Abstract: A Time Division Multiple Access (TDMA) radio system achieves synchronization by performing a two-step synchronization. A simplified frame/slot synchronization is followed by a symbol synchronization of higher accuracy. This symbol timing is passed to a frequency offset unit which determines the amount of frequency drift between the transmitter and receiver and compensates for the frequency drift. This results in improved receiver performance for the TDMA digital radio system.

Abstract: A magnetic resonance imaging system employs a sequence of radio frequency pulses and magnetic field gradients to detect and measure the spin-relaxation time of moving blood within a subject. Spin-lattice relaxation times are determined by first inverting longitudinal spin magnetization and then detecting the recovery of this magnetization with a series of detection radio frequency pulses. The inversion pulse is applied to the entire subject, but the detection pulses are applied only to a selection portion of the subject. Blood motion causes the blood in the detection region to be replaced for each detection pulse, thereby increasing the accuracy of the measurement and permitting the use of multiple detection pulses after a single inversion pulse. In-vivo application of this invention can be used to assess renal function in individual kidneys.

Abstract: Surgery is performed with a pulsed heat-producing device that selectively heats a region in a specific tissue within a patient destroying the tissue. The pulsed heat-producing device may be a coherent optical source that is guided by laser fiber to the tissue to be destroyed. In another embodiment, the pulsed heat-producing device is a focussed ultrasound transducer which concentrates ultrasonic energy at a focal point within the specific tissue. A magnetic resonance imaging system employing a real-time temperature-sensitive pulse sequence monitors the heated region of the tissue to provide temperature profiles allowing an operator to alter the position and size of the heated region.

Abstract: Surgery is performed with a pulsed heat-producing device that selectively heats a region in a specific tissue within a patient destroying the tissue. The pulsed heat-producing device may be a coherent optical source that is guided by laser fiber to the tissue to be destroyed. In another embodiment, the pulsed heat-producing device is a focussed ultrasound transducer which concentrates ultrasonic energy at a focal point within the specific tissue. A magnetic resonance imaging system employing a real-time temperature-sensitive pulse sequence monitors the heated region of the tissue to provide temperature profiles allowing an operator to alter the position and size of the heated region.

Abstract: An automated system for determining artifacts in images indicating defects in an imaging device being tested employs a constant radiation source which supplies radiation of spatially uniform intensity to the imaging device to be tested. The imaging device then creates a flood image A.sup.(0). A region of interest (ROI) mask unit for all pixel values of flood image A.sup.(0) sets values to zero outside of the imaging devices field of view to produce a flood image A.sup.(1). An image normalization unit normalizes flood image A.sup.(1) to have an average value of zero producing a normalized flood image A. A unitary transform unit performs a unitary transformation of normalized flood image A to produce an transform field which is then masked to select portions of the transform field. The squared magnitudes of the transform values of the selected regions are summed and the resulting sum is normalized for mask shape and flood image intensity to determine and quantify the presence of specific artifacts.

Abstract: A tracking system employs magnetic resonance signals to monitor the position and orientation of at least one device such as a catheter within a subject. The device has a plurality of receiver coils which are sensitive to magnetic resonance signals generated in the subject. These signals are detected in the presence of magnetic field gradients and thus have frequencies which are substantially proportional to the location of the coil along the direction of the applied gradient. Signals are detected responsive to sequentially applied mutually orthogonal magnetic gradients to determine the device's position and orientation in several dimensions. The position and orientation of the device as determined by the tracking system is superimposed upon independently acquired medical diagnostic images. One or more devices can be simultaneously tracked.

Abstract: An interactive system for producing acceptable quality fluoroscopy images determines X-ray tube photon count and voltage while minimizing X-ray radiation dosage to a subject. Parameters of the subject and the type of image to be produced are provided to the system. X-ray tube voltage U and photon count Q are initialized at a fraction of conventional values for a portion of a subject to be imaged. An image is created and sectioned into rectangles. Rectangles having the greatest and least gradient values are used to determine variances indicating signal and noise power respectively. Images are produced and adjusted until the maximum transmitted power is reached, or the signal-to-noise ratio does not increase beyond a quality increment. The process is repeated to optimize X-ray tube voltage. The X-ray fluoroscopy procedure is then performed with the optimum X-ray tube photon count and the optimum X-ray tube voltage thereby reducing X-ray dosage. The optimization is repeated periodically to readjust the system.

Abstract: A method for suppressing sampling-ring artifacts produced by spiral-scan-based 2D selective excitation pulses, such as a those exciting a `pencil-shaped` region, employs a 2D annular saturation pulse followed by a gradient `crusher` lobe which dephases the transverse magnetization in the annular region. The annular saturation pulse is itself based on a spiral k-space trajectory having a limited number of cycles and a small outer radius, and is designed to saturate magnetization of tissue of the subject corresponding to the artifact rings of an excitation region while not affecting a central region. The annular saturation pulse may also be reshaped to limit the peak RF power to levels currently used for clinical MR imaging, while preserving bandwidth and the 2D excitation profile.

Abstract: An optimum communication system employs an encoder coupled to a mapper and two parallel branches, each branch having a transmit filter a digital-to-analog converter, a low pass filter and a modulator coupled in series. Both modulators are coupled to a summer which provides an rf signal to a transmit antenna. A second antenna is coupled to a first down converter, an IF filter, a second down converter, an analog-to-digital converter and a decoder. The encoder is optimized by choosing a desired minimum Euclidean distance between symbols multiplied by the average to peak transmit power ratio (MPDR), an encoder alphabet and a number of constellation points. All possible encoder states and all possible input symbols are permutated to result in a plurality of encoder sets. The minimum distance between coded symbols and a P.sub.ib /P.sub.ab power ratio for each code set is determined. The encoder is adapted to output an encoder set U having a largest P.sub.ib /P.sub.

Abstract: An optimum communication system for communicating on adjacent frequency bands with minimal interference between adjacent channels comprises an encoder that is serially coupled to a mapper and two parallel processing branches, each processing branch having a transmit filter a digital-to-analog converter, a low pass filter and a modulator coupled in series. Both modulators are coupled to a summer, and an rf amplifier having a transmit antenna. The encoder is optimized by choosing a desired minimum Euclidean distance (DMED) between symbols, an encoder alphabet and a number of constellation points, permutating all possible encoder states and all possible input symbols to result in a plurality of encoder sets U, determining an in-band to adjacent band power ratio P.sub.ib /P.sub.

Abstract: A tracking system employs magnetic resonance signals to monitor the position of a device such as a catheter within a subject. The device has a receiver coil which is sensitive to magnetic resonance signals generated in the subject. These signals are detected in the presence of magnetic field gradients and thus have frequencies which are substantially proportional to the location of the coil along the direction of the applied gradient. Signals are detected responsive to sequentially applied mutually orthogonal magnetic gradients to determine the position of the device in several dimensions. The position of the device as determined by the tracking system is superimposed upon independently acquired medical diagnostic images.

Abstract: Surgery is performed with a pulsed heat-producing device that selectively heats a region in a specific tissue within a patient destroying the tissue. The pulsed heat-producing device may be a coherent optical source that is guided by laser fiber to the tissue to be destroyed. In another embodiment, the pulsed heat-producing device is a focussed ultrasound transducer which concentrates ultrasonic energy at a focal point within the specific tissue. A magnetic resonance imaging system employing a real-time temperature-sensitive pulse sequence monitors the heated region of the tissue to provide temperature profiles allowing an operator to alter the position and size of the heated region.

Abstract: Surgery is performed with pulsed heat means that selectively destroys tissue in a region within a patient. The size of the region destroyed is dependent upon the frequency of the pulses of the pulsed heat means and thermal conductivity of the tissue of the patient. The pulsed heat means can be a coherent optical source that is guided by laser fiber to the tissue to be destroyed. In another embodiment the pulsed heat means is a focussed ultrasound transducer that dissipates ultrasonic energy at a focal point within the region of tissue to be destroyed. A magnetic resonance imaging system employing a temperature sensitive pulse sequence creates an image of the tissue and the region being heated to allow a surgeon to alter the position of the pulsed heat means or vary the pulse frequency.

Abstract: An interactive system for producing acceptable quality fluoroscopy images determines X-ray tube photon count and voltage while minimizing X-ray radiation dosage to a subject. Parameters of the subject and the type of image to be produced are provided to the system. X-ray tube voltage and current are initialized at a fraction of conventional values for a portion of a subject to be imaged. An image is then created and transformed. A power ratio of low frequency components to high frequency components is calculated indicating quality of the image. Images are produced and adjusted until the maximum exposure is reached, or the power ratio does not increase beyond a quality increment. The process is repeated to optimize X-ray tube voltage. The X-ray fluoroscopy procedure is performed with the optimum X-ray tube photon count and the optimum voltage thereby reducing X-ray dosage. The optimization is repeated periodically to readjust the system.

Abstract: Invasive devices, such as laser fiber guides and biopsy needles, constructed of a material which exhibits little or no magnetic susceptibility, have a flexible polymer coating for retaining pieces of the device in the event of a fracture of the invasive device. The polymer coating also allows removal of the pieces of a fractured invasive device from the body of a subject without requiring surgery. The surgical instruments can be used inside a magnetic field during magnetic resonance (MR) imaging, thereby allowing interactive internal images to be produced and displayed to a surgeon during surgery. Since the invasive devices exhibit low susceptibility, they do not distort a created MR image.

Abstract: An optical interferometer and an ultrasonic distance measuring subsystem are used to obtain spectra from the surface of a sample. The interferometer uses a broadband electromagnetic radiation source and modulates the radiation at a frequency which is inversely proportional to wavelength. The modulated radiation impinges on the surface of interest where it is absorbed. The absorption of radiation causes the surface of the sample to expand. This change in dimension is then detected by the ultrasonic distance measuring subsystem which employs a single frequency acoustic radiation source to measure the instantaneous distance between the sample surface and the ultrasonic distance measurement subsystem. The detected changes in distance relate to amplitude of absorption at a given wavelength, thereby allowing absorption spectra for surface point to be generated indicating the chemical composition of each point of the surface.

Abstract: To obtain spectra from the surface of a sample, a first of a pair of interferometers includes a broadband radiation source and modulates the radiation at a frequency which is inversely proportional to wavelength. The modulated radiation impinges on the surface of interest where it is absorbed. The absorption of radiation causes the surface of the sample to expand. This change in dimension is then detected by a second interferometer which employs a monochromatic radiation source to measure the instantaneous distance between the sample surface and the second interferometer. The detection system of the second interferometer can be an imaging device such as a video camera to obtain the spatial distribution of chemical composition of the sample surface.

Abstract: A digital radio receiver for synchronization of radiowave transmissions for digital and analog FM signals in TDMA systems such as cellular telephones uses a tangent type differential detector that minimizes the bit error rate. The differential detector employs an A/D converter circuit that samples a received signal, a sorter circuit that selects a predetermined number of samples to be used in the decoding, a sample and phase adjustment circuit that allows for a carrier phase adjustment and sample timing adjustment, a divider circuit that eliminates the need for a conventional limiter by causing a ratio of amplitudes to be processed instead of absolute signal amplitudes, an inverse tangent circuit creates a decoded phase angle from the ratio, a delay circuit and a summer circuit that create a differential signal, a modulo-2.pi. correction circuit that corrects for wrap-around errors about the real axis, and a four-phase decoder circuit to decode the signal into a pair of bits.

Abstract: A magnetic resonance (MR) surgery system facilitates surgery with a focussed ultrasound transducer that selectively destroys tissue in a region within a subject. The focussed energy transducer dissipates energy at a focal point within the region of tissue to be destroyed. A non-magnetic positioning device having a vertical dimension small enough to fit easily within the bore of an MR magnet moves an energy transducer in a limited vertical space. The positioning device employs a plurality of hydraulic positioners and an inclined plane to position the ultrasound focal point under the control of an operator. An MR imaging system employing a temperature sensitive pulse sequence creates an image of the tissue and the region being heated to allow the operator to adjust the position of the ultrasonic transducer so as to direct ultrasonic energy to the appropriate location.

Abstract: A tracking system employs magnetic resonance signals to monitor the position and orientation of a device, such as a catheter, within a subject. The device has an MR active sample and a receiver coil which is sensitive to magnetic resonance signals generated by the MR active sample. These signals are detected in the presence of magnetic field gradients and thus have frequencies which are substantially proportional to the location of the coil along the direction of the applied gradient. Signals are detected responsive to sequentially applied mutually orthogonal magnetic gradients to determine the device's position in several dimensions. The position of the device as determined by the tracking system is superimposed upon independently acquired medical diagnostic images. One or more devices can be simultaneously tracked.