Patent Publication Number: US-2021169455-A1

Title: System and methods for joint scan parameter selection

Description:
TECHNICAL FIELD 
     Embodiments of the subject matter disclosed herein relate to ultrasound imaging, and more particularly, to improving image quality for ultrasound imaging. 
     BACKGROUND 
     Medical ultrasound is an imaging modality that employs ultrasound waves to probe the internal structures of a body of a patient and produce a corresponding image. For example, an ultrasound probe comprising a plurality of transducer elements emits ultrasonic pulses which reflect or echo, refract, or are absorbed by structures in the body. The ultrasound probe then receives reflected echoes, which are processed into an image. Ultrasound images of the internal structures may be saved for later analysis by a clinician to aid in diagnosis and/or displayed on a display device in real time or near real time. 
     SUMMARY 
     In one embodiment, a method includes acquiring a plurality of ultrasound images of an anatomical region, each ultrasound image acquired at a different combination of parameter values for a first scan parameter and a second scan parameter, selecting a first parameter value for the first scan parameter and a second parameter value for the second scan parameter based on an image quality of each image, and acquiring one or more additional ultrasound images at the first parameter value and the second parameter value. 
     The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  shows a block diagram of an exemplary embodiment of an ultrasound system; 
         FIG. 2  is a schematic diagram illustrating a system for generating ultrasound images at optimized parameter settings, according to an exemplary embodiment; 
         FIG. 3  is a schematic diagram illustrating a process for selecting ultrasound scan parameters, according to an exemplary embodiment; 
         FIG. 4  shows example ultrasound images and associated image quality metrics that may be acquired according to the process of  FIG. 3 ; and 
         FIGS. 5A and 5B  are a flow chart illustrating an example method for selecting ultrasound scan parameters during ultrasound imaging, according to an exemplary embodiment. 
         FIG. 6  shows an example table of ultrasound scan parameters to be applied to acquire ultrasound images usable to select the ultrasound scan parameters, according to the method of  FIGS. 5A and 5B . 
         FIG. 7  shows two example timings of image acquisition relative to a cardiac cycle. 
         FIG. 8  is a flow chart illustrating an example method for selecting image post-acquisition processing parameters during ultrasound image. 
         FIG. 9  is a graph showing a scan sequence for acquiring a single ultrasound image, according to an exemplary embodiment. 
         FIG. 10  is a graph showing a scan sequence for acquiring multiple ultrasound images, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Medical ultrasound imaging typically includes the placement of an ultrasound probe including one or more transducer elements onto an imaging subject, such as a patient, at the location of a target anatomical feature (e.g., abdomen, chest, etc.). Images are acquired by the ultrasound probe and are displayed on a display device in real time or near real time (e.g., the images are displayed once the images are generated and without intentional delay). The operator of the ultrasound probe may view the images and adjust various acquisition parameters and/or the position of the ultrasound probe in order to obtain high-quality images of the target anatomical feature (e.g., the heart, the liver, the kidney, or another anatomical feature). The acquisition parameters that may be adjusted include transmit frequency, transmit depth, gain, beam steering angle, beamforming strategy, and/or other parameters. Varying the acquisition parameters to acquire an optimal image (e.g., of desired quality) can be very challenging and is based on user experience. Image quality variations with acquisition parameters is not a well-studied problem. Thus, the adjustment of the acquisition parameters by the operator in order to acquire an optimal image is often subjective. For example, the operator may adjust various acquisition parameters until an image is acquired that looks optimal to the operator, and the process of adjusting the acquisition parameters may not be defined or repeated from exam to exam. Further, various post-acquisition image parameters that may affect image quality are also adjustable by the operator, such as bandwidth and center frequency of the filtering of the received ultrasound data. This subjectivity and lack of a defined process may lead to irreproducible results and, in many ultrasound exams, images that are as high quality as possible may not be acquired. 
     Thus, according to embodiments disclosed herein, the problem of image acquisition parameter optimization and/or image post-acquisition processing optimization is addressed via a feedback system based on an automated image quality measurement algorithm that is configured to automatically identify the acquisition parameters that will generate the best possible image for the anatomy being imaged. The automated image quality measurement algorithm may include an artificial intelligence-assisted feedback system to optimize the acquisition parameters in a joint fashion, with a plurality of images each acquired at a different combination of scan parameter values to arrive at an optimal acquisition parameter setting based on automatically identified image quality metrics. For example, a set of images and/or cine loops may be acquired, each at a different possible combination of transmit depth and transmit frequency. The image or cine loop that has the highest image quality (e.g., as detected by the artificial intelligence based system) may be identified and the optimal transmit depth and optimal transmit frequency may be set as the depth and frequency at which the identified, highest-quality image was acquired. In doing so, the optimal acquisition parameters (e.g., depth and frequency) for a given scan plane/anatomical feature may be identified in a reproducible manner, which may increase consistency of image quality across different ultrasound exams. Additionally, in some examples, different parameter values for one or more post-acquisition processing parameters may be applied to an image to generate, for each post-acquisition processing parameter, a set of replicate images that each have a different parameter value for that post-acquisition processing parameter. The image quality may be determined for each replicate image, and the replicate image having the highest image quality may be selected. The parameter value for that post-acquisition processing parameter may be set as the parameter value from the selected replicate image and applied to subsequent images. The selection of the optimal acquisition and/or post-acquisition parameters may simplify the operator&#39;s workflow, which may reduce exam time and may facilitate higher quality exams, even for more novice operators. 
     An example ultrasound system including an ultrasound probe, a display device, and an imaging processing system are shown in  FIG. 1 . Via the ultrasound probe, ultrasound images may be acquired and displayed on the display device. The images may be acquired using various scan parameters, such as frequency and depth, which have parameter values that may be selected to increase image quality of the acquired images. To select the scan parameter values, a plurality of images acquired at different scan parameter values may be analyzed to determine which scan parameter values result in images having a highest image quality. An image processing system, as shown in  FIG. 2 , includes one or more image quality models, such as a depth model and one or more frequency models, which may be deployed according to the joint process shown in  FIG. 3  to determine the image quality of each of the plurality of images, as shown in  FIG. 4 , and select scan parameter values that will result in relatively high image quality. A method for jointly selecting scan parameter values during ultrasound imaging is shown in  FIGS. 5A and 5B . The method for jointly selecting scan parameter values may include application of a table of scan parameter values, such as the table shown in  FIG. 6 , which may result in different scan parameters being adjusted in different orders, such as the ordering of frequency values shown in  FIG. 7 . After the target scan parameter values have been selected, different post-acquisition processing parameter values may be applied to an image to create a set of adjusted images, and the image quality models may be deployed to determine which image from the set of adjusted images has the highest image quality and thus which post-acquisition processing parameter value(s) should be applied to that and/or subsequent images, as shown by the method of  FIG. 8 . The images disclosed herein may be acquired according to a scan sequence as shown in  FIG. 9  and/or according to a scan sequence as shown in  FIG. 10 . 
     Referring to  FIG. 1 , a schematic diagram of an ultrasound imaging system  100  in accordance with an embodiment of the disclosure is shown. The ultrasound imaging system  100  includes a transmit beamformer  101  and a transmitter  102  that drives elements (e.g., transducer elements)  104  within a transducer array, herein referred to as probe  106 , to emit pulsed ultrasonic signals (referred to herein as transmit pulses) into a body (not shown). According to an embodiment, the probe  106  may be a one-dimensional transducer array probe. However, in some embodiments, the probe  106  may be a two-dimensional matrix transducer array probe. As explained further below, the transducer elements  104  may be comprised of a piezoelectric material. When a voltage is applied to a piezoelectric crystal, the crystal physically expands and contracts, emitting an ultrasonic spherical wave. In this way, transducer elements  104  may convert electronic transmit signals into acoustic transmit beams. 
     After the elements  104  of the probe  106  emit pulsed ultrasonic signals into a body (of a patient), the pulsed ultrasonic signals are back-scattered from structures within an interior of the body, like blood cells or muscular tissue, to produce echoes that return to the elements  104 . The echoes are converted into electrical signals, or ultrasound data, by the elements  104  and the electrical signals are received by a receiver  108 . The electrical signals representing the received echoes are passed through a receive beamformer  110  that outputs ultrasound data. Additionally, transducer element  104  may produce one or more ultrasonic pulses to form one or more transmit beams in accordance with the received echoes. 
     According to some embodiments, the probe  106  may contain electronic circuitry to do all or part of the transmit beamforming and/or the receive beamforming. For example, all or part of the transmit beamformer  101 , the transmitter  102 , the receiver  108 , and the receive beamformer  110  may be situated within the probe  106 . The terms “scan” or “scanning” may also be used in this disclosure to refer to acquiring data through the process of transmitting and receiving ultrasonic signals. The term “data” may be used in this disclosure to refer to either one or more datasets acquired with an ultrasound imaging system. In one embodiment, data acquired via ultrasound system  100  may be used to train a machine learning model. A user interface  115  may be used to control operation of the ultrasound imaging system  100 , including to control the input of patient data (e.g., patient medical history), to change a scanning or display parameter, to initiate a probe repolarization sequence, and the like. The user interface  115  may include one or more of the following: a rotary element, a mouse, a keyboard, a trackball, hard keys linked to specific actions, soft keys that may be configured to control different functions, and a graphical user interface displayed on a display device  118 . 
     The ultrasound imaging system  100  also includes a processor  116  to control the transmit beamformer  101 , the transmitter  102 , the receiver  108 , and the receive beamformer  110 . The processer  116  is in electronic communication (e.g., communicatively connected) with the probe  106 . For purposes of this disclosure, the term “electronic communication” may be defined to include both wired and wireless communications. The processor  116  may control the probe  106  to acquire data according to instructions stored on a memory of the processor, and/or memory  120 . The processor  116  controls which of the elements  104  are active and the shape of a beam emitted from the probe  106 . The processor  116  is also in electronic communication with the display device  118 , and the processor  116  may process the data (e.g., ultrasound data) into images for display on the display device  118 . The processor  116  may include a central processor (CPU), according to an embodiment. According to other embodiments, the processor  116  may include other electronic components capable of carrying out processing functions, such as a digital signal processor, a field-programmable gate array (FPGA), or a graphic board. According to other embodiments, the processor  116  may include multiple electronic components capable of carrying out processing functions. For example, the processor  116  may include two or more electronic components selected from a list of electronic components including: a central processor, a digital signal processor, a field-programmable gate array, and a graphic board. According to another embodiment, the processor  116  may also include a complex demodulator (not shown) that demodulates the RF data and generates raw data. In another embodiment, the demodulation can be carried out earlier in the processing chain. The processor  116  is adapted to perform one or more processing operations according to a plurality of selectable ultrasound modalities on the data. In one example, the data may be processed in real-time during a scanning session as the echo signals are received by receiver  108  and transmitted to processor  116 . For the purposes of this disclosure, the term “real-time” is defined to include a procedure that is performed without any intentional delay. For example, an embodiment may acquire images at a real-time rate of 7-20 frames/sec. The ultrasound imaging system  100  may acquire 2D data of one or more planes at a significantly faster rate. However, it should be understood that the real-time frame-rate may be dependent on the length of time that it takes to acquire each frame of data for display. Accordingly, when acquiring a relatively large amount of data, the real-time frame-rate may be slower. Thus, some embodiments may have real-time frame-rates that are considerably faster than 20 frames/sec while other embodiments may have real-time frame-rates slower than 7 frames/sec. The data may be stored temporarily in a buffer (not shown) during a scanning session and processed in less than real-time in a live or off-line operation. Some embodiments of the invention may include multiple processors (not shown) to handle the processing tasks that are handled by processor  116  according to the exemplary embodiment described hereinabove. For example, a first processor may be utilized to demodulate and decimate the RF signal while a second processor may be used to further process the data, for example by augmenting the data as described further herein, prior to displaying an image. It should be appreciated that other embodiments may use a different arrangement of processors. 
     The ultrasound imaging system  100  may continuously acquire data at a frame-rate of, for example, 10 Hz to 30 Hz (e.g., 10 to 30 frames per second). Images generated from the data may be refreshed at a similar frame-rate on display device  118 . Other embodiments may acquire and display data at different rates. For example, some embodiments may acquire data at a frame-rate of less than 10 Hz or greater than 30 Hz depending on the size of the frame and the intended application. A memory  120  is included for storing processed frames of acquired data. In an exemplary embodiment, the memory  120  is of sufficient capacity to store at least several seconds&#39; worth of frames of ultrasound data. The frames of data are stored in a manner to facilitate retrieval thereof according to its order or time of acquisition. The memory  120  may comprise any known data storage medium. 
     In various embodiments of the present invention, data may be processed in different mode-related modules by the processor  116  (e.g., B-mode, Color Doppler, M-mode, Color M-mode, spectral Doppler, Elastography, TVI, strain, strain rate, and the like) to form 2D or 3D data. For example, one or more modules may generate B-mode, color Doppler, M-mode, color M-mode, spectral Doppler, Elastography, TVI, strain, strain rate, and combinations thereof, and the like. As one example, the one or more modules may process color Doppler data, which may include traditional color flow Doppler, power Doppler, HD flow, and the like. The image lines and/or frames are stored in memory and may include timing information indicating a time at which the image lines and/or frames were stored in memory. The modules may include, for example, a scan conversion module to perform scan conversion operations to convert the acquired images from beam space coordinates to display space coordinates. A video processor module may be provided that reads the acquired images from a memory and displays an image in real time while a procedure (e.g., ultrasound imaging) is being performed on a patient. The video processor module may include a separate image memory, and the ultrasound images may be written to the image memory in order to be read and displayed by display device  118 . 
     In various embodiments of the present disclosure, one or more components of ultrasound imaging system  100  may be included in a portable, handheld ultrasound imaging device. For example, display device  118  and user interface  115  may be integrated into an exterior surface of the handheld ultrasound imaging device, which may further contain processor  116  and memory  120 . Probe  106  may comprise a handheld probe in electronic communication with the handheld ultrasound imaging device to collect raw ultrasound data. Transmit beamformer  101 , transmitter  102 , receiver  108 , and receive beamformer  110  may be included in the same or different portions of the ultrasound imaging system  100 . For example, transmit beamformer  101 , transmitter  102 , receiver  108 , and receive beamformer  110  may be included in the handheld ultrasound imaging device, the probe, and combinations thereof. 
     After performing a two-dimensional ultrasound scan, a block of data comprising scan lines and their samples is generated. After back-end filters are applied, a process known as scan conversion is performed to transform the two-dimensional data block into a displayable bitmap image with additional scan information such as depths, angles of each scan line, and so on. During scan conversion, an interpolation technique is applied to fill missing holes (i.e., pixels) in the resulting image. These missing pixels occur because each element of the two-dimensional block should typically cover many pixels in the resulting image. For example, in current ultrasound imaging systems, a bicubic interpolation is applied which leverages neighboring elements of the two-dimensional block. As a result, if the two-dimensional block is relatively small in comparison to the size of the bitmap image, the scan-converted image will include areas of poor or low resolution, especially for areas of greater depth. 
     Ultrasound images acquired by ultrasound imaging system  100  may be further processed. In some embodiments, ultrasound images produced by ultrasound imaging system  100  may be transmitted to an image processing system, where in some embodiments, the ultrasound images may be analyzed by one or more machine learning models trained using ultrasound images and corresponding ground truth output in order to assign scan parameter-specific image quality metrics to the ultrasound images. As used herein, ground truth output refers to an expected or “correct” output based on a given input into a machine learning model. For example, if a machine learning model is being trained to classify images of cats, the ground truth output for the model, when fed an image of a cat, is the label “cat”. As explained in more detail below, if a machine learning model is being trained to classify ultrasound images on the basis of an image quality factor associated with depth (e.g., visibility of certain anatomical features), the ground truth output for the model may be a label indicating a level of the image quality factor, e.g., on a scale of 1-5 with 1 being a lowest image quality level (e.g., reflecting insufficient or inadequate depth, the least optimal depth) and 5 being a highest image quality level (e.g., reflecting sufficient depth, the most optimal depth). Similarly, if a machine learning model is being trained to classify ultrasound images on the basis of an image quality factor associated with frequency (e.g., speckling), the ground truth output for the model may be a label indicating a level of the image quality factor, e.g., on a scale of 1-5 with 1 being a lowest image quality level (e.g., reflecting high/not smooth speckling, the least optimal frequency) and 5 being a highest image quality level (e.g., reflecting low/smooth speckling, the most optimal frequency). 
     Although described herein as separate systems, it will be appreciated that in some embodiments, ultrasound imaging system  100  includes an image processing system. In other embodiments, ultrasound imaging system  100  and the image processing system may comprise separate devices. In some embodiments, images produced by ultrasound imaging system  100  may be used as a training data set for training one or more machine learning models, wherein the machine learning models may be used to perform one or more steps of ultrasound image processing, as described below. 
     Referring to  FIG. 2 , image processing system  202  is shown, in accordance with an exemplary embodiment. In some embodiments, image processing system  202  is incorporated into the ultrasound imaging system  100 . For example, the image processing system  202  may be provided in the ultrasound imaging system  100  as the processor  116  and memory  120 . In some embodiments, at least a portion of image processing  202  is disposed at a device (e.g., edge device, server, etc.) communicably coupled to the ultrasound imaging system via wired and/or wireless connections. In some embodiments, at least a portion of image processing system  202  is disposed at a separate device (e.g., a workstation) which can receive images/maps from the ultrasound imaging system or from a storage device which stores the images/data generated by the ultrasound imaging system. Image processing system  202  may be operably/communicatively coupled to a user input device  232  and a display device  234 . The user input device  232  may comprise the user interface  115  of the ultrasound imaging system  100 , while the display device  234  may comprise the display device  118  of the ultrasound imaging system  100 , at least in some examples. 
     Image processing system  202  includes a processor  204  configured to execute machine readable instructions stored in non-transitory memory  206 . Processor  204  may be single core or multi-core, and the programs executed thereon may be configured for parallel or distributed processing. In some embodiments, the processor  204  may optionally include individual components that are distributed throughout two or more devices, which may be remotely located and/or configured for coordinated processing. In some embodiments, one or more aspects of the processor  204  may be virtualized and executed by remotely-accessible networked computing devices configured in a cloud computing configuration. 
     Non-transitory memory  206  may store image quality models  208 , training module  210 , and ultrasound image data  212 . Image quality models  208  may include one or more machine learning models, such as deep learning networks, comprising a plurality of weights and biases, activation functions, loss functions, gradient descent algorithms, and instructions for implementing the one or more deep neural networks to process input ultrasound images. For example, image quality models  208  may store instructions for implementing a depth model  209  and/or one or more frequency models  211 . The depth model  209  and one or more frequency models  211  may each include one or more neural networks. Image quality models  208  may include trained and/or untrained neural networks and may further include training routines, or parameters (e.g., weights and biases), associated with one or more neural network models stored therein. 
     Depth model  209  may be a neural network (e.g., a convolutional neural network) trained to identify far-field structures in the ultrasound images and determine if far-field structures (e.g., structures beyond/below the focal point of the ultrasound beam with respect to the transducers of the ultrasound probe) are at an expected depth. Depth model  209  may be trained to identify the far-field structures in a scan plane/view specific manner. For example, a depth model may be trained to identify far-field structures in a four-chamber view of a heart but not in a parasternal long axis (PLAX) view of the heart. Thus, in some examples, depth model  209  may actually comprise a plurality of depth models, each specific to a different scan plane or anatomical view. Depth model  209  may be trained to output a first image quality metric that reflects a quality of an input ultrasound image as a function of transmit acquisition depth. For example, the far-field structures identified by the depth model may change in appearance/visibility as depth is changed, and the first image quality metric output by the depth model may reflect the appearance/visibility of these structures as an indicator of whether the depth used to acquire the ultrasound image is an optimal depth. 
     The one or more frequency models  211  may include one or more neural networks or other machine learning models trained to output a respective second image quality metric that represents an image quality factor that changes as a function of transmit frequency. The one or more frequency models  211  may include a first frequency model that assesses speckle size (referred to as a speckle model), a second frequency model that assess key landmarks (referred to as a landmark detection model), and a third frequency model that assess global image quality relative to a population-wide library of ultrasound images (referred to as a global image quality model). The speckle model may be trained to output a speckle image quality metric that reflects a level of smoothness of speckling in the input ultrasound image. As speckling smoothness increases as frequency increases, the speckle image quality metric may increase as frequency increases. The landmark detection model may be trained to output a landmark image quality metric that reflects the appearance/visibility of certain anatomical features (landmarks) in the input ultrasound image. For example, as transmit frequency increases, certain anatomical features, such as the valves in the four-chamber view, may start to decrease in image quality/appearance. Thus, the landmark detection model may identify the key landmarks in the input ultrasound image and output the landmark image quality metric based on the image quality/visibility of the identified key landmarks. Because the key landmarks change as the scan plane/anatomical view change, the landmark detection model may include a plurality of different landmark detection models, each specific to a different scan plane or anatomical view. 
     The global image quality model may be trained to assess the overall image quality of an input ultrasound image relative to a population-wide library of ultrasound images. For example, the global image quality model may be trained with a plurality of ultrasound images of a plurality of different patients, with each training ultrasound image annotated or labeled by an expert (e.g., cardiologist or other clinician) with an overall image quality score (e.g., on a scale of 1-5 with 1 being a lowest image quality and 5 being a highest image quality). The global image quality model, after training/validation, may then generate an output of a global image quality metric that reflects the overall image quality of an input ultrasound image relative to the training ultrasound images. By including an overall image quality metric that is not specifically affected by depth or frequency, patient-specific image quality issues may be accounted for. 
     Non-transitory memory  206  may further include training module  210 , which comprises instructions for training one or more of the machine learning models stored in image quality models  208 . In some embodiments, the training module  210  is not disposed at the image processing system  202 . The image quality models  208  thus includes trained and validated network(s). 
     Non-transitory memory  206  may further store ultrasound image data  212 , such as ultrasound images captured by the ultrasound imaging system  100  of  FIG. 1 . The ultrasound image data  212  may comprise ultrasound image data as acquired by the ultrasound imaging system  100 , for example. The ultrasound images of the ultrasound image data  212  may comprise ultrasound images that have been acquired by the ultrasound imaging system  100  at different parameter values for different scan parameters, such as different frequencies and/or different depths. Further, ultrasound image data  212  may store ultrasound images, ground truth output, iterations of machine learning model output, and other types of ultrasound image data that may be used to train the image quality models  208 , when training module  210  is stored in non-transitory memory  206 . In some embodiments, ultrasound image data  212  may store ultrasound images and ground truth output in an ordered format, such that each ultrasound image is associated with one or more corresponding ground truth outputs. However, in examples where training module  210  is not disposed at the image processing system  202 , the images/ground truth output usable for training the image quality models  210  may be stored elsewhere. 
     In some embodiments, the non-transitory memory  206  may include components disposed at two or more devices, which may be remotely located and/or configured for coordinated processing. In some embodiments, one or more aspects of the non-transitory memory  206  may include remotely-accessible networked storage devices configured in a cloud computing configuration. 
     User input device  232  may comprise one or more of a touchscreen, a keyboard, a mouse, a trackpad, a motion sensing camera, or other device configured to enable a user to interact with and manipulate data within image processing system  202 . In one example, user input device  232  may enable a user to make a selection of an ultrasound image to use in training a machine learning model, to indicate or label a position of an interventional device in the ultrasound image data  212 , or for further processing using a trained machine learning model. 
     Display device  234  may include one or more display devices utilizing virtually any type of technology. In some embodiments, display device  234  may comprise a computer monitor, and may display ultrasound images. Display device  234  may be combined with processor  204 , non-transitory memory  206 , and/or user input device  232  in a shared enclosure, or may be peripheral display devices and may comprise a monitor, touchscreen, projector, or other display device known in the art, which may enable a user to view ultrasound images produced by an ultrasound imaging system, and/or interact with various data stored in non-transitory memory  206 . 
     It should be understood that image processing system  202  shown in  FIG. 2  is for illustration, not for limitation. Another appropriate image processing system may include more, fewer, or different components. 
     Turning to  FIG. 3 , it shows a process  300  for jointly selecting scan parameter values for two scan parameters, herein depth and frequency. The scan parameter values may be selected according to which scan parameter values result in a highest image quality, where the image quality is determined by machine learning models. Process  300  may be carried out with the components of  FIGS. 1-2 , e.g., images may be acquired via ultrasound probe  106  and the parameter value selection may be carried out by image processing system  202 . As shown, image acquisition may commence at  304  once the operator of the ultrasound system positions the ultrasound probe to image a target scan plane (shown at  302 ). The image acquisition may include acquiring a plurality of images each at a different combination of depth and frequency. For example, a first plurality of images may be acquired with each image of the first plurality of images acquired at a single, first frequency (e.g., 1.4 MHz) from a set of frequencies, and a different depth value from a set of depth values (e.g., a first image at 30 cm, a second image at 17 cm, and a third image at 10 cm); a second plurality of images may be acquired with each image of the second plurality of images at a single, second frequency (e.g., 1.7 MHz) from the set of frequencies, and a different depth value from the set of depth values; and one or more additional pluralities of images may be acquired, with each additional plurality of images acquired at next frequency (e.g., a one at 2 MHz and one at 2.3 MHz) in the set of frequencies and at the different depth values. In this way, an image may be acquired for each possible combination of depths and frequencies from the set of depths and the set of frequencies. 
     Each image of the plurality of images is entered into a plurality of models, including a depth model  306 , which may be a non-limiting example of depth model  209  of  FIG. 2 . The depth model  306  may be a machine learning model, such as a neural network, trained to determine a first image quality score that reflects a quality of an input image from the perspective of whether one or more key anatomical features in the target scan plane are sufficiently visible/of high enough quality. The one or more key anatomical features may be features that change in visibility/quality as depth changes, and thus may be used as a marker for which depth value may result in a high quality image. 
     The one or more models may include a global image quality model  310 , a landmark detection model  308 , and a speckle model  312  (which may be non-limiting examples of the global image quality model, landmark detection model, and speckle model described above with respect to  FIG. 2 ). Each of the global image quality model  310 , landmark detection model  308 , and speckle size model  312  may be a machine learning model, such as a neural network. The global image quality model  310  may be trained to assign a score (e.g., on a scale of 1-5) to each image based on the image quality of that image in a population-wide manner. The landmark detection model  308  and speckle size model  312  may each output scores that reflect how much a given patient&#39;s images change in quality as a function of ultrasound transmit frequency, as speckles on ultrasound images may smooth/change in size as frequency increases and certain key anatomical landmarks may become more or less visible as frequency changes. The scores output from each of the global image quality model, landmark detection model, and speckle size model may be combined to generate a cumulative, second image quality score. The image quality metrics (e.g., from each of the models discussed herein) may be output at  314 . 
     Thus, after each image is input into the models, each image may be assigned two scores, a first image quality score output from the depth model  306  and a second image quality score that is a cumulative score calculated from the output of each of the global image quality model  310 , the landmark detection model  308 , and the speckle size model  312 . The image from the plurality of images having the highest combined image quality score (e.g., the first image quality score combined with the second image quality score) may be identified as the selected image, as shown at  316 . If there are two or more images having the same, highest combined image quality score, the image acquired at the highest frequency may be selected. The depth used to acquire the selected image may be set as the selected depth value and the frequency used to acquire the selected image may be set as the selected frequency value. Any additional images of that target scan plane or view desired by the operator and/or dictated by a scanning protocol may be acquired at the selected depth value and the selected frequency value, as shown at  318 . According to the joint process shown in  FIG. 3 , the depth value and frequency value are only selected once all images have been acquired. 
     The joint process shown in  FIG. 3  may result in a total of m×n images being acquired in order to select the depth value and frequency value for subsequent acquisition. The m number of images may be based on how many depth values are available/selected to be optimized. As described above, there may be three possible depth values, but other numbers of depth values may be possible, such as two or four or more. Likewise, the n number of images may be based on how many frequency values are available/selected to be optimized. As described above, there may be four possible frequency values, but other numbers of frequency values may be possible, such as three, five, etc. Further, while  FIG. 3  shows a process for selecting values of two scan parameters, more scan parameters may be selected/optimized, such as gain, beam steering, beamforming strategy, filtering, etc. In such examples, the number of acquired images may be m×n×1, where the 1 number of images is based on the values of gain (or other parameter, such beam steering) available to be optimized. In this way, an image may be acquired for each possible combination of depth, frequency, and/or any other acquisition parameter values. 
     The joint process described above may result in more images being acquired than a sequential process where m+n images are acquired and a first scan parameter is selected (e.g., depth) before a second scan parameter is selected (e.g., frequency), which may make the sequential process more practical and easier to implement than a joint process. However, the overall time to select the parameter values for the scan parameters may be lower for the joint process. Further, when scan parameters are dependent on each other, the joint process, where all possible combinations are acquired, may reveal any unexpected combinations that result in high image quality, while the sequential process may leave out possible combinations on the assumption that changing frequency (for example) will not affect depth-based image quality. 
       FIG. 4  shows a plurality of ultrasound images  400  that may be acquired and analyzed during the process illustrated in  FIG. 3 . The plurality of ultrasound images  400  includes a first plurality of images  401 . Each image of the first plurality of images  401  was acquired at a different depth value (e.g., a first image  402  acquired at 30 cm, a second image  404  acquired at 17 cm, and a third image  406  acquired at 10 cm) and at the same first frequency (e.g., 1.4 MHz). The plurality of ultrasound images  400  further includes a second plurality of images  410 . Each image of the second plurality of images  410  was acquired at a different depth value and at the same second frequency (e.g., (e.g., a first image  412  acquired at 30 cm, a second image  404  acquired at 17 cm, and a third image  406  acquired at 10 cm, which of these images acquired at 1.7 MHz). The plurality of ultrasound images  400  further includes a third plurality of images  420 . Each image of the third plurality of images  420  was acquired at a different depth value and at the same third frequency (e.g., (e.g., a first image  422  acquired at 30 cm, a second image  424  acquired at 17 cm, and a third image  426  acquired at 10 cm, which each of these images acquired at 2.0 MHz). The plurality of ultrasound images  400  further includes a fourth plurality of images  430 . Each image of the fourth plurality of images  430  was acquired at a different depth value and at the same fourth frequency (e.g., (e.g., a first image  432  acquired at 30 cm, a second image  434  acquired at 17 cm, and a third image  436  acquired at 10 cm, with each of these images acquired at 2.3 MHz). 
     Each image shown in  FIG. 4  includes two quality indicators, a predicted IQ rating and a cumulative score. The cumulative score may be determined based on output from one or more of the models illustrated in  FIG. 3 , such as the depth model, the landmark model, the global image quality model, and the speckle size model. The predicted IQ rating may be obtained from the cumulative scores using empirical thresholds determined during the training process. The predicted IQ rating classifies the input ultrasound image or cine loop into three levels of image quality, such as 1 for bad/low image quality, 2 for acceptable image quality, and 3 for good/high image quality, while the cumulative score is a continuous number which is used to select the best acquisition from a set of acquisitions. 
     The image having the highest combined score (e.g., the predicted IQ score and the cumulative score) from the plurality of images may be selected, and the selected depth value and selected frequency value may be the depth value and frequency value used to acquire the selected image. For example, as shown, image  404  has a predicted IQ score of 3 and a cumulative score of 6, which is higher than the scores of the remaining images. Thus, the selected depth value may be 17 cm, as image  404  was acquired with a depth value of 17 cm, and the selected frequency may be 1.4 MHz, as image  404  was acquired with a frequency value of 1.4 MHz. 
       FIGS. 5A and 5B  show flow chart illustrating an example method  500  for joint ultrasound imaging parameter selection according to an embodiment. In particular, method  500  relates to acquiring a plurality of ultrasound images at different parameter values of difference scan parameters and then processing the acquired ultrasound images with multiple machine learning models to select optimal scan parameter values, which may improve the image quality of displayed ultrasound images. Method  500  is described with regard to the systems and components of  FIGS. 1-2 , though it should be appreciated that the method  500  may be implemented with other systems and components without departing from the scope of the present disclosure. Method  500  may be carried out according to instructions stored in non-transitory memory of a computing device, such as image processing system  202  of  FIG. 2 . 
     At  502 , ultrasound images are acquired and displayed on a display device. For example, the ultrasound images may be acquired with the ultrasound probe  106  of  FIG. 1  and displayed to an operator via display device  118 . The images may be acquired and displayed in real time or near real time, and may be acquired with default or user-specified scan parameters (e.g., default depth, frequency, etc.). At  504 , method  500  determines if an indication that a target scan plane is being imaged has been received. The target scan plane may be a scan plane specified by a scanning protocol or designated by an operator as being a target scan plane. For example, the ultrasound images may be acquired as part of an ultrasound exam where certain anatomical features are imaged in certain views/axes in order to diagnose a patient condition, measure aspects of the anatomical features, etc. For example, during a cardiac exam, one or more target scan planes (also referred to as views) of the heart of a patient may be imaged. The target scan planes may include a four-chamber view, a two-chamber view (which may also be referred to as a short axis view), and a long axis view (which may also be referred to as a PLAX view or three-chamber view). One or more images may be acquired in each scan plane and saved as part of the exam for later analysis by a clinician such as a cardiologist. When acquiring the images for the exam, the ultrasound operator (e.g., sonographer) may move the ultrasound probe until the operator determines that the target scan plane is being imaged, and then the operator may enter an input (e.g., via user interface  115 ) indicating that the target scan plane is being imaged. In another example, the ultrasound system (e.g., via the image processing system  202 ) may automatically determine that the target scan plane is being imaged. For example, each acquired ultrasound image (or some frequency of the acquired ultrasound images, such as every fifth image) may be entered into a detection model that is configured to automatically detect the current scan plane. If the current scan plane is the target scan plane, the indication may be generated. 
     If an indication that the target scan plane is being imaged is not received, method  500  returns to  502  to continue to acquire and display ultrasound images (e.g., at the default or user-set scan parameters). If an indication is received that the target scan plane is being imaged, method  500  proceeds to  505  to optionally select a parameter selection acquisition protocol according to the target plane. When the parameter selection acquisition protocol is carried out, a plurality of images are acquired (e.g., in a sequential manner), where two or more scan parameters (such as depth and frequency) are varied for each image, such that images are acquired at all possible combinations of parameter values. The relative order of the image acquisition may be varied based on the target scan plane in some examples. For example, the images may be acquired according to a first acquisition protocol where depth is held constant at a first value while a first set of images is acquired each at a different frequency value, then depth is changed to a second value and held constant while a second set of images is acquired each at a different frequency value, then depth is changed to a third value and held constant while a third set of images is acquired each at a different frequency value, and so forth. In the second acquisition protocol, frequency is held constant at a first value while a first set of images is acquired each at a different depth value, then frequency is changed to a second value and held constant while a second set of images is acquired each at a different depth value, then frequency is changed to a third value and held constant while a third set of images is acquired each at a different depth value, etc. Other acquisition protocols are possible, such as more random distribution in the changes in both depth and frequency rather the more ordered combinations described above with respect to the first acquisition and second acquisition protocol. 
     The decision of which acquisition protocol to carry out may be based on the target scan plane. For example, the first acquisition protocol may be carried out when imaging a four-chamber view of the heart while the second acquisition protocol may be carried out when imaging a PLAX view of the heart. As will be explained in more detail below with respect to  FIG. 7 , the second acquisition protocol may result in all images having a first frequency value being acquired during the same relative phase of the cardiac cycle, all images having a second frequency value being acquired during a different phase of the cardiac cycle than the images acquired at the first frequency, but the images acquired at the second frequency are all acquired at the same relative phase to each other, and so forth. When comparing images acquired at different frequency values but the same depth value, the fact that the images are also taken at different phases of the cardiac cycle may result in some of the frequency-based changes being confounded or harder to detect. However, the opposite may be true of depth-related changes. In contrast, the first acquisition protocol may result in a first set of images, acquired at the same depth and different frequencies, to be acquired at the same relative cardiac phase, a second set of images (acquired at the same, next depth and different frequencies) to be acquired at the same relative cardiac phase (though different than the first set), etc. When comparing images acquired at different frequency values but the same depth value, the fact that the images are taken at the same relative phase of the cardiac cycle may result in fewer of the frequency-based changes being confounded or harder to detect. However, the opposite may be true of depth-related changes. Thus, the decision of which acquisition protocol to select may be based on whether depth-based or frequency-based changes are more important to detect when selecting the parameter values, as well as the type of anatomy being scanned (e.g., whether the anatomy exhibits periodic motion). Once an acquisition protocol is selected, the images may be acquired according to the protocol, as explained below. However, in some examples only one protocol may be available, and thus there may be no selection process. 
     At  506 , a first set of images is acquired, with each image acquired at a first parameter value of a first set of parameter values for a first scan parameter and a different parameter value of a second set of parameter values for a second scan parameter. For example, the first scan parameter may be depth and the first set of parameter values may be the different depth values described above (e.g., 10 cm, 17 cm, and 30 cm). Thus, the first set of images may be acquired at one of the depth values (e.g., 10 cm). The second scan parameter may be frequency and the second set of parameter values may be the different frequencies described above (e.g., 1.4 MHz, 1.7 MHz, 2 MHz, and 2.3 MHz). Thus, each image of the first set of images may be acquired at a different one of the second set of parameter values (e.g., one at 1.4 MHz, one at 1.7 MHz, one at 2 MHz, and one at 2.3 MHz). The first set of images may include four images, or more than four images if more than four frequency values are to be selected from. During acquisition of the first set of images, any other scan parameters (e.g., gain, etc.) that may be optimized may be held constant. Further, during acquisition of the first set of images, the acquired images may be displayed on the display device at the frame rate at which the images are acquired, at least in some examples. In some examples, a set of cine loops may be acquired, or a mix of images and cine loops. When cine loops are acquired, the acquisition of the different cine loops may be carried out as explained above, e.g., at the same depth value and at different frequency values. 
     At  508 , a second set of images (and/or cine loops) are acquired, each at a second parameter value of the first set of parameter values for the first scan parameter and a different parameter value of the second set of parameter values for the second scan parameter. For example, each image the second set of images may be acquired at one of the depth values (e.g., 17 cm) that is different than the first value described above. Each image of the second set of images may be acquired at a different one of the second set of parameter values (e.g., one at 1.4 MHz, one at 1.7 MHz, one at 2 MHz, and one at 2.3 MHz). The second set of images may include four images, or more than four images if more than four frequency values are to be selected from. During acquisition of the second set of images, any other scan parameters (e.g., gain, etc.) that may be optimized may be held constant. Further, during acquisition of the second set of images, the acquired images may be displayed on the display device at the frame rate at which the images are acquired, at least in some examples. 
     At  510 , method  500  includes determining if a set of images has been acquired for each parameter value of the first set of parameter values. For example, the method may include determining, after acquiring the first set of images and/or the second set of images, how many parameter values are in the first set of parameter values and whether a corresponding set of images (e.g., with one image acquired at each different parameter value of the second set of parameter values) has been acquired for each possible parameter value of the first set of parameter values. If not, for example if additional images are to be acquired to complete the parameter selection acquisition protocol where an image is acquired at each different possible combination of parameter values, method  500  proceeds to  512  to acquire one or more respective sets of images (and/or sets of cine loops) for each remaining parameter value of the first set of parameter values, and then method  500  proceeds back to  510  to determine if a set of images has been acquired for each parameter value of the first set of parameter values (e.g., if the acquisition protocol is complete). 
     If it is determined that a set of images has been acquired for each parameter value of the first set of parameter values (e.g., that the acquisition protocol is complete), method  500  proceeds to  514  to determine a quality metric for each image of each set of images (e.g., each image acquired according to the parameter selection acquisition protocol) (and/or for each cine loop). The quality metric may be determined from a plurality of models, as indicated at  516 . For example, as explained previously, a first quality metric may be determined by a depth model, such as depth model  209  of  FIG. 2 . Each image may be entered as an input to the depth model, and the depth model may output, for each input image, a respective first quality metric. In some examples, the model may be selected based on the target scan plane. For example, a first depth model may be selected when the target scan plane is a four-chamber view and a second depth model may be selected when the target scan plane is a two-chamber view. Further, a second quality metric may be determined one or more frequency-related models, such as the one or more frequency models  211  of  FIG. 2 . For example, each image may be entered as an input to a speckle model, a landmark detection model, and/or a global image quality model, and the models may output, for each input image, a respective sub-metric. The respective sub-metrics may be combined (e.g., added or averaged) to generate the second quality metric. In some examples, the model(s) may be selected based on the target scan plane. For example, a first landmark model may be selected when the target scan plane is a four-chamber view and a second landmark model may be selected when the target scan plane is a two-chamber view. The first metric and the second metric for a given image may be combined to arrive at the quality metric for that image. 
     At  518 , the image having the highest quality metric is selected. For example, referring back to  FIG. 4 , second image  404  was assigned an image metric (e.g., overall score) of 9, which is the highest quality metric of all the images acquired according to the acquisition protocol described above with respect to  FIG. 4 . Thus, second image  404  may be selected. In examples where more than one image has the highest quality metric, the image that was acquired at the highest frequency may be selected. For example, in the example presented in  FIG. 4 , if second image  414  had a quality metric of 9 (e.g., rather than 8.9 as shown), second image  414  may be selected rather than second image  404  due to second image  414  being acquired at 1.7 MHz rather than 1.4 MHz. 
     At  520 , shown in  FIG. 5B , a first parameter value for the first scan parameter at which the selected image was acquired is identified and set as the selected parameter value of the first scan parameter. For example, if the first scan parameter is depth and the selected image was acquired at a depth of 17 cm, the depth value of 17 cm may be identified as the selected parameter value. At  522 , a second parameter value for the second scan parameter at which the selected image was acquired is identified and set as the selected parameter value of the second scan parameter. For example, if the second scan parameter is frequency and the selected image was acquired at a frequency of 1.4 MHz, the frequency value of 1.4 MHz may be identified as the selected parameter value. In some examples, the selection of both the first parameter value and the second parameter value may only be performed once all images dictated by the parameter selection acquisition protocol have been acquired. 
     At  523 , method  500  optionally includes setting target post-acquisition processing parameters, which is explained in more detail below with respect to  FIG. 8 . Briefly, once the acquisition scan parameter values have been selected as explained above, target values for one or more post-acquisition processing parameters may be selected based on the image quality of one or more sets of adjusted images. For example, an image may be replicated, with different post-acquisition processing parameter values applied to each replicate, to create a set of adjusted images. The image from the adjusted set of images that has the highest image quality may be selected, and the parameter value(s) for that image may be applied to subsequent images. Example post-acquisition processing parameters include filtering parameters (e.g., bandwidth, center frequency), image contrast, image gain, etc. 
     At  524 , one or more ultrasound images are acquired at the selected value for the first scan parameter and the selected value for the second scan parameter. Thus, once the scan parameter values have been selected for the target scan plane based on the determined image quality metric as described above, the selected scan parameter values may be set and any additional images acquired by the ultrasound probe may be acquired at the set, selected scan parameter values. This may include setting the transmit depth of the ultrasound probe to the selected depth value and setting the transmit frequency of the ultrasound probe to the selected frequency. In some examples, the selected scan parameter values for the target scan plane may be saved in memory. Then, if the operator moves the ultrasound probe so that the target scan plane is not imaged, but then later moves the ultrasound probe back so that the target scan plane is imaged again, the previously determined selected scan parameter values for that scan plane may be automatically applied. Additionally, if target post-acquisition processing parameters are set (e.g., according to the method of  FIG. 8 ), the one or more ultrasound images that are acquired at  524  may be processed according to the target post-acquisition processing parameters, e.g., the received ultrasound data may be filtered according to parameter values for the filtering (e.g., bandwidth and center frequency) that are determined according to the method of  FIG. 8 . 
     At  526 , method  500  determines if the current exam includes more target planes. The determination of whether the current exam includes more target planes may be made on the basis of user input. For example, the operator may enter a user input indicating that a new scan plane is being imaged, that a new scan plane is about to be imaged, or that the exam is over. In other examples, the determination of whether the exam includes more target planes may be made automatically based on the system determining a different scan plane is being imaged or that scanning has been terminated. If the exam does not include more target scan planes, for example if the current exam is complete and imaging is terminated, method  500  proceeds to  528  to display acquired images, quality metrics, and selected parameter settings, and then method  500  returns. It is to be understood that acquired images may be displayed at  524  and/or other points during method  500 . Further, the selected parameter settings may be displayed at  524  to allow the operator to view and confirm the parameter settings. The quality metrics may also be displayed at other points in time, such as at  524 . Further, the images acquired at  524  may be archived when requested by the operator. 
     If the exam does include more target scan planes, method  500  proceeds to  530  to determine if an indication that the next target plane is being imaged has been received, similar to the determination made at  504  and explained above. If the indication has not been received, method  500  proceeds to  532  to continue to acquire images at the selected values for the first and second scan parameters (e.g., as explained above with respect to  524 ), and then method  500  returns to  530  to continue to determine if the indication has been received. If the indication has been received, method  500  proceeds to  534  and optionally restricts the parameter values for one or both of the first and second scan parameters. For example, as explained above, the first scan parameter may have three possible parameter values and the second scan parameter may have four possible scan values. However, once the selected parameter values have been determined for a given scan plane, those selected parameter values may be applied to the next target plane, thus restricting the available values that may be optimized. For example, if the first target plane was a four-chamber view, and the next target plane is a two-chamber view, one or both of the selected values may be used to acquire images in the two-chamber view. If one of the selected values is used but not the other (e.g., the selected depth is used), the selection of the selected value for the other scan parameter (e.g., frequency) may be re-performed for the next target plane. However, when switching from the four-chamber view to the PLAX view, for example, both parameter values may be re-determined and thus  534  may not be performed. 
     At  536 ,  505 - 524  may be repeated for the next target plane. For example, a plurality of images may be acquired of the next target scan plane, each at a different combination of parameter values for the first scan parameter and second scan parameter, a quality metric may be determined for each image, and an image may be identified that has the highest quality metric. The acquisition settings used to acquire the selected image (e.g., the depth and frequency values) may be set as the selected values for the first and second scan parameters, and one or more additional images of the next target scan plane may then be acquired with the selected values for the first and second scan parameters. This process may be repeated for all additional target scan planes, until the exam is complete. 
     While method  500  was described above with regard to varying depth and frequency jointly to determine target depth and frequency values that will result in a high quality image, other acquisition scan parameters may be varied according to the method described above without departing from the scope of this disclosure. For example, beamforming strategy and frequency may be varied jointly. Beamforming strategy may include the type of beamforming which is employed, e.g., the strength/type of ACE processing. Example beamforming strategies (which may be considered the different “parameter values” for the beamforming strategy) may include delay sum, coherent plane wave compounding, and divergent beam. To select a target beamforming strategy and frequency, a set of images may be acquired, each at a different combination of beamforming strategy and frequency (e.g., a first image at a first beamforming strategy and a first frequency, a second image at a second beamforming strategy and the first frequency, a third image at the first beamforming strategy and a second frequency, a fourth image at the second beamforming strategy and the second frequency, and so forth). Each image of the set of images may be assigned a quality metric, as described above. For example, each image may be input to the speckle model, the landmark detection model, and/or the global image quality model, and the models may output, for each input image, a respective sub-metric. The respective sub-metrics may be combined (e.g., added or averaged) to generate the quality metric for each image. The image having the highest quality metric may be selected, and the beamforming strategy and frequency used to acquire the selected image may be set for subsequent image acquisition. In examples where depth is not a scan parameter to be varied and selected, the depth model explained above may be omitted from the quality metric determination. 
       FIG. 6  shows a table  600  of different combinations of scan parameter values (e.g., depth and frequency) that may be applied to acquire 12 images, such as the 12 images shown in  FIG. 4 . Table  600  is an example of an acquisition protocol, which may dictate the order in which the images are acquired (e.g., the order of which combinations of acquisition parameter settings will be used). The ultrasound system may have a frame rate of 10 Hz, and thus an image may be acquired once every tenth of a second. As appreciated from table  600 , the images may be acquired such that a first set of images is acquired with the same, first depth (from a set of three depths) and a different frequency (from a set of four frequencies), a second set of images is acquired with the same, second depth (from the set of three depths) and a different frequency (from the set of four frequencies), and a third set of images is acquired with the same, third depth (from the set of three depths) and a different frequency (from the set of four frequencies). In this way, for the first four images, depth may held constant while frequency is varied. For the next four images, depth is held constant (at a different depth than the first four images) and frequency is varied, and for the last four images, depth is held constant at a different depth and the frequency is varied. 
     As appreciated by table  600 , an image will be acquired for each possible combination of parameter values for a first set of parameter values having three values and a second set of parameter values having four values. Table  600  may be stored in memory of a computing device (e.g., memory  120  of  FIG. 1 ) and, during parameter selection as described above with respect to  FIGS. 5A and 5B , the images may be acquired according to table  600 . 
     Because motion of the imaged anatomical features may contribute to fluctuations in image quality, it may be desirable to obtain the images described herein (e.g., used to determine the optimal scan parameters) during periods where motion is not occurring, or during periods where motion among the images is comparable. When imaging the heart, obtaining images with no motion or comparable motion may be challenging, given the movement of the heart over the course of a cardiac cycle. For example, for a patient having a heart rate of 60 beats per minute, a cardiac cycle may last one second, which is approximately the same amount of time used to acquire all 12 images according to the table of  FIG. 6 . Thus, the decision of whether frequency is held constant for a duration while depth is varied (as shown by  FIG. 4 ), or whether depth is held constant while frequency is varied (as shown by  FIG. 6 ) may depend on what anatomy is being imaged (e.g., whether the heart is being imaged, and if so, which view of the heart). 
       FIG. 7  shows two example plots of ultrasound frequency as a function of time during a parameter selection acquisition protocol where a plurality of images are acquired. Each plot in  FIG. 7  also shows an approximation of a cardiac cycle time aligned with the frequency. First plot  702  illustrates frequency as a function of time relative to the cardiac cycle when, for each frequency, the frequency is held constant while depth is varied. This arrangement of scan parameter variability during acquisition may result in all images having the first frequency (f 1 ) being obtained during a first phase of the cardiac cycle (e.g. beginning of systole), all images having the second frequency (f 2 ) being obtained during a second phase of the cardiac cycle (e.g., end of systole), all images having the third frequency (f 3 ) being obtained during a third phase of the cardiac cycle (e.g., beginning of diastole), and all images having the fourth frequency (f 4 ) being obtained during a fourth phase of the cardiac cycle (e.g., end of diastole). 
     In contrast, second plot  704  illustrates frequency as a function of time relative to the cardiac cycle when, for each depth, the depth is held constant while frequency is varied. This arrangement of scan parameter variability during acquisition may result in an image having frequency f 1  being obtained at each cardiac phase (e.g., one during beginning of systole, one during the end of systole, one during the beginning of diastole, and one during the end of diastole. The remaining frequencies may follow a similar distribution (e.g., one image, for each frequency, at each phase of the cardiac cycle). The distribution shown in plot  704  may be advantageous relative to the distribution shown by plot  702  when motion affects the frequency-based image quality detection to a higher degree than the depth-based image quality detection. When images of different frequency but the same depth are compared to one another to determine which image has the highest image quality, a more reliable determination may be made when all the images being compared are acquired in the same relative phase of the cardiac cycle. For example, as shown in plot  704 , the first four frames of each image are each acquired at a different frequency, but occur during the same phase of the cardiac cycle. 
     Turning now to  FIG. 8 , a method  800  for determining post-acquisition processing parameters for ultrasound images is presented. Method  800  may be carried out as part of method  500 , for example once acquisition parameter values for a target plane have been determined. In other examples, method  800  may be carried out independently of method  500 , for example in response to a user request to set post-acquisition processing parameter values. Method  800  may be carried out according to instructions stored in non-transitory memory of a computing device, such as image processing system  202  of  FIG. 2 . 
     At  802 , ultrasound information for a single image is obtained. The ultrasound information may be acquired with an ultrasound probe in response to execution of method  800 , or the ultrasound information may be retrieved from memory. In one non-limiting example, the ultrasound information may be ultrasound information sufficient to generate one image, and the ultrasound information may be obtained with target acquisition scan parameters as discussed above (e.g., at a target depth, a target frequency, etc.). 
     At  804 , different parameter values for a first post-acquisition parameter are applied to the obtained ultrasound information to generate a first set of adjusted images. For example, the first post-acquisition parameter may be a filtering center frequency, and the different parameter values may be different center frequencies (e.g., 3.2 MHz, 3.4 MHz, and 3.6 MHz, or different multiples of the transmission frequency, such as the transmission frequency, twice the transmission frequency, and three times the transmission frequency). In another example, the first post-acquisition parameter may be a filtering bandwidth and the different parameter values may be different bandwidths (e.g., 1 MHz, 1.2 MHz, and 1.4 MHz). Each different parameter value may be applied to the information to generate an image for each parameter value. For example, when the first post-acquisition parameter is the filtering center frequency, the first set of adjusted images may include a first image generated with a center frequency of 3.2 MHz, a second image generated with a center frequency of 3.4 MHz, and a third image generated with a center frequency of 3.6 MHz. The same ultrasound information may be used to generate each image in the first set of adjusted images. Any other post-acquisition parameters may be held constant at a default or commanded value. 
     At  806 , a quality metric of each image in the first set of adjusted images is determined. The quality metric of each image may be determined by entering each image as input to one or more image quality models, as explained above with respect to  FIGS. 2, 3, 5A, and 5B . For example, each image may be entered as input to a global image quality model, a landmark detection model, and a speckle model, and each model may output a respective quality sub-metric that may be summed or averaged to arrive at an overall image quality metric for each image. 
     At  808 , the image of the first set of adjusted images having the highest image quality metric is selected. If two or more images have the same, highest image quality metric, an additional metric may be used to select from among the two or more images, such as the global image quality model sub-metric. At  810 , the first post-acquisition parameter is set to the parameter value of the selected image. For example, if the selected image was generated with a filter center frequency of 3.2 MHz, the filter center frequency may be set at 3.2 MHz. 
     At  812 , the above process may be repeated for any additional post-acquisition parameters. For example, after selecting the first post-acquisition parameter value, the ultrasound information may again be used to generate replicate images, with each replicate image having a different parameter value for a second post-acquisition parameters, such as filter bandwidth, to form a second set of adjusted images. When the first post-acquisition parameter has been set, the images of the second set of adjusted images may be generated with the set parameter value for the first post-acquisition parameter. The image quality metric may be determined for each image in the second set of adjusted images, and the image having the highest image quality metric may be selected. The parameter value for the second post-acquisition parameter of the image having the highest image quality metric may be set as the parameter value for the second post-acquisition parameter. At  814 , the set parameter value for each post-acquisition parameter is applied to any subsequent images, e.g., of the current view plane. Method  800  then ends. 
     While method  800  was described above as including a sequential process for selecting parameter values for two or more post-acquisition parameters, a joint process may be used instead. In the joint process, one set of replicate images may be generated, where each image has a different combination of parameter values for the two or more post-acquisition parameters. The image quality of each image may be determined as described above, and the image having the highest image quality metric may be selected. The parameter values for the two or more post-acquisition parameters used to generate the selected image may be selected and set as the parameter values for subsequent image processing. 
     The image acquisition process used to acquire the ultrasound images described herein may be carried out according to a suitable scan sequence.  FIG. 9  shows a graph  900  illustrating a first example scan sequence that may be executed to acquire ultrasound information that may be used to generate a single image. Graph  900  shows a sector scan, though other scan geometries are also possible. Each line in graph  900  represents a transmit direction, and the transmits are fired sequentially from, for example, left to right. When a transmit parameter is varied, such as frequency, the transmits may all be fired at the same parameter value (e.g., at the same frequency, P 1 ) to generate a first image. Then, the frequency may be adjusted to a second frequency, and the transmits may all be fired sequentially at the second frequency to generate a second image. 
     The scan sequence of  FIG. 9  would result in subsequent images being obtained with different parameter values, when exploring for the target parameter value. However, subsequent shots within an image are be possible to be acquired with different parameters. This scan process for acquisition would include firing in the same transmit direction N times to record data for that direction with N different parameter values before moving on to the next transmit direction. This scan process is shown in  FIG. 10 , which shows a graph  1000  illustrating a second example scan sequence that may be executed to acquire ultrasound information that may be used to generate multiple images. Graph  1000  shows a sector scan, though other scan geometries are also possible. Each solid line in graph  1000  represents a transmit direction and a first parameter value, while each dashed line represents a different parameter value (fired at the transmit direction of the solid line to its left) and the transmits are fired sequentially from, for example, left to right. Instead of including only one transmit parameter value, graph  1000  includes four transmit parameter values, P 1 -P 4 . For example, the transmit parameter may be frequency and each parameter value may be a different frequency. 
     During image acquisition, the transmits may be fired sequentially, but for each transmit direction, a transmit may be fired for each parameter value before moving on to the next transmit direction. For example, for a first transmit direction, a transmit may be fired at P 1 , a transmit may be fired at P 2 , a transmit may be fired at P 3 , and a transmit may be fired at P 4  (while the different solid/dashed lines are placed besides each other for illustration purposes, it is to be understood that each transmit for P 1 -P 4  for the first transmit direction would be fired at the same transmit direction). The transmit direction may be updated to a second transmit direction, and a set of transmits may be fired at the second transmit direction, one for each parameter value. The process may repeat until all transmit directions have been fired at all parameter values. A first image may be generated from information acquired while firing at the first parameter value, a second image may be generated from information acquired while firing at the second parameter value, a third image may be generated from information acquired while firing at the third parameter value, and a fourth image may be generated from information acquired while firing at the fourth parameter value. This scan sequence for parameter exploration would fire several times in each direction before moving on to the next transmit direction. This may result in longer time to acquire all directions of an image, but would result in very low lag between the different parameters that are to be compared for image quality. 
     The scan sequence shown in  FIG. 10  may be executed during the image acquisition for parameter selection as described above with respect to  FIGS. 5A and 5B , at least in some examples. In other examples, the scan sequence shown in  FIG. 9  may be executed during the image acquisition for parameter selection. 
     A technical effect of jointly selecting scan parameter values includes increased image quality and reduced operator workflow demands. Another technical effect is more consistent image quality across multiple exams. 
     In another representation, a system includes an ultrasound probe, a memory storing instructions, and a processor communicably coupled to the memory and when executing the instructions, configured to: process ultrasound information obtained with the ultrasound probe into a first set of replicate images, each replicate image processed according to a different post-acquisition processing parameter value of a plurality of post-acquisition processing parameter values for a first post-acquisition processing parameter; determine an image quality metric of each replicate image of the first set of replicate images; select the replicate image having the highest image quality metric; and process additionally acquired ultrasound information according to the post-acquisition processing parameter value used to process the ultrasound information into the selected replicate image. In an example, each replicate image of the first set of replicate images is processed from the same ultrasound information, such that the replicate images are identical other than the different post-acquisition processing parameter values used to create the replicate images. In an example, the processor is configured to, after selecting the replicate image having the highest image quality metric: process the ultrasound information into a second set of replicate images, each replicate image of the second set of replicate images processed according to a different post-acquisition processing parameter value of a plurality of post-acquisition processing parameter values for a second post-acquisition processing parameter; determine an image quality metric of each replicate image of the second set of replicate images; select the replicate image of the second set of replicate images having the highest image quality metric; and process additionally acquired ultrasound information according to the post-acquisition processing parameter value for the second post-acquisition processing parameter used to process the ultrasound information into the selected replicate image. In an example, each replicate image of the first set of replicate images is processed according to a different parameter value for a second post-acquisition processing parameter, and the additionally acquired ultrasound information is processed according to the parameter value for the second post-acquisition processing parameter used to process the ultrasound information into the selected replicate image. In an example, the ultrasound information may be acquired with the ultrasound probe at a first target scan parameter value and a second target scan parameter value selected according to the joint process described above with respect to  FIGS. 5A and 5B . 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “first,” “second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. As the terms “connected to,” “coupled to,” etc. are used herein, one object (e.g., a material, element, structure, member, etc.) can be connected to or coupled to another object regardless of whether the one object is directly connected or coupled to the other object or whether there are one or more intervening objects between the one object and the other object. In addition, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     In addition to any previously indicated modification, numerous other variations and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of this description, and appended claims are intended to cover such modifications and arrangements. Thus, while the information has been described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred aspects, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, form, function, manner of operation and use may be made without departing from the principles and concepts set forth herein. Also, as used herein, the examples and embodiments, in all respects, are meant to be illustrative only and should not be construed to be limiting in any manner.