WO2021012041A1 - System and method for ultrasound perfusion imaging - Google Patents
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Definitions
- the present invention pertains to perfusion imaging of tissues in vivo using ultrasound. I n particular, the present invention pertains to a method and system for non- invasive perfusion imaging of live tissues using ultrasound and noise reduction of ultrasound images.
- Ultrasonic imaging or sonography is used to image live tissues in animals and humans.
- Diagnostic sonography also referred to as ultrasonography, is an ultrasound-based diagnostic imaging technique used for visualizing subcutaneous body structures of a patient, such as tendons, muscles, joints, vessels and internal organs for possible pathology or lesions.
- Ultrasound images or sonograms are made by sending a pulse of ultrasound into tissue by using an ultrasound transducer or probe.
- the sound reflects and echoes off of parts of the tissue, and the echo or reflected sound is recorded and displayed as an image to the operator of a medical-imaging system, usually with denser tissues showing up as bright areas and less dense tissues showing up as darker areas in the sonogram image.
- the commonest form of ultrasound image is a B-mode image (brightness-mode), which displays the changes in acoustic impedance of a two- or three-dimensional cross-section of tissue.
- Doppler ultrasonography is used to study blood flow, including direction and velocity of flow, and muscle motion.
- the different detected speeds of flow and movement with Doppler images are often represented in color for ease of interpretation.
- Ultrasound contrast agents comprising encapsulated gaseous microbubbles can be used to increase echogenicity in tissues, or improved ability to echo sound waves.
- the contrast medium is intravenously administered to introduce the gas-filled microbubble contrast agent to the systemic circulation, and the increased echogenicity provides an enhanced image used to image blood perfusion in organs.
- Perfusion imaging provides information about physiological tissue behaviour such as blood volume, blood flow, mean transit time (MTT) and time to peak (TTP) in vascularized tissue.
- MTT mean transit time
- TTP time to peak
- I n perfusion imaging typically a bolus of a contrast agent is injected and its distribution is followed by a repeated acquisition of subsequent images covering the volume of interest.
- the contrast agent works as a tracer of the blood and provides signal changes to indicate blood flow.
- either the short-term distribution ( ⁇ 1 min) of blood flow (perfusion) or the long-term (> 1 min) diffusion process of the tracer particles through the membranes of the micro-vessels (tissue kinetics) are encoded in the varying signal of the image voxels.
- the extracted time-intensity curves for each voxel are typically converted into relative concentration-time curves.
- Conventional ultrasound resolution limits the minimum side-length of the voxel to > 150 microns.
- High frequency ultrasound also known as micro-ultrasound
- micro-ultrasound is becoming a valuable diagnostic technique due to the development of high-frequency ultrasound array transducers.
- the slice data is combined by projecting the data in the elevation dimension to produce an elevationally combined slice image and the image data is combined by means of an averaging or maximum intensity detection or weighting process or by raycasting in the elevation dimension in a volumetric rendering process.
- the combined slice image provides a measure of perfusion.
- An object of the present invention is to provide an ultrasonic imaging system and method which provides perfusion data without requiring a contrast agent.
- an imaging processing method comprising, processing a plurality of digital images comprising sequential B-Mode ultrasound reflectivity data, calculating decorrelation trends of autocorrelated data to determine flow and perfusion level.
- the method reduces noise content in the ultrasound data using the decorrelation trends.
- the method forms a visual representation of the perfusion level based on the decorrelation trends.
- the method reduces noise content in the autocorrelated data using the decorrelation trends; and forms a visual representation of the perfusion level based on the decorrelation trends.
- the method has an image capture rate of 20 frames/sec or higher.
- the image data is standardized before autocorrelation.
- the autocorrelated data is normalized.
- the decorrelation trend of the autocorrelated data is determined by linear regression, average difference, or overall magnitude change.
- the autocorrelated data with non-linear trends are processed to determine one or more of period, exponential decay rate, time to local minima, or another measure of decorrelation.
- the autocorrelation is calculated using a Spearman correlation, Pearson correlation, or Fourier Transform.
- the method further comprises a smoothing step prior to visual representation of the signal.
- the method further comprises application of thresholds and rescaling to the decorrelation trends before visual representation.
- the method further comprises a logarithmic transformation of the decorrelation trend.
- the decorrelation trends are mapped to different colour or grayscale values for representation in an image.
- the method further comprises comprising alignment of the plurality of digital images to correct for movement by matching local signal patterns between frames.
- the method includes at least 5 frames of sequential B-Mode ultrasound reflectivity data.
- a subset of the image field is processed from each image to decrease processing time.
- the image is downsampled to a lower resolution to decrease processing time.
- the ultrasound data is high frequency ultrasound with a frequency range greater than 15 MegaHertz.
- a perfusion imaging system comprising, a high frequency ultrasound transducer for capturing and/or collecting a plurality of digital images comprising sequential B-Mode ultrasound reflectivity data, a signal processing unit, operatively connected to the transducer, the signal processing unit configured to calculate decorrelation trends of autocorrelated data to determine blood flow and perfusion level.
- Another aspect is to provide, a computer readable storage medium, comprising executable instructions that when executed by a process cause the processor to, process a plurality of digital images comprising sequential B-Mode ultrasound reflectivity data obtained using a micro-ultrasound, calculate decorrelation trends of autocorrelated data to determine blood flow and perfusion level.
- Figure 1 illustrates a high frequency medical-imaging system
- Figures 2A and 2B are example ultrasound images before and after denoising by eliminating low-correlation pixels
- Figure 3 shows an example of a perfusion signal from a blood vessel as compared to an area of noise in the image
- Figure 4 shows an example of the signal from unaligned and aligned images
- Figures 5A-C are examples before and after activation of a forearm muscle.
- Figure 6 is a flowchart illustrating an example method of ultrasound perfusion imaging.
- an ultrasound mode for perfusion imaging of tissues is provided.
- the present system and method provides an ultrasonic imaging system and method which provides perfusion data without requiring the use of an injected contrast agent.
- perfusion of blood can be detected and differentiated from what would otherwise be noise in the ultrasound signal. I n this way, perfusion within biological tissues can be measured without the need for a contrast agent.
- the detection and imaging of the perfusion of blood through tissues can be done by examining the time-decorrelation signal at the pixel level of a micro-ultrasound image configured to a very high frame rate. For example, use in a technique such as plane wave imaging. At the high frame rate and small voxel size provided by micro-ultrasound, the movement of individual reflectors into and out of the sensitive detectable area cause slow changes over time. The detection of these changes over time as a result of blood perfusion through the tissue contrasts with both noise, which is entirely uncorrelated over time, and solid tissue which is correlated over time.
- Measurement of perfusion in this way may be more difficult in conventional ultrasound because the sensitive area (voxel) in the tissue is too large and too many reflectors pass in and out at once causing the intensity variation to be small due to averaging. Further, conventional ultrasound is not sensitive to the individual reflectors in the blood, while higher frequency micro-ultrasound is. I n another embodiment, it is predicted that measurement of perfusion using conventional ultrasound may be possible with the use of another reflector. For example, a large protein or a macrophage may function as a reflector for convention ultrasound.
- red blood cells are the most abundant cell in the blood accounting for about 40 to 45 percent of its volume. Red blood cells have a diameter of approximately 6-8 pm, which is in the same size range as ultrasound microbubble contrast agents, and can have sufficient echogenicity that can be detected by micro-ultrasound. Capillary blood flow rates are on the order of less than a millimetre/second, or around 0.03 cm/s, and perfusion at these rates can be detected using high frequency micro ultrasound with the presently described imaging mode.
- Capillaries are about 5-1 0 microns (pm) in diameter, so small that red blood cells can generally only travel through them in single file.
- the average density of capillaries in human tissue is ⁇ 600/mm 3 which implies a mean separation of ⁇ 40 microns between adjacent capillaries.
- contrast agents may burst or dissipate over time. Contrast agents may work in ultrasound because they are filled with gas and due to the way they oscillate and produce a non-linear response.
- the frame rate must be at least as fast as reflector movement to ensure that blood perfusion through the tissue can be captured.
- the frame rate is approximately at least a frame rate of greater than or equal to (>) 20 s -1 and motion compensation is also required.
- the voxel or sensitive area size imaged in the tissue must be small enough to observe and detect individual or some number of reflectors (i.e. so that some portion of reflectors are present in the same voxel across frames) as they perfuse through the voxel.
- the voxel size is on the order of 70 pm.
- voxel size varies with the frequency of the ultrasound.
- I ncreased blood flow in a tissue can occur during exercise, and an increase in vascularization brought on by angiogenesis is characteristic of many cancers and tumours.
- Under conventional ultrasound blood looks dark, and with high frequency ultrasound in the absence of signal decorrelation blood looks like noise.
- increased capillary vascularization can be visualized by changing the micro-ultrasound imaging settings so that images are collected fast enough to monitor changes in the ultrasound signal by limiting the number of scan lines and focal zones and isolating the decorrelated signal characteristic of capillary blood flow.
- I n particular it has been found that by observing how the noise in high frequency ultrasound changes over time in a particular location, the signal coming from vascularized tissue previously observed as noise can be identified as echo-reflective blood. The present technique is thus able to identify and image areas of perfusion inside tissues.
- the detection of echogenicity in each measured voxel in the tissue imaged using the presently described high frequency ultrasound method is agnostic with regard to capillary orientation.
- the present imaging mode is entirely ag nostic in regard to direction of flow. That means if there are a bundle of capillaries in the same voxel, with each capillary flowing in different and/or opposite directions, the present imaging mode would still be able determine the total flow rate over all of them.
- conventional Doppler ultrasound even if you had two vessels in the same voxel aligned with the imaging plane, if they were flowing in opposite directions one would not see any signal because they would cancel out.
- B-mode (brightness mode) ultrasound, also referred to as 2D mode, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two- dimensional image on screen.
- B-mode is an ultrasound imaging mode that digitally highlights moving reflectors, likely to be mainly red blood cells, while suppressing the signals from the surrounding stationary tissue. B-mode can thus visualize flowing blood and surrounding stationary tissues simultaneously.
- Each pixel in the B-mode image represents a volume of tissue 70miti in breadth.
- a typical capillary has a diameter of less than 70miti, so the image collected is aggregated over capillaries within a tissue volume, which provides a brightness correlated with increased capillary flow to the perfused region.
- Data of the resolution provided by micro-ultrasound in B-mode produces a perfusion image that is approximately 5 megapixels/image, with areas of increased blood perfusion showing up as areas of brightness in the image.
- images are collected at a high frame rate (at least 20 frames per second) for a quantity of frames sufficient for comparison and data autocorrelation, for example at least 5 frames.
- Image processing of the micro-ultrasound data uses the time constant of brightness variation in each pixel and looks at the rate of statistical change between time points and over time.
- the image may be processed to decrease processing time, for example by selecting a subset of pixels or through the creation of a lower resolution downsampled version of the image.
- the image may also be optionally processed spatially or temporally to reject noise, smooth the image, and improve fidelity. For example, in an embodiment, a low pass or a filter may be applied first to the image.
- the signal is the slope of correlation trend, which is the decorrelation rate.
- the slope of the decorrelation provides information about how quickly fluid in the perfused area is flowing.
- Autocorrelation is then calculated to look at repetition of the standardized signal at each pixel, using x nor m as the basis for the correlation. Autocorrelation looks at the similarity between the signal at the pixel and the signal at the same pixel after period of time, for example 1 to 4 frames later (0.03 to 0.1 3 seconds at 30 frames per second.)
- i and j represent the 2D coordinates of a pixel
- t is the time index of one image frame being processed
- lag is the amount of time between that frame and another frame measured in number of frames.
- n is the number of time points (i.e. frames) collected for analysis.
- Some other methods that may be used to calculate autocorrelation of the data include Spearman correlation, Pearson correlation, or Fourier Transform.
- the calculated autocorrelation can be smoothed, for example using a gaussian kernel function.
- the decorrelation rate is the trend in the normalized autocorrelation of the standardized B-Mode signal over time.
- the decorrelation rate may be used to measure tissue perfusion, including rates of flow, and to differentiate between tissue types.
- time scales can be chosen where signal changes linearly over time, and therefore the decorrelation rate can be determined quantitatively by applying linear regression to fit to a straight line, average difference (by taking the mean of the difference between each point at t and t+1 ), or the overall magnitude change (max(y)— min(y ).
- Other calculations could be applied to fit more complex data and give other information about flow, and may include determination of period, exponential decay rate, or time to local minima.
- Voxels with very low or negligible decorrelation rates represent noise since noise is an uncorrelated process.
- voxels with decorrelation rate below a specified threshold are set to 0 in the B-Mode image before display, reducing the noise content of the image, improving the signal to noise ratio and contrast.
- brightness of pixels in the B-Mode image is reduced based on the decorrelation rate when this rate is below a certain threshold as shown in the following equation.
- decorrelation rate ⁇ threshold It is useful to create a visual representation of the decorrelation rate, which represents aspects of perfusion.
- I n one simple mapping, decorrelation values are assigned a brightness (0 - 255) which can be displayed on the screen as an image.
- Other transformations of the data may also be applied as determined to be useful to highlight aspects of interest, which may include flow rate.
- I n some representations, different colours may be used to further discriminate between aspects of interest.
- the perfusion imaging and the noise reduction are based on the decorrelation rate of the voxels.
- the perfusion imaging and noise reduction may be applied independently of each other. Or, the perfusion imaging and noise reduction may be used together.
- Ultrasound systems which can be used to collect the data for the present imaging method should be those adapted to receive ultrasound signals having a frequency of at least 15 megahertz (MHz) with a frame rate of at least 20 frames per second (fps).
- MHz megahertz
- fps frames per second
- high frequency (H F) imaging higher than 15 MHz
- the signal processing as presently described requires a higher frame rate to produce an ultrasound image from the acquired ultrasound signal.
- the signal processing may work with conventional ultrasound frequencies with strong reflectors, such as microbubble contrast agents and/or nanoparticle contrast agents.
- the transducer used for image collection can be a linear array transducer, a phased array transducer, a two-dimensional (2-D) array transducer, or a curved array transducer.
- the center transmit frequency of the transducer used is preferably equal to or greater than 1 5 M Hz.
- the center transmit frequency can be approximately 15 M Hz, 20 M Hz, 30 M Hz, 40 M Hz, 50 MHz, 55 M Hz or higher.
- the ultrasound transducer can transmit ultrasound into the subject at a center frequency within the range of about 1 5 M Hz to about 80 M Hz.
- the transducer comprises a high frequency linear array, with an imaging system in the 20-50 M Hz range.
- Figure 1 shows a high frequency medical-imaging system 100 for use with the present methods includes an ultrasound transducer 1 02 having transducer elements 104, an ultrasound-transducer interface 106, a spatial sensor 1 08, and a server 1 10.
- the ultrasound transducer 1 02 is configured to: (A) convert the echo sound signal that was received (by the ultrasound transducer 1 02) into ultrasound information; and (B) transmit the ultrasound information (via an output port).
- the ultrasound transducer 102 is also called an ultrasound probe.
- the ultrasound transducer 102 has the transducer elements 104 arranged in an array; for example, the transducer elements 104 may be aligned along a row, relative to each other, one after the other.
- the transducer elements 1 04 are configured to be activated (they may be selectively activated or not activated).
- the transducer elements 1 04 are also called transmit and receive elements, in that they transmit ultrasound pulses and receive reflections of the ultrasound pulses.
- a collection of the transducer elements 1 04 is also called the transducer array.
- the ultrasound transducer 102 is also known as an ultrasonic transceiver for the case where the ultrasound transducer 102 is configured to both send (an outgoing ultrasonic pulse) and receive (a reflected ultrasonic pulse).
- the medical-imaging system 1 00 uses the ultrasound transducer 1 02 on a principle similar to radar or sonar, in which the medical-imaging system 100 is configured to evaluate attributes of a target by interpreting the echoes (reflections) from sound waves.
- the ultrasound transducer 1 02 is configured to: (A) generate relatively higher frequency sound waves; and (B) receive the echo from the target.
- the medical-imaging system 100 is configured to: (A) evaluate the ultrasound information provided by the ultrasound transducer 1 02; (B) calculate the time interval between sending the outgoing signal (from the ultrasound transducer 1 02) and receiving the echo; (C) determine the distance to the target or an object based on the time interval that was calculated.
- the ultrasound transducer 102 is configured to generate sound waves in the ultrasonic range, above about generally 18 KHz (Kilo Hertz), by turning electrical energy into sound; then, upon receiving the echo, the ultrasound transducer 1 02 is configured to turn the reflected sound waves into electrical energy, which can be measured and displayed by the medical-imaging system 1 00.
- Ultrasound is an oscillating sound pressure wave with a frequency greater than the upper limit of the human hearing range. Although this limit varies from person to person, it is approximately 20 KHz in healthy, young adults. Some ultrasound devices operate with frequencies from about 20 kHz up to several gigahertz (GHz).
- the ultrasound transducer 102 is configured to transmit a signal that includes short bursts of ultrasonic energy. After each burst, the ultrasound transducer 1 02 is configured to receive a return (reflected) signal within a small window of time corresponding to the time taken for the energy to pass through the tissue of the patient; the signals received during this period then qualify for additional signal processing by the medical-imaging system 1 00.
- the ultrasound transducer 102 (medical ultrasonic transducer or probe) may be configured to have any variety of different shapes and sizes for use in making pictures of different parts of the body.
- the ultrasound transducer 102 may be passed over the surface of the body (patient), inserted laparoscopically, or into an orifice (body opening) of the patient, such as the esophagus, rectum, or vagina.
- the ultrasound transducer 102 may be configured (by clinicians or operators who perform ultrasound-guided procedures) for use with a probe-positioning system (not depicted and known) configured to hold and/or move the ultrasound transducer 102; the ultrasound transducer 102 includes an array of the transducer elements 104.
- the row of the transducer elements 104 of the ultrasound transducer 102 may be aligned in a rectilinear arrangement, or in a curvilinear arrangement.
- Each of the transducer elements 104 are configured to: (A) transmit an incident sound signal toward a target; and (B) receive an echo sound signal representing sound being reflected back from the target to the transducer elements 1 04.
- the ultrasound-transducer interface 1 06 is configured to control operation of the ultrasound transducer 1 02.
- the ultrasound-transducer interface 1 06 is depicted in FIG . 1 as a software program (in accordance with an option).
- the processor assembly 120 controls the ultrasound transducer 1 02 via the ultrasound-transducer interface 106.
- the ultrasound- transducer interface 1 06 is also called a beam-former.
- the ultrasound-transducer interface 106 may include server-executable code (a software program) tangibly stored in a non-transitory computer-readable medium 1 1 2 (hereafter referred to as the memory 1 1 2) of the server 1 10; in accordance with another example, the ultrasound-transducer interface 1 06 includes a combination of electronic hardware components that cooperate with server-executable code.
- the ultrasound-transducer interface 106 is configured to: (A) operatively connect to the ultrasound transducer 102 (via the output port of the ultrasound transducer 1 02); (B) control the shape of the incident sound signal to be transmitted by the transducer elements 1 04; (C) receive the ultrasound information from the ultrasound transducer 1 02; and (D) provide the scan lines that are mapped to the transducer elements 1 04 that are activated in such a way as to generate the scan lines to be provided (not all of the transducer elements 104 will be activated and thus these unused instances of the transducer elements 1 04 will be inactivated).
- the ultrasound-transducer interface 1 06 is a device configured to facilitate electronic controlled focusing of the ultrasound energy emitted and/or received by the ultrasound transducer 1 02.
- the spatial sensor 1 08 is configured to: (A) detect spatial movement of the ultrasound transducer 1 02; and (B) provide spatial information indicating spatial movement of the ultrasound transducer 102 while the ultrasound transducer 1 02 transmits ultrasound information to the ultrasound-transducer interface 106.
- the spatial sensor 108 may be attached to the ultrasound transducer 1 02.
- the spatial sensor 1 08 may be integrated with the ultrasound transducer 1 02.
- the server 1 1 0 is also known as a computer, etc. Generally, the server 1 1 0 is configured to: (A) interface with the ultrasound-transducer interface 1 06; (B) interface with the spatial sensor 1 08; and (C) have a memory 1 1 2 tangibly storing the executable code 1 14 (also called processor-executable code, and hereafter referred to as the program 1 14).
- the program 1 1 4 is a combination of operational tasks to be executed by the server 1 1 0.
- the server 1 10 is a system that is a combination of software and suitable computer hardware.
- the server 1 10 may include a dedicated computer or a combination of computers.
- the server 1 10 may be configured for client-server architecture (if so desired).
- the memory 1 12 may refer to the physical devices used to store computer executable programs or processor executable programs (sequences of instructions or operations) and/or data (e.g. prog ram state information) on a temporary basis or a permanent basis for use in the server 1 10 and anything equivalent thereof.
- Primary memory is used for the information in physical systems which function at hig h-speed (such as, RAM or Random Access Memory), as a distinction from secondary memory, which are physical devices for program and data storage which are slow to access but offer higher memory capacity.
- Primary memory stored on secondary memory is called “virtual memory” .
- the memory 1 12 may include volatile memory and/or non-volatile memory.
- the memory 1 1 2 may include secondary memory such as tape, magnetic disks and optical discs (CD-ROM or Compact Disc ROM, and DVD-ROM or Digital Video Disc ROM), etc.
- the program 1 14 is constructed using known software tools as known to those skilled in the art; computer programmed instructions are assembled, in a high level computer programming language, and a compiler and other tools are used to convert the computer programmed instructions into the executable code. It will be appreciated that the program 1 14 provides a method or a sequence of operations to be executed by the processor assembly 120.
- the memory 1 1 2 includes (tangibly stores) the executable code 1 1 4 (also called the program 1 14).
- the executable code 1 14 includes a combination of operational tasks to be executed by the processor assembly 1 20. For instance, the executable code 1 1 4 is configured to direct the server 1 10 to receive ultrasound information associated with a scan-line set having a limited number of selectable scan lines of the ultrasound transducer 102.
- the scan-line set may have a limited number of scan lines that are mapped with a limited set of the transducer elements 104 of the ultrasound transducer 102 (that were used to generate the selected scan lines of the scan-line set), if so desired.
- the server 1 1 0 is configured (programmed) to receive ultrasound information associated with a scan-line set having a limited number of selectable scan lines of the ultrasound transducer 1 02.
- the non-transitory computer-readable medium 1 12 includes executable code 1 1 4 that is tangibly stored in the non-transitory computer-readable medium 1 12; the executable code 1 1 4 includes a combination of operational tasks that are executable by the server 1 10); the executable code 1 14 is configured (programmed) to direct the server 1 10 to receive ultrasound information associated with the scan-line set having the limited number of selectable scan lines of the ultrasound transducer 102.
- the server 1 1 0 also includes a display assembly 1 16; an input/output interface module 1 1 8; a processor assembly 120; a database 122 tangibly stored in the memory 1 1 2; ultrasound data 123; and spatial data 1 24.
- the ultrasound data 123 and the spatial data 124 are stored in the database 1 22 or are stored in the memory 1 12.
- the input/output interface module 1 1 8 is configured to operatively connect the processor assembly 1 20 with the display assembly 1 16, the ultrasound-transducer interface 106 (and indirectly, the ultrasound transducer 1 02) and the spatial sensor 1 08.
- the processor assembly 120 may control operations of the display assembly 1 16, the ultrasound-transducer interface 1 06, and the spatial sensor 1 08, and also control the ultrasound transducer 1 02 via direct control of the ultrasound-transducer interface 106.
- the input/output interface module 1 18 is also configured to interface the processor assembly 1 20 with user-interface devices (such as a keyboard, a mouse, a touch-screen display assembly, etc.).
- the processor assembly 120 (also called a central processing unit or CPU or a central processor unit) is the hardware within the server 1 10 that carries out the instructions as set out in the program 1 1 4 by performing the arithmetical, logical, and i nput/output operations.
- the processor assembly 120 may have one or more instances of the CPU.
- the CPU may include a microprocessor (meaning the CPU is contained on a single silicon chip).
- Some integrated circuits (ICs) may contain multiple CPUs on a single chip; those ICs are called multi core processors.
- An IC containing a CPU may also contain peripheral devices, and other components of a computer system; this is called a system on a chip (SoC).
- SoC system on a chip
- the processor assembly 1 20 may include an array processor or a vector processor that has multiple parallel computing elements, with no one unit considered the "center” .
- I n the distributed computing model, problems are solved by a distributed interconnected set of processors.
- the images to be displayed by a medical-imaging system 100 may be displayed i n real-time and/or after an acquisition or processing delay (via the display assembly 1 16).
- Figures 2A and 2B are ultrasound images before and after denoising by eliminating pixels with very short decorrelation times. These pixels are typically a product of random noise in the received signal rather than true biological effects, as distinct from pixels with measurable medium or long decorrelation times which are related to flow or static anatomical structures.
- Figure 2A shows an image before correction. While Figure 2B shows the same image with the short decorrelation time pixels removed (after correction).
- the brightness signals of areas of the surrounding stationary tissue can be suppressed to provide contrast between perfused and non-perfused tissue.
- Figure 3 shows an example of a perfusion signal from a blood vessel as compared to an area of noise in the image.
- the blood signal has a clear linear slope. While the noise signal appears random, with no overall trend.
- Figure 4 shows an example of the signal from unaligned and aligned images with the aberrant signal from movement during imaging removed. Movement of or within the target area may also occur during image collection. For example, this may occur due to the patient moving, or movements of tissues and organs in the body.
- images may be aligned to correct for this movement by matching local signal patterns between frames. I n one alignment method, the neighbourhood of each pixel is identified and the time-dependent cross-correlation of signal across the 2D grid of pixel neighbourhoods is matched to remove aberrant signals. Faster imaging rates may be useful to reduce alignment issues.
- FIGS. 5A-C are before and after activation of a forearm muscle.
- Fig ures 5A shows the anatomy of the wrist in a B mode micro-ultrasound image.
- Figure 5B shows an image of the flexor digitorum at rest.
- Figure 5C shows an image of the flexor digitorum at rest after being activated for 1 min.
- FIG. 6 is a flowchart illustrating an example method of an ultrasound imaging mode for imaging perfusion in tissue.
- a plurality of B-Mode ultrasound image data is collected using high frequency ultrasound.
- the plurality of B-Mode high frequency ultrasound image data (frames) are processed 202 from the memory 1 12.
- decorrelation trends are calculated for the autocorrelated image data to determine flow and perfusion level 204 between selected image frames for each pixel in the image frames.
- one of three steps may take place.
- noise content in the image data is reduced by using the decorrelation trends 206.
- a visual representation of the perfusion level is formed based on the decorrelation trends 208.
- Step 210 is the same as 206, and step 21 2 is the same as 208. Steps 210 and 21 2 may happen in any order. Also, the image data may be standardized at each pixel overall all images before autocorrelation (not shown).
- Clause 1 An imaging processing method comprising: processing a plurality of digital images comprising sequential B-Mode ultrasound reflectivity data; calculating decorrelation trends of autocorrelated data to determine flow and perfusion level.
- Clause 2 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, further comprising: reducing noise content in the ultrasound data using the decorrelation trends.
- Clause 3 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, further comprising: forming a visual representation of the perfusion level based on the decorrelation trends.
- Clause 4 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, further comprising: reducing noise content in the autocorrelated data using the decorrelation trends; and forming a visual representation of the perfusion level based on the decorrelation trends.
- Clause 5 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the method has an image capture rate of 20 frames/sec or higher.
- Clause 6 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the image data is standardized before autocorrelation.
- Clause 7 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the autocorrelated data is normalized.
- Clause 8 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the decorrelation trend of the autocorrelated data is determined by linear regression, average difference, or overall magnitude change.
- Clause 9 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the autocorrelated data with non-linear trends are processed to determine one or more of period, exponential decay rate, time to local minima, or another measure of decorrelation.
- Clause 1 0 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the autocorrelation is calculated using a Spearman correlation, Pearson correlation, or Fourier Transform.
- Clause 1 1 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, further comprising a smoothing step prior to visual representation of the signal.
- Clause 12 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, further comprising application of thresholds and rescaling to the decorrelation trends before visual representation.
- Clause 13 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, further comprising a logarithmic transformation of the
- Clause 1 6 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the method includes at least 5 frames of sequential B-Mode ultrasound reflectivity data
- Clause 1 7 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein a subset of the image field is processed from each image to decrease processing time.
- Clause 18 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the image is downsampled to a lower resolution to decrease processing time.
- Clause 19 A method of any of the clauses, or any portion of any clause, mentioned in this paragraph, where in the ultrasound data is high frequency ultrasound with a frequency range greater than 15 MegaHertz.
- a perfusion imaging system comprising: a high frequency ultrasound transducer for capturing collecting a plurality of digital images comprising sequential B-Mode ultrasound reflectivity data; a signal processing unit, operatively connected to the transducer, the signal processing unit configured to calculate decorrelation trends of autocorrelated data to determine flow and perfusion level.
- Clause 21 A system of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein, the signal processing unit is further configured to reduce noise content in the ultrasound data using the decorrelation trends.
- Clause 22 A system of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the signal processing unit is further configured to form a visual representation of the perfusion level based on the decorrelations trends.
- Clause 23 A system of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the sig nal processing unit is further configured to reduce noise content in the ultrasound data using the decorrelation trends, and form a visual representation of the perfusion level based on the decorrelations trends.
- Clause 24 A system of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the system has an image capture rate of 20 frames/sec or higher
- Clause 25 A system of any of the clauses, or any portion of any clause, mentioned in this paragraph, wherein the signal processing unit is configured to standardize the image data before autocorrelation.
- Clause 26 A computer readable storage medium, comprising executable instructions that when executed by a process cause the processor to: process a plurality of digital images comprising sequential B-Mode ultrasound reflectivity data obtained using a micro-ultrasound; calculate decorrelation trends of autocorrelated data to determine flow and perfusion level.
- Clause 27 A computer readable storage medium of any of the clauses or any portion of any clause, mentioned in this paragraph, further comprising instructions to: reduce noise content in the ultrasound data using the decorrelation trends.
- Clause 28 A computer readable storage medium of any of the clauses or any portion of any clause, mentioned in this paragraph, further comprising instructions to: form a visual representation of the perfusion level based on the decorrelation trends.
- Clause 29 A computer readable storage medium of any of the clauses or any portion of any clause, mentioned in this paragraph, further comprising instructions to: reduce noise content in the ultrasound data using the decorrelation trends; and form a visual representation of the perfusion level based on the decorrelation trends.
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ZHOU XIAOWEI ET AL.: "IEEE TRANSACTIONSON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL", vol. 65, 2018, IEEE, article "3-D Velocity and Volume Flow Measurment $In-Vivo$ Using Speckle Decorrelation and 2-D High-Frame-Rate Contrast-Enhanced Ultrasound", pages: 2233 - 2244 |
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US20220265241A1 (en) | 2022-08-25 |
JP7526781B2 (en) | 2024-08-01 |
EP4003178A4 (en) | 2023-08-16 |
EP4003178A1 (en) | 2022-06-01 |
JP2022542848A (en) | 2022-10-07 |
CA3144769A1 (en) | 2021-01-28 |
CN114466620A (en) | 2022-05-10 |
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