Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-07-09
2004-02-03
Imam, Ali M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S453000
Reexamination Certificate
active
06685636
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image display apparatus or the like that displays a blood flow in an ultrasonic diagnostic apparatus, and more particularly, to an image display apparatus involving a B-mode method (tomogram display).
2. Description of the Related Art
The ultrasonic diagnostic apparatus is to display a tomogram based on an ultrasonic signal reflected from an object body, and a method of displaying the tomogram in real time is referred to as a B-mode method.
The B-mode method has a disadvantage in that, while it allows tissues of the object body to be displayed with good quality, when displaying a blood flow in a blood vessel, the image thereof becomes blurred. To overcome the disadvantage, an attempt involving a digital technology has been made as follows.
FIG. 10
illustrates an operation of a method of displaying a blood flow in the conventional ultrasonic diagnostic apparatus. This is referred to as a B-Flow, which is disclosed in the web site of http://www.gemedicalsystems.com/rad/us/education/msutut4.html.
With reference to
FIG. 10
, the operation of the conventional ultrasonic diagnostic apparatus will be described below. First, an encoder
20
emits an ultrasonic beam. The ultrasound reflected from a human body
2
(referred to as an echo, hereinafter) is decoded in a decoder
21
, and then displayed in B-mode.
Here, as shown in
FIG. 16
, a blood flow
161
lies deeper in the object body than a tissue
160
. Thus, for an incident ultrasonic beam
162
, a blood flow echo
163
b
and a tissue echo
163
a
return with a time lag, so that the two echoes can be distinguished. Since the blood flow echo is weaker than the tissue echo, the sensitivity is enhanced when receiving the blood flow echo. The time lag between the reflection echoes is due to a fact that the tissue echo is contributed by a reflection from a blood vessel wall and the blood flow echo is primarily contributed by a scattering from a red blood cell in the blood vessel. The encoder
20
and the decoder
21
are used to distinguish and superimpose the weak reflection echoes. That is, according to an encoded pattern, signals received at the timing of “1” are added, and the result is regarded as the received echo. Strictly speaking, the reflection echo due to the thickness of the tissue
160
includes echoes from a tissue surface and from an interface with the blood flow. For simplicity, however, only the latter is shown in FIG.
16
.
According to the above arrangement, however, the blood flow echo and the tissue echo are distinguished based on the time lag therebetween, and thus, cannot be separated if they are close to each other. That is, it is difficult to display the blood flow near the blood vessel wall or the blood flow in a thin blood vessel. In addition, since the blood flow echo and the tissue echo are close to each other, it is difficult to adjust the amplification factor thereof. For example, if the amplification factor is enhanced to be adapted for the blood flow, there is a possibility that the whole image becomes too bright, and a whitish image is provided.
In short, with the conventional ultrasonic tomography, when a tomogram for the whole object body is generated in B-mode, a vivid image of the blood flow cannot be produced.
There is another approach of utilizing the Doppler effect to derive from the received ultrasonic signal a phase difference between a wave reflected from the blood flow and a wave reflected from the tissue, calculating velocity data of a section of the blood flow, that is, direction and intensity data thereof based on the phase difference, generating a color image reflecting the velocity of the flow, and superimposing the color image on the B-mode image for display. This approach is referred to as Color Flow, and is disclosed in “Basic Ultrasonic Medicine” (Ishiyaku Publishing Inc.), p. 55-57 and U.S. Pat. No. 4,622,977, for example. The entire disclosure of the each publication is incorporated herein by reference in its entirety.
However, the Color Flow requires dedicated image processing means that involves an enormous amount of complicated calculation such as an autocorrelation operation or fast Fourier transform, and thus, the whole apparatus is complicated and the cost is increased. Furthermore, the Color Flow cannot provide an actual image of the blood flow, so that the image provided is poor in reality.
In view of the problems described above, this invention aims to provide an ultrasonic tomography apparatus and an ultrasonic tomography method that can, with a simple and inexpensive arrangement, display an image of a tissue and blood flow in an object body in B-mode such vividly that they can be easily distinguished.
SUMMARY OF THE INVENTION
One aspect of the present invention is an ultrasonic tomography apparatus, comprising:
ultrasonic transmitting means of transmitting an ultrasound to an object body;
ultrasonic receiving means of receiving the ultrasound reflected from said object body and producing an ultrasonic signal;
filtering means of extracting components of said ultrasonic signal in at least two different frequency bands; and
image generating means of generating an ultrasonic tomogram of said object body based on said extracted ultrasonic signal component in a first frequency band and said extracted ultrasonic signal component in one or more second frequency bands,
wherein said first frequency band centers on a frequency band at the time of said transmission, and
said second frequency band is shifted from the frequency band at the time of said transmission.
Another aspect of the present invention is an ultrasonic tomography apparatus, comprising:
ultrasonic transmitting means of transmitting an ultrasound to an object body;
ultrasonic receiving means of receiving the ultrasound reflected from said object body and producing an ultrasonic signal;
filtering means of extracting components of said ultrasonic signal in at least two different frequency bands; and
image generating means of generating a first partial ultrasonic tomogram of said object body based on said extracted ultrasonic signal component in a first frequency band and a second partial ultrasonic tomogram of said object body based on said ultrasonic signal component in one or more second frequency bands,
wherein said first frequency band centers on a frequency band at the time of said transmission, and
said second frequency band is shifted from the frequency band at the time of said transmission.
Still another aspect of the present invention is the ultrasonic tomography apparatus further comprising:
image processing means of performing an image processing on at least one of said first partial ultrasonic tomogram and said second partial ultrasonic tomogram; and
image synthesizing means of producing an ultrasonic tomogram by performing any of (1) synthesis of the first partial ultrasonic tomogram subject to said image processing and the second partial ultrasonic tomogram not subject to said image processing, (2) synthesis of the first partial ultrasonic tomogram not subject to said image processing and the second partial ultrasonic tomogram subject to said image processing, and (3) synthesis of the first partial ultrasonic tomogram subject to said image processing and the second partial ultrasonic tomogram subject to said image processing.
Yet still another aspect of the present invention is the ultrasonic tomography apparatus, wherein said second frequency band is set centering on a frequency for which a signal component having a level more than predetermined one is detected by scanning a predetermined bandwidth allowing for a potential Doppler shift from said first frequency band.
Still yet another aspect of the present invention is the ultrasonic tomography apparatus, wherein said second frequency band is set centering on a frequency for which a signal component having a level more than predetermined one is detected by frequency-analyzing said received reflected ultrasonic.
A further aspect of the present invention is the
Migita Manabu
Okabayashi Ichiro
Imam Ali M.
RatnerPrestia
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