Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-11-04
2001-02-13
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S447000, C600S440000
Reexamination Certificate
active
06186950
ABSTRACT:
This invention relates to ultrasonic diagnostic imaging systems which separate fundamental and harmonic frequency signals by the pulse inversion technique and, in particular, to the enhancement of such systems by reducing the effects of motion.
U.S. Pat. No. 5,706,819 and 5,951,478 describe a technique for separating the fundamental and harmonic frequency components of ultrasonic signals known as pulse inversion. As described in those patents, a target is insonified by two or more fundamental frequency pulses of different phase or polarity and echoes are received following each pulse. The received echoes will contain both fundamental and harmonic frequency components, due either to the presence of contrast agents in the body or the nonlinear response of tissue to the transmitted waves. When depth-corresponding received echoes of the two pulse transmissions are combined, the fundamental frequency components of the echo signals will cancel due to the linear nature of those components and the differing phase or polarity of the transmit pulses. The harmonic components however, being quadratically proportional to the incident pressure wave, will not cancel but will reinforce each other. As the patents indicate, when the target medium is stationary or quasi-stationary, almost complete cancellation of the fundamental components will occur, leaving separated harmonic components.
While the assumption of a stationary or quasi-stationary medium may be relatively valid for static tissue and organs, it is only an approximation for moving tissue such as the beating heart. For example, when myocardial perfusion is being assessed by pulse inversion harmonic techniques, the continually moving heart walls will introduce motional effects into the echoes received from the multiple transmit pulses. As a result, the fundamental components will only partially cancel and the residual fundamental components will constitute unwanted noise or artifacts in the desired harmonic signals. Hence it would be desirable to enhance the practice of the pulse inversion technique so that fundamental components would be virtually completely cancelled, even in the presence of these motional effects.
In accordance with the principles of the present invention, the pulse inversion technique is enhanced to reduce motional effects by insonifying a target with three or more transmit pulses of differing phase or polarity. Pairs of echoes from the target from oppositely phased or poled transmit pulses are combined to form partial echo sums, and the partial sums are accumulated to form a full echo sum comprising harmonic signals in which fundamental components are significantly reduced. In general, the use of a greater number of transmit pulses and echoes results in greater fundamental component reduction. In a preferred embodiment, a sequence of echoes from a target from phase- or polarity-alternating pulses is processed by a filter structure utilizing a continually varying sequence of weighting coefficients. The coefficients may exhibit a Gaussian variation and may conveniently be computed for any number of samples by using the rule of Pascal's triangle. Preferably the filter coefficients are scaled so that the separated harmonic signals are concurrently normalized in amplitude.
REFERENCES:
patent: 5623928 (1997-04-01), Wright et al.
patent: 5706819 (1998-01-01), Hwang et al.
patent: 5833613 (1998-11-01), Averkiou et al.
patent: 5951478 (1999-09-01), Hwang et al.
patent: 5961463 (1999-10-01), Rhyne et al.
patent: WO 99/30617 (1999-06-01), None
U.S. application No. 09/156,097, Burns et al., filed Sep. 17, 1998.
Simpson et al., “Pulse Inversion Doopler: A New Method for Detecting Nonlinear Echoes from Microbubble Contrast Agents.” pp. 1-30, Mar. 31, 1998.
Averkiou Michalakis
Powers Jeffry E.
ATL Ultrasound
Lateef Marvin M.
Patel Maulin
Yorks, Jr. W. Brinton
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