System and method for improved mute multi-gradient echo magnetic resonance imaging

Abstract

The invention relates to an improved mute multi-gradient echo magnetic resonance imaging system and method. Methods and systems for generating muted multi-gradient echo magnetic resonance images include employing iterative applications of small updates to the magnetic field gradient followed by short non-selective radio frequency pulse excitation, and for free induction decay data acquisition. Updating of the magnetic field gradient allows for a muted self-refocusing pulse sequence. Each magnetic field gradient is based in part on a k-space spoke. A closed k-space trajectory is generated when multiple spokes are cascaded, which results in a self-refocusing pulse sequence. The k-space spokes in the k-space spoke sequence forming the closed k-space trajectory oscillate inside and outside the plane of the frequency space. Subsequent application of the magnetic field gradient allows multiple echo data acquisition.

Description

Background Art

[0001] The subject matter disclosed herein relates to medical imaging and, more particularly, to systems and methods for improved silent multi-gradient echo magnetic resonance imaging.

[0002] Non-invasive imaging techniques allow images of internal structures or features of a patient / subject to be obtained without performing an invasive procedure on the patient / subject. Specifically, such non-invasive imaging techniques rely on various physical principles (such as differential transmission of X-rays through a target volume, reflection of acoustic waves within a volume, paramagnetism of different tissues and materials within a volume, decomposition of target radionuclides within the body, etc.) to acquire data and construct an image or otherwise represent the observed internal features of the patient / subject.

[0003] During MRI, when a substance, such as human tissue, is subjected to a uniform magnetic field (polarization field B0), the individual magnetic moments of the spins in the tissue attempt to align with the polarization field, but precess around it in a random order at their unique Larmor frequencies. If the substance or tissue is subjected to a magnetic field (excitation field B1) that lies in the xy plane and is close to the Larmor frequency, the net alignment moment or "longitudinal magnetization" M z can be rotated or "tilted" into the xy plane to produce a net transverse magnetic moment M t After the excitation signal B1 is terminated, a signal is emitted by the excited spins, and this signal can be received and processed to form an image.

[0004] When these signals are used to generate images, magnetic field gradients (G x , G y and G z Typically, the area to be imaged is scanned in a series of measurement cycles in which these gradient fields are varied according to the particular positioning method being used. The resulting set of received nuclear magnetic resonance (NMR) signals is digitized and processed to reconstruct an image using one of the well-known reconstruction techniques.

[0005] Looping Star is a novel time-multiplexed multi-gradient echo (GRE) MR acquisition solution. Its unique features include quiet scanning (≤15 dBA with ambient scanner acoustic noise), three-dimensional (3D) isotropic image encoding, high sampling efficiency, and acquisition of free induction decay (FID) images. Looping Star has been used for functional MR imaging (e.g., T2*BOLD functional MRI (fMRI)) and high-resolution susceptibility-weighted structural MR imaging. Summary of the Invention

[0006] The following is an overview of certain embodiments disclosed herein. It should be understood that these aspects are provided merely to provide the reader with a brief overview of these specific embodiments, and these aspects are not intended to limit the scope of the present disclosure. In fact, the present disclosure may encompass various aspects that may not be shown below.

[0007] In one embodiment, a computer-implemented method for silent multi-gradient echo magnetic resonance imaging is provided. The computer-implemented method includes acquiring, via a processor, a free induction decay (FID) dataset from a subject using a magnetic resonance scanner, wherein the FID dataset is obtained by performing a free induction decay (FID) acquisition process in an iterative process, each iteration corresponding to a k-space spoke in a k-space spoke sequence in 3D k-space. Each iteration of the FID acquisition process includes: updating a magnetic field gradient based on a k-space spoke in the k-space spoke sequence corresponding to the iteration of the FID acquisition process; applying a radio frequency excitation pulse while maintaining a total magnetic field gradient to encode the k-space spoke corresponding to the iteration of the FID acquisition process; and acquiring a first dataset corresponding to the k-space spoke corresponding to the iteration of the FID acquisition process, wherein the first dataset is at least a portion of the FID dataset. The k-space spokes in the k-space spoke sequence are interconnected to form a closed k-space trajectory that refocuses the FID signal generated by the application of the radio frequency excitation pulse in the initial iteration of the FID acquisition process, wherein the k-space spokes in the k-space spoke sequence oscillate in and out of a plane of frequency space.

[0008] In another embodiment, a system for silent multi-gradient echo magnetic resonance imaging is provided. The system includes a memory that encodes a processor-executable routine. The system also includes a processor configured to access the memory and execute the processor-executable routine, wherein the processor-executable routine, when executed by the processor, causes the processor to perform an action. The action includes acquiring a free induction decay (FID) dataset from a subject using a magnetic resonance scanner, wherein the FID dataset is obtained by performing a free induction decay (FID) acquisition process in an iterative process, each iteration corresponding to a k-space spoke in a k-space spoke sequence in 3D k-space. The iteration of the FID acquisition process includes: updating a magnetic field gradient based on a k-space spoke in the k-space spoke sequence corresponding to the iteration of the FID acquisition process; applying a radio frequency excitation pulse while maintaining the total magnetic field gradient to encode the k-space spoke corresponding to the iteration of the FID acquisition process; and acquiring a first dataset corresponding to the k-space spoke corresponding to the iteration of the FID acquisition process, wherein the first dataset is at least a portion of the FID dataset. The interconnection of k-space spokes in a k-space spoke sequence forms a closed k-space trajectory that refocuses the FID signal resulting from application of the radio frequency excitation pulse of an initial iteration of the FID acquisition process, wherein the k-space spokes in the k-space spoke sequence oscillate in and out of the plane of frequency space.

[0009] In yet another embodiment, a non-transitory computer-readable medium comprising processor-executable code that, when executed by a processor, causes the processor to perform an action. The action comprises acquiring a free induction decay (FID) dataset from a subject using a magnetic resonance scanner, wherein the FID dataset is obtained by performing a free induction decay (FID) acquisition process in an iterative process, each iteration corresponding to a k-space spoke in a k-space spoke sequence in 3D k-space. The iteration of the FID acquisition process comprises: updating a magnetic field gradient based on a k-space spoke in the k-space spoke sequence corresponding to an iteration of the FID acquisition process; applying a radio frequency excitation pulse while maintaining a total magnetic field gradient to encode the k-space spoke corresponding to the iteration of the FID acquisition process; and acquiring a first dataset corresponding to the k-space spoke, the k-space spoke corresponding to the iteration of the FID acquisition process, wherein the first dataset is at least a portion of the FID dataset. The interconnection of k-space spokes in a k-space spoke sequence forms a closed k-space trajectory that refocuses the FID signal resulting from application of the radio frequency excitation pulse of an initial iteration of the FID acquisition process, wherein the k-space spokes in the k-space spoke sequence oscillate in and out of the plane of frequency space. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other features, aspects, and advantages of the present subject matter will be better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters represent like parts throughout, and in which:

[0011] Figure 1 An embodiment of a magnetic resonance imaging (MRI) system suitable for use with the disclosed technology is illustrated;

[0012] Figure 2 Schematic diagram illustrating Looping Star as a modification of the standard zero echo time (ZTE) for time-multiplexed gradient echo imaging;

[0013] Figure 3 Schematic diagram illustrating a hexagonal Looping Star k-space trajectory for an even number of spokes according to aspects of the present disclosure;

[0014] Figure 4 Schematic diagram illustrating a pentagonal Looping Star k-space trajectory for an odd number of spokes according to aspects of the present disclosure;

[0015] Figure 5 A schematic diagram illustrating a conventional Looping Star trajectory for a single loop;

[0016] Figure 6 Schematic diagram illustrating a Wave Looping Star trajectory for a single loop according to aspects of the present disclosure;

[0017] Figure 7 Schematic diagram illustrating conventional Looping Star trajectories for the first three loops;

[0018] Figure 8 Schematic diagram illustrating Wave Looping Star trajectories for the first three loops according to aspects of the present disclosure;

[0019] Figure 9 Schematic diagram illustrating a conventional Looping Star trajectory for one volume (i.e., 32 k-space loops);

[0020] Figure 10 Schematic diagram illustrating WaveLooping Star trajectories for one volume (i.e., 32 k-space loops) in accordance with aspects of the present disclosure;

[0021] Figure 11 illustrates a perspective view of a spiral spoke according to aspects of the present disclosure;

[0022] Figure 12Illustrate various aspects of the present disclosure Figure 11 End view of the spiral spokes in;

[0023] Figure 13 depicts an image from a Looping Star functional MRI scan reconstructed using 3D nearest neighbor gridding (nnGRID) and conjugate gradient sensitivity encoding (cgSENSE) in accordance with aspects of the present disclosure;

[0024] Figure 14 depicts images of conventional Looping Star (reconstructed using nnGRID), Wave Looping Star (reconstructed using nnGRID), and Wave Looping Star (reconstructed using cgSENSE) from a phantom in accordance with aspects of the present disclosure;

[0025] Figure 15 depicts images from conventional Looping Star and Wave Looping Star reconstructed using both nnGRID and cgSENSE in accordance with aspects of the present disclosure;

[0026] Figure 16 A flowchart illustrating a method for performing silent multi-gradient echo magnetic resonance imaging according to aspects of the present disclosure is provided; and

[0027] Figure 17 Illustrate a method for generating and Figure 16 Flowchart of the method for using a self-refocusing multi-gradient encoding sequence in conjunction with the method. DETAILED DESCRIPTION

[0028] One or more specific embodiments are described below. In order to provide a concise description of these embodiments, not all features of an actual implementation are necessarily described in the specification. It should be understood that in the development of any such actual implementation, as in any engineering or design project, many implementation-specific decisions must be made to achieve the developer's specific goals, such as complying with system-related and business-related constraints that may vary from implementation to implementation. Furthermore, it should be understood that such development efforts may be complex and time-consuming, but remain a routine task of design, fabrication, and manufacturing for those of ordinary skill having the benefit of this disclosure.

[0029] When introducing elements of various embodiments of the present subject matter, the articles "a," "an," "the," and "said" are intended to indicate that there are one or more elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements besides the listed elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus the appended numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

[0030] While various aspects of the following discussion are presented in the context of medical imaging, it should be understood that the technology disclosed herein is not limited to such medical contexts. Indeed, examples and explanations are provided in such medical contexts merely to facilitate explanation by providing examples of real-world implementations and applications. However, the technology disclosed herein may also be used in other contexts, such as image reconstruction for non-destructive inspection of manufactured parts or goods (i.e., quality control or quality review applications) and / or non-invasive inspection of packages, boxes, luggage, etc. (i.e., security or screening applications). Generally speaking, the technology disclosed herein may be used in any imaging or screening context or image processing or photography field where a set or class of acquired data undergoes a reconstruction process to generate an image or volume.

[0031] In the following description, it must be understood that the term "loop" can have two different meanings. In some cases, a "loop" can refer to a closed trajectory in frequency space (or k-space). In other cases, a "loop" refers to a portion of a repeatable method. The intended meaning should be clear from the context.

[0032] Magnetic resonance imaging (MRI) uses a system capable of producing images that reflect specific properties of the gyromagnetic material of the object being imaged. More specifically, the MRI system measures RF emissions from gyromagnetic nuclei of the object being imaged in response to magnetic field perturbations generated by the MRI system's coils. Typically, the subject is immersed in a strong, constant magnetic field and subjected to variable magnetic field gradients and RF excitation pulses. RF emissions are sensed at predefined acquisition times.

[0033] Based on the data obtained from the MRI system, various types of images can be obtained. Examples of image types include intensity images, complex (amplitude and phase) images, T1, T2, or T2*-weighted images, T1, T2, or T2* maps, and R1, R2, or R2* maps, where R1 represents the inverse of T1, R2 represents the inverse of T2, and R2* represents the inverse of T2*. Based on the type of image created, a customized pulse sequence can be applied to enable the acquisition of appropriate data using the MRI system.

[0034] The present disclosure enables an MRI system to generate 3D images using a silent multi-gradient echo pulse sequence. The sequence can use a collection of data sets corresponding to segments of frequency space or k-space. Each segment of k-space can include multiple spokes oriented outward from a center. The spoke group for a segment can be generated using an acquisition trajectory similar to a circular geometry, which allows for self-refocusing of the signal, as described in detail below. For each segment, a data set corresponding to the FID and gradient echo can be collected. A data set related to the entire volume of interest in k-space can be obtained by sampling multiple segments.

[0035] For each segment (a collection of k-space spokes), a segment pulse sequence (e.g., known as LoopingStar) can be applied. The segment pulse sequence can use a spatial encoding technique in which an RF excitation pulse can occur while applying magnetic field gradients corresponding to the spokes of the segment. This technique can initially generate a certain number of free induction decay (FID) data sets resulting from the RF excitation pulse. Each FID data set can be obtained by starting an acquisition immediately after the RF excitation pulse (TE=0). Applying all magnetic field gradients during the FID data set acquisition allows the initial RF excitation pulse to be refocused. Therefore, repeatedly applying the same magnetic field (but without RF pulses) in the same order as during the FID data set acquisition can allow a gradient echo data set to be acquired with an echo time TE=TE1. Subsequent gradient echo data sets can be similarly acquired with echo times of TE=2*TE, 3*TE, and so on.

[0036] The small magnetic field gradient updates that can be used according to embodiments of the present invention can reduce large changes in the strong currents applied to the coils of the MRI system. As a result, the use of the technology proposed herein can result in significantly reduced acoustic noise of the MRI system during operation. The acoustic noise caused by changes in coil current and associated switching within the circuit can interfere with patients undergoing medical imaging procedures. In medical diagnostic techniques, such as during functional magnetic resonance imaging (fMRI), such interference with the patient can hinder diagnostic results. For example, when assessing the association between brain activity and cognitive function during fMRI acquisition, the acoustic noise level can affect the patient's cognitive function. As described in detail below, the acoustic noise in the hole where the patient is located during surgery can be similar to the background noise before imaging is performed.

[0037] Looping Star can be used for typical applications of mGRE (Dixon-type fat-water imaging, susceptibility-weighted imaging, quantitative susceptibility mapping, spectral chemical shift imaging) and silent MR imaging (e.g., pediatric, geriatric, hyperacusis, etc.). Looping Star can also be used with functional MRI (e.g., silent functional BOLD fMRI) to provide advantages over methods based on standard loud echo planar imaging. The technology described herein can be used with the technology for Looping Star described in the following patents: U.S. Patent No. 10,088,539, entitled “SILENT MULTI-GRADIENT ECHO MAGNETIC RESOANCE IMAGING,” issued on October 2, 2018, and U.S. Patent No. 11,550,013, entitled “SYSTEMS AND METODS OF SILENT MULTI-GRADIENT ECHO DYNAMIC MAGNETIC RESOANCE IMAGING,” the entire contents of which are incorporated herein by reference.

[0038] The present disclosure provides systems and methods for improved silent multi-gradient echo magnetic resonance imaging (e.g., improved LoopingStar). LoopingStar encodes spatial information in a 3D radial manner, where spokes are grouped into a predetermined number of spokes per loop or segment, which cumulatively form a closed polygon or loop, thereby providing gradient echo refocusing. For 3D spatial encoding, the spokes within each loop rotate in a 3D pseudo-random manner. The predetermined number of spokes per loop is determined by the interaction of desired resolution, TE, and bandwidth (BW). In previous implementations of LoopingStar, the spokes forming the polygon / loop were always arranged in a purely 2D planar manner (e.g., in the same plane of frequency space). The disclosed system and method arranges the spokes within each polygon / loop in a more efficient encoding manner (e.g., in a new trajectory). In particular, out-of-plane oscillation is provided, which also provides additional out-of-plane image encoding. In addition, the disclosed system and method utilizes automatically calibrated parallel imaging (e.g., using acquired zero-TE FID images for parallel image coil sensitivity calibration and intrinsic signal normalization). The disclosed system and method significantly improves spatiotemporal encoding efficiency, thereby increasing the utility of Looping Star in various MR imaging applications. In addition, the disclosed system and method improves image quality by reducing streak artifacts, reducing background signals, and increasing clarity.

[0039] Disclosed embodiments include acquiring a free induction decay (FID) dataset from a subject using a magnetic resonance scanner, wherein the FID dataset is obtained by performing a free induction decay (FID) acquisition process in an iterative process, each iteration corresponding to a k-space spoke in a k-space spoke sequence. Each iteration of the FID acquisition process includes: updating a magnetic field gradient based on a k-space spoke in the k-space spoke sequence corresponding to the iteration of the FID acquisition process; applying a radio frequency excitation pulse to encode the k-space spoke corresponding to the iteration of the FID acquisition process while maintaining the overall magnetic field gradient; and acquiring a first dataset corresponding to the k-space spoke corresponding to the iteration of the FID acquisition process, wherein the first dataset is at least a portion of the FID dataset. The k-space spokes in the k-space spoke sequence are interconnected to form a closed k-space trajectory that refocuses the FID signal generated by the application of the radio frequency excitation pulse in the initial iteration of the FID acquisition process, wherein the k-space spokes in the k-space spoke sequence oscillate in and out of a plane of frequency space. All of the k-space spokes provide coverage of 3D k-space by rotating along the closed trajectory.

[0040] In some embodiments, a first group of k-space spokes in the k-space spoke sequence are out of plane in a first direction, and a second group of k-space spokes in the k-space spoke sequence are out of plane in a second direction opposite to the first direction. In some embodiments, the amplitude and frequency of the out-of-plane oscillations of the spokes can change whenever the cumulative trajectory is refocused. In some embodiments, at least one k-space spoke in the k-space spoke sequence is helical (thus, repeatedly moves in and out of a plane). In some embodiments, a first group of k-space spokes in the k-space spoke sequence are out of plane in a first direction, and a second group of k-space spokes in the k-space spoke sequence are out of plane in a second direction opposite to the first direction, and wherein at least one k-space spoke in the k-space spoke sequence is helical.

[0041] In some embodiments, acquisition of the first dataset begins immediately after application of the radio frequency excitation pulse, such that the silent multi-gradient echo magnetic resonance imaging is a zero echo time imaging sequence. In some embodiments, the disclosed embodiments include acquiring at least a portion of a gradient echo dataset from a subject using a magnetic resonance scanner in the same sequence and in the same k-space spoke order as a FID acquisition process, wherein the gradient echo acquisition process is performed by repeating iterations of the FID acquisition process but without applying radio frequency excitation, thereby obtaining the portion of the gradient echo dataset. In some embodiments, the disclosed embodiments include generating a reconstructed image from the gradient echo dataset based on both the FID dataset and the gradient echo dataset using automatically calibrated parallel imaging reconstruction (e.g., conjugate gradient sensitivity encoding (cgSENSE)). In some embodiments, the disclosed embodiments include generating a coil sensitivity map for each coil of the magnetic resonance scanner from the FID image acquired at zero echo time; and utilizing the coil sensitivity map to intrinsically normalize the reconstructed image relative to the FID image.

[0042] In certain embodiments, the disclosed embodiments include applying a preparatory pulse sequence prior to an iteration of an FID acquisition process. The disclosed embodiments include acquiring two or more gradient echo data sets from a subject using a magnetic resonance imaging system in the same sequence and in the same k-space spoke order as the FID acquisition process, wherein the two or more gradient echo data sets are obtained by performing two or more corresponding gradient echo acquisition processes, the two or more corresponding gradient echo acquisition processes each repeating an iteration of the FID acquisition process without applying radio frequency excitation, and wherein the two or more corresponding gradient echo acquisition processes are performed sequentially.

[0043] Considering the above, Figure 1 , a magnetic resonance imaging (MRI) system 100 is schematically illustrated as including a scanner 102, scanner control circuitry 104, and system control circuitry 106. According to embodiments described herein, the MRI system 100 is generally configured to perform MR imaging.

[0044] The system 100 also includes a remote access and storage system or device, such as a picture archiving and communication system (PACS) 108, or other devices, such as teleradiology equipment, that enable on-site or off-site access to data acquired by the system 100. In this way, MR data can be acquired and then processed and evaluated on-site or off-site. Although the MRI system 100 can include any suitable scanner or detector, in the illustrated embodiment, the system 100 includes a whole-body scanner 102 having a housing 120 through which an aperture 122 is formed. An examination table 124 can be moved into the aperture 122 to allow a patient 126 (e.g., a subject) to be positioned therein for imaging selected anatomical structures within the patient's body.

[0045] The scanner 102 includes a series of associated coils for generating a controlled magnetic field for exciting gyromagnetic material within the anatomy of the patient being imaged. Specifically, a primary magnetic coil 128 is provided for generating a primary magnetic field B0 that is generally aligned with the orifice 122. A series of gradient coils 130, 132, and 134 allow for the generation of controlled gradient magnetic fields during an examination sequence for position encoding of certain gyromagnetic nuclei within the patient 126. A radio frequency (RF) coil 136 (e.g., an RF transmit coil) is configured to generate radio frequency pulses for exciting certain gyromagnetic nuclei within the patient. In addition to the coils that may be located locally within the scanner 102, the system 100 also includes a set of receive coils or RF receive coils 138 (e.g., a coil array) configured for placement proximal to (e.g., against) the patient 126. For example, the receive coils 138 may include a cervical / thoracic / lumbar (CTL) coil, a head coil, a single-sided spine coil, and the like. Generally, receive coil 138 is placed near or on top of patient 126 to receive the weak RF signals (relative to the transmit pulses generated by the scanner coils) generated by certain gyromagnetic nuclei in the patient's body when patient 126 returns to his or her relaxed state.

[0046] The various coils of the system 100 are controlled by external circuitry to generate the desired fields and pulses and to read the emissions from the gyromagnetic material in a controlled manner. In the illustrated embodiment, a main power supply 140 provides power to the primary field coil 128 to generate the primary magnetic field Bo. A power input (e.g., power from a utility or grid), a power distribution unit (PDU), a power supply (PS), and a drive circuit 150 can collectively provide power to pulse the gradient field coils 130, 132, and 134. The drive circuit 150 can include amplification and control circuitry for supplying current to the coils as defined by the digitized pulse sequence output by the scanner control circuitry 104.

[0047] Another control circuit 152 is provided for regulating the operation of the RF coil 136. Circuit 152 includes a switching device for alternating between an active mode of operation and a passive mode of operation, in which the RF coil 136 transmits and does not transmit signals, respectively. Circuit 152 also includes amplification circuitry configured to generate RF pulses. Similarly, the receive coil 138 is connected to a switch 154 that switches the receive coil 138 between a receive mode and a non-receive mode. Thus, in the receive mode, the receive coil 138 resonates with RF signals generated by gyromagnetic nuclei released from the patient 126, and in the non-receive mode, they do not resonate with RF energy from the transmit coil (i.e., coil 136) to prevent undesirable operation. Additionally, the receive circuit 156 is configured to receive data detected by the receive coil 138 and may include one or more multiplexing and / or amplification circuits.

[0048] It should be noted that while the scanner 102 and the control / amplification circuitry are illustrated as being coupled by a single line, in practice, multiple such lines may exist. For example, separate lines may be used for control, data communication, power transmission, and the like. Furthermore, appropriate hardware may be provided along each type of line to properly process data and current / voltage. In practice, various filters, digitizers, and processors may be provided between the scanner and either or both of the scanner control circuitry 104 and the system control circuitry 106.

[0049] As shown, the scanner control circuit system 104 includes an interface circuit 158 ​​that outputs signals for driving the gradient field coils and the RF coils and for receiving data representing magnetic resonance signals generated during an examination sequence. The interface circuit 158 ​​is coupled to a control and analysis circuit 160. Based on a defined protocol selected via the system control circuit 106, the control and analysis circuit 160 executes commands for driving the circuits 150 and 152.

[0050] The control and analysis circuitry 160 is also used to receive magnetic resonance signals and perform subsequent processing before transmitting the data to the system control circuitry 106. The scanner control circuitry 104 also includes one or more memory circuits 162 that store configuration parameters, pulse sequence descriptions, examination results, etc. during operation.

[0051] Interface circuitry 164 is coupled to control and analysis circuitry 160 for exchanging data between scanner control circuitry 104 and system control circuitry 106. In certain embodiments, control and analysis circuitry 160, although illustrated as a single unit, may include one or more hardware devices. System control circuitry 106 includes interface circuitry 166, which receives data from scanner control circuitry 104 and transmits data and commands back to scanner control circuitry 104. Control and analysis circuitry 168 may include a CPU in a general-purpose or special-purpose computer or workstation. Control and analysis circuitry 168 is coupled to memory circuitry 170 to store programming code for operating MRI system 100 and to store processed image data for later reconstruction, display, and transmission. The programming code may implement one or more algorithms that, when executed by a processor, are configured to perform reconstruction of the acquired data as described below. In certain embodiments, image reconstruction may occur on a separate computing device having processing circuitry and memory circuitry.

[0052] Additional interface circuitry 172 may be provided for exchanging image data, configuration parameters, and the like with external system components, such as the remote access and storage device 108. Finally, the system control and analysis circuitry 168 may be communicatively coupled to various peripheral devices for facilitating operator interface and generating hard copies of reconstructed images. In the illustrated embodiment, these peripheral devices include a printer 174, a monitor 176, and a user interface 178, which may include devices such as a keyboard, a mouse, a touch screen (e.g., integral to the monitor 176), and the like.

[0053] Figure 2 Schematic diagram explaining Looping Star as a modification of the standard zero echo time (ZTE) for time-multiplexed gradient echo imaging is illustrated. Figure 2 The top row 180 of FIG. 1 illustrates standard ZTE. The top portion 182 of the top row 180 illustrates a pulse sequence 184 and associated spoke directions for standard ZTE. Standard ZTE includes hard-pulsed RF excitation 186 in the presence of a constant-amplitude readout gradient 188. The bottom portion 190 of the top row 180 illustrates the creation and evolution of signals in k-space (indicated by reference numeral 192).

[0054] Figure 2The middle row 193 of FIG illustrates gradient-refocused ZTE (e.g., single-coherence ZTE gradient refocusing). The top portion 194 of the middle row 193 illustrates a pulse sequence 196 (and associated spoke directions) that utilizes a single-pulse RF excitation 198 in the presence of a constant-amplitude readout gradient 199. The bottom portion 200 of the middle row 193 illustrates the formation of a self-refocusing k-space trajectory, as indicated by reference numeral 202. As shown, by way of example, six spokes with angular increments of 60 degrees result in a self-refocusing hexagonal k-space trajectory 204.

[0055] Figure 2 The bottom row 206 of FIG. 1 illustrates a coherence-resolved Looping Star that improves the time efficiency of the single coherence gradient refocusing in the middle row 193 via time multiplexing. The top portion 208 of the bottom row 206 illustrates a pulse sequence 210 (and associated spoke directions) for a single loop showing three RF pulses 212 stimulating three signal coherences in the presence of a constant-amplitude readout gradient 214. The loop can be repeated multiple times and rotated in k-space. Each single coherence provides a radial center-outward FID spoke 216, followed by a radially inward center-outward gradient echo spoke 218. The coherence-resolved Looping Star leaves time gaps during the excitation phase to provide sufficient time during the refocusing phase so that the gradient echo signals (from subsequent coherences) do not overlap. The bottom portion 220 of the bottom row 206 illustrates the formation of a self-refocusing k-space trajectory, as indicated by reference numeral 222. As shown, as an example, three signal coherences have corresponding self-refocusing hexagonal spatial trajectories 223, 224, and 226.

[0056] Figure 3 and Figure 4 Different Looping Star k-space trajectories are illustrated. Figure 3 A schematic diagram of a hexagonal Looping Star k-space trajectory 228 for an even number of spokes is illustrated. Figure 3 As shown, the loops or segments include 6 spokes per loop to form a hexagonal Looping Star k-space trajectory 228. Utilizing an even number of spokes per loop results in an accumulated trajectory where the echo input signal (thin dashed line 230) overlaps the echo output signal (thick solid line 232).

[0057] Figure 4 A schematic diagram of a pentagonal Looping Star k-space trajectory 234 for an odd number of spokes is illustrated. Figure 4As shown, the loops or segments include five spokes per loop to form a pentagonal Looping Star k-space trajectory 234. Utilizing an odd number of spokes per loop results in an accumulated trajectory where the echo input signal (thin dashed line 236) and the echo output signal (thick solid line 238) do not overlap. This improves encoding efficiency (i.e., there are more unique spokes within the main encoding region, indicated by circle 240 with radius kmax = res / pi).

[0058] Typically, for a single loop or segment, the Looping Star's trajectory appears in the same plane of frequency space. As disclosed herein, introducing or adding adjustable out-of-plane oscillations (which also provide additional out-of-plane image coding) can improve or significantly increase spatiotemporal coding efficiency. A Looping Star that introduces out-of-plane oscillations can be referred to as a Wave Looping Star.

[0059] Figures 5 to 10 The trajectories of the regular Looping Star and the Wave Looping Star are compared. Figures 5 to 10 In

[15] , a large number of spokes per loop is used (e.g., 26 spokes per loop), which is typical for fMRI (e.g., Silent BOLD Looping Star fMRI). To achieve sufficient temporal resolution for fMRI, relatively few loops are scanned per volume (e.g., 32 loops per volume). Due to the relatively small number of loops per volume, it is important that each loop provides optimal encoding (e.g., with Wave Looping Star). Figures 9 and 10 , only the endpoints of the spokes are illustrated.

[0060] Figure 5 A schematic diagram of a conventional Looping Star trajectory 242 for a single loop in 3D k-space is illustrated. As shown, each spoke 244 lies in a single two-dimensional (2D) plane 246. Figure 6A schematic diagram of a Wave Looping Star trajectory 247 for a single loop in 3D k-space is illustrated. The Wave Looping Star trajectory 247 has additional out-of-plane encoding (e.g., via quadrature oscillations). The Wave Looping Star trajectory 247 includes alternating between out-of-plane spokes 248 in a first direction and out-of-plane spokes 250 in a second direction opposite the first direction. Thus, the Wave Looping Star trajectory 247 has a first set 252 of out-of-plane spokes 248 along the first direction and a second set 254 of out-of-plane spokes 250 along the second direction. Each spoke 248, 250 is a curve that is out of plane (i.e., each spoke 248, 250 starts at the center and curves out of plane, drawing a sinusoidal curve at the edge of a sphere described by all of the spokes 248, 250). Although Figure 6 The spokes 248, 250 are depicted as being pushed out in opposite directions, but in certain embodiments, the amplitude and frequency of the out-of-plane oscillations of the spokes 248, 250 may be varied whenever the cumulative trajectory is refocused.

[0061] Figure 7 A schematic diagram of a conventional Looping Star trajectory 256 is illustrated for the first three loops in 3D k-space. Figure 8 A schematic diagram of the Wave Looping Star trajectory 258 for the first three loops in 3D k-space is illustrated. Figure 9 A schematic diagram of a conventional Looping Star trajectory 260 for a 3D imaging volume (containing 32 k-space loops) is illustrated. Figure 10 A schematic diagram of a Wave Looping Star trajectory 262 for an imaging volume (containing 32 k-space loops) is illustrated. Figures 7 to 10 In , the loop rotates pseudo-randomly in 3D k-space. As in comparing the conventional Looping Star trajectory with the WaveLooping Star trajectory (in particular, for Figures 7 to 10 It can be seen from the sampling pattern obtained in that Wave Looping Star provides more evenly distributed sampling positions, significantly improving coding efficiency.

[0062] like Figures 2 to 4 As shown, the spokes can be straight. In some embodiments, the spokes can be curved (e.g., Figures 5 and 6 ). In order to further improve the coding efficiency, the spokes 264 can even be spiral, such as Figure 11 and Figure 12As shown. A single spoke 264 oscillates itself in and out of plane 266. Spiral spokes 264 can result in louder acoustic noise. In some embodiments, one or more spokes in the Wave Looping Star trajectory can be spiral. In some embodiments, a combination of one or more spokes being spiral and one group of spokes being out of plane in a first direction and one group of spokes being out of plane in a second direction opposite the first direction (e.g., Figure 6 depicted).

[0063] Conventional Looping Star image reconstruction is based on 3D gridding (e.g., nnGRID) followed by Fourier transform and square sum root coil combination. As disclosed herein, automatically calibrated parallel imaging reconstruction can be used in combination with Wave Looping Star to further improve overall image encoding efficiency. For example, non-Cartesian conjugate gradient sensitivity encoding (cgSENSE) including coil compression and noise pre-whitening can be utilized. The FID image of each coil (at TE=0) can be used as a pseudo-coil sensitivity (coil sensitivity map), thereby providing inherent normalization of the reconstructed image (i.e., normalized relative to the complex FID image), so that the obtained GRE image can be directly used for quantitative T2* and / or magnetic susceptibility mapping. Because Looping Star acquires FID and GRE data simultaneously and at the same spatial resolution and coverage, the FID pseudo-coil sensitivity map perfectly matches the GRE image, without being affected by spatiotemporal inconsistencies due to motion, geometric distortion, or resampling errors.

[0064] Figure 13 An image from a Looping Star fMRI scan (e.g., FID+2GRE Looping Star fMRI) reconstructed using 3D nearest neighbor gridding (nnGRID) and conjugate gradient sensitivity encoding (cgSENSE) is shown. The Looping Star fMRI scan conditions were: TE = [0, 14.3, 28.6] milliseconds (ms), resolution = 3 millimeters (mm), bandwidth = ±41.625 kHz, FA = 2°, and time / volume = 2.2 seconds. Figure 13 The first row 268 on the left depicts FID images (eg, sagittal, coronal, and axial views of the brain) acquired from three fMRI series and reconstructed using nnGRID. Figure 13 The second row 270 from the left depicts sagittal, coronal, and axial GRE (GRE1) images of the brain at TE=14.3 ms reconstructed using nnGRID. Figure 13The third row 272 from the left depicts sagittal, coronal, and axial GRE (GRE2) images of the brain at TE = 28.6 ms reconstructed using nnGRID. Figure 13 The fourth row 274 on the left depicts sagittal, coronal, and axial temporal signal-to-noise ratio (tSNR) maps for the last echo (ie, GRE2) reconstructed using nnGRID.

[0065] Figure 13 The first row 276 on the right depicts the absolute values ​​of the FID-based coil sensitivity maps of the brain obtained from the first twelve virtual coils after coil compression for the cgSENSE reconstruction. Figure 13 The second row 278 from the right depicts sagittal, coronal, and axial GRE (GRE1) images of the brain at TE = 14.3 ms reconstructed using cgSENSE. Figure 13 The third row 280 on the right depicts sagittal, coronal, and axial GRE (GRE2) images of the brain at TE = 28.6 ms reconstructed using cgSENSE reconstruction. Figure 13 The fourth row 282 on the right depicts sagittal, coronal, and axial temporal signal-to-noise ratio (tSNR) plots for the last echo (ie, GRE2) reconstructed using cgSENSE reconstruction. Figure 13 As shown, reconstruction with auto-calibrated cgSENSE yields enhanced image quality, as evidenced by reduced streak artifacts, reduced background signal, and increased clarity. Furthermore, a more uniform tSNR map is obtained for cgSENSE (although with reduced amplitude).

[0066] Figure 14Depicted are images of conventional Looping Star, Wave Looping Star, and Wave Looping Star (with cgSENSE reconstruction) from a phantom. Both conventional (coherently resolved) Looping Star and Wave Looping Star scans utilized 26 spokes per loop, 32 loops per scan volume, and a total of 832 spokes per volume. The top row 283 of different images 284 of the phantom were derived from conventional Looping Star using conventional reconstruction (nnGRID reconstruction). Due to undersampling, there are noticeable streak artifacts in image 284. The middle row 285 of different images 286 of the phantom (corresponding to image 284) were derived from Wave Looping Star using conventional reconstruction (nnGRID reconstruction). Image 286 has improved encoding and corresponding reduction in streaks compared to image 284. The bottom row 287 of different images 288 of the phantom (corresponding to images 284 and 286) were derived from Wave LoopingStar using automatically calibrated parallel imaging reconstruction (specifically cgSENSE). Image 288 has further improved image quality compared to both images 284 and 286. For the cgSENSE reconstruction of image 288, coil sensitivity maps derived from the FID image at TE = 0 were utilized. For the reasons described above, these coil sensitivity maps have ideal properties for coil sensitivity calibration.

[0067] Figure 15 Depicted are images (fMRI images) from conventional Looping Star and WaveLooping Star reconstructed using both nnGRID and cgSENSE. The fMRI images were derived from a typical fMRI acquisition with the following conditions: TE = 26.88 ms, resolution = (3 mm) 3 , bandwidth = ±41.625 kHz, FA = 2°, and time / volume = 2.7 seconds. Figure 15 The upper left row 290 of includes sagittal, coronal, and axial fMRI images of the brain acquired at TE = [0, 26.88 ms] using conventional Looping Star and reconstructed using nnGRID. Figure 15 The upper right row 292 of includes sagittal, coronal, and axial fMRI images of the brain acquired at TE = [0, 26.88 ms] using conventional Looping Star and reconstructed using cgSENSE. Figure 15 The lower left column 294 includes sagittal, coronal, and axial fMRI images of the brain acquired at TE = [0, 26.88 ms] using Wave Looping Star and reconstructed using nnGRID. Figure 15The lower right row 296 of FIG. 2 includes sagittal, coronal, and axial fMRI images of the brain acquired at TE = [0, 26.88 ms] using Wave Looping Star and reconstructed using cgSENSE. Comparing the arrows in the images in the upper left row 290 with the corresponding arrows in the lower right row 296 shows that the best image quality was achieved using the combination of Wave Looping Star encoding and cgSENSE reconstruction.

[0068] Figure 16 A flow chart illustrating a method 298 for performing silent multi-gradient echo magnetic resonance imaging is shown. One or more steps of the method 298 may be performed by Figure 1 One or more of the steps of method 298 may be performed simultaneously or sequentially. Figure 16 The order shown is different from the order in which it is executed.

[0069] For an object within the MRI system, a preparation pulse sequence (block 300) may be applied. The preparation pulse sequence (block 300) may include an RF excitation pulse sequence that prepares the magnetization of the gyromagnetic nuclei of the imaged object for improved data acquisition. The preparation pulse sequence (block 300) may include a pulse sequence for selecting a spatial volume of the object to be imaged. In certain embodiments, the preparation pulse sequence (block 300) may also prepare the sample to optimize the generation of data suitable for generating T1, T2, or T2* weighted images. The preparation pulse sequence (block 300) may be used prior to collecting data associated with each self-refocusing segment.

[0070] A self-refocusing segment pulse sequence (block 302) may then be performed. As described below, the segment pulse sequence (block 302) may include the sequential application of gradient updates, multiple RF excitation pulses, and data acquisition cycles. The segment pulse sequence (block 302) may sample data through a plurality of k-space spokes via an acquisition trajectory having a closed geometry (e.g., a loop acquisition trajectory). As described above, the k-space spokes in the k-space spoke sequence oscillate in and out of the plane of frequency space. In some embodiments, a first set of k-space spokes in the k-space spoke sequence are out of plane in a first direction, and a second set of k-space spokes in the k-space spoke sequence are out of plane in a second direction opposite to the first direction. In some embodiments, the amplitude and frequency of the out-of-plane oscillations of the spokes may vary as long as the cumulative trajectory refocuses. In some embodiments, at least one k-space spoke in the k-space spoke sequence is helical (thus, repeatedly moves in and out of plane). In some embodiments, a first set of k-space spokes in the k-space spoke sequence are out of plane in a first direction, and a second set of k-space spokes in the k-space spoke sequence are out of plane in a second direction opposite the first direction, and wherein at least one k-space spoke in the k-space spoke sequence is helical. A segment pulse sequence (block 302) may be used to obtain FID and gradient echo data related to a k-space region associated with the segment pulse sequence (block 302).

[0071] To cover the desired k-space volume, data corresponding to multiple k-space segments can be acquired through an iterative process. To this end, magnetic field gradients can be applied to prepare the subject for acquisition of the next k-space segment (block 304), followed by an iteration (block 306). Each iteration can include applying a preparation pulse sequence (block 306), a segment pulse sequence corresponding to the k-space segment (block 302), and applying the magnetic field gradients for the next segment (block 304). In some embodiments, the preparation pulse sequence (block 300) can be skipped to reduce time, for example, if the type of image being generated does not necessarily require a preparation pulse. In embodiments where it is desired to repeat or resample data corresponding to a previously acquired segment, the gradient preparation (block 304) can retain the initial magnetic field gradients employed. Data acquired during the multiple segment pulse sequences (block 302) can be stored in memory (block 308) (e.g., in memory circuitry 170). In some implementations, the data (block 306) can be stored during or after each completed iteration. The stored data can be saved in memory for later use, such as to perform image reconstruction (block 310). Image reconstruction (block 310) may include generating a reconstructed image from the gradient echo dataset based on both the FID dataset and the gradient echo dataset using, for example, auto-calibrated parallel imaging reconstruction (e.g., cgSENSE). In particular, image reconstruction (block 310) may include generating a coil sensitivity map for each coil of the MR scanner from an FID image acquired at zero echo time (TE=0); and utilizing the FID-based coil sensitivity map to inherently normalize the reconstructed image relative to the complex FID image.

[0072] As described above, method 298 may be used to acquire data associated with a region of k-space using a multi-segment pulse sequence. The actions performed according to each segment pulse sequence (block 302) may be referred to as Figure 17 Further understanding, Figure 17 A method 312 of performing a self-refocusing segment pulse sequence to acquire data associated with a k-space segment is illustrated. One or more steps of the method 312 may be performed by Figure 1 One or more of the steps of method 312 may be performed simultaneously or sequentially. Figure 17 It should be noted that methods 298 and 312 can be used in conjunction with fMRI.

[0073] In this article Figure 17 In the description of the method, the term "loop" should be understood as the repetitive portion of the method. The initial setup phase includes the initialization of the loop counter, which keeps track of the iterations within a segment, and the gradient encoding and initialization of the spoke counter (block 314). This can be done by Figure 1 The gradient encoding is established by the gradient coils of the MRI system 100. The amplitude of the gradient encoding established according to block 314 can remain substantially the same in a pulse sequence for each k-space segment (eg, comprising a plurality of spokes) being sampled.

[0074] As described above, a segment pulse sequence can be used to obtain FID and gradient echo data sets corresponding to a k-space segment formed by a plurality of spokes. Method 312 may include an FID acquisition process during the first acquisition process of the segment, i.e., when the loop counter is 1 (connector 316). During this FID acquisition process, application of RF excitation may be performed (block 318), followed by acquisition of FID data 319 (block 320). This process is repeated for each k-space spoke until all spokes are covered during the FID acquisition process, as indicated by a "yes" connector from decision block 322. To obtain data related to the next k-space spoke in the sequence, the encoding gradient may be updated (block 324) and the spoke counter may be incremented.

[0075] During each FID acquisition process, RF excitation may be applied (block 318) (e.g., using Figure 1 The RF coil 136 is provided. The RF excitation 318 can be a short, non-selective RF excitation. The RF excitation can cause the gyromagnetic core to precess around the local magnetic field. In some implementations, the RF excitation (block 318) can cause the gyromagnetic spin axis to have an angle substantially less than 90° with the local magnetic field.

[0076] After RF excitation (block 318), the acquisition coil (e.g., Figure 1 The acquisition coil 38 of the RF sensor 300 may be set to acquire FID data 319 (block 320) to obtain a portion of the FID data set 319 corresponding to the k-space spoke being sampled in the current iteration. The acquisition (block 320) may occur immediately after the RF excitation is applied (block 318), thereby producing an FID data set 319 with TE=0 or a very small (e.g., negligible) TE.

[0077] The gradient encoding update (block 324) may be used to prepare the spokes for the next iteration of the FID acquisition process. The gradient encoding update (block 324) may be a small change to the magnetic field gradient. Thus, the gradient update causes only a slight change in the current of the gradient coils, thereby enabling quiet operation of the system 100. In some embodiments, the gradient encoding update performed according to the actions represented by block 324 may also be performed at a smaller pace, such as concurrently with data acquisition (block 320).

[0078] Once all k-space spokes have been sampled, the FID acquisition process ends, as represented by connector "NO" 316 from decision block 322. Completion of the k-space spokes corresponding to the segments being sampled during the FID acquisition process may form a loop geometry, as described above. In certain implementations, this loop geometry may result in signal refocusing, which may be used to collect additional echo signals. More specifically and by way of example, the sequential spatial encoding of a series of RF excitation pulses (block 318) and gradient updates (block 324) performed during the FID acquisition process (in this example, i_loop = 1) may result in the signal associated with the RF excitation pulse (block 318) from the first iteration (i_spoke = 1) of the FID acquisition process being refocused after the last spoke (i_spoke = number of spokes per loop). Furthermore, subsequent application of gradient updates (block 324 ) corresponding to the k-space spoke sequence used in the first iteration (i_loop=1) may provide a refocusing signal sequence associated with the RF excitation applied during the FID acquisition (block 318 ).

[0079] As indicated by a "yes" connector 326, a first gradient echo acquisition process 328 may follow the gradient update (block 324). Refocusing from subsequent gradient updates corresponding to the RF excitation sampled during the FID acquisition process (i_loop=1) (block 318) provides gradient echo data 330 that can be acquired (block 328). The gradient update (block 332) during the gradient echo acquisition process (i_loop>1) may substantially follow the gradient update sequence of the FID acquisition process (i_loop=1). As a result, the k-space trajectory during the gradient echo acquisition process may substantially trace the k-space trajectory during the FID acquisition process. Thus, as described above, the k-space spokes in the k-space spoke sequence oscillate in and out of plane in frequency space. In certain embodiments, a first set of k-space spokes in the k-space spoke sequence are out of plane in a first direction, and a second set of k-space spokes in the k-space spoke sequence are out of plane in a second direction opposite the first direction. In certain embodiments, the amplitude and frequency of the out-of-plane oscillations of the spokes may vary as long as the cumulative trajectory refocuses. In some embodiments, at least one k-space spoke in the sequence of k-space spokes is helical (thus, repeatedly moves in and out of a plane). In some embodiments, a first set of k-space spokes in the sequence of k-space spokes are out of plane in a first direction, and a second set of k-space spokes in the sequence of k-space spokes are out of plane in a second direction opposite the first direction, and wherein at least one k-space spoke in the sequence of k-space spokes is helical.

[0080] As described above, each iteration of the gradient echo acquisition process has a corresponding iteration in the FID acquisition process. At the beginning of each iteration of the first gradient echo acquisition process, the signal from the RF excitation (box 318) of the corresponding iteration of the FID acquisition process can be refocused. The data acquisition at the beginning of each iteration (box 328) provides a portion of the first gradient echo data set 330 corresponding to the k-space spoke associated with the iteration. As an example, if the FID data set of the first spoke is acquired in the first iteration of the FID acquisition process (i_loop=1 and i_spoke=1), the corresponding gradient echo data set 330 of the first spoke can be acquired in the first iteration of the first gradient echo acquisition process (i_loop=2 and i_spoke=1). The resulting echo time can be TE=TE1, where TE1 is substantially the same as the duration of the FID acquisition process.

[0081] A gradient update (block 332) corresponding to the next spoke in the spoke sequence may be applied to acquire the next echo. The amplitude and direction of the gradient update sequence (block 332, when i_loop > 1) may be substantially similar to the gradient update sequence (block 324, when i_loop = 1) of the FID acquisition process. Furthermore, the time intervals between the gradient updates (block 332, when i_loop > 1) may be substantially similar to the time intervals between the gradient updates (block 34, when i_loop > 1) of the FID acquisition process. As a result, the spoke sequence sampled during the FID acquisition process may be substantially similar in order and dimensions to the spoke sequence sampled during the first gradient echo acquisition process. Thus, the set of gradient echo data sets acquired during the first gradient echo acquisition process (block 328) corresponds to the FID data set acquired during the FID acquisition process (block 320). Iterations of the gradient echo acquisition process continue until all k-space spokes corresponding to the segment have been acquired, as indicated by decision block 334.

[0082] In some implementations, multiple gradient echo acquisition processes substantially similar to the first gradient echo acquisition process can be used to obtain multiple gradient echo data sets corresponding to the same k-space segment. This can be represented by an example of method 312, where the number of loops is greater than 2. As shown in decision block 336, if more gradient echo data sets are desired within the segment (i.e., the number of loops is greater than 2), the gradient echo acquisition process can be repeated. For example, a second gradient echo data set (i_loop=3) can be acquired by performing a second gradient echo acquisition immediately after the first gradient echo acquisition process (i_loop=2). The resulting echo time of the second gradient echo data set can be TE=2*TE1, where TE1 is substantially similar to the duration of the FID acquisition process. As another example, a self-refocusing pulse sequence may include an FID acquisition process (i_loop=1) for acquiring a first FID dataset, a first gradient echo acquisition process (i_loop=2) for acquiring a first gradient echo dataset, a second gradient echo acquisition process (i_loop=3) similar to the first gradient echo acquisition process for acquiring a second gradient echo dataset, and a third gradient echo acquisition process (i_loop=4) similar to the first gradient echo acquisition process for acquiring a third gradient echo dataset. Because RF excitation (block 318) is performed during the FID acquisition process, the second, third, and fourth gradient echo datasets can be used together with the FID dataset (without further RF excitation) to improve the measurement of T2* relaxation time and magnetic susceptibility information according to the desired image weighting. In addition, quantification and generation of T2* and / or magnetic susceptibility maps and other images can use only a subset of the acquired gradient echo and FID datasets.

[0083] The technical effects of the disclosed subject matter include improved silent multi-gradient echo magnetic resonance imaging (e.g., improved Looping Star). The technical effects of the disclosed subject matter include arranging spokes in each polygon / loop in a more efficient encoding manner (e.g., with new trajectories). In particular, out-of-plane oscillations are provided, which also provide additional out-of-plane image encoding. The technical effects of the disclosed subject matter include utilizing parallel imaging with automatic calibration (e.g., utilizing acquired zero-TE FID images for parallel image coil sensitivity calibration and intrinsic signal normalization). The technical effects of the disclosed subject matter include significantly improving spatiotemporal encoding efficiency, thereby increasing the utility of Looping Star in different MR imaging applications. In addition, the technical effects of the disclosed subject matter include improving image quality by reducing streak artifacts, reducing background signals, and increasing clarity.

[0084] The technology presented and claimed herein is referred to and applied to physical and concrete examples of a practical nature that clearly improves upon the state of the art and, therefore, is not abstract, intangible, or purely theoretical. Furthermore, if any claim appended to the end of this specification contains one or more elements designated as "means for [performing] the function of ..." or "steps for [performing] the function of ...," it is intended that such elements be construed under 35 U.S.C. § 112(f). However, for any claim containing elements designated in any other manner, it is not intended that such elements be construed under 35 U.S.C. § 112(f).

[0085] This written description uses examples to disclose the subject matter, including the best mode, and also to enable any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insignificant differences from the literal language of the claims.

Claims

1. A computer-implemented method for silent multi-gradient echo magnetic resonance imaging, the computer-implemented method comprising: Acquiring, via a processor, a free induction decay (FID) dataset from a subject using a magnetic resonance scanner, wherein the FID dataset is obtained by performing a free induction decay (FID) acquisition process in an iterative process, each iteration corresponding to a k-space spoke in a sequence of k-space spokes in three-dimensional k-space, and wherein an iteration of the FID acquisition process comprises: updating a magnetic field gradient based on a k-space spoke in the k-space spoke sequence corresponding to the iteration of the FID acquisition process; applying radio frequency excitation pulses while maintaining the overall magnetic field gradient to encode the k-space spokes corresponding to the iteration of the FID acquisition process; and acquiring a first data set corresponding to the k-space spoke corresponding to the iteration of the FID acquisition process, wherein the first data set is at least a portion of the FID data set; and wherein the interconnection of the k-space spokes in the k-space spoke sequence forms a closed k-space trajectory that refocuses the FID signal resulting from application of the radio frequency excitation pulse of an initial iteration of the FID acquisition process, wherein the k-space spokes in the k-space spoke sequence oscillate in and out of a plane of frequency space.

2. The computer-implemented method of claim 1 , wherein a first set of k-space spokes in the k-space spoke sequence are out of the plane in a first direction, and a second set of k-space spokes in the k-space spoke sequence are out of the plane in a second direction opposite the first direction. 3 . The computer-implemented method of claim 1 , wherein at least one k-space spoke in the k-space spoke sequence is helical.

4. The computer-implemented method of claim 1 , wherein a first set of k-space spokes in the k-space spoke sequence are out of the plane in a first direction, and a second set of k-space spokes in the k-space spoke sequence are out of the plane in a second direction opposite the first direction, and wherein at least one k-space spoke in the k-space spoke sequence is helical. 5 . The computer-implemented method of claim 1 , wherein acquiring the first data set begins immediately after application of the radio frequency excitation pulse, such that the silent multi-gradient echo magnetic resonance imaging is a zero echo time imaging sequence.

6. The computer-implemented method of claim 5 , further comprising acquiring, via the processor, at least a portion of a gradient echo dataset from the subject using the magnetic resonance scanner in the same sequence and in the same k-space spoke order as the FID acquisition process, wherein the portion of the gradient echo dataset is obtained by performing the gradient echo acquisition process by repeating the iterations of the FID acquisition process without applying radio frequency excitation.

7. The computer-implemented method of claim 6, further comprising generating, via the processor, a reconstructed image from the gradient echo dataset based on both the FID dataset and the gradient echo dataset using auto-calibrated parallel imaging reconstruction.

8. The computer-implemented method of claim 7, further comprising: generating a coil sensitivity map for each coil of the magnetic resonance scanner from the FID image acquired at zero echo time; as well as The coil sensitivity map is used to intrinsically normalize the reconstructed image with respect to the FID image.

9. The computer-implemented method of claim 1, further comprising applying, via the processor, a preparatory pulse sequence prior to the iteration of the FID acquisition process.

10. The computer-implemented method of claim 1 , further comprising acquiring, via the processor, two or more gradient echo data sets from the subject using the magnetic resonance imaging system in the same sequence and in the same k-space spoke order as the FID acquisition process, wherein the two or more gradient echo data sets are obtained by performing two or more corresponding gradient echo acquisition processes, the two or more corresponding gradient echo acquisition processes each repeating the iteration of the FID acquisition process without applying radio frequency excitation, and wherein the two or more corresponding gradient echo acquisition processes are performed sequentially.

11. A system for silent multi-gradient echo magnetic resonance imaging, the system comprising: a memory encoding processor-executable routines; and a processor configured to access the memory and to execute the processor-executable routine, wherein the processor-executable routine, when executed by the processor, causes the processor to: A free induction decay (FID) dataset is acquired from a subject using a magnetic resonance scanner, wherein the FID dataset is obtained by performing a free induction decay (FID) acquisition process in an iterative process, each iteration corresponding to a k-space spoke in a sequence of k-space spokes in three-dimensional k-space, and wherein an iteration of the FID acquisition process comprises: updating a magnetic field gradient based on a k-space spoke in the k-space spoke sequence corresponding to the iteration of the FID acquisition process; applying radio frequency excitation pulses while maintaining the overall magnetic field gradient to encode the k-space spokes corresponding to the iteration of the FID acquisition process; and acquiring a first data set corresponding to the k-space spoke corresponding to the iteration of the FID acquisition process, wherein the first data set is at least a portion of the FID data set; and wherein the interconnection of the k-space spokes in the k-space spoke sequence forms a closed k-space trajectory that refocuses the FID signal resulting from application of the radio frequency excitation pulse of an initial iteration of the FID acquisition process, wherein the k-space spokes in the k-space spoke sequence oscillate in and out of a plane of frequency space.

12. The system of claim 11, wherein a first set of k-space spokes in the k-space spoke sequence are out of the plane in a first direction, and a second set of k-space spokes in the k-space spoke sequence are out of the plane in a second direction opposite the first direction.

13. The system of claim 11, wherein at least one k-space spoke in the k-space spoke sequence is helical.

14. The system of claim 11 , wherein a first set of k-space spokes in the k-space spoke sequence are out of the plane in a first direction, and a second set of k-space spokes in the k-space spoke sequence are out of the plane in a second direction opposite the first direction, and wherein at least one k-space spoke in the k-space spoke sequence is helical. 15 . The system of claim 11 , wherein acquisition of the first data set begins immediately after application of the radio frequency excitation pulse, such that the silent multi-gradient echo magnetic resonance imaging is a zero echo time imaging sequence.

16. The system of claim 15 , wherein the routine, when executed by the processor, further causes the processor to acquire at least a portion of a gradient echo dataset from the subject using the magnetic resonance scanner in the same sequence and in the same k-space spoke order as the FID acquisition process, wherein the gradient echo acquisition process is performed by repeating the iterations of the FID acquisition process but without applying radio frequency excitation, thereby obtaining the portion of the gradient echo dataset.

17. The system of claim 16, wherein the routine, when executed by the processor, further causes the processor to generate a reconstructed image from the gradient echo dataset based on both the FID dataset and the gradient echo dataset using auto-calibrated parallel imaging reconstruction.

18. The system of claim 17, wherein the routine, when executed by the processor, further causes the processor to: generating a coil sensitivity map for each coil of the magnetic resonance scanner from the FID image acquired at zero echo time; and The coil sensitivity map is used to intrinsically normalize the reconstructed image with respect to the FID image.

19. A non-transitory computer-readable medium comprising processor-executable code that, when executed by a processor, causes the processor to: A free induction decay (FID) dataset is acquired from a subject using a magnetic resonance scanner, wherein the FID dataset is obtained by performing a free induction decay (FID) acquisition process in an iterative process, each iteration corresponding to a k-space spoke in a sequence of k-space spokes in three-dimensional k-space, and wherein an iteration of the FID acquisition process comprises: updating a magnetic field gradient based on a k-space spoke in the k-space spoke sequence corresponding to the iteration of the FID acquisition process; applying radio frequency excitation pulses while maintaining a total magnetic field gradient to encode the k-space spokes corresponding to the iteration of the FID acquisition process; and acquiring a first data set corresponding to the k-space spoke corresponding to the iteration of the FID acquisition process, wherein the first data set is at least a portion of the FID data set; and wherein the interconnection of the k-space spokes in the k-space spoke sequence forms a closed k-space trajectory that refocuses the FID signal resulting from application of the radio frequency excitation pulse of an initial iteration of the FID acquisition process, wherein the k-space spokes in the k-space spoke sequence oscillate in and out of a plane of frequency space.

20. The non-transitory computer-readable medium of claim 19, wherein a first set of k-space spokes in the k-space spoke sequence are out of the plane in a first direction and a second set of k-space spokes in the k-space spoke sequence are out of the plane in a second direction opposite to the first direction, at least one k-space spoke in the k-space spoke sequence is spiral, or a combination thereof.

Images