Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-03-15
2002-09-03
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S459000
Reexamination Certificate
active
06443900
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-072854, filed Mar. 15, 2000; and No. 2001-048579, filed Feb. 23, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic transducer and ultrasonic transducer system for use in harmonic imaging ultrasonic diagnosis, and particularly to an ultrasonic transducer which transmits a fundamental ultrasound having a center frequency f
0
, and detects the reflected ultrasound having a center frequency nf
0
(n: integer of 2 or more), generated by the propagation of the fundamental ultrasound.
In recent years, harmonic imaging ultrasonic diagnosis has attracted attention. A diagnosis method is roughly classified into a contrast harmonic imaging using a contrast medium, and tissue harmonic imaging of detecting the non-linearity of an elastic property of a living tissue, and displaying the non-linearity in an image. The situation is described in detail in “special issue on electronics clinical medicine ultrasound—Latest Ultrasound—: distributed text of 1999 academic lecture by the Japan Society of Ultrasound in Medicine”.
The tissue harmonic imaging is a technique of transmitting an ultrasonic pulse having a center frequency f
0
to a living tissue without using the ultrasonic contrast medium, extracting a high order harmonic component nf
0
(n being an integer of 2 or more) included in a returned echo signal, and displaying a relation between an amplitude of the component and an echo signal receiving time in a tomographic image to obtain a diagnosis image.
For an in vitro purpose, a diagnosis apparatus with the aforementioned function mounted thereon is already on the market. In the tissue harmonic imaging diagnosis method, heart structures such as a left chamber wall can be relatively clearly observed, even in an overweight person, an aged person or a person who smokes, whose echo image has been frequently blurred because of mixed noise.
The ultrasonic diagnosis method is at present used only for the in vitro purpose, and a second order high harmonic wave (n=2), that is, the ultrasound having a center frequency of 2f
0
is used. In a conventional ultrasonic transducer, transmission of the ultrasound having a center frequency f
0
and reception of the ultrasound having a center frequency 2f
0
are performed by the same ultrasonic vibrator. Therefore, the ultrasonic vibrator used needs to have a remarkably broad band.
Moreover, to further enhance the resolution, utilization of a third order harmonic signal is expected, but an ultra-broad band ultrasonic vibrator which can detect an ultrasound having a center frequency of 3f
0
, that is, a third order harmonic signal has not been realized yet.
It is usually said that the sensitivity of a second order harmonic signal is deteriorated by 15 to 20 dB, and a third order harmonic signal is further deteriorated by 15 to 20 dB as compared with the fundamental frequency signal. Therefore, the aforementioned sensitivity deterioration with the broadened band disadvantageously causes further deterioration of the diagnosis image.
Furthermore, since the transmission of the ultrasound having the center frequency f
0
and the reception of the ultrasound having the center frequency 2f
0
are performed by the same ultrasonic vibrator, a fundamental wave and various unnecessary vibrations are unavoidably superimposed onto a received ultrasonic signal.
To improve such disadvantages, Jpn. Pat. Appln. KOKAI Publication No. 11-155863 discloses an ultrasonic transducer which has a transmitting piezoelectric resonator and receiving piezoelectric resonator in one case which can efficiently receive the high order harmonic component. A constitution of the ultrasonic transducer is shown in FIG.
31
.
As shown in
FIG. 31
, an ultrasonic transducer
1000
has a transmitting piezoelectric resonator
1002
, and a receiving polymer piezoelectric resonator
1004
disposed in front of the transmitting piezoelectric resonator. The receiving polymer piezoelectric resonator
1004
and transmitting piezoelectric resonator
1002
are layered and disposed via an acoustic matching layer
1006
.
Front electrodes of the transmitting piezoelectric resonator
1002
and receiving polymer piezoelectric resonator
1004
are both connected to a grounding lead wire
1008
and are kept at a ground potential. A back-side electrode of the transmitting piezoelectric resonator
1002
is connected to a transmitting shielding wire
1010
, and a drive signal is supplied via the wire. A back-side electrode of the receiving polymer piezoelectric resonator
1004
is connected to a receiving shielding wire
1012
, and a received signal is extracted via the wire.
The transmitting piezoelectric resonator
1002
has a resonant frequency or an antiresonant frequency which agrees with a resonant frequency of the ultrasonic contrast medium or a frequency having a specific relation with respect to the ultrasonic contrast medium. On the other hand, the receiving polymer piezoelectric resonator
1004
is a non-resonating piezoelectric resonator, and can receive even the high order harmonic component generated based on the nonlinear behavior of the ultrasonic contrast medium.
Since the acoustic matching layer
1006
is disposed between the transmitting piezoelectric resonator
1002
and the receiving polymer piezoelectric resonator
1004
in the ultrasonic transducer
1000
, only a portion with the ultrasonic contrast medium present therein, such as a blood vessel in a human body and a cancer tissue with capillary concentrated on a peripheral portion thereof, can be depicted more clearly than other portions.
Since the ultrasonic transducer
1000
has separate transmitting and receiving piezoelectric resonators, the band is easily broadened, and properties suitable for harmonic imaging are expected to be displayed, as compared with the conventional ultrasonic transducer for general use for performing transmission/reception with the single piezoelectric resonator.
However, in the conventional ultrasonic transducer shown in
FIG. 31
, the transmitting and receiving ultrasonic vibrators are superposed and disposed. Therefore, when a transmitted ultrasonic wave is passed through the receiving ultrasonic vibrator, the ultrasonic wave excites the receiving ultrasonic vibrator and is modulated by the vibration. As a result, undesired vibration of the resonant frequency of a receiving ultrasonic vibrator film is mixed in with the transmitted ultrasonic wave. This means that it is impossible to judge whether the signal detected by the receiving ultrasonic vibrator is the high order harmonic signal from the ultrasonic contrast medium or the signal mixed during transmission. Therefore, the mixture of the undesired vibration causes a large deterioration of the resolution.
Moreover, for use in a so-called tissue harmonic imaging (THI) for detecting a nonlinear ultrasonic wave generated with propagation of the fundamental ultrasonic wave in the living tissue, the high order harmonic wave needs to be securely selected and detected, because a sound pressure level of the nonlinear ultrasonic wave generated with the propagation of the fundamental ultrasound in the living tissue is as small as about −20 dB, as is well known. However, in the conventional ultrasonic transducer shown in
FIG. 31
, since the receiving ultrasonic vibrator has a non-resonating broad-band property, also for the received signal, the high order harmonic signal level is −20 dB lower with respect to the fundamental wave and such a situation is unchanged.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a technique of an ultrasonic transducer which has a transmitting piezoelectric resonator and receiving piezoelectric resonator contained in the same case, but which can detect a harmonic signal with a high sensitivity without being adversely affected by resolution
Adachi Hideo
Wakabayashi Katsuhiro
Jaworski Francis J.
Olympus Optical Co,. Ltd.
Scully Scott Murphy & Presser
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