Method and apparatus for backscatter imaging of vascular activity at microscopic scale

Abstract

A method of imaging vascular activity at microscopic scale in at least one region of a network of blood vessels of a human or animal organ, the method comprising: (a) emitting a series of consecutive incident ultrasound waves in the at least one region by an ultrasound transducer array extending in at least one direction, the incident ultrasonic waves are propagated in the direction perpendicular to the transducer array; (b) acquiring a set of raw data from the backscattered ultrasound by the transducer array; (c) generating a series of continuous ultrasound images according to the original data; (d) detecting at least one isolated ultrasound contrast agent in the ultrasound image; (e) locating the position of the at least one isolated ultrasound contrast agent at a precision lower than the wavelength of the wave; (f) generating an at least two-dimensional backscatter amplitude image by assigning, to each pixel, a value representative of the measured backscatter amplitude of the at least one isolated ultrasound contrast agent detected in that pixel.

Description

Technical Field

[0001] This invention discloses a method and apparatus for backscatter imaging of vascular activity at a microscopic scale in humans or animals. Background Technology

[0002] One type of imaging that has attracted much attention is ultrasound localization microscopy (ULM), particularly for its spatial resolution and depth of penetration.

[0003] This is particularly described by Errico et al. in [Errico, C. et al., “Ultrafast ultrasound localization microscopy for deep super-resolution vascular imaging,” Nature 527, 499–+ (2015)] and Demene et al. in [Demene, C. et al., “Transcranial ultrafast ultrasound localization microscopy for vascular imaging in the brain of patients,” Nature Biomedical Engineering 5, 219–228 (2021)]. By imaging isolated intravenously injected microvessels circulating in blood vessels at ultra-high frame rates and locating the center of their respective point spread functions with sub-resolution accuracy, it is able to map the microvascular system of organs at a resolution of tens of micrometers and the dynamic velocity of blood flow.

[0004] However, in traditional ULM images based on microbubble counting, the signal is driven by blood flow. In other words, the greater the blood flow, the more microbubbles are detected within the acquisition time. Therefore, many small blood vessels are not visible in traditional ULM images due to noise levels in areas where microbubbles are sparsely detected.

[0005] Furthermore, ULMs are typically implemented in two dimensions and provide two-dimensional images because linear transducer arrays and drive electronics are far more common and less expensive than the matrix arrays, raw column arrays, and multiplexing electronics required for performing three-dimensional ultrasonic localization microscopy. Therefore, velocity quantization is limited to in-plane velocities, which underestimates the velocity measurement of microbubble flows not aligned with the ULM imaging plane. The lack of information in the orthogonal directions of the imaging plane leads to inaccurate velocity determination.

[0006] Therefore, there is a need for an improved method for imaging vascular activity at the microscale that is less sensitive to noise, allows for the detection of small vessels, and improves the accuracy of velocity quantization using two-dimensional ULM. Summary of the Invention

[0007] Therefore, the present invention proposes a method for imaging vascular activity at a microscopic scale in at least one region of the vascular network of a human or animal organ, the method comprising:

[0008] (a) A series of continuous incident ultrasonic waves are emitted in the at least one region by an ultrasonic transducer array extending in at least one direction and the incident ultrasonic waves propagate in a direction perpendicular to the transducer array.

[0009] (b) Acquire a set of raw data from backscattered ultrasound through the transducer array;

[0010] (c) Generate a series of consecutive ultrasound images based on the raw data;

[0011] (d) Detecting at least one isolated ultrasound contrast agent in the ultrasound image;

[0012] (e) Positioning of the at least one isolated ultrasound contrast agent with an accuracy below the wavelength of the wave;

[0013] (f) Generate at least one two-dimensional backscatter amplitude image by assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in the pixel to each pixel.

[0014] The proposed method advantageously allows, depending on the embodiment, the acquisition of backscattered ULM images with higher sensitivity compared to conventional ULM images. During the processing of generating the ULM image, microbubbles are detected as the brightest local maxima. The value of this maxima on the B-mode image is extracted and correlated with the detection of each localized microbubble. This value is referred to as the backscatter amplitude. Instead of assigning the number of microbubbles detected in that pixel during the entire acquisition period to pixels of each ULM image, the average backscatter amplitude of the microbubbles detected in that pixel is assigned. Since the backscatter amplitude of each individual microbubble circulating in the blood vessel is measured, missing information about the out-of-plane motion of the microbubbles can be retrieved. Therefore, backscattered ULM images allow for physically relevant 3D rendering perception within the blood vessel map. Information can be collected from individual ULM images. Collecting information from individual ULM images reduces the acquisition cycle of individual ULM images while maintaining high spatial resolution.

[0015] The following features may be implemented individually or in combination with each other:

[0016] In at least one embodiment, the value calculated in step (f) may correspond to the average of the measured backscatter amplitudes of all isolated ultrasound contrast agents detected in the pixel.

[0017] In at least one embodiment, the value calculated in step (f) may correspond to a function of the backscattering amplitude of the at least one isolated ultrasound contrast agent detected in the pixel.

[0018] In one embodiment, the method may further include a tracking step, wherein at least one isolated ultrasound contrast agent detected is tracked in several ultrasound images generated in step (c) to determine its trajectory and velocity.

[0019] In some embodiments, the ultrasonic transducer array may be a one-dimensional array extending along a direction X, and the incident ultrasonic wave propagates along a direction Z perpendicular to the transducer array, and the image generated in step (f) is a two-dimensional backscatter amplitude image.

[0020] In an embodiment where the ultrasonic transducer array is a one-dimensional array, steps (a) to (f) can be repeated on multiple parallel ultrasonic imaging planes XZ spaced apart from each other within the width of the ultrasonic beam along the direction Y to generate multiple two-dimensional parallel backscatter amplitude images.

[0021] In some embodiments, the method may further include a step of calculating the velocity of the at least one tracked isolated ultrasound contrast agent at a given location (x, z), the step comprising:

[0022] (i) Generate the relationship between the backscattering amplitude of the at least one tracked isolated contrast agent and the position y of the imaging plane along direction Y within the width of the ultrasound beam;

[0023] (ii) By fitting a function to the spatial variation of the measured backscatter amplitude, the position y of the at least one tracked isolated contrast agent is calculated, where the position y of the at least one isolated contrast agent is the location of the maximum spatial variation of the backscatter amplitude.

[0024] (iii) Calculate the three velocity components V of the at least one tracked isolated ultrasound contrast agent along the three directions X, Y, and Z. x V y and V z .

[0025] In one or more embodiments, the method may further include a step of calculating a speed for each pixel at a given location (x,z), the step comprising:

[0026] (i) Generate the relationship between the backscattering amplitude of each pixel and the position y of the imaging plane along the direction Y within the width of the ultrasonic beam;

[0027] (ii) By fitting the function to the spatial variation of the measured backscatter amplitude, the position y of each pixel is calculated. The position y of each pixel is the location of the maximum value of the backscatter amplitude variation.

[0028] (iii) Calculate the three velocity components V of each pixel along the three directions X, Y, and Z. x Vy and V z .

[0029] In one or more embodiments, the fitting function may be a Gaussian function: Where α is the backscattering amplitude, w is the width of the ultrasonic beam along direction Y, and y0 is the position of the maximum value of the backscattering amplitude variation.

[0030] In one or more embodiments, the width w of the ultrasonic beam along the Y direction may be an experimental value.

[0031] In one or more embodiments, the width w of the ultrasonic beam along the direction Y can be a simulated value.

[0032] In one or more embodiments, the plurality of parallel ultrasonic imaging planes can be obtained by moving the one-dimensional ultrasonic transducer array within the width (w) of the ultrasonic beam along a direction Y perpendicular to the ultrasonic imaging plane (x,z).

[0033] In one or more embodiments, the method may further include the step of positioning the one-dimensional ultrasonic transducer array by comparing a first backscatter amplitude image and a second backscatter image, such that the imaging plane associated with the first backscatter amplitude image and the imaging plane associated with the second backscatter image coincide.

[0034] In some embodiments, the method may further include the step of generating at least a two-dimensional ultrasound localization microscope (ULM) image of the at least one region by assigning a number of ultrasound contrast agents detected in each pixel to each pixel.

[0035] In some embodiments, the method may further include the step of generating at least one two-dimensional ultrasound localization microscope (ULM) image of the at least one region by assigning a number of ultrasound contrast agents detected in each pixel to each pixel.

[0036] In one embodiment, the method may further include a step of quantizing the correction velocity of at least one blood vessel based on the two-dimensional backscatter amplitude image, the quantization step including:

[0037] (i) Selecting the at least one blood vessel from the at least one backscatter amplitude image;

[0038] (ii) Calculate the velocity V of the ultrasound contrast agent belonging to the selected blood vessel. xz ;

[0039] (ii) Obtain a backscattering amplitude profile along the selected blood vessel centerline;

[0040] (iii) Calculate the angle θ between the selected vessel centerline along its backscatter amplitude profile and its projection on the ultrasound imaging plane;

[0041] (iv) Calculate the correction velocity for each ultrasound contrast agent belonging to the selected vessel using the calculated angle: V corr =V xz / cosθ.

[0042] In some embodiments, the step of generating a series of consecutive two-dimensional ultrasound images from the raw data may include a filtering step to distinguish the ultrasound signal of a single ultrasound contrast agent from the tissue signal.

[0043] In one or more embodiments, at least one vascular parameter can be extracted from the measured backscatter amplitude, the vascular parameter being selected from the group consisting of blood flow, blood flow velocity, blood volume, blood pressure, and any combination thereof.

[0044] Calculating kinetic parameters selected from blood flow, blood flow velocity, blood volume, blood pressure, and any combination thereof can allow the derivation of the behavior of at least one region of the vascular network, thereby enabling the quantification of the activity of the at least one region without the need for large amounts of information from different types of data.

[0045] In one or more embodiments, the method may further include the step of automatically segmenting blood vessels in at least one region of a vascular network based on the at least two-dimensional backscatter amplitude image, wherein at least one dimensional parameter of the blood vessel is quantized from the segmentation step. For example, the diameter can be obtained by applying different segmentation techniques to the backscatter amplitude image. In its simplest form, it can be defined as the width of the blood vessel at a threshold set by the half-maximum of the resting profile.

[0046] The present invention also relates to an apparatus for imaging vascular activity at a microscopic scale in at least one region of a vascular network in a human or animal organ, the apparatus comprising:

[0047] (a) An ultrasonic probe having an array of ultrasonic transducers extending in at least one direction, the ultrasonic probe being configured to emit incident ultrasonic waves along a propagation direction perpendicular to the transducer array and acquire a set of raw data.

[0048] (b) The calculation module is configured as follows:

[0049] - Generate a series of consecutive ultrasound images based on the raw data;

[0050] - Detect at least one isolated ultrasound contrast agent in an ultrasound image;

[0051] - Position the at least one isolated ultrasound contrast agent with an accuracy below the wavelength of the wave;

[0052] - Track the at least one isolated ultrasound contrast agent to determine its trajectory;

[0053] - By assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in that pixel to each pixel, at least a two-dimensional backscatter amplitude image is generated.

[0054] In embodiments of the device, the following features may be used alone or in combination:

[0055] In one or more embodiments, the ultrasonic transducer array may be a one-dimensional ultrasonic transducer array extending along a direction X, used to generate a two-dimensional backscatter amplitude image.

[0056] In some embodiments, the probe may further include a motor configured to move the ultrasonic transducer array within the width (w) of the ultrasonic beam in a direction perpendicular to the ultrasonic imaging plane to generate a plurality of parallel ultrasonic imaging planes.

[0057] In one or more embodiments, the computing module may be further configured as follows:

[0058] - Generate the relationship between the backscattering amplitude of the at least one tracked isolated contrast agent and the position y of the imaging plane along direction Y within the width of the ultrasound beam;

[0059] - The position y of the at least one tracked isolated contrast agent is calculated by fitting a function to the spatial variation of the measured backscatter amplitude, and the position y of the at least one isolated contrast agent is the location of the maximum value of the backscatter amplitude variation.

[0060] - Calculate the three velocity components V of the at least one tracked isolated ultrasound contrast agent along the three directions X, Y, and Z. x V y and V z .

[0061] In another aspect, computer software is proposed, including instructions that, when executed by a processor, are used to implement a method for imaging vascular activity at a microscopic scale in at least one region of a vascular network in a human or animal organ, the method comprising:

[0062] (a) A series of continuous incident ultrasonic waves are emitted in the at least one region by an ultrasonic transducer array extending in at least one direction and the incident ultrasonic waves propagate in a direction perpendicular to the transducer array.

[0063] (b) Acquire a set of raw data from backscattered ultrasound through the transducer array;

[0064] (c) Generate a series of consecutive ultrasound images based on the raw data;

[0065] (d) Detecting at least one isolated ultrasound contrast agent in the ultrasound image;

[0066] (e) Positioning of the at least one isolated ultrasound contrast agent with an accuracy below the wavelength of the wave;

[0067] (f) Generate at least a two-dimensional backscatter amplitude image by assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in the pixel to each pixel.

[0068] In another aspect, a computer-readable non-transient recording medium is proposed, on which software is registered, which, when executed by a processor, is used to implement a method for imaging vascular activity at a microscopic scale in at least one region of a vascular network in a human or animal organ, the method comprising:

[0069] (a) A series of continuous incident ultrasonic waves are emitted in the at least one region by an ultrasonic transducer array extending in at least one direction and the incident ultrasonic waves propagate in a direction perpendicular to the transducer array.

[0070] (b) Acquire a set of raw data from backscattered ultrasound through the transducer array;

[0071] (c) Generate a series of consecutive ultrasound images based on the raw data;

[0072] (d) Detecting at least one isolated ultrasound contrast agent in the ultrasound image;

[0073] (e) Positioning of the at least one isolated ultrasound contrast agent with an accuracy below the wavelength of the wave;

[0074] (f) Generate at least a two-dimensional backscatter amplitude image by assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in the pixel to each pixel. Attached Figure Description

[0075] Other features, details, and advantages will be shown in the following detailed description and accompanying drawings, wherein:

[0076] Figure 1

[0077] [ Figure 1 [Illustration 1] is a block diagram illustrating an embodiment of the device according to the present invention.

[0078] Figure 2

[0079] [ Figure 2 [Illustration used] Figure 1 A block diagram illustrating an embodiment of a method for obtaining two-dimensional or three-dimensional backscatter amplitude ULM images and two-dimensional or three-dimensional conventional ULM images using a device.

[0080] Figure 3

[0081] [ Figure 3 The illustration shows the use of Figure 1 This is a possible method for obtaining two-dimensional or three-dimensional backscatter amplitude ULM images and two-dimensional or three-dimensional conventional ULM images using equipment.

[0082] Figure 4

[0083] [Figure 4(a)] schematically illustrates an ultrasound beam generated by a linear transducer array and microbubbles or isolated contrast agents (MBs) flowing through blood vessels across the imaging plane at times t1 and t2.

[0084] [Figure 4(b)] illustrates two B-mode images of the microbubble at times t1 and t2 in the Y direction perpendicular to the imaging plane.

[0085] [Figure 4(c)] illustrates the simulated curve of the backscattered ultrasound intensity as a function of y at a fixed position (x0, y0).

[0086] Figure 5

[0087] [Figure 5(a)] illustrates the simulated backscattering intensity in the YZ plane at the X center location (X=0), and the simulated backscattering intensity in the YZ plane at the X center location (X=0) normalized for each depth along the Z direction.

[0088] [Figure 5(b)] illustrates the decrease in ultrasonic intensity profile with depth along the Z direction at x = 0 and y = 0.

[0089] [Figure 5(c)] illustrates the ultrasonic intensity profile along the Y direction at a given depth z, normalized for each depth.

[0090] Figure 6

[0091] [ Figure 6 According to an embodiment of the method of the present invention, an example of a ULM image representing the backscatter amplitude of blood vessels in the rat thalamus is illustrated.

[0092] Figure 7

[0093] [Figure 7(a)] schematically illustrates the variation in backscattering amplitude of microbubbles flowing through blood vessels along the Y-direction through the ultrasound beam.

[0094] [Figure 7(b)] shows that inFigure 6 The above is a function of the normalized backscatter amplitude of a microbubble flowing in a blood vessel (shown as a white line) as a function of time.

[0095] Figure 8

[0096] [Figure 8(a)] schematically illustrates the variation in backscattering amplitude of microbubbles flowing through blood vessels parallel to the imaging plane and distributed along the Y direction.

[0097] [Figure 8(b)] illustrates an example of an image showing the backscatter amplitude of blood vessels in the rat cortex.

[0098] Figure 9

[0099] [ Figure 9 [a] Schematic illustration of the ultrasound intensity changes of five imaging planes spaced apart from each other in the Y direction and three microbubbles located at a fixed position (x,z) flowing through a blood vessel passing through the ultrasound beam in the Y direction.

[0100] [ Figure 9 (b) schematically illustrates the backscattering amplitude of the three microbubbles measured in five imaging planes.

[0101] Figure 10

[0102] [ Figure 10 The image shows backscatter amplitude images of five coronal planes in the rat thalamus, which are spaced 100 μm apart in the elevation direction Y.

[0103] Figure 11

[0104] [ Figure 11 ] Shows the target Figure 10 The image shows the normalized values ​​of the five backscatter amplitudes measured at pixel M, and the Gaussian function fitted to these five points.

[0105] Figure 12

[0106] [Figure 12(a)] shows four selected blood vessels on a backscatter amplitude image.

[0107] [Figure 12(b)] schematically illustrates a geometric configuration for determining the angle θ between the selected blood vessel numbered 2 and its projection on the imaging plane. Detailed Implementation

[0108] In the accompanying drawings, the same reference numerals denote the same or similar elements.

[0109] This invention provides a method and apparatus for backscatter amplitude imaging of vascular activity in at least one region of a human or animal organ. This backscatter amplitude imaging utilizes backscatter amplitude in ultrasound positioning microscopy to provide two-dimensional or three-dimensional ultrasound backscatter amplitude images with higher sensitivity compared to conventional ultrasound positioning microscopy images. Due to the inherently lower spatial noise, small blood vessels invisible in conventional ULM images can be visualized. Because the backscatter amplitude varies along the orthogonal direction of the two-dimensional imaging plane of the ultrasound probe, three-dimensional perception can also be presented in the two-dimensional vascular images.

[0110] Furthermore, in embodiments where the ultrasound probe includes a linear array suitable for generating two-dimensional images of the area of ​​interest, the backscatter amplitude image can invert the relative distance and three-dimensional positioning of the ultrasound contrast agent to the two-dimensional imaging plane, achieving more accurate velocity quantization by utilizing missing information about microbubble out-of-plane motion. In other words, the present invention provides a method and apparatus for calculating three-dimensional flow and velocity from two-dimensional ULM images obtained using a one-dimensional ultrasound probe.

[0111] Two-dimensional or three-dimensional conventional ULM images can be obtained based on methods known in the art and explained in the aforementioned articles by Errico et al. (2015) and Demene et al. (2021).

[0112] The backscatter amplitude image was generated from the same set of raw data used to generate a conventional ULM image.

[0113] Figure 1 An example of a vascular activity imaging device 1 (VA APP) that can be used to perform the method according to the invention is shown.

[0114] The device 1 may include a processor 2 (PROC), such as a dedicated signal processing device controlled by a computer or a group of computers, including a computer group that may include a server.

[0115] Processor 2 may include computing module 3 (COMP), the operation of which will be explained later.

[0116] Processor 2 can control ultrasound contrast agent injection device 4 (INJ).

[0117] The ultrasound contrast agent injection device 4 may contain an ultrasound contrast agent. The ultrasound contrast agent may be a microbubble, such as those described by Dayton et al. [Dayton, PA et al., Frontiers in Bioscience 12, 5124-5142 (2007)], or an equivalent ultrasound contrast agent. In some embodiments, the ultrasound contrast agent may be based on…

[0118] In this example, the ultrasound contrast agent injection device 4 can be a bolus syringe.

[0119] The ultrasound contrast agent injection device 4 may include a magnet to mix a solution containing an ultrasound contrast agent.

[0120] Processor 2 can control ultrasonic probe 5 (PRB).

[0121] The ultrasonic probe 5 may include an ultrasonic transducer array 7 (ARR). The array may be a linear array suitable for generating a two-dimensional backscattered amplitude image of a slice of the region to be imaged, or a two-dimensional array suitable for generating a three-dimensional backscattered amplitude image of the region. When the array is a two-dimensional array, it may be a sparse transducer matrix as known in the art.

[0122] The process of generating backscatter amplitude images is similar for both one-dimensional and two-dimensional arrays. The following detailed description is for the case of linear arrays.

[0123] Figure 4(a) illustrates an example of a linear ultrasonic transducer array arranged along the X-axis, suitable for emitting ultrasonic waves along the Z-axis perpendicular to the X-axis. Therefore, the imaging plane 14 of the ultrasonic probe extends into the XZ plane. A typical ultrasonic probe can contain hundreds of transducers, suitable for imaging multiple lines in a region along the depth Z direction from the transducer, allowing the device to generate a two-dimensional image with pixels. Furthermore, each transducer has geometric focusing in a direction perpendicular to the imaging XZ plane along the Y-axis (referred to as the elevation direction or out-of-plane direction). For all examples illustrated in this invention, the one-dimensional array ultrasonic probe contains 128 ultrasonic transducers spaced 110 μm apart.

[0124] The transducer can be adapted to transmit and receive ultrasonic waves with center frequencies, for example, between 0.5 and 100 MHz, or, for example, between 1 and 20 MHz. An example of a usable center frequency is 15 MHz.

[0125] Figures 5(a)-5(c) The ultrasonic beam pressure field and intensity obtained by simulating the linear array shown in Figure 4(a) are displayed. The spatial ultrasonic field transmitted by the ultrasonic probe was simulated using Field II software. The simulation parameters are given in Table 1.

[0126] [Table 1]

[0127]

[0128] After emitting a plane wave, the spatial and temporal distribution of the three-dimensional pressure field was simulated. Therefore, a pressure signal p(t) was recorded at each point (x,y,z) in space.

[0129] Figure 5(a) shows the ultrasonic intensity map obtained in the YZ plane at the x-center position (x=0), and the normalized ultrasonic intensity map in the YZ plane at the x-center position for each depth z.

[0130] Figure 5(b) shows that the ultrasonic intensity decreases exponentially with depth z due to ultrasonic attenuation along the Z-axis.

[0131] Figure 5(c) shows the ultrasonic intensity profiles along the Y-axis at four given depths z (1 mm, 3 mm, 6 mm, and 9 mm), with normalization applied for each depth. Simulations show that the ultrasonic intensity varies in three-dimensional space. Specifically, the simulations show that the ultrasonic beam has a certain width w in the direction perpendicular to the imaging plane, which varies along the Z-axis. Therefore, for a fixed position (x0, z0) in the imaging plane 14, the ultrasonic intensity is maximum in the middle and decreases towards both sides, as shown in Figure 5(c).

[0132] In some embodiments, probe 5 may further include a motor drive 6 (MOT) adapted to move array 7 along the XYZ triaxial axes.

[0133] According to one embodiment, the motor drive device 6 is configured to move the one-dimensional ultrasound transducer array within the width w of the ultrasound beam along the Y direction, perpendicular to the ultrasound imaging plane XZ, to generate multiple parallel ultrasound imaging planes along the Y-axis. Therefore, the same region can be imaged, and the same blood vessels belonging to that region will appear on the two-dimensional ultrasound image.

[0134] Now we will combine Figure 2 and Figure 3 An example of a conventional ultrasonic positioning microscopy imaging method, which is known in the art and described above in the 2021 article by Demene et al.

[0135] The ultrasound contrast agent injection device 4 can be controlled by the processor 2 to intravenously inject S1 (MB_INJ) microbubbles or ultrasound contrast agent into a region of the vascular network.

[0136] The ultrasound contrast agent can be injected as a bolus injection, with a maximum injection volume of 40 mL / kg for rats (equivalent to 12 mL for a 300g rat and 3 mL for a 70g mouse). Typical injection volumes are 6 mL for rats and 2 mL for mice. For humans, the maximum injectable volume is 10 mL. For example, two 2.4 mL bolus injections can be administered to a human.

[0137] The ultrasound contrast agent can be injected continuously. For example, the continuous injection flow rate can be between 3 mL / h / kg and 60 mL / h / kg, preferably about 10 mL / h / kg (or typically 3.5 mL / h for 300g rats and 1.0 mL / h for 70g mice). Continuous injection can maintain a stable number of microbubbles for more than 20 minutes, with approximately 30 microbubbles per ultrasound image (i.e., composite image).

[0138] The processor 2 can control the transducer array 7 to acquire composite images of the vascular network region S2 (DATA_ACQ) during or after the injection of ultrasound contrast agent.

[0139] The calculation module 3 can be configured to process the composite image of the region acquired by S3(DATA_PROC) to obtain the filtered image of the region.

[0140] The calculation module 3 can be configured to calculate S4(C_ULM_COMP) of the two-dimensional or three-dimensional conventional ULM image of the vascular network region based on the filtered image of the region.

[0141] The calculation module 3 can be further configured to calculate S5(B_ULM_COMP) a two-dimensional or three-dimensional backscatter amplitude image of the vascular network region based on the filtered image of the region.

[0142] Processor 2 controls a one-dimensional ultrasound transducer array 7 to acquire S2 composite images by emitting ultrasound waves towards the vascular network region to be imaged and receiving the generated backscattered ultrasound waves, at a rate, for example, 5 kHz (Pulse Repetition Frequency, PRF), i.e., once every 0.2 ms. More generally, the PRF can exceed 500 Hz. The received signals can be recorded as a set of raw data for each emitted ultrasound wave. Continuous emitted waves can have propagation directions tilted at different consecutive angles relative to the depth direction Z of the region to be imaged.

[0143] For each image of the region, Np ultrasonic waves can be continuously emitted at different angles, and the Np sets of original data are coherently added together to synthesize the image of the region, thus making the image a composite image.

[0144] For example, in Figure 3In the example shown, Np can be 5, with angle values ​​of -5 degrees, -2 degrees, 0 degrees, +2 degrees, and +5 degrees. With Np = 5 and PRF = 5 kHz, the composite image rate (frame rate) for this region is therefore 1 kHz. Np can be different from 5, in which case the frame rate of the composite image will be different. For example, Np = 11 can be used. The transducer array 7 can be placed on the skull of a human or animal for transcranial experiments, or placed directly on the brain of a human or animal for experiments involving craniotomy. The ultrasound waves can be divergent, plane, or unfocused.

[0145] Based on the continuous composite images of this vascular network region, the S3-filtered image can then be calculated by calculation module 3. Figure 3 In the example, each filtered image uses N C A series of composite images. The N... C A series of consecutive composite images can be sequential in time, or they can partially overlap in the time dimension. For example, N C The number can be between 10 and 1000, for example, between 200 and 600. An example of the number of consecutive composite images available for a single filtered image is 400. The time position can be associated with the filtered image. The time position of a given filtered image can correspond to the average acquisition time of the Nc composite images that constitute that filtered image.

[0146] In an embodiment where the ultrasonic transducer array is a linear array as shown in Figure 4(a), the spatial variation of the measured backscatter amplitude of at least one isolated ultrasonic contrast agent at a given location (x, z) can be generated as a function of the position y of the imaging plane along the Y direction within the width of the ultrasonic beam to determine the position y of the at least one isolated ultrasonic contrast agent. In this embodiment, the processor 2 can be configured to move the one-dimensional array along the Y direction to generate multiple parallel ultrasonic imaging planes spaced apart from each other within the width of the ultrasonic beam along the Y direction. For example, the probe is moved to generate 5 imaging planes along the Y-axis, with a step size of 100 μm between these 5 planes. For the first imaging plane, a data block containing 400 composite images is acquired before moving to the next imaging plane to generate the data block containing 400 composite images. At the end of the fifth imaging plane, the one-dimensional ultrasonic transducer array is moved back to the first imaging plane to begin measuring the second data block containing 400 composite images. Thus, according to one example, 525 data blocks containing 400 composite images are acquired for each imaging plane. A 150ms pause may be required between the two imaging planes to allow sufficient time for the motor to move the one-dimensional ultrasonic transducer array. These 525 data blocks, each containing 400 composite images, can be used to create two-dimensional backscatter amplitude images and conventional two-dimensional ULM images.

[0147] The filtered image can be calculated, for example, by Singular Value Decomposition (SVD). More specifically, an SVD spatiotemporal clutter filter, as described by Demene et al. [Demene, C. et al., “Spatiotemporal clutter filtering of ultrafast ultrasound data significantly improves Doppler and functional ultrasound sensitivity.” Published in IEEE Transactions on Medical Imaging 34, 2271-2285 (2015)], can be applied. Figure 3 In the example, each filtered image can be applied to N C The SVD of a composite image is a singular value or the sum of multiple singular values. In some embodiments, as described by Hingot et al. [Hingot, V. et al., Subwavelength Motion Correction for Ultrafast Ultrasonic Positioning Microscopy. Published in Ultrasonics 77, 17-21 (2017)], the ultrasound characteristics of a single ultrasound contrast agent can be distinguished from the tissue signal (due to cardiac and respiratory pulsatility) of the region by speckle tracking correlation analysis of the composite image before applying SVD. Alternatively, by means of SVD of the composite image, the ultrasound characteristics of a single ultrasound contrast agent can be distinguished from the tissue signal of the region for each filtered image. Tissue signals can be filtered out by discarding some singular values ​​of the SVD. For example, the first 10 singular values ​​of the SVD, which mainly reflect the tissue signal of the region, can be discarded.

[0148] Each filtered image can be interpolated. For example, each filtered image can be interpolated using the Lanczos interpolation kernel. Interpolation can be performed on each filtered image to achieve a sampling rate of approximately (α / 6 x ε / 6), where α is the spatial spacing between the probes and ε is the wavelength of the ultrasound.

[0149] The filtered image stack can be filtered based on vascular filtering, as described by Jerman et al. [Jerman, T. et al., “Enhancement of vascular structures in 3D and 2D angiography images”. Published in IEEE Transactions on Medical Imaging 35, 2107–2118 (2016)].

[0150] In the composite image processing step S3, ultrasound contrast agents can be detected in the filtered image. For example, the ultrasound contrast agent can be detected as the brightest local maximum with a high correlation to the point spread function. High correlation can be defined as a correlation above a threshold. The threshold can be a value between 0.5 and 1. For example, the threshold can be equal to 0.7. The point spread function is the imaging response of an isolated ultrasound contrast agent and can be modeled as a Gaussian spot with axial and lateral dimensions of ε. Sub-pixel maximum localization can be performed using fast local second-order polynomial fitting. The neighborhood used for fast local second-order polynomial fitting can be a 5x5 pixel neighborhood. The coordinates of the located sub-pixel maximum can be rounded to a selected pixel size. The selected pixel size can be smaller than the pixel size of the filtered image. For example, the selected pixel size can be a sub-multiple of the pixel size of the filtered image. This sub-multiple can be a multiple of 2. For example, this sub-multiple can be equal to 16. For example, the selected pixel size can be equal to the initial pixel size / 8.

[0151] In the composite image processing step S3, the ultrasound contrast agent can be tracked in the filtered image. Tracking of the ultrasound contrast agent can be performed using particle tracking algorithms known in the art. Trajectories can be calculated based on the tracking of the ultrasound contrast agent in the filtered image. A trajectory can correspond to the position of the tracked ultrasound contrast agent in the filtered image. Each position of the tracked ultrasound contrast agent in the filtered image can be associated with a time position corresponding to the time position of that position in the filtered image. Trajectories of ultrasound contrast agents detected in a predetermined number of consecutive filtered images can be calculated. The predetermined number of consecutive filtered images can be between 1 and 100. For example, the predetermined number of consecutive filtered images can be 10. Spatial interpolation can be performed on each trajectory to obtain an ultrasound contrast agent at each pixel along the path between two consecutive pixels on the trajectory.

[0152] The continuous positions of the ultrasound contrast agent along a trajectory can be used to calculate velocity parameters. For example, for two-dimensional imaging, the inter-frame ultrasound contrast agent velocity vector components can be calculated along the probe x-axis and the depth z-axis.

[0153] Based on the filtered image, calculation module 3 can calculate S4(ULM_COMP) of the traditional two-dimensional ULM image. The traditional ULM image can be calculated based on trajectories, which in turn are based on the filtered image. Figure 3 In the example, each ULM image uses N F Image after filtering. Each traditional ULM image can be filtered by selecting the pixel size and N... F The image is constructed by classifying each detected ultrasound contrast agent in the filtered image into each pixel. In some embodiments, N FIn the filtered image, the pixel values ​​of pixels with accumulated detected ultrasound contrast agent values ​​below a threshold are set to zero. The threshold can be between 1 and 10, preferably 5.

[0154] A ULM (Ultra-Large Scale) image can be generated based on the detected ultrasound contrast agent count. For example, a ULM count image can be generated by calculating the number of ultrasound contrast agents detected in the corresponding pixels of a filtered image for each pixel. Figure 3 In the example, for each pixel, it can be used in N F The amount of ultrasound contrast agent detected in the corresponding pixels of the image after amplitude filtering. For example, the pixel size used to construct the image is approximately 13 μm.

[0155] Slow motion drift may occur in ULM images, possibly due to recording periods longer than cardiac and respiratory cycles. Slow motion drift can also originate in anesthetized humans or animals. In cases of craniotomy, potential brain swelling may also cause slow motion drift. Slow motion drift can be corrected using intensity-based spatial registration. This intensity-based spatial registration can be one of a translational transformation, a translation plus rotational transformation, or a more complex non-rigid transformation. The intensity-based spatial registration can be based on ULM images with shorter recording periods within the recording period. For example, a 10-second ULM count image can be used to correct drift occurring in ULM images with longer recording periods. Correcting slow motion drift allows for the observation of dynamic events of the subject matter that are caused by factors other than cardiac pulsatility and may be slower than cardiac pulsatility (e.g., the dynamic event may correspond to neural activity and / or an inflammatory response).

[0156] As mentioned above, the construction of traditional two-dimensional ULM images is based on the (x,z) positions of ultrasound contrast agents or microbubble features represented by point spread functions on the image. The (x,z) position of a microbubble is precisely located using the local feature amplitude of the microbubble in the (x,z) plane. Therefore, traditional two-dimensional ULM images are obtained by calculating the number of microbubbles detected in each pixel, thus generating a microbubble count map, commonly referred to as a microbubble density map.

[0157] When using a one-dimensional ultrasound transducer array, for traditional two-dimensional imaging, due to the lack of information along the Y direction, the velocity map can only be calculated based on the components of the inter-frame ultrasound contrast agent velocity vector along the probe x-axis and depth z-axis.

[0158] Therefore, when using a two-dimensional PSF function for microbubbles distributed in three-dimensional space, it is impossible to obtain information about the elevation direction (i.e., along the Y-axis), especially to locate microbubbles or ultrasound contrast agents flowing through blood vessels that cross the XZ imaging plane.

[0159] One embodiment of the present invention aims to provide a method that utilizes the amplitude of the backscattering characteristics of an isolated ultrasound contrast agent, which is a function of the (x,z) position of the microbubble in three-dimensional space, thereby enabling the collection of missing elevation direction Y information from two-dimensional ULM imaging.

[0160] Figures 4(a)-4(c) This describes the physical phenomenon that relates the intensity of the backscattering of an ultrasound contrast agent or microbubble to its y-position in the Y-direction perpendicular to the imaging plane.

[0161] Each microbubble used in the ULM imaging method is smaller than the length of the ultrasound wave, acting as a single Rayleigh scatterer. When the ultrasound propagates in a homogeneous medium and all microbubbles have the same diameter and therefore the same cross-section, the backscattering intensity of each microbubble depends only on the amplitude of the ultrasound received by the microbubble. Therefore, the amplitude of each microbubble signal is directly related to its position in three-dimensional space within the emitted ultrasound field. For a given position (x0, z0), as shown in Figure 5(c), since the ultrasound intensity received by the microbubble varies along the Y-axis, the ultrasound intensity backscattered by the microbubble also varies along the Y-axis. Therefore, by determining the variation of the backscattered energy along the Y-axis at a given depth Z, information about the microbubble's position in the elevation plane can be extracted.

[0162] In Figure 4(a), a microbubble 12 flows through a blood vessel 13 that passes through the imaging plane 14 at times t1 and t2.

[0163] Figure 4(b) shows that for microbubbles 12 located at the same position (x0, z0) in the ULM image but at two different positions y along the Y-axis, two different backscattered ultrasound intensities were detected in the microbubbles counted in that pixel due to the variation of the ultrasonic field along the Y-axis.

[0164] Figure 4(c) shows that for a given location (x0, z0) in a two-dimensional ULM image, the two backscattering intensities correspond to two locations y1 and y2 within the ultrasonic beam. The backscattering intensity corresponding to location y1 is lower than that at location y2. At time t2, this is because the microbubble is closer to the center of the ultrasonic beam.

[0165] Therefore, backscatter amplitude imaging provides a new informational parameter that is related to the position of microbubbles in three-dimensional space within an ultrasonic beam using a one-dimensional transducer array.

[0166] In one embodiment of this disclosure, based on the filtered image obtained in step S3, calculation module 3 can calculate a two-dimensional backscatter amplitude ULM image (S5, B_ULM_COMP). During step S3, isolated ultrasound contrast agents are detected as the brightest local maximum value on the B-mode image that correlates well with the PSF. The value of this maximum value on the B-mode image is extracted and associated with each located ultrasound contrast agent detection. This value is referred to as the backscatter amplitude. Instead of assigning each ULM image pixel to the number of microbubbles detected in that pixel as described with reference to step S4, the two-dimensional backscatter amplitude image is constructed by assigning each pixel a value representing the measured backscatter amplitude of all ultrasound contrast agents detected in that pixel. For example, this value could be the average of the backscatter amplitudes of all ultrasound contrast agents detected in that pixel. The selected grid could be the same as the grid selected for microbubble counting. Alternatively, the value could be a function of the backscatter amplitude of the at least one isolated ultrasound contrast agent detected in the pixel.

[0167] Figure 6 This image shows a backscattered amplitude image obtained in the rat thalamus with a blood vessel passing through an ultrasound beam (i.e., perpendicular to the imaging plane). The vessel extends out-of-plane and appears as a white line on the image. In backscattered amplitude images, such vessels passing through the imaging plane are brightest at the center of the ultrasound beam and gradually darken as they approach the edge of the beam. For example, in… Figure 6 In the image, arrows numbered 1, 3, 4, and 6 indicate blood vessels located near the edge of the ultrasound beam, with lower backscatter amplitude; arrows numbered 2 and 5 indicate blood vessels located at the center of the beam, with the largest backscatter amplitude.

[0168] Figure 7(a) illustrates the trajectory of microbubbles or ultrasound contrast agents flowing through such vessels and their backscatter amplitude profile. When a microbubble enters the ultrasound beam, it receives the least incident ultrasound intensity, and therefore experiences the least backscatter intensity. The backscatter intensity is greatest when the microbubble reaches the center of the ultrasound beam, where the incident intensity reaches its peak. Then, as the microbubble leaves the ultrasound beam, the backscatter amplitude decreases.

[0169] Figure 7(b) shows the situation in... Figure 6 The trajectory is shown as a microbubble flowing in a blood vessel as a white line, and the normalized backscatter amplitude is detected as a function of time.

[0170] Figure 8(a) and 8(b) The case where the blood vessels are parallel to the imaging plane is considered, therefore the backscattering amplitude of the microbubbles does not change significantly. This situation corresponds to blood vessels belonging to the cortex when imaging in the coronal or sagittal plane.

[0171] Figure 8(a) schematically illustrates the backscattering intensity of microbubbles 12 flowing in parallel blood vessels but located at different positions along the Y-axis. For example, blood vessel 15 is located at the beam center, where the ultrasound intensity emitted by the linear array is the highest. Blood vessel 16 is located at the beam edge, where the ultrasound field emitted by the linear array is the lowest. Therefore, the backscattering intensity of microbubbles flowing through blood vessel 15 will be higher than that of microbubbles flowing through blood vessel 16.

[0172] Figure 8(b) shows three vessels in the cortex on a backscatter amplitude image. The vessel closest to the center of the beam (arrow 3) is brighter, while the vessels closer to the edge of the beam (arrows 1 and 2) are darker.

[0173] In the case of a linear ultrasonic transducer array, the measured backscattering amplitude of microbubbles can invert the relative distance between the ultrasonic contrast agent and the two-dimensional imaging plane, as well as the position y of the ultrasonic contrast agent detected in the two-dimensional ultrasonic image. The three velocity components V along the X, Y, and Z directions can be calculated. x V y and V z This improves the accuracy of microbubble velocity calculations. In other words, this disclosure provides a method and apparatus for calculating three-dimensional flow and velocity from two-dimensional ULM images obtained using a one-dimensional ultrasonic probe. Backscatter amplitude imaging allows for the avoidance of complex use of two-dimensional ultrasonic transducer arrays.

[0174] Figure 9 The illustration shows how to extract the out-of-plane positioning of the ultrasound contrast agent from a series of two-dimensional filtered images obtained through multiple parallel imaging planes.

[0175] Instead of using a single imaging plane to calculate the individual backscatter amplitude of the ultrasound contrast agent detected and tracked in the two-dimensional filtered image, a relationship is generated between the backscatter amplitude of the ultrasound contrast agent at a given location (x,z) and the y-axis along the Y-direction within the ultrasound beam width w. The location y of the isolated ultrasound contrast agent is then calculated by fitting a function to the change in backscatter amplitude.

[0176] In one embodiment, the spatial variation of the backscatter amplitude of an isolated ultrasound contrast agent at a given location (x, z) can be generated as a function of the position y of the imaging plane along the Y direction within the width of the ultrasound beam. For example, processor 2 can be configured to move a one-dimensional array 7 along the Y direction to generate multiple parallel ultrasound imaging planes spaced apart from each other within the width of the ultrasound beam along the Y direction. The spatial step size between two consecutive imaging planes can be constant. The spatial step size and the number of imaging planes are chosen such that the total length L of all imaging planes is equal to or less than the width w of the ultrasound beam. Thus, the same blood vessel can be imaged. In other words, while the position of the blood vessel in the XZ plane does not change across all imaging planes, its position along the Y axis may vary depending on the plane. Therefore, for a given location (x, z), the ultrasound intensity measured by the ultrasound contrast agent detected in each two-dimensional image associated with each imaging plane will vary.

[0177] exist Figure 9 In the example, the probe is moved to generate five imaging planes along the Y-axis, with a step size of 100 μm between these five planes. Because the beamwidth exceeds 500 μm, the ultrasound probe images the same blood vessel. For each imaging plane positioned at a given location y along this direction, a series of two-dimensional filtered images are generated. Each sequence of filtered images is associated with a spatial location along the Y-direction.

[0178] Figure 9 (a) illustrates this situation for three ultrasound contrast agents A, B, and C. Each ultrasound contrast agent is imaged by five imaging planes: plane 1, plane 2, plane 3, plane 4, and plane 5. The intensity of the incident ultrasound received by each ultrasound contrast agent is different on each imaging plane.

[0179] For the ultrasound contrast agent located at pixel A, it lies outside the ultrasound beam on imaging planes 1, 2, and 3, and at the beginning of the ultrasound beam on imaging planes 4 and 5. Therefore, for imaging planes 1, 2, and 3, the ultrasound contrast agent receives neither incident ultrasound intensity nor backscattered ultrasound intensity. For imaging planes 4 and 5, the microbubble receives the minimum incident and backscattered ultrasound intensity. This backscattered ultrasound intensity varies spatially with y as follows: Figure 9 As shown in (b).

[0180] For the ultrasound contrast agent located at pixel B, it is situated at the center of the ultrasound beam on imaging plane 3. In the five acquired images, the position (x...) B ,z BThe associated microbubble intensity is maximum at imaging plane 3 and decreases towards imaging planes 1 and 5. This backscattered ultrasound intensity varies with y as follows: Figure 9 As shown in (a).

[0181] For the ultrasound contrast agent located at pixel C, the situation is similar to that of ultrasound contrast agent A. It is closer to the center of the ultrasound beam at imaging plane 1 and further away from the center towards imaging plane 5. The intensity of the backscattered ultrasound decreases as a function of the imaging plane position y. This spatial variation of the backscattered ultrasound intensity with y is as follows: Figure 9 As shown in (b).

[0182] The spatial variation of backscatter amplitude from the five imaging planes is used to calculate the position y of the isolated contrast agent along the Y direction at a given location (x,z) by fitting a function to the variation of backscatter amplitude.

[0183] In one embodiment, the fitting function is a Gaussian function: Where 'a' represents the amplitude of decrease along depth Z due to ultrasonic attenuation, 'w' is the width of the ultrasonic beam, which is larger near the transducer, converges to a minimum at the focal length, and then diverges, and 'y0' is the location of the maximum change in backscattering amplitude, corresponding to the position of the microbubble in the Y direction. The parameter 'w', which quantifies the Gaussian fit width, can be an experimental value. Alternatively, the beamwidth can be obtained through simulation.

[0184] exist Figure 9 In the example, five imaging planes are used to generate curves containing five backscatter amplitudes to perform fitting. The number of imaging planes and the number of backscatter amplitudes can be adjusted as needed.

[0185] In traditional two-dimensional ULM imaging, velocity parameters can be calculated using the continuous positions of the ultrasound contrast agent along its trajectory. Figure 9 In the example, the velocity components of the ultrasound contrast agent B located at position (x,z) along the probe's X-axis and the depth Z-axis can be calculated. Thanks to the variation in backscattering amplitude within the width of the ultrasound beam in the elevation direction, the sub-resolution position of the isolated microbubble is used to calculate the velocity component along the Y-axis. The absolute velocity magnitude can be calculated. Therefore, the velocity of the ultrasound contrast agent flowing through the blood vessel across the imaging plane can be accurately calculated.

[0186] In a similar manner, instead of determining the sub-resolution position of isolated microbubbles in the Y direction to calculate the absolute velocity magnitude of each ultrasound contrast agent, it is possible to determine the relationship between the backscattering amplitude of each pixel at a given position (x,z) and the position y in the Y direction of each pixel (x,z) by fitting a function to the change in backscattering amplitude.

[0187] The steps for calculating the speed for each pixel at a given location (x,z) include:

[0188] (i) The region of interest is imaged on multiple parallel ultrasound imaging planes XZ spaced apart from each other within the width of the ultrasound beam along the Y direction.

[0189] (ii) A two-dimensional backscatter amplitude image is generated for each imaging plane XZ by assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in that pixel to each pixel;

[0190] (iii) Generate the spatial relationship between the backscattering amplitude of each pixel and the position y of the imaging plane along the Y direction within the width of the ultrasonic beam;

[0191] (iv) By fitting the function to the spatial variation of the measured backscatter amplitude, the position y of each pixel is calculated. The position y of each pixel is the location of the maximum value of the backscatter amplitude variation.

[0192] (v) Calculate the three velocity components V of each pixel along the three directions X, Y, and Z. x V y and V z .

[0193] Figure 10 The illustration shows five backscatter amplitude images associated with five parallel imaging planes positioned along the Y-direction within the beamwidth. The backscatter amplitude of pixel M at a given location (x, z) is generated as a function of y along the Y-direction within the ultrasonic beamwidth w. The position y of that pixel is then calculated by fitting a function to the change in backscatter amplitude.

[0194] In the rat thalamus, five backscattered amplitude images were generated for five coronal imaging planes spaced 100 μm apart in the Y-direction of elevation. Therefore, these five imaging planes are located within the width of the ultrasound beam. Figure 9 The five images shown exhibit the same blood vessels. For each pixel at a given location (x, z) in the five images, a relationship is generated between the backscatter amplitude and the position of the imaging plane along the Y direction within the ultrasound beam width w. For each pixel (x, z), a function can be fitted to the backscatter amplitude curves measured for the five imaging planes. This fit is used to determine the sub-resolution location of the maximum value of the backscatter amplitude function, corresponding to the pixel's position y0 in the elevation direction. For example, the fit could be a Gaussian fit: Where 'a' is the magnitude of the decrease along depth Z due to ultrasonic attenuation, 'w' is the width of the ultrasonic beam, which is larger near the transducer, converges to a minimum at the focal length, and then diverges, and 'y0' is the location of the maximum change in backscatter amplitude, corresponding to the pixel's position in the Y direction. The parameter 'w' for quantizing the Gaussian fit width can be an experimental value. Alternatively, the beamwidth can be obtained through simulation.

[0195] Figure 11 The diagram shows... Figure 10 The image shows five backscattering amplitudes measured at pixel M, indicated by a cross. Curve G is a Gaussian fit of these five backscattering amplitudes. The position of pixel M is given by the position of the fitted maximum value: y0. In this example, y0 = 20 μm.

[0196] Backscattering information available in 2D ULM imaging in the XZ plane can be used to locate the position of each pixel (x,z) in the Y direction. The velocity components along the probe's X-axis and depth Z-axis, as well as the velocity component along the Y-axis, can also be calculated for each pixel at position (x,z). The absolute velocity magnitude of each pixel can be calculated. Therefore, the velocity of the blood vessel crossing the imaging plane can be accurately calculated, and a 3D velocity map can be generated.

[0197] In another embodiment, the calculation module 3 is adapted to correct the positioning of a one-dimensional ultrasonic transducer array along the Y-direction within the width of the ultrasonic beam by comparing backscatter amplitude images generated from two sets of raw data acquired at two different times. For example, the first set of raw data is acquired by a one-dimensional array positioned at a given location y1 along the Y-axis, having a first imaging plane. A first backscatter amplitude image is generated from this first set of raw data, as described above, by assigning parameters related to the backscatter amplitude of all microbubbles or ultrasonic contrast agents detected in that pixel to each pixel. A second set of raw data is acquired from the same one-dimensional array. A second backscatter amplitude image is generated from this second set of raw data. In cases where it is necessary to position the one-dimensional array to image a region using the same imaging plane as the first measurement configuration, the calculation module 3 is configured to compare each pixel in the first backscatter amplitude image and the second backscatter image to determine whether the imaging plane associated with the first backscatter amplitude image coincides with the imaging plane associated with the second backscatter image.

[0198] Figure 12 illustrates how to invert the missing velocity component in the Y direction from a backscatter amplitude image generated by acquiring (x,z) through a single imaging plane.

[0199] In traditional ULM imaging, blood flow velocity can only be obtained from the two in-plane components of the velocity vector (i.e., component V). x and V zThe in-plane two-dimensional component of blood flow velocity is determined using the differential of the ultrasound contrast agent's continuous position in the trajectory. Therefore, the velocity is underestimated, especially for vessels crossing the imaging plane.

[0200] Backscatter information acquired from a single imaging plane is used to determine the position of the blood vessel relative to the imaging plane. Furthermore, the method includes a step of quantizing the correction velocity of at least one blood vessel based on a backscatter amplitude image acquired from a single imaging plane. This quantization step uses a geometric model of the out-of-plane angle of the blood vessel, deriving the missing component by assuming the blood vessel passes in a straight line through the ultrasound beam (as shown in Figure 12(b)).

[0201] The quantification step includes the following steps:

[0202] (i) Select at least one blood vessel from at least one backscatter amplitude image generated in step S5. For example, Figure 12 shows four selected blood vessels 1-4;

[0203] (ii) As described above, calculate the in-plane velocity Vxz of the ultrasound contrast agent belonging to the selected blood vessel;

[0204] (iii) Obtain a backscattering amplitude profile along the selected blood vessel centerline;

[0205] (iv) Calculate the angle θ using the formula tan(θ) = HM / OH, where θ is the angle between the backscatter amplitude profile along the selected vessel centerline and its projection onto the ultrasound imaging plane. HM is the beam width, and OH is dS, which can be evaluated by the full width at half maximum (FWHM) of the backscatter profile along the curve abscissa of the centerline (as shown in Figure 12(a)).

[0206] (v) Calculate the correction velocity of each ultrasound contrast agent belonging to the selected vessel using the calculated angle: Vcorr = Vxz / cosθ.

[0207] Because backscatter amplitude is measured in ULM imaging, computation module 3 is able to depict more small vessels than conventional ULM images due to its inherently lower spatial noise. Backscatter ULM imaging is less sensitive to noise and allows for the detection of smaller vessels compared to conventional ULM images based on ultrasound contrast agent counts. In conventional ULM images, each pixel is associated with an ultrasound contrast agent count. Therefore, the signal is driven by blood flow. In small vessels, the signal is also low due to the low blood flow, making them difficult to detect. In backscatter imaging, the signal is driven by the vessel's position within the ultrasound beam and is independent of hemodynamics. Although backscatter amplitude images and conventional ULM images are generated from the same set of raw data measured by a one-dimensional transducer array, the impact of noise signals in backscatter imaging is less than in conventional ULM.

[0208] Advantageously, backscatter imaging may be more suitable for segmentation algorithms and can provide better insights into the size and level of detected branching capillaries compared to ULM imaging.

[0209] In one embodiment, the method includes the step of automatically segmenting blood vessels in at least one region of a vascular network based on a two-dimensional backscatter amplitude image or a three-dimensional backscatter amplitude image. Therefore, at least one dimensional parameter of the blood vessels can be quantified from the segmented image. For example, the dimensional parameter could be the vessel diameter or the length of each segment of the vessel.

[0210] Furthermore, backscatter amplitude ULM imaging allows for more precise velocity quantization. Combining localization techniques with backscatter amplitude imaging across multiple imaging planes provides three-dimensional localization of vessels in out-of-plane directions with subwavelength resolution. While it is not possible to invert the exact position of the ultrasound contrast agent relative to the imaging plane using a single imaging plane acquisition, the angle between the vessel and its projection onto the imaging plane can be estimated to provide three-dimensional correction of the velocity vector.

[0211] Based on the backscatter amplitude measured for each isolated contrast agent, and from the backscatter amplitude image, at least one vascular dynamic parameter can be accurately calculated. The at least one vascular dynamic parameter can be selected from the group consisting of: blood flow, blood flow velocity, blood volume, blood pressure, vessel diameter, and any combination thereof.

[0212] In this invention, the vascular network described is the vascular network of the nervous system. However, the described methods and devices are applicable to any vascular network.

Claims

1. A method for imaging vascular activity at a microscopic scale in at least one region of a vascular network in a human or animal organ, the method comprising: (a) A series of continuous incident ultrasonic waves are emitted in the at least one region by an ultrasonic transducer array (7) extending in at least one direction and the incident ultrasonic waves propagate in a direction perpendicular to the transducer array. (b) Acquire a set of raw data from backscattered ultrasound through the transducer array; (c) Generate a series of consecutive ultrasound images based on the raw data; (d) Detecting at least one isolated ultrasound contrast agent in the ultrasound image; (e) Positioning of the at least one isolated ultrasound contrast agent with an accuracy below the wavelength of the wave; (f) Generate at least one two-dimensional backscatter amplitude image by assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in the pixel to each pixel.

2. The method according to claim 1, characterized in that, The value calculated in step (f) corresponds to the average of the measured backscatter amplitudes of all isolated ultrasound contrast agents detected in the pixel.

3. The method according to claim 1, characterized in that, The value calculated in step (f) corresponds to a function of the backscattering amplitude of the at least one isolated ultrasound contrast agent detected in the pixel.

4. The method according to any one of claims 1 to 3, further comprising a tracking step, characterized in that, In the ultrasound images generated in step (c), at least one isolated ultrasound contrast agent detected is traced to determine its trajectory and velocity.

5. The method according to any one of claims 1 to 4, characterized in that, The ultrasonic transducer array (7) is a one-dimensional array extending along a direction X, and the incident ultrasonic wave propagates along a direction Z perpendicular to the transducer array. The image generated in step (f) is a two-dimensional backscatter amplitude image.

6. The method according to claim 5, characterized in that, Steps (a) to (f) are repeated on multiple parallel ultrasound imaging planes XZ spaced apart from each other within the width of the ultrasound beam along the Y direction to generate multiple two-dimensional parallel backscatter amplitude images.

7. The method of claims 4 and 6, further comprising the step of calculating the velocity of the at least one tracked isolated ultrasound contrast agent at a given location (x, z), the step comprising: (i) Generate the relationship between the backscattering amplitude of the at least one tracked isolated contrast agent and the position y of the imaging plane along direction Y within the width of the ultrasound beam; (ii) By fitting a function to the spatial variation of the measured backscatter amplitude, the position y of the at least one tracked isolated contrast agent is calculated, where the position y of the at least one isolated contrast agent is the location of the maximum spatial variation of the backscatter amplitude. (iii) Calculate the three velocity components V of the at least one tracked isolated ultrasound contrast agent along the three directions X, Y, and Z. x V y and V z .

8. The method of claim 6, further comprising the step of calculating a speed for each pixel at a given location (x, z), the step comprising: (i) Generate the relationship between the backscattering amplitude of each pixel and the position y of the imaging plane along the direction Y within the width of the ultrasonic beam; (ii) By fitting the function to the spatial variation of the measured backscatter amplitude, the position y of each pixel is calculated. The position y of each pixel is the location of the maximum value of the backscatter amplitude variation. (iii) Calculate the three velocity components V of each pixel along the three directions X, Y, and Z. x V y and V z .

9. The method according to claim 7 or 8, characterized in that, The fitting function is a Gaussian function: Where α is the backscattering amplitude, w is the width of the ultrasonic beam along direction Y, and y0 is the position of the maximum value of the backscattering amplitude variation.

10. The method according to claim 9, characterized in that, The width w of the ultrasonic beam along direction Y is an experimental value.

11. The method according to claim 9, characterized in that, The width w of the ultrasonic beam along the Y direction is a simulated value.

12. The method according to any one of claims 6 to 11, characterized in that, The plurality of parallel ultrasound imaging planes are obtained by moving the one-dimensional ultrasound transducer array within the width (w) of the ultrasound beam along a direction Y perpendicular to the ultrasound imaging plane (x,z).

13. The method of claim 6, further comprising the step of positioning the one-dimensional ultrasonic transducer array by comparing a first backscatter amplitude image and a second backscatter amplitude image, such that the imaging plane associated with the first backscatter amplitude image and the imaging plane associated with the second backscatter image coincide.

14. The method according to any one of claims 1 to 13, further comprising the step of generating at least one two-dimensional ultrasound localization microscope (ULM) image of the at least one region by assigning an amount of ultrasound contrast agent detected in each pixel to each pixel.

15. The method of claim 5, further comprising the step of quantizing the correction velocity of at least one blood vessel based on the two-dimensional backscatter amplitude image, the quantization step comprising: (i) Selecting the at least one blood vessel from the at least one backscatter amplitude image; (ii) Calculate the velocity Vxz of the ultrasound contrast agent belonging to the selected blood vessel; (ii) Obtain a backscattering amplitude profile along the selected blood vessel centerline; (iii) Calculate the angle θ between the selected vessel centerline along its backscatter amplitude profile and its projection on the ultrasound imaging plane; (iv) Calculate the correction velocity for each ultrasound contrast agent belonging to the selected vessel using the calculated angle: V corr =V xz / cosθ.

16. The method according to any one of claims 1 to 15, characterized in that, The step of generating a series of consecutive two-dimensional ultrasound images from the raw data includes a filtering step to distinguish the ultrasound signals of a single ultrasound contrast agent from the tissue signals.

17. The method according to any one of claims 1 to 16, characterized in that, At least one vascular parameter is extracted from the measured backscatter amplitude, the vascular parameter being selected from the group including blood flow, blood flow velocity, blood volume, blood pressure and any combination thereof.

18. The method of claim 1, further comprising the step of automatically segmenting blood vessels in at least one region of an organ vascular network based on the at least two-dimensional backscatter amplitude image, wherein at least one dimensional parameter of the blood vessel is quantized from the segmentation step.

19. An apparatus (1) for imaging vascular activity at a microscopic scale in at least one region of a vascular network in a human or animal organ, said apparatus comprising: (a) An ultrasonic probe (5) having an ultrasonic transducer array (7) extending in at least one direction, the ultrasonic probe being configured to emit incident ultrasonic waves in a propagation direction perpendicular to the transducer array and acquire a set of raw data. (b) Calculation module (3), configured as follows: - Generate a series of consecutive ultrasound images based on the raw data; - Detect at least one isolated ultrasound contrast agent in an ultrasound image; - Position the at least one isolated ultrasound contrast agent with an accuracy below the wavelength of the wave; - Track the at least one isolated ultrasound contrast agent to determine its trajectory; - By assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in that pixel to each pixel, at least a two-dimensional backscatter amplitude image is generated.

20. The device according to claim 19, characterized in that, The ultrasonic transducer array is a one-dimensional ultrasonic transducer array extending along a direction X, used to generate a two-dimensional backscatter amplitude image.

21. The device according to claim 20, characterized in that, The probe (5) further includes a motor (6) configured to move the ultrasonic transducer array (7) within the width (w) of the ultrasonic beam in a direction perpendicular to the ultrasonic imaging plane to generate a plurality of parallel ultrasonic imaging planes.

22. The device according to claim 21, characterized in that, The computing module (3) is further configured as follows: - Generate the relationship between the backscattering amplitude of the at least one tracked isolated contrast agent and the position y of the imaging plane along direction Y within the width of the ultrasound beam; - The position y of the at least one tracked isolated contrast agent is calculated by fitting a function to the spatial variation of the measured backscatter amplitude, and the position y of the at least one isolated contrast agent is the location of the maximum value of the backscatter amplitude variation. - Calculate the three velocity components V of the at least one tracked isolated ultrasound contrast agent along the three directions X, Y, and Z. x V y and V z .

23. A computer software (2) comprising instructions, when executed by a processor, for implementing a method for imaging vascular activity at a microscopic scale in at least one region of a vascular network in a human or animal organ, the method comprising: (a) A series of continuous incident ultrasonic waves are emitted in the at least one region by an ultrasonic transducer array extending in at least one direction and the incident ultrasonic waves propagate in a direction perpendicular to the transducer array. (b) Acquire a set of raw data from backscattered ultrasound through the transducer array; (c) Generate a series of consecutive ultrasound images based on the raw data; (d) Detecting at least one isolated ultrasound contrast agent in the ultrasound image; (e) Positioning of the at least one isolated ultrasound contrast agent with an accuracy below the wavelength of the wave; (f) Generate at least a two-dimensional backscatter amplitude image by assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in the pixel to each pixel.

24. A computer-readable non-transient recording medium having software registered thereon, which, when executed by a processor (2), performs a method for imaging vascular activity at a microscopic scale in at least one region of a vascular network in a human or animal organ, the method comprising: (a) A series of continuous incident ultrasonic waves are emitted in the at least one region by an ultrasonic transducer array extending in at least one direction and the incident ultrasonic waves propagate in a direction perpendicular to the transducer array. (b) Acquire a set of raw data from backscattered ultrasound through the transducer array; (c) Generate a series of consecutive ultrasound images based on the raw data; (d) Detecting at least one isolated ultrasound contrast agent in the ultrasound image; (e) Positioning of the at least one isolated ultrasound contrast agent with an accuracy below the wavelength of the wave; (f) Generate at least a two-dimensional backscatter amplitude image by assigning a value representing the measured backscatter amplitude of at least one isolated ultrasound contrast agent detected in the pixel to each pixel.

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