Abstract: Magnetic resonance imaging hardware (A) defines a patient receiving region (20) that is surrounded by a bore liner (22). A socket (50) is mounted in the bore liner with an appropriate receptacle for receiving a standard plug (52) of a conventional pulse oximetry system. Conventional pulse oximetry systems include a sensor unit (54) connected with a cable (56) having the plug (52) at one end thereof. A notch filter (62) attenuates currents near the resonance frequency of the imager. A preamplifier (60) amplifies signals from the sensor unit. Within the shielding (66) of the preamplifier, a low pass filter (68) is provided to remove induced radio frequency components from the preamplified sensor unit signal. A radio frequency filter (70) mounted at the shield of the shielded room (B) prevents radio frequency signals from reaching an exterior processing and display unit (E) and prevents radio frequency signals from a clock (72) of the processing and display unit from being conveyed into the shielded room (B).

Abstract: A magnetic resonance imaging apparatus includes one or more digital transmitters (B), one or more digital receivers (C), and digital data processing circuitry (D) which are all clocked and controlled by a single clock (F). Each digital transmitter includes a numerically controlled modulated oscillator (20) which processes digital phase and frequency signals to produce an output which addresses a wave-form map stored in a PROM (22). Each wave-form output of the PROM is multiplied (24) by a digital amplitude profile signal to generate a phase, frequency, and amplitude modulated digital RF signals. A clock gate (30) controls clocking of the digital modulation to create RF pulses. A digital-to-analog converter (28) converts the digital information to an analog RF pulse which is applied to a subject in an image region. The receivers each include an analog-to-digital converter (60) which digitizes the magnetic resonance signal emanating from the subject in the image region with four fold oversampling.

Abstract: Radio frequency apparatus for a magnetic resonance system is provided which includes an r.f. coil and DC controlled circuitry for selectively altering the characteristics of the coil. A loading coil is provided which is selectively activated to de-Q the coil during r.f. transmission so as to minimize the loading effects of the subject and their effect on coil impedance. A switched network is provided which selectively destroys the normal resonant condition of the coil when a second r.f. coil is operative to minimize interaction between the two coils.

Abstract: A family of high Q radio frequency coils for an NMR imaging system is provided. The coil family includes a transmitting coil for transmitting an r.f. field aligned with a given plane. The transmitting coil is used with one of the described receiving coils, each of which is responsive to NMR signals in a plane oriented orthogonally to said given plane. The receiving coils employ an open, arcuate configuration, which alleviates sensations of confinement characteristic of fully enclosing coil forms. Arcuate sections of the receiving coils are curved away from the patient, to decrease signal reception at areas from which meaningful signals cannot be gathered. To prevent interaction between the transmitting and receiving coils, means are provided for rendering each coil nonresponsive to NMR and radio signal frequencies when the coils are not being operated.

Abstract: Compensation is provided for a gradient field of an NMR imaging system which compensates for the effects of eddy fields developed in the static magnetic field from metallic components during gradient field switching. The compensation comprises providing current overshoot to the gradient coil during gradient switching. The overshoot current decays with a time constant chosen to substantially offset the decay of eddy fields following gradient switching. In a preferred embodiment, a time constant network representative of eddy field decay is coupled in combination with a feedback signal from a current sampling resistor of the gradient coil.