CN115372873A - K space trajectory correction system and method applied to miscellaneous nuclear imaging - Google Patents
K space trajectory correction system and method applied to miscellaneous nuclear imaging Download PDFInfo
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Abstract
The invention discloses a k-space trajectory correction system and a k-space trajectory correction method applied to heteronuclear imaging, and belongs to the technical field of imaging. The track correction system comprises a sampling sequence and signal processing system, a spectrometer control system and a magnet and radio frequency system, wherein the sampling sequence and signal processing system is connected with the spectrometer control system, and the spectrometer control system is connected with the magnet and the radio frequency system through an amplifier and an auxiliary control part. The k space trajectory correction method applied to the heteronuclear imaging is used for correcting target k space trajectory deviation caused by insufficient gradient hardware or incompletely eliminated eddy current effect, so that the influence of image artifacts is reduced or eliminated. The method does not need a separate sequence for measuring the k-space trajectory, the scanning time is hardly increased, and the measured gradient waveform, namely the imaging gradient used in actual imaging, can avoid the influence of insufficient stability of a gradient system.
Description
Technical Field
The invention relates to the technical field of imaging, in particular to a k-space trajectory correction system and a k-space trajectory correction method applied to heteronuclear imaging.
Background
A conventional magnetic resonance imaging system and 1 the H nucleus is an observation nucleus, mainly obtains anatomical images with different tissue contrasts, and has limited reflected metabolic and functional information. Heteronuclear imaging by imaging a plurality of non-proton magnetic nuclei (e.g. nuclear magnetic resonance imaging) 19 F， 23 Na， 31 P), metabolism and function information can be effectively expanded, the limitation of the traditional magnetic resonance is broken, and massive important biological information contained in weak biological signals is excavated.
However, heteronuclear imaging still faces a few challenges in practical applications. As is known, magnetic resonance imaging acquires data in k-space, which is then fourier transformed to obtain an image. The deformation of the k-space trajectory may cause artifacts such as deformation, wrap around, etc. on the image. Modern magnetic resonance apparatuses rely primarily on gradient self-shielding coils and gradient pre-emphasis techniques in order to mitigate distortions of the k-space trajectory. For traditional cartesian k-space acquisition, good correction effect can be achieved in scanning because the acquisition mode is insensitive to trajectory deformation. In heteronuclear imaging, the magnetic resonance physical characteristics of heteronuclei are similar to those of conventional imaging 1 The H-nuclei are very different, and non-cartesian scan sequences such as Radial and Spiral are preferred in many situations. non-Cartesian acquisition may provide benefits in many ways, such as reduced motion sensitivity for scanning, acquisition of signals for ultra-fast relaxing tissue, natural compatibility with compressive sensing techniques, etc., whereas non-Cartesian imaging sequences place high demands on gradient hardwareDeficiencies in the gradient hardware or eddy current effects that are not completely eliminated during the system calibration phase can cause the target K-space trajectory to deviate and cause image artifacts. Therefore, in magnetic resonance imaging, k-space trajectory correction of a non-cartesian acquisition sequence applied to the imaging is indispensable to reduce the eddy current effect due to insufficient or incomplete elimination of gradient hardware, thereby improving the image quality.
One way to compensate for these trajectory distortions is to estimate the k-space trajectory, which treats the Gradient system as a linear time invariant system, measures the Gradient Impulse Response Function (GIRF) of the Gradient system by a certain method, then estimates the actual k-space trajectory and applies it to image reconstruction. Or similarly, the GIRF can be used to estimate the applied predistortion gradient waveforms required to produce the ideal k-space trajectory and to compensate during acquisition. Another compensation method is to use a high signal-to-noise ratio prior to acquiring non-Cartesian scan data of the heterokaryon 1 The H-kernel signal first measures the actual k-space trajectory and then applies this information to the image reconstruction of the miscellaneous kernel, resulting in improved image quality.
The first compensation method mentioned above requires the measurement of the frequency response function of the gradient system, the measurement process itself is complex, and the frequency response function tends to change slightly with the passage of time and some operations during the maintenance of the machine, and in practice, the accuracy of this method is difficult to guarantee.
The second compensation method requires that the track measurement is performed on the independent sequence, then the non-cartesian data acquisition is performed, and finally the image reconstruction is performed by using the measured track. The technology can generally obtain a relatively stable compensation effect, but the scanning time is prolonged; in addition, because the trajectory data and the image data are respectively acquired, a certain delay exists in time, actually measured gradient waveforms are not applied during imaging, and if the stability of a gradient system is insufficient, the method is also influenced, and a certain risk of measurement failure exists.
Disclosure of Invention
The present invention is directed to a k-space trajectory correction system and method applied to a hetero-nuclear imaging, so as to solve the problems mentioned in the background art.
In order to achieve the purpose, the invention provides the following technical scheme:
a k-space trajectory correction system applied to heteronuclear imaging comprises a sampling sequence and signal processing system, a spectrometer control system and a magnet and radio frequency system, wherein the sampling sequence and signal processing system is connected with the spectrometer control system, and the spectrometer control system is connected with the magnet and the radio frequency system through an amplifier and an auxiliary control part.
As a further technical scheme of the invention: the amplifier comprises a heteronuclear RF amplifier, 1 An H nuclear species RF amplifier, 1 An H-species RF preamplifier, a heteronuclear RF preamplifier, and a gradient amplifier.
As a further technical scheme of the invention: the sampling sequence and signal processing system comprises a sampling sequence and image processing module and a main control system.
As a further technical scheme of the invention: the magnet and the radio frequency system are adopted by 1 Consisting of H-coils and hetero-nuclear coils 1 H and a heteronuclear radio frequency transmitting and receiving integrated coil.
As a further technical scheme of the invention: the spectrometer control system comprises a broadband multi-core signal excitation control system, a receiver, a gradient and radio frequency power system and a gradient control and system main control module.
Further, when the k-space trajectory correction system applied to the heteronuclear imaging works, the sampling sequence and the signal processing system are used for 1 H, sending control instructions, imaging sequences, parameters and the like of the miscellaneous kernel to a spectrometer control system; the broadband multi-core signal excitation control system of the spectrometer control system receives parameters, generates radio frequency pulse small signals with specific frequency, bandwidth, phase and amplitude through frequency synthesis, waveform generation, quadrature modulation and the like, and amplifies the radio frequency pulse small signals through a radio frequency power amplifier 1 Generating RF magnetic field in transmitting part of H and heteronuclear RF transmitting-receiving integrated coil to excite imaging object 1 H and miscellaneous nucleiGenerating resonance, simultaneously receiving parameters by a gradient waveform generating part of a spectrometer control system, then calculating and processing the gradient waveform in a sequence, outputting a gradient waveform signal, and driving a gradient coil in a magnet to generate a gradient magnetic field after the gradient waveform signal is amplified by a gradient power amplifier; 1 h and resonance signal generated by heteronuclear 1 The receiving part of the H and heteronuclear radio frequency transmitting-receiving integrated coil generates a high-frequency modulation signal 1 H, amplifying the signals by the heteronuclear preamplifier, sending the amplified signals to a receiver of a spectrometer system, and filtering, amplifying, demodulating, collecting and transmitting the signals by the receiver to form magnetic resonance signals which can be collected; finally, collected 1 And transmitting the H/heteronuclear magnetic resonance signal back to the sampling sequence and signal processing system, and processing the data to obtain a required magnetic resonance image.
A k-space trajectory correction method applied to heteronuclear imaging adopts the system and comprises the following steps:
step 1: before the heteronuclear imaging sequence unit 1 Applying a layer selection excitation unit to the H channel;
and 2, step: in the heteronuclear imaging sequence unit, firstly, the heteronuclear channel emits radio frequency pulse to excite the heteronuclear to generate signals, and then the signals are respectively enabled in the signal receiving stage 1 Receive chain of H/miscellaneous core channel, collection 1 H/heteronuclear signals; collected to obtain 1 The H signal is processed to generate measured k space trajectory data; acquiring acquired heteronuclear signals, and recording the acquired heteronuclear signals as heteronuclear signal k-space data;
and 3, step 3: and (3) reconstructing the k space formed by the heteronuclear signals in the step (2) by using the k space trajectory data generated in the step (2) to obtain a track-corrected heteronuclear image.
As a further technical scheme of the invention: the above-mentioned 1 A layer-selecting excitation unit on the H channel, comprising 1 H selective excitation pulse and corresponding slice selection gradient selectively excite an off-center layer.
As a further technical scheme of the invention: the described 1 The gradient direction of the selected layer in the selected layer excitation unit on the H channel should be imaged with the heteronuclearThe readout gradient direction in the sequence unit is the same.
Preferably, in the k-space trajectory correction method applied to the heteronuclear imaging, only k-space trajectories in several readout gradient directions may be selectively measured, and then a complete k-space trajectory is obtained by a least square method and data interpolation.
Preferably, in the k-space trajectory correction method applied to the hetero-nuclear imaging, in the signal reception phase, if a dephasing gradient exists before the read gradient in the hetero-nuclear imaging sequence unit, 1 the H-channel data needs to be acquired as soon as the dephasing gradient begins to be applied. In the phase of acquisition of the heteronuclear signals, 1 the H/heteronuclear signals need to be acquired synchronously.
Compared with the prior art, the invention has the beneficial effects that: the k space trajectory correction system and method applied to the heteronuclear imaging, provided by the invention, are used for correcting target k space trajectory deviation caused by insufficient gradient hardware or incompletely eliminated eddy current effect, so that the influence of image artifacts is reduced or eliminated. The method does not need a separate sequence for measuring the k-space trajectory, the scanning time is hardly increased, and the measured gradient waveform, namely the imaging gradient used in actual imaging, can avoid the influence of insufficient stability of a gradient system. The correction system and method can be conveniently applied to various heterogeneous kernels and various heterogeneous kernel imaging sequences.
Drawings
FIG. 1 is a system block diagram for k-space trajectory correction for heteronuclear imaging.
Fig. 2 is a 3D UTE sequence chart.
FIG. 3 is a drawing showing 1 H and 23 the Na parallel imaging system is used for a k-space trajectory correction pulse sequence chart of 3D UTE applied to heteronuclear imaging.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1: referring to fig. 1, a k-space trajectory correction system for heteronuclear imaging includes a sampling sequence and signal processing system, a spectrometer control system, and a magnet and radio frequency system, wherein the sampling sequence and signal processing system is connected to the spectrometer control system, and the spectrometer control system is connected to the magnet and radio frequency system through an amplifier and an auxiliary control unit.
The amplifier comprises a heteronuclear RF amplifier, 1 An H nuclear species RF amplifier, 1 An H-species RF preamplifier, a heteronuclear RF preamplifier, and a gradient amplifier. The sampling sequence and signal processing system comprises a sampling sequence and image processing module and a main control system. The magnet and the radio frequency system adopt 1 Consisting of H-coils and hetero-nuclear coils 1 H and a heteronuclear radio frequency transmitting and receiving integrated coil. The spectrometer control system comprises a broadband multi-core signal excitation control system, a receiver, a gradient and radio frequency power system and a gradient control and system main control module.
When the system is working, the sampling sequence and the signal processing system will 1 H, sending control instructions, imaging sequences, parameters and the like of the miscellaneous kernel to a spectrometer control system; the broadband multi-core signal excitation control system of the spectrometer control system receives parameters, generates radio frequency pulse small signals with specific frequency, bandwidth, phase and amplitude through frequency synthesis, waveform generation, quadrature modulation and the like, and amplifies the radio frequency pulse small signals through a radio frequency power amplifier 1 Generating RF magnetic field in transmitting part of H and heteronuclear RF transmitting-receiving integrated coil to excite imaging object 1 H and the heteronuclear generate resonance, meanwhile, a gradient waveform generating part of a spectrometer control system receives parameters, then calculates and processes a gradient waveform in a sequence, outputs a gradient waveform signal, and drives a gradient coil in a magnet to generate a gradient magnetic field after the gradient waveform signal is amplified by a gradient power amplifier; 1 h and resonance signal generated by heteronuclear 1 H and the receiving part of the heteronuclear radio frequency transmitting and receiving integrated coil generates a high-frequency modulation signal, and the high-frequency modulation signal is transmitted and received by the receiving part 1 The H and heteronuclear preamplifier is amplified and then sent to a receiver of a spectrometer system, and signals are filtered by the receiverThe method comprises the steps of wave, amplification, signal demodulation, signal acquisition and signal transmission to form a magnetic resonance signal which can be acquired; finally, collected 1 And transmitting the H/heteronuclear magnetic resonance signal back to the sampling sequence and signal processing system, and processing the data to obtain a required magnetic resonance image.
The design also discloses a k-space trajectory correction method applied to the heteronuclear imaging, and the system comprises the following steps:
step 1: before the heteronuclear imaging sequence unit 1 Applying a layer selection excitation unit to the H channel;
and 2, step: in the heteronuclear imaging sequence unit, firstly, the heteronuclear channel emits radio-frequency pulses to excite the heteronuclear to generate signals, and then in the signal receiving stage, the signals are respectively enabled 1 Receive chain of H/miscellaneous core channel, collection 1 H/heteronuclear signals; collected to obtain 1 The H signal is processed to generate measured k space trajectory data; acquiring acquired heteronuclear signals, and recording the acquired heteronuclear signals as heteronuclear signal k-space data;
and step 3: and (3) reconstructing the k space formed by the heteronuclear signals in the step (2) by using the k space track data generated in the step (2) to obtain a track-corrected heteronuclear image.
Example 2: on the basis of example 1, to collect 23 A3D-UTE signal of Na will be described as an example.
3D-UTE basic sequence diagram As shown in FIG. 2, after an excitation pulse, three physical gradient axes output three paths of spatially encoded gradients with respective gradient values:
wherein, G r To read the gradient magnitude, G x 、G y 、G z The magnitudes of the gradient values on the three physical gradient axes are respectively, and psi and theta are respectively a polar angle and an azimuth angle in the spherical coordinate system. The 3D-UTE sequence during the ADC turn-on, i.e. from the encoding gradient edge, the receiving system starts acquiring k-space data. Such non-Cartesian acquisition requires trajectory correctionIs very high. In practice, it is common practice to utilize 1 The H-signal is previously dedicated to determining its k-space trajectory.
The k-space trajectory correction method applied to the hetero-nuclear imaging according to the present invention is applied to the UTE sequence, and a sequence chart thereof is shown in fig. 3. In contrast to fig. 2, the read gradient of UTE is not represented as a waveform on the gradient axis in the three physical coordinate systems of X, Y and Z in fig. 3, but is directly expressed as a path of gradient in the logical coordinate system. In the logical coordinate system, the read gradient waveforms of UTE are unchanged, but the applied direction is rotated in k-space, which can be achieved by changing the rotation matrix of the gradient system. Furthermore, the sequence of FIG. 3 is compared to the basic 3D-UTE sequence 23 Na is added before the radio frequency pulse 1 The H rf pulse, simultaneously, adds a gradient in the readout gradient direction of the UTE. The gradient is as 1 The H-channel slice selection gradient and the slice refocusing gradient can selectively excite a thin slice which is eccentric. Receiving system synchronous acquisition during ADC turn-on 1 H/ 23 The signal of the Na is transmitted to the probe, 23 the signal of Na is k-space data acquired by UTE sequence 1 The phase expression of the H signal then satisfies the following formula:
wherein γ is 1 Magnetic rotation ratio of H, D r For the selected off-center distance of the thin layer, t is a time variable, r is a space variable, G r (t) is the 3D-UTE read gradient waveform, k r And (t) is the measured k-space trajectory. The first term integral on the right side of the formula is a spin phase caused by 3D-UTE read gradient, and can be seen to be in proportional relation with a k-space trajectory; second item
Spin phase due to other system factors such as magnetic field inhomogeneity.
For eliminating system factors 1 The influence of H signal phase can be controlled during UTE track designEach readout gradient direction has an opposite readout gradient direction. As shown in fig. 3, each UTE read gradient can find another read gradient opposite to it, and the signal acquisition process is repeated, then 1 The phase expression of the H signal is as shown in equation (3):
observing the formulas (2) and (3), and subtracting the phases of the two measured MR signals, namely eliminating the phases caused by system factors, so as to obtain a k-space trajectory:
k r (t)＝ΔΦ r (t)/2D r (4)
such a group 1 The H-signal can determine the k-space trajectory in the direction of the read gradient, which is denoted here as kr.
When k-space trajectories in m different directions are obtained through measurement, kx, ky and kz (namely k-space trajectories when the read gradient directions are three physical gradient axes of X, Y and Z respectively) can be estimated:
wherein, T is a coefficient matrix determined by the measured reading gradient direction, n is the number of track data sampling points, and m is the number of the collected directions. For a 3D-UTE sequence, kx, ky and kz can be estimated as long as m is more than or equal to 3, and then a complete k-space track can be synthesized through a certain interpolation algorithm. Most simply, when the read gradient is selected to coincide with the three physical axes X, Y, Z respectively 1 When H signal collects track data, formula (6) is unit matrix, and measured track kr 1 、kr 2 、kr 3 Corresponding to kx, ky, kz, respectively. When m is>3 hours, the number of measurements can be increasedAccording to the accuracy, the method can obtain the following results by using a least square method:
since only k-space trajectories in several directions need to be measured, and for 23 In the case of Na, the sodium hydroxide is, 1 the gradient applied during the H rf pulse corresponds to a spoiling gradient and can be combined with the spoiling gradient of the own UTE sequence, which is typically only a few milliseconds, so this approach hardly extends the scan time. In addition, since the gradient waveform of the trajectory measurement is the gradient used for actually acquiring k-space data, the method can also avoid the influence of insufficient stability of the gradient system.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (10)
1. A k-space trajectory correction system applied to heteronuclear imaging is characterized by comprising a sampling sequence and signal processing system, a spectrometer control system and a magnet and radio frequency system, wherein the sampling sequence and signal processing system is connected with the spectrometer control system, and the spectrometer control system is connected with the magnet and the radio frequency system through an amplifier and an auxiliary control part.
2. The k-space trajectory correction system for heteronuclear imaging of claim 1, wherein the amplifier comprises a heteronuclear RF amplifier, 1 An H nuclear species RF amplifier, 1 An H-species RF preamplifier, a heteronuclear RF preamplifier, and a gradient amplifier.
3. The k-space trajectory correction system for use in heteronuclear imaging of claim 1, wherein the sampling sequence and signal processing system comprises a sampling sequence and image processing module and a host system.
4. The k-space trajectory correction system for use in heteronuclear imaging as defined in claim 1, wherein the magnet and radio frequency system employs a radio frequency transmit receive integrated coil.
5. The system of claim 1, wherein the spectrometer control system comprises a broadband multi-kernel signal excitation control system, a receiver, a gradient and radio frequency power system, and a gradient control and system master control module.
6. A k-space trajectory correction method for use in heteronuclear imaging, using the system of any of claims 1-5, comprising a new pulse sequence unit and corresponding data processing, characterized by:
step 1. Before the heteronuclear imaging sequence unit, in 1 Applying a layer selection excitation unit to the H channel;
step 2, in the heteronuclear imaging sequence unit, firstly, the radio frequency pulse is emitted in the heteronuclear channel to excite the heteronuclear to generate signals, and then in the signal receiving stage, the signals are respectively enabled 1 Receive chain of H/miscellaneous core channel, acquisition 1 H/heteronuclear signal; the acquired heteronuclear signal is the heteronuclear signalk-space data; collected to obtain 1 The H signal is processed to generate measured k space trajectory data;
and 3, reconstructing a k space formed by the heteronuclear signals by using the k space track data to obtain a track corrected heteronuclear image.
7. The method of claim 6, wherein the k-space trajectory correction method is applied to heteronuclear imaging 1 A layer-selective excitation unit on the H channel, comprising 1 H selective excitation pulse and corresponding slice selection gradient selectively excite an off-center layer.
8. The method of claim 6, wherein the k-space trajectory correction method is applied to heteronuclear imaging 1 The gradient direction of the selection layer in the selection layer excitation unit on the H channel is the same as the readout gradient direction in the heteronuclear imaging sequence unit.
9. The method of claim 6, wherein k-space trajectory data in a plurality of readout gradient directions are selectively measured, and then a complete k-space trajectory is obtained by least squares and data interpolation.
10. The method of k-space trajectory correction for use in heteronuclear imaging as defined in claim 6 wherein, in the signal reception phase, if a dephasing gradient precedes the read gradients in the units of the heteronuclear imaging sequence, 1 h channel data needs to be collected when dephasing gradient begins to be applied; in the phase of acquisition of the heteronuclear signals, 1 the H/heteronuclear signals need to be acquired synchronously.
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| CN116930836B (en) * | 2023-09-18 | 2023-11-24 | 哈尔滨医科大学 | Multi-core synchronous integrated imaging optimal pulse power measuring method and system |
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