Pulse sequence generation system and method for reducing acoustic noise in a magnetic resonance system

Abstract

The present invention is entitled "Pulse sequence generation system and method for reducing acoustic noise in a magnetic resonance system". The present invention discloses a pulse sequence generation computing device for a magnetic resonance imaging (MRI) system, the device including a processor in communication with a memory device. The processor is programmed to: receive a pulse sequence including a plurality of gradient pulses, and provide a pulse sequence threshold function corresponding to an acoustic noise reduction level. For each gradient pulse in the pulse sequence, the processor is programmed to: determine the amplitude and slew rate of the gradient pulse, determine a threshold amplitude and a threshold slew rate for the gradient pulse, and compare the determined amplitude and slew rate with the threshold amplitude and threshold slew rate. If the determined amplitude or slew rate exceeds the threshold amplitude or the threshold slew rate, the processor adjusts at least one of the amplitude and slew rate of the gradient pulse to the amplitude and slew rate as defined by the pulse sequence threshold function.

Description

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0002] This disclosure was made with Government support under Contract No. W81XWH-16-2-0054 awarded by the Department of Defense under the Congressionally Directed Medical Research Program. The Government has certain rights in the inventions. Background Art

[0003] The field of the present disclosure relates generally to systems and methods for generating pulse sequences in a magnetic resonance (MR) system, and more particularly to systems and methods for reducing acoustic noise in an MR system.

[0004] MR imaging (MRI) has proven useful for the diagnosis of many diseases. MRI provides detailed images of soft tissue, abnormal tissue (such as tumors), and other structures that cannot be easily imaged by other imaging modalities such as computed tomography (CT). In addition, MRI operates without exposing the patient to ionizing radiation experienced in modalities such as CT and X-rays.

[0005] In MR imaging, acoustic noise affects patient and operator safety. Acoustic noise causes Lorenz forces between the main magnetic field and the conductors carrying time-varying currents in the gradient system. The interaction causes vibrations that produce acoustic pressure waves, which can be harmful if not controlled or mitigated. Summary of the invention

[0006] In one aspect, a pulse sequence generation computing device for a magnetic resonance imaging (MRI) system is provided. The pulse sequence generation computing device includes at least one processor in communication with at least one memory device. The at least one processor is programmed to receive a pulse sequence including a plurality of gradient pulses and provide a pulse sequence threshold function corresponding to an acoustic noise reduction level of acoustic noise generated by switching gradients in the MRI system. The pulse sequence threshold function indicates a plurality of threshold amplitudes of the gradient pulses and a plurality of threshold slew rates of the gradient pulses, each threshold slew rate being associated with one of the plurality of threshold amplitudes. For each gradient pulse in the pulse sequence, the at least one processor is further programmed to determine an amplitude of the gradient pulse and a slew rate of the gradient pulse, determine a threshold amplitude corresponding to the determined slew rate and a threshold slew rate corresponding to the determined amplitude, compare the determined amplitude to the threshold amplitude and compare the determined slew rate to the threshold slew rate, and if the determined amplitude exceeds the amplitude threshold or the determined slew rate exceeds the slew rate threshold, the at least one processor is further configured to modify the gradient pulse by adjusting at least one of the amplitude and the slew rate of the gradient pulse to the slew rate as defined by the pulse sequence threshold function.

[0007] In another aspect, a computer-implemented method for generating a pulse sequence in a magnetic resonance imaging (MRI) system is provided. The method includes: receiving a pulse sequence including a plurality of gradient pulses, and providing a pulse sequence threshold function corresponding to an acoustic noise reduction level of acoustic noise generated by switching gradients in the MRI system. The pulse sequence threshold function indicates a plurality of threshold amplitudes of the gradient pulse and a plurality of threshold slew rates of the gradient pulse, each threshold slew rate being associated with one of the plurality of threshold amplitudes. The method also includes: determining, for each gradient pulse in the pulse sequence, an amplitude of the gradient pulse and a slew rate of the gradient pulse; determining a threshold amplitude corresponding to the determined slew rate and a threshold slew rate corresponding to the determined amplitude; comparing the determined amplitude with the threshold amplitude and comparing the determined slew rate with the threshold slew rate; and if the determined amplitude exceeds an amplitude threshold or the determined slew rate exceeds a slew rate threshold, modifying the gradient pulse by adjusting at least one of the amplitude and slew rate of the gradient pulse to the amplitude and slew rate as defined by the pulse sequence threshold function. The method also includes causing the modified pulse sequence to be generated by the MRI system.

[0008] In yet another aspect, a pulse sequence generation computing device for a magnetic resonance imaging (MRI) system is provided. The pulse sequence generation computing device includes at least one processor in communication with at least one memory device. The at least one processor is programmed to receive a pulse sequence including a plurality of gradient pulses and provide a pulse sequence threshold function corresponding to an acoustic noise reduction level of acoustic noise generated by switching gradients in the MRI system. The pulse sequence threshold function indicates a plurality of threshold amplitudes of the gradient pulses and a plurality of threshold slew rates of the gradient pulses, each threshold slew rate being associated with one of the plurality of threshold amplitudes. For at least one gradient pulse in the pulse sequence, the at least one processor is further programmed to determine an amplitude of the gradient pulse and a slew rate of the gradient pulse, determine a threshold amplitude corresponding to the determined slew rate and a threshold slew rate corresponding to the determined amplitude, compare the determined amplitude to the threshold amplitude and compare the determined slew rate to the threshold slew rate, and if the determined amplitude exceeds the amplitude threshold or the determined slew rate exceeds the slew rate threshold, the at least one processor is further configured to modify the gradient pulse by adjusting at least one of the amplitude and the slew rate of the gradient pulse to the slew rate as defined by the pulse sequence threshold function. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic diagram of an exemplary magnetic resonance imaging (MRI) system.

[0010] Figure 2 is used with Figure 1 An exemplary pulse sequence for use with an MRI system is shown.

[0011] Figure 3 yes Figure 2 Exemplary gradient pulses of the pulse sequence shown.

[0012] Figure 4 is a flow chart of an exemplary method of generating a pulse sequence.

[0013] Figure 5 It is shown for Figure 4 A graph of an exemplary pulse sequence threshold function for the method shown.

[0014] Figure 6 is used Figure 4 A plot of the equivalent continuous acoustic noise level of a pulse train derived by the method shown.

[0015] Figure 7 is used Figure 4 A plot of the peak acoustic noise level of a pulse train derived by the method shown.

[0016] Figure 8 is a block diagram of an exemplary computing device. DETAILED DESCRIPTION

[0017] The present disclosure includes systems and methods for generating pulse sequences in a magnetic resonance (MR) system using a pulse sequence threshold function that can be adjusted using configuration variables. The pulse sequence threshold function indicates a plurality of threshold gradient amplitudes for a gradient pulse and a plurality of threshold slew rates for a gradient pulse or waveform, each threshold slew rate being associated with one of the plurality of threshold gradient amplitudes. The systems and methods disclosed herein provide acoustic noise reduction in an MR system by modulating a derating of gradient pulse or waveform characteristics, such as pulse amplitude and slew rate, to the pulse characteristics of individual pulses or waveforms according to the pulse sequence threshold function. In contrast to general derating in which static pulse characteristic thresholds are set globally, the use of a pulse sequence threshold function allows for an active or dynamic derating scheme in which a plurality of thresholds can be provided and selected for any individual pulse or waveform to achieve a desired pulse or waveform characteristic and a desired lower level of acoustic noise in the MR system. Thus, each pulse or waveform or a plurality of pulses or waveforms are individually adjusted according to the threshold function, wherein each pulse or waveform or a group of pulses or waveforms has a different gradient pulse or waveform rise time and amplitude characteristic. The gradient pulse or waveform rise time and amplitude values ​​are consistent with the threshold function. An MR imaging (MRI) pulse sequence is shown as an example. The systems and methods described herein may also be applied to other MR pulse sequences such as pulse sequences for MR spectroscopy. Methodological aspects will in part be apparent and in part be explicitly discussed in the following description.

[0018] In magnetic resonance imaging (MRI), a subject is placed in a magnet. As used herein, a subject is a human, an animal, a phantom, or any object scanned by an MR system. When the subject is in a magnetic field generated by a magnet, the magnetic moment of a nucleus such as a proton attempts to align with the magnetic field, but precesses around the magnetic field in a random order at the Larmor frequency of the nucleus. The magnetic field of the magnet is referred to as B0 and extends in the longitudinal or z direction. In the process of collecting MRI images, a magnetic field (referred to as an excitation field B1) in the xy plane and close to the Larmor frequency is generated by a radio frequency (RF) coil, and can be used to rotate or "tilt" the net magnetic moment Mz of the nucleus from the z direction toward the transverse or xy plane. After the excitation signal B1 terminates, the nucleus emits a signal, which is referred to as an MR signal. In order to generate an image of the subject using MR signals, magnetic field gradient pulses (Gx, Gy, and Gz) are used. Gradient pulses or waveforms (used interchangeably herein) are used to scan the reverse of the space or distance through k-space, spatial frequency. There is a Fourier relationship between the acquired MR signals and the image of the subject, so the image of the subject can be derived by reconstructing the MR signals.

[0019] Figure 1A schematic diagram of an exemplary MRI system 10 is shown. In an exemplary embodiment, the MRI system 10 includes a workstation 12 having a display 14 and a keyboard 16. The workstation 12 includes a processor 18, such as a commercially available programmable machine running a commercially available operating system. The workstation 12 provides an operator interface that allows a scan plan to be entered into the MRI system 10. The workstation 12 is connected to a pulse sequence server 20, a data acquisition server 22, a data processing server 24, and a data storage server 26. The workstation 12 and each server 20, 22, 24, and 26 communicate with each other.

[0020] In an exemplary embodiment, the pulse sequence server 20 operates the gradient system 28 and the radio frequency (RF) system 30 in response to instructions downloaded from the workstation 12. The instructions are used to generate gradient waveforms and RF waveforms in the MR pulse sequence. The RF coil 38 and the gradient coil assembly 32 are used to perform the prescribed MR pulse sequence. The RF coil 38 is shown as a whole body RF coil. The RF coil 38 can also be a local coil that can be placed near the anatomical structure to be imaged, or a coil array including multiple coils.

[0021] In the exemplary embodiment, a gradient waveform for performing a delimiting scan is generated and applied to a gradient system 28, which excites the gradient coils in a gradient coil assembly 32 to generate a magnetic field gradient G for position encoding of the MR signals. x , G y , and G z The gradient coil assembly 32 forms part of a magnet assembly 34 , which also includes a polarizing magnet 36 and an RF coil 38 .

[0022] In an exemplary embodiment, the RF system 30 includes an RF transmitter for generating RF pulses used in an MR pulse sequence. The RF transmitter responds to the scanning scheme and direction from the pulse sequence server 20 to generate RF pulses with a desired frequency, phase, and pulse amplitude waveform. The generated RF pulse or waveform can be applied to the RF coil 38 by the RF system 30. The response MR signal detected by the RF coil 38 is received by the RF system 30 and amplified, demodulated, filtered, and digitized under the instruction of the command generated by the pulse sequence server 20. The RF coil 38 is described as a transmitter and receiver coil, so that the RF coil 38 transmits RF pulses and detects MR signals. In one embodiment, the MRI system 10 may include a transmitter RF coil that transmits RF pulses and a separate receiver coil that detects MR signals. The transmission channel of the RF system 30 can be connected to the RF transmission coil, and the receiver channel can be connected to a separate RF receiver coil. Typically, the transmission channel is connected to the whole body RF coil 38, and each receiver segment is connected to a separate local RF coil.

[0023] In an exemplary embodiment, the RF system 30 also includes one or more RF receiver channels. Each RF receiver channel includes an RF amplifier that amplifies the MR signals received by the RF coil 38 to which the channel is connected; and a detector that detects and digitizes the I quadrature component and the Q quadrature component of the received MR signal. The magnitude of the received MR signal can then be determined as the square root of the sum of the squares of the I component and the Q component, as shown in the following equation (1):

[0024]

[0025] And the phase of the received MR signal can also be determined as shown in the following equation (2):

[0026]

[0027] In an exemplary embodiment, the digitized MR signal samples generated by the RF system 30 are received by the data acquisition server 22. The data acquisition server 22 can operate in response to instructions downloaded from the workstation 12 to receive real-time MR data and provide a buffer memory so that no data is lost due to data overflow. In some scans, the data acquisition server 22 only passes the acquired MR data to the data processing server 24. However, in scans where information derived from the acquired MR data is needed to control further execution of the scan, the data acquisition server 22 is programmed to generate the required information and transmit it to the pulse sequence server 20. For example, during a pre-scan, MR data is acquired and used to calibrate the pulse sequence executed by the pulse sequence server 20. In addition, navigator signals can be acquired during the scan and used to adjust the operating parameters of the RF system 30 or the gradient system 28, or to control the view order in which k-space is sampled.

[0028] In an exemplary embodiment, the data processing server 24 receives MR data from the data acquisition server 22 and processes the MR data according to instructions downloaded from the workstation 12. Such processing may include, for example, Fourier transforming the raw k-space MR data to produce a two-dimensional or three-dimensional image, applying filters to reconstructed images, performing back-projection image reconstruction on the acquired MR data, generating functional MR images, and calculating motion or flow images.

[0029] In an exemplary embodiment, the image reconstructed by the data processing server 24 is transmitted back to the workstation 12 and stored there. In some embodiments, the real-time image is stored in a database memory cache ( Figure 1In the example of FIG. 1 , the real-time images can be output from the database memory cache to the operator display 14 or a display 46 located near the magnet assembly 34 for use by the attending physician. Batch mode images or selected real-time images can be stored in a disk storage device 48 or a host database on the cloud. When such images have been reconstructed and transferred to the storage device, the data processing server 24 notifies the data storage server 26. The operator can use the workstation 12 to archive images, generate films, or send images to other facilities via the network.

[0030] Figure 2 2 is a pulse sequence diagram of a fast spin echo sequence 202. The fast spin echo sequence 202 includes an RF pulse or waveform 208 and a gradient pulse or waveform 210. The gradient pulse 210 may be along a readout direction 212 or a phase encoding direction 215. The gradient pulse 210 may be along a slice encoding direction (not shown) or a second phase encoding direction (not shown) in a three-dimensional (3D) pulse sequence. The diagram of the fast spin echo sequence 202 may also show MR signals in a signal channel 220. In the fast spin echo sequence 202, the RF pulse 208 includes an excitation pulse 214 and a plurality of refocusing pulses 216. The excitation pulse 214 excites the magnetization and rotates the magnetization relative to the xy plane. The refocusing pulse 216 refocuses the dephased magnetization so that an echo 221 is formed. The signal channel 220 includes a series of echoes 221 or an echo train 222. The k-space position of the echo in the ky direction or the phase encoding direction is determined by the phase encoding gradient 217. The time between repetitions of the pulse sequence 202 is called the repetition time (TR). The number of echoes in one TR of the fast spin echo sequence 202 is called the echo train length (ETL). The ETL can be any number between two and the image matrix size in the phase encoding direction. In operation, a slice in the subject is selected and excited by an excitation pulse 214 and refocused by a refocusing pulse 216. The k-space is scanned by a varying gradient pulse 210. Echoes 221 corresponding to multiple ky lines in the k-space are collected in one TR of the ETL. The sequence 202 is repeated to scan through the k-space to collect MR signals at other ky lines. The MR signals are used to reconstruct the MR image.

[0031] Figure 3 is a schematic diagram of an exemplary gradient pulse 210. Figure 2 Schematically shown as a rectangle in the readout direction, but as Figure 3 As shown, due to the limited switching rate of the MRI system, the gradient pulse 210 has a substantially trapezoidal shape. Specifically, the gradient pulse 210 has a gradient amplitude (G p), typically measured in millitesla per meter (mT / m) or gauss per centimeter (G / cm). The integral of the gradient amplitude over the total pulse width 234 of the gradient pulse is proportional to the k-space position sampled by the gradient pulse 210. In MRI, k-space is sampled by varying the gradient pulse 210 in a readout direction 212 and a phase encoding direction 215, where the readout direction corresponds to kx, the phase encoding direction corresponds to ky, and the second phase encoding direction corresponds to kz. The spatial resolution of the MRI image in the x, y, and z directions determines the maximum kx, ky, or kz, respectively. That is, the spatial resolution determines the maximum value of the integral of the gradient pulse 210 over the duration 234. Therefore, in order to achieve the desired spatial resolution, the amplitude G of the gradient pulse 210 can be adjusted. p and / or the duration 234 of the gradient pulse 210. The amplitude G of the gradient pulse 210 p The maximum gradient amplitude is limited by the peak or maximum gradient amplifier capability of the scanner 10 system and the maximum gradient slew rate. Superconducting whole body scanners may have maximum gradient strengths in the range of 20 mT / m to 100 mT / m. This includes magnets with field strengths up to and exceeding 7.0 Tesla (T), with typical whole body MRI scanners operating in the range of 0.5T to 3.0T.

[0032] Due to the finite slew rate, the gradient pulse 210 does not instantaneously reach its required amplitude G p and is limited by the maximum voltage that can be supplied by the gradient amplifier (not shown) of the gradient system 28. In addition to the plateau segment 236, the gradient pulse 210 thus comprises a gradient pulse 210 rising to a gradient amplitude G p The ramp-up portion (rise time) 230 and the gradient pulse from the gradient amplitude G p The ramp-down portion (ramp-down time) 232 of the gradient pulse 210 is shown as the ramp-down portion of the gradient pulse 210 to reach the gradient amplitude (G p ) amount of time. The duration of the gradient waveform 210 at the plateau segment 236 may also be referred to as the gradient pulse width. The total gradient pulse width 234 includes the constant amplitude 236 plus the duration of the ramp-up portion 230 and the ramp-down portion 232. Typically the rise time 230 and the fall time 232 of the gradient pulse or waveform have the same value. The slew rate (SR) of the gradient pulse 210, typically measured in Teslas per meter per second (T / m / s), is shown as the slope of the gradient pulse 210 over the rise time (τ) period. The slew rate (SR) δ of the gradient pulse 210 is equal to the gradient amplitude (G p)δ divided by the rise time (τ). That is, the slew rate (SR) is inversely proportional to the rise time (τ). The faster the slew rate (SR), the shorter the rise time (τ). Therefore, for a given amplitude (G p ), a faster slew rate (SR) shortens the duration 234 of the gradient pulse 210. The maximum available slew rate (SR) of the gradient pulse 210 is limited by the slew rate specification of the scanner (i.e., the maximum voltage that the gradient amplifier can supply). For example, a scanner with a high slew rate allows fast switching between gradient pulses with high amplitudes. When designing a pulse sequence, the slew rate (SR) of all gradient pulses 210 in the pulse sequence may be the same. Alternatively, the slew rate (SR) may be adjusted for each gradient pulse 210 individually, but the maximum slew rate (SR) may not be exceeded.

[0033] refer to Figure 1 During operation, providing an electrical signal to the current-carrying conductors in the gradient coil assembly 32 may induce a Lorentz force in the magnet assembly 34, which in turn generates an acoustic pressure wave that produces acoustic noise within the magnet assembly 34 and the gradient coil assembly 32. Specifically, the Lorentz force and the resulting acoustic noise are generated by switching the gradient pulses 210 in the gradient coil assembly 32, and propagate throughout the magnet assembly 34. Acoustic noise in MRI affects patient and operator safety of MRI, and is one of the major categories of significant risk to clinical MR systems considered by the U.S. Food and Drug Administration (FDA). The FDA specifies the acoustic noise limit for non-significant risk operation as an A-weighted root mean square (rms) sound pressure level less than or equal to 99 A-weighted decibel equivalent continuous sound level (LAeq) with hearing protection in place and less than or equal to 140 decibel (dB) unweighted peak sound level (Lpeak). Even with hearing protection in place, acoustic noise is a major source of patient discomfort, increasing with increasing magnetic field strength, affecting both adult and pediatric populations, especially at 3.0 T and above. In addition, acoustic noise from gradients impedes communication between the patient and the scan operator. Acoustic noise is an important issue in certain brain imaging, and has specifically been shown to have an impact on the results of functional MRI (fMRI) studies. In addition, quiet or silent MRI has significant advantages when studying pediatric populations, especially for assessing brain function or brain development and assessing the effects of sleep on brain function.

[0034] Brain MRI usually uses echo planar imaging (EPI) pulse sequences that are beneficial for acoustic noise reduction. EPI usually uses a trapezoidal readout with short echo spacing and phase encoding gradient pulse trains. Data are collected at a high readout bandwidth (61.25kHz to 500kHz), and EPI pulse sequences tend to have higher acoustic noise than their counterparts in standard imaging. Fast gradient switching and high gradient amplitudes (characteristics of EPI) are the main causes of high acoustic noise levels in fMRI and brain diffusion imaging, both of which usually use EPI pulse sequences.

[0035] refer to Figure 3 The total acoustic noise level is affected by the gradient amplitude (G p ) and rise time (τ), where a higher acoustic noise level is associated with a larger gradient amplitude (G p ) and at least one of a shorter rise time (τ). For example, fast gradient switching and high gradient amplitudes in echo planar imaging are the main causes of high acoustic noise levels in diffusion imaging and fMRI. In addition, some superconducting MRI scanners may have peak gradient strengths exceeding the conventional 20mT / m to 80mT / m range, with peak gradient strengths in the 200mT / m to 400mT / m range and slew capabilities up to 500T / m / s to 900T / m / s. For such scanners, the acoustic noise level may be limited when operating at maximum gradient and slew rate parameters.

[0036] In order to reduce the acoustic noise level in MRI systems, pulse sequence derating methods that change the pulse characteristics of gradient pulses in a manner that reduces acoustic noise have previously been used. For example, some derating methods use a general derating scheme in which static amplitude and slew rate thresholds are set and the gradient pulses of the pulse sequence are modified to be at or equal to the thresholds. Such methods may change the pulse sequence to reduce the amplitude of any gradient in the pulse sequence that exceeds the threshold amplitude and / or reduce the slew rate of any gradient in the pulse sequence that exceeds the threshold slew rate. Because these methods do not consider the combined effects of slew rate and amplitude on the acoustic noise level, the use of static thresholds may result in unnecessary increased gradient rise times and reduced phase encoding bandwidths for all imaging sequences and all applications, and thereby lead to reduced MRI performance. In addition, global derating methods affect MRI image quality by increasing echo time (TE) and overall MRI repetition time (TR).

[0037] Some methods of reducing the acoustic noise level in MRI systems have included the use of dedicated gradient waveforms. For example, dedicated pulse sequences that minimize gradient waveform amplitude variation or slopes, which use three-dimensional radial k-space trajectories and high bandwidth or swept RF excitation. In addition, shaped rather than linear gradient ramps or rise / fall times have also been used. In some such methods, gentle step-like or slowly varying gradient pulses are used to reduce noise. However, these dedicated pulse sequences may have a limited range of image contrast and power and time resolution, making dedicated pulse sequences unfeasible for certain MRI applications (such as functional MRI and diffusion weighted imaging). For example, compared with, for example, an EPI pulse sequence, a scan using a three-dimensional radial k-space trajectory takes longer to scan through k-space. Dedicated pulse sequences may encounter image reconstruction problems. In addition, the generation of swept RF excitation also requires additional hardware and software to generate the dedicated sequence.

[0038] Compared to previous derating systems and methods, targeted derating of gradient pulses according to the pulse sequence threshold function described herein to achieve acoustic noise reduction and / or a desired acoustic noise level provides improved overall MRI performance. Specifically, the pulse sequence threshold function allows for derating of individual gradient pulses using multiple threshold combinations of both the amplitude and slew rate of the gradient pulse. In contrast to general derating methods that utilize static thresholds, the disclosed method allows for selective modification of slew rate and / or amplitude based on a range of potential threshold combinations each associated with an acoustic noise level. In one example, the acoustic noise level in an MR scanner can be reduced by modifying the gradient slew rate to be equal to a threshold slew rate associated with the gradient amplitude while maintaining the gradient amplitude. That is, the gradient rise time or slew rate is a function of the gradient pulse amplitude. This operation is particularly suitable for functional imaging and diffusion weighted imaging, in which EPI sequences are used and general derating methods tend to exacerbate image distortion in echo planar readout sequences commonly used in brain imaging. Furthermore, in diffusion-weighted imaging, the diffusion encoding gradient is at maximum amplitude, whereas the EPI readout trapezoidal gradient pulse train can be between 30mT / m and 50mT / m. Therefore, enforcing a global slew rate is inefficient, but it is better to adjust or set the slew rate of each gradient waveform as a function of the gradient amplitude to maximize the efficiency of the MRI pulse sequence.

[0039] The method also allows acoustic noise reduction to be achieved with different pulse sequences for different clinical applications without the need to use dedicated pulse sequences. For example, for sleep studies, the acoustic noise level should be relatively low, such as 70dB to 80dB. The gradient pulses of the EPI pulse sequence are derated based on a threshold function corresponding to the target acoustic noise level. For applications where the acoustic noise level may be at a higher level, the gradient pulses of the EPI pulse sequence may not be derated, or the gradient pulses of the EPI pulse sequence may be derated based on a threshold function corresponding to a higher acoustic level, thereby achieving a higher pulse sequence performance level (i.e., lower TE, echo spacing, and minimum TR time).

[0040] The systems and methods described herein can also be used to reduce eddy current effects and reduce the onset of peripheral nerve stimulation (PNS). For example, the amplitude of the eddy current generated in the conductor is affected by the rate of change of the excitation magnetic field. Therefore, the rapid imaging sequence in which the gradient is quickly pulsed on and off produces the largest and most serious eddy current problem. Other sequences most likely to be affected by eddy currents include diffusion-weighted imaging, MR spectroscopy, and any sequence with very short TE. Peripheral nerve stimulation refers to the excitation of the limb nerves by the voltage potential induced by the rapidly changing magnetic gradient. When mild peripheral nerve stimulation can be perceived as a slight sensation, it is usually unexpected to the patient, but does not show actual discomfort or physical danger. As the intensity of the stimulation increases, motor nerve depolarization produces gradually severe and painful muscle fasciculation / contraction. Peripheral nerve stimulation is also usually performed with a pulse sequence (such as echo planar imaging) using rapid gradient switching. In other words, both eddy currents and peripheral nerve stimulation are usually affected by the gradient switching speed and gradient amplitude. Therefore, the derating methods described herein, while reducing acoustic noise levels, can also be used to mitigate peripheral nerve stimulation and eddy currents generated by the pulse sequence and / or provide an operating threshold based on considerations of peripheral nerve stimulation and eddy currents.

[0041] Figure 4 is a flow chart of an exemplary method 400 of generating a pulse sequence. Figure 5 It is shown for Figure 4 Schematic diagram of pulse sequence threshold functions 502-508 of the method shown. The exemplary method 400 described herein is implemented on a computing device, which may include a pulse sequence server 20, a workstation 12, and a pulse sequence server 20, a workstation 12, or a gradient system 28 ( Figure 1 At least one of any other computing devices that communicate with the .

[0042] The method 400 includes receiving 402 a pulse sequence 202 including a plurality of gradient pulses 210 ( Figure 24. In particular, the pulse sequence 202 is received in the form of instructions to generate the pulse sequence 202 in the magnet assembly 34. The instructions for the pulse sequence 202 are received at a computing device in communication with at least one of the pulse sequence server 20 and the workstation 12. Although discussed herein with respect to the fast spin echo pulse sequence 202, it should be understood that the exemplary method 400 may be used to derate any suitable pulse sequence used in an MRI system.

[0043] The method 400 further includes providing 404 a pulse sequence threshold function 502-508 corresponding to an acoustic noise reduction level of acoustic noise generated by switching gradients in the MRI system. Figure 5 , four pulse train threshold functions 502-508 are shown as curves on a graph indicating the gradient amplitude along the Y-axis and the slew rate along the X-axis. Figure 5 The threshold curves 502-508 (also referred to as "threshold curves") each indicate a plurality of threshold maximum amplitudes of the gradient pulses and a plurality of threshold slew rates of the gradient pulses, each threshold slew rate being associated with one of the plurality of threshold gradient amplitudes. In other words, the threshold curves 502-508 can be used to determine a threshold gradient amplitude of a gradient pulse based on a given slew rate of the gradient pulse and / or a threshold slew rate, based on a given gradient amplitude of the gradient pulse. For example, in Figure 5 , the first threshold curve 502 indicates a threshold gradient amplitude and an associated threshold slew rate located along the first threshold curve 502. In addition, each of the pulse sequence threshold functions 502-508 is associated with an acoustic noise threshold.

[0044] In an exemplary embodiment, threshold curves 502-508 are representative curves and are associated with a given (measured) sound pressure level for a particular pulse sequence. Thus, for the particular pulse sequence used, the acoustic noise level is typically constant along a range of gradient pulse parameter values ​​for any of curves 502-508. For example, in Figure 5 In an exemplary embodiment of the present invention, for an axial 3D fast imaging steady-state acquisition (FIESTA) R / L sequence, the first acoustic noise threshold of the first threshold curve 502 is approximately 120 dBA Laeq and 130 dB Lpeak. Therefore, the gradient pulses of the axial 3D FIESTA R / L sequence having the slew rate and amplitude parameters along the first threshold curve 502 will be at or equal to 120 dBA LAeq and 130 dB Lpeak. In addition, the acoustic noise thresholds associated with the threshold curves 502-508 may vary depending on the specific pulse sequence used. For example, as described below with respect to Figure 6 and Figure 7As shown, the acoustic noise level of the T2 fast spin echo (FSE) sequence along the first threshold curve 502 is different from the acoustic noise level of the axial 3D FIESTA R / L sequence. Specifically, the acoustic noise level of the T2 FSE sequence along the first threshold curve 502 is about 115 dBA LAeq and about 126 dB Lpeak. Therefore, in some embodiments, and as described in more detail below, the threshold curves 502-508 can be selected and / or generated based on the desired acoustic noise threshold and the specific pulse sequence to be used.

[0045] In other embodiments, the first threshold curve 502 may correspond to an average acoustic noise level for different pulse sequences. More specifically, in such embodiments, the first acoustic noise threshold is the average acoustic noise level of gradient pulses having gradient amplitudes and slew rates along the first threshold curve 502 when used for a plurality of different pulse sequences, such as: a T2 FSE sequence, a 3D FIESTA R / L sequence, an axial susceptibility weighted imaging (SWAN) R / L sequence, a functional magnetic resonance imaging (fMRI) R / L sequence, a 3D FIESTA A / P sequence, an axial Swan A / P sequence, and an fMRI A / P sequence (collectively referred to herein as "exemplary pulse sequences"). In other words, while a gradient pulse having a pulse characteristic along the first curve 502 may generate an acoustic noise level different from the first acoustic noise threshold when used for any single pulse sequence in the exemplary pulse sequences, the average acoustic noise level of the gradient pulses along the first curve 502 for each of the different exemplary pulse sequences will be approximately equal to the first acoustic noise threshold in such embodiments. In yet further alternative embodiments, the pulse sequence threshold function 502-508 may be a maximum acoustic noise level for the exemplary pulse sequence. For example, in some such embodiments, for each pulse sequence in the exemplary pulse sequence, a gradient pulse 210 having a pulse characteristic along a given pulse sequence threshold function 502-508 will not generate acoustic noise greater than the associated acoustic noise threshold.

[0046] In an exemplary embodiment, the threshold gradient amplitude G is determined by providing a threshold gradient amplitude G with a given slope coefficient (α) and intercept coefficient (β) as a linear function of the rise time (τ) of the gradient pulse. p (τ) to determine the pulse sequence threshold function, as shown in the following equation (3):

[0047] G p (τ)=ατ+β (3),

[0048] Among them G p(τ) is in Tesla / meter (T / m), the rise time is in seconds, the slope coefficient (α) is in T / m / s and the intercept coefficient (β) is in T / m. The slope coefficient (α) and the intercept coefficient (β) are selected so that the gradient amplitude is less than G p The gradient amplitude of the acoustic noise level of a pulse sequence with a pulse rise time (τ) does not produce an acoustic noise level exceeding the desired acoustic noise level threshold on average for the exemplary pulse sequence. In other words, the pulse sequence threshold function provided by equation (3) provides a threshold gradient amplitude G based on a given pulse rise time (τ) p (τ), where the resulting acoustic noise level generated by the gradient pulses is less than or equal to the desired acoustic noise level threshold on average for multiple pulse trains. As the threshold curves 502-508 move toward the origin of the graph, further changing the threshold curves by changing the slope coefficient (α) and intercept coefficient (β) parameters will result in further noise reduction.

[0049] In some operations, the pulse sequence threshold functions 502-508 are selected or determined based on the selected pulse sequence and the desired acoustic noise reduction or acoustic noise level threshold. Figure 6 and Figure 7 As shown, different pulse sequences modified based on the same threshold function may have different acoustic noise levels. After selecting a pulse sequence for a scanning application, a computing device or operator may select or generate a pulse sequence threshold function that will modify the selected pulse sequence based on the desired acoustic noise level. For example, referring to Figure 6 , where an axial Swan A / P sequence is selected and the desired acoustic noise threshold is 110 dBA LAeq, a low sound pressure level (SPL) threshold function 508 is selected. In contrast, where an fMRI A / P sequence is selected for the same acoustic noise threshold, different pulse sequence threshold functions 502-506 may be used, or a new pulse sequence threshold function may be generated by selecting different slope coefficients (α) and / or intercept coefficients (β) to achieve the desired acoustic noise threshold of 110 dBA LAeq. As indicated, with the global setting, different pulse sequences achieve different acoustic noise levels. By setting the slope coefficient (α) and intercept coefficient (β) parameters, the threshold curves may be set individually for different pulse sequences so that a uniform sound pressure level may be achieved for all pulse sequences. The global threshold setting will end the performance derating for all pulse sequences. The method of the present disclosure achieves the same level of uniform sound pressure level / acoustic noise so that not all pulse sequences are adversely affected by the threshold curve setting. For example, in the case of axial 3D FIESTA (with R / L readout), the sound pressure level is about 120 dBA ( Figure 6). The fMRI sequence with R / L readout is about 110 dBA at the same threshold function 502. If it is desired to maintain a 110 dBA sound pressure level across all pulse sequences, then only 3DFIESTA is subjected to a different threshold function curve with different slope coefficient (α) and intercept coefficient (β) values ​​to achieve the same sound pressure level as the fMRI pulse sequence (unmodified).

[0050] The slope coefficient (α) and intercept coefficient (β) can be obtained by p ) and rise time (τ) of a gradient pulse by measuring the acoustic noise level of the MRI system. The slope coefficient (α) and the intercept coefficient (β) may be determined empirically. For example, the first slope coefficient (α) may be between 1 T / m / s and 300 T / m / s, and the first intercept coefficient (β) may be between 0.001 T / m and 1.0 T / m. Different slope coefficient (α) and intercept coefficient (β) values ​​may be selected to provide a plurality of pulse sequence threshold functions 502-508 that each correspond to a different acoustic noise threshold of the MRI system 10. In addition, since the rise time (τ) of the gradient pulse is equal to the gradient amplitude (G p ) divided by the slew rate (SR), Equation 3 can be rewritten to provide the threshold amplitude as a function of the slew rate as shown in Equation (4) below:

[0051] G p (SR) = β*SR / (SR-α) (4).

[0052] Equation (4) provides that the intercept coefficient (β) multiplied by the slew rate (SR) divided by the slew rate (SR) minus the slope coefficient (α) equals the threshold gradient amplitude G for a given slew rate p (SR). By inputting a series of slew rate values ​​into the pulse train threshold function of equation (4), threshold curves 502-508 indicating threshold gradient amplitudes for each slew rate can be generated. Equation (4) can also be rewritten to provide the threshold slew rate as a function of amplitude, as shown in equation (5) below:

[0053] SR(G p )=G p *α / (G p -β) (5).

[0054] Equation (5) provides the gradient amplitude (G p ) multiplied by the slope coefficient and divided by the gradient amplitude (G p ) minus the intercept coefficient (β) equals the threshold slew rate SR(G) for a given gradient amplitude p ).

[0055] refer to Figure 5, four pulse sequence threshold curves 502-508 are generated from equation (4) provided above, where each pulse sequence threshold function has a different slope coefficient α and intercept coefficient β. The first or "high SPL" pulse sequence threshold function 502 has a slope coefficient α of 161 and an intercept coefficient β of 0.061 T / m. The second pulse sequence threshold function 504 has a slope coefficient α of 123 T / m / s and an intercept coefficient β of 0.047 T / m. The third pulse sequence threshold function 506 has a slope coefficient α of 92 T / m / s and an intercept coefficient β of 0.035 T / m. The fourth or "low SPL" pulse sequence threshold function 508 has a slope coefficient α of 72 T / m / s and an intercept coefficient β of 0.028 T / m. Since the slope coefficient α and the intercept coefficient β are different, Figure 5 Each of the threshold curves 502-508 shown is associated with a different acoustic noise threshold. For example, the high pulse train threshold function 502 provides the maximum acoustic noise threshold level (i.e., results in less acoustic noise reduction), while the low pulse train threshold function 508 provides the lowest acoustic noise threshold level (i.e., results in greater acoustic noise reduction).

[0056] In some embodiments, the method 400 further includes selecting a pulse sequence threshold function 502-508 from a plurality of threshold sequence threshold functions 502-508 based on a desired acoustic noise threshold for a particular MRI application. For example, during use, an operator may select a high pulse sequence threshold function 502 for use during general MRI applications, while a low pulse sequence threshold function 508 may be used in MRI applications where a lower acoustic noise level is more desirable, such as during a sleep study. For example, during a sleep study, the acoustic noise threshold may be between 70 dB and 80 dB to make the scanner run quiet enough to allow the patient to sleep comfortably in the machine. In one embodiment, an operator of the workstation 12 inputs a desired acoustic noise level threshold, and one of the processor 18 or the pulse sequence server 20 determines the pulse sequence threshold function and / or the values ​​of the slope coefficient α and the intercept coefficient β based on the desired acoustic noise level threshold.

[0057] Reference again Figure 4 , the method 400 further includes, for each gradient pulse 210 in the pulse sequence, analyzing 405 the gradient pulse 210. The analyzing 405 includes determining 406 the amplitude of the gradient pulse and the slew rate of the gradient pulse 210. In an exemplary embodiment, the amplitude and / or slew rate of the gradient pulse is determined by retrieving stored amplitude and / or slew rate values ​​associated with a particular pulse sequence. For example, a fast spin echo sequence 202 ( Figure 2The waveform parameters of each gradient pulse (shown in FIG. 4 ) are stored on a memory of the computing device, and the computing device retrieves the waveform parameters from the memory. Alternatively, one of the pulse sequence server 20 or the workstation 12 may be programmed to estimate the expected amplitude and slew rate of the pulse sequence based on the pulse sequence instruction received at step 402. Figure 5 In the example shown, the amplitude of the gradient pulse 210 in the gradient pulse sequence is determined to be 160 mT / m, and the slew rate is 400 T / m / s.

[0058] The method 400 also includes determining 408 a threshold amplitude corresponding to the determined slew rate and determining a threshold slew rate corresponding to the determined amplitude. Specifically, equation (4) provided above is used to determine the threshold amplitude based on the determined slew rate (400 T / m / s) of the gradient pulse 210, and equation (5) is used to determine the threshold slew rate based on the determined amplitude of 160 mT / m of the gradient pulse 210. Figure 5 In an exemplary embodiment, at a first point 510 on the first threshold curve 502, the threshold slew rate of the determined amplitude is determined to be approximately 260 T / m / s, and at a second point 512 on the first threshold curve 502, the threshold amplitude of the determined slew rate is determined to be approximately 102 mT / m.

[0059] The method 400 also includes comparing 410 the determined amplitude to a threshold amplitude and comparing 411 the determined slew rate to a threshold slew rate. Figure 5 In the depicted example, a gradient amplitude of 160 mT / m of the gradient pulse 210 is determined to be greater than a threshold amplitude of 102 mT / m, and a slew rate of 400 T / m / s of the gradient pulse 210 is determined to be greater than a threshold slew rate of 260 T / m / s. Thus, the gradient pulse 210 is determined to be above the first threshold curve 502, indicating that the gradient pulse will generate an acoustic noise level greater than a desired acoustic noise level associated with the first threshold curve 502.

[0060] The method 400 also includes modifying 412 the gradient pulse by adjusting at least one of the amplitude and the slew rate to the amplitude and slew rate as defined by the pulse sequence threshold function if the determined amplitude exceeds the threshold amplitude or the determined slew rate exceeds the threshold slew rate. Specifically, in an exemplary embodiment, in response to determining that the gradient pulse 210 exceeds the first threshold curve 502, at least one of the amplitude and the slew rate of the gradient pulse 210 is modified to be at or below the first threshold curve 502. For example, in a first operation, the amplitude of the gradient pulse 210 is unchanged and the slew rate is reduced to a threshold slew rate of 260 T / m / s. In the first operation, the gradient pulse 210 is modified to be at a first point 510 on the first threshold curve 502. In a second alternative operation, the slew rate is unchanged and the amplitude of the gradient pulse 210 is reduced to a threshold amplitude of 102 mT / m. When in the second operation, the gradient pulse 210 is modified to be at a second point 512 on the first threshold curve 502.

[0061] In a third operation, both the amplitude and the slew rate of the gradient pulse 210 are adjusted so that the modified gradient pulse sequence is positioned between the first point 510 and the second point 512 along or near the first threshold curve 502. For example, in one embodiment, the amplitude is first adjusted to an amplitude selected within a range between the determined amplitude (160 mT / m) and the amplitude threshold (102 mT / m), such as, for example, 140 mT / m. The slew rate is then adjusted to a slew rate corresponding to the adjusted amplitude (140 mT / m) as determined by the pulse sequence threshold function 502, such as, for example, about 285 T / m / s. Alternatively, in another embodiment, the slew rate is first adjusted to a slew rate between the slew rate (400 T / m / s) of the gradient pulse 210 and the slew rate threshold (260 T / m / s). The gradient amplitude is then adjusted to a gradient amplitude corresponding to the adjusted slew rate as determined by the pulse sequence threshold function 502. In some embodiments, the optimal adjustment of the slew rate and the gradient amplitude may be determined based on the pulse sequence threshold function and one or more operating parameters of the MRI system. For example, but not limited to, in some such embodiments, the pulse sequence server 20 ( Figure 1 510 and 512) can model the effects of all amplitude and slew rate combinations along the pulse sequence threshold function between a first point 510 and a second point 512 on one or more operating parameters (such as image quality) on the MRI system. A modified slew rate and gradient amplitude combination can then be selected based on the modeling to provide a modified gradient pulse that is optimized based on the one or more operating parameters.

[0062] In some embodiments, method 400 may further include determining whether to perform a first operation (in which only the slew rate is modified), a second operation (in which only the amplitude is modified), or a third operation (in which both the amplitude and the slew rate are modified). Specifically, in some such methods, the determination is based on the MRI application being performed. For example, in diffusion weighted imaging, maintaining the gradient amplitude of the diffusion encoding gradient is more beneficial than maintaining the slew rate to limit the impact of the diffusion encoding gradient on TE and TR, especially at high b values. In functional MRI, in order to limit geometric distortion, maintaining the slew rate of the EPI readout trapezoidal gradient pulse train is more beneficial than maintaining the gradient amplitude. In another application such as phase contrast imaging, it is desired that the first gradient moment is minimized in time and the eddy current effect is minimized, in which case the time and amplitude of the gradient pulse are balanced to ensure minimal eddy currents and a more compact total pulse width or waveform time. For such applications, the computing device may automatically determine whether to perform the first operation, the second operation, or the third operation based on the MRI application. In another embodiment, the computing device may be configured to receive a user input command indicating which operation should be performed.

[0063] In an alternative operation, one or more gradient pulses 210 in the pulse sequence 202 are compared with the pulse sequence threshold function, and the remaining gradient pulses 210 can be modified based on the modification of the analyzed gradient pulse 210. For example, the gradient pulse in the pulse sequence with the highest gradient amplitude among the gradient pulses of the pulse sequence is analyzed using the pulse sequence threshold function to derive a slew rate, while the highest gradient amplitude remains the same. The derived slew rate is applied to all gradient pulses in the pulse sequence. Alternatively, a pair of slew rates and a new highest gradient amplitude are derived for the gradient pulse with the highest amplitude. The derived slew rate is applied to the rest of the gradient pulses. The threshold function is used to modify the gradient pulses with amplitudes greater than the new highest gradient amplitude, while the remaining gradient pulses maintain the original amplitude. This strategy takes into account that gradient pulses with higher gradient amplitudes and faster slew rates cause more acoustic noise than gradient pulses with lower gradient amplitudes and slower slew rates. Alternatively, the transfer function based on the gradient pulse waveform shape, rise / fall time and amplitude can be characterized by slope coefficient α and intercept coefficient β values ​​and corresponding sound pressure levels. In this case, each gradient pulse or waveform in the pulse train can be adjusted individually to achieve the desired sound pressure level.

[0064] refer to Figure 4 After modifying the gradient pulses 210, the analysis 405 is repeated for each gradient pulse 210 in the pulse sequence 202. After each gradient pulse in the pulse sequence 202 has been compared to the pulse sequence threshold function 502, and if modified, the method 400 may further include causing 414 the modified gradient pulse sequence to be generated by the MRI system 10.

[0065] Figure 6 and Figure 7 The results of acoustic noise testing using a derated pulse sequence according to the method described herein are shown. Specifically, Figure 6 Is to use from Figure 4 Plot of the A-weighted equivalent continuous acoustic noise level (LAeq) generated by the pulse train derived by the method shown. Figure 7 Is to use from Figure 4 Graph of the peak unweighted (Lpeak) acoustic noise level generated by the pulse train derived by the method shown. Figure 5 The test is performed after the gradient pulses of each pulse sequence in the exemplary pulse sequence are derated (as shown in FIG. 1 ). The pulse sequence is derated by adjusting the slew rate and gradient amplitude of the gradient pulses in the pulse sequence according to the third operation described above. Acoustic measurements are performed using a sound analyzer. A microphone is placed at the imaging isocenter of the MRI system perpendicular to the patient axis. Figure 6 As shown, the A-weighted equivalent continuous sound level (L Aeq ).like Figure 7 As shown, the unweighted peak sound level is recorded in decibels (dB). De-rating the gradient pulses according to the low pulse train threshold function 508 relative to the high pulse train threshold function 502 results in L Aeq The average 12dBA and maximum 18.5dBA reduction for L peak Similar results were observed with an average 11.5 dBA and a maximum 16 dBA reduction.

[0066] The workstation 12 and computing device described herein may be any suitable computing device 800 and software implemented in the computing device. Figure 8 800. In an exemplary embodiment, the computing device 800 includes a user interface 804 that receives at least one input from a user. The user interface 804 may include a keyboard 806 that enables the user to enter relevant information. The user interface 804 may also include, for example, a pointing device, a mouse, a stylus, a touch-sensitive panel (e.g., a touchpad and a touch screen), a gyroscope, an accelerometer, a position detector, and / or an audio input interface (e.g., including a microphone).

[0067] In addition, in this exemplary embodiment, the computing device 800 includes a presentation interface 817 that presents information such as input events and / or verification results to the user. The presentation interface 817 may also include a display adapter 808 coupled to at least one display device 810. More specifically, in an exemplary embodiment, the display device 810 may be a visual display device such as a cathode ray tube (CRT), a liquid crystal display (LCD), a light emitting diode (LED) display, and / or an "electronic ink" display. Alternatively, the presentation interface 817 may include an audio output device (e.g., an audio adapter and / or a speaker) and / or a printer.

[0068] The computing device 800 also includes a processor 814 and a memory device 818. The processor 814 is coupled to the user interface 804, the presentation interface 817, and the memory device 818 via the system bus 820. In an exemplary embodiment, the processor 814 communicates with the user, such as by prompting the user via the presentation interface 817 and / or by receiving user input via the user interface 804. The term "processor" generally refers to any programmable system, including system and microcontrollers, reduced instruction set computers (RISC), complex instruction set computers (CISC), application specific integrated circuits (ASICs), programmable logic circuits (PLCs), and any other circuits or processors capable of performing the functions described herein. The above examples are exemplary only and are therefore not intended to limit the definition and / or meaning of the term "processor" in any way.

[0069] In an exemplary embodiment, the memory device 818 includes one or more devices that enable information (such as executable instructions and / or other data) to be stored and retrieved. In addition, the memory device 818 includes one or more computer-readable media, such as but not limited to dynamic random access memory (DRAM), static random access memory (SRAM), solid state disk, and / or hard disk. In an exemplary embodiment, the memory device 818 stores but is not limited to application source code, application object code, configuration data, additional input events, application status, assertion statements, verification results, and / or any other type of data. In an exemplary embodiment, the computing device 800 may also include a communication interface 830 connected to the processor 814 via the system bus 820. In addition, the communication interface 830 is communicatively connected to a data acquisition device.

[0070] In an exemplary embodiment, processor 814 may be programmed by encoding operations using one or more executable instructions and providing the executable instructions in memory device 818. In an exemplary embodiment, processor 814 is programmed to select a plurality of measurements received from a data collection device.

[0071] In operation, a computer executes computer executable instructions embodied in one or more computer executable components stored on one or more computer readable media to implement various aspects of the present disclosure described and / or shown herein. Unless otherwise specified, the execution or implementation order of the operations in the embodiments of the present disclosure shown and described herein is not required. That is, unless otherwise specified, these operations may be performed in any order, and embodiments of the present disclosure may include more or fewer operations than those disclosed herein. For example, it is conceivable that it is within the scope of various aspects of the present disclosure to perform or implement a particular operation before, simultaneously with, or after another operation.

[0072] At least one technical effect of the systems and methods described herein includes: (a) reduction of acoustic noise of pulse sequences; (b) improvement of MR imaging performance; (c) reduction of eddy currents in MRI systems; and (d) reduction of peripheral nerve stimulation.

[0073] Exemplary embodiments of systems and methods for generating pulse sequences in magnetic resonance imaging (MRI) systems are described in detail above. These systems and methods are not limited to the specific embodiments described herein, but the components of the systems and / or the operations of the methods can be used independently and separately from other components and / or operations described herein. In addition, the components and / or operations described can also be defined in other systems, methods and / or devices, or used in combination with other systems, methods and / or devices, and are not limited to being practiced only with the systems described herein.

[0074] Although specific features of various embodiments of the present disclosure may be shown in some drawings and not in other drawings, this is for convenience only. According to the principles of the present disclosure, any feature of a drawing may be referenced and / or claimed in combination with any feature of any other drawing.

[0075] This written description uses examples to disclose the present disclosure, including the best mode, and also to enable those skilled in the art to practice the present disclosure, including making and using any devices or systems and performing any included methods. The patentable scope of the present disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to fall 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 minor differences from the literal language of the claims.

Claims

1. A pulse sequence generation computing device for a magnetic resonance imaging system, the pulse sequence generation computing device comprising at least one processor in communication with at least one memory device, and the at least one processor being programmed to: receiving a pulse sequence including a plurality of gradient pulses; providing a pulse sequence threshold function corresponding to an acoustic noise reduction level of acoustic noise generated by switching gradients in the magnetic resonance imaging system, the pulse sequence threshold function indicating a plurality of threshold amplitudes of the gradient pulses and a plurality of threshold slew rates of the gradient pulses, each threshold slew rate being associated with one of the plurality of threshold amplitudes; For each gradient pulse in the pulse sequence, determining an amplitude of the gradient pulse and a slew rate of the gradient pulse; determining a threshold amplitude corresponding to the determined slew rate and a threshold slew rate corresponding to the determined amplitude; comparing the determined amplitude to the threshold amplitude and comparing the determined slew rate to the threshold slew rate; and The at least one processor is configured to modify the gradient pulse by adjusting at least one of the amplitude and the slew rate of the gradient pulse to an amplitude and a slew rate as defined by the pulse sequence threshold function if the determined amplitude exceeds the threshold amplitude or the determined slew rate exceeds the threshold slew rate.

2. The computing device of claim 1 , wherein the at least one processor is further configured to modify the gradient pulses by: maintaining the amplitude at the determined amplitude; and The slew rate is adjusted to be less than or equal to the threshold slew rate corresponding to the determined amplitude.

3. The computing device of claim 1 , wherein the at least one processor is further configured to modify the gradient pulses by: maintaining the slew rate at the determined slew rate; and The amplitude is adjusted to be less than or equal to the threshold amplitude corresponding to the determined slew rate.

4. The computing device of claim 1 , wherein the at least one processor is further configured to modify each gradient pulse in the pulse sequence by: adjusting the amplitude to an amplitude selected within a range between the determined amplitude and the threshold amplitude; and The slew rate is adjusted to a slew rate corresponding to the adjusted amplitude and determined by the pulse train threshold function.

5. The computing device of claim 1 , wherein the at least one processor is further configured to modify each gradient pulse in the pulse sequence by: adjusting the slew rate to a slew rate selected between the determined slew rates; and The amplitude is adjusted to an amplitude corresponding to the adjusted slew rate and determined by the pulse train threshold function.

6. The computing device of claim 1 , wherein the threshold amplitude is provided by the pulse sequence threshold function as a linear function of a rise time of the gradient pulse, and wherein the at least one processor is further configured to: selecting a first acoustic noise threshold of the magnetic resonance imaging system; and A first slope coefficient α and a first intercept coefficient β of the pulse sequence threshold function are determined based on the selected first acoustic noise threshold. 7 . The computing device of claim 6 , wherein the first slope coefficient α is between 1 Tesla / meter / second and 300 Tesla / meter / second.

8. The computing device of claim 6, wherein the first intercept coefficient β is between 0.001 Tesla / meter and 1.0 Tesla / meter.

9. The computing device of claim 6, wherein the first acoustic noise threshold is selected based on a first magnetic resonance imaging application, and wherein the processor is further programmed to determine a second slope coefficient α and a second intercept coefficient β associated with a second acoustic noise threshold for a second magnetic resonance imaging application.

10. The computing device of claim 9, wherein the second magnetic resonance imaging application is a sleep study, the second acoustic noise threshold is less than the first acoustic noise threshold, and wherein the second slope coefficient α and the second intercept coefficient β are each less than the first slope coefficient α and the first intercept coefficient β, respectively, and wherein the second acoustic noise threshold is between 70 decibels and 80 decibels.

11. The computing device of claim 1, wherein the at least one processor is further configured to cause generation of the modified pulse sequence by the magnetic resonance imaging system.

12. A computer-implemented method for generating a pulse sequence in a magnetic resonance imaging system, comprising: receiving a pulse sequence including a plurality of gradient pulses; providing a pulse sequence threshold function corresponding to an acoustic noise reduction level of acoustic noise generated by switching gradients in the magnetic resonance imaging system, the pulse sequence threshold function indicating a plurality of threshold amplitudes of the gradient pulses and a plurality of threshold slew rates of the gradient pulses, each threshold slew rate being associated with one of the plurality of threshold amplitudes; For each gradient pulse in the pulse sequence, determining an amplitude of the gradient pulse and a slew rate of the gradient pulse; determining a threshold amplitude corresponding to the determined slew rate and a threshold slew rate corresponding to the determined amplitude; comparing the determined amplitude to the threshold amplitude and comparing the determined slew rate to the threshold slew rate; and if the determined amplitude exceeds the threshold amplitude or the determined slew rate exceeds the threshold slew rate, modifying the gradient pulse by adjusting at least one of the amplitude and the slew rate of the gradient pulse to an amplitude and a slew rate as defined by the pulse sequence threshold function; as well as The modified pulse sequence is caused to be generated by the magnetic resonance imaging system.

13. The method of claim 12, wherein modifying the gradient pulse further comprises: maintaining the amplitude at the determined amplitude; as well as The slew rate is adjusted to be less than or equal to the threshold slew rate corresponding to the determined amplitude.

14. The method of claim 12, wherein modifying the gradient pulse further comprises: maintaining the slew rate at the determined slew rate; as well as The amplitude is adjusted to be less than or equal to the threshold amplitude corresponding to the determined slew rate.

15. The method of claim 12, wherein modifying the gradient pulse further comprises: adjusting the amplitude to an amplitude selected within a range between the determined amplitude and the threshold amplitude; as well as The slew rate is adjusted to a slew rate corresponding to the adjusted amplitude and determined by the pulse train threshold function.

16. The method of claim 12, wherein modifying the gradient pulse further comprises: adjusting the slew rate to a slew rate selected between the determined slew rates; as well as The amplitude is adjusted to an amplitude corresponding to the adjusted slew rate and determined by the pulse train threshold function.

17. The method of claim 12, wherein the threshold amplitude is provided by the pulse sequence threshold function as a linear function of the rise time of the gradient pulse, and wherein the method further comprises: selecting a first acoustic noise threshold of the magnetic resonance imaging system; as well as A first slope coefficient α and a first intercept coefficient β of the pulse sequence threshold function are determined based on the selected first acoustic noise threshold.

18. The method of claim 17, wherein the first slope coefficient α is between 50 Tesla / m / s and 200 Tesla / m / s. The method of claim 17 , wherein the first intercept coefficient β is between 0.01 Tesla / meter and 0.1 Tesla / meter.

20. A pulse sequence generation computing device for a magnetic resonance imaging system, the pulse sequence generation computing device comprising at least one processor in communication with at least one memory device, and the at least one processor being programmed to: receiving a pulse sequence including a plurality of gradient pulses; providing a pulse sequence threshold function corresponding to an acoustic noise reduction level of acoustic noise generated by switching gradients in the magnetic resonance imaging system, the pulse sequence threshold function indicating a plurality of threshold amplitudes of the gradient pulses and a plurality of threshold slew rates of the gradient pulses, each threshold slew rate being associated with one of the plurality of threshold amplitudes; For at least one gradient pulse in the pulse sequence, determining an amplitude of the gradient pulse and a slew rate of the gradient pulse; determining a threshold amplitude corresponding to the determined slew rate and a threshold slew rate corresponding to the determined amplitude; comparing the determined amplitude to the threshold amplitude and comparing the determined slew rate to the threshold slew rate; and The at least one processor is configured to modify the gradient pulse by adjusting at least one of the amplitude and the slew rate of the gradient pulse to an amplitude and a slew rate as defined by the pulse sequence threshold function if the determined amplitude exceeds the threshold amplitude or the determined slew rate exceeds the threshold slew rate.

Images