Systems and methods for flow suppression

Abstract

Systems and methods for flow suppression in magnetic resonance imaging (MRI) are disclosed. The techniques described herein include determining, for one or more MRI scans, an MRI sequence comprising a flow suppression segment to suppress signal from fluid flow in the one or more MRI scans. The flow suppression segment include an excitation block, a first gradient block including gradients in a plurality of axes, a refocusing block, a second gradient block including gradients in the plurality of axes. The flow suppression segment may include one or more eddy-preparation gradient blocks. The techniques include performing, via an MRI system, the one or more MRI scans using the MRI sequence to obtain one or more MR images.

Description

SYSTEMS AND METHODS FOR FLOW SUPPRESSIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 745,216 filed January 14, 2025, and U.S. Provisional Patent Application No. 63 / 640,695 filed April 30, 2024 with the title “Flow Suppression By Diffusion Prepared Spin Echo Sequences,” the entirety of each of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The present disclosure relates generally to the field of magnetic resonance (MR) imaging (MRI) and enhancement of features such as contrast and flow suppression in MR images, such as by using flow suppression segments in MR sequences to reduce appearance of fluid flow in a region of interest (RO I) of a subject being imaged.BACKGROUND

[0003] Magnet resonance imaging (MRI) systems are used to generate images of the inside of the human body. MRI systems may be used to detect magnetic resonance (MR) signals in response to applied electromagnetic fields.SUMMARY

[0004] The systems and methods of this technical solution provide techniques for flow suppression, for example, by diffusion prepared spin echo sequences or other MR sequences. Basic spin echo MR sequences can provide image signal resulting from both flowing blood and static blood. While flowing blood is expected in normal healthy subjects, static blood may be more clinically relevant because it could indicate, for example, a bleed or blocked vasculature.

[0005] The MR sequences used in imaging can be modified to suppress signal from flowing blood relative to signal from static blood. This can allow for easier differentiation of blood in normal, healthy vasculature from a pathological bleed or blocked flow in, for example, large veins.

[0006] One way to suppress signal from flowing blood can be to apply crushing gradients along the spin echo train. This method can be used with high-field (e.g., greater than 0.5 T) MRI systems. The flow suppressing gradients can suppress spurious signal from imperfect refocusing pulses, and out of volume signal from slice or slab -selective sequences. The crushing gradients can make the spin echo sequence more eddy-current sensitive.

[0007] Low-field MRI systems (e.g., less than or equal to 0.5 T) may not have slice or slab selective sequences, and may not have well-performing RF pulses. Crushing gradients usedin high-field MRI systems may present control challenges in low-field MRI systems. Low-field MRI systems can use a diffusion-preparation segment (e.g., flow suppression sequence block). For example, the flow suppression sequence block can be implemented before the spin echo train.

[0008] At least one aspect of the present disclosure is directed to a method. The method can include determining, for one or more magnetic resonance imaging (MRI) scans, an MRI sequence. The MRI sequence can include a flow suppression segment to suppress signal from fluid flow in the one or more MRI scans. The flow suppression segment can include an excitation block, a first gradient block including gradients in a plurality of axes, a refocusing block, and a second gradient block including gradients in the plurality of axes. The method can include performing, via an MRI system, the one or more MRI scans using the MRI sequence to obtain one or more MR images.

[0009] Another aspect of the present disclosure is directed to a system. The system can include at least one radio frequency (RF) coil. The system can include at least one controller configured to determine, for one or more MRI scans, an MRI sequence. The MRI sequence can include a flow suppression segment to suppress signal from fluid flow in the one or more MRI scans. The flow suppression segment can include an excitation block, a first gradient block including gradients in a plurality of axes, a refocusing block, and a second gradient block including gradients in the plurality of axes. The at least one controller can be configured to control the at least one RF coil to perform, using the MRI sequence, the one or more MRI scans to obtain one or more MR images.

[0010] Another aspect of the present disclosure is directed to a non-transitory computer- readable storage medium. The non-transitory computer-readable storage medium includes instructions that, when executed by one or more processors of a magnetic resonance imaging (MRI) system or a computing system, are configured to determine, for one or more MRI scans, an MRI sequence. The MRI sequence can include a flow suppression segment to suppress signal from fluid flow in the one or more MRI scans. The flow suppression segment can include an excitation block, a first gradient block including gradients in a plurality of axes, a refocusing block, and a second gradient block including gradients in the plurality of axes. The instructions can be configured to perform, via the MRI system, the one or more MRI scans using the MRI sequence to obtain one or more MR images.

[0011] These and other aspects and implementations are discussed in detail below. The foregoing information and the following detailed description include illustrative examples of various aspects and implementations, and provide an overview or framework for understandingthe nature and character of the claimed aspects and implementations. The drawings provide illustration and a further understanding of the various aspects and implementations, and are incorporated in and constitute a part of this specification. Aspects may be combined and it will be readily appreciated that features described in the context of one aspect of the present disclosure may be combined with other aspects. Aspects may be implemented in any convenient form. In a non-limiting example, by appropriate computer programs, which may be carried on appropriate carrier media (computer readable media), which may be tangible carrier media (e.g. disks) or intangible carrier media (e.g. communications signals). Aspects may also be implemented using suitable apparatus, which may take the form of programmable computers running computer programs arranged to implement the aspect. As used in the specification and in the claims, the singular form of “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings are not intended to be drawn to scale. Like reference numbers and designations in the various drawings indicate like elements. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

[0013] FIG. 1 illustrates example components of a magnetic resonance imaging system, which may be utilized to implement the techniques for flow suppression, in accordance with one or more implementations;

[0014] FIG. 2A illustrates an example flow suppression segment, in accordance with one or more implementations;

[0015] FIG. 2B illustrates another example flow suppression segment, in accordance with one or more implementations;

[0016] FIG. 3 illustrates an MRI sequence, in accordance with one or more implementations;

[0017] FIG. 4 illustrates a table of simulated signal levels, in accordance with one or more implementations;

[0018] FIG. 5 illustrates images of non-flow suppressed FLAIR and flow-suppressed FLAIR, in accordance with one or more implementations;

[0019] FIG. 6 illustrates images of non-flow suppressed FLAIR and flow-suppressed FLAIR, in accordance with one or more implementations;

[0020] FIG. 7 illustrates a flowchart of an example method for flow suppression, in accordance with one or more implementations; and

[0021] FIG. 8 is a block diagram of an example computing system suitable for use in the various arrangements described herein, in accordance with one or more example implementations.DETAILED DESCRIPTION

[0022] Below are detailed descriptions of various concepts related to and implementations of techniques, approaches, methods, apparatuses, and systems for flow suppression. The various concepts introduced above and discussed in detail below may be implemented in any of numerous ways, as the described concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0023] Magnetic resonance imaging (MRI) systems use magnetic fields and electromagnetic signals to create detailed internal images of a patient in a non-invasive manner. In MR imaging, a magnetic field is applied to temporarily align protons in the patient, and one or more radiofrequency pulses are transmitted through the patient, which stimulate the protons and cause them to spin out of equilibrium. As the protons return to their original positions, they transmit radio signals that are detected by corresponding receive coils of the MRI systems. The received signals encode information about the structure and delineation of different tissues within the patient and can be used to reconstruct two-dimensional (2D) or three-dimensional (3D) internal images using image reconstruction techniques.

[0024] The radiofrequency signals returned from the patient have low power, and therefore are susceptible to electromagnetic interference from the environment. These effects may be more pronounced in MRI systems that have weaker magnetic fields, such as low-field MRI systems. Low-field MRI systems are MRI systems that can operate with a lower magnetic field strength than conventional MRI systems. Low-field MRI systems may include portable MRI systems, which may have a field strength that may be, in a non-limiting example, less than or equal to 0.5 T. For example, the low-field MRI system can include an MRI system with a magnetic field strength no greater than 200 mT (e.g., less than or equal to 200 mT). Low-field MRI systems can have a lower signal-to-noise ratio (SNR) compared to high-field MRI systems. To compensate for the lower SNR, low-field MRI systems can implement 3D fluid-attenuated inversion recovery (FLAIR) instead of 2D FLAIR. Magnetic resonance images obtained from 3D FLAIR, however, can lack flow suppression that can be found in MR images obtained from 2D FLAIR. Radiologists may expect MR images to deemphasize flowing blood in vasculaturebased on their experiences with images generated using high-field MRI systems (e.g., 1.5 T to 3T).

[0025] The systems and methods described herein provide techniques for flow suppression. As described in further detail herein, the flow suppression techniques can exclude or at least reduce the appearance of fluid movement (e.g., flowing blood) from MR images (e.g., 3D FLAIR images). A flow suppression module can prepare the spins by sensitizing them to movement. Thus, fluid movements can be deemphasized in the image (e.g., be suppressed). The flow suppression sequence can include a gradient pulse along each axis. This can allow for the suppression of flow regardless of which direction fluid is flowing (e.g., which way blood in a blood vessel is traveling).

[0026] FIG. 1 illustrates an example MR system 100 (e.g., MRI system) which may be utilized in connection with the flow suppression techniques described herein. In FIG. 1, MR system 100 may include a computing device 104, a controller 106, a pulse sequences repository 108, a power management system 110, and magnetics components 120. The MR system 100 is illustrative, and an MR system 100 may have one or more other components of any suitable type in addition to or instead of the components illustrated in FIG. 1. Additionally, the implementation of components for a particular MR system may differ from those described herein. Non-limiting examples of low-field MR systems may include portable MR systems, which may have a field strength that may be, in a non-limiting example, less than or equal to 1.5 T, less than or equal to 0.5 T, that may be less than or equal to 0.2 T, that may be within a range from 1 mT to 100 mT, that may be within a range from 50 mT to 0.1 T, that may be within a range of 40 mT to 80 mT, that may be about 64 mT, etc.

[0027] The magnetics components 120 may include Bo magnets 122, shims 124, RF transmit and receive coils 126, and gradient coils 128. The Bo magnets 122 may be used to generate a main magnetic field Bo. Bo magnets 122 may be any suitable type or combination of magnetics components that may generate a desired main magnetic Bo field. In some embodiments, Bo magnets 122 may be one or more permanent magnets, one or more electromagnets, one or more superconducting magnets, or a hybrid magnet comprising one or more permanent magnets and one or more electromagnets or one or more superconducting magnets. In some embodiments, Bo magnets 122 may be configured to generate a Bo magnetic field having a field strength that may be less than or equal to 0.2 T or within a range from 50 mT to 0.1 T.

[0028] In some implementations, the Bo magnets 122 may include a first and second Bo magnet, which may each include permanent magnet blocks arranged in concentric rings about acommon center. The first and second Bo magnet may be arranged in a bi-planar configuration such that the imaging region is located between the first and second Bo magnets. In some embodiments, the first and second Bo magnets may each be coupled to and supported by a ferromagnetic yoke configured to capture and direct magnetic flux from the first and second Bo magnets.

[0029] The gradient coils 128 may be arranged to provide gradient fields and, in a nonlimiting example, may be arranged to generate gradients in the Bo field in three substantially orthogonal directions (X, Y, and Z). Gradient coils 128 may be configured to encode emitted MR signal by systematically varying the Bo field (the Bo field generated by the Bo magnets 122 or shims 124) to encode the spatial location of received MR signal as a function of frequency or phase. In a non-limiting example, the gradient coils 128 may be configured to vary frequency or phase as a linear function of spatial location along a particular direction, although more complex spatial encoding profiles may also be provided by using nonlinear gradient coils. In some embodiments, the gradient coils 128 may be implemented using laminate panels (e.g., printed circuit boards), in a non-limiting example. Note that while substantially orthogonal gradient coils are described as an example, the techniques described herein can utilize any orientation or method of spatially encoding MR signal.

[0030] MRI scans are performed by exciting and detecting emitted MR signal using transmit and receive coils 126, respectively (referred to herein as radio frequency (RF) coils). The MR system 100 can include at least one RF coil. The transmit and receive coils 126 include separate coils for transmitting and receiving, multiple coils for transmitting or receiving, or the same coils for transmitting and receiving. Thus, a transmit / receive component may include one or more coils for transmitting, one or more coils for receiving, or one or more coils for transmitting and receiving. The transmit / receive coils may be referred to as Tx / Rx or Tx / Rx coils to generically refer to the various configurations for transmit and receive magnetics components of an MR system. These terms are used interchangeably herein. In FIG. 1, RF transmit and receive coils 126 may include one or more transmit coils that may be used to generate RF pulses to induce an oscillating magnetic field Bi. The transmit coil(s) may be configured to generate any type of suitable RF pulses.

[0031] Reference coils 130 may also be operated in connection with the transmit and receive coils 126 to capture the electromagnetic noise of the environment without capturing MR signal data. In particular, the reference coils 130 may be positioned in or near the MR system 100 such that, during an MR scan, the reference coils 130 do not receive signals including MR image data, and instead only receive and / or capture electromagnetic interference emitted withinthe environment in which the scan is being performed. In contrast, the receive coil(s) of the MR system can capture both MR signal data emitted via a patient 102 as well as electromagnetic interference from the environment. Signal data captured via the reference coils 130 may be stored (e.g., by the controller 106, the computing device 104, etc.) in computer storage in association with corresponding signal data captured via the transmit and receive coils 126. The signal data captured via the reference coils 130 may be utilized in connection with the flow suppression approaches to suppress signal from flowing blood, as described herein. As used herein, signals that include both imaging and noise data (e.g., captured via the transmit and receive coils 126) may be referred to as “image channels,” “imaging channels,” “MR signal channels,” or “signal channels,” while signals that include only noise data (e.g., captured via the reference coils 130) may be referred to as “reference channels.”

[0032] The power management system 110 includes electronics to provide operating power to one or more components of the MR system 100. In a non-limiting example, the power management system 110 may include one or more power supplies, energy storage devices, gradient power components, transmit coil components, or any other suitable power electronics needed to provide suitable operating power to energize and operate components of MR system 100. As illustrated in FIG. 1, the power management system 110 may include a power supply system 112, power component(s) 114, transmit / receive circuitry 116, and may optionally include thermal management components 118 (e.g., cryogenic cooling equipment for superconducting magnets, water cooling equipment for electromagnets).

[0033] The power supply system 112 may include electronics that provide operating power to magnetic components 120 of the MR system 100. The electronics of the power supply system 112 may provide, in a non-limiting example, operating power to one or more gradient coils (e.g., gradient coils 128) to generate one or more gradient magnetic fields to provide spatial encoding of the MR signal. Additionally, the electronics of the power supply system 112 may provide operating power to one or more RF coils (e.g., RF transmit and receive coils 126, the reference coils 130) to generate or receive one or more RF signals from the subject or EMI signals from the environment.

[0034] In a non-limiting example, the power supply system 112 may include a power supply configured to provide power from mains electricity to the MR system 100 or an energy storage device. The power supply may, in some embodiments, be an AC-to-DC power supply that converts AC power from mains electricity into DC power for use by the MR system 100. The energy storage device may, in some embodiments, be any one of a battery, a capacitor, an ultracapacitor, a flywheel, or any other suitable energy storage apparatus that may bi-directionally receive (e.g., store) power from mains electricity and supply power to the MR system 100. Additionally, the power supply system 112 may include additional power electronics including, but not limited to, power converters, switches, buses, drivers, and any other suitable electronics for supplying the MR system 100 with power.

[0035] The amplifiers(s) 114 may include one or more RF receive (Rx) pre-amplifiers that amplify MR signal detected by one or more RF receive coils (e.g., coils 126, the reference coils 130), one or more RF transmit (Tx) power components configured to provide power to one or more RF transmit coils (e.g., coils 126), one or more gradient power components configured to provide power to one or more gradient coils (e.g., gradient coils 128), and may provide power to one or more shim power components configured to provide power to one or more shims (e.g., shims 124). In some implementations, the shims 124 may be implemented using permanent magnets, electromagnetics (e.g., a coil), or combinations thereof. The transmit / receive circuitry 116 may be used to select whether RF transmit coils or RF receive coils and the reference coils 130 are being operated.

[0036] As illustrated in FIG. 1, the MR system 100 may include one or more controllers 106 (also referred to as a console), which may include control electronics to send instructions to and receive information from power management system 110. The controller 106 may be configured to implement one or more pulse sequences, which are used to determine the instructions sent to power management system 110 to operate the magnetic components 120 in a desired sequence (e.g., parameters for operating the RF transmit and receive coils 126, parameters for operating gradient coils 128, parameters for operating the reference coils 130, etc.). Additionally, the controller 106 may execute processes to suppress signal from flowing blood according to various techniques described herein. A pulse sequence may generally describe the order and timing in which the RF transmit and receive coils 126 and the gradient coils 128 operate to acquire resulting MR data. In a non-limiting example, a pulse sequence may indicate an order and duration of transmit pulses, gradient pulses, and acquisition times during which the receive coils acquire MR data.

[0037] A pulse sequence (e.g., stored in the pulse sequence repository 108) may be organized into a series of periods. In a non-limiting example, a pulse sequence may include a pre-programmed number of pulse repetition periods, and applying a pulse sequence may include operating the MR system 100 in accordance with parameters of the pulse sequence for the preprogrammed number of pulse repetition periods. In each period, the pulse sequence may include parameters for generating RF pulses (e.g., parameters identifying transmit duration, waveform, amplitude, phase, etc.), parameters for generating gradient fields (e.g., parameters identifyingtransmit duration, waveform, amplitude, phase, etc.), timing parameters governing when RF or gradient pulses are generated or when the receive coil(s) are configured to detect MR signal generated by the subject and the reference coil(s) 130 are configured to detect electromagnetic signals from the environment, among other functionality.

[0038] Examples of pulse sequences include but are not limited to zero or ultra-short echo time (ZTE, UTE) pulse sequences, free induction decay pulse sequences, steady-state pulse sequences, gradient echo pulse sequences, inversion recovery pulse sequences, echo-planar pulse sequences, spin echo pulse sequences including conventional spin echo (CSE) pulse sequences, multi-shot fast-spin echo (FSE) pulse sequences, turbo spin echo (TSE) pulse sequences or any multi-spin echo pulse sequences such a diffusion weighted spin echo pulse sequences, inversion recovery spin echo pulse sequences, arterial spin labeling pulse sequences, spectroscopy or spectroscopic imaging sequences, and Overhauser imaging pulse sequences, among others.

[0039] The MR system 100 can include at least one controller 106. The controller 106 can determine, for one or more MRI scans, an MRI sequence that includes a flow suppression segment (e.g., fluid flow suppression segment). The flow suppression segment can suppress signal from sample movement (e.g., fluid flow) in the one or more MRI scans. Once imaging channels from the receive coil(s) 126 and reference channels from the reference coils 130 have been received (e.g., after an MR scan has been completed or during an MR scan), the controller 106 can implement the flow suppression process (e.g., flow suppression segment), as described in further detail herein. The flow suppression segment can include an excitation block, a first gradient block that includes gradients in a plurality of axes, a refocusing block, and a second gradient block that includes gradients in the plurality of axes. The controller 106 can control the at least one RF coil to perform, using the MRI sequence, the one or more MRI scans to obtain one or more MR images.

[0040] As illustrated in FIG. 1, the controller 106 may communicate with the computing device 104, which may be programmed to process received MR data (e.g., the filtered signal data). In a non-limiting example, the computing device 104 may process received MR data to generate one or more MR images using any suitable image reconstruction processes. Additionally or alternatively, the controller 106 may process received MR data to perform image reconstruction, and the reconstructed image may be provided to the computing device 104 for display. Additionally or alternatively, the controller 106 may process received MR data to perform calibrations, testing, or corrections that may be used in acquiring or reconstructing MRimages. The controller 106 may provide information about one or more pulse sequences to computing device 104 for the processing of data by the computing device 104.

[0041] The computing device 104 may be any electronic device configured to process acquired MR data and generate one or more images of a subject being imaged. The computing device 104 may include at least one processor and a memory (e.g., a processing circuit). The memory may store processor-executable instructions that, when executed by a processor, cause the processor to perform one or more of the operations described herein. The processor may include a microprocessor, an application-specific integrated circuit (ASIC), a field- programmable gate array (FPGA), a graphics processing unit (GPU), a tensor processing unity (TPU), etc., or combinations thereof. The memory may include, but is not limited to, electronic, optical, magnetic, or any other storage or transmission device capable of providing the processor with program instructions. The memory may further include a floppy disk, CD-ROM, DVD, magnetic disk, memory chip, ASIC, FPGA, read-only memory (ROM), random-access memory (RAM), electrically erasable programmable ROM (EEPROM), erasable programmable ROM (EPROM), flash memory, optical media, or any other suitable memory from which the processor may read instructions. The instructions may include code generated from any suitable computer programming language. The computing device 104 may include any or all of the components and perform any or all of the functions of the computer system 1000 described in connection with FIG. 10. In some implementations, the computing device 104 may be located in a same room as the MR system 100 or coupled to the MR system 100 via wired or wireless connection.

[0042] In some implementations, computing device 104 may be a fixed electronic device such as a desktop computer, a server, a rack-mounted computer, or any other suitable fixed electronic device that may be configured to process MR data and generate one or more images from MR signal captured using the MR system 100. Alternatively, computing device 104 may be a portable device such as a smart phone, a personal digital assistant, a laptop computer, a tablet computer, or any other portable device that may be configured to process MR signal data (e.g., perform image reconstruction, other processing operations, etc.). In some implementations, computing device 104 may comprise multiple computing devices of any suitable type, as aspects of the disclosure provided herein are not limited in this respect. In some implementations, operations that are described as being performed by the computing device 104 may instead be performed by the controller 106, or vice-versa. In some implementations, certain operations may be performed by both the controller 106 and the computing device 104 via communications between said devices.

[0043] The MR system 100 may include one or more external sensors 178. The one or more external sensors may assist in detecting one or more error sources (e.g., motion, noise) which degrade image quality. The controller 106 may be configured to receive information from the one or more external sensors 178. In some embodiments, the controller 106 of the MR system 100 may be configured to control operations of the one or more external sensors 178, as well as collect information from the one or more external sensors 178. The data collected from the one or more external sensors 178 may be stored in a suitable computer memory and may be utilized to assist with various processing operations of the MR system 100.

[0044] The MR system 100 may be a portable MR system, and therefore may include portable subsystems 150. The portable subsystems 150 may include at least one power subsystem 152 and at least one motorized transport system 154. The power subsystem 152 may include any device or system that enables or supports the portability of the MR system 100. In a non-limiting example, the power subsystem 152 may include any of the functionality of the power supply 112, and may further include other circuitry enabling the provision of electric power, including but not limited to as batteries and associated circuitry, AC -DC converters, DC- DC converters, switching power converters, voltage regulators, or battery charging circuitry, among others. The power subsystem 152 may include connectors that support the portability of the MR system 100, such as connectors and cables of a suitable size for a portable system. In some implementations, the power subsystem 152 may include circuitry that provides power to the MR system 100. In some implementations, the power subsystem 152 may include circuitry or connectors that enable the MR system 100 to receive power from one or more power outlets, which may include standard power outlets.

[0045] The motorized transport system 154 can include any device or system that allows the MR system 100 to be transported to different locations. The motorized transport system 154 may include one or more components configured to facilitate movement of the MR system 100 to a location at which MRI is needed. In some implementations, the motorized transport system 154 may include a motor coupled to drive wheels. In such implementations, the motorized transport system 154 may provide motorized assistance in transporting the MR system 100 to one or more locations. The motorized transport system 154 may include a plurality of castors to assist with support and stability as well as facilitating transport.

[0046] In some implementations, the motorized transport system 154 includes motorized assistance controlled using a controller (e.g., a joystick or other controller that can be manipulated by a person) to guide the portable MR system 100 during transportation to desired locations. The motorized transport system 154 may include power assist circuitry (e.g.,including accelerometers and vibration sensors, etc.) that detects when force is applied to the MR system 100 and, in response, engages the motorized transport system 154 to provide motorized assistance in the direction of the detected force. In some implementations, the motorized transport system 154 can detect when force is applied to one or more portions of the MR system 100 (e.g., by an operator pushing on or applying force to a rail, housing, etc., of the MR system 100) and, in response, provide motorized assistance to drive the wheels in the direction of the applied force. The MR system 100 can therefore be guided to locations where MRI is needed. The power subsystem 152 can be utilized to provide power to the MR system 100, including the motorized transport system 154.

[0047] In some implementations, the motorized transport system 154 may include a safety mechanism that detects collisions. In a non-limiting example, the motorized transport system 154 can include one or more sensors that detect the force of contact with another object (e.g., a wall, bed, or other structure). Upon detection of a collision, the motorized transport system 154 can generate a signal to one or more motors or actuators of the motorized transport system 154, to cause a motorized locomotion response away from the source of the collision. In some implementations, the MR system 100 may be transported by having personnel move the system to desired locations using manual force. In such implementations, the motorized transport system 154 may include wheels, bearings, or other mechanical devices that enable the MR system 100 to be repositioned using manual force.

[0048] FIG. 2A illustrates a flow suppression segment 200A (used interchangeably with flow suppression sequence, flow suppression sequence block, and flow suppression block) that may be implemented in various MR sequences of different types. The flow suppression segment 200A can be used in (e.g., added to, included in) fluid-attenuated inversion recovery. The flow suppression segment 200 A can be added to an MRI sequence. For example, the flow suppression segment 200 A can be added to an FSE-based sequence (e.g., by or via controller 106, and / or one or more other components depicted in FIG. 1). The flow suppression segment 200A can be used to reduce or remove fluid flow (e.g., flowing fluid, flowing blood) in MRI images generated based on an MR sequence that includes the flow suppression segment 200A. The flow suppression segment 200A can be used for suppressing signal resulting from fluid flow so as to deemphasize or eliminate the depiction of fluid flow in corresponding MR images. The fluid flow can include a flow of blood in a region of interest (ROI) of a subject (e.g., patient 102) being scanned. For example, the region of interest can include the brain of the subject, and blood flow in the brain can be suppressed.

[0049] The flow suppression segment 200A can include one or more excitation blocks 205 (e.g., excitation pulses). The excitation block 205 can occur at a time, t = ti. For example, the excitation block 205 can start at t = ti and end after t = ti. The excitation block 205 can end before t = t2. t = t2 can occur after t = ti. The excitation pulse can include an RF pulse. The excitation pulse can include a 90° pulse. The excitation pulse can have a tipping angle of 90°. In the MR system 100, the main magnetic field can be oriented along the z-axis. The excitation pulse can rotate the spins (e.g., spins of protons in tissue). The excitation pulse can reorient the spins from the z-axis to the xy-plane (e.g., transverse plane). The excitation pulse can tip the spins into the transverse plane. The excitation pulse can be made insensitive to artifacts from Bo and Bi inhomogeneities (e.g., eddy currents) by, for example, designing RF pulses such as composites pulses, adiabatic pulses, or frequency swept chirp pulses.

[0050] The flow suppression segment 200A can include one or more gradient blocks 210A. For example, the gradient block 210A can include a first gradient block. The first gradient block can include gradients (e.g., gradient pulses) in a plurality of axes. The plurality of axes can include an x-axis, a y-axis, and / or a z-axis. The gradient blocks 210A can be performed in all three axes to remove flow in all three dimensions. The first gradient block can include a first gradient pulse along the y-axis, a first gradient pulse along the x-axis, and / or a first gradient pulse along the z-axis. The first gradient pulse along the y-axis can include a magnetic field along the y-axis. The first gradient pulse along the x-axis can include a magnetic field along the x-axis. The first gradient pulse along the z-axis can include a magnetic field along the z-axis. The gradient pulse can impart a phase to the spins along their respective axes. For example, a gradient pulse along the y-axis (e.g., y-gradient) can impart a phase to the spins along the y-axis. The y-gradient can give the spins a spatially dependent phase along the y-axis. A gradient pulse along the x-axis (e.g., x-gradient) can impart a phase to the spins along the x-axis. The x- gradient can give the spins a spatially dependent phase along the x-axis. A gradient pulse along the z-axis (e.g., z-gradient) can impart a phase to the spins along the z-axis. The z-gradient can give the spins a spatially dependent phase along the z-axis. It is noted that the gradient pulses can have a different ordering, such that, for example, the y-gradient may occur after the x- and z-gradients or between the x- and z-gradients, the x-gradient may occur before the y- and z- gradients or after the y- and z-gradients, and the z-gradient may occur before the x- and y- gradients or between the x- and y-gradients.

[0051] The first gradient pulse along the y-axis can have the same shape or a different shape as the first gradient pulse along the x-axis. The first gradient pulse along the x-axis can have the same shape or a different shape as the first gradient pulse along the z-axis. The firstgradient pulse along the z-axis can have the same shape or a different shape as the first gradient pulse along the y-axis. The first gradient pulse along the y-axis can have a trapezoidal shape. The first gradient pulse along the x-axis can have a trapezoidal shape. The first gradient pulse along the z-axis can have a trapezoidal shape. The first gradient pulse along the x-axis, the first gradient pulse along the y-axis, and the first gradient pulse along the z-axis can be determined by the gradient hardware system. The first gradient pulse along the x-axis, the first gradient pulse along the y-axis, and the first gradient pulse along the z-axis can have a high amplitude gradient with shortest time to avoid signal loss.

[0052] The amplitude (e.g., magnitude) of the first gradient pulse along the y-axis can be the same as or different from the amplitude of the first gradient pulse along the x-axis. The amplitude of the first gradient pulse along the x-axis can be the same as or different from the amplitude of the first gradient pulse along the z-axis. The amplitude of the first gradient pulse along the z-axis can be the same as or different from the amplitude of the first gradient pulse along the y-axis. The magnitude of the pulse can be large enough to sensitize the sequence to a target velocity of flow. For example, the magnitude of the pulse can sensitize the sequence to blood flowing in a range of 0.5 to 1.5 mm / s. The magnitude of the pulse can sensitize the sequence to blood flowing in a range of 700 to 800 mL / min. The magnitude of the pulse can sensitize the sequence to cerebral blood flow. The first gradient pulse along the x-axis, the first gradient pulse along the y-axis, and the first gradient pulse along the z-axis can have a high amplitude gradient.

[0053] The first gradient pulse along the y-axis can have a duration less than a difference in time between t3 and t2. The duration of the first gradient pulse along the y-axis can be the same as or different from the duration of the first gradient pulse along the x-axis. The first gradient pulse along the x-axis can have a duration less than a difference in time between t4 and t3. The duration of the first gradient pulse along the x-axis can be the same as or different from the duration of the first gradient pulse along the z-axis. The first gradient pulse along the z-axis can have a duration less than a difference in time between ts and U. The duration of the first gradient pulse along the z-axis can be the same as or different from the duration of the first gradient pulse along the y-axis. The first gradient pulse along the x-axis, the first gradient pulse along the y-axis, and the first gradient pulse along the z-axis can have a short time.

[0054] The gradient pulse along the y-axis can occur at a time, t = t2. For example, the first gradient pulse along the y-axis can start at t = t2 and end after t = t2. The first gradient pulse along the y-axis can end before t = t3. t = t3 can occur after t = t2. The gradient pulse along the x- axis can occur at a time, t = t3. For example, the first gradient pulse along the x-axis can start at t= t3 and end after t = t3. The first gradient pulse along the x-axis can end before t = U. t = U can occur after t = t3. The gradient pulse along the z-axis can occur at a time, t = U. For example, the first gradient pulse along the z-axis can start at t = U and end after t = U. The first gradient pulse along the z-axis can end before t = ts. t = ts can occur after t = U. The gradient pulses along the y-axis, x-axis, and z-axis can occur in any order. For example, the first gradient pulse along the y-axis can occur before the first gradient pulse along the x-axis. The first gradient pulse along the y-axis can occur before the first gradient pulse along the z-axis. The first gradient pulse along the x-axis can occur before the first gradient pulse along the z-axis. The first gradient pulse along the x-axis can occur before the first gradient pulse along the y-axis. The first gradient pulse along the z-axis can occur before the first gradient pulse along the x-axis. The first gradient pulse along the z-axis can occur before the first gradient pulse along the y-axis.

[0055] The first gradient pulse along the y-axis can occur after the first gradient pulse along the x-axis. The first gradient pulse along the y-axis can occur after the first gradient pulse along the z-axis. The first gradient pulse along the x-axis can occur after the first gradient pulse along the z-axis. The first gradient pulse along the x-axis can occur after the first gradient pulse along the y-axis. The first gradient pulse along the z-axis can occur after the first gradient pulse along the x-axis. The first gradient pulse along the z-axis can occur after the first gradient pulse along the y-axis. The first gradient block can start at t = t2 and end after t = U. The first gradient block can end before t = ts.

[0056] The first gradient pulse along the y-axis can occur after the excitation block 205. The first gradient pulse along the x-axis can occur after the excitation block 205. The first gradient pulse along the z-axis can occur after the excitation block 205. The excitation block 205 can occur before the first gradient pulse along the y-axis. The excitation block 205 can occur before the first gradient pulse along the x-axis. The excitation block 205 can occur before the first gradient pulse along the z-axis.

[0057] The flow suppression segment 200A can include one or more refocusing blocks 215A (e.g., refocusing pulses). The refocusing block 215A can occur at a time, t = ts. For example, the refocusing block 215A can start at t = ts and end after t = ts. The refocusing pulse can include an RF pulse. The refocusing pulse can include a 180° pulse. The refocusing pulse can reorient the spins by 180°. For example, the spins can start in the xy-plane before the refocusing pulse and be oriented in the opposite direction in the xy-plane after the refocusing pulse. The spins can be oriented in the opposite direction after the refocusing pulse. The refocusing pulse can be made insensitive to artifacts from Bo and Bi inhomogeneities.

[0058] The refocusing block 215 A can occur after the first gradient pulse along the y- axis. The refocusing block 215 A can occur after the first gradient pulse along the x-axis. The refocusing block 215 A can occur after the first gradient pulse along the z-axis. The first gradient pulse along the y-axis can occur before the refocusing block 215 A. The first gradient pulse along the x-axis can occur before the refocusing block 215 A. The first gradient pulse along the z-axis can occur before the refocusing block 215 A.

[0059] The gradient block 210A can include a second gradient block. The second gradient block can occur after the first gradient block. The first gradient block can occur before the second gradient block. The first gradient block and the second gradient block can be the same or different. The first gradient block and the second gradient block can be different if the amount of phase from the first gradient block and from the second gradient block are the same. The second gradient block can include gradients (e.g., gradient pulses) in a plurality of axes. The plurality of axes can include an x-axis, a y-axis, and / or a z-axis. The second gradient block can include a second gradient pulse along the y-axis, a second gradient pulse along the x-axis, and / or a second gradient pulse along the z-axis. The second gradient pulse along the y-axis can include a magnetic field along the y-axis. The second gradient pulse along the x-axis can include a magnetic field along the x-axis. The second gradient pulse along the z-axis can include a magnetic field along the z-axis. The second gradient pulse along the y-axis can allow for detection of which of the spins along the y-axis have moved or remained stationary. The second gradient pulse along the x-axis can allow for detection of which of the spins along the x-axis have moved or remained stationary. The second gradient pulse along the z-axis can allow for detection of which of the spins along the z-axis have moved or remained stationary.

[0060] The second gradient pulse along the y-axis can have the same shape or a different shape as the second gradient pulse along the x-axis. The second gradient pulse along the x-axis can have the same shape or a different shape as the second gradient pulse along the z-axis. The second gradient pulse along the z-axis can have the same shape or a different shape as the second gradient pulse along the y-axis. The second gradient pulse along the y-axis can have a trapezoidal shape. The second gradient pulse along the x-axis can have a trapezoidal shape. The second gradient pulse along the z-axis can have a trapezoidal shape. The second gradient pulse along the y-axis can have the same shape or a different shape as the first gradient pulse along the y-axis. The second gradient pulse along the x-axis can have the same shape or a different shape as the first gradient pulse along the x-axis. The second gradient pulse along the z-axis can have the same shape or a different shape as the first gradient pulse along the z-axis. The shape of the gradient pulse in each direction (e.g., along the x-axis, along the y-axis, and along the z-axis)can be the same in order to provide symmetry. If there are any unknown gradient errors (e.g., from the gradient system or from eddy currents), the symmetry of the gradient block 210A about the refocusing pulse 125 can cancel or reduce phase error.

[0061] The amplitude of the second gradient pulse along the y-axis can be the same as or different from the amplitude of the second gradient pulse along the x-axis. The amplitude of the second gradient pulse along the x-axis can be the same as or different from the amplitude of the second gradient pulse along the z-axis. The amplitude of the second gradient pulse along the z- axis can be the same as or different from the amplitude of the second gradient pulse along the y- axis. The magnitude of the pulse can be large enough to sensitize the sequence to a target velocity of flow. For example, the magnitude of the pulse can sensitize the sequence to blood flowing in a range of 0.5 to 1.5 mm / s. The magnitude of the pulse can sensitize the sequence to blood flowing in a range of 700 to 800 mL / min. The magnitude of the pulse can sensitize the sequence to cerebral blood flow.

[0062] The second gradient pulse along the y-axis can have a duration less than a difference in time between t? and te. The duration of the second gradient pulse along the y-axis can be the same as or different from the duration of the second gradient pulse along the x-axis. The second gradient pulse along the x-axis can have a duration less than a difference in time between ts and t7. The duration of the second gradient pulse along the x-axis can be the same as or different from the duration of the second gradient pulse along the z-axis. The second gradient pulse along the z-axis can have a duration less than a difference in time between t9 and ts. The duration of the second gradient pulse along the z-axis can be the same as or different from the duration of the second gradient pulse along the y-axis.

[0063] The amount of phase apportioned to the first gradient pulse along the y-axis and the second gradient pulse along the y-axis can be the same. The amount of phase apportioned to the first gradient pulse along the x-axis and the second gradient pulse along the x-axis can be the same. The amount of phase apportioned to the first gradient pulse along the z-axis and the second gradient pulse along the z-axis can be the same.

[0064] A time (e.g., a non-zero time) can elapse between the first gradient pulse and the second gradient pulse. In some embodiments, the time can be zero. The time can be in a range of 10 ms to 30 ms. A shorter time can avoid signal loss during the flow suppression block. A time can elapse between the first gradient pulse along the y-axis and the second gradient pulse along the y-axis. The time between the end of the first gradient pulse along the y-axis and the start of the second gradient pulse along the y-axis can be greater than zero. During the time between the end of the first gradient pulse along the y-axis and the start of the second gradient pulse alongthe y-axis, the spins along the y-axis can acquire phase. A longer time between the first gradient pulse along the y-axis and the second gradient pulse along the y-axis can allow the spins along the y-axis to acquire more phase. A time can elapse between the first gradient pulse along the x- axis and the second gradient pulse along the x-axis. The time between the end of the first gradient pulse along the x-axis and the start of the second gradient pulse along the x-axis can be greater than zero. During the time between the end of the first gradient pulse along the x-axis and the start of the second gradient pulse along the x-axis, the spins along the x-axis can acquire phase. A longer time between the first gradient pulse along the x-axis and the second gradient pulse along the x-axis can allow the spins along the x-axis to acquire more phase. A time can elapse between the first gradient pulse along the z-axis and the second gradient pulse along the z-axis. The time between the end of the first gradient pulse along the z-axis and the start of the second gradient pulse along the z-axis can be greater than zero. During the time between the end of the first gradient pulse along the z-axis and the start of the second gradient pulse along the z- axis, the spins along the z-axis can acquire phase. A longer time between the first gradient pulse along the z-axis and the second gradient pulse along the z-axis can allow the spins along the z- axis to acquire more phase.

[0065] The gradient pulse along the y-axis can occur at a time, t = te. For example, the second gradient pulse along the y-axis can start at t = te and end after t = te. The second gradient pulse along the y-axis can end before t = t7. t = t? can occur after t = te. The gradient pulse along the x-axis can occur at a time, t = t7. For example, the second gradient pulse along the x-axis can start at t = t? and end after t = t7. The second gradient pulse along the x-axis can end before t = ts. t = ts can occur after t = t7. The gradient pulse along the z-axis can occur at a time, t = ts. For example, the second gradient pulse along the z-axis can start at t = ts and end after t = ts. The second gradient pulse along the z-axis can end before t = t9. t = t9 can occur after t = ts. The gradient pulses along the y-axis, x-axis, and z-axis can occur in any order. For example, the second gradient pulse along the y-axis can occur before the second gradient pulse along the x- axis. The second gradient pulse along the y-axis can occur before the second gradient pulse along the z-axis. The second gradient pulse along the x-axis can occur before the second gradient pulse along the z-axis. The second gradient pulse along the x-axis can occur before the second gradient pulse along the y-axis. The second gradient pulse along the z-axis can occur before the second gradient pulse along the x-axis. The second gradient pulse along the z-axis can occur before the second gradient pulse along the y-axis.

[0066] The second gradient pulse along the y-axis can occur after the second gradient pulse along the x-axis. The second gradient pulse along the y-axis can occur after the secondgradient pulse along the z-axis. The second gradient pulse along the x-axis can occur after the second gradient pulse along the z-axis. The second gradient pulse along the x-axis can occur after the second gradient pulse along the y-axis. The second gradient pulse along the z-axis can occur after the second gradient pulse along the x-axis. The second gradient pulse along the z- axis can occur after the second gradient pulse along the y-axis. The second gradient block can start at t = te and end after t = ts. The second gradient block can end before t = t9.

[0067] The second gradient pulse along the y-axis can occur after the refocusing block 215 A. The second gradient pulse along the x-axis can occur after the refocusing block 215 A. The second gradient pulse along the z-axis can occur after the refocusing block 215 A. The refocusing block 215 A can occur before the second gradient pulse along the y-axis. The refocusing block 215 A can occur before the second gradient pulse along the x-axis. The refocusing block 215A can occur before the second gradient pulse along the z-axis.

[0068] The second gradient pulse along the y-axis can occur after the first gradient pulse along the y-axis. The second gradient pulse along the y-axis can occur after the first gradient pulse along the x-axis. The second gradient pulse along the y-axis can occur after the first gradient pulse along the z-axis. The second gradient pulse along the x-axis can occur after the first gradient pulse along the x-axis. The second gradient pulse along the x-axis can occur after the first gradient pulse along the y-axis. The second gradient pulse along the x-axis can occur after the first gradient pulse along the z-axis. The second gradient pulse along the z-axis can occur after the first gradient pulse along the z-axis. The second gradient pulse along the z-axis can occur after the first gradient pulse along the y-axis. The second gradient pulse along the z- axis can occur after the first gradient pulse along the x-axis.

[0069] The flow suppression segment 200A can include one or more storage blocks 220A (e.g., storage pulses). In some embodiments, the flow suppression segment 200A does not include the storage block 220A. The storage block 220A can occur at a time, t = t9. For example, the storage block 220A can start at t = t9 and end after t = t9. The storage pulse can include an RF pulse. The storage pulse can increase the SNR of the signal obtained by the MR system 100. For example, the storage block can help recover signal loss from a short Tl. The storage block 220A can follow the second gradient block. For example, the storage block 220A can occur after the second gradient block.

[0070] The storage block 220A can occur after the second gradient pulse along the y- axis. The storage block 220A can occur after the second gradient pulse along the x-axis. The storage block 220A can occur after the second gradient pulse along the z-axis. The second gradient pulse along the y-axis can occur before the storage block 220A. The second gradientpulse along the x-axis can occur before the storage block 220A. The second gradient pulse along the z-axis can occur before the storage block 220A.

[0071] In MRI, the b-value can measure the degree of diffusion weighting applied. The b-value can be defined as the amount of diffusion sensitization in a diffusion-weighted sequence. The b-value can be used for MRI with diffusion-weighted imaging. The flow suppression segment 200A can have a b-value in a range of 1.5 to 2 s / mm2. The flow suppression segment 200A can have a b-value of less than 10 s / mm2. The flow suppression segment 200 A can be made insensitive to artifacts from Bo and Bi inhomogeneities. The flow suppression segment 200 A can be made insensitive to Bo and Bi inhomogeneities to improve performance in systems with imperfect gradient control or large Bo and Bi inhomogeneities.

[0072] FIG. 2B illustrates a flow suppression segment 200B, which can be used in the same or similar manner and for the same or similar purpose(s) as flow suppression segment 200A. The discussion of flow suppression segment 200A and its components thus can also be equally applicable to flow suppression segment 200B. Similar to the flow suppression segment 200A, the flow suppression segment 200B includes one or more excitation blocks 205B (e.g., excitation pulses), gradient blocks 210B, refocusing blocks 215B (e.g., refocusing pulses), storage blocks 220B (e.g., storage pulses), which are analogous to the one or more excitation blocks 205 A, gradient blocks 210A, refocusing blocks 215 A, and storage blocks 220 A, respectively. In various embodiments, flow suppression segment 200B also includes one or more eddy-preparation gradient blocks 21 OP incorporated therein, prior to the one or more excitations blocks 205B. In example embodiments, flow suppression segment 200 A includes zero eddy -preparation gradient blocks 21 OP, whereas flow suppression segment 200B includes any integer number of eddy-preparation gradient blocks 21 OP (one, two, three, four, five, six, seven, etc.). In example embodiments, flow suppression segment 200B is otherwise effectively identical to flow suppression segment 200A, except for the addition of a “preparation stage” or “preparation phase” that includes one or more eddy-preparation gradient blocks 21 OP.

[0073] Example embodiments of the MRI systems disclosed herein have residual eddy currents, which can behave as gradients that decay over time. In some cases, without eddypreparation blocks 21 OP, a time dependent gradient may cause the MRI system to decrease intensities in the image. The preparation stage may allow the time dependent part to “settle down” by gradually decaying towards zero. Once settled down, the actual imaging can proceed without, or with decreased, time variant effect. In example embodiments, image quality improves because of the pulses in the preparation stage.

[0074] The number of eddy-preparation blocks 21 OP that is implemented can be determined empirically. For example, if adding one eddy-preparation block 210P does not have a desired effect on a quality of an image from the MRI system, then zero (0) eddy-preparation blocks 21 OP may be added, as with flow suppression segment 200 A depicted in FIG. 2 A. Similarly: if adding one eddy-preparation block 21 OP has a desired effect on a quality of an image from the MRI system, but adding two eddy-preparation blocks 21 OP has no additional desired effect, then one (1) eddy-preparation block 21 OP may be added; if adding two eddypreparation blocks 21 OP has a desired effect on a quality of an image from the MRI system, but adding three eddy-preparation blocks 21 OP has no further desired effect, then two (2) eddypreparation blocks 21 OP may be added; and so on. Thus, in example embodiments, eddypreparation blocks 21 OP may be added until adding additional eddy-preparation blocks 21 OP does not, for example, significantly improve image quality or have another desired effect. Because these eddy currents have time dependence, at some point a steady state will be reached and there will be no time-dependent gradients to be added by adding more pulses through one or more additional eddy -preparation blocks 21 OP.

[0075] FIG. 3 illustrates an example MRI sequence 300. The MRI sequence 300 can include an inversion-recovery fast spin echo sequence with a flow suppression block. The MRI sequence 300 can include a fluid-attenuated inversion recovery sequence. The timing parameters of the sequence elements can be configured (e.g., optimized) for flow suppression and target signal contrasts. For example, the timing parameters can be optimized by running one or more compile time simulations. Inversion time from fluid-attenuated inversion recovery can be optimized when the sequence is compiled to ensure that the fluid is nulled while keeping the target echo time for the target T2 contrast.

[0076] The MRI sequence 300 can include one or more main segments 305 (e.g., main segment of the MRI sequence). The MRI sequence 300 can include a plurality of main segments 305. The main segment 305 can include a spin echo block. The spin echo block can include a fast spin echo. The spin echo block can include a signal decay period. The timing parameters of the spin echo block can be configured (e.g., optimized) for blood flow suppression. The timing parameters of the spin echo block can be configured for target signal contrasts. The spin echo block can include an inversion-recovery fast spin echo (FSE), a diffusion-prepared turbo spin echo (dprep-TSE), or a diffusion-prepared FSE. The spin echo block can include the excitation block 205 A. The spin echo block can include one or more refocusing blocks 215 A. The spin echo block can include the storage block 220A.

[0077] The MRI sequence 300 can include a recovery period. The MRI sequence 300 can include an inversion block 310. The MRI sequence 300 can include the flow suppression segment 200. For example, the flow suppression segment 200 can be performed during the recovery period. The recovery period timing parameter can be optimized at compile time using MR physics simulations. The flow suppression segment 200 can be modular. The flow suppression segment 200 can be added to the MRI sequence 300. For example, the flow suppression segment 200 can be added to an FSE-based sequence. The flow suppression segment 200 can occur after the spin echo block. The flow suppression segment 200 can occur before the spin echo block. The inversion block 310 can occur between a first main segment 305 and a first flow suppression segment 200.

[0078] The MRI sequence 300 can include a delay time, di (e.g., delay parameter, timing delay parameter). The delay time can range from, for example, 0 to 25 ms. The delay time can be the same order of magnitude as the duration of the flow suppression segment 200. The delay time can increase the SNR of the signal obtained by the MR system 100. The delay time can be configured (e.g., optimized) for blood flow suppression. The delay time can be configured for minimal signal loss for target (e.g., subject) tissues for which signal is desired. The delay time can be configured for target signal contrasts. The flow suppression segment 200 can precede the main segment 305 in the MRI sequence 300. For example, the flow suppression segment 200 can precede the main segment 305 by the delay time. The main segment 305 can precede the flow suppression segment 200 in the MRI sequence 300. Each of the plurality of main segments 305 can be preceded by one or more flow suppression segments 200. The flow suppression segment 200 can succeed the main segment 305 in the MRI sequence 300. The ratio of the number of flow suppression blocks 200 to the number of main segments 305 can be 1 : 1. The number of flow suppression blocks 200 can be greater than the number of the number of main segments 305.

[0079] The MRI sequence 300 can include a first pair of main segments 305 and a second pair of main segments 305. The MRI sequence 300 can be generated such that a first delay time between the first pair of main segments 305 differs from a second delay time between the second pair of main segments 305. The MRI sequence 300 can have variable delay times. The MRI sequence timings can depend on the sequence contrast, gradient system, and / or hardware. The MRI sequence 300 can be generated such that the first delay time between the first pair of main segments 305 is the same as the second delay time between the second pair of main segments 305. The MRI sequence 300 can be generated such that the first delay time between the first pair of main segments 305 is different from (greater or smaller than) the seconddelay time between the second pair of main segments 305. The first delay time and the second delay time can be timing parameters that are configured for flow suppression and / or target signal contrast (e.g., using MR physics simulations).

[0080] FIG. 4 illustrates a table 400 of simulated signal levels. The simulated signal levels are organized by tissue type. The depicted tissue types include fat, gray matter (GM), white matter (WM), cerebrospinal fluid (CSF), pathology, stationary blood, flowing blood, and muscle. The table 400 shows signal simulations for FLAIR without flow suppression (middle column) compared with FLAIR with flow suppression (right column). The blood flow suppressed FLAIR sequence can be optimized to keep all signal levels the same for all signals not resulting from flowing blood. With the added flow suppression module, the image can look the same apart from the nulled flowing spins. If the added flow suppression module is not taken into account, the image contrast and / or signal levels can be altered. Stationary blood and flowing blood in the non-flow compensated FLAIR sequence can have the same signal level (e.g., for blood imaging). For the flow-suppressed FSE sequence, the spin echo block sequence timings, flow suppression block, and delay time can be optimized to suppress signals due to flowing blood and maintain other tissue signal levels the same as they would be without the flow suppression. The signal simulations can be performed with various sequence timings and tissue relaxation parameters. The signal simulations can be performed in a system that has a magnetic field strength of, for example, 64 mT or other field strengths discussed above. As shown in the table 400, for a sequence without flow suppression, stationary blood and flowing blood can have signals that are discernable from each other and from other tissues on the corresponding MRI image. For a sequence with flow suppression, stationary blood can have a signal that is discernable from other tissues on the corresponding MRI image, but flowing blood can have a signal that is not discernable from other tissues and / or from stationary blood on the corresponding MRI image.

[0081] FIG. 5 illustrates images of non-flow suppressed FLAIR and flow-suppressed FLAIR. Image 500A illustrates non-flow suppressed FLAIR. Image 500B illustrates flow- suppressed FLAIR. The images show a phantom with Tl, T2, and diffusion contrast vials. Since there is no fluid flow in the vials, the image 500A and the image 500B appear the same, as would be expected. This helps illustrate that embodiments of the disclosed flow suppression approach do not negatively impact portions of images that do not have fluid flow, helping maintain the integrity of the imaging process.

[0082] FIG. 6 illustrates images of non-flow suppressed FLAIR and flow-suppressed FLAIR. Image 600A illustrates non-flow suppressed FLAIR. Image 600B illustrates flow-suppressed FLAIR. The images show MRI scans of a patient. The blood flowing in the veins are visible in the image 600A as white regions (shown in dashed circles). These regions (shown in dashed circles) are not visible in the flow-suppressed FLAIR MRI scans of the image 600B. This helps illustrate that embodiments of the disclosed flow suppression approach suppress the visibility of fluid flow in MR images.

[0083] FIG. 7 illustrates a flowchart of an example method for flow suppression. The method 700 may be executed using any suitable computing system (e.g., the controller 106, the computing device 104 of FIG. 1, the computing system 800 of FIG. 8, etc.) of an MR system (e.g., the MR system 100). It may be appreciated that certain steps of the method 700 may be executed in parallel (e.g., concurrently) or sequentially, while still achieving useful results.

[0084] The method 700 may include block 705, in which the MR system (e.g., the MR system 100) determines an MRI sequence. The MRI system can determine the MRI sequence for one or more MRI scans. One or more of the MRI sequences can include one or more flow suppression segments. The flow suppression segments can suppress signal from fluid flow in the one or more MRI scans. The fluid flow can include a flow of blood in a region of interest of a subject being scanned. One or more flow suppression segments can precede or follow one or more main segments in the MRI sequences. Each flow suppression segment may precede or follow the main segment by a delay time. The one or more main segments of the MRI sequence can include, for example, a spin echo block. The spin echo block can include a fast spin echo. The spin echo block can include an inversion-recovery fast spin echo, a diffusion-prepared turbo spin echo, or a diffusion-prepared FSE.

[0085] Each of the one or more flow suppression segments can include elements discussed above, such as any suitable combination of one or more excitation blocks, one or more gradient blocks, one or more refocusing blocks, one or more refocusing blocks, and one or more storage blocks. A flow suppression segment can include a first gradient block with gradients in a plurality of axes, and a second gradient block with gradients in the same or different plurality of axes. The plurality of axes can include an x-axis, a y-axis, and a z-axis. One or more refocusing blocks may be positioned between pairs of gradient blocks, and one or more storage blocks can follow one or more gradient blocks.

[0086] The MRI sequence can include a plurality of main segments. Each of the plurality of main segments can be preceded by one or more flow suppression segments. The MRI sequence can be generated such that a first delay time between a first pair of main segments differs from a second delay time between a second pair of main segments. The first delay time and the second delay time can be timing parameters that are configured for flow suppression andtarget signal contrast. The MRI sequence can include an inversion block between a first main segment and a first flow suppression segment.

[0087] The method may include block 710, in which the MRI system performs the one or more MRI scans. The MRI system can perform the one or more MRI scans using the MRI sequence to obtain one or more MR images. The MRI sequence can be a fluid-attenuated inversion recovery sequence. The MRI system can be a low-field MRI system, such as one having a field strength that is no greater than 200 mT. Following the one or more scans at block 710, method may end, or may return to block 705 for determination of one or more additional MRI sequences.

[0088] FIG. 8 illustrates a component diagram of an example computing system suitable for use in the various implementations described herein, according to an example implementation. In a non-limiting example, the computing system 800 may implement a computing device 104 or controller 106 of FIG. 1, or various other example systems and devices described in the present disclosure.

[0089] The computing system 800 includes a bus 802 or other communication component for communicating information and a processor 804 coupled to the bus 802 for processing information. The computing system 800 also includes main memory 806, such as a RAM or other dynamic storage device, coupled to the bus 802 for storing information, and instructions to be executed by the processor 804. Main memory 806 may also be used for storing position information, temporary variables, or other intermediate information during execution of instructions by the processor 804. The computing system 800 may further include a ROM 808 or other static storage device coupled to the bus 802 for storing static information and instructions for the processor 804. A storage device 810, such as a solid-state device, magnetic disk, or optical disk, is coupled to the bus 802 for persistently storing information and instructions.

[0090] The computing system 800 may be coupled via the bus 802 to a display 814, such as a liquid crystal display, or active matrix display, for displaying information to a user. An input device 812, such as a keyboard including alphanumeric and other keys, may be coupled to the bus 802 for communicating information, and command selections to the processor 804. In another implementation, the input device 812 has a touch screen display. The input device 812 may include any type of biometric sensor, or a cursor control, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to the processor 804 and for controlling cursor movement on the display 814.

[0091] In some implementations, the computing system 800 may include a communications adapter 816, such as a networking adapter. Communications adapter 816 maybe coupled to bus 802 and may be configured to enable communications with a computing or communications network or other computing systems. In various illustrative implementations, any type of networking configuration may be achieved using communications adapter 816, such as wired (e.g., via Ethernet), wireless (e.g., via Wi-Fi, Bluetooth), satellite (e.g., via GPS) preconfigured, ad-hoc, LAN, WAN, and the like.

[0092] According to various implementations, the processes of the illustrative implementations that are described herein may be achieved by the computing system 800 in response to the processor 804 executing an implementation of instructions contained in main memory 806. Such instructions may be read into main memory 806 from another computer- readable medium, such as the storage device 810. Execution of the implementation of instructions contained in main memory 806 causes the computing system 800 to perform the illustrative processes described herein. One or more processors in a multi-processing implementation may also be employed to execute the instructions contained in main memory 806. In alternative implementations, hard-wired circuitry may be used in place of or in combination with software instructions to implement illustrative implementations. Thus, implementations are not limited to any specific combination of hardware circuitry and software.

[0093] Various example implementations and embodiments include, without limitation:

[0094] Embodiment AA: A method comprising determining, for one or more magnetic resonance imaging (MRI) scans, an MRI sequence comprising a flow suppression segment to suppress signal from fluid flow in the one or more MRI scans, the flow suppression segment comprising: an excitation block; a first gradient block comprising gradients in a plurality of axes; a refocusing block; and a second gradient block comprising gradients in the plurality of axes; and performing, via an MRI system, the one or more MRI scans using the MRI sequence to obtain one or more MR images.

[0095] Embodiment AB: The method of any of Embodiments AA or AC - AU, wherein the flow suppression segment precedes a main segment in the MRI sequence.

[0096] Embodiment AC: The method of any of Embodiments AA, AB, or AD - AU, wherein the flow suppression segment succeeds a main segment in the MRI sequence.

[0097] Embodiment AD: The method of any of Embodiments AA - AC or AE - AU, wherein the main segment of the MRI sequence comprises a spin echo block.

[0098] Embodiment AE: The method of any of Embodiments AA - AD or AF - AU, wherein the spin echo block comprises a fast spin echo (FSE).

[0099] Embodiment AF: The method of any of Embodiments AA - AE or AG - AU, wherein the spin echo block comprises an inversion-recovery fast spin echo (FSE), a diffusion- prepared turbo spin echo (dprep-TSE), or a diffusion-prepared FSE.

[0100] Embodiment AG: The method of any of Embodiments AA - AF or AH - AU, wherein the flow suppression segment precedes the main segment by a delay time.

[0101] Embodiment AH: The method of any of Embodiments AB - AG or Al - AU, wherein the MRI sequence comprises a plurality of main segments, each of the plurality of main segments being preceded by one or more flow suppression segments.

[0102] Embodiment Al: The method of any of Embodiments AA - AH or AJ - AU, wherein the MRI sequence is generated such that a first delay time between a first pair of main segments differs from a second delay time between a second pair of main segments.

[0103] Embodiment AJ: The method of any of Embodiments AA - Al or AK - AU, wherein the first delay time and the second delay time are timing parameters that are configured for flow suppression and target signal contrast.

[0104] Embodiment AK: The method of any of Embodiments AA - AJ or AL- AU, wherein the MRI sequence further comprises an inversion block between a first main segment and a first flow suppression segment.

[0105] Embodiment AL: The method of any of Embodiments AA - AK or AM - AU, wherein the flow suppression segment further comprises a storage block following the second gradient block.

[0106] Embodiment AM: The method of any of Embodiments AA - AL or AN - AU, wherein the plurality of axes comprises an x-axis, a y-axis, and a z-axis.

[0107] Embodiment AN: The method of any of Embodiments AA - AM or AO - AU, wherein the MRI sequence is a fluid-attenuated inversion recovery (FLAIR) sequence.

[0108] Embodiment AO: The method of any of Embodiments AA - AN or AP - AU, wherein the fluid flow is a flow of blood in a region of interest of a subject being scanned.

[0109] Embodiment AP: The method of any of Embodiments AA - AO or AQ - AU, wherein the MRI system has a field strength no greater than 0.2 T.

[0110] Embodiment AQ: The method of any of Embodiments AA - AP or AR - AU, wherein the MRI system has a field strength no greater than 0.1 T.[OHl] Embodiment AR: The method of any of Embodiments AA - AQ, AS - AU, wherein the MRI system has a field strength no greater than 200 ml.

[0112] Embodiment AS: The method of any of Embodiments AA - AR, AT, or AU, further comprising a preparation stage prior to a first gradient block.

[0113] Embodiment AT: The method of any of Embodiments AA - AS or AU, further comprising one or more eddy-preparation gradient blocks.

[0114] Embodiment AU: The method of any of Embodiments AA - AT, further comprising determining a number of eddy-preparation gradient blocks or eddy-preparation pulses to use.

[0115] Embodiment BA: A magnetic resonance imaging (MRI) system comprising: at least one radio frequency (RF) coil; and at least one controller configured to: determine, for one or more MRI scans, an MRI sequence comprising a flow suppression segment to suppress signal from fluid flow in the one or more MRI scans, the flow suppression segment comprising: an excitation block; a first gradient block comprising gradients in a plurality of axes; a refocusing block; and a second gradient block comprising gradients in the plurality of axes; and control the at least one RF coil to perform, using the MRI sequence, the one or more MRI scans to obtain one or more MR images.

[0116] Embodiment BB: The system of any of Embodiments BA or BC - BO, wherein the flow suppression segment precedes or succeeds a main segment in the MRI sequence.

[0117] Embodiment BC: The system of any of Embodiments BA, BB, or BD - BO, wherein the main segment of the MRI sequence comprises a spin echo block.

[0118] Embodiment BD: The system of any of Embodiments BA - BC or BE - BO, wherein the spin echo block comprises a fast spin echo.

[0119] Embodiment BE: The system of any of Embodiments BA - BD or BF - BO, wherein the spin echo block comprises an inversion-recovery fast spin echo, a diffusion- prepared turbo spin echo, or a diffusion-prepared FSE.

[0120] Embodiment BF : The system of any of Embodiments BA - BE or BG - BO, wherein the flow suppression segment precedes the main segment by a delay time.

[0121] Embodiment BG: The system of any of Embodiments BA - BF or BH - BO, wherein the MRI sequence comprises a plurality of main segments, each of the plurality of main segments being preceded by one or more flow suppression segments.

[0122] Embodiment BH: The system of any of Embodiments BA - BG or BI - BO, wherein the MRI sequence is generated such that a first delay time between a first pair of main segments differs from a second delay time between a second pair of main segments.

[0123] Embodiment BI: The system of any of Embodiments BA - BH or BI - BO, wherein the first delay time and the second delay time are timing parameters that are configured for flow suppression and target signal contrast.

[0124] Embodiment BJ: The system of any of Embodiments BA - BI or BK - BO, wherein the MRI sequence further comprises an inversion block between a first main segment and a first flow suppression segment.

[0125] Embodiment BK: The system of any of Embodiments BA - BJ or BL - BO, wherein the flow suppression segment further comprises a storage block following the second gradient block.

[0126] Embodiment BL: The system of any of Embodiments BA - BK or BM - BO, wherein the plurality of axes comprises an x-axis, a y-axis, and a z-axis.

[0127] Embodiment BM: The system of any of Embodiments BA - BL, BN, or BO, wherein the MRI sequence is a fluid-attenuated inversion recovery sequence.

[0128] Embodiment BN: The system of any of Embodiments BA - BM or BO, wherein the fluid flow is a flow of blood in a region of interest of a subject being scanned.

[0129] Embodiment BO: The method of any of Embodiments BA - BN, wherein the MRI system has a field strength no greater than 0.2 T.

[0130] Embodiment BP: The method of any of Embodiments BA - BO, wherein the MRI system has a field strength no greater than 0.1 T.

[0131] Embodiment BQ: The system of any of Embodiments BA - BP, wherein the system has a field strength no greater than 200 ml.

[0132] Embodiment CA: A non-transitory computer-readable storage medium comprising instructions that, when executed by one or more processors of a magnetic resonance imaging (MRI) system or a computing system, are configured to: determine, for one or more MRI scans, an MRI sequence comprising a flow suppression segment to suppress signal from fluid flow in the one or more MRI scans, the flow suppression segment comprising: an excitation block; a first gradient block comprising gradients in a plurality of axes; a refocusing block; and a second gradient block comprising gradients in the plurality of axes; and perform, via the MRI system, the one or more MRI scans using the MRI sequence to obtain one or more MR images.

[0133] Embodiment CB: The medium of any of Embodiments CA or CC - CO, wherein the flow suppression segment precedes or succeeds a main segment in the MRI sequence.

[0134] Embodiment CC: The medium of any of Embodiments CA, CB, or CD - CO, wherein the main segment of the MRI sequence comprises a spin echo block.

[0135] Embodiment CD: The medium of any of Embodiments CA - CC or CE - CO, wherein the spin echo block comprises a fast spin echo.

[0136] Embodiment CE: The medium of any of Embodiments CA - CD or CF - CO, wherein the spin echo block comprises an inversion-recovery fast spin echo, a diffusion- prepared turbo spin echo, or a diffusion-prepared FSE.

[0137] Embodiment CF : The medium of any of Embodiment CA - CE or CG - CO, wherein the flow suppression segment precedes the main segment by a delay time.

[0138] Embodiment CG: The medium of any of Embodiments CA - CF or CH - CO, wherein the MRI sequence comprises a plurality of main segments, each of the plurality of main segments being preceded by one or more flow suppression segments.

[0139] Embodiment CH: The medium of any of Embodiments CA - CG or CI - CO, wherein the MRI sequence is generated such that a first delay time between a first pair of main segments differs from a second delay time between a second pair of main segments.

[0140] Embodiment CI: The medium of any of Embodiments CA - CH or CJ - CO, wherein the first delay time and the second delay time are timing parameters that are configured for flow suppression and target signal contrast.

[0141] Embodiment CJ: The medium of any of Embodiments CA - CI or CK - CO, wherein the MRI sequence further comprises an inversion block between a first main segment and a first flow suppression segment.

[0142] Embodiment CK: The medium of any of Embodiments CA - CJ or CL - CO, wherein the flow suppression segment further comprises a storage block following the second gradient block.

[0143] Embodiment CL: The medium of any of Embodiments CA - CK or CM - CO, wherein the plurality of axes comprises an x-axis, a y-axis, and a z-axis.

[0144] Embodiment CM: The medium of any of Embodiments CA - CL CN, or CO, wherein the MRI sequence is a fluid-attenuated inversion recovery sequence.

[0145] Embodiment CN: The medium of any of Embodiments CA - CM or CO, wherein the fluid flow is a flow of blood in a region of interest of a subject being scanned.

[0146] Embodiment CO: The medium of any of Embodiments CA - CN, wherein the MRI system has a field strength no greater than 0.2 T.

[0147] Embodiment CP: The medium of any of Embodiments CA - CO, wherein the MRI system has a field strength no greater than 0.1 T.

[0148] Embodiment CQ: The medium of any of Embodiments CA - CP, wherein the MRI system has a field strength no greater than 200 ml.

[0149] Embodiment DI : A magnetic resonance imaging (MRI) system comprising one or more processors and being configured to perform any of the methods of Embodiments AA - AP.

[0150] Embodiment D2: The MRI system of Embodiment DI, wherein the MRI system comprises an MRI scanner in communication with one or more separate computing devices to transmit / exchange commands and / or outputs.

[0151] Embodiment El : A non-transitory computer-readable storage medium comprising instructions to be executed by one or more processors of one or more devices or systems to perform any of the methods of Embodiments AA - AP.

[0152] The implementations described herein have been described with reference to drawings. The drawings illustrate certain details of specific implementations that implement the systems, methods, and programs described herein. Describing the implementations with drawings should not be construed as imposing on the disclosure any limitations that may be present in the drawings.

[0153] It should be understood that no claim element herein is to be construed under the provisions of 35 U.S.C. § 112(f), unless the element is expressly recited using the phrase “means for.”

[0154] As used herein, the term “circuit” may include hardware structured to execute the functions described herein. In some implementations, each respective “circuit” may include machine-readable media for configuring the hardware to execute the functions described herein. The circuit may be embodied as one or more circuitry components including, but not limited to, processing circuitry, network interfaces, peripheral devices, input devices, output devices, sensors, etc. In some implementations, a circuit may take the form of one or more analog circuits, electronic circuits (e.g., integrated circuits (IC), discrete circuits, system on a chip (SOC) circuits), telecommunication circuits, hybrid circuits, and any other type of “circuit.” In this regard, the “circuit” may include any type of component for accomplishing or facilitating achievement of the operations described herein. In a non-limiting example, a circuit as described herein may include one or more transistors, logic gates (e.g., NAND, AND, NOR, OR, XOR, NOT, XNOR), resistors, multiplexers, registers, capacitors, inductors, diodes, wiring, and so on.

[0155] The “circuit” may also include one or more processors communicatively coupled to one or more memory or memory devices. In this regard, the one or more processors may execute instructions stored in the memory or may execute instructions otherwise accessible to the one or more processors. In some implementations, the one or more processors may be embodied in various ways. The one or more processors may be constructed in a mannersufficient to perform at least the operations described herein. In some implementations, the one or more processors may be shared by multiple circuits (e.g., circuit A and circuit B may comprise or otherwise share the same processor, which, in some example implementations, may execute instructions stored, or otherwise accessed, via different areas of memory). Alternatively or additionally, the one or more processors may be structured to perform or otherwise execute certain operations independent of one or more co-processors.

[0156] In other example implementations, two or more processors may be coupled via a bus to enable independent, parallel, pipelined, or multi -threaded instruction execution. Each processor may be implemented as one or more general-purpose processors, ASICs, FPGAs, GPUs, TPUs, digital signal processors (DSPs), or other suitable electronic data processing components structured to execute instructions provided by memory. The one or more processors may take the form of a single core processor, multi-core processor (e.g., a dual core processor, triple core processor, or quad core processor), microprocessor, etc. In some implementations, the one or more processors may be external to the apparatus, in a non-limiting example, the one or more processors may be a remote processor (e.g., a cloud-based processor). Alternatively or additionally, the one or more processors may be internal or local to the apparatus. In this regard, a given circuit or components thereof may be disposed locally (e.g., as part of a local server, a local computing system) or remotely (e.g., as part of a remote server such as a cloud based server). To that end, a “circuit” as described herein may include components that are distributed across one or more locations.

[0157] An exemplary system for implementing the overall system or portions of the implementations might include a general purpose computing devices in the form of computers, including a processing unit, a system memory, and a system bus that couples various system components including the system memory to the processing unit. Each memory device may include non-transient volatile storage media, non-volatile storage media, non-transitory storage media (e.g., one or more volatile or non-volatile memories), etc. In some implementations, the non-volatile media may take the form of ROM, flash memory (e.g., flash memory such as NAND, 3D NAND, NOR, 3D NOR), EEPROM, MRAM, magnetic storage, hard discs, optical discs, etc. In other implementations, the volatile storage media may take the form of RAM, TRAM, ZRAM, etc. Combinations of the above are also included within the scope of machine- readable media. In this regard, machine-executable instructions comprise, in a non-limiting example, instructions and data, which cause a general-purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions. Each respective memory device may be operable to maintain or otherwise storeinformation relating to the operations performed by one or more associated circuits, including processor instructions and related data (e.g., database components, object code components, script components), in accordance with the example implementations described herein.

[0158] It should also be noted that the term “input devices,” as described herein, may include any type of input device including, but not limited to, a keyboard, a keypad, a mouse, joystick, or other input devices performing a similar function. Comparatively, the term “output device,” as described herein, may include any type of output device including, but not limited to, a computer monitor, printer, facsimile machine, or other output devices performing a similar function.

[0159] It should be noted that although the diagrams herein may show a specific order and composition of method steps, it is understood that the order of these steps may differ from what is depicted. In a non-limiting example, two or more steps may be performed concurrently or with partial concurrence. Also, some method steps that are performed as discrete steps may be combined, steps being performed as a combined step may be separated into discrete steps, the sequence of certain processes may be reversed or otherwise varied, and the nature or number of discrete processes may be altered or varied. The order or sequence of any element or apparatus may be varied or substituted according to alternative implementations. Accordingly, all such modifications are intended to be included within the scope of the present disclosure as defined in the appended claims. Such variations will depend on the machine-readable media and hardware systems chosen and on designer choice. It is understood that all such variations are within the scope of the disclosure. Likewise, software and web implementations of the present disclosure could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various database searching steps, correlation steps, comparison steps, and decision steps.

[0160] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any disclosures or of what may be claimed, but rather as descriptions of features specific to particular implementations of the systems and methods described herein. Certain features that are described in this specification in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation may also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimedcombination may in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0161] In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products.

[0162] Having now described some illustrative implementations and implementations, it is apparent that the foregoing is illustrative and not limiting, having been presented by way of example. In particular, although many of the examples presented herein involve specific combinations of method acts or system elements, those acts and those elements may be combined in other ways to accomplish the same objectives. Acts, elements, and features discussed only in connection with one implementation are not intended to be excluded from a similar role in other implementations.

[0163] The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” “characterized by,” “characterized in that,” and variations thereof herein, is meant to encompass the items listed thereafter, equivalents thereof, and additional items, as well as alternate implementations consisting of the items listed thereafter exclusively. In one implementation, the systems and methods described herein consist of one, each combination of more than one, or all of the described elements, acts, or components.

[0164] Any references to implementations or elements or acts of the systems and methods herein referred to in the singular may also embrace implementations including a plurality of these elements, and any references in plural to any implementation or element or act herein may also embrace implementations including only a single element. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements to single or plural configurations. References to any act or element being based on any information, act, or element may include implementations where the act or element is based at least in part on any information, act, or element.

[0165] Any implementation disclosed herein may be combined with any other implementation, and references to “an implementation,” “some implementations,” “an alternate implementation,” “various implementation,” “one implementation,” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described in connection with the implementation may be included in at least oneimplementation. Such terms as used herein are not necessarily all referring to the same implementation. Any implementation may be combined with any other implementation, inclusively or exclusively, in any manner consistent with the aspects and implementations disclosed herein.

[0166] References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms.

[0167] Where technical features in the drawings, detailed description or any claim are followed by reference signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the drawings, detailed description, and claims. Accordingly, neither the reference signs nor their absence have any limiting effect on the scope of any claim elements.

[0168] The foregoing description of implementations has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from this disclosure. The implementations were chosen and described in order to explain the principals of the disclosure and its practical application to enable one skilled in the art to utilize the various implementations and with various modifications as are suited to the particular use contemplated. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and implementation of the implementations without departing from the scope of the present disclosure as expressed in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method comprising: determining, for one or more magnetic resonance imaging (MRI) scans, an MRI sequence comprising a flow suppression segment to suppress signal from fluid flow in the one or more MRI scans, the flow suppression segment comprising: an excitation block; a first gradient block comprising gradients in a plurality of axes; a refocusing block; and a second gradient block comprising gradients in the plurality of axes; and performing, via an MRI system, the one or more MRI scans using the MRI sequence to obtain one or more MR images.

2. The method of claim 1, wherein the flow suppression segment precedes or succeeds a main segment in the MRI sequence.

3. The method of claim 2, wherein the main segment of the MRI sequence comprises a spin echo block.

4. The method of claim 3, wherein the spin echo block comprises a fast spin echo (FSE).

5. The method of claim 3, wherein the spin echo block comprises an inversion-recovery fast spin echo (FSE), a diffusion-prepared turbo spin echo (dprep-TSE), or a diffusion-prepared FSE.

6. The method of claim 2, wherein the flow suppression segment precedes the main segment by a delay time.

7. The method of claim 2, wherein the MRI sequence comprises a plurality of main segments, each of the plurality of main segments being preceded by one or more flow suppression segments.

8. The method of claim 7, wherein the MRI sequence is generated such that a first delay time between a first pair of main segments differs from a second delay time between a second pair of main segments.

9. The method of claim 8, wherein the first delay time and the second delay time are timing parameters that are configured for flow suppression and target signal contrast.

10. The method of claim 7, wherein the MRI sequence further comprises an inversion block between a first main segment and a first flow suppression segment.

11. The method of claim 1, wherein the flow suppression segment further comprises an eddy-preparation gradient block prior to the first gradient block.

12. The method of claim 1, wherein the plurality of axes comprises an x-axis, a y-axis, and a z-axis.

13. The method of claim 1, wherein the MRI sequence is a fluid-attenuated inversion recovery (FLAIR) sequence.

14. The method of claim 1, wherein the fluid flow is a flow of blood in a region of interest of a subject being scanned.

15. The method of claim 1, wherein the MRI system has a field strength no greater than 200 mT.

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