Steven George Karr

A New Time Domain Technique for Velocity Measurements Using Doppler Ultrasound

A new technique for determining the Doppler frequency shift in a phase-coherent pulsed Doppler system is presented. In the new approach, the Doppler frequency shift is given directly in the time domain in terms of the measured I and Q components of the measured Doppler signal. The algorithm is based on an expression for the instantaneous rate of change of phase which separates rapidly varying from slowly varying terms. It permits noise smoothing in each term separately. Since the technique relies solely on signal processing in the time domain, it is significantly simpler to implement than the classic Fourier transform approach. In addition, the algorithm can be shown to give rigorously accurate values for instantaneous frequency and outperform the Fourier transform approach in poor signal-to-noise environments. Experimental results are presented which confirm the superiority of the new domain technique.

Method and apparatus for coherent imaging system

A method and apparatus for improved digital processing of the analog echo signals in a coherent imaging system is described which simplifies the channel circuitry requirements. The analog echo signals detected with a phased array of transducer elements are first compressed in a non-linear manner then expanded non-linearly with analog-to-digital converter means to provide increased instantaneous dynamic range in the overall system. Representative phased array coherent imaging systems having the improved digital processing means are also disclosed.

A high speed FIR filter designed by compiler

Digital-serial computation is a hybrid between bit-serial computation and parallel computation. In digit-serial computation, data is divided into digits of N bits, and computations take place one digit of data at a time. The PARSIFAL silicon compiler is a software environment for designing chips using this basic computational architecture. The authors report on a four-tap FIR (finite-impulse response) filter built using this compiler. In order to avoid the throughput loss inherent in serial computation, two parallel computations are interleaved to achieve a 35-MHz-per-sample throughput rate

Architecture for ultrasonic imaging

An ultrasonic imaging processing system includes transducers and means to generate in an analog fashion, in-phase and quadrature phase signals. These signals are converted to digital form and a butterfly phase rotator circuit is employed to correct for phase differences in beam steering and focusing. In particular, speed and simplicity is achieved through the utilization of read only memory means providing appropriate function values for phase correction in conjunction with digital multiplication and summing circuitry.

Technical alternatives in nuclear magnetic resonance (NMR) imaging

In this paper we consider the choice of the magnetic field for an imaging system based on the nuclear magnetic resonance of hydrogen. We show by analysis that the quality, or contrast-to-noise ratio, of images based on T1 discrimination increases with field or frequency up to 2 T or 85 MHz. After a brief discussion of potential engineering limitations we present results showing that images of the human head with excellent anatomic detail can be produced at 1.5 T or 64 MHz.