Image generation device, image generation method, and image generation program

Abstract

To generate a magnetic resonance image with improved image quality.SOLUTION: An image generation device according to an embodiment includes an acquisition unit, a composition unit, and an image generation unit. The acquisition unit acquires magnetic resonance data collected in a plurality of lead-out directions including a first lead-out direction and a second lead-out direction intersecting with the first lead-out direction, a plurality of filter sensitivity distributions that correspond to the plurality of lead-out directions indicating sensitivity distributions of low-pass filters, and a plurality of coil sensitivity distributions corresponding to a plurality of coil elements used for collecting the magnetic resonance data. The composition unit generates a composite sensitivity distribution in each lead-out direction by compositing the filter sensitivity distributions and the coil sensitivity distributions in each lead-out direction. The image generation unit generates an MR image on the basis of the composite sensitivity distributions and the magnetic resonance data.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The embodiments disclosed in this specification and the drawings relate to an image generating device, an image generating method, and an image generating program. [Background technology]

[0002] A common issue in imaging with magnetic resonance imaging (MRI) devices is image aliasing, which is caused by an insufficient sampling rate for the received magnetic resonance (MR) signals (in other words, an insufficient field of view, which corresponds to the reciprocal of the sampling interval). Techniques to address this issue include setting a low-pass filter that matches the sampling rate and oversampling the MR signals.

[0003] However, in scans with variable readout directions, such as radial scans, when the low-pass filter used in this technology is applied to MR signals, the amount of signal cut by the low-pass filter varies depending on the readout direction. As a result, the consistency of MR data arranged in k-space between different readout directions is lost. This causes a problem of noise, such as line-like artifacts called streaks, in MR images generated by scans with variable readout directions, resulting in poor image quality. To resolve this image quality degradation, it is necessary to widen the transmission (pass) band of the low-pass filter. However, due to performance limitations of MRI systems and the trade-off with a decrease in the signal-to-noise ratio (S / N), the pass band of the low-pass filter cannot (should not) be sufficiently widened. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-115967 Summary of the Invention [Problem to be solved by the invention]

[0005] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to generate magnetic resonance images with improved image quality. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems. [Means for solving the problem]

[0006] An image generating device according to an embodiment includes an acquisition unit, a synthesis unit, and an image generation unit. The acquisition unit acquires MR data collected in multiple readout directions, including a first readout direction and a second readout direction intersecting the first readout direction, multiple filter sensitivity distributions corresponding to the multiple readout directions and indicating the distribution of sensitivity of low-pass filters, and multiple coil sensitivity distributions corresponding to the multiple coil elements used to collect the MR data. The synthesis unit generates a synthetic sensitivity distribution for each readout direction by synthesizing the filter sensitivity distribution and the coil sensitivity distribution for each readout direction. The image generation unit generates an MR image based on the synthetic sensitivity distribution and the MR data. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram illustrating an example of an image generating apparatus according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing an example of a magnetic resonance imaging apparatus according to an embodiment. [Figure 3] FIG. 3 is a diagram showing an example of the configuration of a receiving circuit according to the embodiment. [Figure 4]FIG. 4 is a diagram showing an example of a trajectory in k-space relating to readout of MR signals in a main scan according to the embodiment. [Figure 5] FIG. 5 is a flowchart showing an example of a procedure of an image generation process according to the embodiment. [Figure 6] FIG. 6 is a diagram showing an example of MR data in k-space, a signal region in image space, a user FOV, a reconstruction region, a stop band and a cutoff position corresponding to a cutoff frequency, and a filter sensitivity distribution according to the embodiment. [Figure 7] FIG. 7 is a diagram showing an example of MR data in k-space, a signal region in image space, a user FOV, a reconstruction region, a stop band and a cutoff position corresponding to a cutoff frequency, and a filter sensitivity distribution according to the embodiment. [Figure 8] FIG. 8 is a diagram showing an example of MR data in k-space, a signal region in image space, a user FOV, a reconstruction region, a stop band, a cutoff position corresponding to a cutoff frequency, and a filter sensitivity distribution according to the embodiment. [Figure 9] FIG. 9 is a diagram showing an example of an MR image generated by an existing reconstruction method for MR data as a comparative example, and an MR image generated by the image generation process according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of an image generating device, an image generating method, and an image generating program will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an example of an image generating device 1. The image generating device 1 is installed, for example, in a modality equipped with various functions of the image generating device 1, or in a server in a hospital. Note that the various functions of the image generating device 1 may also be installed in a server of a medical image management system (hereinafter referred to as PACS (Picture Archiving and Communication Systems)) or a server of a hospital information system (hereinafter referred to as HIS (Hospital Information System)).

[0009] The modality is, for example, a medical image diagnostic device related to MRI, such as a magnetic resonance imaging (MRI) device, a PET (Positron Emission Tomography)-MRI device, or a SPECT (Single Photon Emission Computed Tomography)-MRI device. Hereinafter, for the sake of specificity, it is assumed that the image generating device 1 is mounted on the MRI device. In this case, the MRI device has various functions in the processing circuitry 15.

[0010] (Embodiment) 2 is a diagram showing an example of an MRI apparatus 100 according to this embodiment. As shown in FIG. 2, the MRI apparatus 100 includes a static magnetic field magnet 101, a gradient magnetic field coil 103, a gradient magnetic field power supply 105, a bed 107, a bed control circuit 109, a transmission circuit 113, a transmission coil 115, a reception coil 117, a reception circuit 119, an imaging control circuit (imaging control unit) 121, a system control circuit (system control unit) 123, a memory 13, an input interface 127, a display 129, a communication interface 11, and a processing circuit 15. Note that the image generating device 1 may further include the input interface 127 and the display 129 in addition to the communication interface 11, the memory 13, and the processing circuit 15.

[0011] The static magnetic field magnet 101 is a magnet formed in a hollow, approximately cylindrical shape. The static magnetic field magnet 101 generates a substantially uniform static magnetic field in the internal space. For example, a superconducting magnet or the like is used as the static magnetic field magnet 101.

[0012] The gradient magnetic field coil 103 is a hollow, approximately cylindrical coil and is disposed on the inner surface of the cylindrical cooling vessel. The gradient magnetic field coil 103 receives current individually from a gradient magnetic field power supply 105 to generate gradient magnetic fields whose magnetic field strength changes along the mutually orthogonal X, Y, and Z axes. The gradient magnetic fields of the X, Y, and Z axes generated by the gradient magnetic field coil 103 form, for example, a slice selection gradient magnetic field, a phase encoding gradient magnetic field, and a frequency encoding gradient magnetic field. The slice selection gradient magnetic field is used to arbitrarily determine an imaging cross section. The phase encoding gradient magnetic field is used to change the phase of a magnetic resonance signal (hereinafter referred to as an MR (Magnetic Resonance) signal) according to a spatial position. The frequency encoding gradient magnetic field is used to change the frequency of the MR signal according to a spatial position.

[0013] The gradient magnetic field power supply 105 is a power supply device that supplies current to the gradient magnetic field coil 103 under the control of the imaging control circuit 121 .

[0014] The bed 107 is a device equipped with a top plate 1071 on which the subject P is placed. The bed 107 inserts the top plate 1071 on which the subject P is placed into the bore 111 under the control of a bed control circuit 109.

[0015] The bed control circuit 109 is a circuit that controls the bed 107. The bed control circuit 109 drives the bed 107 in response to instructions from the operator via the input / output interface 17, thereby moving the tabletop 1071 in the longitudinal direction, the up-down direction, and in some cases the left-right direction.

[0016] The transmission circuit 113 supplies radio frequency pulses modulated at the Larmor frequency to the transmission coil 115 under the control of the imaging control circuit 121. For example, the transmission circuit 113 includes an oscillator, a phase selection unit, a frequency conversion unit, an amplitude modulation unit, an RF amplifier, and the like. The oscillator generates an RF pulse at a resonance frequency specific to the target atomic nucleus in a static magnetic field. The phase selection unit selects the phase of the RF pulse generated by the oscillator. The frequency conversion unit converts the frequency of the RF pulse output from the phase selection unit. The amplitude modulation unit modulates the amplitude of the RF pulse output from the frequency conversion unit according to, for example, a sinc function. The RF amplifier amplifies the RF pulse output from the amplitude modulation unit and supplies it to the transmission coil 115.

[0017] The transmission coil 115 is an RF (Radio Frequency) coil arranged inside the gradient magnetic field coil 103. In response to the output from the transmission circuit 113, the transmission coil 115 generates an RF pulse corresponding to a high frequency magnetic field.

[0018] The receiving coil 117 is an RF coil arranged inside the gradient magnetic field coil 103. The receiving coil 117 receives MR signals emitted from the subject P by a high frequency magnetic field. The receiving coil 117 outputs the received MR signals to a receiving circuit 119. The receiving coil 117 is, for example, a coil array having one or more, typically a plurality of coil elements. For the sake of concreteness, the receiving coil 117 will be described below as a coil array having a plurality of coil elements.

[0019] The receive coil 117 may be configured by a single coil element. Although the transmit coil 115 and receive coil 117 are shown as separate RF coils in Fig. 2, the transmit coil 115 and receive coil 117 may be implemented as an integrated transmit / receive coil. The transmit / receive coil corresponds to the imaging region of the subject P and is, for example, a local transmit / receive RF coil such as a head coil.

[0020] The receiving circuit 119 generates digital MR signals (hereinafter referred to as MR data) based on the MR signals output from the receiving coil 117 under the control of the imaging control circuit 121. Specifically, the receiving circuit 119 performs signal processing such as detection and filtering on the MR signals output from the receiving coil 117, and then performs analog-to-digital (A / D) conversion (hereinafter referred to as A / D conversion) on the data that has undergone the signal processing to generate MR data. The receiving circuit 119 outputs the generated MR data to the imaging control circuit 121. For example, MR data is generated for each coil element and output to the imaging control circuit 121 together with a tag that identifies the coil element.

[0021] 3 is a diagram showing an example of the receiving circuit 119. The receiving circuit 119 has, for example, a low pass filter 191 and an A / D converter 193. Note that in addition to the low pass filter 191 and the A / D converter 193, the receiving circuit 119 may also be equipped with various circuits, such as a detector, that correspond to the above signal processing.

[0022] A cutoff frequency set by the setting function 153 is input to the low-pass filter 191 via the imaging control circuit 121. In other words, the pass band of the low-pass filter 191 is set by the setting function 153. The cutoff frequency may be input directly to the low-pass filter 191 from the processing circuit 15. The low-pass filter 191 filters the MR signal using the input cutoff frequency.

[0023] The sampling rate set by the setting function 153 is input to the A / D converter 193 via the imaging control circuit 121. In other words, the sampling interval in the low-pass filter 191 is set by the setting function 153. The A / D converter 193 samples the MR signal that has passed through the low-pass filter 191 at a sampling timing according to the sampling rate. As a result, the A / D converter 193 generates MR data.

[0024] The imaging control circuit 121 controls the gradient magnetic field power supply 105, the transmission circuitry 113, the reception circuitry 119, etc. in accordance with the imaging protocol output from the processing circuitry 15, and performs imaging of the subject P. The imaging protocol has a pulse sequence according to the type of examination. The imaging protocol defines the magnitude of the current supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, the timing at which the gradient magnetic field power supply 105 supplies the current to the gradient magnetic field coil 103, the magnitude and time width of the radio frequency pulse supplied to the transmission coil 115 by the transmission circuitry 113, the timing at which the radio frequency pulse is supplied to the transmission coil 115 by the transmission circuitry 113, the timing at which the MR signal is received by the reception coil 117, etc. The imaging control circuit 121 drives the gradient magnetic field power supply 105, the transmission circuitry 113, the reception circuitry 119, etc. to image the subject P, and then receives MR data from the reception circuit 119 and stores the received MR data in the memory 13.

[0025] The imaging control circuit 121 executes a pulse sequence for imaging to acquire MR data. The imaging executed in this embodiment corresponds to a scan for acquiring a plurality of MR signals corresponding to a plurality of readout directions including a first readout direction and a second readout direction intersecting the first readout direction.

[0026] Fig. 4 is a diagram showing an example of a trajectory kTra in k-space related to the readout of MR signals in the main scan. The main scan may be, for example, a two-dimensional radial acquisition R2D, a three-dimensional radial acquisition (stack-of-stars Sos, koosh-ball KB), a propeller (periodically rotated overlapping parallel lines with enhanced reconstruction) acquisition PRP, or another acquisition using, for example, two blades BL2, as shown in Fig. 3.

[0027] For the sake of concreteness, the following description will be given assuming that the main scan is a two-dimensional radial acquisition R2D. Hereinafter, the two-dimensional radial acquisition R2D will be simply referred to as radial acquisition. The number of readouts in the radial acquisition performed as the main scan on the subject P, i.e., the number of trajectories kTra in the readout direction, is set in advance prior to the main scan.

[0028] The imaging control circuit 121 collects MR data (hereinafter referred to as sensitivity data) related to the generation of each of a plurality of coil sensitivity distributions by an arbitrary imaging technique. The plurality of coil sensitivity distributions correspond to a plurality of coil elements used to collect MR data and indicate the distribution of sensitivity of the coil elements. Each of the plurality of coil sensitivity distributions is expressed by complex number data. The collection of sensitivity data is performed by the imaging control circuit 121, for example, in a pre-scan including a locator scan prior to a radial acquisition R2D as a main scan. The imaging control circuit 121 is realized, for example, by a processor.

[0029] The term "processor" refers to circuits such as a CPU, a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a programmable logic device (e.g., a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)).

[0030] The system control circuit 123 has hardware resources such as a processor, a read-only memory (ROM), a random access memory (RAM), etc. (not shown), and uses a system control function to control the MRI apparatus 100. Specifically, the system control circuit 123 reads a system control program stored in the memory, expands it on the memory, and controls each circuit of the MRI apparatus 100 according to the expanded system control program.

[0031] For example, the system control circuit 123 reads out an imaging protocol from the memory 13 based on imaging conditions input by the operator via the input interface 127. The system control circuit 123 transmits the imaging protocol to the imaging control circuit 121 and controls imaging of the subject P. The system control circuit 123 is realized by, for example, a processor. The system control circuit 123 may be incorporated into the processing circuit 15. In this case, the system control function is executed by the processing circuit 15, and the processing circuit 15 functions as a substitute for the system control circuit 123. The processor that realizes the system control circuit 123 is similar to that described above, and therefore a description thereof will be omitted.

[0032] The memory 13 stores various programs related to the system control functions executed in the system control circuit 123, various imaging protocols, imaging conditions including a plurality of imaging parameters that define the imaging protocols, etc. The memory 13 also stores a setting function 153, an acquisition function 155, a synthesis function 157, and an image generation function 159 that are realized by the processing circuitry 15 in the form of programs executable by a computer.

[0033] The memory 13 also stores MR images generated by the image generation function 159 and prescan images generated by a prescan such as a locator scan. The prescan images are, for example, positioning images (also referred to as locator images) for setting the imaging field of view (hereinafter referred to as FOV (Field of view)) in the main scan, and coil sensitivity distributions used for generating (reconstructing) MR images in the main scan. For example, the memory 13 stores a plurality of coil sensitivity distributions respectively corresponding to a plurality of coil elements in the receive coil 117. The memory 13 also stores the FOV set in the locator image.

[0034] The memory 13 stores the sampling rate (also referred to as sampling frequency) or sampling interval used in the A / D converter 193 for the main scan that is executed after the prescan. The memory 13 also stores the cutoff frequency used in the low-pass filter 191 for the main scan. The memory 13 stores MR data related to the main scan and an algorithm for reconstructing an MR image based on the MR data.

[0035] The memory 13 may store various data received via the communication interface 11. For example, the memory 13 stores information about an examination order for the subject P (such as a region to be imaged, a purpose of the examination, etc.) received from an information processing system in a medical institution, such as a Radiology Information System (RIS).

[0036] The memory 13 is realized by, for example, a semiconductor memory element such as a ROM, a RAM, or a flash memory, a hard disk drive (HDD), a solid state drive (SSD), an optical disk, etc. The memory 13 may also be realized by a drive device that reads and writes various information from and to a portable storage medium such as a CD (Compact Disc)-ROM drive, a DVD (Digital Versatile Disc) drive, or a flash memory.

[0037] The input interface 127 accepts various instructions (e.g., a power-on instruction) and information input from an operator. The input interface 127 may be realized by, for example, a trackball, a switch button, a mouse, a keyboard, a touchpad that performs input operations by touching the operation surface, a touchscreen that integrates a display screen and a touchpad, a non-contact input circuit using an optical sensor, and a voice input circuit. The input interface 127 is connected to the processing circuitry 15 and converts input operations received from the operator into electrical signals and outputs the signals to the processing circuitry 15. Note that, in this specification, the input interface 127 is not limited to those having physical operation components such as a mouse and a keyboard. For example, an electrical signal processing circuit that receives electrical signals corresponding to input operations from an external input device provided separately from the MRI apparatus 100 and outputs the electrical signals to a control circuit is also included as an example of the input interface 127.

[0038] The input interface 127 inputs an FOV in response to a user instruction for a locator image displayed on the display 129. Specifically, the input interface 127 inputs an FOV in response to a user instruction to set a range in the locator image displayed on the display 129. Furthermore, the input interface 127 inputs various imaging parameters for the main scan in response to a user instruction based on an examination order.

[0039] The display 129 displays various GUIs (Graphical User Interfaces), MR images generated by the processing circuitry 15, pre-scan images such as locator images, and the like under the control of the processing circuitry 15 or the system control circuitry 123. The display 129 also displays various information related to imaging parameters for the main scan and pre-scan, and image processing. The display 129 is realized by, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display or monitor known in the art.

[0040] The communication interface 11 performs data communication with, for example, an HIS, a PACS, etc. Any standard may be used for communication between the communication interface 11 and the hospital information system, and examples thereof include HL7 (Hearth Level 7), DICOM, or both. The communication interface 11 receives information about an examination order for a subject P (such as an imaging target region and an examination purpose) received from an information processing system in a medical institution, such as an RIS. Furthermore, if the MRI apparatus 100 is not equipped with the image generating apparatus 1, the communication interface 11 in the image generating apparatus 1 receives MR data from the MRI apparatus 100 or the like that images the subject P in an examination on the subject P. At this time, the received MR data is stored in the memory 13.

[0041] The processing circuit 15 is realized by, for example, the above-mentioned processor. The processing circuit 15 includes a setting function 153, an acquisition function 155, a composition function 157, an image generation function 159, and the like. The processing circuits 15 that respectively realize the setting function 153, the acquisition function 155, the composition function 157, and the image generation function 159 correspond to a setting unit, an acquisition unit, a composition unit, and an image generation unit. Each function, such as the setting function 153, the acquisition function 155, the composition function 157, and the image generation function 159, is stored in the memory 13 in the form of a program executable by a computer. For example, the processing circuit 15 realizes the function corresponding to each program by reading and executing the program from the memory 13. In other words, the processing circuit 15 in a state in which each program has been read has each function, such as the setting function 153, the acquisition function 155, the composition function 157, and the image generation function 159.

[0042] In the above description, an example has been described in which the "processor" reads and executes a program corresponding to each function from memory 13, but the embodiment is not limited to this. If the processor is, for example, a CPU, the processor realizes the function by reading and executing a program stored in memory 13. On the other hand, if the processor is an ASIC, instead of storing a program in memory 13, the function is directly incorporated into the processor circuit as a logic circuit. Note that each processor in this embodiment is not limited to being configured as a single circuit per processor, and multiple independent circuits may be combined to configure a single processor and realize its function. Furthermore, although the description has been given assuming that a single storage circuit stores a program corresponding to each processing function, multiple storage circuits may be distributed and the processing circuit 15 may read the corresponding program from each storage circuit.

[0043] The processing circuitry 15 sets a sampling rate according to the FOV input by the user (hereinafter referred to as user FOV) using the setting function 153. Specifically, the setting function 153 sets the sampling rate using the reciprocal of the user FOV as the sampling interval. The setting function 153 outputs the set sampling rate to the A / D converter 193 via the imaging control circuit 121. As a result, MR data is generated by sampling the MR signal at the sampling rate set according to the imaging field of view.

[0044] The setting function 153 may set a sampling rate corresponding to oversampling (hereinafter referred to as an oversampling rate) by multiplying the reciprocal of the size of the user FOV by a constant. In this case, since the upper limit of the oversampling rate (hereinafter referred to as an upper limit rate) is set in advance based on the performance limit of the MRI apparatus 100, the setting function 153 sets the oversampling rate to a value equal to or lower than the upper limit rate. The MR data generated by the receiving circuitry 119 corresponds to k-space data obtained by sampling MR signals at a sampling rate according to the user FOV or an oversampling rate (a sampling rate higher than the sampling rate corresponding to the field of view input by the user).

[0045] Oversampling corresponds to expanding the imaging field of view relative to the user FOV. Oversampling is set when it is necessary to increase the acquisition rate, for example, when the user FOV set in the prescan image is smaller than the region in the imaging space where protons such as water molecules exist. In this case, the reconstruction region is performed for the expanded FOV. For the sake of concrete explanation, the sampling rate is assumed to be the reciprocal of the user FOV.

[0046] The processing circuitry 15 sets a cutoff frequency for the passband of the MR signal in the low-pass filter 191 based on the set sampling rate using the setting function 153. Specifically, the setting function 153 sets the cutoff frequency using the user FOV in the main scan, which is a scan of the subject P in multiple readout directions, and the strength of the gradient magnetic field in the main scan. For example, the setting function 153 sets the provisional cutoff frequency using the band of the low-pass filter 191 in the following equation: User FOV [cm] = (2 × low-pass filter bandwidth [Hz]) / readout gradient magnetic field strength [Hz / cm] In the above equation, the readout gradient magnetic field strength corresponds to the strength of the gradient magnetic field in the main scan.

[0047] The setting function 153 generates a filter sensitivity distribution indicating the distribution of the sensitivity of the low-pass filter 191 in the k-space for each readout direction based on the set cutoff frequency and readout direction. The setting function 153 stores a plurality of filter sensitivity distributions corresponding to a plurality of readout directions in the memory 13 in association with the readout directions.

[0048] The processing circuitry 15 acquires, from the memory 13, MR data acquired in multiple readout directions, multiple filter sensitivity distributions corresponding to the multiple readout directions, and multiple coil sensitivity distributions corresponding to the multiple coil elements, using the acquisition function 155. The acquired MR data is acquired using multiple readout directions including a first readout direction and a second readout direction intersecting the first readout direction. The multiple coil sensitivity distributions correspond to multiple coil elements in the receive coil 117 related to the acquisition of MR data and indicate the distribution of sensitivity of the coil elements. The multiple filter sensitivity distributions correspond to the multiple readout directions and indicate the distribution of sensitivity of the low-pass filter 191.

[0049] The processing circuitry 15 uses the synthesis function 157 to synthesize the filter sensitivity distribution and the coil sensitivity distribution for each readout direction. As a result, the synthesis function 157 generates a synthetic sensitivity distribution for each readout direction. The synthetic sensitivity distribution indicates a distribution of synthetic sensitivities obtained by synthesizing the sensitivities of the coil elements and the sensitivities of the low-pass filter 191 for each readout direction. That is, the synthesis function 157 generates multiple synthetic sensitivity distributions corresponding to multiple readout directions. Specific processing contents executed by the synthesis function 157 will be described in detail in the process of generating an MR image based on MR data acquired using multiple readout directions including a first readout direction and a second readout direction intersecting the first readout direction (hereinafter referred to as image generation processing).

[0050] The processing circuitry 15 acquires MR data (hereinafter referred to as pre-scan data) generated by a pre-scan on the subject P from the receiving circuitry 119, arranges the data in k-space, and generates a pre-scan image based on the pre-scan data arranged in k-space using the image generation function 159. The image generation function 159 stores the generated pre-scan image in the memory 13.

[0051] For example, the processing circuitry 15 uses the image generation function 159 to acquire MR data generated by a scan related to the generation of a locator image from the receiving circuitry 119 and arrange it in k space, and generate (reconstruct) the locator image based on the MR data arranged in k space. Also, the image generation function 159 acquires sensitivity data generated by a scan related to the generation of a sensitivity map from the receiving circuitry 119 and arranges it in k space, and generates (reconstructs) a sensitivity map based on the sensitivity data arranged in k space. Since existing reconstruction methods can be used to generate the locator image, sensitivity map, etc., a description thereof will be omitted.

[0052] The processing circuitry 15 generates an MR image corresponding to the actual scan based on the composite sensitivity distribution and the MR data using the image generation function 159. The image generation function 159 generates the MR image by, for example, applying sensitivity encoding using the composite sensitivity distribution (hereinafter referred to as SENSE (SENSitivity Encoding)) to the MR data. Note that the image generation function 159 may generate the MR image using a regularization term related to compressed sensing (CS) or super-resolution as a regularization term related to the generation of the MR image. Specific processing contents executed by the image generation function 159 will be described in detail in the section (referred to as image generation processing).

[0053] The image generation process executed by the MRI apparatus 100 and the image generation apparatus 1 of this embodiment configured as described above will be described with reference to Fig. 5 to Fig. 8. Fig. 5 is a flowchart showing an example of the procedure of the image generation process. First, various processes performed prior to the execution of the image generation process will be described, and then the image generation process will be described.

[0054] The imaging control circuitry 121 executes a prescan on the subject P. The processing circuitry 15 generates a prescan image based on the prescan data using the image generation function 161. The image generation function 161 stores the generated prescan image, for example, a locator image and a coil sensitivity map, in the memory 13. The system control circuitry 123 displays the locator image on the display 129.

[0055] Input interface 127 inputs an FOV (hereinafter referred to as user FOV) in a locator image in response to a user instruction. The user FOV is stored in memory 13. Processing circuitry 15 sets a sampling rate according to the user FOV using setting function 153, and outputs the set sampling rate to A / D converter 193 prior to execution of a main scan.

[0056] The processing circuitry 15 sets the cutoff frequency of the low-pass filter 191 to be applied to the MR signals received by the main scan using the setting function 153. Specifically, the setting function 153 sets the cutoff frequency based on the strength of the gradient magnetic field in the main scan and the user FOV. The setting function 153 outputs the set cutoff frequency to the low-pass filter 191.

[0057] The imaging control circuit 121 executes radial acquisition as a main scan for the subject P. Specifically, the imaging control circuit 121 executes imaging along one readout direction in the main scan. As a result, the receiving coil 117 receives MR signals in the readout direction. The MR signals received by the receiving coil 117 are output to the receiving circuit 119. At this time, the MR signals are detected by a detector.

[0058] The low-pass filter 191 filters the detected MR signal using a set cutoff frequency. The filtering of the MR signal by the low-pass filter 191 reduces unnecessary signals outside the user FOV. As a result, the filtered MR signal, with an improved S / N ratio, is output to the A / D converter 193.

[0059] The A / D converter 193 samples the MR signals output from the low-pass filter 191 using the sampling rate set by the setting function 153. As a result, the A / D converter 193 generates MR data. That is, the A / D converter 193 performs A / D conversion on the MR signals that have passed through the low-pass filter 191 at the sampling rate, and generates MR data. The MR data is stored in the memory 13 via the imaging control circuit 121. When the collection of MR signals has been completed for all readout directions (i.e., all trajectories kTra in the readout directions) preset in the main scan, image generation processing is started.

[0060] (Image generation processing) (Step S501) The processing circuitry 15 uses the acquisition function 155 to acquire, from the memory 13, the MR data generated in the main scan, a plurality of coil sensitivity distributions generated by a pre-scan preceding the main scan, and a plurality of filter sensitivity distributions according to the readout direction. Note that if the MRI apparatus 100 is not equipped with the image generating device 1, the acquisition function 155 acquires the MR data, the plurality of coil sensitivity distributions, and the plurality of filter sensitivity distributions from various MRI apparatuses via the communication interface 11 and a network.

[0061] 6 is a diagram showing an example of the readout direction ROD and sampling points SP in the k-space ks, the signal area SA in the image space IS, the user FOV UF, the reconstruction area RR, the stop band SB, the cutoff position CP corresponding to the cutoff frequency, and the filter sensitivity distribution FSD. The signal area SA in FIG. 6 corresponds to the area in the imaging space where protons such as water molecules exist. The stop band SB indicates the band in which the MR signal output from the receive coil 117 is blocked by the low-pass filter 191.

[0062] As shown in Fig. 6, the readout direction ROD passes through the center of the k-space ks and is parallel to the kx direction. The user FOV UF shown in Fig. 6 corresponds to the sampling interval and is therefore the same as the FOV defined by the adjacent sampling points SP. As shown in Fig. 6, the cutoff position CP corresponding to the cutoff frequency corresponds to the inflection point of the curve showing the sensitivity in the filter sensitivity distribution FSD.

[0063] Fig. 7 is a diagram showing an example of the readout direction ROD and sampling points SP in k space ks, the signal area SA in image space IS, the user FOV UF, the reconstruction area RR, the stop band SB, the cutoff position CP corresponding to the cutoff frequency, and the filter sensitivity distribution FSD. The difference between Fig. 6 and Fig. 7 is that the readout direction ROD in Fig. 7 passes through the center of k space ks and is parallel to the ky direction.

[0064] Fig. 8 shows an example of the readout direction ROD and sampling points SP in k-space ks, the signal area SA in image space IS, various FOVs, the reconstruction area RR, the stopband SB, and the cutoff position CP corresponding to the cutoff frequency, and the filter sensitivity distribution FSD. The difference between Fig. 8 and Fig. 6 and Fig. 7 is that the readout direction ROD in Fig. 8 passes through the center of k-space ks and is tilted at 45° with respect to the kx direction or the ky direction. As shown in Fig. 6 to Fig. 8, the filter sensitivity distribution FSD has a semi-cylindrical sensitivity distribution that differs depending on the readout direction.

[0065] (Step S502) The processing circuit 15 uses the synthesis function 157 to synthesize the filter sensitivity distribution and the coil sensitivity distribution for each readout direction, and generate a synthesized sensitivity distribution for each readout direction. The coil sensitivity distribution for the coil element i is expressed as S i and lead-out direction

number

number

number

[0066] The composite sensitivity distribution S in the above equation k corresponds to masking the coil sensitivity distribution. The synthesis function 157 calculates a synthesized sensitivity distribution according to the total number of coil elements for each readout direction. The calculated synthesized sensitivity distribution S k is stored in the memory 13 in association with the read-out direction.

[0067] (Step S503) The processing circuit 15 generates a composite sensitivity distribution S k For example, the image generation function 159 generates an MR image for the actual scan based on the composite sensitivity distribution S k By applying SENSE using the formula (2) to the MR data, an MR image is generated using the formula (2).

[0068]

number

[0069] If the coil sensitivity map is not used, the composite sensitivity distribution S k is equal to the filter sensitivity distribution for the kth readout, and equations corresponding to various assumptions regarding the actual scan image are incorporated into the regularization term R(x). The image generation function 159 generates the actual scan image by determining x so as to satisfy equation (1). Furthermore, the reconstruction of the actual scan image by the image generation function 159 is not limited to the above-mentioned SENSE. For example, an MR image may be generated using a regularization term related to compressed sensing (CS) or super-resolution as the regularization term R(x) for generating the MR image in equation (1).

[0070] The processing circuitry 15 stores the generated MR image in the memory 13 using the image generation function 159. At this time, the system control circuitry 123 may display the generated MR image on the display 129. Furthermore, if the MRI apparatus 100 is not equipped with the image generation device 1, the generated MR image is output to, for example, a PACS server or an HIS server via the communication interface 11 and a network.

[0071] According to the image generating device 1 of the embodiment described above, MR data collected in multiple readout directions including a first readout direction and a second readout direction intersecting the first readout direction, multiple filter sensitivity distributions corresponding to the multiple readout directions and indicating the distribution of sensitivity of the low-pass filter 191, and multiple coil sensitivity distributions corresponding to the multiple coil elements used to collect the MR data are acquired, and the filter sensitivity distributions and coil sensitivity distributions are combined for each readout direction to generate a composite sensitivity distribution for each readout direction, and an MR image is generated based on the composite sensitivity distribution and the MR data. The size of the MR image generated by this image generating device 1 can be larger than the field of view corresponding to the sampling rate of the MR data.

[0072] For example, the image generating device 1 of this embodiment generates an MR image by applying sensitivity encoding (SENSE) using a composite sensitivity distribution to MR data. Also, the image generating device 1 of this embodiment may generate an MR image by using a regularization term related to compressed sensing (CS) as the regularization term R(x) related to the generation of the MR image.

[0073] As described above, according to the image generating device 1 of the embodiment, even if the passband of the low-pass filter 191 cannot be sufficiently widened due to performance limitations of the MRI device 100, a trade-off with a decrease in S / N, or the like, it is possible to generate an MR image while ensuring consistency with the MR data by taking into account the influence of the low-pass filter 191 in the k-space. As a result, according to the present image generating device 1, it is possible to obtain a high-quality image with few streaks.

[0074] 10 shows an example of an MR image (1) generated by an existing reconstruction method for MR data that does not take into account the influence of the low-pass filter 191 as a comparative example, and an MR image (2) generated by the image generation process of this embodiment, taking into account the influence of the low-pass filter 191. As shown in FIG. 10, the MR image (2) generated by the image generation process of this embodiment has reduced streak artifacts and improved image quality compared to the MR image (1). Therefore, according to the image generation device 1 of this embodiment, as shown in FIG. 10, even if the passband of the low-pass filter 191 cannot be sufficiently widened due to the performance limit of the MRI device 100 or a trade-off with a decrease in S / N, an MR image with improved image quality can be generated for the main scan.

[0075] When the technical idea of ​​this embodiment is realized by an image generation method, the image generation method acquires MR data collected in multiple readout directions including a first readout direction and a second readout direction intersecting the first readout direction, multiple filter sensitivity distributions corresponding to the multiple readout directions and indicating the distribution of sensitivity of the low-pass filter 191, and multiple coil sensitivity distributions corresponding to the multiple coil elements used to collect the MR data, and generates a composite sensitivity distribution for each readout direction by combining the filter sensitivity distribution and the coil sensitivity distribution for each readout direction, and generates an MR image based on the composite sensitivity distribution and the MR data. The image generation process procedure and effects of this image generation method are the same as those described in the embodiment, so a description thereof will be omitted.

[0076] When the technical idea of ​​this embodiment is realized by an image generation program, the image generation program causes a computer to acquire MR data collected for multiple readout directions including a first readout direction and a second readout direction intersecting the first readout direction, multiple filter sensitivity distributions corresponding to the multiple readout directions and indicating the distribution of sensitivity of the low-pass filter 191, and multiple coil sensitivity distributions corresponding to the multiple coil elements used to collect the MR data, synthesize the filter sensitivity distributions and the coil sensitivity distributions for each readout direction to generate a composite sensitivity distribution for each readout direction, and generate an MR image based on the composite sensitivity distribution and the MR data.

[0077] For example, the image generation process can be realized by installing an image generation program in a computer in a modality such as the MRI apparatus 100 or a PACS server, and expanding the program in memory. In this case, the program that can cause the computer to execute the method can also be stored and distributed on a storage medium such as a magnetic disk (hard disk, etc.), an optical disk (CD-ROM, DVD, etc.), or a semiconductor memory. The procedure and effect of the image generation process using the image generation program are the same as those in this embodiment, so a description thereof will be omitted.

[0078] According to at least one of the embodiments described above, it is possible to generate magnetic resonance images with improved image quality. That is, according to at least one of the embodiments, even if the passband of the low-pass filter 191 cannot be sufficiently widened in a scan in which the readout direction changes, it is possible to generate MR images with consistency in the k-space, and it is possible to obtain high-quality MR images with few streaks.

[0079] Although several 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 within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0080] 1. Image generation device 11 Communication Interface 13. Memory 15 Processing circuit 100 Magnetic resonance imaging device 101 Static Magnetic Field Magnet 103 Gradient magnetic field coil 105 Gradient magnetic field power supply 107 Sleeper 109 Bed control circuit 111 Bore 113 Transmitting circuit 115 Transmitting Coil 117 Receiving Coil 119 Receiving circuit 121 Imaging control circuit 123 System Control Circuit 127 input interface 129 Display 153 Setting Function 155 Acquisition Function 157 Composition Function 159 Image generation function 191 Low-pass filter 193 A / D converter

Claims

1. an acquisition unit that acquires magnetic resonance data collected in a plurality of readout directions including a first readout direction and a second readout direction intersecting the first readout direction, to which a low-pass filter has been applied, a plurality of filter sensitivity distributions that correspond to the plurality of readout directions and indicate a distribution of sensitivity of the low-pass filter with respect to positions in an image space, and a plurality of coil sensitivity distributions that correspond to a plurality of coil elements used to collect the magnetic resonance data; a synthesis unit that synthesizes the filter sensitivity distribution and the coil sensitivity distribution for each of the readout directions to generate a synthesized sensitivity distribution for each of the readout directions; an image generating unit that generates a magnetic resonance image based on the composite sensitivity distribution and the magnetic resonance data; An image generating device comprising:

2. the size of the magnetic resonance image is larger than an imaging field of view corresponding to a sampling rate of the magnetic resonance data; The image generating device of claim 1 .

3. the image generation unit generates the magnetic resonance image by applying sensitivity encoding using the composite sensitivity distribution to the magnetic resonance data.

3. The image generating device according to claim 1 or 2.

4. the image generation unit generates the magnetic resonance image by using a regularization term related to compressed sensing as a regularization term related to generation of the magnetic resonance image.

3. The image generating device according to claim 1 or 2.

5. acquiring magnetic resonance data collected in a plurality of readout directions including a first readout direction and a second readout direction intersecting the first readout direction, to which a low-pass filter has been applied, a plurality of filter sensitivity distributions corresponding to the plurality of readout directions and indicating a distribution of sensitivity of the low-pass filter with respect to positions in an image space, and a plurality of coil sensitivity distributions corresponding to a plurality of coil elements related to the collection of the magnetic resonance data; generating a composite sensitivity distribution for each of the readout directions by combining the filter sensitivity distribution and the coil sensitivity distribution for each of the readout directions; generating a magnetic resonance image based on the composite sensitivity distribution and the magnetic resonance data; An image generating method comprising:

6. On the computer, acquiring magnetic resonance data collected in a plurality of readout directions including a first readout direction and a second readout direction intersecting the first readout direction, to which a low-pass filter has been applied, a plurality of filter sensitivity distributions corresponding to the plurality of readout directions and indicating a distribution of sensitivity of the low-pass filter with respect to positions in an image space, and a plurality of coil sensitivity distributions corresponding to a plurality of coil elements used to collect the magnetic resonance data; generating a composite sensitivity distribution for each of the readout directions by combining the filter sensitivity distribution and the coil sensitivity distribution for each of the readout directions; generating a magnetic resonance image based on the composite sensitivity distribution and the magnetic resonance data; An image generation program that achieves this.

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