Magnetic resonance scanning imaging method and magnetic resonance imaging system

Abstract

The embodiment of the invention provides a magnetic resonance scanning imaging method and a magnetic resonance imaging system, and the method comprises the steps: determining a to-be-adjusted pulse in a scanning sequence, the to-be-adjusted pulse comprising a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse; determining an adjustment factor according to the first gradient pulse and the shortest repetition time related to the specific absorption rate of radio frequency energy; adjusting the scanning sequence according to the adjustment factor; and performing diagnosis scanning on the to-be-examined part by using the adjusted scanning sequence to obtain a magnetic resonance image.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of medical equipment technology, and in particular to a magnetic resonance scanning imaging method and a magnetic resonance imaging system. Background Art

[0002] Magnetic resonance (MR) imaging systems have been widely used in the field of medical diagnosis. Magnetic resonance systems usually have a main magnet, a gradient amplifier, a radio frequency amplifier, a gradient coil, a transmission chain module, a transmission / receiving coil, a receiving chain module, etc., wherein the transmission chain module generates a pulse signal and transmits it to the transmission / receiving coil, and the transmission / receiving coil generates a radio frequency excitation signal to excite the scanned object to generate a magnetic resonance signal. After the excitation is completed, the transmission / receiving coil collects the magnetic resonance signal after spatial encoding and fills it into the K space to reconstruct the medical image.

[0003] In the process of imaging the scanned object using a magnetic resonance imaging system, a radio frequency transmitting coil is used to transmit radio frequency excitation pulses to the tissue to be imaged. A large part of the radio frequency excitation pulse power is absorbed by the scanned object and converted into heat energy. If the tissue to be imaged absorbs too much radio frequency energy in a short period of time, local burns may occur or even cause greater safety problems. The radio frequency energy absorption rate (SAR) refers to the amount of radio frequency power absorbed per unit mass of tissue, and the unit is watts per kilogram (W / kg). It can be used as an indicator to measure the safety of MRI. At present, some safety regulations and international standards have detailed provisions for the upper limit of SAR for various types of scanned objects and various parts of the body during magnetic resonance scanning. Summary of the invention

[0004] The embodiments of the present application provide a magnetic resonance scanning imaging method and a magnetic resonance imaging system.

[0005] According to one aspect of an embodiment of the present application, a magnetic resonance imaging method is provided, the method comprising:

[0006] Determining a pulse to be adjusted in a scanning sequence, wherein the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse;

[0007] determining an adjustment factor based on the first gradient pulse and a shortest repetition time associated with a specific absorption rate of radio frequency energy;

[0008] adjusting the scanning sequence according to the adjustment factor;

[0009] The adjusted scanning sequence is used to perform a diagnostic scan on the part to be examined to obtain a magnetic resonance image.

[0010] According to one aspect of an embodiment of the present application, a magnetic resonance imaging system is provided, the system comprising:

[0011] Scanning unit;

[0012] A controller is used to determine a pulse to be adjusted in a scanning sequence, wherein the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse; determine an adjustment factor according to the first gradient pulse and a shortest repetition time related to a specific absorption rate of radio frequency energy; adjust the scanning sequence according to the adjustment factor; and control the scanning unit to perform a diagnostic scan on a part to be examined using the adjusted scanning sequence to obtain a magnetic resonance image.

[0013] One of the beneficial effects of the embodiments of the present application is that an adjustment factor is determined based on a first gradient pulse applied simultaneously with a first radio frequency pulse and a shortest repetition time related to a specific absorption rate of radio frequency energy, a scanning sequence is adjusted based on the adjustment factor, and a diagnostic scan is performed on the part to be examined using the adjusted scanning sequence, thereby minimizing the scanning time as much as possible in a low SAR mode with a low computational cost.

[0014] With reference to the following description and accompanying drawings, the specific implementation of the embodiment of the present application is disclosed in detail, indicating the way in which the principle of the embodiment of the present application can be adopted. It should be understood that the implementation of the present application is not limited in scope. Within the scope of the spirit and clauses of the attached claims, the implementation of the present application includes many changes, modifications and equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The included drawings are used to provide a further understanding of the embodiments of the present application, which constitute a part of the specification, are used to illustrate the implementation methods of the present application, and together with the text description, explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other implementation methods can be obtained based on these drawings without creative work. In the drawings:

[0016] Figure 1 This is a schematic diagram of the scanning time in normal SAR mode;

[0017] Figure 2 This is a schematic diagram of the scanning time in low SAR mode;

[0018] Figure 3 It is a schematic diagram of the relationship between scanning time and SAR value;

[0019] Figure 4 is a schematic diagram of a magnetic resonance scanning imaging method according to an embodiment of the present application;

[0020] Figure 5 is a schematic diagram of scanning time for an original scanning sequence and an adjusted scanning sequence according to an embodiment of the present application;

[0021] Figure 6 is a schematic diagram of a first radio frequency pulse and a first gradient pulse in an embodiment of the present application;

[0022] Figure 7 is a schematic diagram of the adjusted first radio frequency pulse and the first gradient pulse in an embodiment of the present application;

[0023] Figure 8 is the adjustment factor of the embodiment of the present application and max_seqsar and t min Relationship diagram;

[0024] Fig. 9 is a schematic diagram of a magnetic resonance scanning imaging method according to an embodiment of the present application;

[0025] Fig.10 is a schematic diagram of a magnetic resonance imaging system according to an embodiment of the present application;

[0026] Fig.11 Schematic diagram of an adjustment factor determination device according to an embodiment of the present application. DETAILED DESCRIPTION

[0027] With reference to the accompanying drawings, the foregoing and other features of the embodiments of the present application will become apparent through the following description. In the description and the accompanying drawings, specific embodiments of the present application are specifically disclosed, which show some embodiments in which the principles of the embodiments of the present application can be adopted. It should be understood that the present application is not limited to the described embodiments. On the contrary, the embodiments of the present application include all modifications, variations and equivalents that fall within the scope of the attached claims.

[0028] In the embodiments of the present application, the terms "first", "second", etc. are used to distinguish different elements in terms of title, but do not indicate the spatial arrangement or temporal order of these elements, etc., and these elements should not be limited by these terms. The term "and / or" includes any one and all combinations of one or more of the associated listed terms. The terms "comprising", "including", "having", etc. refer to the presence of the stated features, elements, components or components, but do not exclude the presence or addition of one or more other features, elements, components or components.

[0029] In the embodiments of the present application, the singular forms "a", "the", etc. include plural forms and should be broadly understood as "a kind" or "a type" rather than being limited to the meaning of "one"; in addition, the term "said" should be understood to include both singular and plural forms, unless the context clearly indicates otherwise. In addition, the term "according to" should be understood as "at least in part according to...", and the term "based on" should be understood as "at least in part based on...", unless the context clearly indicates otherwise.

[0030] Features described and / or shown for one embodiment may be used in one or more other embodiments in the same or similar manner, combined with features in other embodiments, or replace features in other embodiments. The term "includes / comprising" when used herein refers to the presence of a feature, an entirety, a step, or a component, but does not exclude the presence or addition of one or more other features, entireties, steps, or components.

[0031] For ease of understanding, Fig.10 A magnetic resonance imaging (MRI) system 100 of some embodiments of the present invention is shown.

[0032] The MRI system 100 includes a scanning unit 111. The scanning unit 111 is used to perform magnetic resonance scanning on an object (eg, a human body) 170 to generate image data of a region of interest of the object 170, where the region of interest may be a predetermined anatomical site or anatomical tissue.

[0033] The operation of the MRI system 100 is controlled by an operator workstation 110, which includes an input device 114, a control panel 116, and a display 118. The input device 114 can be a joystick, a keyboard, a mouse, a trackball, a touch-activated screen, voice control, or any similar or equivalent input device. The control panel 116 can include a keyboard, a touch-activated screen, voice control, buttons, a slider, or any similar or equivalent control device. The operator workstation 110 is coupled to and communicates with a computer system 120, which enables an operator to control the generation and viewing of images on the display 118. The computer system 120 includes multiple components that communicate with each other via electrical and / or data connection modules 122. The connection module 122 can be a direct wired connection, an optical fiber connection, a wireless communication link, etc. The computer system 120 can include a central processing unit (CPU) 124, a memory 126, and an image processor 128. In some embodiments, the image processor 128 can be replaced by image processing functions implemented in the CPU 124. The computer system 120 may be connected to an archival media device, permanent or backup storage, or a network. The computer system 120 may be coupled to and communicate with a separate MRI system controller 130 .

[0034] The MRI system controller 130 includes a set of components that communicate with each other via an electrical and / or data connection module 132. The connection module 132 can be a direct wired connection, an optical fiber connection, a wireless communication link, etc. The MRI system controller 130 can include a CPU 131, a sequence pulse generator 133 that communicates with the operator workstation 110, a transceiver (or RF transceiver) 135, a memory 137, and an array processor 139. In some embodiments, the sequence pulse generator 133 can be integrated into the resonance assembly 140 of the scanning unit 111 of the MRI system 100. The MRI system controller 130 can receive commands from the operator workstation 110, coupled to the scanning unit 111, to indicate the MRI scanning sequence to be performed during the MRI scan, so as to control the scanning unit 111 to perform the above-mentioned magnetic resonance scanning process. The MRI system controller 130 is also coupled to and communicates with a gradient driver system 150, which is coupled to the gradient coil assembly 142 to generate a magnetic field gradient during the MRI scan.

[0035] The sequence pulse generator 133 may also receive data from a physiological acquisition controller 155, which receives signals from a plurality of different sensors (such as electrocardiogram (ECG) signals from electrodes attached to the patient) connected to a subject or patient 170 undergoing an MRI scan. The sequence pulse generator 133 is coupled to and in communication with a scan room interface system 145, which receives signals from various sensors associated with the state of the resonance assembly 140. The scan room interface system 145 is also coupled to and in communication with a patient positioning system 147, which sends and receives signals to control the movement of the patient table to a desired position for an MRI scan.

[0036] The MRI system controller 130 provides gradient waveforms to the gradient driver system 150, which includes a G x (x direction), G y (y direction) and G z (z direction) amplifier, etc. Each G x , G y and G z The gradient amplifiers all excite corresponding gradient coils in a gradient coil assembly 142 to generate magnetic field gradients for spatially encoding MR signals during an MRI scan. The gradient coil assembly 142 is disposed within a resonance assembly 140, which also includes a superconducting magnet having superconducting coils 144 that, in operation, provide a static uniform longitudinal magnetic field B throughout a cylindrical imaging volume 146. 0 The resonance assembly 140 also includes an RF body coil 148 that provides a transverse magnetic field B during operation. 1 , the transverse magnetic field B 1The cylindrical imaging volume 146 is substantially perpendicular to B. 0 The resonance assembly 140 may also include an RF surface coil 149 for imaging different anatomical structures of a patient undergoing an MRI scan. The RF body coil 148 and the RF surface coil 149 may be configured to operate in a transmit and receive mode, a transmit mode, or a receive mode.

[0037] The x direction can also be called the frequency encoding direction or the k direction in K space. x The y direction can be called the phase encoding direction or the k direction in K space. y Direction. x It can be used for frequency encoding or signal readout and is usually called frequency encoding gradient or readout gradient. y Can be used for phase encoding, usually called phase encoding gradient. G z It can be used for slice (layer) position selection to obtain K-space data. It should be noted that the slice selection direction, phase encoding direction and frequency encoding direction can be modified according to actual needs.

[0038] An MRI scanned subject or patient 170 may be positioned within a cylindrical imaging volume 146 of the resonance assembly 140. A transceiver 135 in the MRI system controller 130 generates RF excitation pulses that are amplified by an RF amplifier 162 and provided to an RF body coil 148 via a transmit / receive switch (T / R switch) 164.

[0039] As described above, the RF body coil 148 and the RF surface coil 149 can be used to transmit RF excitation pulses and / or receive the resulting MR signals from the patient undergoing the MRI scan. The MR signals emitted by the nuclei excited in the patient's body of the MRI scan can be sensed and received by the RF body coil 148 or the RF surface coil 149 and sent back to the preamplifier 166 through the T / R switch 164. The T / R switch 164 can be controlled by a signal from the sequence pulse generator 133 to electrically connect the RF amplifier 162 to the RF body coil 148 during the transmit mode, and to connect the preamplifier 166 to the RF body coil 148 during the receive mode. The T / R switch 164 can also enable the RF surface coil 149 to be used in the transmit mode or the receive mode.

[0040] In some embodiments, the MR signals sensed and received by the RF body coil 148 or the RF surface coil 149 and amplified by the preamplifier 166 are stored as a raw k-space data array in the memory 137 for post-processing. A reconstructed magnetic resonance image can be acquired by transforming / processing the stored raw k-space data.

[0041] In some embodiments, the MR signals sensed and received by the RF body coil 148 or the RF surface coil 149 and amplified by the preamplifier 166 are demodulated, filtered, and digitized in the receive portion of the transceiver 135 and transmitted to the memory 137 in the MRI system controller 130. For each image to be reconstructed, the data is rearranged into a separate k-space data array, and each of these separate k-space data arrays is input to an array processor 139, which is operated to Fourier transform the data into an array of image data.

[0042] The array processor 139 uses a transform method, most commonly a Fourier transform, to create images from the received MR signals. These images are transmitted to the computer system 120 and stored in the memory 126. In response to commands received from the operator workstation 110, the image data may be stored in long-term storage or may be further processed by the image processor 128 and transmitted to the operator workstation 110 for presentation on the display 118.

[0043] In various embodiments, components of computer system 120 and MRI system controller 130 may be implemented on the same computer system or multiple computer systems. Fig.10 The MRI system 100 shown is for illustration purposes. Suitable MRI systems may include more, fewer, and / or different components.

[0044] The MRI system controller 130 and the image processor 128 may include a computer processor and a storage medium, respectively or in common, on which a program for predetermined data processing to be executed by the computer processor is recorded, for example, the storage medium may store a program for implementing scanning processing (e.g., scanning process, imaging sequence), image reconstruction, image processing, etc. For example, a program for implementing the magnetic resonance imaging method of the embodiment of the present invention may be stored. The above-mentioned storage medium may include, for example, a ROM, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, or a non-volatile memory card.

[0045] The above-mentioned "imaging sequence" (hereinafter also referred to as scanning sequence or pulse sequence) refers to a combination of pulses with specific amplitude, width, direction and timing applied when performing magnetic resonance imaging scanning, and these pulses can generally include, for example, radio frequency pulses and gradient pulses. The radio frequency pulses can include, for example, radio frequency excitation pulses, radio frequency refocusing pulses, inversion recovery pulses, etc. The gradient pulses can include, for example, the above-mentioned gradient pulses for layer selection, gradient pulses for phase encoding, gradient pulses for frequency encoding, gradient pulses for phase offset (phase shift), gradient pulses for discrete phase (dephasing), etc.

[0046] Generally, a plurality of scanning sequences can be pre-set in a magnetic resonance system so that a sequence suitable for clinical detection requirements can be selected. The clinical detection requirements may include, for example, imaging site, imaging function, imaging effect, and the like.

[0047] Before scanning, you need to set the scanning parameters, including the SAR value. At present, when the scanned object is an infant or a pregnant woman, or the scanned object has a special disease (heart disease patient, fever patient or impaired secretion patient), or the scanned object wears an implant (prosthesis, pacemaker, stent, etc.) in or on the body, it is necessary to perform magnetic resonance scanning in low SAR mode. Therefore, the SAR value needs to be set relatively low when setting the parameters.

[0048] Figure 1 is a schematic diagram of scanning time in normal SAR mode (for example, SAR=3), Figure 2 is a schematic diagram of the scanning time in low SAR mode (for example, SAR=0.5), Figure 1 and Figure 2 Use the same scanning sequence as Figure 1 and 2 As shown, t min It indicates the shortest time required to transmit the scanning sequence, or the shortest scanning time required for the scanning sequence without considering the SAR value limit; after the scanning sequence is transmitted, a large part of it is absorbed by the scanned object and converted into heat energy, the SAR value will rise, and the waiting time t w Indicates the time required to wait for the heat energy to dissipate so that the SAR value returns to below the set value; max_seqsar is equal to t w With t min The sum of represents the shortest scanning time required for this scanning sequence considering the SAR value limitation. Figure 1 and Figure 2 As shown, if the SAR value is set to a lower value, the waiting time will be longer. Figure 3 This is a schematic diagram of the relationship between scanning time and SAR value, such as Figure 3 As shown in the figure, for the same scanning sequence, as the SAR value decreases, the scanning time increases significantly. In other words, since the low SAR mode has a very low SAR value limit, it will cause a significant increase in scanning time.

[0049] In order to solve at least one of the above problems, the embodiments of the present application provide a magnetic resonance scanning imaging method and a magnetic resonance imaging system.

[0050] The following is a description with reference to embodiments.

[0051] The present application embodiment provides a magnetic resonance scanning imaging method, Figure 4 Schematic diagram of the magnetic resonance imaging method according to an embodiment of the present application. Figure 4 As shown, the method includes:

[0052] 401, determining a pulse to be adjusted in a scanning sequence, where the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse;

[0053] 402, determining an adjustment factor according to the first gradient pulse and a shortest repetition time related to a specific absorption rate of radio frequency energy;

[0054] 403, adjusting the scanning sequence according to the adjustment factor;

[0055] 404 , use the adjusted scanning sequence to perform a diagnostic scan on the part to be examined to obtain a magnetic resonance image.

[0056] In some embodiments, the scanning sequence includes at least a radio frequency pulse and a gradient pulse applied along with the radio frequency pulse. The radio frequency pulse may include at least one of an excitation pulse and a refocusing pulse. Optionally, it may also include pre-preparation pulses such as an inversion recovery pulse and a fat suppression pulse. The gradient pulse may include at least one of a gradient pulse for layer selection, a gradient pulse for frequency encoding, and a gradient pulse for phase encoding. Optionally, the scanning sequence may also include a gradient pulse that is not applied along with the radio frequency pulse, and the embodiments of the present application are not limited thereto. For example, the scanning sequence may include a gradient echo pulse sequence (GRE), a fast spin echo pulse sequence (FSE), etc., which are not listed one by one here.

[0057] In some embodiments, in 401, a pulse to be adjusted in a scanning sequence is determined, the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse, and the first radio frequency pulse includes at least one of an excitation pulse and a refocusing pulse. That is, the first radio frequency pulse to be adjusted can be selected from the radio frequency pulses in the scanning sequence, if the radio frequency pulses in the scanning sequence are at least one of an excitation pulse or a refocusing pulse, and the radio frequency pulses in the scanning sequence are all accompanied by the application of gradient pulses, then the radio frequency pulses in the scanning sequence can all be used as the first radio frequency pulse. In other words, if there is an radio frequency pulse in the scanning sequence that is an inversion recovery pulse or a fat suppression pulse, or there is an radio frequency pulse that is not accompanied by the application of a gradient pulse, then the radio frequency pulse cannot be used as the first radio frequency pulse. Therefore, the radio frequency pulse accompanied by the application of a gradient pulse in the scanning sequence and that is an excitation pulse or a refocusing pulse is used as the first radio frequency pulse. In addition, the first gradient pulse to be adjusted is a gradient pulse applied along with the first radio frequency pulse, which can include at least one of a gradient pulse for layer selection, a gradient pulse for frequency encoding, and a gradient pulse for phase encoding.

[0058] The above is only an example, but the embodiments of the present application are not limited thereto. For example, when all RF pulses in a scanning sequence are excitation pulses and are accompanied by gradient pulses, only some of the RF pulses may be selected as the first RF pulses. Examples are not given one by one here.

[0059] In some embodiments, the scanning sequence further includes a second gradient pulse that is not accompanied by the first radio frequency pulse; wherein, the second gradient pulse that is not accompanied by the first radio frequency pulse may be a gradient pulse that is not accompanied by all radio frequency pulses in the scanning sequence (scenario one), or may be a gradient pulse that is accompanied by an inversion recovery pulse or a fat suppression pulse in the scanning sequence (scenario two). The following embodiments are illustrated by taking scenario one as an example in which the second gradient pulse is an example. In addition, when there are multiple gradient pulses that meet the conditions in scenario one and scenario two, any gradient pulse can be selected from them as the second gradient pulse, and the embodiments of the present application are not limited thereto.

[0060] In some embodiments, after the pulse to be adjusted is selected in 401, the waveform and timing of the scanning sequence can be generated according to the set scanning parameters (such as layer thickness, scanning matrix size, sampling bandwidth and other parameters) and the type of scanning sequence.

[0061] In an embodiment of the present application, an adjustment factor is determined according to the first gradient pulse and a shortest repetition time associated with a specific absorption rate (SAR) of radio frequency energy, or the adjustment factor is determined according to the first gradient pulse, the second gradient pulse, and a shortest repetition time associated with a specific absorption rate of radio frequency energy, and a scanning sequence is adjusted based on the adjustment factor determined in the above manner, and scanning is performed using the adjusted scanning sequence, thereby minimizing the scanning time and the repetition time TR in the low SAR mode. The principle is first described below.

[0062] like Figure 1 and Figure 2 As shown, in the low SAR mode, the scanning time is greatly increased due to the increase in the waiting time. If the waiting time is reduced, the scanning time can be saved, but this may not meet the SAR value limit. Therefore, in the low SAR mode, it is possible to consider adjusting the scanning sequence, for example, by reducing the amplitude value of the first RF pulse and the first gradient pulse in the scanning sequence, and increasing the width of the first RF pulse and the first gradient pulse, so that the transmission time of the scanning sequence becomes longer and the amplitude value becomes smaller, thereby reducing the SAR value without requiring a longer waiting time and meeting the SAR value limit. As for how to reduce the above amplitude value and increase the above width, the inventors found that when the waiting time is set to 0, that is, max_seqsar is equal to t min When the scan time and repetition time TR can be minimized, Figure 5Schematic diagram of scanning time for the original scanning sequence and the adjusted scanning sequence according to an embodiment of the present application. Figure 5 As shown, for the same SAR value, by reducing the amplitude value and increasing the width, the max_seqsar' of the adjusted scanning sequence is equal to t min ', compared to max_seqsar using the original scan sequence, it can save about t reduction Therefore, when the shortest time required to transmit the scanning sequence is equal to the shortest scanning time required for the scanning sequence considering the SAR value limitation, the scanning time and repetition time TR can be minimized. That is, the calculation makes max_seqsar equal to t min The adjustment factor is used, and the scanning sequence is adjusted according to the adjustment factor. The adjusted scanning sequence is used for scanning, thereby minimizing the scanning time and the repetition time TR in the low SAR mode.

[0063] The following explains the principle of how the adjustment factor is calculated.

[0064] Figure 6 is a schematic diagram of a first radio frequency pulse and a first gradient pulse in an embodiment of the present application, Figure 7 is a schematic diagram of a first radio frequency pulse and a first gradient pulse adjusted according to an adjustment factor in an embodiment of the present application, Figure 6 and Figure 7 For the same SAR value limit, the adjustment factor is greater than 0 and less than 1. The first radio frequency pulse may be a sinc wave, but the embodiment of the present application is not limited thereto. The pulse width of the first radio frequency pulse is t L The maximum gradient intensity of the first gradient pulse is G max The gradient climbing time indicates the time required for the gradient field to reach the maximum gradient intensity value from 0, and the gradient descending time indicates the time required for the gradient field to decrease from the maximum gradient intensity value to 0. The gradient climbing time is equal to the gradient descending time. For the convenience of explanation, t slop It is expressed as the sum of the gradient climbing time and the gradient descending time, or t slop It is equal to 2 times the climbing time. The gradient switching rate is an indicator that describes the speed of gradient length change. It indicates the change of gradient field strength per unit time. The calculation formula of gradient switching rate is: gradient switching rate = maximum gradient strength value ÷ climbing time. The duration of maximum gradient strength is the upper base length t of the trapezoid. plat .like Figure 6 As shown, for the first RF pulse 61, the amplitude value of each location of the first RF pulse is multiplied by the adjustment factor, and the pulse width of the first RF pulse is divided by the adjustment factor to obtain Figure 7 The adjusted first radio frequency pulse 71 shown, that is, the adjusted pulse width t of the first radio frequency pulse L' increases, the amplitude value decreases, but the area of ​​the figure enclosed by the waveform of the first RF pulse and the time axis before and after the adjustment remains unchanged. Figure 6 As shown, for the first gradient pulse 62, the duration t of the maximum gradient strength of the first gradient pulse is plat Divide by the adjustment factor, the maximum gradient intensity value G of the first gradient pulse max and the rise time (or fall time or t slop ) is multiplied by the adjustment factor, and the gradient switching rate remains unchanged, so we get Figure 7 An adjusted first gradient pulse 72 is shown.

[0065] Figure 8 is the adjustment factor of the embodiment of the present application and max_seqsar and t min Relationship diagram, such as Figure 8 As shown, the inventors found that under the same SAR value limit, max_seqsar decreases approximately linearly with the decrease of the adjustment factor, t min As the adjustment factor decreases, it increases roughly exponentially. As shown in the previous analysis, using max_seqsar equal to t min The adjustment factor at this time can minimize the scanning time and repetition time TR, that is, Figure 8 The adjustment factor corresponding to the intersection of the two lines is the optimal adjustment factor, which can minimize the scanning time and the repetition time TR. The following describes how to calculate the optimal adjustment factor f.

[0066] In some embodiments, when the scanning sequence does not include the second gradient pulse, the adjustment factor is determined according to the first gradient pulse and the shortest repetition time related to the specific absorption rate of radio frequency energy, and when the scanning sequence includes the second gradient pulse, the adjustment factor is determined according to the first gradient pulse, the second gradient pulse and the shortest repetition time related to the specific absorption rate of radio frequency energy. The following are respectively described.

[0067] (I) Scan sequence includes second gradient pulse

[0068] In some embodiments, the first gradient pulse is set to the same value according to the ramp time (eg, t slop ), duration t of the maximum gradient intensity of the first gradient pulse plat , the time difference t between the end time of the second gradient pulse and the end time of the first gradient pulse untouched and the shortest repetition time TR minThe adjustment factor (optimal adjustment factor f) is determined. The adjustment factor (optimal adjustment factor f) is such that: the product of the shortest repetition time and the adjustment factor is equal to the sum of the time difference and the first time and the second time, the first time is equal to twice the product of the climbing time and the adjustment factor, and the second time is equal to the ratio of the duration to the adjustment factor.

[0069] like Figure 6 and Figure 7 As shown, the scanning sequence may further include the aforementioned second gradient pulse 60. When calculating the adjustment factor, the second gradient pulse needs to be considered, but the second gradient pulse does not need to be adjusted by the adjustment factor. The time difference between the end time of the second gradient pulse and the end time of the first gradient pulse is expressed as t untouched max_seqsar can be set based on the shortest repetition time TR associated with the specific absorption rate of RF energy (e.g. the SAR value set in low SAR mode). min Sure, Wherein, JSTD represents the heat energy (known quantity) generated by each single standard pulse, in joules, #stdrf represents the number of standard pulses in the scanning sequence, mass represents the mass of the detected object, and SAR represents the set SAR value, such as the SAR value set in the low SAR mode.

[0070] Before the scanning sequence is adjusted, t min =t plat +t slop +t untouched ,max_seqsar=TR min =t min +t w ,like Figure 7 As shown, after adjusting the scan sequence using the adjustment factor f, max_seqsar' after adjusting the scan sequence = max_seqsar×f (this is due to Figure 8 As shown, max_seqsar is linearly related to f), and t after adjusting the scanning sequence min '=t plat '+t slop '+t untouched =t plat / f+t slop ×f+t untouched , the first time is t slop ', the second time is t plat ', the adjustment factor (optimal adjustment factor f) is such that: after adjusting the scanning sequence, the waiting time t w is 0, max_seqsar' = t min', that is, the product of the shortest repetition time and the adjustment factor is equal to the sum of the time difference and the first time and the second time: TR min ×f=t plat '+t slop '+t untouched =t plat / f+t slop ×f+t untouched In the above formula, there is only the unknown quantity f, then

[0071] In some embodiments, after the waveform and timing of the scanning sequence are generated, t can be determined according to the waveform and timing of the scanning sequence, the second gradient pulse and the selected first gradient pulse. untouched , t slop , t flat The value of , determines the number of standard pulses in the scanning sequence, the mass of the object to be detected and the SAR value in the set parameters, and substitutes them into formula (1) to calculate TR min , the above value t untouched , t slop , t flat , TR min Substitute into formula (2) to calculate the value of the adjustment factor f. In addition, the adjustment factor must be greater than 0 and less than 1.

[0072] (ii) The scanning sequence does not include the second gradient pulse

[0073] In some embodiments, the adjustment factor (optimal adjustment factor f) is determined according to the rise time of the first gradient pulse, the duration of the maximum gradient intensity of the first gradient pulse, and the shortest repetition time. The adjustment factor (optimal adjustment factor f) is an adjustment factor such that: the product of the shortest repetition time and the adjustment factor is equal to the sum of the first time and the second time, the first time is equal to twice the product of the rise time and the adjustment factor, and the second time is equal to the ratio of the duration to the adjustment factor.

[0074] The difference from (a) is that since the second gradient pulse is not included, t untouched is 0, therefore, replace t in formula (1) untouched Set to 0, and get After the waveform and timing of the scanning sequence are generated, t slop , t flat The value of , determines the number of standard pulses in the scanning sequence, the mass of the object to be detected and the SAR value in the set parameters, and substitutes them into formula (1) to calculate TR min , the above value t slop , tflat , TR min Substitute into formula (3) and calculate the value of the adjustment factor f. In addition, the adjustment factor must be greater than 0 and less than 1.

[0075] In some embodiments, the size of the adjustment factor is also related to the image quality. When the adjustment factor is larger (for example, closer to 1), the image quality is better, the image is clearer, and the contrast is higher. When the adjustment factor is smaller (for example, closer to 0), the image quality is worse, the image is more blurred, and the contrast is lower. In other words, if the calculated adjustment factor is too small, the quality of the magnetic resonance image will be poor. Therefore, the method may also include: when the adjustment factor is less than or equal to the preset factor, the value of the adjustment factor is replaced by the value of the preset factor. In other words, when the adjustment factor is less than or equal to the preset factor size, the preset factor is used to adjust the scanning sequence. In this way, the scanning time can be saved in the low SAR mode while ensuring the image quality. The preset factor can be predefined and unchanged or can be set adjustable by the operator. Its size is related to the image quality requirements. For example, the preset factor can be set to 0.5, etc., and the present application is not limited to this.

[0076] In some embodiments, after determining the adjustment factor, in 403, the scanning sequence is adjusted according to the adjustment factor, including adjusting the first radio frequency pulse and the first gradient pulse selected in the scanning sequence according to the adjustment factor, and other pulses (if any) in the scanning sequence do not need to be adjusted. The amplitude value of the first radio frequency pulse, the maximum gradient intensity value of the first gradient pulse, and the climbing time of the first gradient pulse in the scanning sequence are multiplied by the adjustment factor respectively; the pulse width of the first radio frequency pulse and the duration of the maximum gradient intensity of the first gradient pulse are divided by the adjustment factor to obtain the adjusted scanning sequence.

[0077] In some embodiments, for the first radio frequency pulse, the amplitude value of each part of the first radio frequency pulse is multiplied by the adjustment factor, and the pulse width of the first radio frequency pulse is divided by the adjustment factor. After adjustment, the pulse width of the first radio frequency pulse increases, and the amplitude value decreases, but the area of ​​the graph formed by the waveform of the first radio frequency pulse and the time axis before and after the adjustment remains unchanged. For the first gradient pulse, the duration t of the maximum gradient intensity of the first gradient pulse is plat Divide by the adjustment factor, multiply the maximum gradient intensity value of the first gradient pulse and the rise time (and fall time) of the first gradient pulse by the adjustment factor, and keep the gradient switching rate unchanged. After adjusting the first RF pulse and the first gradient pulse, the timing of some other pulses (if any) in the scanning sequence may change accordingly (for example, be delayed, etc.), and the waveform and timing of the scanning sequence can be regenerated.

[0078] In some embodiments, in 404, the adjusted scanning sequence is used to perform a diagnostic scan on the part to be examined to obtain a magnetic resonance image. When the adjusted scanning sequence is used to scan the part to be examined, the shortest time t required to transmit the adjusted scanning sequence is min = is equal to the shortest scanning time max_seqsar required for the adjusted scanning sequence considering the limitation of the SAR value. In addition, the method for acquiring magnetic resonance images can refer to the relevant technology, and the embodiments of the present application are not limited thereto.

[0079] In some embodiments, if the next scanning object is to be scanned, the above scanning imaging method will be repeatedly performed.

[0080] Fig. 9 Schematic diagram of the magnetic resonance imaging method according to an embodiment of the present application. Fig. 9 As shown, the method includes:

[0081] 901, determining a pulse to be adjusted in a scanning sequence, where the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse;

[0082] 902, determining a second gradient pulse;

[0083] 903, generate the waveform and timing of the scanning sequence, determine t untouched , t slop , t flat , TR min ;

[0084] 904, determine the adjustment factor;

[0085] 905, judging whether the adjustment factor is less than or equal to the preset factor; if the judgment result is yes, proceed to 906, otherwise, proceed directly to 907;

[0086] 906, replacing the value of the adjustment factor with the value of the preset factor;

[0087] 907, adjusting the scanning sequence according to the adjustment factor;

[0088] 908 , use the adjusted scanning sequence to perform a diagnostic scan on the part to be examined to obtain a magnetic resonance image.

[0089] The specific implementation of 901-908 has been described above and will not be repeated here.

[0090] Through the above embodiment, an adjustment factor is determined according to the first gradient pulse applied simultaneously with the first radio frequency pulse and the shortest repetition time related to the specific absorption rate of radio frequency energy, the scanning sequence is adjusted according to the adjustment factor, and the adjusted scanning sequence is used to perform a diagnostic scan on the part to be examined, thereby minimizing the scanning time as much as possible in the low SAR mode, and the calculation cost is low.

[0091] The present application also provides a magnetic resonance imaging system. The magnetic resonance imaging system is composed of Fig.10 As shown, the repeated parts will not be repeated.

[0092] In some embodiments, Fig.10 The difference between the aforementioned magnetic resonance imaging system and the aforementioned magnetic resonance imaging system is that the controller 130 is configured to execute the aforementioned magnetic resonance scanning imaging method, that is, it is also used to determine the pulse to be adjusted in the scanning sequence, and the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse; determine an adjustment factor according to the first gradient pulse and the shortest repetition time related to the specific absorption rate of radio frequency energy; adjust the scanning sequence according to the adjustment factor; control the scanning unit to use the adjusted scanning sequence to perform a diagnostic scan on the part to be examined to obtain a magnetic resonance image.

[0093] In some embodiments, the controller 130 (which may also be a processor) includes a computer processor and a storage medium, on which a program for predetermined data processing to be executed by the computer processor is recorded. For example, the storage medium may store a program for implementing scanning processing (for example, including waveform design / conversion, etc.), image reconstruction, image processing, etc. For example, a program for implementing the adjustment factor determination method of an embodiment of the present invention may be stored, the adjustment factor determination method including determining a pulse to be adjusted in a scanning sequence, the pulse to be adjusted including a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse; determining an adjustment factor according to the first gradient pulse and the shortest repetition time related to the specific absorption rate of radio frequency energy, optionally, the scanning sequence may also be adjusted according to the adjustment factor, and the specific implementation method thereof is as described above and will not be repeated here. The above-mentioned storage medium may include, for example, a ROM, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, or a non-volatile memory card.

[0094] The present application also provides a device for determining an adjustment factor. Fig.11 Schematic diagram of the adjustment factor determination device of the embodiment of the present application. Fig.11 As shown, the device 1100 includes:

[0095] A first determining unit 1101 is configured to determine a pulse to be adjusted in a scanning sequence, wherein the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse;

[0096] A first determining unit 1102 is configured to determine an adjustment factor according to the first gradient pulse and a shortest repetition time associated with a specific absorption rate of radio frequency energy.

[0097] The implementation of the first determining unit 1101 and the first determining unit 1102 are as described above and will not be repeated here.

[0098] An embodiment of the present application also provides a computer-readable program, wherein when the program is executed in a device or an MRI system, the program enables a computer to execute the adjustment factor determination method described in the above embodiment in the device or the MRI system.

[0099] An embodiment of the present application also provides a storage medium storing a computer-readable program, wherein the computer-readable program enables a computer to execute the adjustment factor determination method described in the above embodiment in a device or an MRI system.

[0100] The above devices and methods of the present application can be implemented by hardware, or by hardware combined with software. The present application relates to such a computer-readable program, which, when executed by a logic component, enables the logic component to implement the above-mentioned devices or components, or enables the logic component to implement the various methods or steps described above. The present application also relates to a storage medium for storing the above program, such as a hard disk, a magnetic disk, an optical disk, a DVD, a flash memory, etc.

[0101] The method / device described in conjunction with the embodiments of the present application may be directly embodied as hardware, a software module executed by a processor, or a combination of the two. For example, one or more of the functional block diagrams shown in the figure and / or one or more combinations of the functional block diagrams may correspond to various software modules of the computer program flow or to various hardware modules. These software modules may correspond to the various steps shown in the figure, respectively. These hardware modules may be implemented by solidifying these software modules, for example, using a field programmable gate array (FPGA).

[0102] The software module may be located in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. A storage medium may be coupled to a processor so that the processor can read information from the storage medium and write information to the storage medium; or the storage medium may be an integral part of the processor. The processor and the storage medium may be located in an ASIC. The software module may be stored in a memory of a mobile terminal or in a memory card that can be inserted into the mobile terminal. For example, if a device (such as a mobile terminal) uses a large-capacity MEGA-SIM card or a large-capacity flash memory device, the software module may be stored in the MEGA-SIM card or the large-capacity flash memory device.

[0103] For one or more of the functional blocks described in the drawings and / or one or more combinations of functional blocks, it can be implemented as a general-purpose processor, digital signal processor (DSP), application-specific integrated circuit (ASIC), field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware component or any appropriate combination thereof for performing the functions described in the present application. For one or more of the functional blocks described in the drawings and / or one or more combinations of functional blocks, it can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in communication with a DSP, or any other such configuration.

[0104] The present application is described above in conjunction with specific implementation methods, but it should be clear to those skilled in the art that these descriptions are exemplary and are not intended to limit the scope of protection of the present application. Those skilled in the art can make various modifications and variations to the present application based on the principles of the present application, and these modifications and variations are also within the scope of the present application.

[0105] Notes

[0106] 1. A method for determining an adjustment factor, characterized in that the method comprises:

[0107] Determining a pulse to be adjusted in a scanning sequence, wherein the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse;

[0108] An adjustment factor is determined based on the first gradient pulse and a shortest repetition time associated with a specific absorption rate of radio frequency energy.

[0109] 2. The method according to Note 1, characterized in that the method further comprises:

[0110] The scanning sequence is adjusted according to the adjustment factor.

[0111] 3. The method according to Supplementary Note 1, characterized in that the scanning sequence further comprises a second gradient pulse applied without accompanying the first radio frequency pulse;

[0112] Furthermore, the adjustment factor is determined according to the first gradient pulse, the second gradient pulse, and a shortest repetition time related to a specific absorption rate of radio frequency energy.

[0113] 4. The method according to Note 1, wherein determining the adjustment factor according to the first gradient pulse and the shortest repetition time associated with the specific absorption rate of radio frequency energy comprises:

[0114] The adjustment factor is determined according to a rise time of the first gradient pulse, a duration of a maximum gradient intensity of the first gradient pulse, and the shortest repetition time.

[0115] 5. The method according to Note 4 is characterized in that the product of the shortest repetition time and the adjustment factor is equal to the sum of the first time and the second time, the first time is equal to twice the product of the climbing time and the adjustment factor, and the second time is equal to the ratio of the duration to the adjustment factor.

[0116] 6. The method according to Note 3, characterized in that determining the adjustment factor according to the first gradient pulse, the second gradient pulse and the shortest repetition time related to the specific absorption rate of radio frequency energy comprises:

[0117] The adjustment factor is determined according to the rise time of the first gradient pulse, the duration of the maximum gradient intensity of the first gradient pulse, the time difference between the end time of the second gradient pulse and the end time of the first gradient pulse, and the shortest repetition time.

[0118] 7. The method according to Note 6 is characterized in that the product of the shortest repetition time and the adjustment factor is equal to the sum of the time difference, the first time and the second time, the first time is equal to twice the product of the climbing time and the adjustment factor, and the second time is equal to the ratio of the duration to the adjustment factor.

[0119] 8. The method according to Supplement 1, characterized in that the method further comprises:

[0120] When the adjustment factor is less than or equal to the preset factor, the value of the adjustment factor is replaced by the value of the preset factor.

[0121] 9. The method according to Note 2, wherein adjusting the scanning sequence according to the adjustment factor comprises:

[0122] multiplying the amplitude value of the first radio frequency pulse in the scanning sequence, the maximum gradient intensity value of the first gradient pulse, and the climbing time of the first gradient pulse by the adjustment factor respectively;

[0123] The pulse width of the first radio frequency pulse and the duration of the maximum gradient intensity of the first gradient pulse are divided by the adjustment factor to obtain an adjusted scanning sequence.

[0124] 10. A device for determining an adjustment factor, characterized in that the device comprises:

[0125] A first determining unit, which determines a pulse to be adjusted in a scanning sequence, wherein the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse;

[0126] A second determining unit is configured to determine an adjustment factor according to the first gradient pulse and a shortest repetition time associated with a specific absorption rate of radio frequency energy.

Claims

1. A magnetic resonance imaging method, characterized in that: The method comprises: Determining a pulse to be adjusted in a scanning sequence, wherein the pulse to be adjusted includes a first radio frequency pulse and a first gradient pulse applied along with the first radio frequency pulse; determining an adjustment factor based on the first gradient pulse and a shortest repetition time associated with a specific absorption rate of radio frequency energy; adjusting the scanning sequence according to the adjustment factor; The adjusted scanning sequence is used to perform a diagnostic scan on the part to be examined to obtain a magnetic resonance image.

2. The method according to claim 1, characterized in that The first radio frequency pulse includes at least one of an excitation pulse and a refocusing pulse.

3. The method according to claim 1, characterized in that The scanning sequence further includes a second gradient pulse applied not accompanying the first radio frequency pulse; Furthermore, the adjustment factor is determined according to the first gradient pulse, the second gradient pulse, and a shortest repetition time associated with a specific absorption rate of radio frequency energy.

4. The method according to claim 1, characterized in that: Determining the adjustment factor according to the first gradient pulse and the shortest repetition time associated with the specific absorption rate of radio frequency energy comprises: The adjustment factor is determined according to a rise time of the first gradient pulse, a duration of a maximum gradient intensity of the first gradient pulse, and the shortest repetition time.

5. The method according to claim 4, characterized in that The product of the shortest repetition time and the adjustment factor is equal to the sum of a first time and a second time, the first time is equal to twice the product of the climbing time and the adjustment factor, and the second time is equal to the ratio of the duration to the adjustment factor.

6. The method according to claim 3, characterized in that Determining the adjustment factor according to the first gradient pulse, the second gradient pulse, and the shortest repetition time associated with the specific absorption rate of radio frequency energy comprises: The adjustment factor is determined according to the rise time of the first gradient pulse, the duration of the maximum gradient intensity of the first gradient pulse, the time difference between the end time of the second gradient pulse and the end time of the first gradient pulse, and the shortest repetition time.

7. The method according to claim 6, characterized in that The product of the shortest repetition time and the adjustment factor is equal to the sum of the time difference, a first time, and a second time, the first time is equal to twice the product of the climbing time and the adjustment factor, and the second time is equal to the ratio of the duration to the adjustment factor.

8. The method according to claim 1, characterized in that The method further comprises: When the adjustment factor is less than or equal to the preset factor, the value of the adjustment factor is replaced by the value of the preset factor.

9. The method according to claim 1, characterized in that: Adjusting the scanning sequence according to the adjustment factor includes: multiplying the amplitude value of the first radio frequency pulse in the scanning sequence, the maximum gradient intensity value of the first gradient pulse, and the climbing time of the first gradient pulse by the adjustment factor respectively; The pulse width of the first radio frequency pulse and the duration of the maximum gradient intensity of the first gradient pulse are divided by the adjustment factor to obtain an adjusted scanning sequence.

10. The method according to claim 1, characterized in that The adjustment factor is greater than 0 and less than 1.

11. A magnetic resonance imaging system, characterized in that: The system comprises: Scanning unit; A controller configured to execute the magnetic resonance scanning imaging method according to any one of claims 1 to 10.

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