Magnetic resonance oxygen metabolism imaging method and device based on adiabatic T2 preparation

Abstract

The invention discloses a rapid magnetic resonance oxygen metabolism imaging method and equipment based on adiabatic T2 preparation. The method comprises the following steps: firstly, utilizing a global saturation module to zero a magnetization vector; secondly, inhibiting a static tissue signal and an artery blood signal at the initial position of the sequence by using a background inhibition module and an artery inhibition module; then adding a heat insulation T2 preparation module to realize T2 weighted regulation and control on the spin signal; then, a speed selection module based on Fourier transform is used for extracting a vein blood flow signal, and signal collection is conducted on a K space through plane echo imaging; and finally, fitting the signals under different effective echo times to obtain a vein blood T2 value, obtaining a vein oxygen saturation value by using a calibration model, and further calculating an oxygen uptake fraction and an oxygen metabolism rate. According to the method, the T2 value of the vein blood is stably measured under the condition of a non-uniform magnetic field, so that the robustness of oxygen metabolism imaging is improved, and clinical transformation of magnetic resonance oxygen metabolism imaging is facilitated.

Description

Technical Field

[0001] This application relates to the field of magnetic resonance technology, and more particularly to the field of magnetic resonance oxygen metabolism imaging. Background Technology

[0002] Magnetic resonance oxygen metabolism imaging (MRI) is an important MRI technique that utilizes the T2 dependence of venous blood on oxygen saturation to non-invasively detect the oxygen uptake fraction and metabolic rate of living organs. Therefore, MRI provides crucial information for the diagnosis and treatment assessment of various diseases, such as neurodegenerative diseases and chronic kidney disease. However, MRI relies on a T2 preparation module, which is highly sensitive to magnetic field inhomogeneities, particularly in regions like the abdomen where effective T2 preparation is difficult, leading to significant measurement errors. Therefore, some researchers have proposed using adiabatic pulses instead of traditional square pulses for T2 preparation, thereby greatly reducing the module's sensitivity to magnetic field inhomogeneities. However, existing methods are primarily used for T2 measurements of static signals such as tissues and are not suitable for flowing blood signals, such as those in the renal vein. The adiabatic T2 preparation module (BIR-n) designed in this invention can perform stable T2 preparation of flowing blood without interference from magnetic field inhomogeneity. The Fourier transform-based velocity selection module (FT-VS) can extract the flowing blood signal from the static tissue background. Combined with the echo planar imaging (EPI) rapid acquisition module and the post-saturation module, accurate oxygen metabolism measurement can be achieved. Summary of the Invention

[0003] The purpose of this invention is to provide a magnetic resonance oxygen metabolism imaging method and device based on adiabatic T2 preparation. It is a field-insensitive T2 relaxation-under-field-insensitive-preparation-and-Fast-Acquisition (TRUFIFA) method, which can realize accurate measurement of T2 of flowing venous blood under non-uniform magnetic resonance main magnetic field (B0 field) and radio frequency field (B1 field), thereby improving the stability of oxygen metabolism imaging.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] In a first aspect, the present invention provides a magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation, which includes the following steps:

[0006] S1: At the start of the acquisition, a global saturation module is added to the imaging target to stabilize the signal acquisition;

[0007] S2: After the global saturation module, the imaging sequence is applied to the imaging target repeatedly in multiple rounds. In the imaging sequence, a background suppression module is first applied to eliminate static tissue signals to suppress interference from adjacent tissues; then an arterial suppression module is applied to eliminate arterial blood flow signals to suppress the influence of adjacent arteries; after waiting for the recovery time, an adiabatic T2 preparation module (BIR-n) consisting of a reverse adiabatic half-channel pulse (rAHP), multiple adiabatic fast channel pulses (AFP), and a third adiabatic half-channel pulse (AHP) is applied to achieve T2 weighted modulation of the spin signal; then a series of excitation pulses and phase cyclic refocusing pulses are applied. A Fourier transform-based velocity selection (FT-VS) module, consisting of velocity coding lobes with alternating polarities, is used to separate blood spin signals from static tissue. Then, an echo-planar imaging (EPI) module is used to acquire signals in K-space. Finally, after K-space signal acquisition, a post-saturation module is applied to destroy residual transverse magnetization vectors, preventing interference with subsequent acquisitions. A recovery time (RT) is then allowed for the longitudinal magnetization vectors to recover before the next round of repeated acquisitions. During the repeated imaging sequence, the effective echo time corresponding to the adiabatic T2 preparation module applied in different rounds varies.

[0008] S3: Reconstruct the K-space signal acquired during each round of imaging sequence application to obtain the image signal, and obtain the T2 value of venous blood by model fitting based on the image signal under different effective echo times;

[0009] S4: Use the calibration model to convert the obtained venous blood T2 value into venous oxygen saturation value, and calculate the oxygen uptake fraction and oxygen metabolism rate based on the venous oxygen saturation value.

[0010] As a preferred embodiment of the first aspect above, the process executed in the global saturation module is as follows:

[0011] Repeatedly apply saturated radio frequency pulses, and simultaneously apply a dephasing gradient along the X, Y, or Z direction to completely eliminate the residual transverse magnetization vector.

[0012] As a preferred embodiment of the first aspect above, the process executed in the background suppression module is as follows:

[0013] Two 180° refocusing pulses are applied, and gradients are applied synchronously in the slice selection direction to suppress static tissue signals that may interfere with the imaging signal.

[0014] As a preferred embodiment of the first aspect mentioned above, the process executed in the arterial inhibition module is as follows:

[0015] A series of 90° saturated radio frequency pulses are applied, and a gradient is applied synchronously in the slice-selected direction to suppress high-speed arterial blood signals; at the same time, after each 90° saturated radio frequency pulse is applied, a dephasing gradient is applied in the slice-selected direction to eliminate any residual transverse magnetization caused by incomplete saturation.

[0016] As a preferred embodiment of the first aspect above, the process executed in the insulation T2 preparation module is as follows:

[0017] First, a reverse adiabatic half-channel pulse (rAHP) is used to flip the blood spin signal to the XY plane. Second, n adiabatic fast channel pulses (AFP) are applied at preset pulse intervals to flip the venous blood spin n times by 180°, where n is an odd number in the range of 1 to 15. The number of adiabatic fast channel pulses n and the pulse interval need to be adjusted to meet the effective echo time (eTE) of the current cycle. Next, an adiabatic half-channel pulse (AHP) is used to flip the blood spin signal back to the direction of the main magnetic field. Finally, after the adiabatic half-channel pulse (AHP) is completed, a dephasing gradient is applied in the X, Y, and Z directions.

[0018] As a preferred embodiment of the first aspect above, the process executed in the Fourier transform-based speed selection (FT-VS) module is as follows:

[0019] First, a series of 10° excitation pulses are applied, and a pair of 180° refocusing pulses are applied between every two adjacent 10° excitation pulses. At the same time, a pair of coded gradient lobes of opposite polarity are applied along the slice selection direction before and after each 180° refocusing pulse, and all 180° refocusing pulses need to adopt a phase cyclic scheme. Then, after the last 10° excitation pulse is applied, a dephasing gradient is applied in the slice selection direction to eliminate transverse magnetization.

[0020] As a preferred embodiment of the first aspect above, the process executed in the planar echo imaging (EPI) module is as follows:

[0021] First, a single 90° excitation pulse and the corresponding layer selection gradient are applied synchronously. Then, a pre-gradient is applied in the phase coding and frequency coding directions, and a phase-gathering gradient is applied in the layer selection direction. After that, a series of alternating gradients are applied in the frequency coding direction, and a phase coding gradient is inserted each time the polarity of the frequency coding gradient changes.

[0022] As a preferred embodiment of the first aspect above, the process executed in the post-saturation module is as follows:

[0023] First, a 90° saturated RF pulse is applied, followed by a dephase gradient in the X and Z directions; then, a 90° saturated RF pulse is applied, followed by a dephase gradient in the Y and Z directions; finally, a 90° saturated RF pulse is applied, followed by a dephase gradient in all three directions (X, Y, and Z) to completely eliminate the residual transverse magnetization vector.

[0024] As a preferred embodiment of the first aspect, in the Fourier transform-based velocity selection (FT-VS) module, there are a total of 9 10° excitation pulses, among which the 16 inserted 180° refocusing RF pulses adopt the MLEV-16 phase cycle scheme, with the phases sequentially being 0°-0°-180°-180°-180°-0°-0°-180°-180°-0°-0°-0°-180°-180°-0°. The encoded gradient lobes applied before and after each 180° refocusing pulse are two triangular gradient pulses with opposite polarities.

[0025] As a preferred embodiment of the first aspect above, the method for obtaining the T2 value of venous blood based on image signal fitting through a model is as follows:

[0026] First, based on the effective echo time eTE used by the adiabatic T2 preparation module in each repeated application of the imaging sequence in S2, the signal M corresponding to the effective echo time is obtained through Bloch equation simulation under a fixed transverse relaxation time T2. z Then, the actual effective echo time eTE corresponding to this effective echo time is calculated. act = -ln(Mz)×T2;

[0027] Then, using the effective echo time eTE of each round and the venous blood signal M acquired in the current round... acq The actual effective echo time (eTE) corresponding to the current round act Venous blood signal M obtained from saturated TR acquisition sat To fit the samples, the model By fitting the data, the actual T2 value of venous blood is obtained.

[0028] As a preferred embodiment of the first aspect above, the formula for the calibration model is: Where T2 is the fitted venous blood T2 value, Y is the venous oxygen saturation value, A1, A2, A3, and A4 are calibration parameters, and Hct is the hematocrit.

[0029] In a second aspect, the present invention provides a computer program product, including a computer program / instruction, which, when executed by a processor, can control an external magnetic resonance scanner to realize the magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in any of the first aspects above.

[0030] Thirdly, the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, can control an external magnetic resonance scanner to realize the magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in any of the first aspects above.

[0031] Fourthly, the present invention provides a computer electronic device, which includes a memory and a processor;

[0032] The memory is used to store computer programs;

[0033] The processor, when executing the computer program, is configured to control an external magnetic resonance scanner to implement the magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in any of the first aspects above.

[0034] Fifthly, the present invention provides a magnetic resonance imaging device, which includes a magnetic resonance scanner and a control unit. The control unit stores a computer program. When the computer program is executed, it can control the magnetic resonance scanner to perform magnetic resonance oxygen metabolism imaging based on adiabatic T2 preparation according to any one of the first aspects above, by executing an imaging sequence to acquire K-space signals and by processing the signal data to obtain venous oxygen saturation value, oxygen uptake fraction and oxygen metabolism rate.

[0035] Compared to existing technologies, this invention offers the following advantages: It proposes an adiabatic T2 preparation module that is insensitive to inhomogeneities in the main magnetic field and radio frequency field, thus providing stable T2-weighted modulation. Furthermore, it is the first to combine this adiabatic T2 preparation module with a rapid acquisition module (EPI), which offers advantages such as rapid imaging, insensitivity to motion, and significantly reduced imaging time. This method improves the performance of magnetic resonance oxygen metabolism imaging and enhances the reliability of quantitative analysis of oxygen metabolism imaging signals, making this invention highly valuable for clinical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a block diagram of an oxygen metabolism imaging sequence based on an adiabatic T2 preparation module.

[0037] Figure 2 The results are a comparison of simulation experiments using magnetic resonance oxygen metabolism imaging sequences based on an adiabatic T2 preparation module and magnetic resonance oxygen metabolism imaging sequences based on a T2 preparation module of the traditional MLEV method.

[0038] Figure 3The results of scanning water films are compared between magnetic resonance oxygen metabolism imaging sequences based on an adiabatic T2 preparation module and magnetic resonance oxygen metabolism imaging sequences based on a T2 preparation module of the traditional MLEV method.

[0039] Figure 4 This is a schematic diagram, result diagram, and fitting curve of measuring renal oxygen metabolism function using a magnetic resonance oxygen metabolism imaging sequence based on an adiabatic T2 preparation module.

[0040] Figure 5 This is a comparison of the results of human scans using magnetic resonance oxygen metabolism imaging sequences based on an adiabatic T2 preparation module and magnetic resonance oxygen metabolism imaging sequences based on a T2 preparation module using the traditional MLEV method. Detailed Implementation

[0041] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in the various embodiments of the present invention can be combined accordingly without mutual conflict.

[0042] In a preferred embodiment of the present invention, an oxygen metabolism imaging method based on an adiabatic T2 preparation module is provided, wherein the magnetic resonance imaging sequence used is as follows: Figure 1 As shown, it includes a background suppression module, an artery suppression module, an adiabatic T2 preparation module, a Fourier transform-based velocity selection (FT-VS) module, an echo-planar imaging (EPI) module, and a post-saturation module. The specific execution method of this sequence and the signal data processing procedure are described in detail below, including the following steps:

[0043] Step 1: At the start of the acquisition, apply a global saturation pulse module to the imaging target to make the magnetization vector start from zero, so as to stabilize the signal acquisition.

[0044] In an embodiment of the present invention, the process executed in the global saturation pulse module is as follows:

[0045] The combination of radio frequency (RF) pulses and gradients is applied three times repeatedly. After each application of a 90-degree saturation RF pulse, a dephasing gradient is applied in the X, Y, or Z direction to eliminate the residual lateral magnetization vector. After applying the three RF pulse and gradient combinations, a waiting period is allowed before applying the same combination three more times to ensure complete elimination of the lateral magnetization vector. A recovery time (RT) is then allowed for the longitudinal magnetization vector to recover. Subsequently, multiple rounds of this process can be repeated on the imaging target after the global saturation module. Figure 1 The imaging sequence is shown below. The specific method for applying the imaging sequence is explained in conjunction with subsequent steps.

[0046] Step 2: Apply a background suppression module at the beginning of the imaging sequence to suppress static tissue signals and thus suppress interference from adjacent tissues.

[0047] In an embodiment of the present invention, the process executed in the background suppression module is as follows:

[0048] Two 180° refocusing pulses are applied, and gradients are simultaneously applied in the corresponding slice direction (i.e., the Z direction) to suppress static tissue signals that may interfere with the imaging signal, ensuring that the static tissue signal is restored to less than 5% before acquisition.

[0049] Step 3: Apply the arterial suppression module after the background suppression module to suppress the influence of adjacent arteries.

[0050] In an embodiment of the present invention, the arterial inhibition module is implemented as follows:

[0051] At the start of the module, a series of consecutive 90° saturated radio frequency pulses are applied (the number of pulses is adjustable; in this embodiment, 40 90° saturated radio frequency pulses are set). Simultaneously with each application of a 90° saturated radio frequency pulse, a layer selection gradient is applied in the layer selection direction (i.e., the Z direction) to suppress high-speed arterial blood signals. In addition, after each application of a 90° saturated radio frequency pulse, a dephasing gradient is applied in the layer selection direction (i.e., the Z direction) to eliminate the residual transverse magnetization vector caused by incomplete saturation, thereby suppressing high-speed arterial blood signals. However, slower-flowing venous blood signals will not be suppressed.

[0052] Step 4: After the arterial inhibition module, apply an adiabatic T2 preparation module (BIR-n) consisting of a reverse adiabatic half-channel pulse (rAHP), multiple adiabatic fast channel pulses (AFP), and a second adiabatic half-channel pulse (AHP) in sequence to achieve T2 weighted modulation of the spin signal.

[0053] In an embodiment of the present invention, the process executed in the insulation T2 preparation module is as follows:

[0054] First, the blood spin signal is flipped to the XY plane using a reverse adiabatic half-channel pulse (rAHP) with a flip angle of 90°. Specifically, the pulse is first applied in the +X axis direction and then swept to the +Z axis direction at a specific frequency (0-5000Hz), thereby flipping the blood spin signal to the XY plane.

[0055] Secondly, n adiabatic fast channel pulses (AFP) are applied according to a preset pulse time interval τ to perform n 180° rotations on the venous blood spin. n is an odd number in the range of 1 to 15, and the number of adiabatic fast channel pulses n and the pulse time interval τ need to be adjusted to meet the effective echo time (eTE) of the current cycle. In this embodiment, the second or third segment in the middle of the four-segment B1-Insensitive Rotation 4 (BIR4) is used as the adiabatic fast channel pulse (AFP). This pulse is first applied in the -Z axis direction, then swept to the -Y axis direction at a specific frequency (0-5000Hz), and then swept from the +X axis to the +Z axis direction, thereby achieving a 180-degree rotation of the venous blood spin.

[0056] Next, an adiabatic half-channel pulse (AHP) with a 90° flip angle is used to flip the blood spin signal back to the direction of the main magnetic field. This AHP pulse is first applied in the -Z axis direction and then swept to the -Y axis direction at a specific frequency (0-5000Hz), thereby flipping the blood spin signal back to the direction of the main magnetic field (Z direction).

[0057] Finally, a divergent gradient is applied simultaneously in the X, Y, and Z directions to complete the execution of the adiabatic T2 preparation module.

[0058] It is important to note that the specific value of the odd number n needs to be determined based on the currently determined effective echo time eTE. The effective echo time eTE is related to n and the pulse time interval τ, and the relationship is eTE = τ * (n + 1) / 2. This adiabatic T2 preparation module generates different effective echo times eTE by adjusting the number of AFP pulses n and the pulse time interval τ, thereby achieving T2 modulation of the blood spin signal. Based on the prior condition that the T2 of venous blood in vivo is approximately in the range of 40-120 ms, it can be determined that the T2 preparation module needs to apply an effective echo time eTE from 0 ms to not less than 160 ms to achieve better T2 weighted modulation. Considering the rate of decrease of the spin signal with T2 relaxation and the limitations of magnetic resonance radio frequency hardware, in this embodiment of the invention, the AFP pulse interval is preferably set to 20 ms. Therefore, an odd number of AFP pulses in the range of 1 to 15 will be set in different repetition times (TR). Each time the adiabatic T2 preparation module is executed, the effective echo time eTE needs to be changed by adjusting the number of AFP pulses n, so as to facilitate subsequent fitting.

[0059] Step 5: After the adiabatic T2 preparation module, apply the Fourier transform-based velocity selection (FT-VS) module, which consists of a series of small-angle excitation pulses, phase cyclic refocusing pulses, and velocity coding lobes with alternating polarities, to separate the blood spin signal from the static tissue.

[0060] In an embodiment of the present invention, the process executed in the Fourier transform-based velocity selection (FT-VS) module is as follows:

[0061] Nine 10° excitation pulses are applied sequentially, and a pair of 180° refocusing RF pulses (a total of 16) are inserted between all adjacent 10° excitation pulses. Both the 10° excitation pulses and the 180° refocusing RF pulses are hard pulses, and all 16 180° refocusing RF pulses adopt the MLEV-16 phase cycle scheme, with the phases being 0°-0°-180°-180°-180°-0°-0°-180°-180°-0°-0°-0°-180°-180°-0°-0°-180°-180°-0°. After the last 10° excitation pulse is applied, a destructive gradient is applied to suppress residual transverse magnetization. Finally, a recovery time is waited for all magnetizations to return to longitudinal direction.

[0062] In addition, while applying the gradient pulse sequence, a pair of coded gradient lobes of opposite polarity need to be applied before and after each 180° refocusing RF pulse along a specified direction. In embodiments of the present invention, the pair of coded gradient lobes of opposite polarity can be implemented using two triangular gradient pulses of opposite polarity. Of course, in other embodiments, the coded gradient lobes can also be in the form of pulses other than triangular gradient pulses, as long as gradient coding can be achieved.

[0063] Step 6: After preparing the adiabatic T2 module, use the planar echo imaging (EPI) module to acquire signals in the K space.

[0064] In embodiments of the present invention, the process executed in the planar echo imaging (EPI) module is as follows:

[0065] First, a single 90° excitation pulse and the corresponding layer selection gradient are applied synchronously. Then, a pre-gradient is applied in the phase coding and frequency coding directions, and a rephase gradient is applied in the layer selection direction. After that, a series of alternating gradients are applied in the frequency coding direction, and a small phase coding gradient is inserted each time the polarity of the frequency coding gradient changes.

[0066] Step 7: After the planar echo imaging (EPI) module completes signal acquisition, apply the post-saturation module to destroy the residual transverse magnetization vector and avoid its interference with subsequent repetition time (TR) acquisition.

[0067] In embodiments of the present invention, the process executed in the post-saturation module is as follows:

[0068] First, apply a 90° saturated RF pulse, then apply a dephase gradient in the X and Z directions; then apply another 90° saturated RF pulse, and apply a dephase gradient in the Y and Z directions; finally, apply a 90° saturated RF pulse, and apply a dephase gradient in all three directions (X, Y, and Z) to completely eliminate the residual transverse magnetization vector.

[0069] Step 8: Performing steps 2 through 7 once is considered as performing one cycle. Figure 1The imaging sequence shown acquired the corresponding K-space signal. Steps two through seven were repeated multiple times, with a different effective echo time (eTE) required for each iteration of the adiabatic T2 preparation module in step four. As mentioned earlier, the effective echo time (eTE) can be changed by fixing the AFP pulse interval τ to 20ms and selecting different values ​​of n within the range of 1 to 15. In this embodiment of the invention, considering the limitation of scan duration, a preferred implementation is to repeat the imaging sequence 5 to 6 times. If repeated 5 times, n in the adiabatic T2 preparation module is set to 1, 3, 5, 7, 11 sequentially during the 5 iterations; if repeated 6 times, n in the adiabatic T2 preparation module is set to 1, 3, 5, 7, 11, 15 sequentially during the 6 iterations. Thus, each execution of the imaging sequence yields the K-space signal at the corresponding effective echo time (eTE) for n. This signal data can be used for subsequent data processing to extract venous oxygen saturation, oxygen uptake fraction, and oxygen metabolism rate. The specific signal data processing procedure is described in detail below.

[0070] Step 9: Reconstruct the K-space signals acquired under different effective echo times (eTE) using GRAPPA to obtain image signals, delineate the region of interest (ROI) of the target vein, obtain the vein signals under different effective echo times (eTE) by averaging the signal values ​​within the ROI, and obtain the T2 value of the vein blood by model fitting.

[0071] In an embodiment of the present invention, the specific method for obtaining the T2 value of venous blood through model fitting is as follows:

[0072] The actual effective echo time (eTE) of the T2 preparation module act It is affected by the longitudinal relaxation during the pulse application time, which is different from the set effective echo time eTE.

[0073] First, based on the effective echo time eTE used by the adiabatic T2 preparation module in each repeated application of the imaging sequence in S2, the signal M corresponding to the effective echo time is obtained through Bloch equation simulation under a fixed transverse relaxation time T2. z Then, the actual effective echo time eTE corresponding to this effective echo time is calculated. act Specifically, assuming the imaging sequence is repeated m times, the value of n in the adiabatic T2 preparation module is set sequentially to n1, n2, ..., n during the m executions. m Therefore, for each value of n, an AFP pulse train needs to be designed according to the fixed AFP pulse interval τ and the number of AFP pulses n used in the actual acquisition in step eight above. Then, the Bloch equation is used to simulate and obtain the signal M of a specific T2 spin signal under this AFP pulse train. zThe actual effective echo time eTE corresponding to the effective echo time eTE of the AFP pulse train is calculated using the following formula. act :

[0074] eTE act =-ln(M z )×T2

[0075] Next, the effective echo time eTE corresponding to each round of the imaging sequence and the venous blood signal M acquired in the current round are used as the basis for the calculation. acq The actual effective echo time (eTE) corresponding to the current round act Venous blood signal M obtained from saturated TR acquisition sat To fit the sample, the following model was fitted to obtain the actual T2 values ​​of venous blood:

[0076]

[0077] It should be noted that the above single fitted sample includes eTE and M. acq eTE act and M sat eTE and M acq eTE act Each needs to correspond to a fixed n. For example, suppose the imaging sequence is repeated m times, and the value of n in the adiabatic T2 preparation module is set to n1, n2, ..., n in the m times of execution. m Therefore, for n1, the actual effective echo time eTE needs to be obtained through simulation using the aforementioned Bloch equations. act Meanwhile, n1 itself has a corresponding effective echo time eTE, which acquires the corresponding venous blood signal M when executing the imaging sequence with n1 AFP pulses in the adiabatic T2 preparation module. scq Combined with the venous blood signal M obtained from the saturated TR acquisition which can be additionally measured, sat This allows us to construct the fitted sample corresponding to n1. For the other n2, ..., n... m Similarly, corresponding fitting samples can be constructed. All fitting samples can be used to fit the A and T2 values ​​in the aforementioned model, and the fitted T2 value can be used as the actual T2 value of venous blood.

[0078] Step 10: Convert the obtained venous blood T2 values ​​into venous oxygen saturation values ​​using a calibration model, and further calculate the oxygen uptake fraction and oxygen metabolism rate. Specifically, calculate the venous oxygen saturation Y based on the fitted T2 values, using the following formula:

[0079]

[0080] The calibration parameters A1, A2, A3, and A4 can be obtained through in vitro calibration experiments. In this embodiment, the calibration parameters used are A1 = 77.5, A2 = 27.8, A3 = 6.95, and A4 = -2.34. Hct is the hematocrit, which can be measured using a complete blood count.

[0081] Furthermore, the oxygen extraction fraction (OEF) can be calculated using the following formula:

[0082]

[0083] Among them, Y a This refers to arterial oxygen saturation.

[0084] Furthermore, the metabolic rate of oxygen (MRO2) can be calculated using the following formula:

[0085] MRO2=(Y a -Y)×BF×C h

[0086] Where BF is blood flow and C is blood flow. h This represents the number of moles of oxygen that a unit volume of blood can carry.

[0087] The technical effects of the above method, based on steps one through ten, are demonstrated below in conjunction with embodiments, so that those skilled in the art can better understand the essence of the present invention.

[0088] Example

[0089] In this embodiment, the specific magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation is described in steps one to ten above, and will not be repeated here. The main focus is on showing the specific implementation details and technical effects.

[0090] In the examples described below, all scans were performed using a Siemens Prisma 3.0T scanner.

[0091] Experiment 1, to compare the sensitivity of the adiabatic T2 preparation module BIR-n and the traditional MLEV method's T2 preparation module to magnetic field inhomogeneity, we designed the following simulation experiment: Setting the T2 of venous blood to 100 ms, we performed adiabatic T2 preparation or traditional MLEV T2 preparation under different main magnetic field inhomogeneities (off-resonance) and different radio frequency field inhomogeneities (B1 scale). We obtained the corresponding magnetization vector signal through Bloch simulation and then performed T2 fitting on this signal. For example... Figure 2As shown, the T2 value obtained by fitting under adiabatic T2 preparation differs little from the set value, while the T2 value obtained by fitting under traditional MLEV preparation is significantly higher or lower when the magnetic field is non-uniform. Therefore, adiabatic T2 preparation can effectively suppress the T2 measurement error caused by magnetic field non-uniformity.

[0092] Experiment 2, to compare the actual measurement results of the adiabatic T2 preparation module BIR-n and the traditional MLEV method T2 preparation module under magnetic field inhomogeneity conditions, we designed the following water film experiment: A 64-channel head coil was used to measure the adiabatic T2 preparation sequence and the MLEV T2 preparation sequence of a water film containing a colloidal tube with 9 different T2 values. The adiabatic T2 preparation sequence used 1, 3, 5, and 7 AFP pulses with a pulse interval of 20 ms, achieving eTE values ​​of 36.75, 73.55, 110.53, and 147.75 ms; the MLEV T2 preparation module used eTE values ​​of 0, 40, 80, and 160 ms. The main magnetic field B0 offset was manually adjusted to -200, -100, 0, 100, and 200 Hz, and the radio frequency field B1 offset ratio was 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, and 1.3 times. Other scanning parameters included FOV = 200*200 mm. 2 Layer thickness = 5mm, matrix = 64*64, TE / TR = 8.5ms / 4000ms, bandwidth = 3126Hz, GRAPPA = 2, repetition count = 3, scan duration = 57s. Figure 3 As shown, under different magnetic field offset conditions, the T2 measurement error obtained by adiabatic T2 preparation is less than 12%, while the T2 measurement error obtained by MLEV T2 preparation is as high as 60%. This water film experiment proves that adiabatic T2 preparation can effectively suppress the T2 measurement error caused by magnetic field inhomogeneity.

[0093] Experiment 3, to compare the actual measurement results of the adiabatic T2 preparation module BIR-n and the traditional MLEV method T2 preparation module under magnetic field inhomogeneity conditions, we designed the following human experiment: Renal vein oxygen metabolism measurements were performed on 10 healthy subjects (aged 26.0±8.4 years, 7 males, 3 females) using an 18-channel abdominal coil, employing both the adiabatic T2 preparation sequence and the MLEV T2 preparation sequence. Bidirectional tilting was used for scanning positioning to ensure the imaging plane was perpendicular to the renal vein (e.g., ...). Figure 4 (As shown) The adiabatic T2 preparation sequence uses 1, 3, 5, and 7 AFP pulses with a pulse interval of 20 ms, achieving eTE values ​​of 36.75, 73.55, 110.53, and 147.75 ms, respectively; the MLEV T2 preparation module uses eTE values ​​of 0, 40, 80, and 160 ms. Other scan parameters include FOV = 200*200 mm. 2Layer thickness = 5mm, matrix = 64*64, TE / TR = 8.5ms / 4000ms, bandwidth = 3126Hz, GRAPPA = 2, number of repetitions = 25, scan duration = 6min. Figure 5 The scan images and measured T2 values ​​under different T2 preparation modules are shown. We can see that, due to the sensitivity of the MLEV T2 preparation module to magnetic field inhomogeneity, the measured T2 values ​​are higher and more dispersed, while the T2 values ​​measured by the adiabatic T2 preparation module are concentrated and evenly distributed, reflecting better inter-subject differences and having good repeatability.

[0094] Therefore, compared with the traditional oxygen metabolism imaging technology based on the MLEV T2 preparation module, the oxygen metabolism imaging method based on adiabatic T2 preparation of the present invention effectively improves the measurement stability under magnetic field inhomogeneity, which is conducive to the clinical translation of magnetic resonance oxygen metabolism imaging technology.

[0095] It should be noted that the method steps shown in S1 to S4 of the above-described invention, as well as steps one to ten of the preferred implementation, mainly describe the generation of control signals corresponding to the imaging sequence and the processing of the acquired data. Essentially, these can be implemented as computer programs or software functional modules. Of course, the execution of the imaging sequence requires software program control of an external magnetic resonance imaging device, which is prior art and will not be elaborated further.

[0096] Therefore, based on the same inventive concept, the present invention also provides a computer electronic device corresponding to the magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation provided in the above embodiments, which includes a memory and a processor.

[0097] The memory is used to store computer programs;

[0098] The processor, when executing the computer program, is configured to control an external magnetic resonance scanner to implement the blood-brain barrier water extraction rate imaging method based on arterial labeling and velocity selection as described above.

[0099] Furthermore, the logical instructions in the aforementioned memory can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention.

[0100] Therefore, based on the same inventive concept, this invention provides a computer-readable storage medium corresponding to a magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation. The storage medium stores a computer program, which, when executed by a processor, can control an external magnetic resonance scanner to realize the blood-brain barrier water extraction rate imaging method based on arterial labeling and velocity selection as described above.

[0101] Therefore, based on the same inventive concept, the present invention provides a computer program product, including a computer program / instruction, which, when executed by a processor, can control an external magnetic resonance scanner to realize the blood-brain barrier water extraction rate imaging method based on arterial labeling and velocity selection as described above.

[0102] It is understood that the aforementioned storage media may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Furthermore, the storage media may also be various media capable of storing program code, such as USB flash drives, external hard drives, magnetic disks, or optical discs.

[0103] It is understood that the processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0104] It should also be noted that those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process of the system described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here. In the embodiments provided in this application, the division of steps or modules in the system and method is merely a logical functional division, and there may be other division methods in actual implementation. For example, multiple modules or steps may be combined or integrated together, and a module or step may also be split.

[0105] Based on the above-described adiabatic T2-prepared oxygen metabolism imaging method, in other embodiments, a magnetic resonance imaging device may be further provided, which includes a magnetic resonance scanner and a control unit. The control unit stores a computer program. When the computer program is executed, it can control the magnetic resonance scanner to perform the magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in any one of claims 1 to 6, by executing an imaging sequence to acquire K-space signals and by processing the signal data to obtain venous oxygen saturation value, oxygen uptake fraction, and oxygen metabolism rate.

[0106] It should be noted that the hardware structure of the magnetic resonance scanner and control unit here can be implemented using a conventional magnetic resonance imaging system. The magnetic resonance scanner should include a magnet part and a magnetic resonance spectrometer part, and the control unit should contain the data processing and image reconstruction software necessary for imaging. The computer program corresponding to the oxygen metabolism imaging method based on adiabatic T2 preparation can be read by the control unit and used to control the magnetic resonance scanner. In other words, the oxygen metabolism imaging method sequence based on adiabatic T2 preparation of the present invention can be directly applied to the corresponding magnetic resonance imaging equipment.

[0107] It should be noted that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A magnetic resonance imaging method for oxygen metabolism based on adiabatic T2 preparation, characterized in that, Includes the following steps: S1: At the start of the acquisition, a global saturation module is added to the imaging target to stabilize the signal acquisition; S2: After the global saturation module, the imaging sequence is applied to the imaging target repeatedly in multiple rounds; in the imaging sequence, the background suppression module is first applied to eliminate static tissue signals to suppress interference from adjacent tissues; the arterial suppression module is then applied to eliminate arterial blood flow signals to suppress the influence of adjacent arteries. After waiting for the recovery time, an adiabatic T2 preparation module consisting of a reverse adiabatic half-channel pulse, multiple adiabatic fast channel pulses, and an adiabatic half-channel pulse in sequence is applied to achieve T2 weighted modulation of the spin signal; then a velocity selection module based on Fourier transform, consisting of a series of excitation pulses, phase cyclic refocusing pulses, and velocity coding lobes with alternating polarities, is applied to separate the blood spin signal from the static tissue. Then, the planar echo imaging module is used to acquire signals in the K space. Finally, after the K space signal acquisition is completed, the post-saturation module is applied to destroy the residual transverse magnetization vector to avoid its interference with subsequent acquisitions. After waiting for a recovery time, the longitudinal magnetization vector is restored before the next round of repeated acquisitions is performed. During the repeated application of the imaging sequence, the effective echo time corresponding to the adiabatic T2 preparation module applied in different rounds is different. S3: Reconstruct the K-space signal acquired during each round of imaging sequence application to obtain the image signal, and obtain the T2 value of venous blood by model fitting based on the image signal under different effective echo times; S4: Use the calibration model to convert the obtained venous blood T2 value into venous oxygen saturation value, and calculate the oxygen uptake fraction and oxygen metabolism rate based on the venous oxygen saturation value.

2. The magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in claim 1, characterized in that, The process executed in the global saturation module is as follows: Repeatedly apply saturated radio frequency pulses, and simultaneously apply a dephasing gradient along the X, Y, or Z direction to completely eliminate the residual transverse magnetization vector.

3. The magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in claim 1, characterized in that, The preferred execution flow for one or more modules in the imaging sequence is as follows: Preferably, the process executed in the background suppression module is as follows: Two 180° refocusing pulses are applied, and gradients are applied synchronously in the slice selection direction to suppress static tissue signals that may interfere with the imaging signal. Preferably, the process executed in the arterial inhibition module is as follows: A series of 90° saturated radio frequency pulses are applied, and a gradient is applied synchronously in the slice-selected direction to suppress high-speed arterial blood signals; at the same time, after each 90° saturated radio frequency pulse is applied, a dephasing gradient is applied in the slice-selected direction to eliminate any residual transverse magnetization caused by incomplete saturation. Preferably, the process executed in the insulation T2 preparation module is as follows: First, a reverse adiabatic half-channel pulse is used to flip the blood spin signal to the XY plane. Second, n adiabatic fast channel pulses are applied at preset pulse time intervals to flip the venous blood spin n times by 180°, where n is an odd number in the range of 1 to 15. The number of adiabatic fast channel pulses n and the pulse time interval need to be adjusted to meet the effective echo time of the current round. Next, an adiabatic half-channel pulse is used to flip the blood spin signal back to the direction of the main magnetic field. Finally, after the adiabatic half-channel pulse is completed, a dephasing gradient is applied in the X, Y, and Z directions. Preferably, the process executed in the speed selection module based on Fourier transform is as follows: First, a series of 10° excitation pulses are applied, and a pair of 180° refocusing pulses are applied between every two adjacent 10° excitation pulses. At the same time, a pair of coded gradient lobes of opposite polarity are applied along the slice selection direction before and after each 180° refocusing pulse, and all 180° refocusing pulses need to adopt a phase cyclic scheme. Then, after the last 10° excitation pulse is applied, a dephasing gradient is applied in the slice selection direction to eliminate transverse magnetization. Preferably, the process executed in the planar echo imaging module is as follows: First, a single 90° excitation pulse and the corresponding layer selection gradient are applied synchronously. Then, a pre-gradient is applied in the phase coding and frequency coding directions, and a phase-gathering gradient is applied in the layer selection direction. After that, a series of alternating gradients are applied in the frequency coding direction, and a phase coding gradient is inserted each time the polarity of the frequency coding gradient changes. Preferably, the process executed in the post-saturation module is as follows: First, a 90° saturated RF pulse is applied, followed by a dephase gradient in the X and Z directions; then, a 90° saturated RF pulse is applied, followed by a dephase gradient in the Y and Z directions; finally, a 90° saturated RF pulse is applied, followed by a dephase gradient in all three directions (X, Y, and Z) to completely eliminate the residual transverse magnetization vector.

4. The magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in claim 1, characterized in that, In the Fourier transform-based velocity selection module, there are a total of 9 10° excitation pulses. Among them, the 16 inserted 180° refocusing RF pulses adopt the MLEV-16 phase cycle scheme, with the phases sequentially being 0°-0°-180°-180°-180°-0°-0°-180°-180°-0°-0°-0°-180°-180°-0°. The encoded gradient lobes applied before and after each 180° refocusing pulse are two triangular gradient pulses with opposite polarities.

5. The magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in claim 1, characterized in that, The method for obtaining the T2 value of venous blood based on image signal fitting using a model is as follows: First, based on the effective echo time eTE used by the adiabatic T2 preparation module in each repeated application of the imaging sequence in S2, the signal M corresponding to the effective echo time is obtained through Bloch equation simulation under a fixed transverse relaxation time T2. z Then, the actual effective echo time eTE corresponding to this effective echo time is calculated. act = -ln(Mz)×T2; Then, using the effective echo time eTE of each round and the venous blood signal M acquired in the current round... acq The actual effective echo time (eTE) corresponding to the current round act Venous blood signal M obtained from saturated TR acquisition sat To fit the samples, the model By fitting the data, the actual T2 value of venous blood is obtained.

6. The magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in claim 1, characterized in that, The formula for the calibration model is: Where T2 is the fitted venous blood T2 value, Y is the venous oxygen saturation value, A1, A2, A3, and A4 are calibration parameters, and Hct is the hematocrit.

7. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they can control an external magnetic resonance scanner to implement the magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in any one of claims 1 to 6.

8. A computer-readable storage medium, characterized in that, The storage medium stores a computer program, which, when executed by a processor, can control an external magnetic resonance scanner to realize the magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in any one of claims 1 to 6.

9. A computer electronic device, characterized in that, Including memory and processor; The memory is used to store computer programs; The processor, when executing the computer program, is configured to control an external magnetic resonance scanner to implement the magnetic resonance oxygen metabolism imaging method based on adiabatic T2 preparation as described in any one of claims 1 to 6.

10. A magnetic resonance imaging device, characterized in that, The device includes a magnetic resonance scanner and a control unit. The control unit stores a computer program. When the computer program is executed, it controls the magnetic resonance scanner to perform magnetic resonance oxygen metabolism imaging based on adiabatic T2 preparation as described in any one of claims 1 to 6. By executing an imaging sequence, it acquires K-space signals and obtains venous oxygen saturation value, oxygen uptake fraction, and oxygen metabolism rate through signal data processing.

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