Method and apparatus for ultrasound imaging using acoustic impedance reconstruction
First Claim
1. An ultrasound imaging system, comprising:
- a transducer adapted to emit an incident ultrasonic signal toward a specimen, said transducer receiving a reflection of the incident ultrasonic signal from the specimen and generating an electrical signal which represents a reflected ultrasonic signal;
a signal processor which reconstructs an acoustic impedance of a portion of the specimen through which the reflected ultrasonic signal passes by;
computing a Fourier transform of the electrical signal which represents the reflected ultrasonic signal to obtain a reflected signal spectrum;
dividing the reflected signal spectrum by a spectrum of the incident ultrasonic signal to obtain a transfer function;
applying a frequency-domain window function having a sharp, low-frequency cutoff to the transfer function;
computing an inverse Fourier transform of the windowed transfer function to obtain an impulse response; and
calculating the acoustic impedance from the impulse response; and
an imaging device adapted to form an image of the specimen in accordance with the reconstructed acoustic impedance.
4 Assignments
0 Petitions
Accused Products
Abstract
An ultrasound imaging system employs acoustic impedance reconstruction to produce high-resolution images of anatomical structures, which are virtually free of speckle. Determination of the acoustic impedance profile involves prefiltering of the incident ultrasound signal and the ultrasound signal reflected from the specimen to be imaged. A time domain window function is applied to both the incident and reflected signals, and an N-point FFT is computed for both the digitized incident and reflected signals to obtain the incident and reflected spectrums. A complex division of the reflected spectrum by the incident spectrum is performed to obtain the transfer function. A window function having a sharp, low-frequency cutoff is applied to the transfer function prior to performing an inverse FFT to obtain the estimated impulse response. The acoustic impedance of individual A-scans is calculated from the impulse response using the plane wave Born approximation, involving integration and exponentiation of the estimated impulse response. By mechanically or electronically scanning the transducer along a line, a series of A-scan acoustic impedance profiles are calculated and used to produce a two-dimensional, grey-scale B-scan image.
303 Citations
42 Claims
-
1. An ultrasound imaging system, comprising:
-
a transducer adapted to emit an incident ultrasonic signal toward a specimen, said transducer receiving a reflection of the incident ultrasonic signal from the specimen and generating an electrical signal which represents a reflected ultrasonic signal;
a signal processor which reconstructs an acoustic impedance of a portion of the specimen through which the reflected ultrasonic signal passes by;
computing a Fourier transform of the electrical signal which represents the reflected ultrasonic signal to obtain a reflected signal spectrum;
dividing the reflected signal spectrum by a spectrum of the incident ultrasonic signal to obtain a transfer function;
applying a frequency-domain window function having a sharp, low-frequency cutoff to the transfer function;
computing an inverse Fourier transform of the windowed transfer function to obtain an impulse response; and
calculating the acoustic impedance from the impulse response; and
an imaging device adapted to form an image of the specimen in accordance with the reconstructed acoustic impedance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
a memory adapted to store image information derived from the acoustic impedance reconstructed by said signal processor.
-
-
21. The system according to claim 1, further comprising:
a transmitter for transmitting image information to a remote location over at least one of;
a fiber optic medium, a wire and free space.
-
22. A method of generating an ultrasound image, comprising the steps of:
-
a) emitting an incident ultrasonic signal toward a specimen;
b) receiving a reflection of the incident ultrasonic signal from the specimen and generating an electrical signal which represents a reflected ultrasonic signal;
c) computing a Fourier transform of the electrical signal which represents the reflected ultrasonic signal to obtain a reflected signal spectrum;
d) dividing the reflected signal spectrum by a spectrum of the incident ultrasonic signal to obtain a transfer function;
e) applying a frequency-domain window function having a sharp, low-frequency cutoff to the transfer function;
f) computing an inverse Fourier transform of the windowed transfer function to obtain an impulse response;
g) calculating an acoustic impedance profile from the impulse response; and
h) forming an image of the specimen in accordance with the acoustic impedance profile. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
i) applying a time domain pre-filter to the reflected electrical signal prior to computing the Fourier transform of the reflected electrical signal.
-
-
30. The method according to claim 22, further comprising the step of:
i) effecting a scan by repeating steps a) through g) along a plurality of different, adjacent paths within the specimen, wherein step h) includes forming an image using the acoustic impedance calculated for each of the plurality of paths.
-
31. The method according to claim 30, wherein step i) includes controlling a direction of the incident ultrasonic signal by setting relative phases of a phased-array of transducer elements.
-
32. The method according to claim 31, wherein step i) includes scanning in at least one of the following scanning formats:
- linear;
steered linear, sector, and circular.
- linear;
-
33. The method according to claim 30, wherein step i) includes mechanically displacing a transducer to effect scanning.
-
34. The method according to claim 30, wherein the plurality of paths form a plane in the specimen, and wherein step h) includes forming a two-dimensional B-scan image of the specimen.
-
35. The method according to claim 22, wherein step h) includes forming a three-dimensional image of the specimen.
-
36. The method according to claim 22, wherein steps c) through h) are performed in real time.
-
37. The method according to claim 22, wherein step a) includes emitting the incident ultrasonic signal having a center frequency in the range between 3 and 5 MHz, inclusive.
-
38. The method according to claim 22, further comprising the steps of:
-
i) prior to step h), determining whether the acoustic impedance profile meets a predetermined requirement;
j) when the acoustic impedance profile fails to meet the predetermined requirement, constraining values of certain components of the acoustic impedance profile;
k) computing amplitudes of low frequency components of the transfer function below the sharp, low-frequency cutoff from the constrained values of the certain components of the acoustic impedance profile;
l) repeating steps f), g), i), j) and k) at most L times, where L is a positive integer, or until the acoustic impedance profile meets the predetermined requirement in step i).
-
-
39. The method according to claim 38, wherein:
-
the predetermined requirements is that the value of all of the components of the acoustic impedance profile be at least 1.0; and
step j) includes;
dividing the acoustic impedance profile into N regions, where N is an integer greater than 1;
for each region, identifying a component of the acoustic impedance profile having a minimum value within the region;
for each region, if the minimum value is less than 1.0, constraining the value of the identified component in the region to a value no less than 1.0.
-
-
40. The method according to claim 22, further comprising the step of:
i) prior to step f), adjusting amplitudes of components of the transfer function to compensate for attenuation caused by intervening tissue.
-
41. An ultrasound imaging system, comprising:
-
a transducer adapted to emit an incident ultrasonic signal toward a specimen, said transducer receiving a reflection of the incident ultrasonic signal from the specimen and generating an electrical signal which represents a reflected ultrasonic signal;
a signal processor which reconstructs an acoustic impedance of a portion of the specimen through which the reflected ultrasonic signal passes by;
a) computing a Fourier transform of the electrical signal which represents the reflected ultrasonic signal to obtain a reflected signal spectrum;
b) dividing the reflected signal spectrum by a spectrum of the incident ultrasonic signal to obtain a transfer function;
c) applying a frequency-domain window function having a sharp, low-frequency cutoff to the transfer function;
d) computing an inverse Fourier transform of the windowed transfer function to obtain an impulse response;
e) calculating an acoustic impedance profile from the impulse response;
f) determining whether the acoustic impedance profile meets a predetermined requirement;
g) when the acoustic impedance profile fails to meet the predetermined requirement, constraining values of certain components of the acoustic impedance profile;
h) computing amplitudes of low-frequency components of the transfer function below the sharp, low-frequency cutoff from the constrained values of the certain components of the acoustic impedance profile; and
i) repeating steps d) through h) at most L times, where L is a positive integer, or until the acoustic impedance profile meets the predetermined requirement in step f); and
an imaging device adapted to form an image of the specimen in accordance with the acoustic impedance profile. - View Dependent Claims (42)
the predetermined requirements include the requirement that the value of all of the components of the acoustic impedance profile be at least 1.0; and
step g) includes;
dividing the acoustic impedance profile into N regions, where N is an integer greater than 1;
for each region, identifying a component of the acoustic impedance profile having a minimum value within the region;
for each region, if the minimum value is less than 1.0, constraining the value of the identified component in the region to a value no less than 1.0.
-
Specification