Method and device for determining b1 map

Abstract

To determine B1 map at high speed and efficiently.SOLUTION: A method for determining a B1 map according to an embodiment of the present invention includes the steps of: acquiring B1 projection data in which analyte is spatially coded using magnetic resonance imaging apparatus; and determining a transmitting map using only the acquired B1 projection data.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to a method and an apparatus for determining a B1 map.

[0002] The present disclosure relates to patient-specific image intensity correction using radio frequency (RF) magnetic fields (e.g., "B1 magnetic fields") in Magnetic Resonance Imaging (MRI) devices, which is performed in vivo based on B1 projection data acquired along one or more projections on the patient determined according to the anatomy of the patient being imaged, which is a measure of the spatial distribution of the transmit B1 magnetic field of a Whole-Body Coil (WBC). [Background technology]

[0003] Magnetic resonance imaging (MRI) is a non-invasive imaging technique that produces high-resolution images without ionizing radiation to visualize the internal structures and functions of the body, and is widely used in medical diagnosis and research. The quality of MRI images can be affected by various factors, including patient motion, magnetic field inhomogeneity, gradient nonlinearity, and radio frequency (RF) coil configuration. These factors can cause image artifacts and spatial signal intensity variations, which can hinder accurate interpretation of the images.

[0004] To address this issue, researchers have developed various techniques to correct for signal strength variations in MRI images. One such method involves obtaining a B1 map that represents the strength of the B1 field to determine the distribution of the transmit B1 field and the distribution of the receive sensitivity within the patient's body. However, these techniques often require additional scan time and may not be compatible with all MRI devices or coil configurations.

[0005] To generate an MRI image of a patient's inside, a static magnetic field (B0 field) is first applied by the MRI machine to align the nuclear spins of atoms. Then, during the scan, an RF transmitter generates RF pulses by perturbing the local magnetic field. This results in an RF signal being emitted by the nuclear spins, which is detected by an RF receiver to form the image.

[0006] In clinical practice, high-intensity B0 magnetic fields (1.5T to 3.0T or more) are used to generate diagnostic images with higher spatial and contrast resolution. However, as the strength of the B0 magnetic field increases, errors in the contrast of diagnostic images may occur due to non-uniform RF transmission. One of the factors is that the different dielectric properties of various tissues in the human body bring non-uniform local perturbations to the B1 magnetic field. As the B0 magnetic field increases, the distribution of the transmitted B1 magnetic field becomes less uniform, and the variation in signal strength becomes more pronounced.

[0007] To alleviate this problem, a common method is to map the B1 field to obtain a B1 map and calibrate the distribution of the non-uniform transmit B1 field and the receive sensitivity of the transmit and receive coils. A whole-body coil (WBC) is often used as the transmit coil, and a phased array coil (PAC) is often used as the receive coil. A spatially resolved B1 map, where each pixel is a measurement of the transmit B1 field, is obtained as a prescan step and is used during the protocol for calibrating, designing, or correcting data in subsequent data acquisitions. By determining a B1 map (hereinafter referred to as a transmit map) that represents the distribution of the transmit B1 field of the WBC and a B1 map (hereinafter referred to as a receive map) that represents the distribution of the receive sensitivity of both coils, a method is obtained to calculate an accurate receive map of each coil element in the PAC, so that the signal strength of the image can be corrected. Note that mapping the B1 field is an established method for characterizing the B1 field, and there is also a method of obtaining a set of images and using them to calculate the B1 map.

[0008] There are many methods for mapping the B1 field, but a common downside is that the measurement time is unrealistically long, up to about one minute, for reasonable resolution and field of view (FOV). Also, model-based methods, such as Bloch model methods and geometric model methods, contain assumptions that may not be correct in all clinical situations and may introduce errors. Therefore, it is desirable to address these and other deficiencies in current methods. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2016 / 0187438 [Patent Document 2] US Patent Application Publication No. 2019 / 0378270 [Patent Document 3] US Patent Application Publication No. 2021 / 0018583 [Patent Document 4] US Patent Application Publication No. 2012 / 0032676 Summary of the Invention [Problem to be solved by the invention]

[0010] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to determine the B1 map quickly and efficiently. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0011] An embodiment of a method for determining a B1 map includes acquiring spatially encoded B1 projection data of a subject using a magnetic resonance imaging apparatus, and determining a transmission map using only the acquired B1 projection data. [Brief description of the drawings]

[0012] Various embodiments of the present disclosure are described in detail, by way of example only, with reference to the figures listed below, in which like reference numerals refer to like elements, and in which:

[0013] [Figure 1] FIG. 1 shows exemplary B1 maps acquired for two different imaging anatomies: abdomen and head. [Diagram 2] FIG. 2 illustrates a non-limiting example of the imaging anatomy of the human head and a set of polar and azimuth axis orientation patterns separated by 45° in accordance with one embodiment of the present disclosure. [Diagram 3] FIG. 3 illustrates non-limiting examples of different B1 projections, B1 projection data acquired along each of the projections, and associated transmit and receive maps determined using a dictionary lookup in accordance with one embodiment of the present disclosure. [Figure 4] FIG. 4 illustrates non-limiting examples of different B1 projections, B1 projection data acquired along each of the projections, and associated transmission and reception maps determined using a machine learning network in accordance with one embodiment of the present disclosure. [Diagram 5] FIG. 5 is a flow chart illustrating a non-limiting example of a process for determining an intensity corrected magnetic resonance image using a dictionary lookup and referencing pre-computed transmit and receive maps in accordance with one embodiment of the present disclosure. [Figure 6] FIG. 6 is a schematic block diagram of a magnetic resonance imaging apparatus according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present disclosure provides a method for determining a B1 map, comprising acquiring spatially encoded B1 projection data of a subject using a magnetic resonance imaging device, and determining a transmission map using only the acquired B1 projection data.

[0015] In one embodiment, the method further comprises acquiring an image with the magnetic resonance imaging device and correcting signal intensity of the acquired image using the determined transmission map.

[0016] In another embodiment, the method further comprises determining, based on the determined transmission map, a reception map corresponding to the transmission map by referring to pre-calculated and associated transmission and reception maps.

[0017] In another embodiment, the step of correcting the signal strength includes correcting signal strength of the acquired image using both the determined transmit map and the determined receive map.

[0018] In another embodiment, the step of correcting the signal strength includes correcting the signal strength of the acquired image using only the determined transmission map.

[0019] In another embodiment, determining the transmission map includes determining the transmission map using a look-up table that associates B1 projection data with a transmission map corresponding to the B1 projection data.

[0020] In another embodiment, determining the transmission map includes determining the transmission map by applying the acquired B1 projection data to a trained machine learning model.

[0021] In another embodiment, the step of determining the transmission map includes determining the transmission map via an electromagnetic simulation based on the acquired B1 projection data, the B1 projection data being used to derive, correct and / or shape an output of the electromagnetic simulation.

[0022] In another embodiment, acquiring the B1 projection data includes determining an imaging anatomical structure from information about the subject, acquiring a number of projections and a direction pattern of the B1 projection data relative to the determined imaging anatomical structure, and acquiring the B1 projection data based on the acquired number of projections and the direction pattern. In one embodiment, the direction pattern is represented by a set of polar and azimuth axes in a three-dimensional volume.

[0023] In another embodiment, an apparatus for determining a B1 map is provided, the apparatus comprising: a processing circuit for acquiring spatially encoded B1 projection data of a patient using a magnetic resonance imaging device; and determining a transmission map using only the acquired B1 projection data.

[0024] In another embodiment, a method for determining a B1 map is provided that includes acquiring low-resolution Cartesian B1 map data of a subject using a magnetic resonance imaging device and determining a transmission map using only the acquired low-resolution Cartesian B1 map data.

[0025] The present methods and apparatus present a wide range of techniques and options for acquiring B1 projection data, determining transmit and receive maps, and generating intensity corrected images to comprehensively and efficiently address signal intensity inhomogeneity in MRI.

[0026] In one embodiment, acquiring the B1 projection data includes acquiring the B1 projection data using a whole body coil and a phased array coil.

[0027] In another embodiment, the step of acquiring the B1 projection data includes acquiring the spatially encoded B1 projection data using a single two-dimensional slice along the directional pattern within the volume of the subject.

[0028] In another embodiment, the step of acquiring the B1 projection data includes acquiring the spatially encoded B1 projection data using a two-dimensional bar selection along the directional pattern within the volume of the subject.

[0029] In another embodiment, acquiring the B1 projection data includes acquiring the B1 projection data using a spatial encoding technique.

[0030] The present disclosure relates to methods of acquiring and using Magnetic Resonance Imaging (MRI) data to generate a B1 map used to correct the effects of inhomogeneous B1 fields in MRI images, and in particular to methods of acquiring B1 projections using MRI pulse sequences to determine B1 projection data, and the subsequent calculation and use of the projection data to generate a B1 map used for image correction.

[0031] MRI is a non-invasive medical imaging technique that produces high-resolution images of the human body. In MRI, a strong magnetic field is applied to the patient, causing the hydrogen atoms in the body to align with the magnetic field. RF pulses are then applied to the patient, exciting the hydrogen atoms and generating signals that are detected and processed by the MRI machine to produce an image of the patient.

[0032] One of the challenges in such MRI is to correct for variations in the B1 field, which can cause variations in signal strength in the image. Inhomogeneous B1 fields in MRI can lead to significant errors in image signal strength and image contrast. These errors can lead to incorrect diagnoses and retakes of imaging studies, increasing medical costs and patient discomfort. It is therefore useful to correct these errors by characterizing the B1 field, showing its strength.

[0033] Figure 1 shows exemplary B1 maps acquired for two different imaging anatomies, namely the abdomen and the head. The B1 maps shown in Figure 1(a) and 1(b) each have a characteristic distribution that corresponds to a + / - pattern due to dielectric effects. The B1 maps of individual patients fit the same characteristic pattern, although they differ in aspect ratio, spatial scaling, scaling of B1 field inhomogeneity, etc.

[0034] One challenge in mapping the B1 field is the time it takes to acquire the data required to compute a B1 map. Traditionally, such data is acquired using dedicated B1 mapping sequences. However, these sequences are often time consuming and may not be available for all MRI machine and coil configurations.

[0035] To overcome these challenges, the present disclosure proposes a method for fast and efficient B1 map determination, which includes acquiring a series of one-dimensional B1 projection data or low-resolution Cartesian B1 map data using an MRI pulse sequence, and then referencing a unique pre-computed B1 map for each anatomical structure of interest. The method also includes appropriately selecting the number of projections and the projection directions to maximize the information content and determination accuracy of the B1 map, while simultaneously taking into account the advantage of reduced scan time.

[0036] In one embodiment, the method includes acquiring spatially encoded B1 projection data of a patient using an MRI device and determining a transmit map using only the acquired B1 projection data, and in one embodiment, the method further includes determining a receive map corresponding to the determined transmit map based on the determined transmit map by referencing pre-computed and associated transmit and receive maps.

[0037] In one embodiment, the step of acquiring B1 projection data includes acquiring B1 projection data using a WBC and a PAC, which are commonly used to transmit and receive RF signals in an MRI device, respectively. The WBC generates a relatively homogeneous transmit B1 magnetic field, and the receiving coil of the PAC has a higher sensitivity, which can improve the signal-to-noise ratio (SNR).

[0038] Here, there is no method to directly measure the distribution of the receiving sensitivity of WBCs, but on the other hand, there are many methods to correct the distribution of the non-uniform transmit B1 magnetic field of WBCs and the distribution of the receiving sensitivity of PACs. Most methods require the acquisition of a 3D B1 map as a prescan image, for example, using 6 to 8 2D slices to cover the imaging volume. This is time-consuming, and for a reasonable resolution and field of view (FOV), each slice requires an acquisition time of 5 to 10 seconds. Model-based methods also contain assumptions that may not be true in all clinical situations and may result in inaccurate solutions as a result of attempting to solve two unknowns with insufficient data (see J. Wang, M. Qiu, QX Yang, MB Smith, RT Constable, Measurement and correction of transmitter and receiver induced nonuniformities in vivo, Magnetic Resonance in Medicine. 53 (2005) 408-417; J. Wang, M. Qiu, In vivo method for correcting transmit / receive nonuniformities with phased array coils, Magnetic Resonance in Medicine. 53 (2005) 666-674, which are incorporated by reference in their entireties).In addition, the reciprocity method measures and calculates the complex conjugate of the WBC transmission map to derive the PAC reception map value, which is not an exact relationship between B1 transmission and B1 reception and therefore introduces errors (see WM Brink, MJ Versluis, JM Peeters, P. Bornert, AG Webb, Passive radiofrequency shimming in the thighs at 3 Tesla using high permittivity materials and body coil receive uniformity correction, Magnetic Resonance in Medicine. 76 (2016) 1951-1956; H. Watanabe, N. Takaya, F. Mitsumori, Non-uniformity correction of human brain imaging at high field by RF field mapping of B1+ and B1-, Journal of Magnetic Resonance. 212 (2011) 426-430, which are incorporated by reference in their entirety).

[0039] In one embodiment of the present disclosure, the general process includes acquiring a PAC image P(tx+,rx,C) and a WBC image W(tx+,tx-,C), where rx is the PAC receive sensitivity, tx+ is the transmit B1 field, C is the image contrast and structure obtained by the Bloch equation, and tx- is the WBC receive sensitivity. Typically, a receive map S is created for each channel by normalizing the PAC image of each channel in the PAC with the WBC image. In this way, the effects of tx+ and C are removed by calculating the receive map S. However, the receive map S includes the residual WBC receive sensitivity (tx-) in the final calculated data of S.

[0040] In this regard, at low B0 field strengths (1.5T or less), the WBC receive sensitivity (tx-) is nearly uniform, so the effect of tx- in the receive map S is a small issue. However, at high B0 field strengths (3.0T or more), the uniformity of the WBC receive sensitivity (tx-) decreases, and the effect of tx- in the receive map S can become significant. One way to determine how much this affects the data quality is to calculate accurate receive maps for each coil element in the PAC. With the transmit map of the WBC and the receive map of the PAC, accurate intensity correction of the images can be achieved.

[0041] The present disclosure acquires a 3D volume map of Tx+ and a 3D volume map of Tx- of WBC as the transmit map of WBC and the receive map of PAC, for example. Then, the method uses the 3D volume map of Tx- to calculate an accurate 3D volume map of S, which represents the receive map of each coil element in PAC. Here, a simple model such as Tx-=WBC(tx+,tx-,C) / model(tx+,C) may be used to calculate Tx-. This model incorporates the transmit map of WBC (Tx+) and uses a simple Bloch equation model to calculate the value of C. This is because the conventional Bloch equation cannot be solved since the parameter maps, i.e., T1, T2, and M0, are not available. Here, to minimize the effect of C, sequence parameters for acquiring WBC and PAC images may be designed to generate WBC and PAC images with very low contrast. Their objective is to achieve signal intensity correction of images using only the transmit map (Tx+) of the WBC or both the transmit map (Tx) and receive map (Tx-) of the WBC.

[0042] In one embodiment, the step of acquiring B1 projection data includes acquiring B1 projection data using a spatial encoding technique, which is used to encode spatial information in an MRI signal. By acquiring B1 projection data using the spatial encoding technique, the method determines the transmit map and the receive map with higher accuracy and shorter scan time compared to conventional methods.

[0043] In another embodiment, the spatial encoding technique is a two-dimensional bar selection using spin echo along the directional pattern of B1 projection data within the patient volume, which can provide efficient and accurate acquisition of B1 projection data for determining transmit and receive maps.

[0044] In another embodiment, the spatial encoding technique is a single two-dimensional slice using slice-selective magnetic field gradients and specific RF pulses along the orientation pattern of B1 projection data within the patient volume. The data for this slice can be acquired using either field echo or spin echo. This configuration allows for a different method of acquisition of B1 projection data for determining the transmit and receive maps.

[0045] In one embodiment, after the transmission map is determined, it may be used to optimize various aspects of the MRI data acquisition. For example, the transmission map may be used to optimize the design of RF pulses, which is useful for achieving uniform excitation throughout the imaging volume. By using the transmission map to design RF pulses that compensate for the spatially varying B1 field sensitivity, it is possible to achieve more uniform excitation throughout the imaging volume, which can improve image quality.

[0046] In another embodiment, in addition to optimizing the RF pulse design, the transmit map may be used to optimize the selection of imaging parameters such as flip angles and repetition times. By analyzing the transmit map, regions of the imaging volume that may be affected by B1 field inhomogeneities can be identified and the imaging parameters can be adjusted accordingly to ensure that acquired images have sufficient SNR and contrast.

[0047] In yet another embodiment, the method further includes acquiring images using an MRI device and correcting signal intensity of the acquired images using the determined transmission map.

[0048] In one embodiment, the step of correcting the signal strength includes correcting the signal strength of the acquired image using both the set of transmit and receive maps, or only the set of transmit maps, to generate an intensity-corrected image. This correction step can be performed at a post-processing stage. By applying the determined transmit (Tx+) and receive (S) maps, the method effectively corrects spatial signal strength variations in the acquired image. This results in a more accurate and reliable representation of the patient's anatomy.

[0049] It should be noted that the number of dimensions and directions selected for the B1 projection depends on the complexity of the anatomy being imaged and the level of accuracy desired. In general, a greater number of dimensions and directions will provide a more accurate measurement of the B1 field, but will require a longer acquisition time.

[0050] In some embodiments, acquiring the B1 projection data may include determining an imaging anatomical structure from the patient information, acquiring a number of projections and a direction pattern of the B1 projection data for the determined imaging anatomical structure, and acquiring the B1 projection data based on the acquired number of projections and direction pattern. Also, acquiring the image of the patient may include generating gradient magnetic field signals based on the number of projections and the direction pattern of the acquired B1 projection data, and applying the generated gradient magnetic field signals to a gradient coil driver of the magnetic resonance imaging device.

[0051] 2 illustrates a non-limiting example of the imaging anatomy of the human head and a direction pattern of nine B1 projections and a set of polar and azimuth axes separated by 45 degrees, according to one embodiment of the present disclosure. This number of projections and direction pattern provides adequate coverage of the head and allows accurate determination of transmit and receive maps for intensity correction.

[0052] Here, the direction of the projection may be unique for each imaging anatomical structure. The direction of the projection may be selected according to the characteristic B1 pattern of the anatomical structure. For example, for the head, two orthogonal projections oriented at about 45° may be selected. For the abdomen, two orthogonal projections or four projections separated by about 45° may be selected. For the breast and thigh, a single horizontal projection may be used since the B1 pattern is simple. Note that these specific angles are not limiting. Other angular orientations are possible within the present disclosure. For example, instead of 45° as shown in FIG. 2, angles such as 40°, 60°, etc. may be used.

[0053] In one embodiment, after the B1 projection data is acquired, the B1 projection data is used to reference a pre-calculated B1 map specific to the anatomical structure of interest. In a further embodiment, the step of determining the transmit map includes determining a set of transmit maps and a set of receive maps by referencing a transmit map (Tx+) and a receive map (Tx-) of the WBC that are pre-calculated and matched by electromagnetic simulation. These B1 maps may be obtained from a database of pre-calculated B1 maps or may be referenced on-the-fly during the MRI examination (see Y. Lai, X. Zhao, W. Zhang, SJ Garnier, L. Nie, P. Lu, H. Wang; GE Precision Healthcare LLC, Method and apparatus for correcting uniformity of a magnetic resonance image. US10718839B2 (2020), which is incorporated herein by reference in its entirety). By referencing these pre-calculated B1 maps, the method efficiently determines the transmit map (Tx+) and receive map (S) for intensity correction without requiring additional time-consuming measurements or calculations.

[0054] In one embodiment, the step of determining the transmit maps includes determining a set of transmit maps and a set of receive maps using a dictionary lookup method, where the dictionary lookup method includes searching a predefined dictionary or lookup table of transmit maps (Tx+) and / or receive maps (Tx-) of the WBC stored in association with one or more B1 projection data to obtain a transmit map that best fits the acquired B1 projection data. This method provides a fast and efficient method for determining transmit and receive maps for intensity correction. Note that there are many ways to perform the dictionary lookup, and the details of these methods are not important to this disclosure.

[0055] FIG. 3 illustrates a non-limiting example of different B1 projections, B1 projection data acquired along each of the B1 projections, and associated transmit maps (Tx+) of WBC and receive maps (Tx-) of WBC determined using dictionary lookup, according to an embodiment of the present disclosure. FIG. 3(a) illustrates two independent B1 projections and directions, and FIG. 3(b) illustrates the acquired B1 projection data. FIG. 3(c) illustrates a dictionary lookup method in which a best-match transmit map is determined based on pre-computed transmit maps, as shown in FIG. 3(d). FIG. 3(e) illustrates a receive map corresponding to the transmit map shown in FIG. 3(d).

[0056] In another embodiment, the step of determining the transmission maps includes determining a set of transmission maps (Tx+) of the WBC and a set of receive maps (Tx-) of the WBC using a machine learning network. Machine learning techniques such as deep learning or artificial neural networks can be employed to learn the relationship between the acquired B1 projection data and the corresponding transmission and receive maps. The method can accurately determine the transmission and receive maps for intensity correction by training the machine learning network with a large dataset of B1 projection data and the corresponding transmission and receive maps.

[0057] FIG. 4 illustrates a non-limiting example of different B1 projections, projection data acquired along each of the projections, and associated WBC transmit (Tx+) and receive (Tx-) maps determined using a machine learning network, according to an embodiment of the present disclosure. FIG. 4(a) illustrates two independent B1 projections and directions, and FIG. 4(b) illustrates the acquired B1 projection data. FIG. 4(c) illustrates a machine learning network that determines a best fit transmit map based on the learned transmit maps, as shown in FIG. 4(d). FIG. 4(e) illustrates a receive map corresponding to the transmit map shown in FIG. 4(d).

[0058] In another embodiment, the step of determining the transmit maps includes deriving, modifying or shaping the output of a simulation using B1 projection data, which is the basis for a set of transmit maps (Tx+) of the WBC and a set of receive maps (Tx-) of the WBC. By incorporating acquired B1 projection data into the simulation, the method allows for flexible determination of transmit and receive maps for intensity correction.

[0059] In a preferred embodiment, the step of acquiring the B1 projection data includes acquiring the B1 projection data in, for example, 1 to 2 seconds, which shortens the overall scan time for the patient and improves the efficiency of the MRI examination.

[0060] In addition to the above-mentioned embodiments, the method also provides several alternative techniques for acquiring B1 projection data. These techniques are numerous, such as Bloch-Siegert Shift, Double Angle, Actual Flip Angle, Dual Refocusing Echo Acquisition Mode, Phase Sensitive, and Saturation Recovery. However, each of these methods has limitations and challenges. The method uses different techniques to accommodate different imaging scenarios and preferences.

[0061] In another embodiment, the present disclosure provides a method for determining intensity corrected magnetic resonance images including acquiring low resolution Cartesian B1 transmission map data of a patient using an MRI device, determining a set of high resolution transmission maps using only the acquired low resolution Cartesian B1 transmission map data, acquiring images of the patient using the MRI device based on the determined set of high resolution transmission maps, and outputting the acquired images of the patient.

[0062] In a further embodiment, the acquired low-resolution Cartesian B1 transmission map data is a low-resolution three-dimensional Cartesian B1 map having a lower resolution than the determined transmission map. In another further embodiment, the acquired low-resolution Cartesian B1 transmission map data is a low-resolution two-dimensional Cartesian B1 map. These low-resolution Cartesian B1 maps provide a detailed representation of the B1 field in the imaging volume and allow for highly accurate determination of transmission and reception maps for signal intensity correction. In a further embodiment, the low-resolution Cartesian B1 transmission map data is acquired in a time shorter than that required for acquisition of a full-resolution three-dimensional Cartesian B1 transmission map, for example in 30-60 seconds, as opposed to 1-2 minutes or more required for acquisition of a full-resolution three-dimensional Cartesian B1 transmission map. This acquisition time allows for balancing the need to determine an accurate B1 field with the overall efficiency of the MRI examination.

[0063] 5 is a flow chart illustrating a non-limiting example of a process for determining an intensity corrected magnetic resonance image using a dictionary lookup and referencing pre-computed transmit and receive maps according to an embodiment of the present disclosure. The method 500 for determining an intensity corrected magnetic resonance image preferably starts an examination at step 510 and performs a B1 projection scan to acquire B1 projection data, preferably with WBC and PAC, and a map scan to acquire PAC and WBC images at step 520.

[0064] Also, in step 540, a set of transmit maps and a set of receive maps of the WBC are determined using a dictionary lookup technique with the B1 projection data acquired in step 520 and pre-calculated 3D transmit and 3D receive maps acquired from a database 530 of human body models.

[0065] Also, in step 550, a receive map for the PAC is determined by obtaining the receive sensitivity of the PAC using the PAC image and WBC image acquired in step 520 and the set of receive maps for the WBC determined in step 540.

[0066] Also, in step 560, imaging begins.

[0067] Also, in step 570, the patient is scanned.

[0068] Also, in step 580, the set of transmission maps of the WBC determined in step 540 and the receive map of the PAC determined in step 550 are used to correct the signal intensity of the magnetic resonance image acquired in step 570.

[0069] Also, in step 590, the intensity corrected magnetic resonance images are stored and displayed.

[0070] The present disclosure also includes an apparatus for determining intensity corrected magnetic resonance images, the apparatus comprising processing circuitry for acquiring B1 projection data, determining a set of transmission maps using the acquired B1 projection data, acquiring images of a patient using an MRI device based on the determined set of transmission maps, and outputting the acquired images of the patient. The apparatus is capable of efficiently performing the method and producing high quality intensity corrected MRI images.

[0071] 6 shows a non-limiting example of a magnetic resonance imaging (MRI) apparatus 100 for such an apparatus. The MRI apparatus 100 includes a gantry 101, shown in schematic cross-section, and various associated MRI system components 103 that interface with the gantry 101. Typically, at least the gantry 101 is installed in a shielded room. The geometry of the MRI apparatus 100 includes a substantially coaxial cylindrical arrangement of a B0 static magnetic field magnet 111, a Gx, Gy and Gz gradient coil set 113, and a large whole-body RF coil (WBC) 115. An imaging volume 117 is shown along the inner horizontal axis of the elements of this cylindrical arrangement, substantially surrounding the head of a patient 119 supported by a patient table 120.

[0072] One or more small array RF coils 121 may be coupled closer to the patient's head (e.g., referred to as a "scan target" or "target") in the imaging volume 117. As will be appreciated by those skilled in the art, often relatively small coils and / or arrays compared to WBC (whole body coils), such as surface coils, are customized to the shape of different body parts (e.g., arms, shoulders, elbows, wrists, knees, legs, chest, spine, etc.). Such small RF coils are called array coils (AC) or phased array coils (PAC). These array coils may include at least one coil configured to transmit RF signals into the imaging volume 117 and multiple receive coils configured to receive RF signals from a target, such as the patient's head, in the imaging volume.

[0073] The MRI apparatus 100 further includes an MRI system controller 130 having input / output ports connected to a display 124, a keyboard 126, and a printer 128. As will be appreciated by those skilled in the art, the display 124 may be a touch screen for receiving control inputs in addition to a mouse or other I / O devices.

[0074] The MRI system controller 130 interfaces with an MRI sequence controller 140 and controls the Gx, Gy, and Gz gradient coil drivers 132, as well as the RF transmitter 134 and the transmit / receive (T / R) switch 136 (if the same RF coil is used for both transmit and receive). The RF transmitter 134 may be configured with two or more transmit channels to drive two or more RF transmit coils or ports on the coils. The MRI sequence controller 140 includes suitable program code structures 138 for implementing MRI imaging techniques, also known as Nuclear Magnetic Resonance (NMR) imaging techniques. The MRI sequence controller 140 may facilitate one or more preparatory scan (prescan) sequences and a scan sequence for acquiring a main scan Magnetic Resonance (MR) image, also referred to as a diagnostic image. The MR data from the prescan may be used, for example, in a B1 projection scan.

[0075] The MRI system components 103 include an RF receiver 141 that provides input to an MRI data processor 142 for at least producing processed image data that is transmitted to the display 124. The MRI data processor 142 is further configured to access generated MR data, images, and / or B1 projection data (including but not limited to B1 projection data acquired on different transmit channels) and / or system configuration parameters 146, as well as program code structures 144 and 150.

[0076] In one embodiment, the MRI data processor 142 comprises processing circuitry, including devices such as, but not limited to, Application Specific Integrated Circuits (ASICs), programmable logic devices (e.g., Simple Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), Field Programmable Gate Arrays (FPGAs)), and other circuit components configured to perform the functions described in this disclosure.

[0077] The MRI data processor 142 executes one or more sequences of one or more instructions contained in the program code structures 144 and 150. Alternatively, the instructions may be read from another computer readable medium, such as a hard disk or a removable media drive. One or more processors in a multi-processing arrangement may be used to execute the sequences of instructions contained in the program code structures 144 and 150. In other embodiments, hardwired circuitry may be used in place of or in combination with software instructions. Thus, embodiments of the present disclosure are not limited to any particular combination of hardware circuitry and software. For example, the program code structure 150 may store instructions for performing the method 500.

[0078] Moreover, the term "computer readable medium" refers to any non-transitory medium that participates in providing instructions to the MRI data processor 142 for execution. Computer readable media may take various forms such as, but not limited to, non-volatile media or volatile media. Non-volatile media include, for example, optical disks, magnetic disks, and magneto-optical disks, or removable media drives. Volatile media include, but are not limited to, dynamic memory.

[0079] 6 illustrates a generalized depiction of the MRI system program storage (memory) 150, in which stored program code structures, such as instructions for executing the method 500, are stored on a non-transitory computer readable storage medium accessible by the various data processing components of the MRI apparatus 100. As will be appreciated by those skilled in the art, the MRI system program storage 150 may be partitioned and at least partially connected directly to the different processing computers among the MRI system components 103 that most immediately require the program code structures during normal operation (i.e., rather than being stored in a shared manner and directly connected to the MRI system controller 130).

[0080] Also, the MRI device 100 shown in Fig. 6 can be utilized to implement the exemplary embodiments described above. The MRI system components 103 can be divided into different logical collections of "boxes" and typically include a number of digital signal processors (DSPs), microprocessors, and special purpose (e.g., for high speed A / D (Analog to Digital) conversion, fast Fourier transform, array processing, etc.) processing circuits. Each of these processing circuits is typically a clocked "state machine" in which the physical data processing circuitry progresses from one physical state to another physical state every clock cycle (or a predetermined number of clock cycles).

[0081] Moreover, not only do the physical states of processing circuits (e.g., CPUs, registers, buffers, arithmetic units, etc.) change gradually from one clock cycle to another during the course of operation, but the physical states of associated data storage media (e.g., bit storage sites of a magnetic storage medium) are also transformed from one state to another during operation of such systems. For example, at the end of the process of image reconstruction and / or the process of generating image reconstruction maps (e.g., coil receive maps, unfolded maps, ghost maps, distortion maps, etc.), an array of computer-readable and accessible data value stores contained in the physical storage media is transformed from some prior state to a new state, where the physical states of the physical portions of such arrays change between minimum and maximum values ​​to represent real-world physical events and conditions. As will be appreciated by those skilled in the art, such arrays of stored data values ​​represent and constitute physical structures, as well as specific structures of computer control program code that, when sequentially loaded into instruction registers and executed by one or more CPUs of the MRI device 100, generates and transitions through a particular sequence of operating states within the MRI device 100.

[0082] As MRI technology advances, the importance of addressing signal intensity inhomogeneity in images becomes increasingly apparent. The proposed method or apparatus offers a wide range of techniques and options for acquiring B1 projection data, determining transmit and receive maps, and generating intensity corrected images, providing a comprehensive solution to the problem.

[0083] Moreover, the adaptability of the present disclosure to a variety of imaging scenarios and preferences ensures that it remains relevant in the ever-evolving field of medical imaging.The present methods and apparatus contribute to medical advances by improving the quality and speed of MRI scans and facilitating accurate diagnosis, ultimately benefiting patients.

[0084] Those skilled in the art will appreciate from the above detailed description, as well as the drawings and claims, that modifications and variations can be made to the preferred embodiments of the present disclosure described above, within the scope of the present disclosure as defined in the claims.

[0085] According to at least one of the embodiments described above, the B1 map can be determined quickly and efficiently.

[0086] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0087] 100 Magnetic resonance imaging device 142 MRI Data Processor

Claims

1. acquiring spatially encoded B1 projection data of a subject using a magnetic resonance imaging device; Determining a transmit map using only the acquired B1 projection data A method for determining a B1 map, comprising:

2. Obtaining an image using the magnetic resonance imaging device; Correcting signal intensity of the acquired image using the determined transmission map. The method of claim 1 , further comprising:

3. determining a receive map corresponding to the transmit map based on the determined transmit map by referencing pre-calculated and associated transmit and receive maps. The method of claim 2 .

4. and correcting the signal strength includes correcting the signal strength of the acquired image using both the transmit map and the receive map. The method of claim 3 .

5. and correcting the signal strength includes correcting the signal strength of the acquired image using only the transmission map. The method of claim 3 .

6. The step of acquiring the B1 projection data includes acquiring the B1 projection data using a whole body coil and a phased array coil. A method for determining a B1 map according to any one of claims 1 to 5.

7. and acquiring the B1 projection data includes acquiring the B1 projection data using a spatial encoding technique. A method for determining a B1 map according to any one of claims 1 to 5.

8. determining the transmission map includes determining the transmission map using a lookup table that associates B1 projection data with a transmission map corresponding to the B1 projection data. A method for determining a B1 map according to any one of claims 1 to 5.

9. determining the transmission map includes determining the transmission map by applying the acquired B1 projection data to a trained machine learning model. A method for determining a B1 map according to any one of claims 1 to 5.

10. determining the transmission map includes determining the transmission map via electromagnetic simulation based on the acquired B1 projection data; The B1 projection data is used to derive, correct and / or shape the output of the electromagnetic simulation. The method of claim 1 .

11. The step of acquiring B1 projection data includes: determining an imaging anatomical structure from information about the subject; obtaining a projection count and directional pattern of the B1 projection data relative to the determined imaging anatomical structure; Acquiring the B1 projection data based on the acquired number of projections and the directional pattern. The method of claim 1 , comprising:

12. the directional pattern is represented by a set of polar and azimuth axes within a three-dimensional volume; The method of claim 11 .

13. the imaging anatomy is a human head; The number of projections is nine; The directional pattern is a set of polar and azimuth axes separated by 45°.

13. The method of claim 12.

14. The step of acquiring the B1 projection data includes acquiring the spatially encoded B1 projection data using a two-dimensional bar selection along the directional pattern within the volume of the subject. The method of claim 11 .

15. and acquiring the B1 projection data includes acquiring the spatially encoded B1 projection data using a single two-dimensional slice along the orientation pattern within the volume of the subject. The method of claim 11 .

16. The step of acquiring the B1 projection data includes acquiring the B1 projection data using a Bloch-Siegert Shift method, a Double Angle method, an Actual Flip Angle method, a Dual Refocusing Echo Acquisition Mode method, a Phase Sensitive method, or a Saturation Recovery method. The method of claim 1 .

17. acquiring low-resolution Cartesian B1 map data of a subject using a magnetic resonance imaging device; determining a transmit map using only the acquired low resolution Cartesian B1 map data; A method for determining a B1 map, comprising:

18. the low resolution Cartesian B1 map data is a low resolution three-dimensional Cartesian B1 map; 20. The method of claim 17, wherein the B1 map is determined by the

19. the low resolution Cartesian B1 map data is a low resolution two-dimensional Cartesian B1 map; 20. The method of claim 17, wherein the B1 map is determined by the

20. acquiring spatially encoded B1 projection data of the patient using a magnetic resonance imaging device; Determining a transmit map using only the acquired B1 projection data A B1 map determiner comprising a processing circuit.

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