CN108095756B - Super-high resolution plane wave ultrasonic imaging method based on SOFI - Google Patents

Super-high resolution plane wave ultrasonic imaging method based on SOFI Download PDF

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CN108095756B
CN108095756B CN201711232982.7A CN201711232982A CN108095756B CN 108095756 B CN108095756 B CN 108095756B CN 201711232982 A CN201711232982 A CN 201711232982A CN 108095756 B CN108095756 B CN 108095756B
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plane wave
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sofi
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刘欣
吕明雷
束月霞
刘颖
赵丽丽
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University of Shanghai for Science and Technology
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/48—Diagnostic techniques
    • A61B8/481—Diagnostic techniques involving the use of contrast agent, e.g. microbubbles introduced into the bloodstream
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/52—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/5215—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves involving processing of medical diagnostic data
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T3/00—Geometric image transformation in the plane of the image
    • G06T3/40—Scaling the whole image or part thereof
    • G06T3/4053—Super resolution, i.e. output image resolution higher than sensor resolution

Abstract

The invention discloses an ultra-high resolution plane wave ultrasonic imaging method based on SOFI. The method comprises the following steps: under the intervention of an ultrasonic contrast agent (microbubble), carrying out ultrasonic plane wave imaging on an imaging object to obtain a group of plane wave ultrasonic images at different moments; filtering all the obtained plane wave ultrasonic images to remove noise contained in the plane wave ultrasonic images; measuring transverse full width at half maximum FHWM based on ultrasonic plane wave data of an imaging area only containing a single microbubblexFHWM half height and width in longitudinal directionyCalculating to obtain the transverse standard deviationxStandard deviation from longitudinalyGenerating a point diffusion distribution model; and finally, calculating to obtain a second-order (or higher-order) balanced SOFI image by taking the filtered dynamic ultrasonic plane wave image as input data. The method provided by the invention not only can greatly improve the spatial resolution of ultrasonic plane wave imaging, but also can improve the time resolution of ultrasonic imaging, and is suitable for rapid ultrahigh resolution ultrasonic imaging.

Description

Super-high resolution plane wave ultrasonic imaging method based on SOFI
Technical Field
The invention relates to an ultra-high resolution plane wave ultrasonic Imaging method based on SOFI (Super-resolution Optical Imaging). Specifically, under the intervention of an ultrasonic contrast agent (microbubble), ultrasonic plane wave imaging is carried out on an imaging object to acquire a group of plane wave ultrasonic images at different moments; filtering operation is carried out on all the obtained plane wave ultrasonic images based on a wiener filter (or other filters) so as to remove noise contained in the plane wave ultrasonic images; ultrasonic plane wave data based on single microbubble, through measured transverse half-height-width FHWMxFHWM half height and width in longitudinal directionyCalculating to obtain the transverse standard deviationxStandard deviation from longitudinalyGenerating a point spread distribution model based on the point spread distribution model; finally, toAnd (3) calculating to obtain a second-order (or high-order) balanced SOFI image based on the constructed SOFI imaging model, the SOFI calculation formula and the balanced SOFI (bSOFI) processing step. The method provided by the invention not only can greatly improve the spatial resolution of ultrasonic plane wave imaging, but also can improve the time resolution of ultrasonic imaging, and is suitable for rapid ultrahigh resolution ultrasonic imaging.
Background
Ultrasound imaging is one of the leading medical imaging modalities of today, and has been widely used in clinical practice, with the advantage that non-radiation imaging of tissue larger than 10cm can be achieved non-invasively. However, limited by diffraction theory, the spatial resolution of ultrasound imaging is not high, being about half the emission wavelength. This limits, in some respects, further applications of ultrasound in the clinic.
The SOFI (super-resolution fluorescence fluctuation imaging) is an emerging super-resolution imaging method. At present, the method is successfully applied to optical microscopy imaging. Briefly, the SOFI utilizes the fluorescence fluctuation characteristics of fluorescent molecules in optical imaging to generate cumulant equations with different orders; based on this, the width of the imaging Point Spread Function (PSF) can be effectively reduced; further breaking through the limit of the optical diffraction limit theorem and realizing the fluorescence microscopic imaging with ultrahigh resolution.
It is considered that, during contrast agent (microbubble) based ultrasound imaging, microbubbles constantly change their position relative to the ultrasound transducer; therefore, the moving of the microbubbles enables the passing pixel points to experience two different states of brightness and darkness in a short time, which can be similar to the fluorescent fluctuation characteristic in optical imaging. Based on the above, in the invention, the SOFI technology is combined with the ultrasonic imaging so as to break through the limit of the ultrasonic diffraction limit theorem and realize the ultrasonic imaging with ultrahigh resolution. Given that the SOFI has a non-linear response to brightness, this limits, to some extent, the spatial resolution of the resulting ultrasound imaging based on the SOFI approach. In order to overcome the limitation, the invention also adopts balanced SOFI (bSOFI), on the basis, the nonlinear response of the SOFI to the brightness is eliminated, so that the high-order cumulative quantity is applied, and the higher ultrasonic imaging spatial resolution is realized. In addition, in order to further improve the time resolution of imaging, in the invention, a plane wave imaging modality is used to scan an imaging object, thereby realizing ultra-fast ultrasonic imaging.
Disclosure of Invention
The invention aims to provide a plane wave ultrasonic imaging method based on SOFI (soft-object-oriented optical Fidelity), aiming at overcoming the defects of the existing ultrasonic imaging technology, and keeping better time resolution while realizing ultrahigh image spatial resolution.
In order to achieve the above purpose, the idea of the invention is:
under the intervention of an ultrasonic contrast agent (microbubble), carrying out ultrasonic plane wave scanning on an imaging object to obtain a group of plane wave ultrasonic images at different moments; filtering operation is carried out on all the obtained plane wave ultrasonic images based on a wiener filter (or other filters) so as to remove noise contained in the plane wave ultrasonic images; based on the ultrasonic plane wave data of the imaging region only containing a single microbubble by calculationxAndygenerating a point diffusion distribution model; and finally, calculating to obtain a second-order (or high-order) balanced SOFI image by taking the filtered dynamic ultrasonic plane wave image as input data based on the constructed SOFI imaging model, the SOFI calculation formula and the bSOFI processing method. The method provided by the invention not only can greatly improve the spatial resolution of ultrasonic plane wave imaging, but also can improve the time resolution of ultrasonic imaging, and is suitable for rapid ultrahigh resolution ultrasonic imaging.
According to the invention idea, the invention adopts the following technical scheme:
an ultra-high resolution plane wave ultrasonic imaging method based on SOFI comprises the following operation steps:
(1) under the intervention of an ultrasonic contrast agent (microbubble), an imaging object is subjected to ultrasonic plane wave scanning, and a group of plane wave ultrasonic images at different moments are acquired. Each frame of image comprises a plurality of point scatterers (microbubbles) which are randomly distributed in an imaging area;
(2) filtering operation is carried out on all the obtained plane wave ultrasonic images based on a wiener filter (or other filters) so as to remove noise contained in the plane wave ultrasonic images;
(3) constructing an SOFI imaging model, which comprises the following specific steps:
(3-1) calculating a transverse half-width-at-half-height (FHWM) of the plane wave ultrasound data based on the ultrasound plane wave data in which the imaging region contains only a single microbubblex) Longitudinal half width (FHWM)y)；
(3-2) calculating by the formula (3-1) to obtain a transverse standard deviation based on the obtained transverse half-height width and longitudinal half-height widthxStandard deviation from longitudinaly；
Figure BDA0001488476020000021
FHWM in the formula (3-1)xIs a transverse half-height width, FHWMyIs longitudinal half-height width;xandyrespectively a transverse standard deviation and a longitudinal standard deviation;
(3-3) based on the obtainedxAndycalculating to obtain a point diffusion distribution model by applying a formula (3-2);
Figure BDA0001488476020000031
in the formula (3-2), x and y describe an x axis and a y axis, respectively; x is the number of0And y0Describing the abscissa and ordinate values of the central point; psfxAs a function of the lateral probability density, psfyIs a longitudinal probability density function;
(4) the SOFI utilizes the fluctuation characteristic of fluorescent molecules in imaging to generate cumulant equations with different orders, and the cumulant equation CnThe formula (3) is shown as the formula (3-3);
Figure BDA0001488476020000032
in the formula (3-3), U (r) describes the Point Spread Function (PSF) of the system,kis the molecular brightness, wk(τ1,…,τn-1) Is based on a related weighting function, n representing the order of the accumulation;when using an n-order SOFI, spatial resolution may be improved
Figure BDA0001488476020000033
However, the SOFI has a non-linear response to luminance and flicker heterogeneity, resulting in an inability to improve resolution with higher cumulative amounts;
(5) bSOFI processing step: the balance SOFI (bSOFI) is an extended version of the SOFI and can be used for further improving the spatial resolution of imaging; in the bSOFI method, three parameters, i.e., the ratio of the light-emitting states to the time, are extracted
Figure BDA0001488476020000034
Molecular brightness
Figure BDA0001488476020000035
And molecular density
Figure BDA0001488476020000036
Then, deconvoluting the accumulated quantity calculated in the formula (3-3) to eliminate the nonlinear response to the brightness; then, the accumulated quantities are denoised by truncating smaller values (e.g., 1% -5% of the maximum value) and the luminance is linearized; finally, the image and the point spread function are convolved again to obtain a balanced accumulated image;
(6) and (3) taking the denoised plane wave ultrasonic image in the step (2) as an input, and calculating to obtain a second-order (or high-order) balanced SOFI image based on the SOFI imaging model constructed in the step (3) and the SOFI calculation formula in the step (4) and the processing method bSOFI in the step (5).
Through the steps, the SOFI-based ultrahigh-resolution plane wave ultrasonic imaging method can be realized.
Compared with the prior art, the invention has the following evaluation properties and obvious advantages: compared with the existing ultrasonic imaging method, the method can effectively improve the spatial resolution of ultrasonic imaging and realize ultrasonic imaging with ultrahigh resolution; meanwhile, based on the method, the time resolution of ultrasonic imaging can be greatly improved, and ultra-fast ultrasonic imaging is realized.
Drawings
FIG. 1 is a flow chart of the "super high resolution plane wave ultrasonic imaging method based on SOFI" of the present invention;
FIG. 2 is a partial plane wave ultrasound image generated by the Field II simulation platform;
FIG. 3 is a super-resolution ultrasound image obtained based on the method. (a) An original plane wave ultrasound image; (b) a second order SOFI image; (c) a third order SOFI image; (d) a fourth order SOFI image; (e) a bSOFI image;
Detailed Description
The preferred embodiments of the invention are detailed below:
(1) referring to fig. 1, in order to verify the feasibility of the method, an ultrasonic plane wave simulation image is taken as an example, and the method for ultra-high resolution plane wave ultrasonic imaging based on the SOFI includes the following specific steps:
(2) and performing ultrasonic plane wave imaging through a Field II simulation platform to obtain a group of plane wave ultrasonic images at different moments. Each frame of image comprises a plurality of point scatterers (microbubbles) which are randomly distributed in an imaging area; the specific simulation steps are as follows:
(1-1) using a Field II simulation platform, after setting relevant parameters, creating a phantom, containing a plurality of point scatterers at the depth of 30mm to 40mm, and scanning the phantom by using single plane wave emission containing 192 array elements, wherein the relevant parameters of scanning are shown in a table 1-1:
TABLE 1-1 plane wave Scan parameters
Sensor array type Linear array
Spacing of array elements 208μm
Height of array element 4.5mm
Speed of sound, c 1540m/s
Center frequency, f0 7MHz
Bandwidth of 60％
Wavelength of light 220μm
Receive apodization Hanning
(1-2) generating 101 point scatterers along the depth direction of the phantom from 30mm to 40mm, wherein the interval of each point scatterer is 0.1 mm; in each ultrasonic imaging process, randomly selecting 5 point scatterers, and imaging the phantom through a linear array transducer; then, randomly changing the position of the 5 point scatterers in the phantom, and carrying out plane wave imaging on the scatterers again; in order to simulate the movement of the microbubbles in the imaging area, the imaging process is repeated for 100 times to obtain 100 frames of plane wave ultrasonic images;
(1-3) after all plane wave ultrasonic images are obtained, in order to simulate the influence of noise in an actual experiment, 10dB of white Gaussian noise is added to the generated ultrasonic images one by one;
(2) filtering operation is carried out on all the obtained plane wave ultrasonic images based on a wiener filter (or other filters) so as to remove noise contained in the plane wave ultrasonic images;
(3) constructing an SOFI imaging model, which comprises the following specific steps:
(3-1) calculating plane wave ultrasonic data based on ultrasonic plane wave data in which the imaging region contains only a single microbubbleTransverse full width at half maximum (FHWM)x) Longitudinal half width (FHWM)y)；
(3-2) calculating by the formula (3-1) to obtain a transverse standard deviation based on the obtained transverse half-height width and longitudinal half-height widthxStandard deviation from longitudinaly；
Figure BDA0001488476020000051
FHWM in the formula (3-1)xIs a transverse half-height width, FHWMyIs longitudinal half-height width;xandyrespectively a transverse standard deviation and a longitudinal standard deviation;
(3-3) based on the obtainedxAndycalculating to obtain a point diffusion distribution model by applying a formula (3-2);
Figure BDA0001488476020000052
in the formula (3-2), x and y describe an x axis and a y axis, respectively; x is the number of0And y0Describing the abscissa and ordinate values of the central point; psfxAs a function of the lateral probability density, psfyIs a longitudinal probability density function;
(4) the SOFI utilizes the fluorescence fluctuation characteristics of fluorescent molecules in imaging to generate cumulant equations with different orders, and the cumulant equation CnThe formula (3) is shown as the formula (3-3);
Figure BDA0001488476020000053
in the formula (3-3), U (r) describes the Point Spread Function (PSF) of the system,kis the molecular brightness, wk(τ1,…,τn-1) Is based on a related weighting function, n representing the order of the accumulation; when using an n-order SOFI, spatial resolution may be improved
Figure BDA0001488476020000054
However, the SOFI has a non-linear response to luminance and flicker heterogeneity, resulting in the inability to use higher onesCumulatively to increase resolution;
(5) bSOFI processing step: in the bSOFI method, three parameters, i.e., the ratio of the light-emitting states to the time, are extracted
Figure BDA0001488476020000055
Molecular brightness
Figure BDA0001488476020000056
And molecular density
Figure BDA0001488476020000057
Then, deconvoluting the accumulated quantity calculated in the formula (3-3) to eliminate the nonlinear response to the brightness; then, the accumulated quantities are denoised by truncating smaller values (e.g., 1% -5% of the maximum value) and the luminance is linearized; finally, the image and the point spread function are convolved again to obtain a balanced accumulated image;
(6) and (3) taking the denoised plane wave ultrasonic image in the step (2) as an input, and calculating to obtain a second-order (or high-order) balanced SOFI image based on the SOFI imaging model constructed in the step (3) and the SOFI calculation formula in the step (4) and the processing method bSOFI in the step (5).
According to the finally obtained balanced SOFI image, the method provided by the invention can effectively improve the spatial resolution of ultrasonic plane wave imaging and realize ultrasonic imaging with ultrahigh resolution; in addition, due to the use of the plane wave scanning technology, the method can also effectively improve the imaging time resolution and greatly improve the imaging performance of the existing ultrasonic technology.

Claims (1)

1. An ultra-high resolution plane wave ultrasonic imaging method based on SOFI is characterized by comprising the following operation steps:
(1) under the intervention of an ultrasonic contrast agent microbubble, carrying out ultrasonic plane wave imaging on an imaging object to obtain a group of plane wave ultrasonic images at different moments; each frame of image comprises a plurality of point scatterer microbubbles which are randomly distributed in an imaging area;
(2) filtering operation is carried out on all the obtained plane wave ultrasonic images based on a wiener filter or other filters so as to remove noise contained in the plane wave ultrasonic images;
(3) constructing an SOFI imaging model, which comprises the following specific steps:
(3-1) calculating a transverse half-width-at-half-height (FHWM) of the plane wave ultrasound data based on the ultrasound plane wave data in which the imaging region contains only a single microbubblex) Longitudinal half width (FHWM)y)；
(3-2) calculating by the formula (3-1) to obtain a transverse standard deviation based on the obtained transverse half-height width and longitudinal half-height widthxStandard deviation from longitudinaly；
Figure FDA0002613544150000011
FHWM in the formula (3-1)xIs a transverse half-height width, FHWMyIs longitudinal half-height width;xandyrespectively a transverse standard deviation and a longitudinal standard deviation;
(3-3) based on the obtainedxAndycalculating to obtain a point diffusion distribution model by applying a formula (3-2);
Figure FDA0002613544150000012
in the formula (3-2), x and y describe an x axis and a y axis, respectively; x is the number of0And y0Describing the abscissa and ordinate values of the central point; psfxAs a function of the lateral probability density, psfyIs a longitudinal probability density function;
(4) the SOFI utilizes the fluctuation characteristics of molecules to generate cumulant equations with different orders, and cumulant equation CnThe formula (3) is shown as the formula (3-3);
Figure FDA0002613544150000013
in the formula (3-3), U (r) describes the Point Spread Function (PSF) of the system,kis the molecular brightness, wk(τ1,…,τn-1) Is based on phasesA weighting function of interest, n representing the order of the accumulation; spatial resolution is improved when using an n-order SOFI
Figure FDA0002613544150000014
Doubling;
(5) bSOFI processing step: the balance SOFI (bSOFI) is used as an extended version of the SOFI and is used for further improving the spatial resolution of imaging; in the bSOFI method, three parameters, i.e., the ratio of the light-emitting states to the time, are extracted
Figure FDA0002613544150000021
Molecular brightness
Figure FDA0002613544150000022
And molecular density
Figure FDA0002613544150000023
Then, deconvoluting the accumulated quantity calculated in the formula (3-3) to eliminate the nonlinear response to the brightness; then, denoising the cumulant by cutting off a smaller value, and linearizing the luminance; finally, the image and the point spread function are convolved again to obtain a balanced accumulated image;
(6) and (3) taking the denoised plane wave ultrasonic image in the step (2) as an input, and calculating to obtain a second-order or high-order balanced SOFI image based on the SOFI imaging model constructed in the step (3) and the SOFI calculation formula in the step (4) and the bSOFI processing method in the step (5).
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CN114062507A (en) * 2021-11-10 2022-02-18 复旦大学 Ultra-high resolution ultrasonic imaging method based on repeated accumulation analysis

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