Method and system for enhancing acceleration of MRI scans using aldama excitation

Abstract

The invention relates to a method and system for enhancing acceleration of an MRI scan using Adama excitation. A computer-implemented method for generating a magnetic resonance (MR) image of a subject includes applying, via a processing system comprising one or more processors, a sequence of Hadamard-coded radio frequency (RF) excitation pulses to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-coded adjacent slices; multiplexing, via the processing system, the Adamama-encoded adjacent slices with a secondary RF excitation pulse to generate a composite RF pulse; and generating, via the processing system, the MR image of the subject using the composite RF pulse.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 553,270, filed on February 14, 2024, entitled “SYSTEMS AND METHODS FOR ENHANCEDACCELERATION OF MRI SCANS USING HADAMARD EXCITATION,” which is incorporated by reference in its entirety for all purposes. Background Art

[0003] Embodiments disclosed herein relate to medical imaging techniques, and more particularly to a method for obtaining magnetic resonance imaging (MRI) data and a magnetic resonance imaging system.

[0004] Magnetic resonance imaging (MRI) is a noninvasive imaging technique that produces detailed three-dimensional anatomical images without the use of damaging radiation. It is widely used in medical diagnosis, disease staging, and follow-up without exposure to ionizing radiation. However, one of the main challenges of MRI is its long scan time, which can cause patient discomfort and reduce the throughput of diagnostic centers.

[0005] There is a constant demand for innovations that can provide faster MRI scans without sacrificing image quality. Reducing scan time can significantly improve the patient experience by reducing the anxiety associated with long and noisy scans. It also enhances motion robustness, allowing diagnostic centers to accommodate more patients, thereby increasing operational efficiency and revenue.

[0006] The current state of MRI technology includes various approaches to speed up scan times and improve patient comfort. One such approach is the use of multi-band (MB) technology, which allows for the simultaneous acquisition of multiple slices, thereby reducing scan time. This is often combined with parallel imaging techniques such as sensitivity encoding (SENSE) and generalized autocalibrated partially parallel acquisition (GRAPPA) to further speed up scans. However, the speedup factors that can be achieved with these methods are limited by the signal-to-noise ratio (SNR) penalty, often referred to as the g-factor penalty.

[0007] Simultaneous multi-slice (SMS) imaging is another advancement in MRI that aims to reduce scan time by acquiring multiple slices of the anatomy simultaneously. However, the application of SMS has been primarily limited to T2- and proton density (PD)-weighted sequences. The adiabatic nature of conventional inversion pulses poses a challenge when attempting to integrate them with SMS techniques, as the methods used to perform multi-band processing on the refocusing pulses are incompatible with adiabatic inversion pulses.

[0008] The current state of SMS imaging faces several challenges, including the inability to effectively apply SMS to inversion-prepared sequences, the complexity of multi-strip technology, and the need for specialized hardware. These limitations result in longer scan times and reduced patient throughput, which is particularly burdensome in clinical settings where efficiency and patient comfort are paramount.

[0009] Therefore, a novel solution that can overcome the limitations of existing technology and further speed up MRI scans would be highly beneficial to both patients and healthcare providers. Summary of the Invention

[0010] 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.

[0011] In one embodiment, a computer-implemented method for generating a magnetic resonance (MR) image of a subject is provided. The computer-implemented method includes applying, via a processing system including one or more processors, a sequence of Hadamard-coded radio frequency (RF) excitation pulses to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-coded adjacent slices; multiplexing, via the processing system, the Hadamard-coded adjacent slices with secondary RF excitation pulses to generate composite RF pulses; and generating, via the processing system, the MR image of the subject using the composite RF pulses.

[0012] In another embodiment, a system for generating a magnetic resonance (MR) image of an object is provided. The system includes a memory that encodes a processor-executable routine. The system also includes a processing system that includes one or more processors and is configured to access the memory and execute the processor-executable routine, wherein the processor-executable routine, when executed by the processing system, causes the processing system to perform an action. The action includes applying a Hadamard-encoded radio frequency (RF) excitation pulse sequence to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-encoded adjacent slices. The action also includes multiplexing the Hadamard-encoded adjacent slices with a secondary RF excitation pulse to generate a composite RF pulse. The action also includes generating the MR image of the object using the composite RF pulse.

[0013] In another embodiment, a non-transitory computer-readable medium is provided. The non-transitory computer-readable medium includes processor-executable code that, when executed by a processing system including one or more processors, causes the processing system to perform actions. The actions include applying a sequence of Hadamard-encoded radio frequency (RF) excitation pulses to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-encoded adjacent slices. The actions also include multiplexing the Hadamard-encoded adjacent slices with secondary RF excitation pulses to generate composite RF pulses. The actions also include generating the MR image of the object using the composite RF pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features, aspects, and advantages of the present disclosure 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:

[0015] Figure 1 is a schematic diagram of a magnetic resonance imaging (MRI) system according to aspects of the present disclosure;

[0016] Figure 2 is a flow chart of a method for generating an image using Hadamard-coded pulses according to aspects of the present disclosure;

[0017] Figures 3A to 3C illustrates a comparison of various pulse sequence diagrams (utilizing Hadamard-coded pulses and multi-band processing) according to aspects of the present disclosure;

[0018] Figure 4A and Figure 4B Two sets of pulse sequence diagrams (utilizing Hadamard-coded pulses and inversion recovery (IR) sequences) according to aspects of the present disclosure are illustrated;

[0019] Figure 5 depicts an axial image of a fat / water phantom according to aspects of the present disclosure; and

[0020] Figure 6 Depicted is a comparison of images acquired of a subject's knee in accordance with aspects of the present disclosure. DETAILED DESCRIPTION

[0021] One or more specific embodiments will be described below. In order to provide a concise description of these embodiments, not all features of an actual implementation may be 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.

[0022] When introducing elements of various embodiments of the present embodiment, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of these elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that additional elements may be present in addition to the listed elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus the additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments. Furthermore, the terms "circuit," "circuitry," and "controller" may include a single component or multiple components that are active and / or passive and are connected or otherwise coupled together to provide the described functionality.

[0023] In magnetic resonance imaging (MRI), a subject is placed in a magnet. When the subject is in the magnetic field generated by the magnet, the magnetic moments of the nuclei (such as protons) attempt to align with the magnetic field, but precess in a random order around the magnetic field at the Larmor frequency of the nuclei. The magnetic field of the magnet is called B0 and extends in the longitudinal or z-direction. When acquiring MR images, a magnetic field in the xy plane and close to the Larmor frequency (called the excitation field B1) is generated by a radio frequency (RF) coil and can be used to adjust the net magnetic moment (or net magnetization) of the nuclei to M. z Rotate or "flip" from the z direction toward the transverse or xy plane. The net magnetic moment M of the nucleus z This flip of is measured by the flip angle, which is the amount of rotation that the net magnetization undergoes during the application of the RF pulse to the RF coil. After the excitation signal B1 is terminated, the nucleus emits a signal, which is called the MR signal. In order to use the MR signal to generate an image of the object, a magnetic field gradient pulse (G x , G y and G z Gradient pulses are used to scan through k-space, the inverse of spatial frequency or distance. A Fourier relationship exists between the acquired MR signals and the image of the subject, so an image of the subject can be derived by reconstructing the MR signals. The image of the subject may include a two-dimensional (2D) or three-dimensional (3D) image.

[0024] The present disclosure provides systems and methods for accelerating the generation of MR images of an object (e.g., a patient) using a combination of multi-band technology and Hadamard excitation. Disclosed embodiments include systems and methods for generating images of an object. The systems and methods include applying a sequence of Hadamard-encoded radio frequency (RF) excitation pulses to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-encoded adjacent slices. The systems and methods include multiplexing the Hadamard-encoded adjacent slices with secondary RF excitation pulses to generate composite RF pulses. The systems and methods include generating MR images of the object using the composite RF pulses.

[0025] In certain embodiments, the secondary RF excitation pulse comprises a multi-band RF excitation pulse or an inversion recovery (IR) sequence. In certain embodiments, the secondary RF excitation pulse comprises a multi-band RF excitation pulse, and the Hadamard-encoded RF excitation pulse sequence and the multi-band RF excitation pulse are frequency multiplexed using the Larmor frequency of the nearby slice for the Hadamard-encoded RF excitation pulse and the Larmor frequency of the distant slice for the multi-band RF excitation pulse. In certain embodiments, the secondary RF excitation pulse comprises an IR sequence, and the IR sequence uses an increased slice thickness for the purpose of inverting or preparing the adjacent slices encoded by Hadamard. In certain embodiments, the IR sequence is followed by a Cartesian or propeller or radial or spiral readout of Hadamard. In certain embodiments, the secondary RF excitation pulse comprises an IR sequence, and the IR sequence uses adiabatic or non-adiabatic pulses to invert or prepare the adjacent slices encoded by Hadamard. In certain embodiments, a composite RF pulse is used to accelerate a diffusion scan, a perfusion scan, or a functional MRI scan with echo planar imaging (EPI) readout. In certain embodiments, the system and method include increasing the total acceleration factor of an MRI scan by utilizing a parallel imaging technique with a composite RF pulse. In certain embodiments, the parallel imaging technique includes at least one of Cartesian imaging auto-calibration reconstruction (ARC), generalized auto-calibration partially parallel acquisition (GRAPPA), sensitivity encoding (SENSE), array coil spatial sensitivity encoding (ASSET), or compressed sensing. In certain embodiments, the system and method include applying a slice selection gradient to refocus the pulse, the slice selection gradient being half the conventional slice gradient. In certain embodiments, the system and method include decoding a Hadamard-encoded pulse and a secondary-encoded pulse during the reconstruction process to generate a composite magnetic resonance (MR) signal. In certain embodiments, the system and method include increasing the total acceleration factor of an MRI scan by utilizing a pair of simultaneous multi-slices (SMS) with a composite RF pulse. In certain embodiments, slices excited by the SMS are encoded and decoded using a Hadamard or Hadamard-like factor. In certain embodiments, encoding and decoding are performed using a single average value or multiple average values for Hadamard encoding and decoding.

[0026] Embodiments of the present disclosure will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a schematic diagram of a magnetic resonance imaging (MRI) system 10. The operation of the system 10 can be controlled from an operator console 12, which includes an input device 13, a control panel 14, and a display screen 16. The input device 13 can be a mouse, joystick, keyboard, trackball, touch-activated screen, light wand, voice control, and / or other input device. The input device 13 can be used for interactive geometric shape specification. The console 12 communicates with a computer system 20 via a link 18, which enables the operator to control the generation and display of images on the display screen 16. The link 18 can be a wireless or wired connection. The computer system 20 may include modules that communicate with each other via a backplane 20a. The modules of the computer system 20 may include, for example, an image processor module 22, a central processing unit (CPU) module 24, and a memory module 26, which may include, for example, a frame buffer for storing image data arrays. The computer system 20 may be linked to archival media devices, permanent or backup storage, or a network for storing image data and programs, and communicates with the MRI system control 32 via a high-speed signal link 34. The MRI system control 32 may be separate from or integrated with the computer system 20. The computer system 20 and the MRI system control 32 together form an "MRI controller" 33 or "controller."

[0027] In an exemplary embodiment, the MRI system control 32 includes modules connected by a backplane 32a. These modules include a CPU module 36, a calibration module 37, and a pulse generator module 38. The CPU module 36 is connected to the operator console 12 via a data link 40. The MRI system control 32 receives commands from the operator via the data link 40 to indicate the scan sequence to be performed. The CPU module 36 operates the system components to implement the desired scan sequence and generates data indicating the timing, intensity, and shape of the generated RF pulses, as well as the timing and length of the data acquisition window. The CPU module 36 is connected to the components operated by the MRI controller 32, including the pulse generator module 38, which controls the gradient amplifiers 42, the physiological acquisition controller (PAC) 44, and the scan room interface circuit 46.

[0028] In one example, the CPU module 36 receives subject data from a physiological acquisition controller 44, which receives signals from sensors connected to the subject, such as ECG signals received from electrodes attached to the patient. As used herein, a subject is a person (or patient), an animal, or a phantom. The CPU module 36 receives signals from the sensors associated with the condition of the patient and the magnet system via a scan room interface circuit 46. The scan room interface circuit 46 also enables the MRI controller 33 to command a patient positioning system 48 to move the patient to a desired position for scanning.

[0029] The whole-body RF coil 56 is used to transmit waveforms toward the subject's anatomy. The whole-body RF coil 56 can be a body coil. The RF coil can also be a local coil, which can be placed closer to the subject's anatomy than a body coil. The RF coil 56 can also be a surface coil. An RF coil containing RF receiver channels can be used to receive signals from the subject's anatomy. A typical surface coil will have eight receive channels; however, different numbers of channels are possible. It is known to use a combination of the body coil 56 and a surface coil to provide better image quality.

[0030] The pulse generator module 38 operates the gradient amplifiers 42 to achieve the desired timing and shape of the gradient pulses generated during scanning. The gradient waveforms generated by the pulse generator module 38 are applied to the gradient amplifier system 42, which includes Gx, Gy, and Gz amplifiers. Each gradient amplifier excites a corresponding physical gradient coil in the gradient coil assembly 50 to generate magnetic field gradients used to spatially encode the acquired signals. Specifically, Gx corresponds to a flow / frequency encoding gradient, Gy corresponds to a phase encoding gradient, and Gz corresponds to a slice selection gradient. The gradient coil assembly 50 may form part of a magnet assembly 52, which also includes a polarizing magnet 54 (which, in operation, provides a longitudinal magnetic field B0 throughout a target volume 55 enclosed by the magnet assembly 52) and a whole-body RF coil 56 (which, in operation, provides a transverse magnetic field B1 that is substantially perpendicular to B0 throughout the target volume 55). The transceiver module 58 in the MRI system control 32 generates pulses that are amplified by an RF amplifier 60, which is coupled to the RF coil 56 via a transmit / receive switch 62. The resulting signals emitted by the excited nuclei in the subject's anatomy can be sensed by a receive coil (not shown) and provided to a preamplifier 64 via a transmit / receive switch 62. The amplified MR signals are demodulated, filtered, and digitized in the receiver portion of the transceiver 58. The transmit / receive switch 62 is controlled by a signal from the pulse generator module 38 to electrically connect the RF amplifier 60 to the coil 56 during a transmit mode and to connect the preamplifier 64 to the receive coil during a receive mode.

[0031] The MR signals generated by the excitation of the target are digitized by the transceiver module 58. The digitized signals are then processed by the MR system control 32 via a Fourier transform to generate k-space data, which is transmitted to the memory module 66 or other computer-readable medium via the MRI system control 32. "Computer-readable medium" may include, for example, a structure configured such that an electrical, optical, or magnetic state is fixed in a manner perceptible and reproducible by a conventional computer (e.g., text or images printed on paper or displayed on a screen, a compact disc or other optical storage medium, "flash" memory, EEPROM, SDRAM, or other electrical storage medium; a floppy disk or other magnetic disk; a magnetic tape or other magnetic storage medium).

[0032] The scan is complete when an array of raw k-space data is acquired in the computer-readable medium 66. For each image to be reconstructed, the raw k-space data is rearranged into a separate array of k-space data, and each of these k-space data arrays is input to the array processor 68, which operates to reconstruct the data into an array of image data using a reconstruction algorithm such as a Fourier transform. When complete k-space data is obtained, it represents the entire volume of the subject's body, and the k-space so obtained may be referred to as reference k-space. Similarly, when only partial k-space data is obtained, the image may be referred to as partial k-space. The image data is transmitted to the computer system 20 via the data link 34 and stored in memory. In response to commands received from the operator console 12, the image data may be archived in a long-term storage device, or may be further processed by the image processor 22 and transmitted to the operator console 12 and presented on the display 16.

[0033] MR signals are represented by complex numbers, where each position in k-space is represented by a complex number, where the I and Q quadrature MR signals are real and imaginary components. A composite MR image can be reconstructed based on the I quadrature MR signal and the Q quadrature MR signal using a process such as a Fourier transform of the k-space MR data. A composite MR image is an MR image having each pixel represented by a complex number, which also has a real component and an imaginary component. The magnitude M of the received MR signal can be determined as the square root of the sum of the squares of the I quadrature component and the Q quadrature component of the received MR signal, as shown in the following equation (3):

[0034]

[0035] And the phase φ of the received MR signal can also be determined as follows:

[0036]

[0037] MRI scans are long and noisy, frustrating for both patients and clients. Reducing scan time by reusing slices can help reduce patient anxiety, improve scan motion robustness, and allow diagnostic centers to accommodate more patients on the same day.

[0038] Current multi-band scanning techniques, combined with parallel imaging, help accelerate scanning, but the acceleration factor is limited by the g-factor penalty. In one embodiment, a technique is proposed to further accelerate multi-band scanning by supplementing it with Hadamard excitation in a single pulse sequence and combining it with parallel imaging.

[0039] Reducing scan time by reusing slices helps reduce patient anxiety levels, improves scan motion robustness, and allows diagnostic centers to accommodate more patients on the same day. Increasing the acceleration factor helps everyone in the imaging pipeline.

[0040] As described in greater detail below, the CPU module 36 or other computing component of the MRI system 10 (a processing system having one or more processors that execute instructions stored in a memory) is configured to generate magnetic resonance (MR) images of a subject. The CPU module 36 is configured to apply a sequence of Hadamard-encoded radio frequency (RF) excitation pulses to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-encoded adjacent slices. The CPU module 36 is further configured to multiplex the Hadamard-encoded adjacent slices with secondary RF excitation pulses to generate composite RF pulses. The CPU module is further configured to generate MR images of the subject using the composite RF pulses.

[0041] In certain embodiments, the secondary RF excitation pulse comprises a multi-band RF excitation pulse or an inversion recovery (IR) sequence. In certain embodiments, the secondary RF excitation pulse comprises a multi-band RF excitation pulse, and wherein the Hadamard-encoded RF excitation pulse sequence and the multi-band RF excitation pulse are frequency multiplexed using the Larmor frequency of a nearby slice for the Hadamard-encoded RF excitation pulse and the Larmor frequency of a distant slice for the multi-band RF excitation pulse. In certain embodiments, the secondary RF excitation pulse comprises an IR sequence, and wherein the IR sequence employs an increased slice thickness for the purpose of inverting or preparing adjacent slices that are Hadamard-encoded. In certain embodiments, the IR sequence is followed by a Hadamard-encoded Cartesian or propeller or radial or spiral readout. In certain embodiments, wherein the secondary RF excitation pulse comprises an IR sequence, the IR sequence employs adiabatic or non-adiabatic pulses to invert or prepare adjacent slices that are Hadamard-encoded. In certain embodiments, the composite RF pulse is employed to accelerate a diffusion scan, a perfusion scan, or a functional MRI scan with echo planar imaging (EPI) readout.

[0042] In some embodiments, the CPU module 36 is configured to utilize parallel imaging techniques with compound RF pulses to increase the overall acceleration factor of the MRI scan. In some embodiments, the parallel imaging techniques include at least one of Cartesian Imaging Auto-calibration Reconstruction (ARC), Generalized Auto-calibration Partially Parallel Acquisition (GRAPPA), Sensitivity Encoding (SENSE), Array Coil Spatial Sensitivity Encoding (ASSET), or compressed sensing.

[0043] In some embodiments, the CPU module 36 is configured to apply a slice selection gradient to refocus the pulses, which is half the conventional slice selection gradient. In some embodiments, the CPU module is configured to decode the Hadamard-encoded pulses and the secondary-encoded pulses during the reconstruction process to generate a composite magnetic resonance (MR) signal. In some embodiments, the CPU module 36 is configured to increase the overall acceleration factor of the MRI scan by using a pair of simultaneous multi-slices (SMS) with composite RF pulses. In some embodiments, the slices excited by the SMS are encoded and decoded using Hadamard or Hadamard-like factors. In some embodiments, encoding and decoding are performed using a single average or multiple averages for Hadamard encoding and decoding.

[0044] Figure 2 A flow chart of a method 200 for generating an image using Hadamard-coded pulses according to an embodiment of the present technology is shown. One or more steps of the method 200 may be performed by Figure 1 The method 200 is performed by one or more components of the MRI system 10 (e.g., the CPU module 36) in the embodiment of the present invention. The method 200 includes applying Hadamard encoding to a pulse sequence diagram (block 202). Specifically, a Hadamard-encoded radio frequency (RF) excitation pulse sequence is applied to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-encoded adjacent slices. The method 200 also includes multiplexing the Hadamard-encoded adjacent slices with secondary RF excitation pulses to generate composite RF pulses (block 204).

[0045] In some embodiments, a multi-band encoding technique is applied in the pulse sequence diagram (i.e., the secondary RF excitation pulse is a multi-band RF excitation pulse). In some embodiments, a slice selection gradient is applied to refocus the pulses, and the slice selection gradient is half the conventional slice gradient. In some embodiments, the Hadamard-coded RF excitation pulse sequence and the multi-band RF excitation pulse are frequency multiplexed using the Larmor frequency of the nearby slice for the Hadamard-coded RF excitation pulse and the Larmor frequency of the distant slice for the multi-band RF excitation pulse.

[0046] In certain embodiments, the secondary RF excitation pulse is an inversion recovery (IR) sequence. In certain embodiments, the IR sequence employs increased slice thickness for the purpose of inverting or preparing adjacent slices that are Hadamard-encoded. In certain embodiments, the IR sequence is followed by a Hadamard-encoded Cartesian or propeller or radial or spiral readout. In certain embodiments, the IR sequence employs adiabatic or non-adiabatic pulses to invert or prepare adjacent slices that are Hadamard-encoded.

[0047] Method 200 also includes applying the composite RF pulse to generate an MR image of the object using the composite RF pulse (block 206).In certain embodiments, the composite RF pulse is employed to accelerate a diffusion scan, a perfusion scan, or a functional MRI scan with echo planar imaging (EPI) readout.

[0048] In some embodiments, the method 200 includes utilizing parallel imaging techniques with compound RF pulses to increase the overall acceleration factor of the MRI scan (block 208). In some embodiments, the parallel imaging techniques include at least one of Cartesian imaging auto-calibration reconstruction (ARC), generalized auto-calibration partially parallel acquisition (GRAPPA), sensitivity encoding (SENSE), array coil spatial sensitivity encoding (ASSET), or compressed sensing.

[0049] In certain embodiments, method 200 includes increasing the overall acceleration factor of an MRI scan using a pair of simultaneous multi-slice (SMS) excitation slices with a composite RF pulse (block 210). The SMS excited slices are encoded and decoded using Hadamard or Hadamard-like factors. Encoding and decoding are performed using a single average value or multiple average values for Hadamard encoding and decoding.

[0050] Using these pulses, method 200 includes generating a composite MR signal using an MR scanner (block 212). Method 200 also includes decoding the Hadamard-encoded pulses and the secondary-encoded pulses during a reconstruction process to produce a composite MR signal (block 214). Method 200 also includes generating an MR image of the object using the composite MR signal (block 216).

[0051] Figures 3A to 3C A comparison of various pulse sequence diagrams (using Hadamard-coded pulses and multi-band processing) is illustrated. Specifically, Figures 3A to 3CThree sets of pulse diagrams 330, 332, and 334 are shown, corresponding to NEX1 (single-shot acquisition), NEX2 (dual-shot acquisition), and NEX2 simultaneous multi-slice (SMS) acquisitions, respectively. Each pulse diagram 330, 332, and 334 includes an x-gradient waveform, a y-gradient waveform, a z-gradient waveform, and corresponding spin-lattice relaxation (T1p) with parallel imaging and a second simultaneous multi-slice acquisition (SSP3). Pulse diagrams 330 and 332 also show Hadamard-encoded pulses, while pulse diagram 334 shows multi-band excitation remote pulses.

[0052] Generally speaking, in one embodiment, a technique is proposed for multi-band processing of Hadamard-coded pulses using parallel imaging to increase the overall acceleration factor. Quasi-Hadamard-coded pulses can also operate in a similar manner with multi-band and parallel imaging. Both multi-band and Hadamard encoding frequency multiplex RF pulses. Multi-band pulses use the Larmor frequencies of distant slices to generate composite RF pulses. Hadamard uses the Larmor frequencies of nearby slices to generate composite RF pulses. Readout gradients and other gradients are similar to existing sequences. The slice selection gradient for the refocusing pulse is half the size of the conventional slice gradient.

[0053] This technique of multiband processing of Hadamard-coded pulses using parallel imaging is very useful for speeding up diffusion-prepared scans, perfusion scans, or functional MRI scans using single-shot or double-shot echo-planar imaging.

[0054] It is known that multiband processing excitation and refocusing pulses can achieve slice acceleration. It is known that parallel imaging (Asset, ARC, Grappa, Sense, compressed sensing) can achieve in-plane acceleration. Multiband with parallel imaging is used in conjunction with ARC / Grappa. Adama and Adama-like techniques can achieve slice acceleration. Adama with parallel imaging is used in conjunction with ARC / Grappa. In this concept, Adama RF pulses are used to excite adjacent slices, followed by multiband processing of the resulting pulses, and then parallel imaging is applied to achieve total acceleration.

[0055] In another embodiment, the key concept of using Hadamard RF pulses to excite adjacent slices can also be applied to conventional inversion recovery (IR) sequences. Inversion recovery is a common technique for increasing T1 gray matter / white matter contrast. However, these pulses are typically adiabatic, with limited flexibility in their rotation angles. Consequently, their SAR (specific absorption rate) is increased compared to other RF excitation or refocusing pulses.

[0056] Simultaneous multislice (SMS) is a technique used to reduce sequence scan time. Its use is limited to T2 / PD-weighted sequences, primarily because adiabatic pulses are inherently incompatible with multislicing. The adiabatic nature of IR pulses precludes the use of multislicing techniques used to manipulate refocused pulses (e.g., gradient reversal, slew reduction).

[0057] Therefore, in one embodiment, multiple adjacent slices are excited during acquisition using SMS Hadamard and non-Hadamard factors. During the reconstruction phase, linear algebra techniques are used to handle the slice separation of the simultaneously excited slices. In this technique, we show how to adapt IR pulses to the SMS technique when excited with Hadamard / non-Hadamard factors.

[0058] Using this technology, T1-weighted or IR-prepared sequences can also be used in SMS to help reduce scan time and increase SNR in these sequences. T1-prepared sequences are used for pre- and post-contrast examinations to identify patient abnormalities. Therefore, if these sequences benefit from reduced scan time and increased SNR, the end user / customer benefits the most from fewer scan sessions per patient, with patients spending less time within the MR bore. This technology can be used for both 2D and 3D sequences, where the IR pulses excite multiple slices in 2D or multiple slabs in 3D.

[0059] Figure 4A and Figure 4B Two sets of pulse sequence diagrams 400 and 402 corresponding to NEX1 (single-shot acquisition) and NEX2 (double-shot acquisition), respectively, are illustrated (utilizing Hadamard-encoded pulses and an inversion recovery (IR) sequence). Both pulse sequence diagrams 400 and 402 also show Hadamard-encoded pulses. Thus, in one embodiment, an IR preparation module (with the correct inversion time for fat / fluid suppression) is applied to a pair of SMS Hadamard-excited slices, and Hadamard decoding is applied to achieve slice separation in a fast spin echo sequence. This addresses an unmet need in SMS, enabling the use of IR preparation in 2D or 3D SMS sequences. SMS-excited slices can be Hadamard or Hadamard-like encoded and decoded. For SMS encoding / decoding, the excitation can be 2Nex or 1Nex.

[0060] Inversion pulses are applied to prepare multiple adjacent slices by reducing the slice selection gradient. This technique is applicable to any coil (regardless of the number of channels) and simplifies design. It is also suitable for other inversion-prepared sequences, such as T1 FLAIR and T2 FLAIR with extended scan times. It is also effective for contrast-based inversion-prepared cardiac sequences.

[0061] The SMS Hadamard encoding technique for inversion preparation applied to adjacent slices is compatible with existing adiabatic inversion pulses. Current SMS techniques (multi-band) require multi-band processing of a composite adiabatic pulse to inversion prepare multiple, widely separated slices. (In addition to complex crosstalk across multiple TRs, SAR suppression pulses, loss of adiabatic properties, incorrect rotation angles, and the need for RF stretching or gradient inversion are all potential issues with multi-band inversion recovery.) Other inversion preparation schemes require the use of non-selective and slab inversion pulses to excite large slabs. SMS excitation for such prepared sequences provides slightly different TIs for each slice.

[0062] Figure 5 Depicted is an axial image of a fat / water phantom acquired using inversion-prepared SMS Hadamard-coded excitation. The axial image includes 16 slices 2nex from the fat / water phantom. The axial image shows uniform fat suppression across the slices using inversion-prepared SMS Hadamard-coded excitation.

[0063] Figure 6 A comparison of images 600, 602 acquired of a subject's knee is depicted. Image 600 was acquired without using Hadamard coded excitation processing techniques. Image 602 was acquired using Hadamard coded excitation processing techniques. Image 600 shows artifacts in a scan of a human knee, while another image 602 shows the same scan of the knee with artifacts reduced due to the use of Hadamard coded excitation processing techniques.

[0064] The disclosed embodiments have the following technical effects: MR scans are faster and cheaper to acquire due to reduced scan time, as existing hardware for running multi-band on the scanner can be used more efficiently. Furthermore, MR scans are safer because Hadamard or Hadamard-like encoding only adds peak B1 / SAR to the multi-band excitation pulses, while refocusing the multi-band pulses is unaffected.

[0065] 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).

[0066] The present disclosure also provides support for a computer-implemented method for generating a magnetic resonance (MR) image of a subject, the computer-implemented method comprising: applying, via a processing system comprising one or more processors, a sequence of Hadamard-encoded radio frequency (RF) excitation pulses to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-encoded adjacent slices; multiplexing, via the processing system, the Hadamard-encoded adjacent slices with secondary RF excitation pulses to generate composite RF pulses; and generating, via the processing system, the MR image of the subject using the composite RF pulses. In a first example of the computer-implemented method, the secondary RF excitation pulses comprise multi-band RF excitation pulses or inversion recovery (IR) sequences. In a second example of the computer-implemented method, optionally including the first example, the secondary RF excitation pulses comprise the multi-band RF excitation pulses, and wherein the sequence of Hadamard-encoded RF excitation pulses and the multi-band RF excitation pulses are frequency multiplexed using a Larmor frequency for a nearby slice of the Hadamard-encoded RF excitation pulses and a Larmor frequency for a distant slice of the multi-band RF excitation pulses. In a third example of the computer-implemented method, optionally including one or both of the first and second examples, the secondary RF excitation pulse comprises the IR sequence, and wherein the IR sequence employs increased slice thickness for the purpose of inverting or preparing the Hadamard-encoded adjacent slice. In a fourth example of the computer-implemented method, optionally including one or more or each of the first to third examples, the IR sequence is followed by a Hadamard-encoded Cartesian or propeller or radial or spiral readout. In a fifth example of the computer-implemented method, optionally including one or more or each of the first to fourth examples, wherein the secondary RF excitation pulse comprises the IR sequence, and wherein the IR sequence employs adiabatic or non-adiabatic pulses to invert or prepare the Hadamard-encoded adjacent slice. In a sixth example of the computer-implemented method, optionally including one or more or each of the first to fifth examples, employing the composite RF pulse to accelerate a diffusion scan, a perfusion scan, or a functional MRI scan with echo planar imaging (EPI) readout. In a seventh example of the computer-implemented method, optionally including one or more or each of the first to sixth examples, the computer-implemented method further comprises utilizing, via the processing system, a parallel imaging technique with the composite RF pulse to increase a total acceleration factor of the MRI scan. In an eighth example of the computer-implemented method, optionally including one or more or each of the first to seventh examples, the parallel imaging technique comprises at least one of Cartesian Imaging Auto-calibration Reconstruction (ARC), Generalized Auto-calibration Partially Parallel Acquisition (GRAPPA), Sensitivity Encoding (SENSE), Array Coil Spatial Sensitivity Encoding (ASSET), or Compressed Sensing.In a ninth example of the computer-implemented method, optionally including one or more or each of the first through eighth examples, the computer-implemented method further comprises applying, via the processing system, a slice selection gradient to refocus the pulses, the slice selection gradient being half a conventional slice gradient. In a tenth example of the computer-implemented method, optionally including one or more or each of the first through ninth examples, the computer-implemented method further comprises decoding, via the processing system, the Hadamard-encoded pulses and the secondary-encoded pulses during reconstruction to produce composite magnetic resonance (MR) signals. In an eleventh example of the computer-implemented method, optionally including one or more or each of the first through tenth examples, the computer-implemented method further comprises utilizing, via the processing system, a pair of simultaneous multi-slices (SMS) with the composite RF pulses to increase an overall acceleration factor of the MRI scan. In a twelfth example of the computer-implemented method, optionally including one or more or each of the first through eleventh examples, encoding and decoding slices of the SMS excitation using Hadamard or Hadamard-like factors. In a thirteenth example of the computer-implemented method, optionally including one or more or each of the first to twelfth examples, encoding and decoding are performed using a single average value or multiple average values for Hadamard encoding and decoding.

[0067] The present disclosure also provides support for a system for generating a magnetic resonance (MR) image of an object, comprising: a memory encoding a processor-executable routine; and a processing system comprising one or more processors and configured to access the memory and execute the processor-executable routine, wherein the processor-executable routine, when executed by the processing system, causes the processing system to: apply a Hadamard-encoded radio frequency (RF) excitation pulse sequence to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-encoded adjacent slices; multiplex the Hadamard-encoded adjacent slices with a secondary RF excitation pulse to generate a composite RF pulse; and generate the MR image of the object using the composite RF pulse. In a first example of the system, the secondary RF excitation pulse comprises a multi-band RF excitation pulse or an inversion recovery (IR) sequence. In a second example of the system, optionally including the first example, the secondary RF excitation pulse comprises the multi-band RF excitation pulse, and wherein the Hadamard-encoded RF excitation pulse sequence and the multi-band RF excitation pulse are frequency multiplexed using a Larmor frequency for a nearby slice of the Hadamard-encoded RF excitation pulse and a Larmor frequency for a distant slice of the multi-band RF excitation pulse. In a third example of the system, optionally including one or both of the first and second examples, the secondary RF excitation pulse comprises the IR sequence, and wherein the IR sequence employs increased slice thickness for the purpose of inverting or preparing the Hadamard-encoded adjacent slice. In a fourth example of the system, optionally including one or more or each of the first to third examples, the IR sequence is followed by a Hadamard-encoded Cartesian, propeller, radial, or helical readout.

[0068] The present disclosure also provides support for a non-transitory computer-readable medium comprising processor-executable code that, when executed by a processing system comprising one or more processors, causes the processing system to: apply a Hadamard-encoded radio frequency (RF) excitation pulse sequence to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-encoded adjacent slices; multiplex the Hadamard-encoded adjacent slices with secondary RF excitation pulses to generate composite RF pulses; and generate a magnetic resonance (MR) image of an object using the composite RF pulses.

[0069] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any included methods. The patentable scope of the invention 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 generating a magnetic resonance (MR) image of an object, the computer-implemented method comprising: applying, via a processing system including one or more processors, a Hadamard-coded radio frequency (RF) excitation pulse sequence to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-coded adjacent slices; multiplexing, via the processing system, the Hadamard-encoded adjacent slices with secondary RF excitation pulses to generate composite RF pulses; as well as The MR image of the object is generated via the processing system using the composite RF pulse. 2 . The computer-implemented method of claim 1 , wherein the secondary RF excitation pulse comprises a multi-band RF excitation pulse or an inversion recovery (IR) sequence.

3. The computer-implemented method of claim 2 , wherein the secondary RF excitation pulses comprise the multi-band RF excitation pulses, and wherein the sequence of Hadamard-coded RF excitation pulses and the multi-band RF excitation pulses are frequency multiplexed using a Larmor frequency for a nearby slice of the Hadamard-coded RF excitation pulses and a Larmor frequency for a distant slice of the multi-band RF excitation pulses.

4. The computer-implemented method of claim 2, wherein the secondary RF excitation pulses comprise an IR sequence, and wherein the IR sequence employs increasing slice thickness for the purpose of inverting or preparing the Hadamard-encoded adjacent slices.

5. The computer-implemented method of claim 4, wherein the IR sequence is followed by a Hadamard-encoded Cartesian or propeller or radial or spiral readout.

6. The computer-implemented method of claim 2, wherein the secondary RF excitation pulses comprise the IR sequence, and wherein the IR sequence employs adiabatic or non-adiabatic pulses to invert or prepare the Hadamard-encoded adjacent slices.

7. The computer-implemented method of claim 1, wherein the composite RF pulses are employed to accelerate a diffusion scan, a perfusion scan, or a functional MRI scan with echo planar imaging (EPI) readout.

8. The computer-implemented method of claim 1, further comprising utilizing, via the processing system, a parallel imaging technique with the composite RF pulses to increase an overall acceleration factor of the MRI scan.

9. The computer-implemented method of claim 8, wherein the parallel imaging technique comprises at least one of Auto-calibrated Reconstruction with Cartesian Imaging (ARC), Generalized Auto-calibrated Partially Parallel Acquisition (GRAPPA), Sensitivity Encoding (SENSE), Array Coil Spatial Sensitivity Encoding (ASSET), or Compressed Sensing.

10. The computer-implemented method of claim 1, further comprising applying, via the processing system, a slice selection gradient to refocus pulses, the slice selection gradient being half of a conventional slice gradient.

11. The computer-implemented method of claim 1 , further comprising decoding, via the processing system, the Hadamard-encoded pulses and the secondary-encoded pulses in a reconstruction process to produce composite magnetic resonance (MR) signals.

12. The computer-implemented method of claim 1, further comprising utilizing, via the processing system, a pair of slices of simultaneous multi-slice (SMS) excitation with the composite RF pulse to increase an overall acceleration factor of the MRI scan.

13. The computer-implemented method of claim 12, wherein slices of the SMS excitation are encoded and decoded using Hadamard or Hadamard-like factors.

14. The computer-implemented method of claim 13, wherein the encoding and decoding are performed using a single average value or multiple average values for Hadamard encoding and decoding.

15. A system for generating a magnetic resonance (MR) image of a subject, the system comprising: a memory encoding processor-executable routines; a processing system comprising one or more processors and configured to access the memory and execute the processor-executable routine, wherein the processor-executable routine, when executed by the processing system, causes the processing system to: applying a Hadamard-coded radio frequency (RF) excitation pulse sequence to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-coded adjacent slices; multiplexing the Hadamard-encoded adjacent slices with a secondary RF excitation pulse to generate a composite RF pulse; as well as The MR image of the object is generated using the composite RF pulse.

16. The system of claim 15, wherein the secondary RF excitation pulse comprises a multi-band RF excitation pulse or an inversion recovery (IR) sequence.

17. The system of claim 16 , wherein the secondary RF excitation pulses include the multi-band RF excitation pulses, and wherein the Hadamard-coded RF excitation pulse sequence and the multi-band RF excitation pulses are frequency multiplexed using a Larmor frequency for a nearby slice of the Hadamard-coded RF excitation pulses and a Larmor frequency for a distant slice of the multi-band RF excitation pulses.

18. The system of claim 16, wherein the secondary RF excitation pulses comprise the IR sequence, and wherein the IR sequence employs increasing slice thickness for the purpose of inverting or preparing the Hadamard-encoded adjacent slices.

19. The system of claim 18, wherein the IR sequence is followed by a Hadamard-encoded Cartesian or propeller or radial or spiral readout.

20. A non-transitory computer-readable medium comprising processor-executable code that, when executed by a processing system comprising one or more processors, causes the processing system to: applying a Hadamard-coded radio frequency (RF) excitation pulse sequence to adjacent slices within a magnetic resonance imaging (MRI) scanner to generate Hadamard-coded adjacent slices; multiplexing the Hadamard-encoded adjacent slices with a secondary RF excitation pulse to generate a composite RF pulse; and A magnetic resonance (MR) image of the subject is generated using the composite RF pulse.

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