Optimal pulse power measurement method and system for multi-nuclide synchronous integrated imaging

Abstract

An optimal pulse power measurement method and system for multi-nuclide synchronous integrated imaging. The measurement method comprises the following steps: in the same MRI TR, sequentially or synchronously exciting a plurality of nuclides in one slice, then applying a frequency-encoding gradient in the opposite direction of a slice-selection gradient on a slice-encoding gradient channel, and also collecting FID signals of all the nuclides; synchronously changing power values of shaped radio-frequency pulses of all the nuclides multiple times, such that each nuclide obtains a plurality of corresponding FID signals; and respectively performing Fourier transforms on the FID signals of each nuclide, selecting a spectral peak of an absolute-value spectrum, and performing integral comparison, wherein the power value of a shaped radio-frequency pulse corresponding to the maximum value of the signal intensity of each nuclide indicates an optimal power of the shaped radio-frequency pulse corresponding to the current TR. The present measurement method significantly shortens the measurement time for parameter optimization, and also ensures that images of a high signal-to-noise ratio of each nuclide can be obtained in subsequent imaging.

Description

Optimal pulse power measurement method and system for multi-nuclide synchronous integrated imaging Technical Field

[0001] The present invention relates to the technical field of magnetic resonance imaging, and in particular to a method and system for measuring optimal pulse power of multi-nuclide synchronous integrated imaging. Background Art

[0002] Magnetic resonance imaging (MRI) has been widely used in preclinical research and medical diagnosis and treatment. 1 H) imaging, which can provide functional and morphological information. 1 H nuclide phosphorus ( 31 P), sodium ( 23 Na) is also a magnetic resonance sensitive nuclide, which can provide information that cannot be obtained by proton imaging alone; exogenous fluorine ( 19 F), Xe 129 Because probes have no background signal in the body, they are often used as targeting agents, tracers, and developers for in vivo research. Phosphorus-containing substances in the body participate in the body's energy metabolism. During the occurrence and development of tumors, the ratio of different phosphorus-containing substances changes dynamically. However, there are many types of phosphorus-containing substances, and the spectral peak distribution range is wide, with multiple spectral peaks, and even some spectral peaks overlap. This is different from the spectral peaks of water and sodium salts in the body, which are single peaks. Therefore, phosphorus-containing substances in the body cannot be directly imaged and characterized. Spectral imaging methods are usually used to collect the spectral peaks of phosphorus-containing substances, and then they are converted into images through data processing.

[0003] There are many other radionuclides that are sensitive to magnetic resonance in living organisms, such as oxygen ( 17 O), potassium ( 35 / 37 K), etc., multi-nuclide synchronous imaging has gradually attracted widespread attention. However, the transverse relaxation parameter T2 and longitudinal relaxation parameter T1 of each nuclide are very different. Multi-nuclide synchronous imaging is mainly used to obtain non- 1 H nuclide content and spatial distribution information, that is, to obtain high signal-to-noise ratio 1 H nuclide imaging is crucial. Methods such as gradient echo (GRE), ultrashort echo time (UTE), and chemical shift imaging (CSI) are commonly used in multi-nuclide simultaneous imaging. To achieve the highest signal-to-noise ratio within a given pulse sequence repetition period (TR), these methods employ a shaped RF pulse flip angle, the Ernst angle a, where a = arccos(exp(-TR / T1)). This means that the shaped RF pulse power is set to the value corresponding to the Ernst angle.

[0004] As described in invention patent ZL202310366296.8, the flip angle of a nuclide is determined based on its T1. The method for determining multinuclear imaging parameters proposed in invention patent ZL202310366296.8 determines imaging parameters after the relaxation time constants T1 and T2 of the nuclide are known, as well as the relationship between the RF emission voltage (which can be converted into power) and the excitation pulse flip angle. However, in practical applications, the T1 of each nuclide is unknown, and the T1 measurement process is cumbersome and time-consuming. To capture spatiotemporally correlated molecular events in vivo, it is typically necessary to acquire images of multiple nuclides within a defined timeframe. This means that the key parameter influencing imaging time, TR, is fixed or constrained. Therefore, in multinuclear simultaneous imaging, when the TR is given but the T1 of each nuclide is unknown (i.e., the Ernst angle of each nuclide is unknown), it is crucial to determine the RF pulse power for each nuclide to achieve a high signal-to-noise ratio multinuclear image. Currently, no mature method exists. Summary of the Invention

[0005] The present invention proposes a method and system for measuring the optimal pulse power of multi-nuclide synchronous integrated imaging, which significantly shortens the measurement time of parameter optimization and ensures that each nuclide can obtain an image with a high signal-to-noise ratio in the later imaging.

[0006] The technical solution of the present invention is achieved as follows: a method for measuring optimal pulse power of multi-nuclide synchronous integrated imaging comprises the following steps:

[0007] (1) Within the same magnetic resonance imaging (MRI) pulse sequence repetition period (TR), a shaped radiofrequency pulse is used in conjunction with a slice selection gradient to selectively and synchronously excite multiple nuclides within a slice. Then, a frequency encoding gradient is applied in the slice encoding gradient channel in the opposite direction of the slice selection gradient, and the free induction decay (FID) signals of all nuclides are collected simultaneously.

[0008] Alternatively, a shaped RF pulse is used in conjunction with a slice selection gradient to selectively pre-excite one or more nuclides in a slice, and then a frequency encoding gradient is applied in the slice encoding gradient channel in the opposite direction relative to the slice selection gradient, while simultaneously acquiring the FID signal of the pre-excited nuclides; then a shaped RF pulse is used in conjunction with a slice selection gradient to selectively and synchronously excite multiple other nuclides in a slice, and then a frequency encoding gradient is applied in the slice encoding gradient channel in the opposite direction relative to the slice selection gradient, while simultaneously acquiring the FID signals of the multiple other nuclides;

[0009] (2) synchronously changing the shape RF pulse power values ​​of all nuclides multiple times and repeating step (1), so that each nuclide obtains multiple FID signals corresponding to its shape RF pulse power value;

[0010] (3) Fourier transform is performed on the multiple FID signals of each nuclide in step (2) to obtain the spectrum of the nuclide in the layer and its absolute value spectrum; the absolute value spectrum of each nuclide is integrated, and the integral value is marked as the signal intensity of this nuclide in the layer; the shape RF pulse power value corresponding to the maximum signal intensity of each nuclide is the optimal shape RF pulse power corresponding to the current pulse sequence repetition period (TR).

[0011] Furthermore, in step (1), when the nuclides are excited synchronously, the equivalent centers of the RF pulses of all shapes are aligned with the expected center of the slice selection gradient.

[0012] Furthermore, in step (2), the method for synchronously changing the shape RF pulse power of all nuclides is as follows: the shape RF pulse power gradually changes from small to large with equal intervals, and the range of change of the shape RF pulse power must meet the signal intensity change trend of each nuclide, which is to first increase to a maximum value and then decrease.

[0013] Furthermore, the spacing is an interval distinguishable by a radio frequency transmitter of the magnetic resonance imaging system or an integral multiple thereof.

[0014] The present invention proposes a multi-nuclide synchronous integrated imaging optimal pulse power measurement system, which includes the following functional modules:

[0015] The data acquisition module is used to obtain the FID signal data of all imaging nuclides collected by the multi-nuclide MRI system and the power value, shape and width of the corresponding shaped radio frequency pulse, as well as the layer thickness and TR;

[0016] The data processing module is used to perform Fourier transform on the FID signal data of all imaging nuclides, obtain the spectrum and extract the absolute value spectrum, select the spectrum peak of the absolute value spectrum and integrate and compare it to determine the optimal shape of the radio frequency pulse power;

[0017] Data output module: outputs the optimal shape RF pulse power to the multi-nuclide MRI system, and archives the optimal power value, shape and width of the shaped RF pulse of each nuclide, as well as the layer thickness and TR of the slice.

[0018] Beneficial effects of the present invention:

[0019] 1. The optimal pulse power measurement method and system for multi-nuclide synchronous integrated imaging proposed in this invention can synchronously acquire the free induction decay (FID) signals of different nuclides within a given pulse sequence period (TR). Through data processing, the optimal RF pulse power of each nuclide is synchronously obtained, ensuring that each nuclide can obtain a high signal-to-noise ratio image in subsequent imaging.

[0020] 2. After the shaped RF pulse excites the nuclide, the signal of the nuclide is immediately collected. This is equivalent to an echo time that is only equal to the shaped RF pulse width. The short echo time can avoid the influence of MRI system imperfections such as magnetic field inhomogeneity, and the obtained measurement signal has a high signal-to-noise ratio, thereby ensuring the accuracy of the obtained shaped RF pulse power.

[0021] 3. Signals of multiple nuclides are collected within the same TR, significantly shortening the measurement time for parameter optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] FIG1 is a block diagram of the optimal pulse power measurement system for multi-nuclide synchronous integrated imaging according to the present invention;

[0024] Figure 2: 1 H. 19 F. 23 The timing diagram of the MRI pulse sequence of Na trinuclide within one TR, the horizontal axis represents the time axis;

[0025] Figure 3 shows the first excitation of phosphorus 31 P, then synchronously excite 1 H. 19 F. 23 Na magnetic resonance imaging pulse sequence timing diagram within one TR, the horizontal axis represents the time axis;

[0026] Figure 4 shows 31 The curve of the signal intensity of P versus pulse power;

[0027] Figure 5 1 The curve of H signal intensity changing with pulse power;

[0028] Figure 6 19 The curve of F signal intensity changing with pulse power;

[0029] Figure 7 23 The curve of Na signal intensity changing with pulse power;

[0030] Figure 8 shows the synchronous excitation 23 Na, 31 P, then synchronously excite 1 H. 19 F is the timing diagram of the magnetic resonance imaging pulse sequence within one TR, with the horizontal axis representing the time axis. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0032] Figure 1 is a functional block diagram of the optimal pulse power measurement system for multi-nuclide synchronous integrated imaging implemented in the present invention. The measurement method embodiments provided herein can be executed on a computer, terminal, or similar computing system. For example, when executed on a terminal, the terminal can include one or more processors serving as data capture modules to implement data capture functions for acquiring FID signal data for all imaging nuclides collected from the multi-nuclide MRI system, along with the power, shape, and pulse width of the corresponding shaped RF pulses, as well as parameters such as slice thickness and TR that need to be recorded.

[0033] The terminal may also include one or more processors as data processing modules for performing Fourier transform on the FID signal data of all imaging nuclides, obtaining a spectrum and extracting an absolute value spectrum, selecting a spectrum peak in the absolute value spectrum and integrating and comparing it, determining the shaped RF pulse power corresponding to the maximum signal intensity of each nuclide, and determining it as the optimal shaped RF pulse power for each nuclide.

[0034] The terminal may also include one or more processors as data output modules to output the determined optimal shape RF pulse power for each nuclide to the multi-nuclide MRI system, and at the same time archive the current shape RF pulse related parameters shape and pulse width, as well as the layer thickness, TR and the corresponding optimal shape RF pulse power for each nuclide for later use.

[0035] Those skilled in the art will appreciate that a terminal or computing system may implement the functions of the three functional modules shown in FIG1 through a processor, or even implement the functions of the multi-nuclide synchronous integrated imaging optimal pulse power measurement system through a program deployed on a computer. Example 1

[0036] As shown in Figure 2, 1 H. 19 F. 23 The optimal pulse power measurement method for Na tri-nuclides synchronous integrated imaging includes the following steps:

[0037] (1) In the same pulse sequence repetition period (TR), SINC, Hermite and Gauss shaped RF pulses are used in conjunction with slice selection gradients to selectively and synchronously excite the same layer. 1 H. 19 F. 23 The centers of the three shaped radio frequency pulses are aligned with the expected center of the slice selection gradient. The power of the three shaped radio frequency pulses is represented by the same parameter plvl. Then, the frequency encoding gradient is applied in the opposite direction of the slice selection gradient in the slice coding gradient channel Gs while collecting 1 H. 19 F. 23 Free induction decay signals FID1, FID2 and FID3 of three nuclides of Na;

[0038] (2) Synchronous, evenly spaced changes from small to large 1 H. 19 F. 23 Na three nuclides have shape RF pulse power values ​​plvl, repeat step (1), and obtain multiple FID signals corresponding to the shape RF pulse power values ​​plvl for each nuclide;

[0039] (3) Yes 1 H. 19 F. 23 The FID signals of the three nuclides Na, FID1, FID2 and FID3, are Fourier transformed to obtain the 1 H. 19 F. 23 The spectrum of Na nuclide is extracted 1 H. 19 F. 23 The absolute value spectrum of Na is integrated, and the integral value is marked as 1 H. 19 F. 23 The signal intensity of the Na nuclide; the shaped RF pulse power value corresponding to the maximum signal intensity of each nuclide is the optimal shaped RF pulse power corresponding to the current pulse repetition period (TR). Example 2

[0040] As shown in Figure 3, phosphorus 31 P. 1 H. 19 F. 23 The optimal pulse power measurement method for Na four-nuclides synchronous integrated imaging includes the following steps:

[0041] (1) Use SINC shape RF pulses with slice selection gradients to selectively excite the retina within a layer within the same pulse sequence repetition period (TR). 31P nuclide, the radio frequency pulse power value is represented by the parameter plvl, and then the frequency encoding gradient is applied in the opposite direction of the slice selection gradient in the slice encoding gradient channel Gs while collecting 31 The free induction decay signal FID1 of the P nuclide;

[0042] Then, SINC, Hermite and Gauss shaped radio frequency pulses were used in conjunction with slice selection gradients to selectively and synchronously excite the 1 H. 19 F. 23 The equivalent centers of the three shaped RF pulses are aligned with the expected center of the slice selection gradient. The power values ​​of the shaped RF pulses are all represented by the parameter plvl. Then, the frequency encoding gradient is applied in the opposite direction of the slice selection gradient in the slice encoding gradient channel Gs while collecting 1 H. 19 F. 23 Free induction decay signals FID2, FID3 and FID4 of three nuclides of Na;

[0043] (2) Synchronous, changing from small to large 31 P. 1 H. 19 F. 23 Na four nuclides have shape RF pulse powers plvl, and step (1) is repeated, and each nuclide obtains a plurality of FID signals corresponding to its shape RF pulse power plvl.

[0044] (3) Yes 31 P. 1 H. 19 F. 23 The FID signals of the four nuclides Na, FID1, FID2, FID3 and FID4, are Fourier transformed to obtain the 31 P. 1 H. 19 F. 23 The spectrum of Na nuclide is extracted 31 P. 1 H. 19 F. 23 The absolute value spectrum of Na is integrated, and the integral value is marked as 31 P. 1 H. 19 F. 23 The signal intensity of the Na nuclide; the shaped RF pulse power corresponding to the maximum signal intensity of each nuclide is the optimal shaped RF pulse power corresponding to the current pulse repetition period (TR).

[0045] The measurement method of Example 2 was used, with a mixed solution of 2 mmol / mL trifluoroethanol and 0.8 mmol / mL sodium dihydrogen phosphate as the sample, the layer thickness was 10 mm, the width of the shaped radio frequency pulse was set to 2 ms, and the TR was set to 800 ms. The multi-nuclide MRI system was used for online experiments and synchronous testing. 31 P. 1 H. 19 F. 23 The signal intensity of Na changes with pulse power. The results are shown in Figures 4, 5, 6 and 7 respectively. The power of the shaped radio frequency pulse of the multi-nuclide MRI system is expressed in relative dB. The signal change trend of each nuclide is consistent with the expectation of the present invention. 31 P. 1 H. 19 F. 23 The thickness of the four types of Na nuclides in the layer is 10mm, the TR is 800ms, the excitation pulses are SINC, SINC, Hermite and gauss-shaped RF pulses, and the optimal pulse powers when the width is 2ms are 51dB, 55dB, 42dB and 58dB respectively. Example 3

[0046] This embodiment is basically the same as the second embodiment, except that: in step (1), phosphorus is synchronously excited in advance. 23 Na, 31 P, then synchronously excite 1 H. 19 F .

[0047] As shown in Figure 8, 23 Na, 31 P. 1 H. 19 The optimal pulse power measurement method for F four-nuclides synchronous integrated imaging includes the following steps:

[0048] (1) In the same pulse sequence repetition period (TR), Gauss and SINC shaped RF pulses are used in conjunction with slice selection gradients to selectively and synchronously excite the 23 Na, 31 P nuclide, the two radio frequency pulse power values ​​are represented by the parameter plvl, and then the frequency encoding gradient is applied in the opposite direction of the slice selection gradient in the slice encoding gradient channel Gs while collecting 23 Na, 31 Free induction decay signals FID1 and FID2 of P nuclide;

[0049] Then, SINC and Hermite shaped radio frequency pulses were used together with slice selection gradients to selectively and synchronously stimulate the 1H. 19 For F nuclide, the equivalent centers of the two shaped RF pulses are aligned with the expected center of the slice selection gradient. The shaped RF pulse power values ​​are represented by the parameter plvl. Then, the frequency encoding gradient is applied in the opposite direction of the slice selection gradient in the slice encoding gradient channel Gs while collecting 1 H. 19 F free induction decay signals FID3 and FID4 of two nuclides;

[0050] (2) Synchronous, changing from small to large 23 Na, 31 P. 1 H. 19 The shape radio frequency pulse power plvl of the four nuclides F is repeated in step (1), and a plurality of FID signals corresponding to the shape radio frequency pulse power plvl of each nuclide are obtained.

[0051] (3) Yes 23 Na, 31 P. 1 H. 19 The FID signals of the four nuclides FID1, FID2, FID3 and FID4 are Fourier transformed to obtain the 23 Na, 31 P. 1 H. 19 The spectrum of F nuclide is extracted 23 Na, 31 P. 1 H. 19 The absolute value spectrum of F is integrated, and the integral value is marked as 323 Na, 31 P. 1 H. 19 The signal intensity of the F nuclide; the shaped RF pulse power corresponding to the maximum signal intensity of each nuclide is the optimal shaped RF pulse power corresponding to the current pulse repetition period (TR).

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring optimal pulse power of multi-nuclide synchronous integrated imaging, characterized in that: The following steps are involved: (1) In the same MRI pulse sequence repetition period TR, a shaped RF pulse is used in conjunction with a slice selection gradient to selectively and synchronously excite multiple nuclides in a slice. Then, a frequency encoding gradient is applied in the slice encoding gradient channel in the opposite direction of the slice selection gradient, and the free induction decay (FID) signals of all nuclides are collected simultaneously. Alternatively, a shaped radio frequency pulse is used in combination with a layer selection gradient to selectively pre-excite one or more nuclides in a layer, and then a frequency coding gradient is applied in a layer coding gradient channel in a direction opposite to the layer selection gradient, and the free induction decay FID signal of the pre-excited nuclides is collected at the same time, and then a shaped radio frequency pulse is used in combination with a layer selection gradient to selectively and synchronously excite multiple other nuclides in the same layer, and then a frequency coding gradient is applied in a layer coding gradient channel in a direction opposite to the layer selection gradient, and the free induction decay FID signals of multiple other nuclides are collected at the same time; (2) synchronously changing the shape RF pulse power values ​​of all nuclides for multiple times and repeating step (1), so that each nuclide obtains multiple free induction decay (FID) signals corresponding to its shape RF pulse power value; (3) Fourier transform is performed on the multiple free induction decay (FID) signals of each nuclide in step (2) to obtain the spectrum of the nuclide in the layer and extract the absolute value spectrum; the absolute value spectrum of each nuclide is integrated, and the integral value is marked as the signal intensity of this nuclide in the layer; the shaped RF pulse power value corresponding to the maximum signal intensity of each nuclide is the optimal shaped RF pulse power corresponding to the current pulse sequence repetition period TR.

2. The method for measuring optimal pulse power of multi-nuclide synchronous integrated imaging according to claim 1, characterized in that: In step (1), when the nuclides are excited synchronously, the equivalent centers of all RF pulse shapes are aligned with the expected centers of the slice selection gradients.

3. The method for measuring optimal pulse power of multi-nuclide synchronous integrated imaging according to claim 1 or 2, characterized in that: In step (2), the shaped RF pulse power of all nuclides is changed synchronously, and the shaped RF pulse power gradually changes from small to large with equal intervals. The change range of the shaped RF pulse power must meet the signal intensity change trend of each nuclide, which is to first increase to the maximum value and then decrease.

4. The method for measuring optimal pulse power of multi-nuclide synchronous integrated imaging according to claim 3, characterized in that: The spacing is a distance distinguishable by a radio frequency transmitter of the magnetic resonance imaging system or an integral multiple thereof.

5. The optimal pulse power measurement system for multi-nuclide synchronous integrated imaging is characterized by: The measuring method according to any one of claims 1 to 4, comprising The data acquisition module is used to obtain the free induction decay FID signal data of all imaging nuclides collected by the multi-nuclide MRI system and the power value, shape and width of the corresponding shaped radio frequency pulse, as well as the layer thickness and pulse sequence repetition period TR of the layer; The data processing module is used to perform Fourier transform on the free induction decay (FID) signal data of all imaging nuclides, obtain the spectrum and extract the absolute value spectrum, select the spectrum peak in the absolute value spectrum and integrate and compare it, and determine the optimal shape of the radio frequency pulse power; Data output module: output the best shaped RF pulse power to the multi-nuclide MRI system, and archive the best power value, shape and width of the shaped RF pulse of each nuclide, as well as the layer thickness and pulse sequence repetition period TR.

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