Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2003-03-17
2004-03-02
Imam, Ali M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06699192
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic receiving apparatus for receiving ultrasonic waves, and further to an ultrasonic imaging apparatus to be used for medical diagnosis or nondestructive inspection by receiving ultrasonic waves using such an ultrasonic receiving apparatus.
2. Description of a Related Art
Conventionally, in an ultrasonic imaging apparatus, generally a one-dimensional sensor array using a piezoelectric element including a piezoelectric ceramic represented by PZT (Pb (lead) zirconate titanate) or a macromolecule piezoelectric element such as PVDF (polyvinyl difluoride) has been used as an element (vibrator) for transmitting and receiving ultrasonic waves. Two-dimensional images in plural cross sections of an object to be inspected are obtained while mechanically shifting a one-dimensional sensor array as described above, and further, by synthesizing these two-dimensional images, a three-dimensional image is obtained.
However, according to this technique, since a time lag is generated in the shifting direction of the one-dimensional sensor array, cross-sectional images at different time points are synthesized resulting in a blurred synthesized image. Accordingly, the technique is not suitable to such a case where images of a living organism as an object are taken in ultrasonic echo observation or the like.
In order to obtain high quality three-dimensional images using ultrasonic waves, a two-dimensional sensor capable of obtaining two-dimensional images without shifting the sensor array is required.
However, although minute processing on elements and wiring to a number of minute elements are required in the case where the two-dimensional sensor array is manufactured using the above-described PZT or PVDF, further miniaturization and integration of elements exceeding the state of the art are difficult. Also, even when the above-described problems are solved, such problems still remain that the cross talk between elements is increased, the SN-ratio is lowered due to increase of electrical impedance caused from minute wirings, electrodes of minute elements get damaged easily, and so on. Therefore, it is difficult to achieve the two-dimensional sensor array using the PZT or the PVDF.
On the other hand, another type of sensor is also known, in which received ultrasonic wave signal is converted into an optical signal and then detected. As for a photo-detection type ultrasonic sensor, a sensor in which a fiber Bragg grating (abbreviated as FBG) is used (see TAKAHASHI et al., National Defense Academy “Underwater Acoustic Sensor with Fiber Bragg Grating”, OPTICAL REVIEW Vol. 4, No. 6 (1997) p. 691-694), and a sensor in which a Fabry-Perot resonator (abbreviated as FPR) structure is used (see UNO et al., Tokyo Institute of Technology “Fabrication and Performance of a Fiber Optic Micro-Probe for Megahertz Ultrasonic Field Measurement”, T.IEE Japan, Vol. 118-E, No. 11, '98) are reported. When a two-dimensional sensor array is manufactured by using an ultrasonic sensor as described above, the following advantages can be obtained, that is, electrical wiring to a number of minute elements is not required and satisfactory sensitivity is obtained.
Further, a photo-detection type ultrasonic sensor having a two-dimensional detection surface is also known. For example, Beard et al., University College London “Transduction Mechanisms of the Fabry-Perot Polymer Film Sensing Concept for Wideband Ultrasound Detection”, IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 46, NO. 6, NOVEMBER 1999 discloses that a polymer film having a Fabry-Perot structure is used for detecting ultrasonic waves. In a film-like ultrasonic sensor as described above, the cost can be reduced since processing on a number of minute elements is not required.
However, the photo-detection type ultrasonic sensor has the following problem, that is, multiple reflection of an ultrasonic wave is generated on a backside of the ultrasonic wave receiving surface.
Herein, taking a photo-detection type two-dimensional plane sensor as an example, the multiple reflection of an ultrasonic wave will be explained. As shown in
FIG. 15
, an ultrasonic detecting element
100
includes a substrate
101
and an ultrasonic sensing portion
102
. In this example, the ultrasonic sensing portion
102
has a Fabry-Perot resonator structure including a total reflection mirror
103
, a half mirror
104
and a cavity
105
being formed between the total reflection mirror
103
and the half mirror
104
. The member forming the cavity
105
is subjected to a geometrical displacement by being applied with an ultrasonic wave.
While allowing light to enter into the ultrasonic detecting element
100
from the substrate
101
side, an ultrasonic wave is applied to a receiving surface
102
a
of the ultrasonic detecting element
100
. Then, owing to the acoustic pressure changes of the ultrasonic wave, the optical path length L of the cavity
105
changes in accordance with the position of the receiving surface
102
a
, and the light intensity reflected from the ultrasonic sensing portion
102
changes corresponding to the position thereof. By converting the intensity of the reflected light into the intensity of the ultrasonic wave, the intensity of the ultrasonic wave, which corresponds to the position of the receiving surface
102
a
, can be detected.
Referring to
FIGS. 16 and 17A
, the ultrasonic wave propagating from medium and containing information concerning an object to be inspected generates vibration at a point A, and propagates into the inside of the ultrasonic detecting element
100
(ultrasonic wave US
1
). Then, the ultrasonic wave US
1
is reflected at a point B of an interface on the opposite side of receiving surface
102
a
. At this moment, the ultrasonic wave US
1
generates vibration at the point B and returns toward the direction of the receiving surface
102
a
(ultrasonic wave US
2
). Further, the ultrasonic wave US
2
is reflected at the receiving surface
102
a
. At this moment, the ultrasonic wave US
2
generates vibration at a point C and propagates again to the rear surface of the receiving surface
102
a
(ultrasonic wave US
3
). Thus, in the ultrasonic detecting element
100
, the reflection is repeated until the propagated ultrasonic wave fades away. Owing to this phenomenon, as shown in
FIG. 17B
, the signal from the ultrasonic detecting element
100
is mixed with signals generated through the multiple reflection (detection signals at the points C and E) in addition to the signal concerning the object to be inspected (a detection signal at the point A) that is to be normally detected.
The above described multiple reflection of the ultrasonic wave becomes a cause to decrease the SN-ratio in the ultrasonic image, resulting in a decreased image quality. Accordingly, for example, in an ultrasonic receiving apparatus that uses piezoelectric element for transmitting and receiving ultrasonic waves, the ultrasonic wave is attenuated by connecting a backing material including a ferrite core or the like to a piezoelectric element. However, in the photo-detection type ultrasonic receiving apparatus, since it is necessary to take the optical transmissibility into consideration, the backing material same as that of conventional manner can not be used.
SUMMERY OF THE INVENTION
The present invention has been achieved in view of the above-described problems. An object of the present invention is, in a photo-detection type ultrasonic receiving apparatus, to increase the quality of the ultrasonic image by reducing the multiple reflection of the ultrasonic wave. A further object of the present invention is to provide an ultrasonic imaging apparatus to be used for medical diagnosis or nondestructive inspection by receiving ultrasonic waves using such an ultrasonic receiving apparatus.
In order to solve the above-described problems, an ultrasonic receiving apparatus according to a first aspect of the present invention comprises an ultrasonic
Fuji Photo Film Co. , Ltd.
Imam Ali M.
Sughrue & Mion, PLLC
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