Image processing method, magnetic resonance imaging system, and image processing program

Abstract

To set an RF level capable of improving the image quality.SOLUTION: An image processing method comprises: obtaining spatially resolved B1 amplitude measurements obtained using at least one RF parameter; performing at least one spatially resolved analysis on a spatially resolved subset of the obtained spatially resolved B1 amplitude measurements; determining an updated value of the at least one RF parameter to be used in a series of MRI sequences based on the performed spatially resolved analysis; and storing the updated value of the at least one RF parameter.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The embodiments disclosed herein relate generally to a method, system, and computer program product for acquiring a series of magnetic resonance imaging (MRI) images, and in one embodiment, to a system and computer program product for acquiring MRI images by adjusting a series of MRI scan sequences based on spatially resolved B1 amplitude in a single MRI examination. [Background technology]

[0002] When imaging a patient using an MRI system, the patient enters a gantry of the MRI system and undergoes an examination that includes a series of scan sequences (shown as scan sequence 1 to scan sequence n in FIG. 1 ). After the series of scan sequences is completed during the patient's examination, the patient exits the MRI system.

[0003] Known MRI systems are optionally calibrated for each patient prior to the start of an examination, as shown in the optional pre-scan sequence 102 of FIG. 1, to determine a baseline RF transmit gain level (RFL (RF level)). During the pre-scan process, the RFL is calculated for at least one entire slice of a set of 2D slices, resulting in an RFL that represents the average of the voxels in the slice. The baseline RFL value is then used to calculate transmit gain values ​​to achieve the desired 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 also a major determinant of MR signal strength and image contrast. That is, the RFL value has a known and direct relationship to the B1 field (transmit field) and flip angle. By measuring the B1 field, the RFL can be calculated directly and easily. Generally, if the RFL is too low, "under-tipping" occurs. Under-tipping is a condition in which data is acquired at a flip angle that is lower than expected. Conversely, if the RFL is too high, "overtipping" occurs. Overtipping is when data is acquired at a flip angle that is higher than expected. Both under- and over-chipping can result in poor quality MRI images (e.g., black dots in the image).

[0004] However, even within a single MRI image, non-uniform B1 (ΔB1) can result in non-uniform image signals. Non-uniform B1 fields (transmit fields) can result in non-constant flip angles and signal variations. Such effects have been observed at high field strengths (e.g., 3 T and above) where there is a large B1 variation due to dielectric effects. Variations in effective B1 levels result in dark or bright areas in the image compared to areas of the image with the desired B1 level. In conventional spin echo or fast spin echo imaging, the expected flip angle of the excitation pulse is π / 2 and the expected flip angle of the refocusing pulse is π. In this example, the dark areas in the image are due to under-chipping or over-chipping, where the flip angle is below or above the expected flip angle, respectively. In conventional spin echo or fast spin echo imaging, the image signal is expressed as sin 3 Since it is roughly proportional to ((π / 2)*(1+ΔB1)), for example, in the case of -30% under-chipping, the internal term (argument) of sin is (1+ΔB1=1-0.3=0.7), so the signal = sin 3 (0.7π / 2) = 0.71. For example, in the case of +20% overchipping, the internal term (argument) of sin is (1 + ΔB1 = 1 + 0.2 = 1.2), and the signal = sin 3 (1.2π / 2)=0.86. In the field-echo imaging example, the relationship between signal, flip angle, and tissue T1 relaxation is more complex. Thus, in field-echo imaging, dark (low signal) and bright (high signal) regions can appear due to the variation of the flip angle with ΔB1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Pat. No. 1,089,0631 [Patent Document 2] U.S. Patent No. 9,146,293 [Patent Document 3] US Patent Application Publication No. 2020 / 393526 [Patent Document 4] US Patent Application Publication No. 2020 / 341090 [Patent Document 5] US Patent Application Publication No. 2020 / 003856 [Patent Document 6] US Patent Application Publication No. 2018 / 246178 [Patent Document 7] US Patent Application Publication No. 2013 / 271135 [Patent Document 6] US Patent Application Publication No. 2012 / 280683 [Non-patent literature]

[0006] [Non-Patent Document 1] SCHNEIDER, “Selective Excitation MR Imaging with Parallel Transmission (pTx)”, Dissertation, 2014, 116 pages [Non-Patent Document 2] TENDLER et al., “Use of multi-flip angle measurements to account for transmit inhomogeneity and non-Gaussian diffusion in DW-SSFP”, NeuroImage, 2020, 18 pages Summary of the Invention [Problem to be solved by the invention]

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to set an RF level capable of improving image quality. 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]

[0008] An embodiment of an image processing method comprises obtaining spatially-resolved B1 amplitude measurements obtained using at least one RF parameter, performing at least one spatially-resolved analysis on a spatially resolved subset of the obtained spatially-resolved B1 amplitude measurements, determining an update value of the at least one RF parameter to be used for a series of MRI sequences based on the performed spatially-resolved analysis, and storing the update value of the at least one RF parameter. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 illustrates a patient examination including an optional pre-scan and a series of scan sequences. [Diagram 2] FIG. 2 is a schematic block diagram of an MRI system according to one embodiment of the present disclosure. [Diagram 3] FIG. 3 is a flowchart illustrating an example of a processing procedure for adjusting an MRI image based on spatially resolved B1 amplitude. [Figure 4A] FIG. 4A illustrates spatially resolved B1 amplitude data acquired during the determination of a B1 amplitude distribution that may occur when imaging two human thighs with an initial RF transmit gain level (RFL) as the initial RF parameter. [Figure 4B] FIG. 4B shows MRI images of the two thighs of FIG. 4A taken with initial RFL. [Figure 4C] FIG. 4C shows MRI images of the two thighs of FIGS. 4A and 4B taken while gradually increasing the RFL above the initial RFL of FIG. 4B. [Figure 4D] FIG. 4D shows MRI images of the two thighs of FIGS. 4A and 4B taken while gradually increasing the RFL above the initial RFL of FIG. 4B. [Figure 4E] FIG. 4E shows MRI images of the two thighs of FIGS. 4A and 4B taken while gradually increasing the RFL above the initial RFL of FIG. 4B. [Figure 4F]FIG. 4F shows MRI images of the two thighs of FIGS. 4A and 4B taken while gradually increasing the RFL above the initial RFL of FIG. 4B. [Figure 4G] FIG. 4G shows MRI images of the two thighs of FIGS. 4A and 4B taken while gradually increasing the RFL above the initial RFL of FIG. 4B. [Figure 4H] FIG. 4H shows MRI images of the two thighs of FIGS. 4A and 4B taken while gradually increasing the RFL above the initial RFL of FIG. 4B. [Figure 4I] FIG. 4I shows a grayscale image of the spatially resolved B1 amplitude data of FIG. 4A. [Figure 4J] FIG. 4J is an annotated grayscale image of the spatially resolved B1 amplitude data of FIG. 4I showing two dark regions representing B1 amplitude data below the intended average value. [Figure 5A] FIG. 5A is a series of annotated images acquired with initial and increased RFL illustrating the effect of RFL on under- and over-chipping. [Figure 5B] FIG. 5B is a map showing the distribution of a series of annotated B1 amplitude values ​​obtained at the initial RFL of FIG. 5A and at increased RFLs, illustrating the change in B1 amplitude data with changing RFL. [Figure 5C] FIG. 5C shows a grayscale image of the annotated B1 amplitude map of FIG. 5B. [Figure 6A] FIG. 6A is a map showing a distribution of spatially resolved B1 amplitude values ​​that indicate the variation in B1 amplitude over a portion of an imaged object. [Figure 6B] FIG. 6B is an annotated image of a map showing the distribution of spatially resolved B1 amplitude values ​​from FIG. 6A, illustrating a circular region of interest selected for use in determining the amount of correction to the initial RF imaging parameters. [Figure 6C] FIG. 6C shows a grayscale image of the spatially resolved B1 amplitude map of FIG. 6A. [Figure 6D]FIG. 6D is an annotated grayscale image of a map showing the distribution of spatially resolved B1 amplitude values ​​from FIG. 6A, showing a circular region of interest selected for use in determining the amount of correction to the initial RF imaging parameters. [Figure 7A] FIG. 7A is a diagram showing an example of a map showing the distribution of B1 amplitude values ​​of the subject's thigh. [Figure 7B] FIG. 7B illustrates a B1 amplitude projection corresponding to the projection direction represented by line 705 in FIG. 7A. [Figure 7C] FIG. 7C illustrates a B1 amplitude projection corresponding to the projection direction represented by line 710 in FIG. 7A. [Figure 7D] FIG. 7D illustrates a B1 amplitude projection corresponding to the projection direction represented by line 715 in FIG. 7A. [Figure 7E] FIG. 7E illustrates a projection of the B1 amplitude corresponding to the projection direction represented by line 720 in FIG. 7A. [Figure 7F] FIG. 7F is a diagram showing an example of the B1 grayscale map of FIG. 7A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] Reference will now be made to the drawings, in which like reference numbers indicate the same or equivalent parts throughout the various views. 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 500.

[0015] 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 500 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] The bed body 50 of the bed 500 can move the top board 51 vertically and horizontally. The bed body 50 moves the top board 51, on which an object is placed, to a predetermined height before imaging. Then, when imaging the object, the bed body 50 moves the top board 51 horizontally to move the object into the bore.

[0020] 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. The whole-body coil 12 may be referred to as a transmit coil.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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).

[0025] The console 400 is configured as a computer comprising a processing circuit 40 , a memory 41 , a display 42 and an input interface 43 .

[0026] 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.

[0027] The display 42 is a display device such as a liquid crystal display panel, a plasma display panel, or an organic EL panel.

[0028] 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.

[0029] 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 processing based on its own processor and programs.

[0030] The console 400 controls the entire MRI system 1 by 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 causes the sequence controller 34 to execute a scan according to the input imaging conditions, 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.

[0031] In the configuration of the MRI system 1 shown in FIG. 2, the control cabinet 300, the gantry 100 and the bed 500 (ie, all components except the console 400) constitute an imaging section or scanner.

[0032] 3 is a flow chart illustrating an exemplary method 305 including an example procedure for making spatially resolved B1 amplitude-based adjustments to MRI images acquired by MRI system 1. Method 305 begins at step 310, where MRI system 1 (or a remote system in communication and cooperation with MRI system 1) acquires spatially-resolved B1 amplitude measurements of an object (e.g., a person being imaged) using initial RF parameters (e.g., at an initial RFL). The initial RF parameters are set according to multiple MRI sequences acquired for the object. For example, acquisition processing of spatially resolved B1 amplitude data may include, but is not limited to, performing Bloch-Siegert Shift (BSS) processing, Actual Flip Angle Imaging (AFI) method, Dual Refocusing Echo Acquisition Mode (DREAM), Double Angle Method (DAM) processing, Phase-sensitive (PS) processing, Saturation recovery (SR) processing, etc. Spatially resolved B1 amplitude measurements may be acquired as 1D projections, 2D slices, or 3D volumes. A subset of measurements may be used rather than the full set of measurements.

[0033] The spatially resolved B1 amplitude measurements correspond, for example, to a B1 map. The B1 map may be expressed as a one-dimensional B1 map showing the distribution of B1 in one dimension, a two-dimensional B1 map showing the distribution of B1 in two dimensions, or a three-dimensional B1 map showing the distribution of B1 in three dimensions. The one-dimensional B1 map corresponds to the one-dimensional projection. The two-dimensional B1 map corresponds to the 2D slice. The three-dimensional B1 map corresponds to the 3D volume.

[0034] The processing circuitry 40 obtains spatially resolved B1 amplitude measurements obtained using at least one RF parameter, such as a flip angle, a shimming setting, or a gain level of an RF transmission.

[0035] The acquisition of the spatially resolved B1 amplitude measurements is not limited to the acquisition by the processing circuitry 40, and may be acquired by the sequence controller 34. The processing circuitry 40 acquires the spatially resolved B1 amplitude measurements using a Bloch-Siegert shift sequence as described above. The processing circuitry 40 may acquire the spatially resolved B1 amplitude measurements by Actual Flip Angle imaging as described above. The processing circuitry 40 also acquires 1D projections, 2D slices, or 3D volumes.

[0036] As used herein, "acquire" means to receive from the memory 41 or storage system of the MRI system 1, or entirely from an external source. Also, "acquire" means that a portion of information is acquired from one source and combined with additional information or modified so that the combined / modified 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 a spatially resolved B1 amplitude measurement sequence. Similarly, a series of MRI sequences may be acquired from one source (memory 41 or an external device) and modified to change at least one initial RF imaging parameter.

[0037] FIG. 4A illustrates spatially resolved B1 amplitude data acquired (e.g., by the BSS or AFI method of B1 mapping) during the determination of a possible B1 amplitude distribution when imaging two human thighs at an initial RFL (i.e., an RFL where the expected average B1 value for the entire imaging region is 1.0). As shown, a complete B1 amplitude map is acquired corresponding to a particular cross-section of the object (e.g., a human) to be imaged, although the acquired B1 amplitude map for the cross-section may be less than complete. The B1 amplitude data may be acquired during a portion of the pre-scan where the B1 shimming calibration is performed, so as not to increase the overall processing time of the MRI process. Alternatively, a fast projection method requiring a short scan time (e.g., about 60 to 80 ms) may be utilized without the B1 shimming calibration. In yet another embodiment, the B1 amplitude data may be acquired after a portion of the pre-scan where the B1 shimming calibration is performed, so as to match the B1 amplitude data as closely as possible to the time before the spatially resolved B1 amplitude measurements are acquired. In another embodiment, complete or partial B1 amplitude maps for other cross-sections may be acquired.

[0038] FIG. 4B shows MRI images of the two thighs of FIG. 4A imaged with initial RFL. FIG. 4B includes a symbol "-" added to the upper right of the left thigh (left thigh) to highlight the shading of the left thigh. This shading corresponds to the blue and green portions of the B1 map of FIG. 4A and indicates that the B1 amplitude data does not reach the B1 target value of 1.0 (shown in yellow in FIG. 4A) and is below the B1 target value causing signal distortion due to under-chipping. The green portion corresponds to about 80% of the target B1, and the blue portion corresponds to about 60% of the target B1. The amplitude values ​​decrease toward the center of the blue portion and increase away from the center of the blue portion. The blue and green portions of FIG. 4A correspond to the dark portions of the B1 amplitude grayscale map of FIG. 4I. These areas are highlighted on the annotated B1 amplitude map of FIG. 4J. In the map of Figure 4J, the outer white ellipse corresponds to the green region with a B1 value of approximately 80% of the target B1, and the inner white ellipse corresponds to the blue region with a B1 value of approximately 60% of the target B1. In Figure 4J, the amplitude values ​​decrease towards the center of the inner ellipse and increase away from the center of the inner ellipse.

[0039] 4C-4H show MRI images of the two thighs of FIGS. 4A and 4B, imaged at RFLs gradually increasing above the initial RFL (i.e., 1.05, 1.10, 1.15, 1.20, 1.25, 1.30 times the initial RFL). As is evident from FIG. 4C, when imaged at 1.05 times the RFL of FIG. 4B (i.e., 1.05×), the portion of the image containing signal distortion due to under-chipping in FIG. 4B shows improvement (i.e., less shading) compared to FIG. 4B, but the shading still remains. As the RFL increases to 1.10× and 1.15×, the under-chipping effect continues to decrease until about 1.20×. At about 1.20×, the shading starts to disappear in FIG. 4F (indicated by the symbol “=”). However, increasing the RFL produces overchipping in the right thigh, at least from an RFL of 1.15× (Figure 4E), and deteriorates other parts of the image (indicated by the symbol "+"). In Figures 4G and 4H, even with a larger RFL, overchipping is seen in at least two areas (indicated by the symbol "+").

[0040] Returning to the description of method 305 of FIG. 3, once the spatially resolved B1 amplitude measurements have been acquired in step 310, control proceeds to step 315 where spatially-resolved analysis is performed on the spatially resolved subsets of acquired spatially resolved B1 amplitude data in sequence (e.g., to address under-chipping and / or over-chipping issues resulting from an initial RFL of the acquired series of MRI sequences). In one embodiment, the received spatially resolved B1 amplitude measurements are quantized and optionally filtered prior to histogramming. In histogramming, for example, the acquired B1 amplitude data is quantized into different values ​​and used to calculate a histogram.

[0041] Prior to the histogram calculation, filtering of the B1 amplitude data may be performed. For example, B1 amplitude values ​​below a certain threshold are removed since they correspond to air, not tissue, which is of interest to the image reviewer (e.g., a medical professional such as a radiologist). Similarly, values ​​above a statistical threshold (e.g., 4 standard deviations) from the mean B1 amplitude value are removed since they are likely anomalous data. Additionally, a position-based mask may be applied to the data to remove any values ​​outside the mask. The mask region may be automatically selected by the system based on factors such as the type of region being imaged (e.g., thigh, prostate, skull, etc.) and / or patient-specific parameters (e.g., patient weight, which affects the side / location of the region being imaged relative to the center of the region being imaged), obtained via input from the operator of the MRI system 1 or stored in memory 41. Alternatively, the B1 amplitude data may be filtered and then quantized.

[0042] The spatially resolved analysis may be referred to as spatially resolved analysis. The processing circuitry 40 performs at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurement values. Then, the processing circuitry 40 determines an update value of at least one RF parameter used in a series of MRI sequences based on the performed spatially resolved analysis. The histogram processing corresponds to the spatially resolved analysis. The histogram indicates, for example, the frequency of B1 amplitude values. For example, the processing circuitry 40 selects the spatially resolved subset using the histogram. In addition, in the filtering performed before the histogram calculation, the processing circuitry 40 performs a filtering process using a predetermined threshold on a B1 map indicating the distribution of B1 amplitude values ​​in the B1 amplitude data. At this time, the processing circuitry 40 performs at least one spatially resolved analysis on the spatially resolved B1 amplitude measurement values ​​(for example, the B1 map) after filtering.

[0043] The number of occurrences of the quantized data values ​​over the plurality of B1 amplitude values ​​to be processed is determined from the histogram and processing based on the calculated information is performed in step 320. As will be explained in more detail below, the plurality of B1 amplitude values ​​to be processed are obtained from at least one 1D projection, partial or complete slice (i.e., two-dimensional data), or partial or complete three-dimensional volume. In other words, the plurality of B1 amplitude values ​​to be processed are obtained from a B1 map.

[0044] In a first embodiment of step 320, at least one set of extreme values ​​in the B1 amplitude data is addressed by performing a spatially resolved process, which is a process of spatially resolved analysis. For example, a minimum of X% (e.g., 10% or 15%) of the B1 amplitude data is used to increase the average B1 value produced during imaging (herein, "X" is considered to be the percentage of the first extreme value threshold). In such an embodiment, the predetermined target amount B1 obtained in step 310 is target The transmit RFL that produces an average B1 value of (e.g., 1.0) is target Histogram of values ​​(average is B1 low region The B1 amplitude is then modified by dividing it by the average of the smallest X% of the B1 amplitude values ​​(referred to as the B1 amplitude). target The initial RFL that generates the value (RFL initial The new transmission RFL (RFL) is used instead of new ) is calculated using the following formula (1).

[0045] RFL new =RFL initial ×(B1 target ) / (B1 low region ) (Formula 1)

[0046] The spatially resolved subset is the smallest percent of the acquired spatially resolved B1 amplitude measurements. For example, the processing circuitry 40 determines an update value for at least one RF parameter based on a ratio of the average of the smallest percent to a target B1 amplitude value. In equation (1), the average of the smallest X% of the B1 amplitude values ​​in the histogram corresponds to the average of the smallest percent of the acquired spatially resolved B1 amplitude measurements. That is, the B1 in equation (1) low region corresponds to the smallest percentile average of the acquired spatially resolved B1 amplitude measurements. Also, the predetermined target quantity B1 in Eq. target corresponds to the target B1 value, for example. From these facts, the above ratio in the formula (1) is target ) / (B1 low region In addition, the new transmission RFL (RFL new ) corresponds to, for example, an updated value of at least one RF parameter. In other words, the initial RFL (RFL initial ) to ratio (B1 target ) / (B1 low region ) to obtain the updated value of the RF parameters (RFL new ) is obtained.

[0047] Although such a correction increases B1 in dark hole regions, some regions may become over-chipped.

[0048] In another embodiment, to avoid over-chipping, B1 target The value is initially reduced by a reduction factor (RFx, e.g., 0.85) to avoid overly altering the image quality obtained by very low B1 values ​​in the low B1 value region. In such an embodiment, the new transmit RFL is calculated as follows:

[0049] RFL new =RFL initial ×(RFx×B1 target ) / (B1 low region ) (Formula 2)

[0050] In yet another embodiment, the new RFL value is limited by a predefined maximum percentage (maximum factor), for example using a maximum function (max(x,y)) whose result is less than or equal to x. Such an embodiment is described by equation (3) below.

[0051] RFL new =max(RFL initial ×maxfactor,RFL initial ×(B1 target ) / (B1 low region )) (Formula 3)

[0052] In yet another embodiment, rather than addressing under-chipping by increasing the new RFL with a lower extreme value, the RFL can be increased by increasing the higher extreme value (e.g., up to Y%), such as 10% or 15%. new Reduces B1 low region Instead of the average, use the corresponding average (B1 high region ) and / or by using a minimum function instead of a maximum function (herein "Y" is considered as a percentage of the second extreme threshold).

[0053] The above-described embodiment is directed to the RFL used in the imaging sequence. new The value of B is increased or decreased by addressing only the average value of one of the two extreme values. In yet another embodiment of a variation of step 320, a balanced approach addresses the average values ​​of both very high and very low values ​​in the B1 amplitude data (thresholds X and Y for the high and low values ​​may not be the same, e.g., 5% for the high region and 10% for the low region). In such an embodiment, the method increases or decreases B based on the following formula: low region and B. high region B1, which is the average of the high and low averages average Determine the value.

[0054] B1 average =(B1 low region +B1 high region ) / 2 (Equation 4)

[0055] In the above description, the spatially resolved subset is the smallest first percent of the spatially resolved B1 amplitude measurements and the largest second percent of the spatially resolved B1 amplitude measurements. As shown in equation (4), processing circuitry 40 calculates the average of the first percent and the average of the second percent. This allows processing circuitry 40 to calculate the average B1 average At this time, the processing circuit 40 calculates the update value of the RF parameter (RFL new ) is calculated using the following formula (5).

[0056] That is, RFL new is calculated by the following formula (5).

[0057] RFL new =RFL initial ×(B1 target ) / (B1 average ) (Equation 5)

[0058] Such an embodiment does not increase B1 as much in the low region, but has the advantage of avoiding severe overchipping.

[0059] FIG. 5A shows a series of annotated images acquired with initial and increased transmit RFLs by the method of Equation 1 and Equation (5) above (using all values ​​in the B1 amplitude map that were not removed as corresponding to non-air (i.e., greater than the air threshold)). The image in FIG. 5A with the initial RFL (designated 1.00) contains dark shaded areas indicated by arrows. These shaded areas correspond to areas below the target B1 amplitude value (e.g., less than 1.0) on the initial B1 map (designated 1.00) in FIG. 5B. FIG. 5B shows that at the initial RFL, there is at least one area on each leg that is below the target B1 amplitude value. The green areas correspond to approximately 80% of the target B1, and the blue areas correspond to approximately 60% of the target B1. The amplitude values ​​decrease toward the center of the blue area and increase away from the center of the blue area. The blue and green areas in FIG. 5B above correspond to the dark areas of the B1 amplitude grayscale map in FIG. 5C. These areas are highlighted on the annotated B1 amplitude map in FIG. 5C. In Fig. 5C, the outer white ellipse corresponds to a green region with a B1 value of about 80% of the target B1, and the inner white ellipse corresponds to a blue region with a B1 value of about 60% of the target B1. In Fig. 5C, the amplitude values ​​decrease towards the center of the inner ellipse and increase away from the center of the inner ellipse.

[0060] B1 in the above formula 1 low region By the correction method, RFL new The value is increased to 1.2x in the image shown at 1.20, making the original shaded area less dark (as indicated by the top left arrow in the 1.20 image). The change in RFL corresponds to an increase in the B1 value in the corresponding map. For example, the B1 value of the left foot is substantially removed from the range of about 60% of the target B1. This is evident from the substantial elimination of the blue area on the right side of the 1.20B1 amplitude map in FIG. 5B and the disappearance of the inner ellipse on the right side of the 1.20B1 amplitude map in FIG. 5C. However, this approach causes an exemplary strong over-chipping in the areas identified by the top right and bottom left arrows in the image shown at 1.20 and the corresponding B1 amplitude maps in FIGS. 5B and 5C.

[0061] In contrast, for the balanced approach described in relation to equation (5), an increase of only 1.10x results in an improvement (though not complete elimination) of the dark hole in the left front in the image marked 1.10 in FIG. 5A. This improvement corresponds to a reduction in the green and blue areas in FIG. 5C and a reduction in the size of the ellipse in FIG. 5C. There is no excessive over-chipping, although a small amount of over-chipping is observed in the front of the right leg.

[0062] In each of the above embodiments, after determining at least one updated RF parameter (e.g., a new RFL, a new flip angle, or a new B1 shimming setting) to be used for the series of MRI sequences (step 320), control proceeds to step 325. In step 325, the determined at least one updated RF parameter is stored in memory 41 or a storage device (either by itself or as part of a scan sequence for acquiring the series of MRI sequences). In embodiments where steps 310 to 325 are performed within MRI system 1, control proceeds to steps 325 to 330, where MRI system 1 performs (and stores the results of) the series of MRI sequences before terminating method 305. Alternatively, in embodiments where steps 310 to 325 are performed outside MRI system 1, MRI system 1 retrieves the stored at least one updated RF parameter from memory 41 (e.g., when acquiring the corresponding series of MRI sequences) and performs the series of MRI sequences before terminating method 305.

[0063] That is, the processing circuit (RF transmit coil controller) 40 calculates an updated value (RFL new ) in step S330. Also, the sequence controller 34 stores the updated value (RFL new ) to perform a series of MRI sequences.

[0064] The spatially resolved analysis of the received spatially resolved B1 amplitude data is not limited to the above-described processing of steps 315 and 320. In alternative embodiments, the histogram processing is replaced by a number of alternative processing methods, including:

[0065] In a first alternative embodiment, the histogram of the complete slice is replaced by a region of interest process based on analysis (e.g., visual or automated inspection) of one-, two-, or three-dimensional spatially resolved B1 amplitude data. FIG. 6A shows a map showing a distribution of spatially resolved B1 amplitude values ​​representing the variation of B1 amplitude across a two-dimensional portion of an imaged object that can be obtained by the process of step 310. In an embodiment in which the MRI operator is presented with the map of FIG. 6A, the MRI operator can select at least one region of interest on the map using the input interface 43. FIG. 6B shows an example of a region of interest drawn on the B1 amplitude map by the MRI operator to indicate the region of interest (i.e., the system needs to select values ​​to use for statistical processing and determine high and / or low regions for initial RFL modification).

[0066] Figure 6C illustrates a spatially resolved B1 amplitude grayscale map representing the variation of B1 amplitude across a two-dimensional portion of an imaged object that may be obtained by the process of step 310 and may be used in place of the color map of Figure 6A. In embodiments where the MRI operator is presented with the map of Figure 6C, the MRI operator may select at least one region of interest on the map using input interface 43. Figure 6D illustrates an example of a region of interest that the MRI operator has drawn on the B1 amplitude map to indicate the region of interest (i.e., the system needs to select values ​​to use in statistical processing and determine high and / or low regions for initial RFL changes).

[0067] FIG. 6B is an annotated image of the map showing the distribution of spatially resolved B1 amplitude values ​​of FIG. 6A, showing a circular region of interest drawn or selected by the MRI operator. The circular region of interest is used to define a mask indicating where to select values ​​to determine the amount of correction applied to the initial RF imaging parameters. Shapes other than a circle may be used to identify the two-dimensional region of interest. The shape, location and size of the shape may be automatically selected by the system based on factors such as the type of region being imaged (e.g., thigh, prostate, skull) and / or patient-specific parameters (e.g., patient weight affecting the side / location of the imaged region relative to the center of the imaged region). In such a configuration, the two-dimensional region of interest is used as a mask to remove unwanted data outside the two-dimensional region of interest.

[0068] As described above, processing circuitry 40 may use a region of interest to select a spatially resolved subset in a spatially resolved analysis, i.e., performing at least one spatially resolved analysis on a spatially resolved subset of acquired spatially resolved B1 amplitude measurements may include selecting a spatially resolved subset using a region of interest.

[0069] Alternatively, the MRI system 1 may collect the B1 data as 1D projection data. The geometric orientation of the 1D projection may be automatically selected by the system based on factors such as the type of region being imaged (e.g., thigh, prostate, skull) and / or patient-specific parameters (e.g., patient weight affecting the side / location of the region being imaged relative to the center of the region being imaged).

[0070] In an embodiment utilizing an automated examination, the method utilizes (1) an artificial neural network trained to generate correction coefficients from the spatially resolved B1 amplitude data and / or (2) a priori knowledge of the expected locations of low / high B1 regions for automatic selection of regions of interest. For example, based on the region of the object being scanned, the locations of the regions of interest with low / high B1 values ​​can be stored in memory 41 along with factors that may change the location of the regions of interest (e.g., the type of region being imaged and / or patient-specific parameters). For example, due to physical dielectric effects and the approximately cylindrical shape of most patients' legs, the approximate locations of low B1 (ΔB1<1) and high B1 (ΔB1>1) regions for all people will be approximately the same. Thus, the locations of these regions are known and certain a priori. The placement of the regions can be slightly altered based on a preceding positioning image (e.g., a scout image). The positioning images are typically collected during an MR examination to guide the scan plan in the protocol.

[0071] 7A to 7E show how the selection of 1D projection directions improves the sensitivity of B1 measurements. The projection data shown in Fig. 7B to 7E correspond to different projection directions (705, 710, 715, 720) of the B1 map showing the distribution of B1 amplitude values ​​of the subject's thigh in Fig. 7A and the B1 grayscale map in Fig. 7F. The horizontal axis of each of Fig. 7B to 7E corresponds to 128 spatial locations of the projection destinations of each projection direction (705, 710, 715, 720), measured with FOV=45 cm as shown. The projection direction 710 of the B1 projection data shown in Fig. 7C is the preferred direction because it allows observation of areas with low B1 amplitude (e.g., the left anterior part of the thigh). The dip between the black circle (●) and the white circle (○) of the projection data in Fig. 7C corresponds to the average B1 amplitude value obtained approximately between the black circle and the white circle in Fig. 7A and 7F, where the average value is obtained perpendicular to the projection direction.

[0072] Other projection directions (705, 715, 720 shown in Figures 7B, 7D, 7E, respectively) show how the low / high B1 regions are largely unobservable due to averaging of B1 amplitude along the dimension projected orthogonal to each line. Also, as is evident from Figures 7B-7E, in at least one embodiment, an air threshold of 0.6 may be selected.

[0073] The horizontal axis of Fig. 7B shows the spatial position of the destination of projection 705. The horizontal axis of Fig. 7B shows the spatial position of the destination of projection 705. The horizontal axis of Fig. 7C shows the spatial position of the destination of projection 710. The horizontal axis of Fig. 7D shows the spatial position of the destination of projection 715. The horizontal axis of Fig. 7D shows the spatial position of the destination of projection 720.

[0074] Although the analysis of all (non-air) B1 amplitude values ​​for a particular 1D projection is described, any sub-part of the 1D projection may be used. For example, a projection may contain multiple regions with low B1 values ​​(called holes). Also, statistical calculations that do not distinguish between multiple holes combine values ​​from multiple holes during processing (e.g., when determining the minimum X% of non-air values). Some imaging regions may be processed based on information from two holes, while in other embodiments, only the minimum Z% of the hole containing the deeper hole is used.

[0075] In yet another embodiment, the B1 amplitude data can be limited to a particular region of a 2D slice or 3D volume by the process described herein. For example, the process can use the entire data set to determine the (non-air) minimum and select only values ​​within a certain distance from the minimum to be used to calculate the new RFL. Similarly, a region growing method can be applied to the 2D slice or 3D volume to determine all values ​​within a threshold that correspond to holes with the most adjacent low-value data values.

[0076] 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:

[0077] (1) An image processing method comprising, but not limited to, acquiring spatially resolved B1 amplitude measurements obtained using at least one RF parameter, performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements, determining an updated value of the at least one RF parameter to be used for a series of MRI sequences based on the performed spatially resolved analysis, and storing the updated value of the at least one RF parameter.

[0078] (2) The method of (1), further comprising, but not limited to, performing the series of MRI sequences using the updated value of the at least one RF parameter.

[0079] (3) The method according to (1) or (2), wherein the at least one RF parameter is a gain level of an RF transmission.

[0080] (4) A method according to any one of (1) to (3), wherein performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements includes, but is not limited to, selecting the spatially resolved subset using a histogram.

[0081] (5) A method according to any one of (1) to (3), wherein performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements includes, but is not limited to, selecting the spatially resolved subset using a region of interest.

[0082] (6) the spatially resolved subset is a minimum percent of the acquired spatially resolved B1 amplitude measurements; The method of any one of (1) to (3), wherein determining the update value of the at least one RF parameter includes, but is not limited to, determining the update value of the at least one RF parameter based on a ratio between (1) a target B1 amplitude value and (2) a minimum percentile average value of the acquired spatially resolved B1 amplitude measurements.

[0083] (7) the spatially resolved subset is (a) a smallest first percent of the acquired spatially resolved B1 amplitude measurements and (b) a largest second percent of the acquired spatially resolved B1 amplitude measurements; Determining the update value of the at least one RF parameter includes determining the update value of the at least one RF parameter based on a ratio of: (1) Target B1 amplitude value, (2) (2a) an average of a first percentile of the smallest acquired spatially resolved B1 amplitude measurements; and (2b) an average of a second percentile of the largest acquired spatially resolved B1 amplitude measurements. A method according to any one of (1) to (3).

[0084] (8) A method according to any one of (1) to (7), wherein obtaining the spatially resolved B1 amplitude measurements includes, but is not limited to, obtaining the spatially resolved B1 amplitude measurements using a Bloch-Siegert shift sequence.

[0085] (9) A method according to any one of (1) to (7), wherein obtaining the spatially resolved B1 amplitude measurements includes, but is not limited to, obtaining the spatially resolved B1 amplitude measurements by Actual Flip Angle (AFP) imaging.

[0086] (10) A method according to any one of (1) to (9), wherein obtaining the spatially resolved B1 amplitude measurements includes, but is not limited to, obtaining 1D projections.

[0087] (11) A method according to any one of (1) to (9), wherein acquiring the spatially resolved B1 amplitude measurements includes, but is not limited to, acquiring 2D slices.

[0088] (12) A method according to any one of (1) to (9), wherein obtaining the spatially resolved B1 amplitude measurements includes, but is not limited to, obtaining a 3D volume.

[0089] (13) A method according to any one of (1) to (12), wherein performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements includes, but is not limited to, filtering the spatially resolved subset of the acquired spatially resolved B1 amplitude measurements and performing the at least one spatially resolved analysis on the filtered spatially resolved B1 amplitude measurements.

[0090] (14) The method according to any one of (1), (2), and (4) to (13), wherein the at least one RF parameter is a flip angle.

[0091] (15) A method according to any one of (1), (2), and (4) to (13), wherein the at least one RF parameter is a shimming setting.

[0092] (16) A magnetic resonance imaging system including, but not limited to, a gantry, at least one RF transmit coil, and an RF transmit coil controller for performing any one of the procedures described in (1) to (15).

[0093] (17) A computer program product, including, but not limited to, a computer-readable storage medium communicatively connected to a computer processor, the computer instructions including computer instructions that, when executed by the computer processor, cause the computer processor to perform any one of the steps set forth in (1) through (15).

[0094] When the technical idea of ​​the embodiment is realized by an image processing method, the image processing method obtains spatially-resolved B1 amplitude measurements obtained using at least one RF parameter, performs at least one spatially-resolved analysis on a spatially resolved subset of the obtained spatially-resolved B1 amplitude measurements, determines an update value of at least one RF parameter used in a series of MRI sequences based on the performed spatially-resolved analysis, and stores the update value of at least one RF parameter. The procedures and effects of various processes related to this image processing method are the same as those described in the embodiment, so the description will be omitted.

[0095] When the technical idea of ​​the embodiment is realized by an image processing program, the image processing program causes a computer to acquire spatially resolved B1 amplitude measurement values ​​obtained using at least one RF parameter, perform at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurement values, determine an update value of at least one RF parameter used in a series of MRI sequences based on the performed spatially resolved analysis, and store the update value of the at least one RF parameter.

[0096] For example, the image processing program may be installed in a computer in a modality such as an MRI apparatus and developed in memory to realize the processing shown in Fig. 3. In this case, the program that allows the computer to execute the processing may 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 image processing program are the same as those in the embodiment, and therefore will not be described.

[0097] According to at least one of the embodiments described above, it is possible to set an RF level capable of improving image quality. For example, according to the magnetic resonance imaging system 1 in the present embodiment, it is possible to reduce the dark hole region while avoiding excessive over-chip. In addition, according to the magnetic resonance imaging system 1 in the present embodiment, it is possible to realize efficient adjustment of the RF level and accurate automatic calculation of the RF level. That is, according to the magnetic resonance imaging system 1 in the present embodiment, it is possible to add an accurate amount of RFL to each patient with a higher SAR efficiency than the conventional +2 dB method, and it is possible to avoid unnecessary over-chip. In addition, according to the magnetic resonance imaging system 1 in the present embodiment, it is possible to calculate (adjust) the RF level using the same data as the B1 shim calibration, so that it is possible to realize the adjustment of the RF level with zero or a small additional scan time.

[0098] 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]

[0099] 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 500 berths

Claims

1. obtaining a spatially resolved B1 amplitude measurement obtained using at least one RF parameter; performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements; determining an updated value of the at least one RF parameter for use in a series of MRI sequences based on the performed spatially resolved analysis; storing the updated value of the at least one RF parameter; An image processing method comprising:

2. performing the series of MRI sequences using the updated value of the at least one RF parameter; The image processing method of claim 1 further comprising:

3. the at least one RF parameter is a gain level of an RF transmission; The image processing method according to claim 1 .

4. performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements includes selecting the spatially resolved subset using a histogram. The image processing method according to claim 1 .

5. performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements includes selecting the spatially resolved subset using a region of interest. The image processing method according to claim 1 .

6. the spatially resolved subset being a minimum percent of the acquired spatially resolved B1 amplitude measurements; determining an updated value of the at least one RF parameter based on a ratio of a target B1 amplitude value to the minimum percentage average value; The image processing method according to claim 1 .

7. the spatially resolved subset being a smallest first percent of the spatially resolved B1 amplitude measurements and a largest second percent of the spatially resolved B1 amplitude measurements; determining an updated value of the at least one RF parameter based on a ratio of a target B1 amplitude value to an average of the first percentage average value and the second percentage average value; The image processing method according to claim 1 .

8. obtaining the spatially resolved B1 amplitude measurements includes obtaining the spatially resolved B1 amplitude measurements using a Bloch-Siegert shift sequence. The image processing method according to claim 1 .

9. obtaining the spatially resolved B1 amplitude measurements includes obtaining the spatially resolved B1 amplitude measurements by Actual Flip Angle Imaging. The image processing method according to claim 1 .

10. obtaining the spatially resolved B1 amplitude measurements includes obtaining 1D projections. The image processing method according to claim 1 .

11. The image processing method of claim 1 , wherein obtaining the spatially resolved B1 amplitude measurements comprises obtaining 2D slices.

12. obtaining the spatially resolved B1 amplitude measurements includes obtaining a 3D volume. The image processing method according to claim 1 .

13. performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements, performing filtering on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements; performing the at least one spatially resolved analysis on the filtered, spatially resolved B1 amplitude measurements. The image processing method according to any one of claims 1 to 12.

14. the at least one RF parameter is a flip angle; The image processing method according to claim 1 .

15. the at least one RF parameter is a shimming setting; The image processing method according to claim 1 .

16. The gantry, At least one RF transmit coil; an RF transmit coil controller; Equipped with The RF transmit coil controller includes: obtaining spatially resolved B1 amplitude measurements obtained using at least one RF parameter; performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements; determining an updated value of the at least one RF parameter for use in a series of MRI sequences based on the performed spatially resolved analysis; storing the updated value of the at least one RF parameter; Magnetic resonance imaging system.

17. On the computer, obtaining spatially resolved B1 amplitude measurements obtained using at least one RF parameter; performing at least one spatially resolved analysis on a spatially resolved subset of the acquired spatially resolved B1 amplitude measurements; determining an updated value of the at least one RF parameter for use in a series of MRI sequences based on the performed spatially resolved analysis; storing the updated value of the at least one RF parameter; This is an image processing program that realizes this.

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