Medical image processing method, magnetic resonance imaging system, and medical image processing program

Abstract

To maintain a uniform B1 magnetic field through a series of scans.SOLUTION: A medical image processing method according to an embodiment includes: acquiring a first B1 amplitude measurement sequence interspersed within a series of MRI scan sequences which is used in a single MRI examination and includes a first MRI scan sequence and a second MRI scan sequence having a first RF parameter value; executing the first MRI scan sequence and the first B1 amplitude measurement sequence; determining whether to change the first RF parameter value for the second MRI scan sequence according to a measurement result of the first B1 amplitude measurement sequence; when it is determined to change the first RF parameter value according to the measurement result, changing the first RF parameter value to a second RF parameter value different from the first RF parameter value; and executing the second MRI scan sequence using the second RF parameter value.SELECTED DRAWING: Figure 3A

Description

[Technical field]

[0001] The embodiments disclosed in the present specification and drawings relate to a medical image processing method, a magnetic resonance imaging system, and a medical image processing program. The embodiments disclosed in the present specification relate to a method, a system, and a computer program product for modifying a part of a series of magnetic resonance imaging (MRI) scan sequences used in a single MRI examination. In one embodiment, the present invention relates to a method and a system for performing at least one B1 amplitude measurement sequence interspersed in a series of MRI scan sequences, and an RF parameter value (e.g., flip angle or transmit amplification gain) of at least one scan sequence of the series of MRI scan sequences is modified based on a result of performing at least the interspersed B1 amplitude measurement sequence. [Background technology]

[0002] When imaging a patient using an MRI system, the patient enters a gantry of the MRI system and a series of scan sequences (scan sequence 1 to scan sequence 2 in FIG. 1 ) each containing a number of shots (m shots in scan sequence 2 in FIG. 1 ) are performed. n After the patient has completed a series of scan sequences in the patient examination, the patient exits the MRI system.

[0003] Known MRI systems are calibrated for each patient before the start of the examination to determine a reference RF transmission gain level (RFL (RF level): reference RFL value) as shown in the pre-scan sequence of FIG. 1. The reference RFL value is used to calculate a transmission gain value to achieve the intended B1 amplitude for all subsequent RF pulses in the MRI scan sequence. As will be appreciated by those skilled in the art, the B1 amplitude of an RF pulse is directly related to the flip angle of the RF pulse, which is the primary determinant of MR signal strength and image contrast. That is, the RFL value has a known direct relationship with the B1 field and flip angle. By measuring the B1 field, the RFL can be calculated directly and easily.

[0004] It is known that the RFL is affected by (a) the patient weight and (b) the Tx coil (transmit coil) weight, including the receive coil absorbance, and is also affected by the power efficiency (transmit / reflect) which can be affected by the temperature conditions of (1) the Tx coil, (2) the RF shield, (3) the RF amplifier, and (4) the gradient coil.

[0005] Sacolick et al., in “Magnetic Resonance in Medicine 66:1333-1338 (2011)” (herein incorporated by reference), propose using the Bloch-Siegert Shift (BSS) method for RFL calibration. “For transmit gain (TG) to flip angle calibration,” Sacolick et al. + It describes an "automated prescan" in "preparation for an MRI scan" in which the "magnitude of the magnetic field" is measured, and points out that "the relationship between the radiofrequency (RF) power output to the transmit coil and the generated B1 magnetic field depends on the patient's size, orientation, shape, and body composition...the flip angle or B1 transmit field magnitude is measured for one or more starting system TG levels, and the adjustment required to produce the desired flip angle or B1 field RF pulse is calculated." [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 8,558,547 [Patent Document 2] U.S. Pat. No. 9,606,209 [Patent Document 3] U.S. Patent No. 9,977,108 [Patent Document 4] U.S. Patent No. 9,987,617 [Patent Document 5] U.S. Pat. No. 1,064,1853 [Patent Document 6] U.S. Pat. No. 1,083,0851 [Patent Document 7] U.S. Pat. No. 1,089,0631 [Patent Document 8] U.S. Pat. No. 1,147,4173 [Patent Document 9] U.S. Pat. No. 1,157,9219 [Patent Document 10] US Patent Application Publication No. 2011 / 211744 [Patent Document 11] US Patent Application Publication No. 2012 / 271571 [Patent Document 12] US Patent Application Publication No. 2013 / 249553 [Patent Document 13] US Patent Application Publication No. 2013 / 251227 [Patent Document 14] US Patent Application Publication No. 2014 / 103925 [Patent Document 15] US Patent Application Publication No. 2014 / 105476 [Patent Document 16] US Patent Application Publication No. 2014 / 171784 [Patent Document 17] US Patent Application Publication No. 2014 / 350439 [Patent Document 18] US Patent Application Publication No. 2015 / 002149 [Patent Document 19] US Patent Application Publication No. 2015 / 309141 [Patent Document 20] US Patent Application Publication No. 2016 / 018502 [Patent Document 21] US Patent Application Publication No. 2016 / 187438 [Patent Document 22] US Patent Application Publication No. 2018 / 067176 [Patent Document 23] US Patent Application Publication No. 2018 / 246178 [Patent Document 24] US Patent Application Publication No. 2020 / 049786 [Patent Document 25] US Patent Application Publication No. 2020 / 142057 [Patent Document 26] US Patent Application Publication No. 2020 / 319367 [Patent Document 27] US Patent Application Publication No. 2020 / 319372 [Patent Document 28] US Patent Application Publication No. 2020 / 341090 [Patent Document 29] US Patent Application Publication No. 2020 / 393526 [Patent Document 30] US Patent Application Publication No. 2021 / 018583 [Patent Document 31] US Patent Application Publication No. 2021 / 208219 [Patent Document 32] US Patent Application Publication No. 2022 / 0026511 [Patent Document 33] US Patent Application Publication No. 2022 / 397621 [Patent Document 34] International Publication No. 2008 / 135872 [Non-patent literature]

[0007]

Non-licensed literature 1

Non-licensed Document 4

Non-licensed Document 5

Non-licensed Document 6

[0008] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to maintain a uniform B1 magnetic field throughout a series of scans. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0009] A medical image processing method according to an embodiment includes the steps of: acquiring a first B1 amplitude measurement sequence used in one MRI examination and mixed within a series of MRI scan sequences including a first MRI scan sequence and a second MRI scan sequence having a first RF parameter value; executing the first MRI scan sequence and the first B1 amplitude measurement sequence; determining whether or not to change a first RF parameter value for the second MRI scan sequence based on a measurement result of the first B1 amplitude measurement sequence; and, when it is determined based on the measurement result that the first RF parameter value is to be changed, changing the first RF parameter value to a second RF parameter value different from the first RF parameter value, and executing the second MRI scan sequence using the second RF parameter value. [Brief description of the drawings]

[0010] [Figure 1]FIG. 1 illustrates an examination of a patient including a series of scan sequences each including an optional pre-scan and successive shots. [Diagram 2] FIG. 2 is a schematic block diagram of an MRI system according to one embodiment of the present disclosure. [Figure 3A] FIG. 3A is a flow chart illustrating an example procedure for incorporating at least one B1 amplitude measurement within an MRI scan sequence. [Figure 3B] FIG. 3B is a flow chart showing an example of a process for executing at least one B1 amplitude measurement sequence intermixed in a series of MRI scan sequences, where RF parameter values ​​of at least one scan sequence in the series of MRI scan sequences are modified based on results of executing the at least one intermixed B1 amplitude measurement sequence. [Figure 3C] FIG. 3C is a flow chart illustrating step 740 of FIG. 3B in more detail. [Figure 4] FIG. 4 shows the initial series of scan sequences designated for a patient examination prior to the inclusion of the B1 amplitude measurement sequence. [Figure 5A] FIG. 5A illustrates the series scan sequence of FIG. 4 further utilizing a pre-scan of the patient to obtain an RFL calibration, augmented with a first B1 amplitude measurement sequence. [Figure 5B] FIG. 5B illustrates the series scan sequence of FIG. 4 augmented with a first B1 amplitude measurement sequence and without utilizing a pre-scan of the patient to obtain an RFL calibration. [Figure 6] FIG. 6 illustrates the series of scan sequences of FIG. 4 augmented with a series of B1 amplitude measurement sequences interspersed such that a B1 amplitude measurement sequence precedes each scan sequence (after the first scan). [Figure 7]FIG. 7 is a diagram showing a series of scan sequences augmented with a series of B1 amplitude measurement sequences interspersed such that the B1 amplitude measurement sequences are inserted periodically within and between the scan sequences of the series of scan sequences. [Figure 8A] FIG. 8A is a diagram showing a series of scan sequences augmented with a series of B1 amplitude measurement sequences interspersed so as to insert B1 amplitude measurement sequences statically, periodically, and between scan sequences of the series of scan sequences. [Figure 8B] FIG. 8B is a diagram showing the series of scan sequences of FIG. 8A further dynamically augmented with a fourth B1 amplitude measurement sequence interspersed within the series of scan sequences based on the measurement results of a previously performed B1 amplitude measurement sequence. [Figure 9] FIG. 9 is a diagram showing a series of scan sequences augmented with a series of B1 amplitude measurement sequences in which the B1 amplitude measurement sequences are periodically interspersed within each shot of the series of scan sequences. [Figure 10] FIG. 10 is a graph illustrating the non-linear response of an RF power amplifier over a range of RF power inputs. [Figure 11] FIG. 11 is a diagram showing a series of scan sequences augmented with a series of multi-shot B1 amplitude measurement sequences interspersed periodically within and between the series of scan sequences. [Figure 12] FIG. 12 illustrates a variation of the augmented series of scan sequences with the interleaved series of multi-shot B1 amplitude measurement sequences of FIG. 11 in which the RF parameters have been changed as a result of performing the multi-shot B1 amplitude measurement sequences. [Figure 13A] FIG. 13A illustrates changes to a correction table within an RF transmitter to indirectly correct the scan sequence as a result of a B1 amplitude measurement sequence. [Figure 13B]FIG. 13B illustrates changes to the correction tables within the RF transmitter to indirectly correct the scan sequence as a result of the B1 amplitude measurement sequence. [Figure 13C] FIG. 13C illustrates changes to the correction tables within the RF transmitter to indirectly correct the scan sequence as a result of the B1 amplitude measurement sequence. [Figure 13D] FIG. 13D illustrates changes to the correction tables within the RF transmitter to indirectly correct the scan sequence as a result of the B1 amplitude measurement sequence. [Figure 14] FIG. 14 illustrates a series of scan sequences augmented with the series of multi-shot B1 amplitude measurement sequences of FIG. 11 utilizing modifications to a correction table to indirectly correct the series of scan sequences. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Several embodiments are illustrated by way of example in the referenced figures of the drawings. The embodiments and figures disclosed herein are intended to be considered illustrative, not restrictive. The scope of the technology and subsequent claims is not limited to the examples shown and described herein.

[0012] Also, the embodiments are described primarily with respect to certain processes, systems, and computer program products provided in certain examples. However, the processes, systems, and computer program products may also operate effectively in other examples. The terms "embodiment," "one embodiment," "another embodiment," and the like may refer to the same or different embodiments. The embodiments are described with respect to methods and configurations that include certain components. However, such methods and configurations may include more or fewer components than shown. Also, the arrangement and type of components may be modified without departing from the scope of the disclosure.

[0013] Also, the embodiments are described in the context of methods having certain steps, by way of example, although the methods and compositions may still operate validly by adding steps or performing the steps in a different order consistent with the example embodiments. Thus, the present disclosure is not intended to be limited to the embodiments described, but rather to be accorded the widest scope consistent with the principles and features described herein and is limited only by the appended claims.

[0014] Furthermore, when a range of values ​​is given, each value between the upper and lower limits of the range, as well as any other stated or intervening values ​​within the range, are included in the disclosure. When a stated range includes both an upper and lower limit, the range excluding either of the upper and lower limits is also included. Unless otherwise stated, terms used herein have their plain and ordinary meaning as understood by those of ordinary skill in the art. Any definitions are intended to aid the reader in understanding this disclosure and are not intended to modify or limit the meaning of such terms unless otherwise stated.

[0015] Reference will now be made to the drawings, in which like reference numbers indicate the same or equivalent parts throughout the drawings. FIG. 2 is a block diagram showing the overall configuration of an MRI system 1 according to a first embodiment. The MRI system 1 of the first embodiment includes a gantry 100, a control cabinet 300, a console 400, and a bed 501.

[0016] The gantry 100 includes a static magnetic field magnet 10, a gradient coil assembly 11, and a whole body (WB) coil 12. These components are housed in a cylindrical housing. The bed 501 includes a bed body 50 and a top plate 51. The MRI system 1 further includes at least one RF coil 20 disposed in the vicinity of the object.

[0017] The control cabinet 300 includes three gradient coil power supplies 31 (X-axis gradient coil power supply 31x, Y-axis gradient coil power supply 31y, and Z-axis gradient coil power supply 31z), an RF receiver 32, an RF transmitter 33, and a sequence controller 34.

[0018] The static magnetic field magnet 10 of the gantry 100 has a generally cylindrical shape and generates a static magnetic field inside a bore. The bore is a space formed in a cylindrical structure and serves as an imaging region for an object (e.g., a patient). The static magnetic field magnet 10 has a superconducting coil inside. The superconducting coil is cooled to an extremely low temperature by liquid helium. In an excitation mode, the static magnetic field magnet 10 generates a static magnetic field by supplying a current to the superconducting coil from a static magnetic field power supply (not shown). The static magnetic field magnet 10 then transitions to a persistent current mode, and the static magnetic field power supply is disconnected. The static magnetic field magnet 10 transitioned to the persistent current mode continues to generate a strong static magnetic field for a long period of time, such as one year. The static magnetic field magnet 10 may be configured as a permanent magnet.

[0019] The gradient coil assembly 11 also has a substantially cylindrical shape and is fixed inside the static magnetic field magnet 10. The three-channel gradient coil assembly 11 has an X-axis gradient coil 11x, a Y-axis gradient coil 11y, and a Z-axis gradient coil 11z (not shown individually). The X-axis gradient coil 11x receives current supply from an X-axis gradient coil power supply device 31x to generate a gradient magnetic field Gx in the X-axis direction. The Y-axis gradient coil 11y receives current supply from a Y-axis gradient coil power supply device 31y to generate a gradient magnetic field Gy in the Y-axis direction. The Z-axis gradient coil 11z receives current supply from a Z-axis gradient coil power supply device 31z to generate a gradient magnetic field Gz in the Z-axis direction.

[0020] The bed body 50 of the bed 501 can move the top board 51 vertically and horizontally. Before imaging, the bed body 50 moves the top board 51 on which an object is placed to a predetermined height. Thereafter, when imaging the object, the bed body 50 moves the top board 51 horizontally to move the object into the bore. The whole-body coil 12 may be referred to as a transmit coil.

[0021] The whole-body coil 12 has a substantially cylindrical shape surrounding the object, and is fixed inside the gradient coil assembly 11. The WB coil 12 applies an RF pulse transmitted from an RF transmitter 33 to the object, and receives a magnetic resonance (MR) signal emitted from the object due to excitation of hydrogen nuclei.

[0022] The RF coil 20 receives MR signals emitted from an object at a position near the object. The RF coil 20 includes, for example, a plurality of coil members. There are various RF coils 20 for the head, chest, spine, lower limbs, whole body, etc., according to the anatomical imaging part of the object. Among the various RF coils, FIG. 2 shows an RF coil 20 for chest imaging.

[0023] The RF transmitter 33 transmits RF pulses to the WB coil 12 based on instructions from the sequence controller 34. The RF receiver 32 detects MR signals received by the WB coil 12 and / or the RF coil 20, converts the detected MR signals into digital signals, and transmits the raw data acquired by the detection to the sequence controller 34.

[0024] The sequence controller 34 scans an object by driving the gradient coil power supply 31, the RF transmitter 33, and the RF receiver 32 under the control of the console 400. The sequence controller 34 receives raw data from the RF receiver 32 by performing a scan, and transmits the received raw data to the console 400.

[0025] The sequence controller 34 includes a processing circuit (not shown). The processing circuit is configured as, for example, a processor that executes a predetermined program, or hardware such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC).

[0026] The console 400 is configured as a computer comprising a processing circuit 40 , a memory 41 , a display 42 and an input interface 43 .

[0027] The memory 41 is a recording medium including a read-only memory (ROM) and a random access memory (RAM) in addition to an external memory device such as a hard disk drive (HDD) or an optical disk device. The memory 41 stores various programs executed by the processor of the processing circuit 40, as well as various data and information.

[0028] The display 42 is a display device such as a liquid crystal display panel, a plasma display panel, or an organic EL panel.

[0029] The input interface 43 includes various devices for an operator to input various data and information, and is composed of, for example, a mouse, a keyboard, a trackball, and / or a touch panel.

[0030] The processing circuit 40 is, for example, a circuit equipped with a central processing unit (CPU) and / or a special-purpose or general-purpose processor. The processor executes various programs stored in the memory 41 to realize the various functions described below. The processing circuit 40 can be configured with hardware such as an FPGA and an ASIC. The various functions described below can also be realized by such hardware. The processing circuit 40 can also realize the various functions by combining hardware processing and software based on its own processor and programs.

[0031] The console 400 controls the entire MRI system 1 including these components. Specifically, the console 400 accepts imaging conditions such as the type of pulse sequence, various information, and an imaging start command input by a user such as a medical imaging technician via an input interface 43 having a mouse and keyboard. The processing circuitry 40 executes a scan according to the imaging conditions input to the sequence controller 34, and reconstructs an image based on the raw data, i.e., the digital MR signal, transmitted from the sequence controller 34. The reconstructed image is displayed on the display 42 and stored in the memory 41.

[0032] In the configuration of the MRI system 1 shown in FIG. 2, the control cabinet 300, the gantry 100 and the bed 501 (ie, all components except the console 400) constitute an imaging section or scanner.

[0033] To control imaging of the MRI system 1, a series of MRI scan sequences are provided to the sequence controller 34. FIG. 3A is a flow chart showing an example of a procedure for interspersing at least one B1 amplitude measurement in the series of MRI scan sequences. FIG. 3A corresponds to, for example, a process for generating a series of MRI scan sequences. The method 600 starts with acquiring a series of MRI sequences including at least one RF parameter (e.g., flip angle or transmit amplification gain) for the series of MRI sequences, as shown in step 605. Any successive steps are performed to intersperse at least one B1 amplitude measurement in the series of MRI scan sequences. It is not necessary to perform all steps as the series of MRI scan sequences, and it is sufficient that at least one B1 amplitude measurement is interspersed.

[0034] Step 615 is an optional step of adding a prescan including RF level calibration (possibly as part of other prescan processing) to the beginning of a series of MRI scan sequences. Step 625 is an optional step of adding a B1 amplitude measurement that is used for RF level calibration relative to other B1 amplitude measurements added in steps 635 and 645.

[0035] Step 635 is an optional step of interspersing B1 amplitude measurements between the imaging sequence (e.g., at user-specified locations, between the entire sequence, periodically, or based on power measurements of the acquired MRI sequence). This step is described in more detail with reference to Figures 6 and 7. Step 645 is an optional step of interspersing B1 amplitude measurements between shots of the imaging sequence (e.g., at user-specified locations, periodically, or based on power measurements of the acquired MRI sequence). This step is described in more detail with reference to Figure 9.

[0036] After performing the blending process, control proceeds to step 655. In step 655, the resulting set of MRI sequences (with at least one B1 amplitude measurement blended into the set of MRI sequences (optionally including a pre-scan and / or initial calibration)) is stored in memory 41 or a storage device.

[0037] The series of MRI scan sequences interspersed with at least one B1 amplitude sequence are stored in a computer storage device accessible to the MRI system 1, which can acquire and load the resulting sequences into memory 41.

[0038] 3B is a flow chart illustrating (together with FIG. 3C) an example of a process for performing at least one B1 amplitude measurement sequence interspersed within a series of MRI scan sequences, where RF parameter values ​​(e.g., flip angle or transmit amplification gain) of at least one scan sequence of the series of MRI scan sequences are modified based on the results of performing at least one interspersed B1 amplitude measurement sequence. The process 700 begins with acquiring a series of MRI sequences with at least one interspersed B1 amplitude measurement within the series of MRI sequences, as shown in step 705. The B1 amplitude measurement sequence is performed by a Bloch-Siegert shift measurement sequence.

[0039] In one embodiment, the series of MRI sequences further includes at least one of a pre-scan MRI sequence or an RF calibration sequence. The purpose of the RF calibration sequence is to achieve the intended B1 amplitude of the RF pulse in the subsequent MRI scan sequence by calibrating the output of the RF transmit amplifier. However, both the pre-scan MRI sequence and the RF calibration sequence are optional. For example, a system-wide calibration can be performed to determine patient-independent calibration values. Alternatively, a patient-specific calibration sequence can be performed as part of the pre-scan.

[0040] As used herein, "acquired" means received from the memory 41 or storage system of the MRI system 1, or entirely from an external source. "Acquired" also means that a portion of information is acquired from one source and combined with additional information, and the combined information is accessible to the MRI system 1 (e.g., stored in the memory 41 or storage system of the MRI system 1). For example, a series of MRI sequences may be acquired from one source (memory 41 or an external device) and combined with additional information, such as at least one B1 amplitude measurement, intermixed within the series of MRI sequences.

[0041] The method starts the scan in step 710 by acquiring at least one B1 amplitude measurement interspersed in a series of MRI sequences and starts performing an MRI sequence and at least one B1 amplitude measurement. In step 715, the method determines what the next type in the sequence is to be performed. The type corresponds, for example, to a B1 amplitude measurement sequence or an MRI sequence. If in step 715 it is determined that the next type is part of an MRI sequence, control proceeds to step 720 and the next part of the MRI sequence is performed. After performing the part of the MRI sequence, control proceeds to step 725 to determine whether there is more to be performed in the MRI sequence or at least one B1 amplitude measurement (B1AM). If there is not more to be performed, control proceeds to step 730 and the imaging process for the patient ends. However, if there is a part of an MRI sequence or at least one B1 amplitude measurement to be performed, control returns from step 725 to 715.

[0042] If in method step 715 it is determined that the next type is part of at least one B1 amplitude measurement, control passes to step 735, where the current portion of the at least one B1 amplitude measurement (along with other successive B1 amplitude measurements in the sequence) is performed as an RFL check. Control then passes to step 740, where it is determined whether the results of the at least one B1 amplitude measurement (along with other successive B1 amplitude measurements in the sequence) indicate that a change in the RF parameter value (e.g., flip angle or transmit amplification gain) is required for at least a portion of the remaining MRI sequence that has not yet been performed. In general, a change is determined to be required if the measured and calibrated RF values ​​differ by more than a threshold value (or if a function of the two values ​​differs by more than a threshold value).

[0043] As shown in Figure 3C, such a determination is made by first calculating a function (e.g., a difference, a linear function, or a non-linear function) of the result of step 735 and the calibration result in step 740-1. The result of the calculated function is then compared to a threshold in step 740-2. As mentioned above, the calibration value can be determined in a patient-independent manner (e.g., a system-wide constant applied to all patients). The calibration value can also be determined as part of a pre-scan of the patient. In another embodiment, the expected value can be determined using a previous B1 amplitude measurement.

[0044] If the results of the at least one B1 amplitude measurement indicate that no change in the RF parameter value is required, control passes from step 740-2 to step 725 to see if there is more to process. If the results of the at least one B1 amplitude measurement indicate that a change in the RF parameter value is required, control passes from step 740-2 to step 745. In step 745, at least one RF parameter value for at least one of the remaining MRI sequences is updated.

[0045] After performing step 745, in a first embodiment, control skips optional steps 750 and 760 and proceeds to step 725 to see if there are more to process. Alternatively, in a second embodiment where dynamic mixing is applied, control proceeds from step 745 to step 750. In step 750, it is determined whether an additional B1 amplitude measurement should be mixed in (e.g., because the remainder of the MRI sequence is longer than a threshold time, because a comparison function of the two values ​​exceeds a different threshold than the threshold typically used for modification, or a combination of the two methods) or whether an existing B1 amplitude measurement should be removed (e.g., if the two values ​​indicate that the predicted and measured B1 amplitudes are close (<1%-2%)). In an embodiment, either or both of the B1 amplitude measurements can be added and removed. If adding and / or removing a B1 amplitude measurement, control proceeds from step 750 to step 760 to implement the modification and return to step 725. Alternatively, control returns directly from step 750 to step 725.

[0046] FIG. 4 shows an initial set of scan sequences 401 identified for the patient examination and any pre-scans prior to the inclusion of a B1 amplitude measurement sequence. The initial set of scan sequences 401 are often specified by a medical professional and are designed to scan a particular region with a particular set of scan parameters. For example, the medical professional may order a T2-weighted (T2W) scan of a first region, a T1-weighted (T1W) scan of a first region, a T1-weighted (T1W) scan of a second region, a fluid-attenuated inversion recovery (FLAIR) scan of the first region, or any other desired scans. Each scan shown utilizes two or more shots (Sx,y, where x indicates the scan sequence and y indicates the shot number within the sequence). The number of shots in each scan may vary (including one shot). The relative lengths of the scans shown in Figures 4-6 are not meant to imply relative lengths, and the ellipses (...) in Figures 4-6 indicate that any number of shots may be hidden to avoid cluttering the figures. The illustrated scan sequences include initially identified RF parameters used to perform the scan sequences. Such RF parameters include, but are not limited to, flip angles and amplification gains of the RF transmitter 33 (including a variable gain amplifier).

[0047] FIG. 5A shows a pre-scan (including an RF level calibration sequence) and an augmented scan sequence 500 by adding a first B1 amplitude measurement sequence 505 (B11) to the scan sequence of FIG. 4. The first B1 amplitude measurement sequence 505 mixed into the series of MRI scan sequences 500 used in one MRI examination is acquired by, for example, the sequence controller 34. Note that acquisition of the first B1 amplitude measurement sequence 505 may be realized by the processing circuit 40. The method including the B1 amplitude measurement can detect changes (e.g., thermally induced) that occur in the components of the system (e.g., the transmit coil (Tx coil) or whole-body RF coil 12, the RF shield, the RF amplifier (included in the RF transmitter 33)) during the course of the examination. The efficiency of these components is affected by heat, causing changes in transmission / reflection coefficients. For this reason, the RFL acquired during the pre-scan may be inaccurate for use in later stages of the examination. An inaccurate RFL value leads to inaccurate setting of the flip angle, which affects image quality. Hardware and patient safety related measurements (SAR, B1rms, receive coil power absorption) rely on a properly calibrated RFL value, therefore safety related measurements may also be inaccurate.

[0048] As shown in FIG. 5B, the RFL calibration value does not need to be obtained during the prescan. Instead, a system-wide, patient-independent RF calibration value is obtained and used for all patients for whom RFL calibration has not been performed before the imaging sequence. The system-wide, patient-independent RF calibration value can be obtained using an average value over many patients or by modeling the transmission characteristics of the system. In another embodiment, the calibration RFL can be calculated based on a first B1 amplitude measurement made during the imaging process (e.g., before the transmitter overheats), and the results of the first B1 amplitude measurement can be used as a calibration value for subsequent B1 amplitude measurements.

[0049] That is, the sequence controller 34 (or the processing circuitry 40) may obtain the RF level reference value as part of a pre-scan of the patient prior to a series of MRI scan sequences for the patient, and the sequence controller 34 may use the RF level reference value to determine whether to change the first RF parameter value for the second MRI scan sequence based on the measurement result of the executed first B1 amplitude measurement sequence 505.

[0050] For example, the series of MRI scan sequences 500 includes a first MRI scan sequence and a second MRI scan sequence having a first RF parameter value. For the sake of specificity, the first MRI scan sequence is assumed to be an MRI sequence executed before the first B1 amplitude measurement sequence 505 in the series of MRI scan sequences 500. The second MRI scan sequence is assumed to be an MRI sequence executed after the first B1 amplitude measurement sequence 505 in the series of MRI scan sequences 500.

[0051] At this time, as shown in FIG. 3B, the sequence controller 34 first executes a first MRI scan sequence and a first B1 amplitude measurement sequence 505. Then, the sequence controller 34 (or the processing circuit 40) determines whether or not to change the first RF parameter value for the second MRI scan sequence based on the measurement result of the executed first B1 amplitude measurement sequence 505. When it is determined that the first RF parameter value is to be changed based on the measurement result of the executed first B1 amplitude measurement sequence 505, the processing circuit 40 changes the first RF parameter value to a second RF parameter value different from the first RF parameter value. Then, the sequence controller 34 executes the second MRI scan sequence using the second RF parameter value.

[0052] The first and second RF parameter values ​​may be associated with a flip angle, for example. Alternatively, the first and second RF parameter values ​​may be selected from the group consisting of a flip angle and a transmit gain. Changing the first RF parameter value to the second RF parameter value may include changing the pulse sequence applied to the sequence controller 34.

[0053] Also, as shown in FIG. 3B, if the sequence controller 34 determines based on the measurement results of the executed first B1 amplitude measurement sequence that the first RF parameter value should not be changed, the sequence controller 34 executes a second MRI scan sequence using the first RF parameter value.

[0054] Prior to the execution of the series of MRI scan sequences 500 shown in Fig. 5A, for example, as shown in Fig. 3A, the sequence controller 34 executes a process for generating a series of MRI scan sequences. For example, the sequence controller 34 (or the processing circuit 40) mixes a first B1 amplitude measurement sequence 505 into the series of MRI scan sequences 500 before the execution of a first MRI scan sequence of the series of MRI scan sequences as shown in Fig. 3A. Specifically, as shown in Figs. 5A and 5B, the sequence controller 34 mixes at least one B1 amplitude measurement sequence 505 between each MRI scan sequence of the series of MRI scan sequences 500.

[0055] The various methods described herein allow for tracking and compensation of changes in hardware conditions, primarily components associated with the transmit chain, including the Tx coil and RF power amplifier. In one application, a method can track changes in B1 (which indicates a corresponding change in RFL) caused by heating of the Tx coil. During normal operation, application of a voltage to the Tx coil generates a B1 field within the subject. This B1 field generates a flip angle that is used to generate the MR signal on which the images are based.

[0056] During a scan or series of scans, the voltage applied to the Tx coil may heat the conductive material inside the coil. Generally, heating increases the internal resistance of the Tx coil, which reduces the transmission efficiency of the coil (referred to as the "Q" of the coil). As a result, the B1 magnetic field in the subject decreases for the same input power. That is, the B1 magnetic field in the subject may change depending on the temperature condition of the Tx coil.

[0057] For initial RFL calibration, a search for a reference RFL value is typically performed (system-wide or patient-specific). In the search, multiple transmit gain levels are applied and the generated B1 field is measured. The B1 field can be measured directly using a method such as BSS, or indirectly based on a signal generated by the same method, such as signal maximization. In the search for the reference RFL value, multiple shots of B1 measurement can be applied. This is done to average the measurements to obtain a more robust RFL estimate, or to calculate a reference RFL value for curve fitting. As described herein, the multi-shot approach can be used to recalibrate the reference RFL value, although one shot of B1 measurement may be taken. In the case of a single-shot measurement approach, the measured B1 may be compared to one or more previous B1 measurements. That is, a relative change in B1 that is proportional to the relative change in RFL is detected.

[0058] As shown in Fig. 5A, 5B, the B1 amplitude measurement sequence 505 (B11) is inserted before at least one scan sequence after the first scan sequence (shown as the (n-1)th scan sequence) rather than being inserted as part of a prescan or as the first calibration. By using a BSS sequence as the B1 amplitude measurement sequence, the B1 amplitude measurement sequence can be performed very quickly (e.g., about 50 ms) by applying two repetition times (TR) (+ / - BSS frequency offset) per shot. When the B1 amplitude measurement sequence is performed (step 735 in Fig. 3B), the RF receiver 32 receives the measurement result and calculates a function based on the result of the B1 amplitude measurement and the reference B1 measurement value calculated previously (e.g., during the calibration of the entire system, during the prescan, during the execution of the B1 amplitude measurement sequence inserted before the current sequence) (step 740-1 in Fig. 3C). This function can be as simple as a difference, but it can also be other linear or nonlinear functions.

[0059] If the result of the calculated function exceeds an absolute or percentage threshold (e.g., 5% of the baseline B1 measurement) (step 740-2), the system updates the internal RF level calibration values. Based on the internal RF level calibration values, the RF parameters for the subsequent sequence are calculated (step 745), including (a) the flip angle or (b) the RF transmitter amplification gain. Assuming that the RF parameters for the subsequent sequence are based on the most recent B1 measurement, the system automatically compensates for the temperature conditions of the system (i.e., drift compensation). This results in improved uniformity of image quality (e.g., more uniform flip angles result in more uniform image quality).

[0060] In one embodiment, the inserted B1 amplitude measurement sequence 505 is selected to utilize the power level of the scan sequence that follows the inserted B1 amplitude measurement sequence 505. For example, the power level of the B1 amplitude measurement sequence 505 (B11) in Figures 5A and 5B is made equivalent to the power level applied to the scan sequence (n-1). Equivalent power level means that the operating ranges of the transmission amplifiers used in both sequences are equivalent.

[0061] The system may also receive predictions and / or corrections for RF parameters to be used in subsequent scans using a physics model that has information about expected changes in the system during subsequent scan sequences (e.g., due to expected power application for the subsequent scan sequences) and calculates the informed predictions and / or corrections.

[0062] For example, determining whether to change the first RF parameter value based on the measurement results of the performed first B1 amplitude measurement sequence may include inputting the measurement results into a physical model of the system to receive at least one of a predicted value and a corrected value for the first RF parameter value.

[0063] The insertion of the sequence is done automatically based on criteria established by the MRI system 1, or selected by the technician (or other user) via a user input device (e.g., a touch screen, pointing device, pen-type device, or voice controller). For example, the technician selects two adjacent scan sequences and then selects a menu control (or vice versa). The menu control causes the MRI system 1 to insert a B1 amplitude measurement sequence between the selected scan sequences. In this way, the MRI sequence controller 34 updates the pulses transmitted to the RF transmitter 33 to include the inserted B1 amplitude measurement sequence within the original set of scan sequences.

[0064] Although Figures 5A and 5B show one inserted B1 amplitude measurement sequence, any number of B1 amplitude measurement sequences can be inserted in practice. For example, Figure 6 shows the series of scan sequences of Figure 4 (pre-scans omitted for clarity) augmented with a series of B1 amplitude measurement sequences, with a single shot B1 amplitude measurement sequence placed before each scan sequence (after the first scan). That is, in the five scan sequences shown, a B1 amplitude measurement sequence is inserted between each pair of adjacent scan sequences. The operator can select a menu option such as "Automatic RFL Check Between Scan Sequences" from the menu interface to automatically insert a B1 amplitude measurement sequence between each pair of adjacent sequences.

[0065] For example, the first B1 amplitude measurement sequence 505 may have one shot. Alternatively, the first B1 amplitude measurement sequence 505 may have multiple shots. In this case, determining whether to change the first RF parameter value based on the measurement result may determine whether to change the first RF parameter value based on the measurement result based on the multiple shots. That is, the sequence controller 34 may determine whether to change the first RF parameter value based on the measurement result of the B1 distribution based on the multiple shots.

[0066] FIG. 7 shows the series of scan sequences of FIG. 4 (pre-scans omitted for clarity) augmented with a series of B1 amplitude measurement sequences, with the B1 amplitude measurement sequences inserted periodically within and between scans of the series of scan sequences. As shown in the figure, the B1 amplitude measurement sequences are inserted approximately every y seconds, where "y" corresponds to a length of approximately 6 shots. In this configuration, the timing between the B1 amplitude measurement sequences may vary, since the B1 amplitude measurement sequences are inserted between the scan sequences. In the figure, B11 and B14 are inserted after 6 shots, while B12 and B13 are inserted after 7 shots and 5 shots, respectively, since there is no gap between the scan sequences that can be inserted before them. Other positions where the B1 amplitude measurement sequences can be inserted include, but are not limited to, (1) after an absolute or relative threshold change in the RF power level of a portion of the scan sequence from a preceding period, and (2) after an absolute or relative threshold change in the average RF power level of a portion of the scan sequence from a preceding period.

[0067] For example, the processing circuit 40 also mixes the second B1 amplitude measurement sequence into the series of MRI scan sequences 500 before the execution of the first MRI scan sequence. At this time, the first B1 amplitude measurement sequence and the second B1 amplitude measurement sequence are mixed between the MRI scan sequences closest to a specific period in the series of MRI scan sequences 500. Specifically, the first B1 amplitude measurement sequence and the second B1 amplitude measurement sequence are mixed between the shots closest to a specific period in the series of MRI scan sequences. The specific period is, for example, after the absolute or relative threshold of the RF power level of a part of the scan sequence has changed from the period preceding the first B1 amplitude measurement sequence and the second B1 amplitude measurement sequence, or after the absolute or relative threshold of the average RF power level of a part of the scan sequence has changed from the preceding period.

[0068] FIG. 8A shows a series of scan sequences augmented with a series of B1 amplitude measurement sequences, where the B1 amplitude measurement sequences are statically inserted between pairs of scan sequences in the series of scan sequences. For illustration purposes, assume that the B1 amplitude measurement sequences of the inserted series of B1 amplitude measurement sequences are periodically inserted between scan sequences every y seconds. While processing the augmented scan sequence of FIG. 8A, the system determines that the result of the first B1 amplitude measurement (B11) indicates that the RF level has changed from the reference level by more than a threshold (step 740 in FIG. 3B and 3C). Thus, the system updates the RF parameters associated with the subsequent scan sequences (from RF param1 to RF param2) to adapt to the change in RF level. FIG. 8B shows the change in RF parameter value.

[0069] Furthermore, FIG. 8B shows that the original augmented sequence of scans in FIG. 8A is dynamically augmented with a fourth B1 amplitude measurement sequence (B14; shown with a diagonal line in the opposite direction to B11), and the fourth B1 amplitude measurement sequence is inserted into the sequence of scans based on the measurement result of the previously performed B1 amplitude measurement sequence (B11). For example, if the measurement result indicates that the RF level of B11 has changed significantly from the reference value (step 740 in FIG. 3B), the system inserts more B1 amplitude measurement sequences (e.g., B14) than the original insertion number (step 760 in FIG. 3B). This allows the system to more quickly evaluate whether the change made in response to B11 has made the system more closely calibrated. Such dynamic sequence insertion can be performed whenever a significant difference is detected. Alternatively, if there is a sequence of measurement results that match the expected value, the system may dynamically delete the previously inserted B1 amplitude measurement sequence (step 760 in FIG. 3B).

[0070] FIG. 9 shows a series of scan sequences augmented with a series of B1 amplitude measurement sequences, which are periodically inserted between each shot of the series of scan sequences, not only between adjacent scan sequences. As shown in FIG. 9, B1 amplitude measurement sequences are inserted every x shots (6 shots in the figure), i.e., some scan sequences are temporarily interrupted to perform a calibration check, which is important in long sequences with large temperature changes. Sequences with large temperature changes include arterial spin labeling (ASL), magnetization transfer (MT), steady-state free precession (SSFP), and other sequences with frequent application of RF pulses.

[0071] In an embodiment of the MRI system 1, a power amplifier may be used that does not have a linear response to the applied RF power input. FIG. 10 is a graph showing the nonlinear response of an RF power amplifier over a range of RF power inputs. Such nonlinear responses are typical of smaller and less expensive RF power amplifiers. Also, even RF power amplifiers that have a nearly linear response in one operating region do not necessarily have the same linear response over the entire region. Thus, different results may be obtained when operating an RF amplifier in different regions of the operating curve. As a result, it is suboptimal to calibrate the transmitter power during a normal scan in the central region of the operating curve (indicated by stars) when performing a scan based on a sequence of RF pulses that fall in the lower part of the operating curve (indicated by triangles). In the case of MR-compatible implantable devices, the peak of the RF power may be limited due to B1rms limits or the like to ensure the safety of both the patient and the hardware. In this situation, the B1 field for a given input power is different (lower) than the B1 field expected for an amplifier operating in the central region of the operating curve. In this case, a method is used to measure such changes by adjusting the transmit power of the BSS sensitizing RF pulses in the sequence. That is, the BSS method measures the B1 field power in the low range. From this measurement, a correction factor is obtained to correct the B1 power of the sequence, thereby maintaining uniformity.

[0072] Thus, a method is available to track the effects of changing conditions within the hardware of an MRI scanner. This allows the scanner to generate a more uniform B1 field even in the presence of heating and other nonlinearities of operation. This capability of the scanner can also be exploited to reduce the cost of the hardware components. For example, a system designer can choose to build a Tx coil using thinner (more resistive) conductors for the Tx coil and / or incorporate less thermal energy removal. The use of cheaper or smaller, i.e. more nonlinear, RF power amplifiers can reduce cost and / or size. Using the methods described herein, it is possible to maintain a uniform B1 field throughout a series of scans, even in the presence of nonuniformities or defects in the hardware.

[0073] FIG. 11 shows a series of scan sequences augmented with a series of multi-shot B1 amplitude measurement sequences, where the multi-shot B1 amplitude measurement sequences are inserted between the scans of the series of scan sequences periodically within the series of scan sequences. The multi-shot B1 amplitude measurement sequences can be inserted statically or dynamically. Although FIG. 11 shows a multi-shot B1 amplitude measurement sequence inserted between adjacent scan sequences, in another embodiment, it can be inserted between shots within a scan sequence. Furthermore, the number of shots of the multi-shot B1 amplitude measurement sequences in one test may not be the same. FIG. 11 shows a test with two 2-shot B1 amplitude measurement sequences and one 3-shot B1 amplitude measurement sequence. Examples of 2-shot B1 amplitude measurement sequences include a low-mid range shot, a low-high range shot, and a high-mid range shot. The number of shots of the multi-shot B1 amplitude measurement sequences may be other numbers (e.g., 4 or more). The distribution of the shots over the entire operating range of the amplifier may not be uniform. Such multi-shot B1 amplitude measurement sequences can also be statically or dynamically combined with single-shot B1 amplitude measurement sequences. The system can use amplification gain specific calibration to better identify the flip angle to use and / or the amplification gain to apply. Also, by interpolation, correction values ​​at power levels between the power levels used in the multi-shot B1 amplitude sequences can be obtained.

[0074] For example, as shown in Fig. 11, after executing the first B1 amplitude measurement sequence, the processing circuit 40 mixes the second B1 amplitude measurement sequence into the series of MRI scan sequences 500. At this time, as mixing the second B1 amplitude measurement sequence into the series of MRI scan sequences 500, the processing circuit 40 may mix the second B1 amplitude measurement sequence between MRI scan sequences in the series of MRI scan sequences 500. Also, as mixing the second B1 amplitude measurement sequence into the series of MRI scan sequences 500, the sequence controller 34 may mix the second B1 amplitude measurement sequence between shots of one MRI scan sequence in the series of MRI scan sequences.

[0075] B1 measurement methods can be configured as non-selective, slice-selective, 1D spatially selective (pencil beam), 2D spatially selective (map), or 3D spatially selective (volume). For applications where mixing is required between scans or between shots of a single scan, fast methods are preferred. 1D spatially selective pencil beam is the ideal method as it is fast and can be acquired in one or a few shots. For example, when using a BSS sequence (+ / -BSS RF offset frequency), the minimum number of shots required for pencil beam is two shots.

[0076] The advantage of the spatially selective method is that a local region, such as a region of interest (ROI), can be selected from the spatially resolved data; that is, the B1 field is measured only from the selected region, and the RFL value is determined only for the specific ROI. This allows the RFL (and flip angle) to be calculated based on the most significant spatial information for a portion of the image of interest. This is interesting for clinical applications where the anatomy of interest is a small organ, such as the heart, within the thorax. Using the method described herein, spatially resolved B1 measurements can be made in the ROI, and image quality of the anatomy of interest can be maintained by maintaining a uniform RFL.

[0077] For example, the first RF parameter value and the second RF parameter value are related to a flip angle, and spatial selection data is measured by a first B1 amplitude measurement sequence. Specifically, the sequence controller 34 (or the processing circuit 40) acquires a distribution of B1 values ​​(B1 map) in a local region such as a region of interest as spatial selection data based on the data collected by the first B1 amplitude measurement sequence. Then, the sequence controller 34 (or the processing circuit 40) calculates a change value from the first RF parameter value to the second RF parameter value using only the region (local region such as a region of interest) corresponding to the measured spatial selection data (B1 map).

[0078] It is known to those skilled in the art that by setting the gradient amplitudes {Gx, Gy, Gz} of the B1 measurement sequence, the 1D spatial resolution method can be applied at selected projection angles. One projection can be acquired. To improve the detection sensitivity of the ROI, the projection angles used may be limited to the main direction. Also, two or more projections can better identify the B1 data from the ROI.

[0079] The BSS calculation methods described here are spin-echo or field-echo BSS calculation methods. Spin-echo BSS reduces the sensitivity to B0 at the expense of a long TR, i.e., long shot time. Field-echo BSS also provides information about B0 drift. Averaging two TRs of a BSS shot (+ / - BSS RF offset frequency) produces a measurement of the average phase in the projection. This average phase is then observed in the longitudinal direction, where ΔB0=(φupdate-φreference) / TE, where TE is the echo time of the field-echo sequence, as a surrogate measurement of B0 drift.

[0080] FIG. 12 shows a variation of the series of scan sequences augmented with the series of multi-shot B1 amplitude measurement sequences of FIG. 11 in which the RF parameters have been changed as a result of performing the multi-shot B1 amplitude measurement sequence. As shown in the figure, as a result of performing the first multi-shot B1 amplitude measurement sequence pair, scan sequences 2 and 3 are updated in different ways. The RF parameters of scan sequence 2 are updated based on the results of the first B1 amplitude measurement sequence at a first power level equivalent to the power level of scan sequence 2. The RF parameters of scan sequence 3 are updated based on the results of the second B1 amplitude measurement sequence at a second power level equivalent to the power level of scan sequence 3. Similarly, as a result of performing the second multi-shot B1 amplitude measurement sequence pair, scan sequence (n-1) is updated to use RF parameters 4 and 5 (instead of the one RF parameter specified by the original pulse sequence).

[0081] In one embodiment of the above technique, the RF parameters are changed by the MRI sequence controller 34 (functioning as an RF transmit coil controller) or the processing circuitry 40. The updated pulses (from the first received scan sequence pulses of the examination) are sent to the RF transmitter 33. In another embodiment, the RF transmitter 33 includes variable gain hardware (programmable by the processing circuitry 40 functioning as an RF transmit coil controller). The variable gain hardware modifies the amount of gain applied to the pulses that the RF transmitter 33 receives from the MRI sequence controller 34. As shown in Figures 13A-13D, by providing a correction table (CT) in the RF transmitter 33, the processing circuitry 40 can update the correction table and perform corrections that are determined to be necessary as a result of performing at least one B1 amplitude measurement sequence. Figure 13A shows an initial correction table that stores a correction value of 1.0 when no correction is performed for the received RF level (i.e., RF x 1.0 = RF). As shown in Figure 13B, the first B1 amplitude measurement sequence results in a reconfiguration of the correction table to include example correction factors V2 and V3 that correspond to the upper and lower halves, respectively, of the RF curve of Figure 10. As shown in Figure 13C, the second B1 amplitude measurement sequence results in a reconfiguration of the correction table to include example correction factors V5 and V4 that correspond to the upper and lower halves, respectively, of the RF curve of Figure 10. As shown in Figure 13D, the third B1 amplitude measurement sequence results in a reconfiguration of the correction table to include many different correction factors to provide the intended correction to the RF curve of Figure 10.

[0082] As shown in FIG. 14, instead of directly updating the RF parameters of the scan sequence (by changing the values ​​sent from the MRI sequence controller 34 to the RF transmitter 33), the RF parameters of the scan sequence can be indirectly updated by modifying a correction table inside the RF transmitter 33. FIG. 14 illustrates the use of a dynamically reconfigured correction table containing four different sets of correction factors during the course of an examination. In yet another embodiment, the RF transmitter 33 may include an analog gain amplifier (not shown) that directly increases the gain of the RF transmission without changing the digital values ​​provided to the RF transmitter 33 (either directly from the sequence controller 34 or from a correction table interposed between the RF transmitter 33 and the sequence controller 34).

[0083] Thus, changing the first RF parameter values ​​of the second MRI scan sequence to the second RF parameter values ​​may include changing a correction table for RF transmissions.

[0084] In addition to other configurations and methods described herein, further configurations and methods are set forth in the non-limiting parentheticals set forth below, including, but not limited to, the following:

[0085] (1) acquiring a first B1 amplitude measurement sequence intermixed within a series of MRI scan sequences used in a single MRI examination, the series of MRI scan sequences including the first MRI scan sequence and a second MRI scan sequence having a first RF parameter value; performing the first MRI scan sequence and the first B1 amplitude measurement sequence; determining whether a measurement result of the performed first B1 amplitude measurement sequence indicates that a first RF parameter value needs to be changed for the second MRI scan sequence; if it is determined that a measurement result of the executed first B1 amplitude measurement sequence indicates that a first RF parameter value for the second MRI scan sequence needs to be changed, (1) changing a first RF parameter value of the second MRI scan sequence to a second RF parameter value different from the first RF parameter value, and (2) executing the second MRI scan sequence using the second RF parameter value; A medical image processing method including, but not limited to,

[0086] (2) executing the second MRI scan sequence using the first RF parameter value when it is determined that the measurement result of the executed first B1 amplitude measurement sequence does not indicate that the first RF parameter value needs to be changed for the second MRI scan sequence; The method according to (1), further comprising, but not limited to,

[0087] (3) The method according to (1) or (2), wherein the first B1 amplitude measurement sequence is intermixed within the series of MRI scan sequences prior to execution of the first MRI scan sequence of the series of MRI scan sequences.

[0088] (4) before performing the first MRI scan sequence, a second B1 amplitude measurement sequence is also intermixed into the series of MRI scan sequences; The method of claim 3, wherein the first and second B1 amplitude measurement sequences are interspersed between MRI scan sequences that are closest to a particular period in the series of MRI scan sequences.

[0089] (5) The method according to (3), wherein at least one B1 amplitude measurement sequence is interspersed between each MRI scan sequence of the series of MRI scan sequences.

[0090] (6) before performing the first MRI scan sequence, a second B1 amplitude measurement sequence is also intermixed into the series of MRI scan sequences; The method of claim 3, wherein the first and second B1 amplitude measurement sequences are interspersed between shots in the series of MRI scan sequences that are closest to a particular period.

[0091] (7) A method according to any one of (1) to (6), further comprising, but not limited to, mixing a second B1 amplitude measurement sequence into the series of MRI scan sequences after performing the first B1 amplitude measurement sequence.

[0092] (8) The method described in (7), wherein intermixing the second B1 amplitude measurement sequence includes intermixing the second B1 amplitude measurement sequence between MRI scan sequences of the series of MRI scan sequences.

[0093] (9) The method described in (7), wherein intermixing the second B1 amplitude measurement sequence includes intermixing the second B1 amplitude measurement sequence between shots of one MRI scan sequence in the series of MRI scan sequences.

[0094] (10) A method according to any one of (1) to (9), wherein the first B1 amplitude measurement sequence is a Bloch-Siegert shift measurement sequence.

[0095] (11) the first and second RF parameter values ​​are related to a flip angle; said first B1 amplitude measurement sequence measures spatially selective data; The method of claim 1 or 2, further comprising calculating a change from the first RF parameter value to the second RF parameter value using only an area corresponding to the measured spatially selective data.

[0096] (12) The method further includes, without limitation, obtaining a baseline RF level value as part of a pre-scan of a patient prior to the series of MRI scan sequences for the patient; The method according to (1) or (2), wherein determining whether the measurement results of the first B1 amplitude measurement sequence performed indicate that a first RF parameter value needs to be changed for the second MRI scan sequence includes determining whether the measurement results of the first B1 amplitude measurement sequence indicate that a first RF parameter value needs to be changed for the second MRI scan sequence using the RF level reference value.

[0097] (13) A method according to any one of (1) to (12), wherein the first B1 amplitude measurement sequence is one shot.

[0098] (14) the first B1 amplitude measurement sequence includes a plurality of shots; 13. The method of claim 1, wherein determining whether the measurement results indicate a need to change a first RF parameter value for the second MRI scan sequence comprises determining whether the measurement results indicate a need to change a first RF parameter value for the second MRI scan sequence based on the plurality of shots.

[0099] (15) A method according to any one of (1) to (14), wherein determining whether the measurement results of the performed first B1 amplitude measurement sequence indicate that a first RF parameter value needs to be changed for the second MRI scan sequence includes inputting the measurement results into a physical model of the system to receive at least one of a predicted value and a corrected value of the first RF parameter value.

[0100] (16) The method of any one of (1) to (15), wherein the first and second RF parameter values ​​are selected from the group consisting of flip angle and amplification gain.

[0101] (17) The method according to any one of (1) to (16), wherein changing the first RF parameter value of the second MRI scan sequence to the second RF parameter value includes changing a pulse sequence applied by a sequence controller 34.

[0102] (18) The method according to any one of (1) to (17), wherein changing the first RF parameter value of the second MRI scan sequence to the second RF parameter value includes changing an RF transmission correction table.

[0103] (19) A magnetic resonance imaging (MRI) system including, but not limited to, a gantry, at least one RF transmit coil, and an RF transmit coil controller that performs the method according to any one of (1) to (18).

[0104] (20) A method for implementing a method for a computer-readable storage medium, including, but not limited to, a computer-readable storage medium including computer instructions, communicatively coupled to a processor of the computer; The computer instructions, when executed by a computer processor, cause the computer processor to perform a method according to any one of (1) to (18).

[0105] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. The novel method, device, and system can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as defined in the claims, as well as the scope and spirit of the invention.

[0106] When the technical idea of ​​the embodiment is realized by a medical image processing method, the medical image processing method acquires a first B1 amplitude measurement sequence mixed in a series of MRI scan sequences used in one MRI examination, the series of MRI scan sequences includes a first MRI scan sequence and a second MRI scan sequence having a first RF parameter value, executes the first MRI scan sequence and the first B1 amplitude measurement sequence, determines whether the measurement result of the executed first B1 amplitude measurement sequence indicates that the first RF parameter value for the second MRI scan sequence needs to be changed, and if it is determined that the measurement result of the executed first B1 amplitude measurement sequence indicates that the first RF parameter value for the second MRI scan sequence needs to be changed, changes the first RF parameter value of the second MRI scan sequence to a second RF parameter value different from the first RF parameter value, and executes the second MRI scan sequence using the second RF parameter value. The procedures and effects of various processes related to this medical image processing method are the same as those described in the embodiment, so that the description will be omitted.

[0107] When the technical idea of ​​the embodiment is realized by a medical image processing program, the medical image processing program causes a computer to acquire a first B1 amplitude measurement sequence mixed in a series of MRI scan sequences used in one MRI examination, the series of MRI scan sequences including a first MRI scan sequence and a second MRI scan sequence having a first RF parameter value, execute the first MRI scan sequence and the first B1 amplitude measurement sequence, determine whether or not a measurement result of the executed first B1 amplitude measurement sequence indicates that a first RF parameter value for the second MRI scan sequence needs to be changed, and when it is determined that the measurement result of the executed first B1 amplitude measurement sequence indicates that a first RF parameter value for the second MRI scan sequence needs to be changed, change the first RF parameter value of the second MRI scan sequence to a second RF parameter value different from the first RF parameter value, and execute the second MRI scan sequence using the second RF parameter value.

[0108] For example, the processing shown in Figures 3A and 3B can be realized by installing the medical image processing program in a computer in a modality such as an MRI device and expanding the program in memory. In this case, the program that can cause the computer to execute the processing can be stored in a storage medium such as a magnetic disk (hard disk, etc.), an optical disk (CD-ROM, DVD, etc.), or a semiconductor memory and distributed. The processing procedure and effects of the medical image processing program are the same as those in the embodiment, so a description thereof will be omitted.

[0109] According to at least one of the embodiments described above, a uniform B1 magnetic field can be maintained throughout a series of scans.

[0110] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0111] 1. Magnetic Resonance Imaging (MRI) System 10 Static magnetic field magnet 11 Gradient Coil Assembly 12 Whole body (WB) coil 20 RF coil 31 Gradient coil power supply 32 RF Receiver 33 RF transmitter 34 Sequence Controller 40 Processing circuit 41 Memory 42 Display 43 Input Interface 50 Bed body 51 Tabletop 100 Gantry 300 Control Cabinet 400 Console 501 Bed

Claims

1. acquiring a first B1 amplitude measurement sequence interspersed within a series of MRI scan sequences for a single MRI examination, the series including a first MRI scan sequence and a second MRI scan sequence having a first RF parameter value; performing the first MRI scan sequence and the first B1 amplitude measurement sequence; determining whether to change a first RF parameter value for the second MRI scan sequence according to a measurement result of the first B1 amplitude measurement sequence; If it is determined based on the measurement result that the first RF parameter value is to be changed, changing the first RF parameter value to a second RF parameter value different from the first RF parameter value; performing the second MRI scan sequence using the second RF parameter values; Medical image processing method.

2. performing the second MRI scan sequence using the first RF parameter values ​​if the measurements determine not to change the first RF parameter values; The medical image processing method according to claim 1 , further comprising:

3. Prior to execution of the first MRI scan sequence of the series of MRI scan sequences, the first B1 amplitude measurement sequence is intermixed into the series of MRI scan sequences. The medical image processing method according to claim 1 .

4. Prior to execution of the first MRI scan sequence, a second B1 amplitude measurement sequence is also intermixed into the series of MRI scan sequences; the first B1 amplitude measurement sequence and the second B1 amplitude measurement sequence are interspersed between MRI scan sequences that are closest to a particular time period in the series of MRI scan sequences; The medical image processing method according to claim 3.

5. at least one B1 amplitude measurement sequence is interleaved between each MRI scan sequence of the series of MRI scan sequences; The medical image processing method according to claim 3.

6. Prior to execution of the first MRI scan sequence, a second B1 amplitude measurement sequence is also intermixed into the series of MRI scan sequences; the first B1 amplitude measurement sequence and the second B1 amplitude measurement sequence are interspersed between shots of the series of MRI scan sequences that are closest to a particular period; The medical image processing method according to claim 3.

7. intermixing a second B1 amplitude measurement sequence into the series of MRI scan sequences after performing the first B1 amplitude measurement sequence; The medical image processing method according to claim 1 , further comprising:

8. intermixing the second B1 amplitude measurement sequence includes intermixing the second B1 amplitude measurement sequence between MRI scan sequences in the series of MRI scan sequences. The medical image processing method according to claim 7.

9. intermixing the second B1 amplitude measurement sequence includes intermixing the second B1 amplitude measurement sequence between shots of one MRI scan sequence of the series of MRI scan sequences. The medical image processing method according to claim 7.

10. the first B1 amplitude measurement sequence is a Bloch-Siegert shift measurement sequence; The medical image processing method according to claim 1 .

11. the first RF parameter value and the second RF parameter value are related to a flip angle; said first B1 amplitude measurement sequence measures spatially selective data; calculating a change from the first RF parameter value to the second RF parameter value using only the region corresponding to the measured spatially selective data; The medical image processing method according to claim 1 .

12. obtaining a baseline RF level value as part of a pre-scan of a patient prior to said MRI scan sequence of the patient; Further equipped with determining whether to change the first RF parameter value based on the measurement result includes determining whether to change the first RF parameter value using the RF level reference value. The medical image processing method according to claim 1 .

13. the first B1 amplitude measurement sequence has one shot; A medical image processing method according to any one of claims 1 to 12.

14. the first B1 amplitude measurement sequence includes a plurality of shots; determining whether to change the first RF parameter value according to the measurement results includes determining whether to change the first RF parameter value according to the measurement results based on the plurality of shots. A medical image processing method according to any one of claims 1 to 12.

15. determining whether to modify the first RF parameter value in response to the measurement results includes inputting the measurement results into a physical model of a system to receive at least one of a predicted value and a correction value for the first RF parameter value; A medical image processing method according to any one of claims 1 to 12.

16. the first RF parameter value and the second RF parameter value are selected from the group consisting of a flip angle and a transmit amplification gain. A medical image processing method according to any one of claims 1 to 12.

17. changing the first RF parameter value to the second RF parameter value includes changing a pulse sequence applied to a sequence controller. A medical image processing method according to any one of claims 1 to 12.

18. changing the first RF parameter value to the second RF parameter value includes changing an RF transmission correction table. A medical image processing method according to any one of claims 1 to 12.

19. The gantry, at least one RF transmit coil; an RF transmit coil controller; the RF transmit coil controller acquires a first B1 amplitude measurement sequence interspersed within a series of MRI scan sequences for a single MRI examination, the series including a first MRI scan sequence and a second MRI scan sequence having a first RF parameter value; performing the first MRI scan sequence and the first B1 amplitude measurement sequence; a measurement result of the first B1 amplitude measurement sequence determines whether to change a first RF parameter value for the second MRI scan sequence; If it is determined based on the measurement result that the first RF parameter value is to be changed, changing the first RF parameter value to a second RF parameter value different from the first RF parameter value; performing the second MRI scan sequence using the second RF parameter values; Magnetic resonance imaging system.

20. The computer processor acquiring a first B1 amplitude measurement sequence interspersed within a series of MRI scan sequences for a single MRI examination, the series including a first MRI scan sequence and a second MRI scan sequence having a first RF parameter value; performing the first MRI scan sequence and the first B1 amplitude measurement sequence; determining whether to change the first RF parameter value according to a measurement result of the first B1 amplitude measurement sequence; If it is determined based on the measurement result that the first RF parameter value is to be changed, changing the first RF parameter value to a second RF parameter value different from the first RF parameter value; performing the second MRI scan sequence using the second RF parameter values; A medical image processing program that makes this possible.

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