Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2003-04-15
2004-08-10
Ruhl, Dennis W. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06773403
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an ultrasound diagnostic system, and more particularly, to an ultrasonic apparatus and method for automatically measuring the velocities of tissues within the human body by using the Doppler effect.
BACKGROUND OF THE INVENTION
Ultrasound diagnostic systems using the Doppler effect are well known in the art and typically used for detection of the velocities of blood flows and tissues within the human body. These conventional ultrasound diagnostic systems determine the velocity of a target object, such as a red blood cell, by detecting a frequency or phase shift of echo signals, due to movement of the target object, which have been reflected from the target object based on transmitted ultrasound signals.
Referring to
FIG. 1
, the principle of measuring the velocity of blood flow and tissue by using ultrasound signals is explained. Transducer array
103
transmits ultrasound signals toward target object
101
, and repeats sampling operations upon the echo signals reflected from target object
101
, several times, e.g., 2N times.
FIG. 1
exemplifies sampling done at the timing, t=t
0
. As the target object moves, the phases of the signals sampled at the timing, t=t
0
change. From the degree of the phase changes, the velocity of target object
101
, &ngr;, may be calculated according to Equation 1 below:
v
=
Δ
Θ
λ
0
2
π
T
PRF
(
Eq
.
1
)
where T
PRF
is an interval at which ultrasound signals are transmitted, i.e., the reciprocal of a pulse repetition frequency (PRF), &lgr;
0
is a center frequency of the ultrasound signals being transmitted, and &Dgr;
&THgr;
is a phase change.
As can be seen from Equation 1, the velocity of the target object is proportional to the phase change of the echo signals reflected from the target object. Since the frequency shift of the signal is proportional to the phase change, the velocity of the target object, &ngr;, is proportional to the frequency shift of the reflected echo signal. Therefore, measuring the frequency of the echo signals reflected from the target object provides the velocity of the target object.
Referring to
FIG. 2
, which shows a block diagram of a conventional ultrasound diagnostic apparatus for measuring the velocity of blood flow and human tissue, ultrasound diagnostic apparatus
200
comprises transducer array
103
, pre-amplifier
104
, time gain control (TGC) amplifier
105
, analog-to-digital (A/D) converter
106
, quadrature demodulator
107
, digital signal processor
108
, and display
109
.
Transducer array
103
transmits ultrasound signals toward the target object and receives echo signals reflected from the target object. The echo signals are amplified by pre-amplifier
104
. TGC amplifier
105
amplifies the pre-amplified signals from pre-amplifier
104
while varying gain to compensate for attenuation of the ultrasound signals as they propagate inside the human body. A/D converter
106
converts an output signal of TGC amplifier
105
from analog to digital and quadrature demodulator
107
demodulates the signal to be inputted to digital signal processor
108
. Digital signal processor
108
detects the velocity of the target object based on 2N number of sampled data, which are obtained by repeating transmission of an ultrasound signal toward the target object, 2N times, and transmits the detected velocity to display
109
.
The ultrasound signals transmitted by transducer array
103
are reflected from blood, tissues, muscles, and the like within the human body. In the case of blood, the ultrasound signals are reflected from a plurality of red blood cells, each of which has a different velocity. Since the sampled data being inputted to digital signal processor
108
contain a plurality of velocity components, digital signal processor
108
computes a velocity distribution spectrum of the sampled data and transmits the same to display
109
. Display
109
then displays the velocity distribution spectrum of the sampled data thereon.
Referring to
FIG. 3
, which shows a block diagram of digital signal processor
108
shown in
FIG. 2
, digital signal processor
108
comprises clutter filtering part
301
, fast Fourier transform (FFT) part
302
, and post-processing part
303
. Where ultrasound diagnostic apparatus
200
is used for measuring the velocity of blood flow, clutter filtering part
301
cuts off echo signals (so called clutters) reflected from tissues and/or muscles within the human body. These echo signals have low-band frequencies, since movement of tissue and muscle is slower than that of blood within the human body. Thus, clutter filtering part
301
employs a high-pass filter for computing velocity of blood flow.
If ultrasound diagnostic apparatus
200
is used for measuring the velocity of tissue within the human body, clutter filtering part
301
cuts off echo signals reflected from blood. In order to compute the velocity component of tissue, clutter filtering part
301
employs a low-pass filter instead of the high-pass filter to cut off the velocity components of blood flow.
FFT part
302
performs a Fourier transform on the 2N number of sampled data to create frequency distribution data containing 2N number of frequency components. This frequency distribution data corresponds to the velocity distribution data of the target object. Post-processing part
303
performs known signal processing on the frequency distribution data, such as log compression and base line shifting, in order to obtain improved image quality. The frequency distribution data, i.e., the velocity distribution data of the target object, outputted from digital signal processor
108
, is displayed on display
109
.
Referring to
FIG. 4
, which shows a graph of typical frequency distribution data, the X-axis represents frequency components and Y-axis represents the strength of the frequency components. The frequency distribution data may represent the strength of the frequency components or, alternatively, some other value, such as the square of the strength. A positive frequency and a negative frequency represent signal components reflected from target objects that move in opposite direction. That is, “positive” and “negative” denote relative direction of movement. As can be seen from
FIG. 4
, the strength of the negative frequency component tends to be larger than that of the positive frequency component. This means that the blood flows in a certain direction, such as away from transducer array
130
.
Referring to
FIGS. 5 and 6
, employing a low-pass filter to cut off the velocity component of blood flow in order to measure the velocity component of tissue within the human body has some drawbacks. Calculating a cut-off frequency to precisely discriminate the velocity component of tissue from that of blood flow within the human body is very difficult. Changing the calculated cut-off frequency whenever the velocity of tissue is varied is also very difficult.
FIG. 5
shows a diagram of a conventional low-pass filtering scheme for isolating the velocity component of tissue within the human body.
FIG. 6
shows a diagram of a method for designing a cut-off frequency that discriminates the velocity component of tissue from that of blood flow by using a conventional low-pass filtering scheme in a conventional ultrasound diagnostic apparatus.
Referring to
FIG. 5
, in a conventional ultrasound diagnostic apparatus, a low-pass filter
703
is designed on the basis of maximum frequency
701
-
1
in the frequency band representative of a velocity component of tissue
701
, which appears in a low frequency band, in order to isolate the velocity component of tissue
701
. Determining a cut-off frequency
704
for precisely discriminating the velocity component of tissue
701
from that of blood flow
702
is very important. However, the low-pass filtering scheme shown in
FIG. 5
is difficult to adapt to an ultrasound diagnostic apparatus. Therefore, in a conventional ultrasound diagnostic apparatu
Kim Cheol An
Kim Sung Ho
Jain Ruby
Medison Co. Ltd.
Ruhl Dennis W.
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