Method, apparatus and magnetic resonance imaging system for magnetic resonance imaging pre-scan

Abstract

The present disclosure relates to a method for magnetic resonance imaging pre-scan, a magnetic resonance imaging pre-scan device and a magnetic resonance imaging system, the method comprising the steps of: performing a first pulse sequence by means of the magnetic resonance imaging system and acquiring a plurality of magnetic resonance signals at different offset frequencies of the same position from an examination object by a radio frequency antenna unit, and recording corresponding first k-space domain data based on the plurality of magnetic resonance signals; calculating the amount of change between the plurality of first k-space domain data respectively; determining an offset frequency as a compensation frequency for non-uniform magnetic field compensation according to the amount of change. By means of the above method, the compensation frequency can be automatically and quantitatively determined, and the non-uniform magnetic field when generating the pulse sequence for clinical examination by means of the magnetic resonance imaging system is compensated by applying the compensation frequency, which eliminates the artifacts introduced by the non-uniform magnetic field on the images obtained in the magnetic resonance imaging, and improves the quality and efficiency of the clinical examination of the magnetic resonance imaging system.

Description

Technical Field

[0001] This invention relates to the field of medical imaging, and in particular to a method and system for pre-scanning magnetic resonance imaging using a magnetic resonance imaging system. Background Technology

[0002] Magnetic Resonance Imaging (MRI) is a medical imaging technique that uses an antenna to irradiate an object under specific magnetic field conditions, generating images based on the modulated radio frequency signals received from the object. MRI can be used to study the internal structure, material composition, and physiological processes of an object. Radio frequency pulses with Larmor frequencies cause spin nuclei, such as hydrogen nuclei (H+), in the irradiated object to precess at an angle, generating magnetic resonance radio frequency signals. These signals are received by a radio frequency antenna unit and processed by a computer to form an image.

[0003] In some clinical applications, MR imaging systems execute clinical scanning protocols for pulse sequences such as Balanced State Free Precession (SSFP) and True Fast Imaging Steady Precession (TRUFI) for medical imaging or spectral analysis. Balanced SSFP (or SFP, bSSFP) is a magnetic resonance imaging sequence that applies a steady-state magnetic field to construct a balanced magnetic field gradient waveform. Balanced SSFP is typically based on gradient echo sequences with low flip angles and short repetition times. Image contrast with balanced SSFP depends primarily on the repetition time (TR – the time interval between consecutive pulse sequences applied to the same slice) and the relaxation time and flip angle. Balanced SSFP is susceptible to off-resonance artifacts caused by inhomogeneous magnetic fields. Before executing the relevant clinical scanning protocol, the MR imaging system typically performs a frequency scanning protocol to determine an offset frequency as a compensation frequency to eliminate off-resonance artifacts. MR imaging systems acquire multiple images by performing a frequency search scan protocol. The operator must then identify the image with the best quality from these images and use its corresponding known offset frequency as a compensation frequency, which can be achieved, for example, by performing dynamic shimming. However, manually identifying image quality by the operator is not based on quantitative analysis, has considerable errors, and is extremely time-consuming. Summary of the Invention

[0004] In view of this, this disclosure proposes a method for pre-scanning magnetic resonance imaging using a magnetic resonance imaging system, which can automatically and quantitatively determine the offset frequency and apply an electrical signal to the radio frequency antenna unit that generates the magnetic field based on the offset frequency to compensate for the non-uniform magnetic field. The method includes the following steps: executing a first pulse sequence using a magnetic resonance imaging system and acquiring multiple magnetic resonance signals at different offset frequencies from the same location on the object being examined through the radio frequency antenna unit, and recording corresponding first k spatial domain data based on the multiple magnetic resonance signals; calculating the changes between the multiple first k spatial domain data; and determining an offset frequency as the compensation frequency for non-uniform magnetic field compensation based on the changes.

[0005] Another aspect of this disclosure provides a magnetic resonance imaging pre-scanning apparatus for magnetic resonance imaging, comprising: a processing unit configured to execute a first pulse sequence by means of a magnetic resonance imaging system and acquire multiple magnetic resonance signals at different offset frequencies at the same location from the object under examination via a radio frequency antenna unit, and record corresponding first k spatial domain data based on the multiple magnetic resonance signals; and a calculation unit configured to calculate the amount of change between the multiple first k spatial domain data respectively, and determine an offset frequency as a compensation frequency for non-uniform magnetic field compensation based on the amount of change.

[0006] Another aspect of this disclosure provides a magnetic resonance imaging system configured to implement the methods described above.

[0007] Another aspect of this disclosure provides a computer-readable storage medium having stored thereon a program segment readable and operable by the magnetic resonance imaging pre-scanning apparatus, such that when the program segment is run by the magnetic resonance imaging and scanning apparatus, all steps of the method described in any of the preceding claims can be performed.

[0008] One advantage of the method for pre-scanning magnetic resonance imaging using a magnetic resonance imaging system, the magnetic resonance imaging system, and the computer-readable storage medium provided in this disclosure is that it is able to analyze the changes between multiple magnetic resonance signals acquired by the magnetic resonance imaging system during the execution of a first pulse sequence, automatically and quantitatively determine the offset frequency, and use the offset frequency information to generate an electrical signal that acts on the radio frequency antenna element to compensate for the non-uniform magnetic field, eliminate artifacts introduced by the non-uniform magnetic field, and improve the quality and efficiency of the pulse sequence of the magnetic resonance imaging system in performing clinical examinations. Attached Figure Description

[0009] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings, which will make the above and other features and advantages of the invention more apparent to those skilled in the art. In the drawings:

[0010] Figure 1A schematic diagram of a magnetic resonance imaging system of an exemplary embodiment is shown;

[0011] Figure 2 A schematic diagram of the spectral response function of a balanced SSFP pulse sequence according to an exemplary embodiment is shown;

[0012] Figure 3 A schematic flowchart illustrating an exemplary embodiment of a method for pre-scanning magnetic resonance imaging using a magnetic resonance imaging system is shown.

[0013] Figure 4 A schematic diagram of an exemplary embodiment is shown, illustrating a process for calculating changes based on image data to determine an offset frequency as the compensation frequency for non-uniform magnetic field compensation.

[0014] Figure 5 The illustration shows curves of amplitude and energy changes in the image domain between image data obtained by a magnetic resonance imaging system executing a pulse sequence of offset frequencies including frequency steps based on a phantom, and obtaining corresponding image data, as well as the image data obtained at adjacent offset frequencies.

[0015] Figure 6 A flowchart illustrating another exemplary embodiment of calculating the change in k-space domain data based on ROI image data transformation to determine the offset frequency as the compensation frequency for non-uniform magnetic field compensation is shown.

[0016] Figure 7 Another exemplary embodiment is shown, illustrating the region of interest and corresponding k-space domain data based on phantom selection.

[0017] The reference numerals in the attached figures are as follows:

[0018] 10 MR imaging system

[0019] 11 Magnets

[0020] 12 Gradient Coil Units

[0021] 13 Radio Frequency Antenna Units

[0022] 14 Inspection Area

[0023] 15 B0 magnetic field

[0024] 16 Scanning Beds

[0025] 17 Local radio frequency antenna

[0026] 18. Inspection Objects

[0027] 21 Local Radio Frequency Antenna Processing Unit

[0028] 23 Radio Frequency Antenna Processing Unit

[0029] 24 processing units

[0030] 241 Computing Units

[0031] 242 memory

[0032] 243 Reconstruction Unit

[0033] 244 sequence processing units

[0034] 25 Gradient Coil Processing Unit

[0035] 27 Display Units

[0036] 28 Input Units

[0037] 501 Amplitude Change Curve

[0038] The minimum change in 502 and 502'

[0039] 503 Energy Value Change Curve

[0040] 505 Image Data

[0041] 701 Area of ​​Interest

[0042] 703 window Detailed Implementation

[0043] To provide a clearer understanding of the technical features, objectives, and effects of this disclosure, specific embodiments of this disclosure will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same parts.

[0044] Balanced pulse sequences such as SSFP (Steady State Free Precession) and TRUFI (TrueFast Imaging Steady Precession) are widely used in clinical diagnostic MRI due to their excellent contrast and high signal-to-noise ratio. However, TRUFI sequences are highly sensitive to non-uniform magnetic fields, resulting in non-resonance artifacts. These artifacts are particularly severe in higher magnetic fields (e.g., above 3T). Therefore, a frequency search scan (acquisition) must be performed before running a standard TRUFI sequence to define the non-resonance frequency. The operator then needs to examine all the images acquired by the frequency search scans and manually select the offset frequency as the compensation frequency to compensate for the non-uniform magnetic field based on the best quality image. For example, a frequency search scan protocol (e.g., TRUFI sequence) run before performing a routine MRI clinical scan scan scans the same slice or location by setting stepped offset frequencies, comparing images acquired at different offset frequencies to determine the appropriate offset frequency as the compensation frequency to compensate for the non-uniform magnetic field.

[0045] Based on the above considerations, this disclosure provides a data acquisition method that can automatically define the most suitable offset frequency as the compensation frequency based on the image obtained by frequency scouting or swept frequency, making it simpler and more efficient to acquire data using balanced SSFP-compatible sequences such as TRUFI sequences.

[0046] Figure 1 A schematic diagram of a magnetic resonance imaging system according to an exemplary embodiment is shown.

[0047] refer to Figure 1This paper describes an MR imaging system 10, which enables the acquisition of data for magnetic resonance images of a subject 18. In the MR imaging system 10, a magnet 11 generates a static BO magnetic field 15 for imaging the subject 18, which is positioned on a scan bed to adjust its position in the scan space. The MR imaging system 10 includes a gradient coil unit 12 for generating a position-dependent gradient magnetic field superimposed on the BO magnetic field 15. A sequence processing unit 244 is configured to generate position-dependent, three orthogonal magnetic field gradients in response to receiving gradient signals and to generate a pulse sequence including a balanced SSFP-compatible (e.g., a TRUFI pulse sequence). The magnetic field gradients include a slice-selective gradient magnetic field, a phase-encoded gradient magnetic field, and a readout gradient magnetic field applied to the subject. The RF antenna control unit 23 is further configured to provide an alternating magnetic field (i.e., an RF pulse signal) with certain parameters to the RF antenna unit 13. This is used to generate the magnetic field pulse to flip the spin angle of protons within the object being examined to 90° or 180° to obtain a spin echo image, or to flip the angle to less than or equal to 90° to obtain a gradient echo image. The sequence control unit 244, combined with the RF antenna control unit 23, is configured to receive control from the processing unit 24 to control layer selection, phase encoding, readout of the gradient magnetic field, transmission of the RF pulse signal, and detection of the magnetic resonance signal to obtain a magnetic resonance signal representing a planar layer of the object being examined.

[0048] In response to an applied RF pulse signal, RF antenna unit 13 receives the magnetic resonance signal returned from the object under examination 18. This is because the protons in the excited state within the object under examination 18 return to their equilibrium state under the influence of a constructed static B0 magnetic field 15 and a gradient magnetic field, achieving spin refocusing and thus generating a magnetic resonance signal. The magnetic resonance signal is received by RF antenna unit 13 and processed by RF antenna control unit 23, for example, through analog-to-digital signal conversion and low-noise amplification. Image representation data, such as k-space domain data, is transmitted to processing unit 24, where the image is reconstructed using a reconstruction unit 243 with image processing capabilities associated with its computing unit 241. Additionally, a local RF antenna 17, typically located in the region of interest of the object under examination, can also transmit RF pulse signals to the object in response to an RF pulse signal, which is received and processed by the local RF antenna control unit 21. The magnetic resonance signal detected by each RF antenna unit 13 is associated with a corresponding MR measurement channel. The general operating modes for generating magnetic resonance images and detecting magnetic resonance signals are not described in detail here.

[0049] The processing unit 24 includes a memory 242, which can store information such as preset pulse sequences, RF pulse signals / sequences, and magnetic field gradient sequences, as well as preset parameters such as intensity data, timing, orientation, and the spatial volume of the gradient magnetic field acting on the imaging, and the operating program of the MR imaging system 10. The processing unit 24 controls the gradient magnetic field, the RF pulse sequence, and the reception interval of the magnetic resonance signal as a function of a defined pulse sequence. The calculation unit 241 calculates the magnetic resonance image that can be displayed on the display unit 27, which can display a graphical user interface (GUI) to facilitate interaction between the user and the processing unit 24 and allow the user to operate the MR imaging system 10 via the input unit 17. The memory 242 may have an imaging sequence (or pulse sequence) and a program module, wherein one of the program modules includes a program and can be directly loaded into the memory 242 of the programmable computing unit 241 of the processing unit 24 so that when the program is implemented in the computing unit 241 of the processing unit 24, the pulse sequence, the magnetic field gradient sequence and the instructions included in the program are implemented to perform the magnetic resonance imaging pre-scanning method of the present disclosure.

[0050] refer to Figure 2 As shown in the figure, the multiple curves in the graph illustrate the steady-state spectral response functions of different anatomical materials under the application of a TRUFI imaging pulse sequence that can produce a flip angle θ of protons in the body of the examined object. The above curves were obtained under the condition of a flip angle θ = 70°, where the y-axis (vertical axis) is the transverse magnetization function ρ. ∞ And define the transverse magnetization function. As an approximation of the anatomical material signal, the aforementioned steady-state spectral response function curves reveal the characteristics of the steady-state magnetic field. The x-axis (horizontal axis) represents the phase angle of resonance (ranging from 0 to 360 degrees), with the midpoint of β set at 180°. The curves are plotted based on the aforementioned pulse sequence and the variable flip angles θ and β to represent the signals of different anatomical materials, i.e., the presented steady-state spectral response functions. Anatomical materials include, for example, gray matter, fat, and cerebrospinal fluid (CSF), and corresponding steady-state spectral response curves 301 (gray matter), 302 (fat), and 303 (cerebrospinal fluid) are plotted. The total phase angle β (TR) can represent a local non-uniform magnetic field ΔB and a gradient field (or transverse magnetic field). The accumulation between two consecutive stimuli, i.e. Where TR represents the repetition time, i.e., the time length between two excitations, and γ is the gyromagnetism. Furthermore, the offset frequency (ΔB) introduced by the non-uniform magnetic field can be expressed as Δf = ΔB. An offset frequency can be determined and used as a compensation frequency to minimize the influence of the magnetic field on the received magnetic resonance signal, thereby reducing the impact of the non-uniform magnetic field. For example, artifacts or image distortion introduced by the non-uniform magnetic field can be optimized to improve the image quality of magnetic resonance imaging. Therefore, a pulse sequence with a compensation frequency can be constructed to compensate for the non-uniform magnetic field and eliminate the artifacts it introduces.

[0051] Specifically, the TRUFI pulse sequence is a pulse sequence compatible with free steady-state precession sequences, and the evolution of its pulse sequence signal can be represented by the following Bloch equation:

[0052]

[0053]

[0054]

[0055] in

[0056] d=(1-E1cosθ)(1-E2cosβ)-E2(E1-cosθ)(E2-cosβ)

[0057] in, Let be the magnetic field in the x, y, z directions, TE represent the echo time, which is the time interval between sending an RF pulse signal to the object under inspection and the echo signal (i.e., the magnetic resonance signal) returned from the object under inspection; TR represents the repetition time (or the time interval between consecutive excitations); T1 and T2 are relaxation parameters, θ represents the flip angle (of the protons that have received the excitation), and β represents the phase angle of the resonance, which will not be elaborated here.

[0058] The present invention is to provide a method for pre-scanning magnetic resonance imaging, which can automatically analyze, for example, the magnetic resonance signal acquired after performing a frequency search scan and the image data reconstructed based on the magnetic resonance signal using an MR imaging system. For example, it can analyze the relationship between the changes in adjacent image data and quantitatively determine an offset frequency as a compensation frequency for non-uniform magnetic field compensation, so that the off-resonance artifacts introduced by the non-uniform magnetic field can be eliminated when performing, for example, a balanced SSFP pulse imaging sequence.

[0059] Figure 3 An exemplary flowchart of a method for pre-scanning magnetic resonance imaging using a magnetic resonance imaging system according to an embodiment of the present disclosure is shown.

[0060] refer to Figure 3An exemplary method for magnetic resonance imaging pre-scanning is illustrated. In step S1, a first pulse sequence is executed using an MRI imaging system, and multiple magnetic resonance signals at different offset frequencies are acquired from the subject at the same location (or the same slice) via a radio frequency antenna unit. Based on these multiple magnetic resonance signals, corresponding raw k-space domain data is recorded, which can be recorded in a k-space domain matrix along a certain trajectory. Here, the first pulse sequence can be based on a balanced SSFP pulse imaging sequence or a pulse imaging sequence compatible with a balanced SSFP pulse imaging sequence, such as TRUFI. The first pulse sequence is implemented, for example, in a linear and frequency-stepped (progressive offset) manner between individual images acquiring a set of image data about an anatomical region or volume of interest, as a frequency search scan or to provide frequency-oscillating magnetic field changes.

[0061] In step S2, the changes between the multiple original k-space domain data are calculated. In one illustrated embodiment, the change between one of the original k-space domain data and the original k-space domain data obtained at adjacent offset frequencies is calculated, resulting in multiple changes corresponding to the k-space domain data. For example, the k-space domain data corresponding to the nth magnetic resonance signal can be represented as signal. n and the corresponding change Var n For example, the change in amplitude can be expressed as:

[0062] Var n =‖signal n -signal n-1 || / 2+||signal n -signal n+1 ‖ / 2.

[0063] Specifically, in one illustrated embodiment, the change may include the sum of the amplitude changes at multiple k-space locations between an original k-space domain data and two original k-space domain data obtained at adjacent offset frequencies, respectively.

[0064]

[0065] Where Var1(n) can represent the nth original k-space domain data and the original k-space domain data obtained at two adjacent offset frequencies at multiple k-space positions (representing the i-th, i-1, i+1 points, i... The sum of the magnitude changes of the k-space domain data up to the m-th point.

[0066] In addition, calculating the change can also include summing the energy value changes at the k-space position between an original k-space domain data and two original k-space domain data obtained at adjacent offset frequencies, i.e.,

[0067]

[0068] Where Var2(n) can represent multiple k-space positions between the nth original k-space domain data and the two original k-space domain data obtained at adjacent offset frequencies (representing the i-th, i-1, i+1 points, etc.). The sum of the changes in energy value up to the m-th point.

[0069] In step S3, an offset frequency is determined as the compensation frequency for non-uniform magnetic field compensation based on the amount of change. For example, multiple calculated transformation quantities are compared to select the smallest amount of change. The offset frequency corresponding to the original k-space domain data with the smallest amount of change (corresponding to the magnetic resonance signal received by the radio frequency antenna unit at that offset frequency) is used as the compensation frequency for non-uniform magnetic field compensation. This is because the original k-space domain data corresponding to the smallest amount of change shows better consistency with the original k-space domain data obtained at adjacent offset frequencies, and its corresponding offset frequency, as the compensation frequency for non-uniform magnetic field compensation, can eliminate the effects of artifacts, image distortion, etc., introduced by the non-uniform magnetic field.

[0070] In step S4, a second pulse sequence is executed using a magnetic resonance imaging system. At least one radio frequency antenna element responds to the second pulse sequence and applies a compensation frequency to configure the electrical signal to compensate for the non-uniform magnetic field. Here, the second pulse sequence, as a pulse sequence for clinical examination or diagnosis, includes a balanced SSFP pulse sequence (bSSFP) or a true steady-state precession fast imaging pulse sequence (TRUFI) to obtain magnetic resonance imaging or images of the subject being examined.

[0071] Figure 4 The diagram illustrates an exemplary embodiment of a process for calculating changes based on image data to determine an offset frequency as the compensation frequency for non-uniform magnetic field compensation.

[0072] refer to Figure 4In one illustrated embodiment, step S10 involves executing a TRUFI pulse sequence with a frequency-stepped offset using a magnetic resonance imaging system. Multiple magnetic resonance signals from the same location (same layer) of the object being examined are acquired via a radio frequency antenna unit, and corresponding raw k-space domain data are recorded based on these multiple magnetic resonance signals. Here, the gradient coil unit and radio frequency antenna unit can execute, for example, a TRUFI pulse sequence with a frequency-stepped offset, i.e., scanning the same layer or location of the object being examined. The radio frequency antenna unit acquires the echo magnetic resonance signals from the same layer or location. For example, layer selection implemented using the gradient coil control unit determines the released magnetic resonance signals from the same layer or location of the object being examined. The returned magnetic resonance signals are recorded in the k-space domain (i.e., in the k-space matrix) with a certain trajectory, yielding the raw k-space domain data.

[0073] In one illustrated embodiment, to construct a TRUFI pulse sequence that includes a frequency-stepped offset frequency, the frequency-stepped offset frequency can be set sequentially in the gradient echoes corresponding to multiple repetition times, for example, according to the temporal order of the TRUFI pulse sequence.

[0074] In step S20, the k-space domain data is transformed into multiple image data using an inverse Fourier transform. Here, the multiple image data can be sequentially mapped to offset frequencies with set frequency steps.

[0075] In step S30, a region of interest (ROI) is selected from multiple image data. The preset ROI is generally a preset field of view (FOV).

[0076] In step S40, the variation in the image domain between multiple adjacent image data, such as ROI regions, is calculated. This variation includes the sum of the amplitude variations at the voxel or pixel level between each image data and at least two image data obtained at adjacent offset frequencies.

[0077]

[0078] Where Var1(n) can represent the pixels or voxels between the nth image data and the two adjacent image data with offset frequencies (denoted as...). The sum of the amplitude changes of the nth image data (Image, etc.) n This can correspond to the order of offset frequencies with frequency steps set.

[0079] In step S50, the changes between multiple image data in the image domain are calculated. These changes include the sum of the energy value changes between each image data and its adjacent pixels or voxels at corresponding positions, such as between two consecutive image data. Specifically, this sums the energy value changes between each corresponding point in the preceding and following image data.

[0080]

[0081] Where Var2(n) can represent the nth image data and each pixel or voxel of the two preceding and following image data (e.g., represented as the i-th, i-1, and i+1 points, i.e. The sum of the energy value changes between the nth image data and the offset frequencies with set frequency steps is used to calculate the changes between each image data. It should be noted that either step S40 or step S50 can be selected to calculate the changes between each image data.

[0082] In step S60, multiple variables associated with each image data are analyzed, and the magnitudes of these variables are compared to determine the smallest variable. The offset frequency corresponding to the relevant image data is then selected as the compensation frequency for compensating for the non-uniform magnetic field. This offset frequency can serve as the compensation frequency and can be applied to configure an electrical signal. The RF antenna unit, responding to the electrical signal, generates an RF pulse signal that may include the compensation frequency for compensating for the non-uniform magnetic field. In one illustrated embodiment, a pulse sequence is performed as a diagnostic or clinical examination using a magnetic resonance imaging system. The RF antenna unit responds to this pulse sequence and applies the compensation frequency to configure the electrical signal, causing the RF antenna unit to irradiate the examination object with the RF pulse signal.

[0083] refer to Figure 5The illustration shows an exemplary embodiment of a phantom-based magnetic resonance imaging system executing a pulse sequence including frequency-stepped offset frequencies to obtain corresponding image data, and curves 501 and 503 showing the amplitude variation and energy variation of image data obtained at adjacent offset frequencies in the image domain. The MR imaging system executes a TRUFI pulse sequence with an offset frequency Δf set in 25 Hz steps to illuminate the same phantom (or the same location of the phantom) using a radio frequency antenna unit, and the radio frequency antenna unit acquires multiple echo magnetic resonance signals, wherein the offset frequency Δf is set to be between 0 Hz and 275 Hz in 25 Hz steps. The image reconstruction unit generates 12 image data 505, corresponding to image data 505 labeled a1 to a12 (multiple image data 505 correspond to labels a1, a2, ..., a12, etc.), and the offset frequency difference between each image data is 25Hz (for example, image data labeled a1 corresponds to an offset frequency of 0Hz, image data a2 corresponds to an offset frequency of 25Hz, and so on). During steps S40 and S50, amplitude change curve 501 and energy change curve 503 corresponding to the image data 505 can be plotted, respectively. In amplitude change curve 501, the sequential numbering of image data 505 corresponding to the progressive offset frequency Δf is used as the horizontal axis, and the sum of amplitude changes between each point of each image data and the preceding and following image data 505 is used as the vertical axis. In energy change curve 503, the sequential numbering of image data corresponding to the progressive offset frequency Δf is used as the x-axis (horizontal axis), and the sum of energy changes between each point of each image data and the preceding and following image data is used as the y-axis (vertical axis). According to amplitude change curve 501, the sum of amplitude changes of the 7th image data is the smallest change 502, and the sum of energy changes is the smallest change 502'. The image quality of the 7th image data is good (with high consistency with the smallest change between the preceding and following image data). Therefore, its corresponding offset frequency Δf = 150Hz can be selected as the compensation frequency for compensating for non-uniform magnetic fields.

[0084] refer to Figure 6The document also exemplifies a process for calculating changes in k-space domain data based on ROI image data transformation to determine a suitable offset frequency as the compensation frequency for non-uniform magnetic field compensation. In step S100, a TRUFI pulse sequence with a frequency-stepped offset frequency is executed using a magnetic resonance imaging system. Multiple magnetic resonance signals from the same location are acquired from the examination object via a radio frequency antenna unit, and the original k-space domain data is recorded. The examination object is, for example, a phantom, and the scan can be focused on the same layer or location. The magnetic resonance signals are recorded in the k-space domain with a certain trajectory, which can be Cartesian or non-Cartesian. In step S200, the acquired multiple original k-space domain data are transformed to the image domain using an inverse (multidimensional) Fourier transform to obtain multiple image data. The order of the image data can correspond to the set frequency-stepped offset frequency, for example... Figure 5 As shown, in image data 505, image data a1 corresponds to an offset frequency Δf = 0Hz to image data a12 corresponds to Δf = 275Hz. In step S300, regions of interest (ROIs) are selected from multiple image data sets, where the multiple image data sets are based on images acquired at the same layer or location. Figure 7 As shown, the region of interest 701 selected based on the phantom and the corresponding window 703 region in the k-space domain are illustrated. That is, the k-space domain data in the window 703 region is obtained by transforming the region of interest 701 from the image domain to the k-space domain through a multidimensional Fourier transform.

[0085] In step S400, the image data of the ROI region is transformed from the image domain to the k-space domain using a (multidimensional) Fourier transform, resulting in multiple k-space domain data. Each k-space domain data includes multiple rearrangeable points P1, P2, ..., P in the k-space. i , ..., P m .

[0086] In step S500, the changes between multiple k-space domain data are calculated. These changes include the sum of the amplitude changes at multiple k-space locations between each k-space domain data point and two k-space domain data points obtained at adjacent offset frequencies.

[0087]

[0088] Where Var1(n) can represent the position in each k-space region between the nth k-space data and the two preceding and following k-space data (representing the i-th, i-1, and i+1th points). The sum of the amplitude changes of (etc.) means that the nth k spatial domain data can correspond to the nth image data, that is, the order of the offset frequencies with frequency steps set.

[0089] In step S600, calculating the change includes calculating the sum of the energy value changes between a k-space domain data point and multiple corresponding positions of two adjacent k-space domain data points. For example, the sum of the energy value changes at each k-space position (point) between at least two k-space domain data points that are in sequential order.

[0090]

[0091] Var2(n) can represent the k-space positions (i-th, i-1, i+1 points) between the nth k-space data and the two preceding and following k-space data. The sum of the energy changes of (etc.) in k-space domains, the nth k-space domain data can correspond to the nth image data, that is, sequentially correspond to the offset frequency of each frequency step. It should be noted that the advantage of choosing to calculate the changes between multiple k-space domain data in k-space (domain) is that it can avoid offsets or movement of the object being inspected in the image, and avoid possible negative effects from high-frequency signals.

[0092] In step S700, this step is the same as step S60 of the aforementioned exemplary embodiment, and will not be described again here.

[0093] Another aspect of this disclosure provides a magnetic resonance imaging pre-scanning apparatus for magnetic resonance imaging. (Reference) Figure 1 The magnetic resonance imaging pre-scanning device includes: a processing unit 24 configured to execute a first pulse sequence using a magnetic resonance imaging system and acquire multiple magnetic resonance signals at different offset frequencies at the same location from the object under examination via a radio frequency antenna unit, and record / obtain corresponding raw k-space domain data based on the multiple magnetic resonance signals; and a calculation unit 241 configured to calculate the changes between the multiple k-space domain data respectively, and determine an offset frequency as a compensation frequency for non-uniform magnetic field compensation based on the changes. Here, the calculation unit 241 is further configured to calculate the sum of amplitude changes or energy changes in the k-space domain between a first k-space domain data and multiple k-space domain data obtained at adjacent offset frequencies.

[0094] In some exemplary embodiments, to enable the magnetic resonance imaging pre-scanning apparatus to determine an offset frequency as a compensation frequency for compensating for a non-uniform magnetic field by analyzing the changes in image data obtained at different offset frequencies in the image domain, the magnetic resonance imaging pre-scanning apparatus further includes: a reconstruction unit 243 configured to reconstruct corresponding image data based on the original first k spatial domain data; and a calculation unit 241 further configured to calculate the changes between multiple image data in the image domain, the changes including the sum of the amplitude changes or the sum of the energy changes between an image data and image data obtained at adjacent offset frequencies in multiple voxels or pixels.

[0095] In some exemplary embodiments, in order to improve the efficiency of the magnetic resonance imaging pre-scanning apparatus in calculating the amount of change between multiple image data, the processing unit 24 of the magnetic resonance imaging pre-scanning apparatus is further configured to select regions of interest (ROIs) for each of the multiple image data after obtaining multiple image data, and the calculation unit 241 is configured to calculate the amount of change between the multiple ROIs in the image domain.

[0096] In some exemplary embodiments, the computing unit 241 of the magnetic resonance imaging pre-scanning apparatus is configured to transform the ROI in the image data obtained from the magnetic resonance signal to the k-space domain, obtain multiple k-space domain data, and calculate the changes between the multiple k-space domain data in the k-space domain. Here, the changes include the sum of the amplitude changes or the sum of the energy changes between one k-space domain data and at least two k-space domain data obtained at adjacent offset frequencies at multiple k-space locations.

[0097] In some exemplary embodiments, in order to enable the magnetic resonance imaging pre-scanning device to determine an offset frequency for compensating for a non-uniform magnetic field based on the amount of variation between multiple k-space domain data acquired from a pre-scan magnetic resonance signal (including in the image domain or k-space domain), the processing unit 24 is further configured to compare the magnitudes of multiple variations to determine the smallest variation, so as to select the offset frequency corresponding to the corresponding magnetic resonance signal as the compensation frequency for compensating for the non-uniform magnetic field.

[0098] In some exemplary embodiments, the magnetic resonance imaging pre-scanning apparatus further includes a sequence processing unit 244 configured to construct a first pulse sequence as a plurality of offset frequencies including frequency steps, so that the radio frequency antenna unit receives magnetic resonance signals sequentially.

[0099] In some exemplary embodiments, the sequence processing unit 244 is configured to construct a first pulse sequence that includes a balanced SSFP pulse sequence or a true steady-state precession fast imaging pulse sequence.

[0100] In some exemplary embodiments, to generate a pulse sequence based on a selected offset frequency as a compensation frequency to compensate for a non-uniform magnetic field, for obtaining high-quality MR images and counteracting effects such as artifacts and distortions caused by non-uniform magnetic fields on the MR image, the sequence processing unit 244 is configured to generate a second pulse sequence. The second pulse sequence is executed by means of a magnetic resonance imaging system, such that at least one radio frequency antenna element responds to the second pulse sequence and the compensation frequency to configure an electrical signal to generate a compensated non-uniform magnetic field. In some exemplary embodiments, the second pulse sequence generated by the sequence processing unit 244 may include a balanced SSFP pulse sequence or a true steady-state precession fast imaging pulse sequence.

[0101] Another aspect of this disclosure provides a computer-readable storage medium storing program segments readable and executable by the magnetic resonance imaging pre-scanning apparatus, such that when the program segments are run by the magnetic resonance imaging and scanning apparatus, all steps of the method described in any of the preceding claims can be performed. Here, the program segments may include software having source code or implemented software code that has not yet been compiled and linked, or that the source code only needs to be described; the implementable software code only needs to be loaded into a processing unit for implementation. By executing the program segments, the magnetic resonance imaging pre-scanning method can be implemented quickly and reproducibly by means of the processing unit. The program segments are configured such that the apparatus can implement the method steps according to the invention by means of the processing unit.

[0102] For example, the program segment is stored on a computer-readable storage medium, or on a network or server, from which it can be loaded into the processor of the processing unit, which can be directly connected to the processing unit or can be constructed as part of the processing unit. Furthermore, the control information of the program segment can be stored on an electronically readable data carrier. The control information of the electronically readable data carrier can be designed such that the processing unit executes the methods of the present invention when using the data carrier. Examples of electronically readable data carriers are DVDs, hard disks, or portable hard disks, on which electronically readable control information, particularly software, is stored. When this control information is read from the data carrier and stored in the processing unit, all embodiments of the methods described above according to the present invention can be executed.

[0103] The present invention may also relate to computer-readable storage media and / or electronically readable data carriers storing program segments thereon that can be read and executed by a processing unit so as to implement all steps of a method for magnetic resonance imaging pre-scanning when the program segments are executed by the processing unit. Implementation in software form has the advantage that processing units currently in use can be easily modified via software updates to operate according to the invention. In addition to computer programs or program segments, the computer-readable storage medium may, where necessary, include additional components, such as documents and / or additional parts, as well as hardware, such as hardware keys for using the software.

[0104] In this document, “illustrative” means “serving as an example, illustration or description”, and any illustration or implementation described herein as “illustrative” should not be construed as a more preferred or advantageous technical solution.

[0105] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, components with the same structure or function are shown only schematically, or only one is labeled.

[0106] In this document, "a" can mean not only "only one" but also "more than one". In this document, "first", "second", etc., are used only to distinguish them from each other, and not to indicate their importance, order, or mutual preconditions. Furthermore, the term "and / or" as used in this disclosure covers any one of the listed items and all possible combinations. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" relationship.

[0107] While embodiments or examples of this disclosure have been described with reference to the accompanying drawings, it should be understood that the methods, systems, and devices described above are merely exemplary embodiments or examples, and the scope of the invention is not limited by these embodiments or examples, but only by the granted claims and their equivalents. Various elements in the embodiments or examples may be omitted or replaced by their equivalents. Furthermore, the steps may be performed in a different order than that described in this disclosure. Further, various elements in the embodiments or examples may be combined in various ways. Importantly, as the technology evolves, many elements described herein can be replaced by equivalents that appear after this disclosure.

Claims

1. A method for pre-scanning in magnetic resonance imaging, characterized in that, The method includes the following steps: A first pulse sequence is executed using a magnetic resonance imaging system, and multiple magnetic resonance signals at different offset frequencies at the same location are acquired from the object under examination through a radio frequency antenna unit. Based on the multiple magnetic resonance signals, the corresponding first k spatial domain data are recorded. Calculate the changes between multiple data points in the first k spatial domain; and Based on the amount of change, an offset frequency is determined as the compensation frequency for non-uniform magnetic field compensation. Calculating the changes in multiple data points in the first k spatial domain includes: Reconstruct the corresponding image data based on multiple first k spatial domain data; After acquiring multiple image datasets, regions of interest are selected for each dataset; and Multiple regions of interest are transformed to the k-space domain to obtain multiple second k-space domain data. The changes between the multiple second k-space domain data in the k-space domain are calculated respectively. The changes include the sum of the amplitude changes or the sum of the energy changes between a second k-space domain data and the second k-space domain data obtained at adjacent offset frequencies at multiple k-space positions.

2. A method for pre-scanning in magnetic resonance imaging, characterized in that, The method includes the following steps: A first pulse sequence is executed using a magnetic resonance imaging system, and multiple magnetic resonance signals at different offset frequencies at the same location are acquired from the object under examination through a radio frequency antenna unit. Based on the multiple magnetic resonance signals, the corresponding first k spatial domain data are recorded. Calculate the changes between multiple data points in the first k spatial domain; and Based on the amount of change, an offset frequency is determined as the compensation frequency for non-uniform magnetic field compensation. The changes include the sum of the amplitude changes or the sum of the energy changes between a first k spatial domain data and the first k spatial domain data obtained at adjacent offset frequencies at multiple k spatial locations.

3. A method for pre-scanning in magnetic resonance imaging, characterized in that, The method includes the following steps: A first pulse sequence is executed using a magnetic resonance imaging system, and multiple magnetic resonance signals at different offset frequencies at the same location are acquired from the object under examination through a radio frequency antenna unit. Based on the multiple magnetic resonance signals, the corresponding first k spatial domain data are recorded. Calculate the changes between multiple data points in the first k spatial domain; and Based on the amount of change, an offset frequency is determined as the compensation frequency for non-uniform magnetic field compensation. The step of calculating the changes between the multiple first k spatial domain data includes: Reconstruct the corresponding image data based on multiple first k spatial domain data; and Calculate the amount of change between multiple image data in the image domain. The amount of change includes the sum of the amplitude changes or the sum of the energy changes between each image data and the image data obtained at adjacent offset frequencies across multiple voxels or pixels.

4. The method according to claim 3, wherein, After obtaining multiple image data, regions of interest are selected for each image data to calculate the changes in the image domain among the multiple regions of interest.

5. The method according to claim 1, wherein, The first pulse sequence is constructed as an offset frequency including frequency steps, so that the radio frequency antenna element receives the magnetic resonance signal sequentially.

6. The method according to any one of claims 1 to 5, wherein, The step of determining an offset frequency as the compensation frequency for non-uniform magnetic field compensation based on the amount of change includes: The smallest change is determined by comparing the magnitudes of multiple changes, and the offset frequency corresponding to the smallest change is selected as the compensation frequency for compensating the non-uniform magnetic field.

7. The method according to any one of claims 1 to 5, wherein, The first pulse sequence includes either a balanced SSFP pulse sequence or a true steady-state precession fast imaging pulse sequence.

8. The method according to any one of claims 1 to 5, wherein, A second pulse sequence is executed by means of a magnetic resonance imaging system, at least one radio frequency antenna element responds to the second pulse sequence and applies the compensation frequency to configure an electrical signal to compensate for the non-uniform magnetic field.

9. The method according to claim 8, wherein, The second pulse sequence includes either a balanced SSFP pulse sequence or a true steady-state precession fast imaging pulse sequence.

10. A magnetic resonance imaging pre-scanning device, characterized in that, include: The processing unit is configured to execute a first pulse sequence using a magnetic resonance imaging system and acquire multiple magnetic resonance signals at different offset frequencies at the same location from the object under examination using a radio frequency antenna unit, and record corresponding first k-space domain data based on the multiple magnetic resonance signals. The computing unit is configured to calculate the changes between multiple data points in the first k spatial domain, and determine an offset frequency based on these changes as a compensation frequency for non-uniform magnetic field compensation. The reconstruction unit is configured to reconstruct the corresponding image data based on multiple first k spatial domain data; The processing unit is configured to select regions of interest from each of the multiple image data sets after acquiring them. as well as The computing unit is configured to transform multiple regions of interest to the k-space domain to obtain multiple second k-space domain data, and to calculate the amount of change between the second k-space domain data in the k-space domain. The amount of change includes the sum of the amplitude changes or the sum of the energy changes between the second k-space domain data at multiple k-space positions obtained at adjacent offset frequencies of a second k-space domain data domain.

11. A magnetic resonance imaging pre-scanning device, characterized in that, include: The processing unit is configured to execute a first pulse sequence using a magnetic resonance imaging system and acquire multiple magnetic resonance signals at different offset frequencies at the same location from the object under examination using a radio frequency antenna unit, and record corresponding first k-space domain data based on the multiple magnetic resonance signals. The computing unit is configured to calculate the changes between multiple data points in the first k spatial domain, and determine an offset frequency based on these changes as a compensation frequency for non-uniform magnetic field compensation. The computing unit is further configured to calculate the sum of amplitude changes or energy changes between a first k spatial domain data and the first k spatial domain data obtained at adjacent offset frequencies at multiple k spatial locations.

12. A magnetic resonance imaging pre-scanning device, characterized in that, include: The processing unit is configured to execute a first pulse sequence using a magnetic resonance imaging system and acquire multiple magnetic resonance signals at different offset frequencies at the same location from the object under examination using a radio frequency antenna unit, and record corresponding first k-space domain data based on the multiple magnetic resonance signals. The computing unit is configured to calculate the changes between multiple data points in the first k spatial domain, and determine an offset frequency based on these changes as a compensation frequency for non-uniform magnetic field compensation. The reconstruction unit is configured to reconstruct corresponding image data based on multiple first k spatial domain data; as well as The computing unit is also configured to calculate the amount of change between multiple image data in the image domain, which includes calculating the sum of the amplitude changes or the sum of the energy changes between an image data and image data obtained at adjacent offset frequencies in multiple voxels or pixels.

13. The magnetic resonance imaging pre-scanning apparatus according to claim 12, wherein, The processing unit is further configured to select regions of interest for each of the multiple image data after obtaining multiple image data, so that the computing unit can calculate the amount of change between the multiple regions of interest in the image domain.

14. The magnetic resonance imaging pre-scanning apparatus according to any one of claims 10 to 13, wherein, The processing unit is further configured to compare the magnitudes of multiple changes to determine the smallest change, and select the offset frequency corresponding to the smallest change as the compensation frequency for compensating the non-uniform magnetic field.

15. The magnetic resonance imaging pre-scanning apparatus according to claim 10, wherein, It also includes a sequence processing unit configured to construct a first pulse sequence including a balanced SSFP pulse sequence or a true steady-state precession fast imaging pulse sequence.

16. The magnetic resonance imaging pre-scanning apparatus according to claim 15, wherein, The sequence processing unit is configured to construct a first pulse sequence including a frequency-stepped offset frequency, so that the radio frequency antenna unit receives the magnetic resonance signal sequentially.

17. The magnetic resonance imaging pre-scanning apparatus according to claim 16, wherein, The sequence processing unit is configured to generate a second pulse sequence, which is executed by means of a magnetic resonance imaging system, such that at least one radio frequency antenna element responds to the second pulse sequence and applies a selected compensation frequency to configure an electrical signal to compensate for the non-uniform magnetic field.

18. The magnetic resonance imaging pre-scanning apparatus according to claim 17, wherein, The second pulse sequence includes either a balanced SSFP pulse sequence or a true steady-state precession fast imaging pulse sequence.

19. A magnetic resonance imaging system configured to perform the magnetic resonance imaging pre-scanning method according to any one of claims 1 to 9.

20. A computer-readable storage medium having stored thereon a program segment readable and operable by a magnetic resonance imaging pre-scanning apparatus, such that when the program segment is run by the magnetic resonance imaging pre-scanning apparatus, it is capable of performing all the steps of the method according to any one of claims 1 to 9.

Images