Abstract: A two-dimensional ultrasonic phase array is a rectilinear approximation to a circular aperture and is formed by a plurality of transducers, arranged substantially symmetrical about both a first (X) axis and a second (Y) axis and in a plurality of subarrays, each extended in a first direction (i.e. parallel to the scan axis X) for the length of a plurality of transducers determined for that subarray, but having a width of a single transducer extending in a second, orthogonal (the out-of-scan-plane, or Y) direction to facilitate dynamic focussing and/or dynamic apodization. Each subarray transducer is formed of a plurality of sheets (part of a 2-2 ceramic composite) all electrically connected in parallel by a transducer electrode applied to juxtaposed first ends of all the sheets in each transducer, while a common electrode connects the remaining ends of all sheets in each single X-coordinate line of the array.

Abstract: A method for receiving a return signal from each of plurality M of different beam directions in media excited by a single excitation event, is to: assign each of the M directions to be substantially equally separated, by a small angular displacement from a central beam; excite the media with a single energy beam transmitted to be focused at the central beam; receive a return signal from the central beam; and for each of the M different beam directions, independently rotating the phase of the received return signal by an amount predetermined to displace the apparent focus of the response beam to the associated direction.

Abstract: A method for generating an output stream of digital data words, with each data word representing the amplitude of an analog signal at one of a multiplicity F samples each second and with substantially equally spaced time intervals T therebetween, is obtained from a digital baseband demodulation system used for array beam forming. A data stream, formed of interleaved ADC output digital data words acquired from a set of converters, is at a rate of F total samples/second. Subsequent digital demodulation, filtration, and decimation provides digital output signals which need less delay resolution prior to the formation of coherent sum signals, thereby reducing overall channel memory requirements. The output baseband data stream has enhanced dynamic range, thereby reducing the ADC bit density requirements.

Abstract: A method for phase conjugation adaptive reduction of phase aberration effects upon the time delays necessary for information of a beam of coherent energy focused within non-homogeneous medium at a selected range R from, and at an angle .theta. with respect to the normal to, the surface of an array of a plurality N of transducers, each for providing a portion of the energy of the beam when excited and for converting energy reflected thereto to a signal therefrom, first bounces from a large collection of scatterers, contained in a portion of the medium to be investigated, a probe beam for that beam angle .theta.; cross-correlating, for each probe beam, the received signals from each of the (N-1) pairs of adjacent transducers to derive a like number of phase conjugation correction signals; arithmetically operates upon the plurality of phase conjugation correction signals to provide a time correction for the time delay associated with each probe beam transducer, for that range R and angle .theta.

Abstract: A single rotating NMR .pi. pulse provides simultaneous spatially-selective inversion or spin-echo refocussing of nuclear pins in two orthogonal dimensions. The two-dimensional spatially-selective pulse utilizes a single RF pulse, with either a square of an amplitude-modulated or a frequency-modulated envelope, and applied in the presence of an amplitude-modulated magnetic field gradient which reorients through the desired dimensions in which selection is desired while the RF pulse is present. These rotating, or ".rho.", pulses are useful for reduction of aliasing signal artifacts is restricted field-of-view high-resolution NMR imaging and, when combined with one-dimensional-localized chemical shift spectroscpoy techniques (such as those employing surface detection coils) is especially useful for the production of three-dimensionally localized NMR spectra.

Abstract: A method for steering a beam of vibratory energy to a desired angle .theta. with respect to the plane of an array of transducers, uses apparatus which generates a plurality of sampling strobe sequences with each strobe pulse occurring at a time interval T after the preceding strobe pulse, where T satisfies the Nyquist condition. A different one S.sub.j of the strobe signals is assigned to each different transducer channel and the commencement time of the strobe signal in each channel is offset by a time interval which is a first positive integer multiple M.sub.j, selected for each angle .theta., of an offset time interval which is not greater than 1/32nd of the reciprocal of the ultrasonic excitation frequency F.sub.u.

Abstract: A technique has been developed which reduces blood-flow artifacts in multi-echo, multi-slice magnetic resonance (MR) imaging by rephasing spins which have arbitrary velocity as well as static spins. The technique requires tailoring of the gradient structure along at least one of the three axes so as to null out in the preferred embodiment the zeroth and first moments of the gradient distributions.

Abstract: A method for minimizing the inhomogeneity of a static magnetic field, produced by a main magnet, over a selected arbitrary volume, by operation of a plurality N of shimming coils each independently producing an associated shimming magnetic field having an associated inhomogeneity which is a function of spatial location over that same volume, uses the steps of: measuring the magnitude of the main magnet field, in the absence of all shimming fields, at a plurality of locations X.sub.i upon the surface of an imaginary sphere enclosing the arbitrary volume; measuring the polarity and magnitude of each of the N shimming fields, with respect to the polarity and magnitude of a D.C. current flowing through the associated shimming coil, at the same plurality of locations X.sub.i upon the imaginary sphere surface; determining the weighted mean-square variation of the total field at each of another plurality of points Y.sub.

Abstract: Composite pulses are employed in NMR imaging for time-reversal of nuclear spins in a transverse planar region of a sample to produce spin-echo signals. The composite pulses comprise a sequence of pulses for producing a 90.degree. rotation of the spins about a first transverse axis, a 180.degree. rotation of the spins about a substantially orthogonal transverse axis, and a 90.degree. rotation of the nuclear spins about the first transverse axis. The composite pulses minimize time-reversal errors caused by static magnetic field and RF field inhomogeneities, and afford multiple spin-echo NMR imaging sequences.

Abstract: A method for magnetic resonance imaging of fluid flow, and particularly in vivo blood flow, uses multiple-echo phase-contrast sequences of signals both in the magnetic field gradient in the direction in which fluid flow is to be determined, and in the radio-frequency (RF) magnetic field utilized with the magnetic field gradient. The magnetic field gradient has a pair of phase-encoding pulses having a zero mean value effect upon the sample, either alone or with inversion by an intermediate 180.degree. RF pulse signal. A first multi-echo sequence, provided with the phase-encoding pulse pair, provides information of both the amplitude and phase-shift of each pixel of the imaged flowing material while a second multiple echo sequence, devoid of the phase-encoding-gradient pulses, provides information as to the amplitude and the undesired initial phase-shift of each pixel of both stationary and flowing material.

Abstract: Improved B-scan images are obtained in an ultrasonic scanner by means of a phase insensitive imaging system. Backscattered signals are detected by a phased array of detector elements. Signals from each detector element are full wave rectified, low pass filtered and are nonlinearly processed by power law compression. The compressed signals are summed and then expanded by an inverse power law function.

Abstract: Slowly tapering the cone angle as a function of distance along the cone results in a horn transducer that has a sharp focus in the near field and a large depth of field. The horn is simulated by time delaying the excitation pulse sequence to an annular array. An ultrasonic imaging system, particularly for contact B-scanning, uses an annular array to simulate both a horn transmitter and a fixed-focus receiver. This device has good resolution over a large depth of field and is easy to implement.

Abstract: A conventional ultrasonic B-scan image is converted into a volume backscatter image by accounting for four propagation effects: dispersion of transmitted energy, beam width and beam intensity variations, inhomogeneous attenuation of ultrasonic energy, and signals resulting from specular reflections at interfaces. These images are a two-dimensional map of backscatter efficiency, are independent of details of the measurement system, and are quantitative images of an intrinsic property of tissue and other materials.

Abstract: The beam characteristics of individual array elements of a linear transducer array are altered by collimation of ultrasonic waves using critical angle effects. A phased array transducer for a medical imaging system with a 90.degree. image sensor has a collimator which is a thin sheet of polyethylene. Acoustic waves whose angle of incidence is greater than the critical angle are totally reflected. Insignificant ultrasonic energy is generated outside of the imaged sector and there is a modest insertion loss over the acceptance region.