Communications – electrical: acoustic wave systems and devices – Transmitter systems – With beam forming – shaping – steering – or scanning
Reexamination Certificate
1999-10-14
2001-05-01
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Transmitter systems
With beam forming, shaping, steering, or scanning
C367S007000, C367S011000
Reexamination Certificate
active
06226228
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to ultrasound imaging systems, and in particular to improved methods for imaging nonlinear contrast agents with such systems.
Nonlinear contrast agents are described for example by V. Uhlendorf, et al., in “Nonlinear Acoustical Response of Coated Microbubbles in Diagnostic Ultrasound” (1995 Ultrasonic Symposium, pp. 1559-1562). Such agents possess a fundamental resonant frequency. When they are insonified with high intensity ultrasonic energy at this fundamental frequency, they radiate ultrasonic frequency at a harmonic of the fundamental frequency. Such contrast agents are often used to highlight regions containing blood loaded with the contrast agent. For example, in the case of a blood-filled chamber of the heart, the borders of the chamber can be distinguished more easily when contrast agent is used. Since the contrast agent generates harmonic ultrasound energy, echoes from tissue (containing no contrast agent) at the fundamental frequency may be eliminated by filtering at the receive beamformer.
Typically, such agents are used with an imaging system having a transmit beamformer that transmits ultrasonic energy at the fundamental frequency and a receive beamformer responsive to the harmonic. In order to image the contrast agent clearly, it is known to reduce energy at the harmonic in the transmit beam, and to reduce sensitivity of the receive beamformer to energy at the fundamental.
In the past, this has been done by using a burst of square or sine waves to form the transmit beam, and by using appropriate band pass or high pass filters in the receive beamformer. Though a large pulse count reduces energy at the harmonic, it reduces time resolution of the pulse, and therefore spatial resolution of the resulting image.
The present invention is directed to further improvements that enhance the imaging of such nonlinear contrast agents.
SUMMARY OF THE INVENTION
This invention relates to improvements to a method for imaging a target, which method comprises the steps of (a) transmitting ultrasonic energy at a fundamental frequency and (b) receiving reflected ultrasonic energy at a harmonic of the fundamental frequency.
According to a first aspect of this invention, the transmitting step includes the step of transmitting ultrasonic energy in power bursts, each power burst comprising a respective envelope shape, the envelope shapes rising gradually to a respective maximum value and falling gradually from the respective maximum value. This arrangement can reduce harmonic energy in the power burst.
According to a second aspect of this invention, the transmitting step includes the step of generating a transmit waveform and filtering the transmit waveform with a filter adapted to reduce ultrasonic energy in the transmit waveform at the harmonic of the fundamental frequency to at least −30 dB with respect to the fundamental frequency.
According to a third aspect of this invention, the transmitting step includes the step of generating a transmit waveform with a programmable waveform generator such that ultrasonic power in the transmit waveform at the harmonic of the fundamental frequency is reduced by at least −30 dB with respect to ultrasonic power in the transmit waveform at the fundamental frequency.
According to a fourth aspect of this invention, the transmitting step includes the step of focusing ultrasonic energy in a transmit beam having a line focus.
According to a fifth aspect of this invention, the transmitting step includes the step of focusing ultrasonic energy in a transmit beam having an elongated high power region by focusing at least first selected frequency components from at least a first plurality of transducer elements at a first range and focusing at least second frequency components from at least a second plurality of transducer elements at a second range.
Other aspects of the invention relate to the use of switched filters in the transmitting step.
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Cole Christopher R.
Hossack John A.
Mo Jian-Hua
Acuson Corporation
Brinks Hofer Gilson & Lione
Pihulic Daniel T.
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