and lies in a respective plane. The center point of each coil coincides with a reference point on the longitudinal axis of the antenna. The minor axes of the coils of the first channel coil pair are colinear. The minor axes of the coils of the second channel coil pair are also colinear with each other and are perpendicular to the minor axes of the coils of the first channel coil pair. Each of the four planes is inclined approximately forty five degrees (45.degree.) with respect to the longitudinal axis of the antenna.

Abstract: An automatic tuning circuit for a quadrature coil antenna system of a magnetic resonance imaging system is provided which includes a test coil for applying a test signal to each of a first and a second channel of the antenna to produce a first channel signal on the first channel and a second channel signal on the second channel. A phase meter assembly is coupled to the first and second antenna channels for measuring the phase of the second channel signal relative to the phase of the first channel signal to obtain an error signal. An auto-tune assembly is coupled to the phase meter assembly and to the second antenna channel for adjusting the phase of the second channel signal in response to the error signal to obtain a desired phase relationship between the first and second channel signals.

Abstract: A pulse control system for a magnetic resonance imaging transmitter has circuitry for detecting the peak value of the RF current in the transmitter coil for a given RF pulse; circuitry for comparing the detected peak value of the RF current with a desired reference peak value for the RF pulse, for determining the difference between the detected and the desired peak values for the RF pulse, and for determining a gain adjustment factor for the transmitter amplifier for the transmitter necessary to produce the desired peak value of the RF current in the transmitter coil; and circuitry for adjusting the gain of the transmitter amplifier in response to the gain adjustment factor to produce the desired peak value of the RF current for the RF pulse.

Abstract: A coupling circuit for coupling an inductive coil antenna of a magnetic resonance imaging system to receiver circuitry is provided which includes capacitive circuitry, resistive circuitry, and capacitive transformer circuitry. The capacitive circuitry is coupled in parallel with the antenna to provide capacitive reactance to the coupling circuitry. Resisitive circuitry is coupled in parallel with the antenna and with the capacitive circuitry to provide resistance R in the coupling circuit when an AC voltage at the resonant frequency of the coupling circuit is applied. Capacitive transformer circuitry is coupled in series with the antenna for transforming the resistance value R of the resistive circuitry into a transformed resistance value R'. This increases the apparent resistance of the coupling circuit in parallel with the antenna without increasing the actual resistance and power consumption of the coupling circuit.

Abstract: A circuit for stabilizing the electromagnet coil current of a magnetic resonant imaging device is provided which comprises a variable DC power supply coupled to provide current through the series combination of the primary winding of a DC current transformer, the electromagnet coil of the magnetic resonance imaging device, and a sense resistor. Changes in voltage across the sense resistor are monitored to provide rapid reaction to changes in the electromagnet coil current and the output of the DC current transformer is monitored to detect the absolute value of the electromagnet coil current. These two monitored signals are used to control the DC power supply in a manner which stabilizes the resultant electromagnet coil current.