Method and system for coil selection in magnetic resonance imaging

Abstract

The present invention is entitled "Methods and Systems for Coil Selection in Magnetic Resonance Imaging". The present invention provides various methods and systems for selecting coil elements from a plurality of coil elements of a radio frequency (RF) coil array used in a magnetic resonance imaging (MRI) system. In one example, a method includes grouping the plurality of coil elements into receive element group (REG) elements according to receive element group (REG) information, generating a channel sensitivity map for the plurality of coil elements, generating a REG sensitivity map based on the REG information and the channel sensitivity map, marking each REG as selectable or non-selectable based on the REG sensitivity map, selecting one or more REGs from the selectable REGs based on the REG sensitivity map and a region of interest (ROI), and scanning the ROI with the coil elements in the one or more selected REGs activated and without the coil elements in any other selected REGs being deactivated.

Description

[0001] This application is a divisional application of the invention patent application with the application date of May 30, 2019, application number "201910463808.6", and invention name "Method and system for coil selection in magnetic resonance imaging". Technical Field

[0002] Embodiments of the subject matter disclosed herein relate to magnetic resonance imaging, and more particularly, to selecting a radio frequency (RF) coil array during magnetic resonance imaging. Background Art

[0003] Magnetic resonance imaging (MRI) is a medical imaging modality that can create images of the human body without the use of x-rays or other ionizing radiation. MRI uses powerful magnets to generate a strong, uniform static magnetic field, B0. When a person or part of a person is placed in the magnetic field, B0, the nuclear spins associated with the hydrogen nuclei in tissue water become polarized, with the magnetic moments associated with these spins preferentially aligning along the direction of the magnetic field, B0, resulting in a small net tissue magnetization along that axis. MRI systems also include gradient coils, which generate small-amplitude, spatially varying magnetic fields with orthogonal axes to spatially encode magnetic resonance (MR) signals by creating a characteristic resonant frequency at each location in the body. The hydrogen nuclei are excited by a radio frequency signal at or near their resonant frequency, which adds energy to the nuclear spin system. As the nuclear spins relax back to their resting energy state, they release the absorbed energy in the form of an RF signal. This RF signal (or MR signal) is detected by one or more RF coil arrays and converted into an image using a computer and known reconstruction algorithms.

[0004] In some examples, the RF coil array used to receive MR signals can be a local or surface RF coil array that can be placed on or above the imaging subject. The size, position, and / or orientation of such a coil array can be adjusted. For example, based on a given imaging objective, the operator can position a selected surface RF coil array above the imaging subject and insert the RF coil array into the MRI system. Depending on the configuration of the RF coil array and the size of the imaging subject, the operator can position the RF coil array in a first orientation or in a second orientation rotated relative to the first orientation. Summary of the Invention

[0005] In one embodiment, a method for performing magnetic resonance imaging (MRI) using a receive radio frequency (RF) coil array comprising a plurality of coil elements is provided. The method includes grouping the plurality of coil elements into receive element group (REG) elements according to receive element group (REG) information, generating channel sensitivity maps for the plurality of coil elements, generating a REG sensitivity map based on the REG information and the channel sensitivity map, marking each REG as selectable or non-selectable based on the REG sensitivity map, selecting one or more REGs from the selectable REGs based on the REG sensitivity map and a region of interest (ROI), and scanning the ROI with the coil elements in the one or more selected REGs activated and without the coil elements in any other selected REGs deactivated.

[0006] It should be understood that the above brief description is provided to introduce in simplified form selected concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0008] Figure 1 is a block diagram of an MRI system according to an embodiment.

[0009] Figure 2A is an exemplary arrangement of the RF coil array relative to the imaging subject.

[0010] Figure 2B An exemplary RF coil array is schematically shown.

[0011] Figure 3 is a flow chart illustrating an exemplary method of selecting coil elements of an RF coil array for an MRI scan.

[0012] Figure 4 is a flow chart illustrating an exemplary subroutine for determining a dynamic coil mode based on data acquired from a calibration scan.

[0013] Figure 5 Shown by Figure 4 The subroutines process the data.

[0014] Figure 6 An exemplary projection of the calibration data to generate a channel sensitivity map is schematically shown.

[0015] Figure 7 is a flow chart illustrating an exemplary subroutine for processing a raw REG sensitivity map.

[0016] Figures 8A to 8C An exemplary REG sensitivity graph is shown.

[0017] Figure 9 An exemplary method for determining the orientation of an RF coil array is shown.

[0018] Figure 10 Exemplary REG sensitivity plots for non-rotated and rotated coil orientations are shown.

[0019] Figure 11 An exemplary process for selecting REGs to be included in a dynamic coil mode is schematically illustrated.

[0020] Figure 12 is a flow chart illustrating a first exemplary method for performing a whole-body scan.

[0021] Figure 13 Schematically shows the Figure 12 The method performs a whole body scan process.

[0022] Figure 14 is a flow chart illustrating a second exemplary method for performing a whole-body scan.

[0023] Figure 15 Schematically shows the Figure 14 The method performs a whole body scan process. DETAILED DESCRIPTION

[0024] The following description relates to an MRI system such as Figure 1 Various embodiments of automatic radio frequency (RF) coil element selection during magnetic resonance imaging (MRI) in an MRI apparatus as shown in FIG. Figure 2A As shown, multiple RF coil arrays, such as Figure 2B The surface RF coil array can be arranged around the patient's body, and each RF coil array can include multiple coil elements. Each coil element is configured to transmit MR signals to the MRI system via one of multiple channels for ultimate processing into an image. The sensitivity of each coil element to MR signals emitted by the imaging subject depends on the distance of the coil element from the MR signal source. Because the RF coil array can be deformable and the operator can position the surface RF coil array differently for different imaging subjects and / or imaging targets, the coil elements with high sensitivity to MR signals can be changed between scans. Coil elements located outside the imaging region of interest can pick up signals that do not contribute to the reconstructed image but contribute to noise, thereby compromising image quality.

[0025] Thus, according to embodiments disclosed herein, the selected coil elements can be automatically selected based on the sensitivity of each coil element to the MR signal, as determined from low-resolution imaging data acquired during a calibration scan relative to an operator-defined region of interest (ROI), e.g. Figure 3 As will be explained in more detail below, the low-resolution imaging data is projected onto one dimension to generate a channel sensitivity map for each channel, as shown in Figure 6 As shown, the channel sensitivity maps are combined according to various groupings of coil elements, referred to as receive element groups (REGs), to generate one or more REG sensitivity maps, as shown by Figure 4 The method shown in Figure 5 It is shown schematically in FIG. Figure 7 The original REG sensitivity map is processed by the method of , so as to generate a processed REG sensitivity map, such as Figures 8A to 8C The processed REG sensitivity map can be used to identify one or more REGs to be used in a main scan for acquiring MR data to be used to reconstruct one or more images, such as Figure 11 Schematically shown in FIG.

[0026] Additionally, the sensitivity of each coil element can be used to automatically determine the orientation of the RF coil array, e.g. Figure 9 When the RF coil array is in a first orientation, in which the coil elements of a given REG extend along a first axis (e.g., the medial-lateral axis), when low-resolution imaging data is combined for the coil elements of the given REG, the resulting REG sensitivity can be relatively high and have a narrow range on a second axis (e.g., the superior-inferior axis) that is perpendicular to the first axis. However, if the RF coil array is in a second orientation rotated 90° relative to the first orientation, when low-resolution imaging data is combined for the coil elements of the given REG, the resulting REG sensitivity can be relatively low and have a wide range on the second axis due to the fact that the coil elements of the given REG actually extend along the second axis. Figure 10 Graphs of REG sensitivity of the RF coil array in a first orientation and in a second orientation are shown in .

[0027] Additionally, some imaging protocols provide for large areas / lengths of the imaging subject to be imaged, where the desired imaging region of the imaging subject is larger than the MRI system field of view. During such imaging protocols (referred to herein as whole body scans), the MRI system's couch may be moved through multiple positions or stations with the primary imaging scan performed at each station. Figure 12 and Figure 14 The method shown in Figure 13 and Figure 15The coil selection process described above may be performed at each station, as shown in the timeline / process in FIG.

[0028] Figure 1 A magnetic resonance imaging (MRI) apparatus 10 is shown, which includes a static magnetic field magnet unit 12, a gradient coil unit 13, one or more local RF coil arrays (210, 220, and 230), an RF body coil unit 15, a transmit / receive (T / R) switch 20, an RF port interface 21, an RF driver unit 22, a gradient coil driver unit 23, a data acquisition unit 24, a controller unit 25, a patient bed 26, a data processing unit 31, an operation console unit 32, and a display unit 33. The MRI apparatus 10 transmits electromagnetic pulse signals to a subject 16 placed in an imaging space 18, wherein a static magnetic field is formed to perform scanning, for obtaining magnetic resonance (MR) signals from the subject 16, so as to reconstruct images of slices of the subject 16 based on the MR signals obtained by the scanning.

[0029] The static magnetic field magnet unit 12 includes, for example, a generally annular superconducting magnet installed in an annular vacuum container, defines a cylindrical space surrounding the subject 16, and generates a constant primary static magnetic field B0.

[0030] The MRI apparatus 10 also includes a gradient coil unit 13, which generates a gradient magnetic field in an imaging space 18 to provide three-dimensional position information for the magnetic resonance signals received by the radio frequency coil array. The gradient coil unit 13 includes three gradient coil systems, each of which generates a gradient field (the gradient field is tilted toward one of three spatial axes perpendicular to each other). The gradient coil unit 13 generates gradient fields in each of the frequency encoding direction, the phase encoding direction, and the slice selection direction, depending on imaging conditions. More specifically, the gradient coil unit 13 applies a gradient field in the slice selection direction (or scanning direction) of the subject 16 to select a slice; the RF body coil unit 15 or the local RF coil array can transmit RF pulses to the selected slice of the subject 16. The gradient coil unit 13 also applies a gradient field in the phase encoding direction of the subject 16 to phase-encode the magnetic resonance signals from the slice excited by the radio frequency pulses. The gradient coil unit 13 then applies a gradient field in the frequency encoding direction of the subject 16 to frequency-encode the magnetic resonance signals from the slice excited by the RF pulses.

[0031] Three local RF coil arrays 210, 220, and 230 are shown herein. These local RF coil arrays are arranged, for example, to surround a region to be imaged of a subject 16. In a static magnetic field space or imaging space 18 where a static magnetic field B0 is formed by a static magnetic field magnet unit 12, the local RF coil arrays transmit radio frequency pulses, which are electromagnetic waves, to the subject 16 based on control signals from a controller unit 25, thereby generating a high-frequency magnetic field B1. This excites the proton spins in the slice of the subject 16 to be imaged. The local RF coil arrays receive the electromagnetic waves generated when the proton spins return to alignment with the initial magnetization vector as MR signals. In one embodiment, the local RF coils can use the same local RF coil for both transmitting and receiving RF pulses. In another embodiment, the local RF coils can be used only to receive MR signals, but not for transmitting RF pulses. Details of the local RF coil arrays are shown in FIG2.

[0032] The RF body coil unit 15 is disposed, for example, to enclose the imaging space 18 and generates radio frequency magnetic field pulses B1 that are orthogonal to the main magnetic field B0 generated by the static field magnet unit 12 within the imaging space 18 to excite nuclei. In contrast to local RF coil arrays (such as the local RF coil arrays 210 and 220), which can be easily disconnected from the MR device 10 and replaced with another local RF coil, the RF body coil unit 15 is fixedly attached and connected to the MR device 10. Furthermore, while coil arrays can transmit or receive signals only from a local region of the subject 16, the RF body coil unit 15 typically has a larger coverage area and can be used to transmit or receive signals to the entire body of the subject 16. Using a receive-only RF coil array and a transmit body coil provides uniform RF excitation and good image uniformity, at the expense of high RF power deposited within the subject. In contrast to a transmit-receive RF coil array, the coil array provides RF excitation to the region of interest and receives MR signals, thereby reducing RF power deposited within the subject. It will be appreciated that the specific use of the local RF coil array and / or radio frequency body coil unit 15 depends on the imaging application.

[0033] When operating in receive mode, the T / R switch 20 can selectively electrically connect the RF body coil unit 15 to the data acquisition unit 24, and when operating in transmit mode, the T / R switch can selectively electrically connect the RF driver unit 22. Similarly, when one or more local RF coil arrays are operating in receive mode, the T / R switch 20 can selectively electrically connect the local RF coil arrays to the data acquisition unit 24, and when one or more local RF coil arrays are operating in transmit mode, the T / R switch can selectively electrically connect the local RF coil arrays to the RF driver unit 22. When both the local RF coil arrays and the RF body coil unit 15 are used for a single scan, for example, if the local RF coil arrays are configured to receive MR signals and the RF body coil unit 15 is configured to transmit RF signals, the T / R switch 20 can direct control signals from the RF driver unit 22 to the RF body coil unit 15 while directing received MR signals from the local RF coil arrays to the data acquisition unit 24. The RF body coil unit 15 can be configured to operate in transmit-only mode, receive-only mode, or transmit-receive mode. The local RF coil array may be configured to operate in a transmit-receive mode, or a receive-only mode.

[0034] The RF driver unit 22 includes a gate modulator (not shown), an RF power amplifier (not shown), and an RF oscillator (not shown), and is used to drive the RF coil array and form a high-frequency magnetic field in the imaging space 18. The RF driver unit 22 modulates the RF signal received from the RF oscillator into a predetermined timing signal with a predetermined envelope using a gate modulator based on a control signal from the controller unit 25. The RF signal modulated by the gate modulator is amplified by the RF power amplifier and then output to the RF coil array.

[0035] The gradient coil driver unit 23 drives the gradient coil unit 13 based on a control signal from the controller unit 25, thereby generating a gradient magnetic field in the imaging space 18. The gradient coil driver unit 23 includes three driver circuit systems (not shown) corresponding to the three gradient coil systems included in the gradient coil unit 13.

[0036] The data acquisition unit 24 includes a preamplifier (not shown), a phase detector (not shown), and an analog / digital converter (not shown), and is used to acquire MR signals received by the local RF coil array. In the data acquisition unit 24, the phase detector uses the output of the RF oscillator from the RF driver unit 22 as a reference signal to perform phase detection on the MR signals received from the RF coil array and amplified by the preamplifier. The phase-detected analog magnetic resonance signals are then output to the analog / digital converter for conversion into digital signals. The resulting digital signals are then output to the data processing unit 31.

[0037] The MRI apparatus 10 includes an examination table 26 for placing a subject 16 thereon. By moving the table 26 based on a control signal from a controller unit 25, the subject 16 can be moved inside and outside the imaging space 18. One or more RF coil arrays may be coupled to the examination table 26 and move together with the examination table.

[0038] In some embodiments, the controller unit 25 includes a computer and a recording medium on which a program to be executed by the computer is recorded. When executed by the computer, the program causes the various components of the device to perform operations corresponding to a predetermined scan. The recording medium may include, for example, a ROM, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, or a non-volatile memory card. The controller unit 25 is connected to the operation console unit 32 and processes the operation signals input to the operation console unit 32. It also controls the inspection table 26, the RF driver unit 22, the gradient coil driver unit 23, and the data acquisition unit 24 by outputting control signals to them. The controller unit 25 also controls the data processing unit 31 and the display unit 33 based on the operation signals received from the operation console unit 32 to obtain the desired image.

[0039] The operation console unit 32 includes a user input device (such as a keyboard and a mouse). The operator uses the operation console unit 32 to, for example, input data as an imaging protocol and set the area where the imaging sequence is to be executed. The data regarding the imaging protocol and the imaging sequence execution area is output to the controller unit 25.

[0040] The data processing unit 31 includes a computer and a recording medium on which is recorded a program executed by the computer to perform predetermined data processing. The data processing unit 31 is connected to the controller unit 25 and performs data processing based on control signals received from the controller unit 25. The data processing unit 31 is also connected to the data acquisition unit 24 and generates spectral data by applying various image processing operations to the magnetic resonance signals output from the data acquisition unit 24.

[0041] The display unit 33 includes a display device and displays an image on a display screen of the display device based on a control signal received from the controller unit 25. The display unit 33 displays, for example, images regarding input items for inputting operation data by the operator from the operation console unit 32. The display unit 33 also displays slice images of the subject 16 generated by the data processing unit 31.

[0042] Different RF coil arrays can be used for different scanning targets. To this end, one or more RF coil arrays (such as RF coil array 210) can be disconnected from the MRI apparatus 10 so that a different coil array can be connected to the MRI apparatus 10. The RF coil arrays can be coupled to the T / R switch 20 via connectors and the RF port interface 21, and thus to the RF driver unit 22 and the data acquisition unit 24. Each RF coil array can be electrically coupled to one or more connectors (e.g., connectors 17a to 17c). The connectors can be plugged into the RF port interface 21 to electrically couple the RF coil array to the T / R switch 20. For example, the coil array 210 can be electrically connected to the MRI apparatus 10 by plugging the connector 17c into the RF port interface 21. Thus, the local RF coil array can be easily changed.

[0043] Figure 2A Shown Figure 1 1 shows an exemplary arrangement of the RF coil arrays of the MRI apparatus 10 relative to the subject 16. Specifically, the front coil array 210, the head and neck coil array 220, and the rear coil array 230 are located at the upper body, above the head and neck, and the lower body, respectively. Each coil array is a single small piece and can be physically separated from each other. One or more coil arrays (such as the front coil array 210 and the head and neck coil 220) can be connected to or removed from the MRI apparatus 10 by the operator. The rear coil array 230 can be embedded in the examination bed 26 and move with the examination bed. Each coil array may include one or more coil elements, and each coil element receives MR signals generated from a specific volume of the subject 16. The coil elements may overlap or not overlap with each other. For example, the front coil array 210 includes three rows of coil elements (211-213) arranged in the up-down (S / I) direction. Each row (211, 212, 213) can include multiple (e.g., 4, 5, 6, 7, 8, etc.) coil elements along a direction perpendicular to the S / I direction. The head coil array 220 includes four rows of coil elements (221-224) to cover different surface areas of the subject; the rear coil array 230 includes six rows of coil elements (231-236) arranged along the S / I direction. In some embodiments, the relative positions of the coil elements of the coil array can be fixed relative to each other. In some embodiments, the relative positions of the coil elements of the coil array can be variable relative to each other.

[0044] Coil elements of a coil array or coil elements from multiple coil arrays can be grouped into REGs based on receive element (REG) group information. REG information is a predetermined rule for grouping coil elements of a coil array for transmitting and / or receiving MR signals. Different REGs include different combinations of coil elements. A coil element can be included in more than one REG. REG information can be determined based on the imaging target, the geometry of the coil array, hardware limitations (for example, multiple coil elements must be turned on / off at the same time), etc. REG information can also provide dedicated REGs. For example, when a coil element is included in two REGs, the two REGs are mutually exclusive, meaning that they cannot be selected at the same time.

[0045] Take the front coil array 210 as an example. All coil elements in the front coil array 210 can be grouped as the first REG. The coil elements in row 211 can be grouped as the second REG; the coil elements in row 212 can be grouped as the third REG; and the coil elements in row 213 can be grouped as the fourth REG. The coil elements in a column (in a direction perpendicular to the row) can be grouped as the fifth REG. The first REG and the second REG exclude each other because they both include coil elements in row 211. The second REG and the fifth REG exclude each other because they both include coil elements at the intersection of row 212 and the column, and so on. The REGs of the rear coil array 230 can be defined similarly. For another example, the coil elements in rows 223 and 224 of the head and neck coil array 220 can be grouped as a neck REG. In some embodiments, each coil element can represent a separate REG. REG information can be stored in the memory of the MRI device 10.

[0046] Each coil element of the coil array is electrically connected to a controller unit (such as Figure 1 Specifically, each coil element can sense MR signals and transmit the MR signals to a data acquisition unit (such as a controller unit 25) of the MRI device through a corresponding channel. Figure 1 The data acquisition unit 24 then outputs the digitized MR signals to the controller unit. Thus, the channels of the coil array may also be grouped according to the REG information. In some examples, each individual coil element may be coupled to one channel, and each channel may be coupled to only one coil element (e.g., the front coil array 210 may include 12 coil elements coupled to the data acquisition unit via 12 individual channels). In other examples, more than one coil element may be coupled to a given channel (e.g., the front coil array 210 may include 12 coil elements coupled to the data acquisition unit via 6 individual channels).

[0047] An example of an RF coil array 210 is shown in top view. Figure 2B . The RF coil array 210 includes a plurality of RF coil elements arranged in an array. Herein, the RF coil array 210 includes 30 coil elements arranged in an array consisting of six rows (R1-R6) and five columns (C1-C5). However, other configurations are possible, such as an array comprising six rows and five columns, an array of fifteen coil elements arranged in an array of five rows by three columns, or any other suitable configuration. Each coil element (in Figure 2B The coil elements 1-30 in FIG. 1 may include a distributed capacitance loop portion and may be connected to the coil via corresponding coupling electronics and a coil interface cable ( Figure 2B ) coupled to a controller unit, or may be any other suitable configuration.

[0048] The RF coil array 210 is shown in a first orientation whereby each row of coil elements extends along a first direction, e.g., parallel to Figure 2B The x-axis of the coordinate system is parallel to the x-axis of the coordinate system, and each column extends in a second direction, for example, parallel to the y-axis of the coordinate system. During imaging, the operator may position the RF coil array 210 above the patient in a first orientation, such that each of the columns C1-C5 extends along the patient's superior-inferior (S / I) axis, and each of the rows R1-R6 extends perpendicular to the patient's S / I axis. However, depending on the patient size and imaging objectives, the operator may instead position the RF coil array 210 in a second orientation, in which the RF coil array 210 is rotated 90° relative to the first orientation. In the second orientation, the rows now extend in a second direction (e.g., parallel to the y-axis), and the columns extend in the first direction (e.g., parallel to the x-axis). Therefore, during imaging, each of the rows R1-R6 extends along the patient's S / I axis, and each of the columns C1-C5 extends perpendicular to the patient's S / I axis.

[0049] To obtain high-quality images with a desired signal-to-noise ratio, the RF coil array 210 is configured to be arranged into coil element groups (e.g., REGs, as described above) that are collectively activated to acquire MR signals during an MR scan. Thus, if an imaging protocol is selected that allows for selective deactivation of coil elements outside a scan region of interest (ROI), coil elements within the ROI will be activated according to the REG groupings to maintain the desired signal-to-noise ratio. When in a first orientation, the RF coil array 210 may include a first group of REGs, each REG corresponding to a row of coil elements. For example, the first row of coil elements (R1) can define a first REG including coil elements 1-5, the second row of coil elements (R2) can define a second REG including coil elements 6-10, the third row of coil elements (R3) can define a third REG including coil elements 11-15, the fourth row of coil elements (R4) can define a fourth REG including coil elements 16-20, the fifth row of coil elements (R5) can define a fifth REG including coil elements 21-25, and the sixth row of coil elements (R6) can define a sixth REG including coil elements 26-30.

[0050] However, if the RF coil array 210 is positioned on the imaging subject in a second orientation, the first set of REGs defined above no longer extends along the x-axis but rather along the y-axis. Consequently, the coil elements of the RF coil array 210 are configured to be grouped into a second set of REGs, with each REG corresponding to a column of coil elements. For example, the first column of coil elements (C1) may define a seventh REG comprising coil elements 1, 6, 11, 16, 21, and 26, the second column of coil elements (C2) may define an eighth REG comprising coil elements 2, 7, 12, 17, 22, and 27, the third column of coil elements (C3) may define a ninth REG comprising coil elements 3, 8, 13, 18, 23, and 28, the fourth column (C4) may define a tenth REG comprising coil elements 4, 9, 14, 19, 24, and 29, and the fifth column (C5) may define an eleventh REG comprising coil elements 5, 10, 15, 20, 25, and 30.

[0051] In some examples, the RF coil array 210 can include distributed capacitance wire conductors rather than copper traces on a PCB with lumped electronics. Consequently, the RF coil array can be lightweight and flexible, allowing for placement within low-cost, lightweight, waterproof, and / or flame-retardant fabrics or materials. The coupling electronics portion coupled to the loop portion of the RF coil (e.g., the distributed capacitance wire) can be miniaturized and utilize a low-input impedance preamplifier for high source impedance optimization (e.g., due to impedance matching circuitry) and allow for flexible overlap between coil elements in the RF coil array. Furthermore, the RF coil array interface cable between the RF coil array and system processing components can be flexible and include integrated transparency functionality in the form of distributed baluns, which allows for the avoidance of rigid electronics and aids in the dissipation of thermal loads.

[0052] Figure 3 2. MRI systems (such as 210) including surface RF coil arrays are shown. Figure 1 An exemplary method 300 is provided for performing a scan using an MRI apparatus 10 (e.g., a MRI apparatus 10) with an array having a dynamic coil pattern determined based on a calibration scan performed prior to a main scan and an automatically determined orientation of the RF coil array. Specifically, coil elements are selected for receiving MR signals in the main scan based on their sensitivity relative to a scan region of interest (ROI). During the calibration scan, a data set is acquired from each coil element of the RF coil array. The sensitivity of each element is determined by projecting each corresponding data set along a coil selection direction to obtain a channel sensitivity map for each channel. The channel sensitivity maps are then combined into two sets of REG sensitivity maps based on REG grouping and ROI. For example, a first set of REG sensitivity maps may be generated for an RF coil array in which coil elements are grouped into a first set of REGs (e.g., where REGs represent rows of the RF coil array), and a second set of REG sensitivity maps may be generated for an RF coil array in which coil elements are grouped into a second set of REGs (e.g., where REGs represent columns of the RF coil array).

[0053] The first and second sets of REG sensitivity maps can be compared to determine the orientation of the RF coil array. The row and column REG groupings can be made assuming that the RF coil array is in Figure 2B However, if the RF coil array is rotated 90° relative to the first orientation, the rows become columns and vice versa. By comparing the sensitivity values ​​of each set of REG sensitivity maps, the coil orientation can be determined. The set of REG sensitivity maps corresponding to the determined coil orientation can then be selected for comparison with the scan ROI. The range of REG sensitivities in the set of REG sensitivity maps relative to the ROI determines the selection of one or more REGs for the main scan. Method 300 can be performed by Figure 1The controller unit 25 executes according to instructions stored in the non-volatile memory.

[0054] At 302, method 300 includes receiving patient information and a scan protocol. For example, an operator of the MRI system may enter a patient identifier, such as a code or the patient's name, and / or the operator may enter selected information about the patient (e.g., date of birth, age, gender, weight). Furthermore, the operator may select a predetermined scan protocol from a menu, or the operator may enter various scan parameters to set up a scan protocol. The scan protocol may indicate the anatomical structure to be scanned, the diagnostic target of the scan, and / or other parameters that the MRI system may use to identify the position of the examination table, the receiving RF coil array to be used during the scan (e.g., a head and neck RF coil array, a posterior RF coil array, and / or an anterior RF coil array), and other scan parameters. Specifically, the operator may select a protocol based on the anatomical structure to be scanned. By selecting a protocol, the field of view (FOV) may be determined accordingly. The FOV defines the three-dimensional volume of the patient. In one example, the FOV defines the volume to be scanned for the localizer scan and calibration scan (described in more detail below). For example, in cardiac imaging, the FOV is a cube with 20 cm long edges to cover the entire heart. In some examples, the FOV may include the volume of the MRI bore that the entire imaging subject / MRI system can image without moving the couch on which the imaging subject is positioned.

[0055] In response to operator input, the MRI system can move the examination table (e.g. Figure 1 An examination bed 26) is used to position the subject (eg, patient) in an imaging space (eg, Figure 1 Additionally, the MRI apparatus may automatically identify the RF coil array to be used during a scan, for example, by identifying a connector (such as a connector) of the coil array that has been plugged into the MRI system. Figure 1 Once the receiving RF coil array is identified, the MRI system (e.g., the controller unit 25, the RF driver unit 22, and / or the data acquisition unit 24) can obtain REG information indicating the grouping of coil elements of the coil array connected to the MRI apparatus. This information can be stored in a memory of the MRI system or on a remote device in communication with the MRI system. The connected coil arrays can also be displayed to the operator via a display unit.

[0056] The scanning protocol and / or identification of the RF coil arrays to be used during the scan may include identification of one or more rotatable RF coil arrays, as shown in 303. For example, the head and neck RF coil array may not be rotatable because the head and neck RF coil array has a defined shape that matches the shape of the head and neck, and / or because the head and neck RF coil array is relatively rigid and fixed in place. The posterior RF coil array may be embedded in the examination bed of the MRI system and therefore may not be rotatable. On the other hand, the anterior RF coil array may be a surface RF coil array that is placed on the imaging subject by the operator. Thus, the operator can freely position the anterior RF coil array in one of a plurality of orientations, such as Figure 2B , or a second orientation in which the anterior RF coil array is rotated 90° relative to the first orientation. While positioning the anterior RF coil array in the second orientation may enable better imaging of certain anatomical structures of certain imaging subjects (e.g., the torso of a larger patient), dynamic coil pattern generation (described in more detail below) may be disrupted if the MRI system is unaware of the orientation of the anterior RF coil array. Therefore, if a rotatable coil array is used during scanning, the MRI system may automatically determine the RF coil array orientation.

[0057] At 304, method 300 includes performing a localizer scan. A localizer scan can be a low-resolution scan of the FOV. In this context, a low-resolution scan is a scan with a large voxel volume that can be completed in a shortened measurement time. In one example, image data acquired during the localizer scan can be used to reconstruct an MR image of the FOV. The localizer scan can generate three 2D images of the subject, for example, in the sagittal, coronal, and transverse planes.

[0058] At 306, method 300 performs a full-mode, low-resolution calibration scan in the calibration FOV to generate calibration data to be used in determining dynamic coil modes. During the full-mode calibration scan, each coil element of each RF coil array receives MR signals. The MR signals received from each corresponding channel generate a 3D dataset for each channel, which can correspond to one coil element (or two or three coil elements, depending on the configuration of the MRI system and RF coil array). Thus, each 3D dataset corresponds to one of the multiple channels and one coil element electronically coupled to the channel. In some embodiments, MR signals are collected from all channels of all coil arrays. In other embodiments, MR signals are collected from channels of selected coil arrays. Coil arrays can be selected based on their relative position to the imaging region. For example, during the calibration scan, coil arrays within a threshold distance from the FOV are placed in receive mode, while unselected coil arrays do not receive MR signals. The threshold distance can be the distance at which the coil arrays are sensitive to MR signals generated from the imaging region. In one embodiment, a localizer scan and calibration scan can be combined, where a low-resolution 3D scan of the FOV can generate both a localizer scan image and calibration data.

[0059] At 308, method 300 includes determining whether to use the first or second set of REGs to select the REGs for the dynamic coil mode. To determine whether to use the first or second set of REGs for selecting the REGs for the dynamic coil mode, the orientation of the rotatable RF coil array may be determined, and then the first or second set may be selected based on the coil orientation. Additional details regarding automatically determining the orientation of the rotatable RF coil array are provided below. Figure 4 and Figure 9 In short, the data acquired during the lower resolution calibration scan can be used to determine the sensitivity range of each REG in the first and second sets of REGs. An average sensitivity value can be determined for the first and second sets of REGs, and the set of REGs with the higher sensitivity value (in one example) can be selected to determine the dynamic coil mode.

[0060] At 310, method 300 includes receiving a selection of a region of interest (ROI), which may be selected by an operator. For example, images generated by the localizer scan may be displayed on a display unit, and the operator may select an ROI for the main scan based on these images. In at least some examples, the ROI may be smaller than the localizer FOV. For example, the localizer FOV may be 50 cm along the scan direction, and the ROI may be 20 cm-30 cm along the scan direction. In some embodiments, the ROI may be defined by selecting the position of a corner of the 3D volume. In some embodiments, the ROI may be defined by a center position and an extent in each of the superior-inferior, medial-lateral, and posterior-anterior directions. In other embodiments, the ROI may be in the shape of a cube, which is defined by a center position, an extent, and a rotation angle. For example, for a cardiac scan, the ROI may be defined by a center position of the heart, a predetermined extent, and a viewing angle.

[0061] At 312, method 300 determines whether the ROI exceeds the calibration FOV (e.g., exceeds the FOV imaged by the MRI system during the calibration scan). For example, when the operator indicates the ROI, the ROI may extend outside the calibration FOV. If the ROI extends beyond the calibration FOV, method 300 proceeds to 313 to adjust the full mode calibration center and re-perform the full mode calibration scan. For example, the examination table may be moved or other actions may be performed to adjust the center of the calibration FOV so that the ROI remains within the calibration FOV. After adjusting the calibration center and re-performing the calibration scan, method 300 proceeds to 316, described below.

[0062] If the ROI does not extend beyond the calibration FOV, the method 300 proceeds to 316 to generate a dynamic coil pattern based on the determined first set of REGs or the second set of REGs. Once the rotatable RF coil array orientation is determined and the first set of REGs or the second set of REGs is selected, a dynamic coil pattern may be generated based on the dataset acquired during the calibration scan. The dynamic coil pattern identifies the REGs that will be used to image the ROI during the main scan. Figure 4 Generating a dynamic coil pattern is described in more detail.A dynamic coil pattern may be generated for the rotatable RF coil array, and may also be generated for other receive RF coil arrays to be used during a main scan.

[0063] In some examples, a visual representation of the dynamic coil mode can also be displayed along with an image obtained via a localizer scan via a display unit (e.g., display unit 33). For example, an image of an imaged subject acquired during a localizer scan can be displayed along with annotations showing the ROI. The sensitivity range of one or more REGs relative to the ROI can also be displayed. The sensitivity range of a REG can indicate the coverage of the REG along the coil selection direction, for example, how large an area of ​​the ROI is the REG sensitive to. In some examples, if a portion of the ROI is not covered by the REG, a mismatch notification can be output on the display to inform the operator that the ROI may not be adequately imaged with the current RF coil array placement.

[0064] At 318, method 300 includes performing a main scan using the determined dynamic coil mode. During the main scan, MR signals are received from coil elements of the REG selected based on the dynamic coil mode, but MR signals are not received from any coil elements not included in the selected REG. In other words, during the main scan, coil elements in REGs other than the selected REG are turned off. The main scan is a high-resolution 3D scan to generate a high-quality image of the ROI. The main scan has a lower voxel volume than the localizer scan and the calibration scan. Based on the MR signals obtained during the main scan, one or more images can be reconstructed, which can be displayed on a display unit and / or saved in a memory (memory of the MRI system and / or a remote device, such as a hospital PACS).

[0065] Figure 4 An exemplary subroutine 400 is shown for generating a dynamic coil pattern for a main scan based on calibration data (e.g., low-resolution data acquired during a calibration scan) and an ROI. The dynamic coil pattern determines the REGs for the main scan of an imaging subject in the ROI. The dynamic coil pattern is determined based on the REG sensitivity map and the ROI, and also based on the RF coil array orientation (at least in embodiments where a rotatable RF coil array is present). Each REG sensitivity map may be generated by combining channel sensitivity maps based on REG information, such as Figure 4 In the example given herein, two sets of REG sensitivity maps are generated for each rotatable RF coil array. As described herein, one REG sensitivity map can be generated for each REG, but other configurations are possible. Figure 4 The subroutine is described with respect to a single RF coil array and may be repeated for each RF coil array. Figure 5 yes Figure 4 Schematic diagram of the subroutine.

[0066] When performing a full mode calibration scan (see above Figure 3Following the calibration scan at 402, subroutine 400 optionally includes processing the datasets acquired during the calibration scan at 402. Specifically, error correction can be performed on each 3D dataset for each channel. For example, one or more of a frequency map, a phase map, and a slice grayscale error map can be applied to the dataset to correct for spatial distortion. Through preprocessing, the 3D position of each data point of the digitized MR signal can be corrected for errors.

[0067] At 404, a 1D channel sensitivity map is generated for each channel of the RF coil array. Specifically, the 3D data set for each channel acquired during the calibration scan can be projected onto a coil-selected direction. In one example, the coil-selected direction can be the S / I direction. Figure 6 An exemplary channel sensitivity map 610 that can be obtained by projecting a 3D data set 605 into the S / I direction is shown. For example, the 3D data set 605 can first be projected onto a sagittal plane 604 along the medial-lateral (R / L) direction 602. For example, to project the 3D data set into a 2D plane, data points along the medial-lateral direction 602 are summed to obtain data points in the sagittal plane 604. The projected 2D data can then be projected back into the S / I direction.

[0068] At 406, a first set of REG sensitivity maps is generated based on the channel sensitivity maps and the REG information. The channel sensitivity maps can be combined based on the REG information for the RF coil array (which defines the channels included in each REG). For example, for each data point in the coil selection direction, the channel sensitivity maps of the channels associated with the coil elements within each predetermined REG are summed. In this way, the sensitivity of each REG is obtained. In an example where the REG sensitivity maps are used to determine the coil orientation of a rotatable RF coil array, the channel sensitivity maps can be combined twice based on the first REG information and once based on the second REG information. The first REG information can indicate that the coil elements are grouped into a first set of REGs based on rows, while the second REG information can indicate that the coil elements are grouped into a second set of REGs based on columns.

[0069] Then, according to the first REG information, a first set of REG sensitivity maps is generated based on the sensitivity of the selected REGs. Specifically, the sensitivity of each selected REG (e.g., the combined channel sensitivity map of each channel of the selected REG) can first be arranged side by side along the projection direction, such as Figure 5 510 to obtain a raw REG sensitivity map. The raw REG sensitivity map is then processed based on the type and configuration of the coil array. Details for processing the raw REG sensitivity map are given in Figure 7 The first set of REG sensitivity maps may represent the sensitivity of each REG in the first set of REGs.

[0070] At 408, the subroutine 400 includes generating a second set of REG sensitivity maps.The second set of REG sensitivity maps may represent the sensitivity of each REG in the second set of REGs and may be generated similarly to the first set of REG sensitivity maps.

[0071] At 410, the subroutine 400 includes selecting one or more REGs based on the REG sensitivity map and the ROI. In this way, the dynamic coil mode for the main scan is determined based on the REG sensitivity map and the ROI. For example, one or more REGs can be selected based on the range of REG sensitivity relative to the ROI. Figure 11 For a rotatable coil, the orientation of the RF coil array may be determined based on the average sensitivity value of the first set of REG sensitivity maps relative to the average sensitivity value of the second set of REG sensitivity maps, as shown below with respect to Figure 9 The set of REG sensitivity maps corresponding to the determined coil orientation is then selected for use in determining the dynamic coil pattern. Again, either the first or second set of REGs is indicated as selectable based on orientation, and during generation of the dynamic coil pattern, only the REGs indicated as selectable may be selected for inclusion in the dynamic coil pattern.

[0072] Figure 5 yes Figure 4 4. A graphical representation of the subroutine 400 for . The low resolution data acquired during the calibration scan includes pre-processed volumetric (e.g., 3D) data for each channel, shown herein as a 3D data set 502. Each 3D channel group of the 3D data set 502 corresponds to a channel of the RF coil array. A total of n channels are shown here. Each channel group of the 3D data set 502 is projected into a coil selection direction (e.g., S / I direction) to obtain a corresponding 1D channel sensitivity map, thereby generating a plurality of channel sensitivity maps 504. Thus, n channel sensitivity maps are generated for n channels. Details on the projection process are provided in Figure 7 Shown in.

[0073] In one example, the coil selection direction may be a direction in which coil elements have different coverage. In other words, the range of one or more coil elements covers different areas along the coil selection direction. For example, the RF coil array 210 may be arranged into six REGs, each REG including a row of coil elements extending along a first direction (e.g., horizontally). The coil selection direction may be along a second direction (e.g., vertically) perpendicular to the first direction, because the coil elements of each REG have different coverage along the second direction. As described above, if the RF coil array is rotated so that the rows are actually columns, the rows now extend along the second (coil selection) direction. This may disrupt the REG selection process in dynamic coil mode if the rotation of the RF coil array is not detected. In one example, the RF coil array may include REGs with different coverage in more than one direction. The coil selection direction may be one of multiple directions determined based on the imaging protocol. For another example, the coil selection direction may be the same as the slice selection direction during an MRI scan. In other words, the coil selection direction is perpendicular to the plane containing the imaging slice. The coil selection direction may also be the same as the scan direction.

[0074] As shown in subroutine 400, channels are first grouped based on predetermined REG information. As previously described, REG information is a predetermined rule for grouping coil elements of a coil array for transmitting and / or receiving MR signals. Channel sensitivity maps are grouped and combined for each REG. As previously described, each REG may correspond to a group of one or more RF coil elements. Therefore, for a given REG, grouping the channel sensitivity maps may include combining the channel sensitivity maps of each channel coupled to the coil elements belonging to that given REG. Herein, tREG is shown at 506. For example, the REG information defines REG 1 as including channel 1 and channel 2. The channel sensitivity maps of channels 1 and 2 are summed along the S / I direction. Similarly, the channel sensitivity maps of channels 3 and 4 are combined for REG 2. REG t includes channel n, and so on.

[0075] A raw REG sensitivity map is obtained based on the combined sensitivity maps 506 of the t selected REGs. An exemplary set of raw REG sensitivity maps representing the sensitivity of four REGs is shown in 510. The x-axis represents the number of pixels in the S / I direction. Alternatively, the x-axis can be distance (such as centimeters) along the coil selection direction. Each row corresponds to the sensitivity of one REG along the S / I direction. The sensitivity values ​​are displayed in grayscale along the S / I direction. The brighter the grayscale value, the higher the sensitivity value.

[0076] Channel grouping based on REG information and Figure 5The final generation of the REG sensitivity maps shown in FIG can be performed twice for the rotatable RF coil array, once based on first REG information specifying a first set of REGs (e.g., rows), and again based on second REG information specifying a second set of REGs (e.g., columns). The resulting first and second sets of REG sensitivity maps can be generated from the same low-resolution calibration data, but can represent different combinations of projections of the low-resolution calibration data.

[0077] Go to Figure 7 , shows the process for processing raw REG sensitivity maps (such as in Figure 4 The raw REG sensitivity map may be processed based on the type of coil array. Figures 8A to 8C An example of a REG sensitivity map generated based on an original REG sensitivity map via subroutine 700 is shown.

[0078] At 702, the type of coil array represented in the raw REG sensitivity map is determined. For example, the subroutine can determine whether the RF coil array is a couch-fixed coil (e.g., a posterior coil), a floating coil (e.g., an anterior coil), a rigid coil (e.g., a head and neck coil), a flexible coil (e.g., an air coil), or another type of RF coil array. In other examples, the subroutine can determine the length of the RF coil array (e.g., relative to the FOV) and / or the number of REGs in the RF coil array.

[0079] At 704, the sensitivity of each REG in the raw REG sensitivity map may be processed based on the type of coil array. In one example, at 706, the raw REG sensitivity map is thresholded using a threshold sensitivity level. The threshold sensitivity level may be determined based on the noise level of the MR signal. Any data point of the REG sensitivity map having a value below the threshold sensitivity level is set to a fixed low level (such as zero). An exemplary set of raw REG sensitivity maps 801 is shown in FIG. Figure 8A , which is used for an RF coil array with four REGs, such as a head and neck coil array. Figure 5 Each row of the set of raw REG sensitivity graphs 801 represents the combined sensitivity of each channel corresponding to one REG along the coil selection direction. After thresholding, low-level data points are discarded by setting those data points (e.g., pixels) to zero. The sensitivity range of each REG can be determined as the range of non-zero sensitivities of the REG. For example, the sensitivity range 810 of the first REG 811 is Figure 8A Shown in.

[0080] In another example, additionally or alternatively, the processing may include replacing the thresholded sensitivity of each REG with a Gaussian fit of the same range. For example, the Gaussian fit replacement may be applied to the REGs of the front coil array or the rear coil array. In one example, Figure 8B As shown, the thresholded sensitivity of the first REG in the set of original REG sensitivity maps 803 is replaced by a Gaussian fit 822. The Gaussian fit 822 is shown in grayscale in the set of REG sensitivity maps 804. For each row of the set of original REG sensitivity maps, the thresholded sensitivity value is replaced with a Gaussian curve of the same range along the coil selection direction (e.g., the S / I direction). In one example, the Gaussian curve is determined by fitting the thresholded sensitivity of the REG. In another embodiment, the Gaussian curve has a predetermined maximum value and variance determined by the original signal (e.g., the maximum value is the same as or similar to the maximum value of the original signal).

[0081] In one example, at 708, the REG sensitivity map may be extrapolated within the FOV. In one example, the REG sensitivity map may be extrapolated to REGs that did not receive MR signals during the calibration scan. In another example, the REG sensitivity map may be extrapolated to REGs that received low-amplitude MR signals during the calibration scan. The REG sensitivity map may be extrapolated based on information about the REGs of the coil array. For example, if a second REG has the same configuration as a first REG, the sensitivity of the first REG included in the REG sensitivity map may be extrapolated to the second REG. This configuration may include the number and type of coil elements, the relative positions of the coil elements, and the stiffness of the coil array.

[0082] Figure 8B An example of a set of extrapolated REG sensitivity maps 804 for the front coil array based on the set of original REG sensitivity maps 803 is shown. In the set of original REG sensitivity maps 803, the sixth REG has a low value. Therefore, during thresholding, all values ​​for the sixth REG in the set of original REG sensitivity maps 803 are set to zero. Since the sixth REG and the fifth REG are of the same type, and assuming the relative positions of the sixth REG and the fifth REG are the same as the relative positions of the fifth REG and the fourth REG, the sensitivity of the sixth REG can be determined based on the sensitivity of the fifth REG. For example, the sensitivity of the sixth REG 805 can be added to the set of REG sensitivity maps 804 by shifting the sensitivity of the fifth REG based on the relative position between the fifth and sixth REGs. As another example, the sensitivity of the sixth REG can be a Gaussian curve with the same range as the range of the fifth REG. In this way, without additional calibration scans, an extrapolated set of REG sensitivity maps 804 can be generated to cover the full FOV 820 along the S / I direction.

[0083] In yet another example, at 710, the REG sensitivity maps can be extrapolated outside the FOV. The extrapolation can be based on the similarity of the REGs, the coil array stiffness, and the type and position of the coil elements. Extrapolation outside the FOV can be applied to a posterior coil array or other arrays having coil elements that are located outside the FOV and / or are not easily movable or positionally variable. Because the calibration scan may not cover the entire range of the coil array along the coil selection direction, by extrapolating the REG sensitivity maps outside the FOV, a set of REG sensitivity maps for the entire coil array based on one calibration scan of the imaging area can be obtained.

[0084] Figure 8C An example of a set of extrapolated REG sensitivity maps 807 for the posterior coil array based on the set of original REG sensitivity maps 806 is shown. The set of original REG sensitivity maps 806 can be generated by performing a calibration scan within the FOV 830 and projecting the data into the S / I direction. Because the REGs outside the FOV 830 are similar to the REGs within the FOV (similar in that the REGs may have the same number of coil elements, be equally spaced, etc.), the set of REG sensitivity maps can be extrapolated to cover the entire range 831 of the coil array after thresholding and Gaussian fitting. For example, because the relative positions between the coil elements of the posterior array are fixed, the set of REG sensitivity maps can be extrapolated outside the FOV 830 by shifting the REG sensitivity maps within the FOV 830 based on a priori knowledge of the relative positions between the REGs in the posterior coil array.

[0085] Figure 9 is a diagram showing a method for automatically determining a rotatable RF coil array (such as Figure 2B Flowchart of a method 900 for determining the orientation of the RF coil array 210). The method 900 may be performed by a processor executing instructions stored in a non-transitory memory of a computing device, such as Figure 1 The method 900 may be performed as part of the method 300, for example, to determine whether the first set of REGs or the second set of REGs is selectable based on the coil orientation, such as Figure 3 As specified in 308.

[0086] At 902, method 1000 includes determining a first sensitivity value for a first set of REG sensitivity maps. Figure 4 The subroutine 400 described above is used to generate the second set of REG sensitivity maps. The first set of REG sensitivity maps can represent the sensitivity of each REG in the first set of REGs. Assume that the RF coil array is in Figure 2B In the first orientation shown, the first set of REGs may correspond to rows of the RF coil array 210 .

[0087] The first average sensitivity value may be a suitable value representing the range of sensitivity of each REG of the first set of REG sensitivity maps. In one example, the first average sensitivity value may include an average peak sensitivity value, as shown in 904. For example, referring to Figure 8B The set of REG sensitivity graphs 804 is shown, with each REG having multiple sensitivity values ​​extending along the S / I direction. The sensitivity values ​​can be replaced by a Gaussian fit including a peak sensitivity value. For example, the sensitivity values ​​can be represented by pixel brightness values ​​(e.g., from 0 to 255, where 0 is black / no brightness and 255 is white / full brightness), and the peak sensitivity value can represent the brightest sensitivity value of the REG (e.g., a sensitivity value of 200). The peak sensitivity value can be determined for each REG, and then the peak sensitivity values ​​can be averaged to determine an average peak sensitivity value.

[0088] In another example, the first average sensitivity value may include an average sensitivity range, as shown at 906. Referring again to Figure 8B In the set of REG sensitivity graphs 804, the Gaussian fit of each REG includes a plurality of different sensitivity values, ranging from a relatively low sensitivity value (e.g., a sensitivity value of 10) to a relatively high sensitivity value (e.g., a sensitivity value of 200). A range of sensitivity values ​​for each REG can be determined. The range can include a lowest sensitivity value and a highest sensitivity value. For another example, the range can include a histogram of sensitivity values, which represents each different sensitivity value and a relative representation of the value. For another example, the range can include the standard deviation of the Gaussian fit. The range of sensitivity values ​​can be averaged to obtain an average range of sensitivity values.

[0089] In another example, the first average sensitivity value may include an average peak-to-peak distance, as shown at 908. Figure 8B As can be understood from the set of REG sensitivity graphs 804, when a Gaussian fit is used instead of each set of sensitivity values, each REG is represented by a Gaussian fit along the x-axis (in the example shown, the S / I direction). The distance between the first peak and the second peak (along the x-axis) can be determined, the distance between the second peak and the third peak can be determined, and so on. The peak-to-peak distances can be averaged to determine an average peak-to-peak distance. For another example, the first average sensitivity value can include a REG sensitivity range, as shown at 910. The REG sensitivity range can include the distance (along the x-axis) over which the REG has a sensitivity value (e.g., a sensitivity value that is not thresholded). The sensitivity range of each REG can be determined and then averaged to obtain an average REG sensitivity range.

[0090] The average sensitivity value selected as the first sensitivity value may depend on the configuration of the RF coil array. For example, some RF coil arrays may include coil elements of different sizes, and thus different REGs may include different sensitivity ranges and / or different peak-to-peak values. In some examples, more than one first sensitivity value may be selected.

[0091] At 912, method 900 includes determining a second average sensitivity value for the second set of REG sensitivity maps. Figure 4 The subroutine 400 described above is used to generate a second set of REG sensitivity maps. The second set of REG sensitivity maps can represent the sensitivity of each REG in the second set of REGs. Assume that the RF coil array is in Figure 2B In the first orientation shown, the second set of REGs may correspond to columns of the RF coil array 210 .

[0092] The second average sensitivity value can be determined similarly to the first sensitivity value. For example, the second sensitivity value can include an average peak value, as shown at 914, an average sensitivity range, as shown at 916, an average peak-to-peak distance, as shown at 918, and / or an average REG range, as shown at 920. The average sensitivity value selected as the second average sensitivity value can be the same as the value selected as the first sensitivity value. In other words, if the first sensitivity value is an average peak value, the second average sensitivity value will also be an average peak value.

[0093] At 922, method 900 includes determining whether the first and second sensitivity values ​​indicate that the RF coil array is in a rotated configuration. As described above, the RF coil array 210 can be rotated between a first orientation and a second orientation. The first orientation can be a default orientation of the RF coil array, such that assumed rows are actual rows and assumed columns are actual columns. The second orientation can be a rotated configuration. To determine whether the RF coil array is in a non-rotated configuration or a rotated configuration (e.g., in the first orientation or the second orientation), method 900 can compare the first sensitivity value with the second sensitivity value and / or can compare each sensitivity value to a threshold. When the sensitivity values ​​are peak sensitivities, if the first average peak sensitivity is higher than the second peak sensitivity value, or if the first average peak sensitivity value is higher than the threshold and the second average peak sensitivity value is lower than the threshold, the RF coil array can be determined to be in a non-rotated position (the first orientation). If the first average peak sensitivity is lower than the second peak sensitivity value, or if the first average peak sensitivity value is lower than the threshold and the second average peak sensitivity value is higher than the threshold, the RF coil array can be determined to be in a rotated position (the first orientation).

[0094] In another example, when the sensitivity value is an average sensitivity range, if the first average sensitivity range is higher than the second sensitivity range (e.g., has a larger value range), or if the first average sensitivity range is higher than a threshold and the second average sensitivity range is lower than a threshold, it can be determined that the RF coil array is in a non-rotated position (a first orientation). If the first average sensitivity range is lower than the second sensitivity range (e.g., has a smaller value range), or if the first average sensitivity range is lower than a threshold and the second average sensitivity range is higher than a threshold, it can be determined that the RF coil array is in a rotated position (a second orientation).

[0095] In another example, when the sensitivity value is an average peak-to-peak distance, if the first average peak-to-peak distance is measurable (e.g., more than one peak is detected) and if the second average peak-to-peak distance is not measurable (e.g., no discrete peaks are detected), it can be determined that the RF coil array is in a non-rotated position (a first orientation). When the first average peak-to-peak distance is not measurable and the second average peak-to-peak distance is measurable, it can be determined that the RF coil array is in a rotated position (a second orientation). For another example, when the first average peak-to-peak distance is greater than the second average peak-to-peak distance and the RF coil array, it can be determined that the RF coil array is in a non-rotated position (the first orientation), and when the first average peak-to-peak distance is less than the second average peak-to-peak distance, it can be determined that the RF coil array is in a rotated position (the second orientation).

[0096] In yet another example, when the sensitivity value is an average REG sensitivity range, if the first average REG sensitivity range is less than the second average REG sensitivity range, or if the first average REG sensitivity range is less than a threshold value and the second average REG sensitivity range is greater than a threshold value, it may be determined that the RF coil array is in a non-rotated position (first orientation). When the first average REG sensitivity range is greater than the second average REG sensitivity range, or when the first average REG sensitivity range is greater than the threshold value and the second average REG sensitivity range is less than the threshold value, it may be determined that the RF coil array is in a rotated position (second orientation).

[0097] If the first and second sensitivity values ​​do not indicate that the RF coil array is rotated, the method 900 proceeds to 924 to determine a dynamic coil mode based on the first set of sensitivity maps and the ROI, which will be described below with respect to Figure 11 When the RF coil array is not rotating (e.g., the RF coil array is in Figure 2B), REGs may be grouped into rows, resulting in measurable sensitivity values ​​for each row of REGs (represented in the first set of REG sensitivity maps) but not for each column of REGs (represented in the second set of REG sensitivity maps). Thus, the first set of REG sensitivity maps may be used to select REGs for dynamic coil mode, and REGs used to determine dynamic coil mode may be selected only from the first set of REGs. Method 900 then ends.

[0098] If the first and second sensitivity values ​​indicate that the RF coil array is rotated, the method 900 proceeds to 926 to determine a dynamic coil mode based on the second set of REG sensitivity maps and RO I, which will be described below with respect to Figure 11 When the RF coil array is rotated (eg, the RF coil array is in a Figure 2B ) (in a second orientation rotated 90° from the first orientation shown in FIG ), the REGs may be grouped into columns, but because the RF coil array is rotated, the columns are actually rows in a rotated position, resulting in measurable sensitivity values ​​for each column of REGs (represented in the second set of REG sensitivity maps) but not for each row of REGs (represented in the first set of REG sensitivity maps). Therefore, the second set of REG sensitivity maps can be used to select REGs for dynamic coil mode, and REGs used to determine dynamic coil mode can be selected only from the second set of REGs. Method 900 then ends.

[0099] Figure 10 An exemplary REG sensitivity graph showing REG sensitivities of a first set of REGs and a second set of REGs for a first rotatable RF coil array (such as a front RF coil array) and a REG sensitivity graph showing REG sensitivities of a third set of REGs and a fourth set of REGs for a second set of rotatable RF coil array are shown. For example, Figure 2B The RF coil array 210 may be grouped into a first group of REGs corresponding to rows of the RF coil array and a second group of REGs corresponding to columns of the RF coil array.

[0100] The REG sensitivity graphs 1000 include a first set of REG sensitivity graphs representing REG sensitivities of a first set of REGs (row REGs), which are labeled HDAAR1 (High Density Anterior Array Row 1) to HDAAR6 along the y-axis, and a second set of REG sensitivity graphs representing REG sensitivities of a second set of REGs (column REGs), which are labeled HDAAC1 (High Density Anterior Array 1) to HDAAC5 along the y-axis. Also shown are a third set of REG sensitivity graphs for non-rotatable coils (e.g., rear RF coil arrays), which are labeled HDPA1 to HDPA12.

[0101] A first REG sensitivity 1010 is highlighted (e.g., by a white box) and represents the calculated sensitivity for one REG in the first set of REGs (the fifth row of REGs in the front RF coil array). The first REG sensitivity 1010 may include a sensitivity curve 1012 that represents the sensitivity values ​​of the first REG sensitivity 1010 on the first set of REG sensitivity maps. The curve 1012 may have a peak value 1014 and a range 1016. An average peak value of the first set of REG sensitivity maps may be determined by averaging the peak value 1014 with other peak values ​​of the REGs in the first set of REG sensitivity maps (e.g., the row of REGs). Similarly, an average REG range of the first set of REG sensitivity maps may be determined by averaging the range 1016 with other REG ranges determined for other REG ranges in the first set of REG sensitivity maps (e.g., the row of REGs).

[0102] A second REG sensitivity 1002 is highlighted (e.g., by a black box) and represents the calculated sensitivity for one REG in the second set of REGs (the first column of REGs in the front RF coil array). The second REG sensitivity 1002 may include a sensitivity curve 1004 that represents the sensitivity values ​​of the second REG sensitivity 1002 on a second set of REG sensitivity map. The curve 1004 may have a peak value 1006 and a range 1008. An average peak value of the second set of REG sensitivity map may be determined by averaging the peak value 1006 with other peak values ​​of the REGs in the second set of REG sensitivity map (e.g., a column of REGs). Similarly, an average REG range of the second set of REG sensitivity map may be determined by averaging the range 1008 with other REG ranges determined for other REG ranges in the second set of REG sensitivity map (e.g., a column of REGs).

[0103] As can be understood by comparing first REG sensitivity 1010 with second REG sensitivity 1002, the RF coil array is in a non-rotated first orientation. Second REG sensitivity 1002 has a wide range, low sensitivity values, and a narrow range of sensitivity values. In contrast, first REG sensitivity 1010 has a narrow range, high sensitivity values, and a wide range of sensitivity values. For example, peak 1014 is higher than peak 1006, indicating that the REGs in the first set of sensitivity maps have higher sensitivity than those in the second set of sensitivity maps. Furthermore, range 1008 is longer than range 1016, indicating that for the REGs in the first set of REG sensitivity maps, but not the second set of REG sensitivity maps, there are discrete sensitivities related to the position of each REG along the S / I direction. Therefore, the discrete position of each REG (along the S / I direction) can be determined from the first set of REG sensitivity maps, but not the second set of REG sensitivity maps. Therefore, it is determined that the RF coil array is in the first orientation, and the first set of REG sensitivity maps is selected for selecting the dynamic coil mode.

[0104] Figure 10 Also included are REG sensitivity maps 1020 for another RF coil array, including a third set of REG sensitivity maps representing REG sensitivities of a third group of REGs (row REGs), which are represented as R1-R6 along the y-axis, and a fourth set of REG sensitivity maps representing REG sensitivities of a second group of REGs (column REGs), which are represented as C1-C5 along the y-axis.

[0105] A third REG sensitivity 1030 is highlighted (e.g., by a white box) and represents the sensitivity of one REG in the third group of REGs (the first row of REGs in the RF coil array). The third REG sensitivity may include a sensitivity curve 1032 that represents the sensitivity value of the third REG sensitivity 1030 on a sensitivity map of the third group of REGs. Curve 1032 may have a peak value 1034 and a range 1036. An average peak value of the sensitivity map of the third group of REGs may be determined by averaging the peak value 1034 with other peak values ​​of the REGs in the sensitivity map of the third group of REGs (e.g., a row of REGs). Similarly, an average REG range of the sensitivity map of the third group of REGs may be determined by averaging the range 1036 with other REG ranges determined for other REGs in the sensitivity map of the third group of REGs (e.g., a row of REGs).

[0106] A fourth REG sensitivity 1022 is highlighted (e.g., by a white box) and represents the sensitivity of one REG in the fourth group of REGs (the fourth column of REGs in the front RF coil array). The fourth REG sensitivity 1022 may include a sensitivity curve 1024 that represents the sensitivity value of the fourth REG sensitivity 1022 on a sensitivity map of the fourth group of REGs. The curve 1024 may have a peak value 1026 and a range 1028. The average peak value of the sensitivity map of the fourth group of REGs may be determined by averaging the peak value 1016 with the other peak values ​​of the REGs in the sensitivity map of the fourth group of REGs (e.g., the column of REGs). Similarly, the average REG range of the sensitivity map of the fourth group of REGs may be determined by averaging the range 1028 with the other REG ranges determined for the other REG ranges in the sensitivity map of the fourth group of REGs (e.g., the column of REGs).

[0107] As can be understood by comparing fourth REG sensitivity 1022 with third REG sensitivity 1030, the RF coil array represented by REG sensitivity map 1020 is in the rotated second orientation. Fourth REG sensitivity 1022 has a narrow range, high sensitivity values, and a wide range of sensitivity values. In contrast, third REG sensitivity 1030 has a wide range, low sensitivity values, and a narrow range of sensitivity values. For example, peak 1024 is higher than peak 1034, indicating that the REGs in the fourth set of REG sensitivity maps have higher sensitivity than those in the third set of REG sensitivity maps. Furthermore, range 1028 is shorter than range 1036, indicating that for the fourth set of REG sensitivity maps, but not for the third set of REG sensitivity maps, each REG has a discrete sensitivity along the S / I direction. Therefore, the discrete sensitivity of each REG (along the S / I direction) can be determined from the fourth set of REG sensitivity maps, but not from the third set of REG sensitivity maps. Therefore, it is determined that the RF coil array is in the second orientation, and the fourth set of REG sensitivity maps can be selected for selecting the dynamic coil mode.

[0108] Figure 11 An example of REGs identified for various dynamic coil modes used in a main scan based on a selected set of REG sensitivity maps 1101 and ROIs is shown. The selected set of REG sensitivity maps can be selected based on the coil orientation determined above and can represent only REGs that can be selected for dynamic coil modes. In some embodiments, REGs with sensitivity ranges that overlap with the ROI are first identified. For example, ROI 1 extends from P1 to P2 along the S / I direction. The first and second REGs are identified for ROI 1 because their sensitivity ranges overlap with ROI 1. For another example, ROI 2 extends from P2 to P3 along the S / I direction and overlaps with the sensitivity ranges of the first, second, and third REGs. Therefore, the first, second, and third REGs are identified for ROI 2. In one example, REGs can be further identified based on the sensitivity values ​​of the REGs in the set of REG sensitivity maps. For example, REGs with high cumulative sensitivity within the ROI can be identified.

[0109] In another embodiment, it is determined whether the identified REGs are compatible with each other. The identified REGs may be mutually exclusive. For example, if the first REG consists of all coil elements in the front coil array 210 and the second REG consists of coil elements in row 211, the first REG and the second REG are mutually exclusive because they both include coil elements in row 211. Therefore, in some embodiments, a tie-breaking rule can be applied to select one REG from the exclusive REGs. For example, if parallel imaging is used, a larger REG (i.e., the first REG) is preferred; whereas, if it is desired to reduce phase wrapping artifacts, a smaller REG (i.e., the second REG) is preferred. In some embodiments, multiple factors are considered overall, and the REG that achieves the best balance is selected from the exclusive REGs.

[0110] In this way, the sensitivity of each coil element in an RF coil array comprising multiple coil elements can be determined based on low-resolution scan data acquired during a pre-scan (e.g., a calibration scan performed prior to the main imaging scan). The low-resolution scan data can be volumetric data acquired for each channel of the RF coil array (a channel can be defined by receive circuitry that transmits MR signals acquired by the coil elements to a control unit for processing; in some embodiments, each coil element can be individually coupled to a corresponding channel). The low-resolution scan data can be projected into one dimension along the coil-select direction. For example, the 3D data for each channel can be projected into one dimension along the superior-inferior direction, thereby generating multiple channel sensitivity maps. The channel sensitivity maps can be grouped based on the REG information. For example, the coil array can include six rows of coil elements, each with five coil elements, and each row can be constrained so that all coil elements in a row are activated / tuned together. This grouping results in six REGs, each with five coil elements. For a given REG, the channel sensitivity maps corresponding to the five coil elements comprising that REG are combined. The resulting REG sensitivity map then conveys the coverage of each REG along the coil-select direction.

[0111] As mentioned above, the REG sensitivity map conveys the sensitivity along the coil direction of each REG. For example, refer to Figure 2B , REG line 3 (in Figure 2B ) includes five coil elements aligned along the x-axis. When the calibration data for the coil elements of REG R3 are projected into the S / I direction (along the y-axis) and combined (e.g., summed), the discrete sensitivity range along the S / I direction results in a value that roughly corresponds to the average diameter of the coil elements that include REG R3. In contrast, REG column 2 (highlighted in Figure 2B) includes six coil elements aligned along the y-axis. When the calibration data for the coil elements of REG C3 are projected into the S / I direction (along the y-axis) and combined (e.g., summed), the large sensitivity range along the S / I direction results in a combined coil diameter that roughly corresponds to all six coil elements of REG C3.

[0112] Therefore, when the RF coil array is rotatable, it is assumed that the REGs extending perpendicularly to the coil selection direction (row REG) can be turned to extend along the coil selection direction (e.g., along the Figure 2B y-axis in FIG). If the channel sensitivity maps for the channels are combined based solely on row REG groupings, the REG sensitivity range can only be determined when the RF coil array is in a first orientation; when the RF coil array is in a second orientation, the discrete sensitivity of each REG cannot be determined. Therefore, as described with respect to the above embodiments, the sensitivity of two different REGs (rows and columns) can be determined, and the RF coil array orientation can be determined based on the sensitivity (e.g., whether the rows are actually rows or they are columns). The REG sensitivity map corresponding to the orientation of the RF coil array can then be used for subsequent dynamic coil mode determination.

[0113] The selected REG sensitivity map can then be compared with the user-selected imaging ROI. For example, the user-set ROI can have a range along the coil selection direction. In some embodiments, any REGs with sensitivities that overlap with the ROI can be identified. Any REGs that do not overlap with the ROI can be excluded. If the identified REGs include exclusionary REGs, one REG is selected from the exclusionary REGs based on a tie-breaking rule. The selected REG can then be used for imaging during the main scan, and the unselected exclusionary REGs can be excluded from imaging during the main scan. In this way, an RF coil array comprising multiple coil elements can be used to receive MR signals during a main imaging MR scan, wherein only a subset of the coil elements (e.g., some but not all) are activated to receive MR signals. One or more images can then be reconstructed from the received MR signals. By utilizing only a subset of the coil elements to receive MR signals and deactivating the remaining coil elements of the RF coil array, noise that may contribute to the image from coil elements located outside the ROI can be reduced, thereby improving image quality.

[0114] The above embodiment involves projecting the calibration data into the S / I direction and then comparing the REG sensitivity range relative to the ROI along the S / I direction. However, other configurations are also possible. For example, if the imaging protocol selected by the operator of the MRI system indicates that the coil selection direction is along the medial-lateral axis (R / L) or along a different direction (e.g., from front to back), the calibration data can be projected along that direction (e.g., R / L), and the REG can be identified by comparing the REG sensitivity range relative to the ROI along the R / L direction. Such an example assumes that the REGs can be selected along that coil direction, such as being arranged in columns in addition to or instead of rows.

[0115] The dynamic coil pattern determination described above is generally described with respect to one or more ROIs within the same calibration FOV of the imaging subject as defined by the MRI system (e.g., MRI bore length, gradient range, transmit RF coil coverage, etc.). However, some imaging protocols (such as whole-body imaging protocols) may provide that the imaging subject moves through multiple stations (e.g., couch positions) and a main scan is performed at each station to generate images of the entire body or at least a large body region (e.g., a leg). In order to maintain dynamic coil generation at each station, a new calibration scan may be performed for each station. In one example, as Figure 12 and 13 As shown and described below, a series of calibration scans can be performed before any main scan occurs (e.g., once at each station), and the calibration scan data can be stored in memory and retrieved each time a new dynamic coil pattern is determined. Figure 14 and 15 As shown and described below, a calibration scan may be performed each time the couch is moved to a new station, and the dynamic coil pattern determined based on data acquired during the calibration scan.

[0116] Now see Figure 12 , shows a method 1200 for performing a whole body scan according to a first embodiment. The method 1200 may be performed by a processor executing instructions stored in a non-transitory memory of a computing device, such as Figure 1 The controller unit 25 of the MRI apparatus 10 may be configured to perform a whole-body scan. For example, the method 1200 may be performed in response to an instruction to perform a whole-body scan (specified in a scan protocol). Although the term "whole-body scan" is used herein, it should be understood that the following method is not limited to whole-body scans and may be applied to scans that include less than the whole body or scans that include non-human imaging subjects. For example, the method 1200 may be performed in response to an instruction to perform a scan by at least two stations of an examination table of the MRI system.

[0117] At 1202, method 1200 includes receiving patient information and a scan protocol. The patient information and scan protocol may be similar to those described above with respect to Figure 3 The patient information and scan protocol described above are thus equally applicable to the patient information and scan protocol received at 1202. As described above, the scan protocol may indicate a full body scan (or a scan of at least two stations of the examination table is to be performed). At 1204, method 1200 includes performing a localizer scan. The localizer scan performed at 1204 may be similar to Figure 3 The locator scans, therefore, Figure 3 The description of performing the localizer scan at 304 is also applicable to the localizer scan of method 1200, so further description is omitted.

[0118] At 1206, method 1200 includes performing a full mode calibration scan. The full mode calibration scan may be similar to Figure 3 The full mode calibration scan of method 300 is therefore Figure 3 The description of the full mode calibration scan performed at 306 of the method 1200 also applies to the full mode calibration scan of the method 1200. At 1208, the method 1200 includes saving the calibration scan data with an identifier. For example, the low-resolution data acquired during the calibration scan can be saved in the memory of the MRI system along with information that can be used to associate the calibration data with the current examination table position.

[0119] At 1210, method 1200 includes determining whether all full mode calibration scans have been completed. In one example, a calibration scan may be performed for each calibration FOV of a specified imaging target (e.g., a whole body), which may be specified by the scan protocol. If all specified full mode calibration scans have not been completed, method 1200 proceeds to 1211 to move the couch to the next position. The next position of the couch may move the current region of the imaged subject out of the center of the bore of the MRI system and move the next region to be imaged into the center of the bore of the MRI system. Once the first main scan is completed, the MRI system may automatically move the couch, or the MRI may prompt the operator to move the couch. After moving the couch, method 1200 loops back to 1206 to perform a new calibration scan and save the new calibration scan data in memory.

[0120] If all full mode calibration scans have been completed, the method 1200 proceeds to 1212 to receive a selection of a region of interest (ROI). The ROI may be received similarly to Figure 3 The ROI receives, therefore, Figure 3 The description of the reception of the ROI performed at 310 is also applicable to the reception of the ROI performed at 1212 , so further description is omitted.

[0121] At 1214, method 1200 determines a matching calibration scan. For example, the ROI can be compared to one or more calibration scans (previously performed, using calibration data obtained from scans stored in memory) to determine which calibration scan acquired data that overlaps and / or matches the current ROI. The data from the matching calibration scans is then used to generate a REG sensitivity map, as described above with reference to FIG. Figure 4 As stated.

[0122] At 1216, method 1200 includes determining a first dynamic coil mode based on the REG sensitivity map and the current ROI. Figure 4 The subroutine 400 described herein (whereby a REG sensitivity map is generated) and Figure 11 The illustrated process, whereby REGs are identified for inclusion in a dynamic coil pattern based on a REG sensitivity map and a ROI, performs dynamic coil pattern determination.

[0123] At 1218, method 1200 includes performing a main scan of the current ROI using the determined coil mode. The main scan performed at 1210 may be similar to that performed at Figure 3 The main scan is performed at 318, so the above reference Figure 3 The description of the main scan provided is equally applicable to the main scan performed at 1218. Based on the MR signals obtained during the main scan, one or more images of the imaged subject can be reconstructed. However, in some examples, reconstruction can be performed after each station has been imaged.

[0124] At 1220, method 1200 determines whether the examination is complete. Once all areas of the imaged subject have been imaged, the examination can be completed, which can be determined based on operator input, scan protocol, and / or other mechanisms. If the examination is not complete, method 1200 loops back to 1212 to receive a new ROI selection. The new ROI can be outside the current FOV, so method 1200 can also include moving the examination table to the next position. Once the new ROI is received and the examination table is moved (if indicated), a new matching calibration scan can be identified and retrieved, a new dynamic coil mode can be determined, and a new main scan can be performed. If the examination is complete, method 1200 ends.

[0125] Thus, the method 1200 described above includes a whole body scan performed using two head-to-toe (or toe-to-head) scans of the couch position. Thus, all calibration scans are performed before any main scans are performed. By doing so, the time spent performing the main scans can be reduced, which is advantageous in time-sensitive imaging protocols, such as when contrast agent is injected (e.g., the calibration scans can be acquired before the contrast agent is injected). Although the method 1200 is described above as including performing one localizer scan before performing the calibration scans, other configurations are possible. For example, only the calibration scan can be performed during a first scan of the couch position, and one or more localizer scans can be performed during a second scan of the couch position, e.g., one localizer scan can be performed and the ROI acquired before each main scan.

[0126] Figure 13 Shown according to Figure 12 A timeline 1300 of a whole body scan performed by the method 1200 is shown. The timeline 1300 includes 2D images 1310 of an imaged subject. Because the imaged subject is longer than the FOV / bore of the MRI system (in the S / I direction), the imaged subject is imaged in stages. Therefore, the couch on which the imaged subject is positioned can be moved into the MRI bore at different stations (or couch positions). Figure 13 As shown, the first station corresponds to the imaging subject's head, the second station corresponds to the imaging subject's shoulders and chest, the third station corresponds to the imaging subject's upper torso, and so on, and finally the eighth station corresponds to the imaging subject's feet. Figure 13 In the example of , the first couch position may be the position where stations 1 and 2 are placed into the bore of the MRI system. However, other positions are possible, such as starting at the feet instead of the head.

[0127] In addition to the representation 1310 of the imaged subject, Figure 13 The coverage of each calibration scan along the S / I direction is included in 1320. As shown, the first calibration scan 1321 scans stations 1 and 2, the second calibration scan 1322 scans stations 2 and 3, the third calibration scan 1323 scans stations 3, 4, and a portion of station 5, the fourth calibration scan 1324 scans a portion of station 4, station 5, and a portion of station 6, the fifth calibration scan 1325 scans a portion of station 5, station 6, and a portion of station 7, and the sixth calibration scan 1326 scans stations 7 and 8.

[0128] Figure 13An event timeline 1330 is included, which shows each calibration scan, dynamic coil pattern determination, and main scan performed in a whole-body scan as a function of time. Event timeline 1330 includes a first scan of the table position, which begins at time T0 and ends at time T1, and a second scan of the table position, which begins at time T2 and ends at time T3. Each calibration scan is illustrated by a striped bar, each coil pattern determination is illustrated by a white bar, and each main scan is illustrated by a cross-hatched bar. As shown, six calibration scans are performed between T0 and T1. Seven main scans are performed between T2 and T3. Prior to each main scan, a new dynamic coil pattern is determined based on low-resolution data acquired from the corresponding calibration scan. With the exception of the fifth calibration scan, data from each calibration scan is used to determine the dynamic coil pattern for one main scan. However, data from the fifth calibration scan is used for two main scans, namely the fifth and sixth main scans.

[0129] Now see Figure 14 , shows a method 1400 for performing a whole body scan according to a second embodiment. The method 1400 may be performed by a processor executing instructions stored in a non-transitory memory of a computing device, such as Figure 1 The controller unit 25 of the MRI apparatus 10 may be configured to execute method 1400 in response to an instruction to perform a whole-body scan. Although the term "whole-body scan" is used herein, it should be understood that the following method is not limited to whole-body scans and may be applied to scans that include less than the whole body or scans that include non-human imaging subjects. For example, method 1400 may be executed in response to an instruction to perform a scan using at least two stations of an examination table of the MRI system.

[0130] At 1402, method 1400 includes receiving patient information and a scan protocol. The patient information and scan protocol may be similar to those described above with respect to Figure 3 The patient information and scan protocol described above are thus equally applicable to the patient information and scan protocol received at 1402. As described above, the scan protocol may indicate a full body scan (or a scan of at least two stations of the examination table is to be performed). At 1404, method 1400 includes performing a localizer scan. The localizer scan performed at 1404 may be similar to Figure 3 The locator scans, therefore, Figure 3 The description of performing the localizer scan at 304 is also applicable to the localizer scan of method 1400, so further description is omitted.

[0131] At 1406, method 1400 includes performing a full mode calibration scan. The full mode calibration scan may be similar to Figure 3 The full mode calibration scan of method 300 is therefore Figure 3The description of the full mode calibration scan performed at 306 of the method 1400 also applies to the full mode calibration scan of the method 1400. At 1408, the method 1400 includes saving the calibration scan data with an identifier. For example, the low-resolution data acquired during the calibration scan can be saved in the memory of the MRI system along with information that can be used to associate the calibration data with the current examination table position.

[0132] At 1410, method 1400 includes receiving a selection of a region of interest (ROI). The ROI may be received similarly to Figure 3 The ROI receives, therefore, Figure 3 The description of the reception of the ROI performed at 310 is also applicable to the reception of the ROI performed at 1410 , so further description is omitted.

[0133] At 1412, method 1400 determines whether the current ROI matches any calibration scans. For example, the ROI can be compared with one or more calibration scans stored in memory to determine which calibration scan(s) acquired data that overlaps and / or matches the current ROI. The data from the matching calibration scans is then used to generate a REG sensitivity map, as described above with reference to FIG. Figure 4 If the ROI does not match any calibration scan, the method 1400 proceeds to 1413 to adjust the full mode calibration center, re-perform the calibration scan, and save the calibration data. The method 1400 then proceeds to 1414, as described below.

[0134] If a matching calibration scan is determined, the method 1400 proceeds to 1414 to generate a dynamic coil pattern based on the REG sensitivity map and the current ROI. Figure 4 The subroutine 400 described herein (whereby a REG sensitivity map is generated) and Figure 11 The illustrated process, whereby REGs are identified for inclusion in a dynamic coil pattern based on a REG sensitivity map and a ROI, performs dynamic coil pattern determination.

[0135] At 1416, method 1400 includes performing a main scan of the current ROI using the determined coil mode. The main scan performed at 1416 may be similar to that performed at Figure 3 The main scan is performed at 318, so the above reference Figure 3 The description of the main scan provided is equally applicable to the main scan performed at 1416. Based on the MR signals obtained during the main scan, one or more images of the imaged subject can be reconstructed. However, in some examples, reconstruction can be performed after each station has been imaged.

[0136] At 1418, method 1400 determines whether the examination is complete. Once all regions of the imaged subject have been imaged, the examination may be complete, which may be determined based on operator input, the scan protocol, and / or other mechanisms. If the examination is not complete, method 1400 moves the MRI system's table at 1420 and then loops back to 1404 to perform a new localizer scan, a calibration scan, and receive a new ROI. Once the new ROI is received, a new dynamic coil mode may be determined and a new main scan may be performed. If the examination is complete, method 1400 terminates.

[0137] Thus, the above-described method 1400 includes a whole-body scan performed using only one head-to-toe (or toe-to-head) scan of the couch position. Thus, a new calibration scan is performed each time (or nearly each time) the couch is moved. By doing so, patient comfort can be increased by only requiring a sweep of the couch position. Furthermore, depending on the movement of the couch, a new calibration scan does not have to be performed each time the couch is moved. Instead, when the couch is moved, if a calibration scan has already been performed at an earlier couch position, the MRI system can obtain that calibration scan data and determine whether a new dynamic coil mode for the new ROI is required. If the previous calibration scan includes sufficient data to determine the dynamic coil mode for the new ROI, an additional calibration scan can be omitted, thereby improving the efficiency of the whole-body scan.

[0138] Figure 15 Shown according to Figure 14 1400. The timeline 1500 includes a 2D image 1510 of an imaged subject. Because the imaged subject is longer than the FOV / bore of the MRI system (in the S / I direction), the imaged subject is imaged in stages. Therefore, the couch on which the imaged subject is positioned can be moved into the MRI bore at different stations (or couch positions). Figure 15 As shown, the first station corresponds to the imaging subject's head, the second station corresponds to the imaging subject's shoulders and chest, the third station corresponds to the imaging subject's upper torso, and so on, and finally the eighth station corresponds to the imaging subject's feet. Figure 15 In the example of , the first couch position may be the position where stations 1 and 2 are placed into the bore of the MRI system. However, other positions are possible, such as starting at the feet instead of the head.

[0139] In addition to the representation 1510 of the imaged subject, Figure 15The coverage of each calibration scan along the S / I direction is included in 1520. As shown, the first calibration scan 1521 scans stations 1 and 2, the second calibration scan 1522 scans stations 2 and 3, the third calibration scan 1523 scans stations 3, 4, and a portion of station 5, the fourth calibration scan 1524 scans a portion of station 4, station 5, and a portion of station 6, the fifth calibration scan 1525 scans a portion of station 5, station 6, and a portion of station 7, and the sixth calibration scan 1526 scans stations 7 and 8.

[0140] Figure 15 An event timeline 1530 is included, showing each calibration scan, dynamic coil mode determination, and main scan performed as a function of time during a whole-body scan, starting at time T0 and ending at time T1. Each calibration scan is illustrated by a striped bar, each coil mode determination is illustrated by a white bar, and each main scan is illustrated by a cross-hatched bar. For the first, second, third, fourth, and fifth main scans, a calibration scan is performed before each corresponding main scan. However, for the sixth main scan 1532, a dynamic coil mode is determined without performing a new calibration scan. For example, the fifth calibration scan 1525 may have acquired sufficient low-resolution data to determine the dynamic coil mode for both the fifth and sixth main scans.

[0141] A technical effect of automatically determining the RF coil array orientation is that predetermined receive element group (REG) information can be correctly applied to select one or more REGs to be included in the dynamic coil mode, thereby allowing the unselected REGs to be turned off and not used during the main scan, thereby improving the signal-to-noise ratio of the resulting image.

[0142] One example provides a method for performing magnetic resonance imaging (MRI) using a rotatable receive radio frequency (RF) coil array comprising a plurality of coil elements. The method includes grouping the plurality of coil elements into receive element group (REG) elements based on receive element group (REG) information; generating channel sensitivity maps for the plurality of coil elements; generating a REG sensitivity map based on the REG information and the channel sensitivity map; marking each REG as selectable or non-selectable based on the REG sensitivity map; selecting one or more REGs from the selectable REGs based on the REG sensitivity map and a region of interest (ROI); and scanning the ROI with the coil elements in the one or more selected REGs activated and without deactivating the coil elements in any other selected REGs. In a first example of the method, when the RF coil array is in a first orientation, the plurality of coil elements are arranged in an array having a first number of rows and a second number of columns, wherein each coil element in the RF coil array is coupled to a control unit via a channel of a plurality of channels, wherein each channel sensitivity map corresponds to a corresponding channel, and wherein, for a given channel, the corresponding sensitivity map represents the sensitivity of the one or more coil elements coupled to the given channel. In a second example of the method, which optionally includes the first example, generating the channel sensitivity maps includes generating the channel sensitivity maps by projecting 3D scan data acquired on corresponding channels into a single dimension along a coil selection direction, the 3D scan data acquired during a lower resolution calibration performed prior to scanning the ROI. In a third example of the method, which optionally includes one or both of the first and second examples, generating the REG sensitivity maps based on the REG information and the channel sensitivity maps includes generating a first set of REG sensitivity maps from the plurality of sensitivity maps, the first set of REG sensitivity maps representing respective sensitivities of a first plurality of REGs, and wherein each REG in the first plurality of REGs includes coil elements of a corresponding row of the plurality of coil elements. In a fourth example of the method, which optionally includes one or more or each of the first to third examples, generating the first set of REG sensitivity maps includes, for a first REG including a first row of coil elements, combining the channel sensitivity maps for each channel associated with each coil element in the first row, and for each additional REG including a corresponding additional row of coil elements, combining the channel sensitivity maps for each channel associated with each coil element in the corresponding additional row.In a fifth example of the method, the fifth example optionally includes one or more or each of the first to fourth examples, wherein generating the REG sensitivity map based on the REG information and the channel sensitivity map further comprises generating a second set of REG sensitivity maps from the plurality of sensitivity maps, the second set of REG sensitivity maps representing respective sensitivities of a second plurality of REGs, and wherein each REG in the second plurality of REGs comprises coil elements of a corresponding column of the plurality of coil elements. In a sixth example of the method, the sixth example optionally includes one or more or each of the first to fifth examples, wherein generating the second set of REG sensitivity maps comprises, for a first REG comprising a first column of coil elements, combining the sensitivity maps for each channel associated with each coil element in the first column, and, for each additional REG comprising a corresponding additional column of coil elements, combining the sensitivity maps for each channel associated with each coil element in the additional column. In a seventh example of the method, the seventh example optionally includes one or more or each of the first to sixth examples, wherein marking each REG as selectable or non-selectable based on the REG sensitivity map comprises marking each REG as selectable or non-selectable based on the first set of REG sensitivity maps and the second set of REG sensitivity maps. In an eighth example of the method, the eighth example optionally includes one or more or each of the first to seventh examples, and marking each REG as selectable or unselectable based on the first group of REG sensitivity maps and the second group of REG sensitivity maps includes: obtaining the average row sensitivity value of the first group of REG sensitivity maps; obtaining the average column sensitivity value of the second group of REG sensitivity maps; if the average row sensitivity value satisfies a predetermined condition relative to the average column sensitivity value, indicating that each REG in the first plurality of REGs is selectable and each REG in the second plurality of REGs is unselectable; and if the average column sensitivity value satisfies a predetermined condition relative to the average row sensitivity value, indicating that each REG in the second plurality of REGs is selectable and each REG in the first plurality of REGs is unselectable. In a ninth example of the method, the ninth example optionally includes one or more or each of the first to eighth examples, the average row sensitivity value comprises an average peak sensitivity for the first set of REG sensitivity maps, wherein the average column sensitivity value comprises an average peak sensitivity for the second set of REG sensitivity maps, and wherein the average row sensitivity value satisfies the predetermined condition relative to the average column sensitivity value, including the average peak sensitivity for the first set of REG sensitivity maps being greater than the average peak sensitivity for the second set of REG sensitivity maps.In a tenth example of the method, the tenth example optionally includes one or more or each of the first to ninth examples, the average row sensitivity value includes an average range of sensitivity values ​​for the first set of REG sensitivity maps, the average column sensitivity value includes an average range of sensitivity values ​​for the second set of REG sensitivity maps, and wherein the average row sensitivity value satisfies the predetermined condition relative to the average column sensitivity value, including the average range of sensitivity values ​​for the first set of REG sensitivity maps being greater than the average range of sensitivity values ​​for the second set of REG sensitivity maps. In an eleventh example of the method, the eleventh example optionally includes one or more or each of the first to tenth examples, selecting one or more REGs from the selectable REGs based on the REG sensitivity maps and the ROI includes: when the first plurality of REGs are marked as selectable, selecting one or more REGs from the first plurality of REGs having a sensitivity range that overlaps with the ROI determined by the first set of REG sensitivity maps, and when the second plurality of REGs are marked as selectable, selecting one or more REGs from the second plurality of REGs having a sensitivity range that overlaps with the ROI determined by the second set of REG sensitivity maps. In a twelfth example of the method, which optionally includes one or more or each of the first to eleventh examples, the method further includes reconstructing an image from MR signals obtained by coil elements in one or more selected REGs.

[0143] One example provides a magnetic resonance imaging (MRI) system comprising: a radio frequency (RF) coil array comprising a plurality of RF coil elements; a controller unit coupled to the RF coil array, the controller unit comprising a processor and a memory storing instructions executable by the processor, the instructions for: selecting one or more coil elements from the plurality of RF coil elements based on an automatically determined orientation of the RF coil array; obtaining MR signals from the one or more selected coil elements; and reconstructing an image from the obtained MR signals. In a first example of the system, the plurality of RF coil receive elements may be grouped into a first receive element group (REG) and a second REG group, and the instructions are executable to generate a first set of REG sensitivity maps for the first REG group and a second set of REG sensitivity maps for the second REG group based on low-resolution calibration data obtained during a previous scan. In a second example of the system, which may optionally include the first example, the instructions are executable to automatically determine the orientation of the RF coil array based on sensitivity values ​​of the first REG sensitivity maps relative to sensitivity values ​​of the second REG sensitivity maps. In a third example of the system, which optionally includes one or both of the first and second examples, the instructions are executable to: when determining that the RF coil array is in a first orientation, select one or more REGs having a sensitivity range that overlaps with a region of interest (ROI) determined by the first set of REG sensitivity maps, and when determining that the RF coil array is in a second orientation, select one or more REGs having a sensitivity range that overlaps with the ROI determined by the second set of REG sensitivity maps. In a fourth example of the system, which optionally includes one or more or each of the first to third examples, the instructions executable to obtain MR signals from the one or more selected coil elements include instructions executable to activate each coil element in the selected one or more REGs to obtain the MR signals and maintain any remaining coil elements in a deactivated state.

[0144] One example provides a method for performing magnetic resonance imaging (MRI) using a receive radio frequency (RF) coil array comprising a plurality of coil elements. The method includes automatically determining whether the RF coil array is in a first orientation or a second orientation based on a first sensitivity map indicating the sensitivity of each of the plurality of coil elements to an MR signal when the plurality of coil elements are grouped into a first receive element group (REG) relative to a second sensitivity map indicating the sensitivity of each of the plurality of coil elements to an MR signal when the plurality of coil elements are grouped into a second receive element group (REG); selecting one or more REGs in the first receive element group (REG) based on the first sensitivity map and a region of interest (ROI) when the RF coil array is in the first orientation; selecting one or more REGs in the second receive element group (REG) based on the second sensitivity map and the ROI when the RF coil array is in the second orientation; acquiring MR signals only from the selected one or more REGs and not from any unselected REGs during a main scan; and reconstructing an image from the acquired MR signals. In a first example of the method, the main scan is a first main scan of a first region of an imaging subject, wherein the first sensitivity map and the second sensitivity map are generated from low-resolution data acquired during a first calibration scan of the first region, the first calibration scan being performed before the first main scan, and the method further includes: in response to a command to perform a second main scan of a second region of the imaging subject, performing a second calibration scan of the second region of the imaging subject; generating a third sensitivity map from the low-resolution calibration data acquired during the second calibration scan; selecting one or more REGs based on the third sensitivity map and a new ROI; and obtaining MR signals during the second main scan only from the one or more REGs selected based on the third sensitivity map and the new ROI and not from any unselected REGs.

[0145] As used herein, the element or step that is narrated in the singular and begins with word " one " or " an " should be understood as not excluding a plurality of said elements or steps, unless explicitly stated to exclude. In addition, reference to " one embodiment " of the present invention is not intended to be interpreted as excluding the existence of other embodiments that also comprise the described feature. In addition, unless explicitly stated to the contrary, the embodiment that " comprises ", " includes " or " has " an element or has a plurality of elements of a specific attribute may include other such elements that do not have this attribute. The terms " include " and " in ... " are used as the popular language equivalents of the corresponding terms " including " and " wherein ". In addition, the terms " first ", " second " and " third " etc. are only used as marks, and are not intended to impose numerical requirements or specific positional order on their objects.

[0146] This written description uses examples to disclose the invention, including the best mode, and also to enable one of ordinary skill in the relevant art to practice the invention, including making and using any devices or systems and performing any included methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insignificant differences from the literal language of the claims.

Claims

1. A magnetic resonance imaging system comprising: an RF coil array comprising a plurality of RF coil elements, wherein the plurality of RF coil receiving elements are grouped into a first receiving element group and a second receiving element group; a controller unit coupled to the RF coil array, the controller unit comprising a processor and a memory storing instructions executable by the processor, the instructions to: generating a first set of receive element group sensitivity maps for the first set of receive element groups and a second set of receive element group sensitivity maps for the second set of receive element groups based on low-resolution calibration data obtained during a previous scan; automatically determining an orientation of the RF coil array based on sensitivity values ​​of the first set of receive element group sensitivity maps relative to sensitivity values ​​of the second set of receive element group sensitivity maps; selecting one or more coil elements of the plurality of RF coil elements based on the orientation of the RF coil array; obtaining MR signals from the one or more selected coil elements; as well as An image is reconstructed from the acquired MR signals.

2. The system of claim 1 , wherein the instructions are executable to: When the RF coil array is determined to be in a first orientation, one or more receive element groups are selected that have sensitivity ranges that overlap with a region of interest determined by the first set of receive element group sensitivity maps, and When the RF coil array is determined to be in a second orientation, one or more receive element groups are selected that have sensitivity ranges that overlap with the region of interest determined by the second set of receive element group sensitivity maps.

3. The system of claim 2 , wherein the instructions executable to obtain MR signals from the one or more selected coil elements include instructions executable to activate each coil element in the selected one or more receiving element groups to obtain the MR signals and maintain any remaining coil elements in a deactivated state.

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