FSE joint pre-correction method
By separating and fitting the FSE pulse sequence, synchronous correction of RF flip angle and stimulated echo artifacts was achieved, solving the problems of long time and equipment compatibility in the existing technology, and improving the imaging quality and efficiency of FSE.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-28
- Publication Date
- 2026-04-03
AI Technical Summary
In existing technologies, FSE imaging is affected by non-uniform radio frequency fields and echo artifacts, requiring separate STEAM and FSE pre-scans, which leads to increased time and motion artifact risks. Furthermore, the STEAM sequence is missing in some devices, making it impossible to achieve real-time correction of the radio frequency flip angle.
By adjusting the RF pulse phase angle of the FSE pulse sequence, it is separated into spin echo and stimulated echo. The optimal RF pulse gain and flip angle are determined by curve fitting using the RF pulse gain and amplitude-to-signal ratio, and the RF pulse phase is corrected to achieve integrated correction.
Without adding additional scanning sequences, it achieves simultaneous correction of radio frequency flip angle and stimulated echo artifacts, reduces pre-correction time, improves imaging efficiency and equipment compatibility, and is suitable for various MRI devices.
Smart Images
Figure CN121784632A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of magnetic resonance imaging technology, and in particular to a combined FSE pre-correction method. Background Technology
[0002] Fast spin echo (FSE) acquires signals by refocusing the deflected magnetization vector after a 90-degree radio frequency (RF) pulse excitation and then applying multiple 180-degree refocusing pulses. However, in actual patient scanning, the actual flip angle deviates from the system's set value due to factors such as RF field inhomogeneity and patient-specific characteristics. Therefore, FSE imaging is affected not only by the inaccurate RF field flip angle but also by the stimulated echo signal when multiple 180-degree refocusing pulses are applied consecutively.
[0003] In existing technologies, to address the aforementioned issues, the current approach is to correct the radiofrequency flip angle and FSE stimulated echo artifacts separately using two different pulse sequences: STEAM and FSE. However, these solutions require separate pre-scanning procedures based on STEAM and FSE, making it impossible to simultaneously correct the radiofrequency flip angle and FSE stimulated echo artifacts. This results in prolonged total pre-correction time, increased patient waiting time, and higher risks of motion artifacts. Furthermore, the STEAM sequence is not standard equipment on all domestically produced and low-to-mid-range MRI devices, and is widely lacking, especially in primary healthcare institutions. This often prevents patient-specific real-time correction of the radiofrequency flip angle from being implemented, leaving FSE image quality without a fundamental guarantee. Summary of the Invention
[0004] Therefore, it is necessary to provide an FSE joint pre-calibration method to address the aforementioned technical problems.
[0005] The present invention adopts the following technical solution: This invention provides a joint pre-calibration method for FSE, comprising: Obtain the FSE pulse sequence; By adjusting the phase angle of the radio frequency pulses in the FSE pulse sequence, the FSE pulse sequence can be separated into spin echo and stimulated echo. Different radio frequency pulse gains were set on the MRI equipment, and the amplitude signal ratio of stimulated echo to spin echo under different radio frequency pulse gains was determined; wherein, each radio frequency pulse gain corresponds to three radio frequency pulse flip angles with a fixed proportional relationship; Using the amplitude ratio of stimulated echo to spin echo as the dependent variable and the RF pulse gain as the independent variable, a curve fitting was performed on the amplitude ratio of stimulated echo to spin echo and the RF pulse gain. The RF pulse gain corresponding to the lowest point in the curve was determined as the optimal RF pulse gain. Based on the correspondence between the RF pulse gain and the RF pulse flip angle, the optimal RF pulse flip angle was determined to achieve pre-correction of the RF pulse flip angle. Under optimal RF pulse gain, the phase difference between the spin echo and the stimulated echo is determined; based on the phase difference, the phase angle of the RF pulse is corrected to make the phase of the stimulated echo consistent with that of the spin echo, thereby completing the pre-correction of stimulated echo artifacts.
[0006] Preferably, by adjusting the radio frequency pulse phase angle of the FSE pulse sequence, the FSE pulse sequence is separated into spin echo and stimulated echo, specifically including: The radio frequency pulse phase angle of the FSE pulse sequence is adjusted to two different angles. Based on the two different radio frequency pulse phase angles, the FSE pulse sequence is pre-scanned twice to obtain the first FSE original signal and the second FSE original signal. Based on the first and second FSE original signals, the FSE pulse sequence is separated into spin echo and stimulated echo.
[0007] Preferably, in the two sets of different radio frequency pulse phase angles, the first set of radio frequency pulse phase angles are 0°, 0° and 0° respectively; the second set of radio frequency pulse phase angles are 0°, 90° and 90° respectively.
[0008] Preferably, based on the first and second original FSE signals, the FSE pulse sequence is separated into spin echoes and stimulated echoes, specifically including: Based on the principle that the spin echoes in the first and second FSE original signals generated under two different RF pulse phase angles are in the same direction and the stimulated echoes are in opposite directions, the FSE pulse sequence is separated into spin echoes and stimulated echoes, as shown in the formula: ; ; In the formula, For spin echo, For stimulated echo, and These are the first FSE raw signal and the second FSE raw signal generated under two different radio frequency pulse phase angles, respectively.
[0009] Preferably, the amplitude ratio of the stimulated echo to the spin echo is determined by the RF pulse gain corresponding to the flip angles of three RF pulses with a fixed proportional relationship, specifically including: According to the radio frequency pulse flip angle , and as well as , and The fixed proportional relationship between them = =2 The three RF pulse flip angles are uniformly converted into Substitute the basic principle expression of magnetic resonance imaging: ; ; In the formula, For stimulated echo, This is a spin echo, where A is the signal strength value and i is a complex unit. A constant phase shift; The amplitude ratio of the stimulated echo to the spin echo is: ; In the formula, The amplitude signal of the stimulated echo. This is the amplitude signal of the spin echo.
[0010] Preferably, determining the phase difference between the spin echo and the stimulated echo specifically includes: The original signals of the separated spin echo and stimulated echo are subjected to one-dimensional Fourier transform along the frequency coding gradient direction to obtain two complex images. Extract the phase difference by conjugate multiplication of the two complex images obtained after transformation; The average phase difference was calculated in the 1 / 4 region of the echo center.
[0011] Preferably, the correction amount for the phase angle of the radio frequency pulse is half the phase difference between the spin echo and the stimulated echo.
[0012] The above-mentioned at least one technical solution adopted in this invention can achieve the following beneficial effects: In the FSE combined pre-correction method provided by this invention, only the FSE pulse sequence is used. By applying different radio frequency pulse phase angles, the spin echo and stimulated echo are effectively separated. Based on this, curve fitting is performed using the mathematical relationship between the amplitude signal ratio of the separated stimulated echo and spin echo and the radio frequency pulse gain. The gain corresponding to the lowest point of the curve is determined as the optimal radio frequency pulse gain, achieving precise calibration of the radio frequency flip angle in the FSE scan. Simultaneously, by calculating the phase angle of the spin echo and stimulated echo and correcting the radio frequency pulse phase, phase consistency between the two is achieved, effectively suppressing stimulated echo artifacts. This fundamentally solves the problems of lengthy correction procedures, increased patient waiting time, and increased risk of motion artifacts caused by the reliance on two independent pre-scans, STEAM and FSE, in existing technologies. It also overcomes the limitation that radio frequency correction cannot be implemented due to the absence of the STEAM sequence in some MRI devices. Therefore, this invention achieves integrated synchronous correction of radiofrequency flip angle and stimulated echo artifacts without the need for additional scanning sequences. This not only significantly reduces pre-correction time but also improves the pre-correction efficiency and clinical applicability of FSE imaging. Furthermore, it provides a feasible standardized correction scheme for MRI equipment that does not have STEAM sequences, demonstrating good equipment compatibility and promotional value. Attached Figure Description
[0013] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:
[0014] Figure 1 A schematic flowchart of an FSE joint pre-correction method provided by the present invention; Figure 2 The following is a fitting curve of the relationship between the stimulated echo and spin echo signal ratio of a water model and the radio frequency pulse gain for the FSE joint pre-correction method provided by the present invention; Figure 3 The integral curves of gradient echo signal intensity at different flip angles are provided by the present invention for an FSE joint pre-correction method. Figure 4 The graph shows the relationship between the ratio of head-stimulated echo to spin echo signal and radio frequency pulse gain in an FSE joint pre-correction method provided by the present invention. Detailed Implementation
[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments in the specification without creative effort are within the scope of protection of this application.
[0016] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.
[0017] Figure 1 This is a schematic diagram of the FSE joint pre-calibration method of the present invention, which specifically includes the following steps: S101: Obtain the FSE pulse sequence.
[0018] S102: By adjusting the RF pulse phase angle of the FSE pulse sequence, the FSE pulse sequence is separated into spin echo and stimulated echo.
[0019] Optionally, different radio frequency pulse phase angles are applied to the FSE pulse sequence to separate the FSE pulse sequence into spin echo and stimulated echo. Specifically, this includes: applying two different three radio frequency pulse phase angles to the FSE pulse sequence, performing two pre-scans on the FSE pulse sequence to obtain a first FSE original signal and a second FSE original signal; and separating the FSE pulse sequence into spin echo and stimulated echo based on the first FSE original signal and the second FSE original signal.
[0020] Among the two sets of different radio frequency pulse phase angles, the first set of radio frequency pulse phase angles are 0°, 0° and 0° respectively; the second set of radio frequency pulse phase angles are 0°, 90° and 90° respectively.
[0021] Based on the first and second original FSE signals, the FSE pulse sequence is separated into spin echoes and stimulated echoes. Specifically, this involves separating the FSE pulse sequence into spin echoes and stimulated echoes based on the principle that the spin echoes in the first and second original FSE signals generated at the first set of radio frequency pulse phase angles (0°, 0°, and 0°) and the second set of radio frequency pulse phase angles (0°, 90°, and 90°) are in the same direction and the stimulated echoes are in opposite directions. The formula is as follows: ; ; In the formula, For spin echo, For stimulated echo, and The first FSE raw signal and the second FSE raw signal are generated under the first group of radio frequency pulse phase angles (0°, 0° and 0°) and the second group of radio frequency pulse phase angles (0°, 90° and 90°), respectively.
[0022] S103: Set different radio frequency pulse gains on the MRI equipment and determine the amplitude signal ratio of stimulated echo to spin echo under different radio frequency pulse gains; wherein, each radio frequency pulse gain corresponds to three radio frequency pulse flip angles with a fixed proportional relationship.
[0023] S104: Using the amplitude ratio of stimulated echo to spin echo as the dependent variable and the RF pulse gain as the independent variable, a curve fitting is performed on the amplitude ratio of stimulated echo to spin echo and the RF pulse gain; the RF pulse gain corresponding to the lowest point in the curve is determined as the optimal RF pulse gain; based on the correspondence between the RF pulse gain and the RF pulse flip angle, the optimal RF pulse flip angle is determined to achieve pre-correction of the RF pulse flip angle. Optionally, the amplitude ratio of the stimulated echo to the spin echo is determined by the RF pulse gain corresponding to the flip angles of three RF pulses with a fixed proportional relationship, specifically including: According to the radio frequency pulse flip angle , and as well as , and The fixed proportional relationship between them = =2 The three RF pulse flip angles are uniformly converted into Substitute the basic principle expression of magnetic resonance imaging: ; ; In the formula, For stimulated echo, This is a spin echo, where A is the signal strength value and i is a complex unit. A constant phase shift; The amplitude ratio of the stimulated echo to the spin echo is: ; In the formula, The amplitude signal of the stimulated echo. This is the amplitude signal of the spin echo.
[0024] Specifically, the relationship between the three flip angles of the FSE sequence itself is as follows: excitation, and The relationship between them is as follows: = =2 By controlling the phase of the FSE radio frequency pulse, the spin echo and stimulated echo components in the FSE signal can be effectively separated. This is applicable to signals acquired when the phase angle of three consecutive radio frequency pulses is 0°. Signals acquired at three radio frequency pulse positions of 0°, 90°, and 90° respectively The generated spin echo is in the same direction as the stimulated echo, which is out of phase, thus separating the spin echo from the stimulated echo.
[0025] In practical implementation, the RF flip angle is changed by modifying the RF pulse gain RG. By using RG as the independent variable and the ratio of stimulated echo to spin echo signals as the dependent variable, curve fitting can be performed to obtain the optimal gain RG corresponding to a 90-degree flip angle. 90 .
[0026] S105: Under the optimal RF pulse gain, determine the phase difference between the spin echo and the stimulated echo; based on the phase difference, correct the phase angle of the RF pulse to make the phase of the stimulated echo consistent with that of the spin echo, so as to complete the pre-correction of the stimulated echo artifact.
[0027] Optionally, determining the phase difference between the spin echo and the stimulated echo specifically includes: performing a one-dimensional Fourier transform on the original signals of the separated spin echo and stimulated echo along the frequency coding gradient direction to obtain two complex images; extracting the phase difference by conjugate multiplication of the two complex images obtained after the transformation; and calculating the average phase difference in the center 1 / 4 region of the echo.
[0028] Optionally, the phase angle of the radio frequency pulse is corrected by half the phase difference between the spin echo and the stimulated echo.
[0029] Furthermore, in this embodiment, tests were conducted on the water model and volunteers using a 1.5T magnetic resonance imaging system to verify the effectiveness and correctness of the method of the present invention.
[0030] The receiving coil is an 8-channel head coil. Under different RF pulse gains, the signal ratio of the stimulated echo to the spin echo of the water model was calculated. A total of 10 points were collected, and the results are as follows: Figure 2 As shown.
[0031] The ratio of stimulated echo to spin echo signal is The cosine function reaches its minimum value at 90 degrees, therefore Figure 1 The lowest point in the range is the optimal RF gain, at which the RF pulse flip angle is 90 degrees.
[0032] To verify the accuracy of the calculated RF gain in this invention, the RF angle was verified using a gradient echo pulse sequence. To ensure sufficient signal relaxation, the GRE2D pulse sequence was set to TR=1200ms, FOV=400mm, phase encoding was disabled, and Fourier transform was disabled during image reconstruction. The signal strength of GRE2D at different flip angles was analyzed to verify whether the maximum intensity occurred at a 90-degree flip angle. Experimental results are as follows: Figure 3 As shown.
[0033] Next, head scans were performed on the volunteers, and the same conclusion was reached. Figure 4 The radio frequency flip angle is determined by the pre-scan of the volunteer's head using the FSE method.
[0034] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this invention.
Claims
1. A joint pre-calibration method for FSE, characterized in that, include: Obtain the FSE pulse sequence; By adjusting the phase angle of the radio frequency pulses in the FSE pulse sequence, the FSE pulse sequence can be separated into spin echo and stimulated echo. Different radio frequency pulse gains were set on the MRI equipment, and the amplitude signal ratio of stimulated echo to spin echo under different radio frequency pulse gains was determined; wherein, each radio frequency pulse gain corresponds to three radio frequency pulse flip angles with a fixed proportional relationship; Using the amplitude ratio of stimulated echo to spin echo as the dependent variable and the RF pulse gain as the independent variable, a curve fitting was performed on the amplitude ratio of stimulated echo to spin echo and the RF pulse gain. The RF pulse gain corresponding to the lowest point in the curve was determined as the optimal RF pulse gain. Based on the correspondence between the RF pulse gain and the RF pulse flip angle, the optimal RF pulse flip angle was determined to achieve pre-correction of the RF pulse flip angle. Under optimal RF pulse gain, the phase difference between the spin echo and the stimulated echo is determined; based on the phase difference, the phase angle of the RF pulse is corrected to make the phase of the stimulated echo consistent with that of the spin echo, thereby completing the pre-correction of stimulated echo artifacts.
2. The FSE joint pre-calibration method as described in claim 1, characterized in that, The method of separating the FSE pulse sequence into spin echo and stimulated echo by adjusting the radio frequency pulse phase angle of the FSE pulse sequence specifically includes: The radio frequency pulse phase angle of the FSE pulse sequence is adjusted to two different angles. Based on the two different radio frequency pulse phase angles, the FSE pulse sequence is pre-scanned twice to obtain the first FSE original signal and the second FSE original signal. Based on the first and second FSE original signals, the FSE pulse sequence is separated into spin echo and stimulated echo.
3. The FSE joint pre-correction method as described in claim 2, characterized in that, In the two sets of different radio frequency pulse phase angles, the first set of radio frequency pulse phase angles are 0°, 0° and 0° respectively; the second set of radio frequency pulse phase angles are 0°, 90° and 90° respectively.
4. The FSE joint pre-correction method as described in claim 2 or 3, characterized in that, The step of separating the FSE pulse sequence into spin echo and stimulated echo based on the first and second FSE raw signals specifically includes: Based on the principle that the spin echoes in the first and second FSE original signals generated under two different RF pulse phase angles are in the same direction and the stimulated echoes are in opposite directions, the FSE pulse sequence is separated into spin echoes and stimulated echoes, as shown in the formula: ； ； In the formula, For spin echo, For stimulated echo, and These are the first FSE raw signal and the second FSE raw signal generated under two different radio frequency pulse phase angles, respectively.
5. The FSE joint pre-calibration method as described in claim 1, characterized in that, The amplitude ratio of the stimulated echo to the spin echo is determined by the flip angles of three radio frequency pulses with a fixed proportional relationship corresponding to the radio frequency pulse gain, specifically including: According to the radio frequency pulse flip angle , and as well as , and The fixed proportional relationship between them = =2 The three RF pulse flip angles are uniformly converted into Substitute the basic principle expression of magnetic resonance imaging: ； ； In the formula, For stimulated echo, This is a spin echo, where A is the signal strength value and i is a complex unit. A constant phase shift; The amplitude ratio of the stimulated echo to the spin echo is: ； In the formula, The amplitude signal of the stimulated echo. This is the amplitude signal of the spin echo.
6. The FSE joint pre-calibration method as described in claim 1, characterized in that, Determining the phase difference between the spin echo and the stimulated echo specifically includes: The original signals of the separated spin echo and stimulated echo are subjected to one-dimensional Fourier transform along the frequency coding gradient direction to obtain two complex images. Extract the phase difference by conjugate multiplication of the two complex images obtained after transformation; The average phase difference was calculated in the 1 / 4 region of the echo center.
7. The FSE joint pre-calibration method as described in claim 1, characterized in that, The correction amount for the phase angle of the radio frequency pulse is half the phase difference between the spin echo and the stimulated echo.