Magnetic resonance imaging apparatus and image processing method

Abstract

Provided are a magnetic resonance imaging apparatus and an image processing method. An NMR signal is used as a point spread function (PSF) to perform super-resolution processing on an MRI image. Image processing is performed that performs processing to improve resolution using a point spread function on a reconstructed image. The point spread function is a signal obtained by Fourier transforming a nuclear magnetic resonance signal from a phantom obtained without applying frequency encoding and phase encoding after irradiating a high-frequency magnetic field to the phantom disposed in an imaging space.

Description

Technical Field

[0001] This invention relates to a magnetic resonance imaging (MRI) device that measures nuclear magnetic resonance (NMR) signals from hydrogen, phosphorus, etc., in a subject and visualizes the density distribution, relaxation time distribution, etc. of the nuclei, and the device has the function of performing super-resolution processing. Background Technology

[0002] An MRI device is an apparatus that measures NMR signals generated by the nuclear spins of atoms constituting a subject, particularly human tissue, to create two-dimensional or three-dimensional images of the morphology and function of the head, abdomen, limbs, etc. During imaging, the NMR signals are assigned different phase codes based on a tilted magnetic field and are also frequency-coded, thus providing time-series data for measurement. The measured NMR signals are then reconstructed into images through two-dimensional or three-dimensional Fourier transforms.

[0003] Images obtained from MRI machines are used to determine the presence or absence of diseases and conditions, thus requiring consistently high resolution and high image quality. To meet this requirement, numerous technologies have been developed for MRI machines.

[0004] On the other hand, Patent Document 1 discloses a method for approximating the original image by using a function representing transmission characteristics. For example, assuming that points of light are imaged in the original image, the probability density distribution of light imaged in the degraded image is characterized by a point spread function (PSF). It is disclosed that the original image can be calculated (estimated) using the Richardson-Lucy algorithm based on the degraded image and a pre-calculated PSF. Furthermore, the invention in Patent Document 1 also discloses that a lens for an optical system is envisioned as the transmission system, and instead of using PSF, an optical transfer function (OTF) is used.

[0005] Furthermore, Patent Document 2 discloses that in CT images captured by an X-ray computed tomography (CT) device, a point intensity distribution function (PSF) is used for processing (super-resolution processing) to further increase the resolution limit dependent on the spacing of the detection elements. Specifically, a resolution exceeding the resolution limit due to the spacing of the detection elements is achieved by performing a deconvolution operation on the PSF obtained in advance for the CT image. The PSF is the distribution (blurring) of image data obtained by capturing phantoms of metal wires or spheres with a spacing smaller than that of the detection elements of the X-ray CT device.

[0006] Prior technology documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2006 / 041126

[0009] Patent Document 2: JP 2005-95329

[0010] In Patent Document 2, in the case of an X-ray CT apparatus, image data is obtained by taking pictures of a phantom of a metal wire or sphere with a spacing smaller than that of the detection element by the X-ray CT apparatus, and the image data is used as a PSF.

[0011] However, Patent Document 2 describes the main idea that super-resolution processing using PSF can also be performed in an MRI device, but the specific method for calculating PSF in the MRI device is not disclosed at all.

[0012] To apply the method described in Patent Document 2 to an MRI device, a tiny phantom is placed in a static magnetic field space and irradiated with high-frequency magnetic field pulses to induce nuclear magnetic resonance (NMR) in the atomic nuclei of the phantom. The NMR signal, which is frequency-encoded in the x-axis and phase-encoded in the y-axis by applying tilted magnetic fields along the x and y axes respectively, is received. This process is repeated 256 or 512 times while gradually varying the phase encoding. The resulting 256 or 512 NMR signals are then placed in k-space (measurement space) and subjected to a two-dimensional Fourier transform to reconstruct a two-dimensional image of the tiny phantom. The resulting image is used as a PSF (Pressure Sample File). This method requires time to acquire two-dimensional MRI images of the tiny phantom. Summary of the Invention

[0013] The purpose of this invention is to use NMR signals as a point image intensity distribution function (PSF) for super-resolution processing of MRI images.

[0014] To solve the above-mentioned problems, according to the present invention, the device comprises: a static magnetic field generating device that applies a static magnetic field to an imaging space; a high-frequency magnetic field irradiation device that irradiates the spins of atomic nuclei of a subject disposed in the imaging space with a high-frequency magnetic field; a tilting magnetic field generating device that applies tilting magnetic fields in two given directions respectively to assign frequency encoding and phase encoding to the spins of atomic nuclei; a receiving device that receives nuclear magnetic resonance signals generated by the spins of atomic nuclei; an image reconstruction unit that performs two-dimensional Fourier transform on multiple nuclear magnetic resonance signals disposed in a measurement space to reconstruct an image of the subject; and an image processing unit that processes the reconstructed image to improve resolution using a point image intensity distribution function.

[0015] The point image intensity distribution function is a signal as follows: after the phantom arranged in the shooting space is irradiated with the high-frequency magnetic field by the high-frequency magnetic field irradiation device, the receiving device acquires the nuclear magnetic resonance signal from the phantom without assigning the frequency encoding and phase encoding, and performs a Fourier transform on the acquired nuclear magnetic resonance signal to obtain the signal.

[0016] Invention Effects

[0017] According to the present invention, NMR signals can be used as PSFs to stably generate high-resolution MRI images. Attached Figure Description

[0018] Figure 1 This is a block diagram showing the overall structure of the MRI device according to the first embodiment of the present invention.

[0019] Figure 2 This is a functional block diagram of the central processing unit 110 of the MRI apparatus of the first embodiment.

[0020] Figure 3 This is a flowchart illustrating the operation of the MRI device according to the first embodiment.

[0021] Figure 4 This is a flowchart illustrating the operation of the MRI device according to the first embodiment.

[0022] Figure 5 This is a flowchart illustrating the operation of the MRI device according to the first embodiment.

[0023] Figure 6 This is a flowchart illustrating the operation of the MRI device according to the first embodiment.

[0024] Figure 7 This is a diagram illustrating the arrangement of the acquired NMR signals in k-space in the MRI apparatus of the first embodiment.

[0025] Explanation of reference numerals in the attached figures

[0026] 10 subjects

[0027] 20 Camera Space

[0028] 30 beds

[0029] 100 MRI devices

[0030] 110 Central Processing Unit

[0031] 120 Sequence Generator

[0032] 130 Static Magnetic Field Generating Device

[0033] 132 Inclined Magnetic Field Generating Device

[0034] 134 Inclined Magnetic Field Coil

[0035] 136 Inclined Magnetic Field Power Supply

[0036] 140 High-frequency magnetic field irradiation device

[0037] 142 High-frequency oscillator

[0038] 144 modulator

[0039] 146 High-frequency amplifier

[0040] 148 High-frequency coil

[0041] 150 receiving devices

[0042] 152 High-frequency coil

[0043] 154 signal amplifier

[0044] 156 Quadrature Phase Detector

[0045] 158 converter

[0046] 160 processing unit

[0047] 162 CDs

[0048] 164 disks

[0049] 169 Monitor

[0050] 170 Operating device

[0051] 174 Indicating devices

[0052] 176 Keyboard

[0053] 200 Control Department

[0054] 210 Image Reconstruction Department

[0055] 220 Image Processing Department

[0056] 221 PSF Acquisition Department

[0057] 222 PSF Storage Division

[0058] 223 Hyper-resolution Processing Department

[0059] 300 Filming Department Detailed Implementation

[0060] The embodiments of the present invention are illustrated using the accompanying drawings.

[0061] In this embodiment, the image reconstructed by the MRI apparatus is processed with a point spread function to improve resolution. As the point spread function (PSF), the following signal is used: after irradiating a phantom arranged in an imaging space with a high-frequency magnetic field, acquiring a nuclear magnetic resonance signal from the phantom without applying frequency encoding and phase encoding, and performing Fourier transform on the acquired nuclear magnetic resonance signal to obtain the signal.

[0062] Thereby, in an MRI apparatus, the PSF can be directly acquired from NMR signals to perform super-resolution processing.

[0063] When acquiring NMR signals, since position encoding (frequency encoding and phase encoding) is not performed, if the NMR signal of the MRI apparatus is an ideal apparatus without reflection in the signal transmission system, the obtained NMR signal will be a signal equivalent to an optically ideal point image. Therefore, in an actual MRI apparatus, the distortion contained in the NMR signal without position encoding (frequency encoding and phase encoding) is caused by reflection in the signal transmission system of the NMR signal. Thus, by using the NMR signal without position encoding as the PSF, a PSF with higher accuracy can be obtained compared with using a phantom image reconstructed by two-dimensional Fourier transform.

[0064] By applying super-resolution processing to an MRI image using this PSF, a high-resolution MRI image with high accuracy can be obtained.

[0065] In addition, when acquiring the PSF, since it is not necessary to reconstruct a two-dimensional image of the phantom by two-dimensional Fourier transform, the PSF can be acquired in a short time.

[0066] The MRI apparatus of this embodiment will be specifically described below.

[0067] <<<First Embodiment>>>

[0068] <Structure of MRI Apparatus>

[0069] First use Figure 1 to describe the structure of the MRI apparatus 100 according to the first embodiment.

[0070] The MRI apparatus 100 comprises the following elements: a static magnetic field generating device 130; a tilted magnetic field generating device 132 for applying tilted magnetic field pulses to the subject 10; a high-frequency magnetic field irradiation device 140 for irradiating the subject 10 with high-frequency magnetic field pulses (hereinafter referred to as RF pulses); a receiving device 150 for receiving echo signals as NMR signals from the subject 10; a processing device 160 having a central processing unit (hereinafter referred to as CPU) 110; a sequence generator 120; an operating device 170 for performing various operations related to data input, imaging, etc.; and a bed 30.

[0071] The static magnetic field generating device 130 applies a uniform magnetic field to the imaging space 20.

[0072] The bed supports the subject 10, and at least the part of the subject 10 that is to be photographed is arranged in the camera space 20.

[0073] The tilting magnetic field generating device 132, the high-frequency magnetic field irradiation device 140, and the receiving device 150 constitute the imaging unit 300. The imaging unit 300 applies RF pulses and tilting magnetic field pulses to the subject 10 disposed in the imaging space 20 to obtain the NMR signal generated from the subject.

[0074] Central processing unit 110 such as Figure 2 As shown in the functional block diagram, the control unit 200 functions to control the sequence generator 120 so that the imaging unit 300 repeatedly applies high-frequency magnetic field pulses and tilting magnetic field pulses and acquires nuclear magnetic resonance signals at a given timing according to a predetermined imaging pulse sequence.

[0075] In addition, the central processing unit 110 also functions as an image reconstruction unit 210, processing the number of NMR signals required for image reconstruction obtained by the imaging unit 300 to generate a tomographic image (MRI image) of the subject 10.

[0076] Furthermore, the central processing unit 110 also functions as an image processing unit 220, performing processing on the reconstructed MRI image of the subject 10 to improve resolution using a point intensity distribution function (PSF). Therefore, the image processing unit 220 includes: a PSF acquisition unit 221 for acquiring the PSF; a PSF storage unit 222 for storing the acquired PSF; and a super-resolution processing unit 223 for processing the MRI image using the PSF. The PSF storage unit 222 can be a memory built into the central processing unit 110, or it can be implemented using RAM 168, optical disc 162, or the like.

[0077] Furthermore, the details of each part will be explained. The specific structure of the static magnetic field generating device 130 is omitted. In the case of a vertical magnetic field, it generates an extremely uniform static magnetic field in the space surrounding the subject 10 in a direction orthogonal to its body axis. In the case of a horizontal magnetic field, it generates an extremely uniform static magnetic field along the body axis. The static magnetic field generating device 130 is positioned around the subject 10 to generate the aforementioned static magnetic field and includes a permanent magnet, a normally conductive magnet, or a superconducting magnet as the static magnetic field source.

[0078] The high-frequency magnetic field irradiation device 140 excites the nuclear spins of atoms constituting the biological tissue of the subject 10 by irradiating the subject 10 with RF pulses, thereby inducing nuclear magnetic resonance. For example, the high-frequency magnetic field irradiation device 140 includes a high-frequency oscillator 142, a modulator 144, a high-frequency amplifier 146, and a high-frequency coil 148 operating as a transmitting coil. The high-frequency pulses output from the high-frequency oscillator 142 are amplitude modulated by the modulator 144 at timing indicated by the sequence generator 120, and the amplitude-modulated high-frequency pulses are amplified in the high-frequency amplifier 146. The amplified high-frequency pulses are supplied to the high-frequency coil 148, which is positioned close to the subject 10. Thus, the high-frequency coil 148 irradiates the subject 10 with RF pulses.

[0079] The tilting magnetic field generating device 132 includes: tilting magnetic field coils 134 wound in three axial directions (X-axis, Y-axis, and Z-axis) of the coordinate system serving as the MRI device 100, such as a stationary coordinate system; and a tilting magnetic field power supply 136 that supplies drive current for generating tilting magnetic fields in each tilting magnetic field coil. The tilting magnetic field power supply 136 operates according to commands from the sequence generator 120, supplying drive current to the tilting magnetic field coils 134 in the three axial directions (X-axis, Y-axis, and Z-axis). As a result, the tilting magnetic field coils 134 generate tilting magnetic fields Gx, Gy, and Gz in the three axial directions (X-axis, Y-axis, and Z-axis). The generated tilting magnetic fields Gx, Gy, and Gz are applied to the subject 10 within the imaging space 20. During imaging, tilting magnetic field pulses (Gz) for determining the slice plane are applied in a direction orthogonal to the imaging section (slice plane) according to the imaging pulse sequence. Tilted magnetic field pulses (Gx) that assign frequency encoding to the atomic nucleus spin and tilted magnetic field pulses (Gy) that assign phase encoding to the atomic nucleus spin are applied in the remaining two X directions and the Y direction, respectively, which are orthogonal to and mutually orthogonal to the slice plane. In this way, the position information of each direction of the echo signal (NMR signal) emitted from the atomic nucleus spin is encoded.

[0080] The receiving device 150 receives and processes the emitted NMR signal. The receiving device 150 includes: a high-frequency coil 152 operating as a receiving coil on the receiving side; a signal amplifier 154 amplifying the received NMR signal; a quadrature phase detector 156; and an A / D converter 158 converting the analog signal into a digital signal. The high-frequency coil 152 detects the NMR signal emitted by the sample, and the signal amplifier 154 amplifies the detected NMR signal. The quadrature phase detector 156, under timing instructions from the sequence generator 120, splits the NMR signal into two orthogonal systems. The two split system signals are converted into digital quantities in the A / D converter 158 and sent to the central processing unit 110.

[0081] The high-frequency coil 148 and the tilting magnetic field coil 134 on the transmitting side are disposed within the static magnetic field space of the static magnetic field generating device 130 on which the subject 10 is disposed. Regarding their orientation, in the case of a vertical magnetic field, they are disposed opposite to the subject 10; in the case of a horizontal magnetic field, they are disposed to surround the subject 10. Furthermore, the high-frequency coil 152 on the receiving side is disposed opposite to or surrounds the subject 10.

[0082] Under the control of the central processing unit 110, the sequence generator 120 outputs control signals (commands) to the high-frequency magnetic field irradiation device 140, the tilting magnetic field generating device 132, and the receiving device 150 at a given timing. Thus, at the timing of a predetermined imaging pulse sequence, RF pulses and tilting magnetic field pulses are applied to the subject, causing the imaging unit 300 to repeatedly acquire NMR signals while changing the phase encoding amount.

[0083] In addition to the central processing unit 110, the processing device 160 also includes: external storage devices such as optical disc 162 and magnetic disk 164 for storing information; ROM 166 for storing required data and processing programs; RAM 168 for temporary storage of processing data; and a display 169 such as a CRT. Thus, the processing device 160 performs various data processing, displays processing results, and saves them. For example, if the processing result received and processed by the receiving device 150 is input to the processing device 160, the central processing unit 110 of the processing device 160 performs signal processing, image reconstruction, image processing, and other processing. The resulting tomographic image of the subject 10 is displayed on the display 169 and, as needed, recorded to external storage devices such as optical disc 162 and magnetic disk 164. Furthermore, although not shown, it can also be printed or sent to other systems.

[0084] The operating device 170 includes a pointing device 174 such as a trackball or a mouse, and a keyboard 176. An operator inputs various control information of the MRI apparatus 100 and control information for processing performed by the processing device 160 via the operating device 170. The operating device 170 is arranged close to the display 169, so that the operator can interactively perform operations through the operating device 170 while watching the display on the display 169. In addition, the operating device 170 is not limited thereto, and for example, may also include a touch panel disposed on the display surface of the display 169. The operating device 170 is disposed in an operating room away from the main body of the MRI apparatus 100. A part of the operating device 170 is further disposed on the main body of the MRI apparatus 100 and the bed table 30. Accordingly, the configuration allows an operator to perform necessary operations near the subject 10.

[0085] For the MRI apparatus 100, the imaging nuclear species of the subject 10 is, for example, a clinically widespread imaging nuclear species, that is, protons, which are hydrogen nuclei and the main constituent substance of the subject. The MRI apparatus 100 images information related to the spatial distribution of proton density and the spatial distribution of relaxation times in an excited state. Accordingly, the MRI apparatus 100 can two-dimensionally or three-dimensionally image the morphology or function of, for example, the head, abdomen, limbs or other parts of the subject 10, and display the reconstructed image on the display 169. The reconstructed image is stored in an optical disk 162 or a magnetic disk 164 as needed. In addition, the image can be printed based on an operation, or transmitted to other required systems.

[0086] <Imaging Operation of MRI Apparatus>

[0087] Imaging pulse sequences are stored in advance for each of a plurality of imaging methods in a memory built in the central processing unit 110, the magnetic disk 164, the ROM 166, or the like. An operator selects an imaging method via the operating device 170, and further inputs imaging conditions (such as repetition time TR). Accordingly, the central processing unit 110 generates an imaging pulse sequence corresponding to the set imaging conditions.

[0088] Herein, the central processing unit 110 is a processor (computer) such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and is implemented by software by reading and executing programs pre-stored in the ROM 166 Figure 2 the functions of each part. Accordingly, it executes Figures 3-5 the processing shown in the flow. In addition, it can also Figure 2Some or all of the functions are implemented in hardware. For example, the central processing unit 110 may be constructed using custom ICs such as ASICs (Application Specific Integrated Circuits) or programmable ICs such as FPGAs (Field-Programmable Gate Arrays), and the programmable ICs may be designed to perform circuitry. Figure 3 as well as Figure 4 That should suffice.

[0089] use Figure 3 as well as Figure 4 The imaging process of the MRI device in this embodiment is described in detail below.

[0090] (Step 301)

[0091] First, the PSF acquisition unit 221 of the image processing unit 220 performs a pre-capture operation to acquire a PSF, and stores the acquired PSF in the PSF storage unit 222. Step 301 will be explained in more detail below through steps 401 to 405.

[0092] ((Step 401))

[0093] Specifically, firstly, the operator places the subject 10 within the imaging space 20.

[0094] ((Step 402))

[0095] The PSF acquisition unit 221 controls the sequence generator 120 to irradiate the phantom with high-frequency magnetic field pulses from the high-frequency magnetic field irradiation device 140, thereby exciting the phantom's nuclear magnetic spin.

[0096] ((Step 403))

[0097] Without applying a tilted magnetic field for frequency encoding and a tilted magnetic field for phase encoding, the PSF acquisition unit 221 causes the receiving device 150 to receive the NMR signal emitted by the nuclear magnetic spin of the subject at a given timing.

[0098] Because no frequency encoding is performed, and given that the NMR signal from an MRI device does not exhibit frequency spread in the transmission system, and ideal devices such as reflections are absent, the NMR signal does not spread in the frequency direction. Therefore, the NMR signal... Figure 6 As in (b-2), it becomes a single-frequency signal or DC component. This is independent of the size of the subject 10, regardless of whether the subject 10 is... Figure 6Whether it is a tiny (close to a Δ function) object like phantom A (b-1) or a not-so-tiny object like phantom B, as long as the MRI device is ideal, the obtained NMR signal will be a single-frequency signal or a DC component.

[0099] In reality, due to reflections, oscillations, and phase deviations in the NMR signal transmission system of an MRI device, therefore... Figure 6 The (b-2) NMR signal has a distortion component and will not be a completely single frequency or DC component.

[0100] ((Step 404))

[0101] PSF acquisition unit 221 obtains PSF without frequency encoding and phase encoding. Figure 6 Fourier transform of the (b-2) NMR signal.

[0102] because Figure 6 The (b-2) NMR signal is distorted; therefore, the Fourier transform NMR signal is as follows: Figure 6 As in (b-3), it is not a completely single peak (Δ function), but becomes a waveform with extension. This extension characterizes the reflection, oscillation, phase deviation, etc. of the signal transmission system of the NMR signal of the MRI device.

[0103] ((Step 405))

[0104] PSF Acquisition Department 221 will Figure 6 The NMR signal of (b-3) is stored as a PSF in the PSF storage unit 222.

[0105] Therefore, high-precision PSF can be obtained for MRI devices. The difference between PSF in MRI devices and PSF in other optical systems is that PSF is not just one-dimensional data of intensity signal, but complex data of real and imaginary parts (or intensity and phase).

[0106] (Step 302)

[0107] Next, the control unit 200 generates a shooting sequence based on the shooting conditions received from the operator, sets the generated shooting sequence to the sequence generator 120, and causes the imaging unit 300 to perform formal imaging of the subject 10.

[0108] Specifically, the control department has 200 pairs. Figure 6The subject 10, arranged in the imaging space 20 as in (a-1), is irradiated with high-frequency magnetic field pulses from the high-frequency magnetic field irradiation device 140 according to the imaging sequence to excite nuclear magnetic spin. A tilted magnetic field pulse Gy in the Y direction is applied from the tilted magnetic field generating device 132 for phase encoding. At the same time as the tilted magnetic field pulse Gx in the X direction is applied, the NMR signal is received by the receiving device 150.

[0109] Therefore, after configuring Figure 6 In the case of subject 10 as in (a-1), such as Figure 6 As in (a-2), the NMR signal with a waveform similar to the sinc function is received. The receiving device 150 obtains one line of NMR signal by performing a 1-degree AD conversion. In fact, since the one line of NMR signal is detected by QD, complex data with real and imaginary parts is obtained.

[0110] The control unit 200 repeatedly captures the sequence while changing the phase coding amount, and the receiving device 150 sequentially receives 256 or 512 NMR signals with different phase coding amounts.

[0111] (Step 302)

[0112] Image reconstruction unit 210 Figure 7 As shown, the obtained NMR signals are arranged in a measurement space (k-space) with frequency encoding direction kx and phase encoding direction ky. That is, one-dimensional NMR data with different phase encodings are accumulated in the two-dimensional space of frequency encoding direction and phase encoding direction to fill the k-space.

[0113] The image reconstruction unit 210 reconstructs a two-dimensional MRI image (in real space, xy) by performing a two-dimensional Fourier transform on the k-space NMR signal. Thus, it can... Figure 6 In the same way as (a-3), we can obtain MRI images that are close to the solid object (subject 10).

[0114] The image reconstruction unit 210 stores the obtained formally captured MRI images into RAM 168 and the like.

[0115] (Step 304)

[0116] The super-resolution processing unit 223 of the image processing unit 220 performs super-resolution processing on the MRI image obtained in step 303.

[0117] according to Figure 5 The detailed processing of step 304 will be explained by steps 501 to 506 of the process.

[0118] ((Step 501))

[0119] The super-resolution processing unit 223 reads the PSF stored in the PSF storage unit 222 in step 405 above and sets it as the initial value of the PSF.

[0120] ((Step 502))

[0121] The super-resolution processing unit 223 reads out the officially captured MRI images (hereinafter also referred to as degraded images) stored in RAM 168, etc.

[0122] ((Step 503))

[0123] The super-resolution processing unit 223 performs deconvolution on the read-out PSF and the actual captured MRI image. As a result, the degraded image (MRI image) is made up to high resolution.

[0124] ((Step 504))

[0125] The super-resolution processing unit 223 calculates the difference between the degraded image (MRI image) and the image that has been high-resolution in step 503 by performing calculations.

[0126] ((Step 505))

[0127] If the difference obtained in step 504 is above a predetermined threshold, the super-resolution processing unit 223 proceeds to step 506.

[0128] ((Step 506))

[0129] The super-resolution processing unit 223 corrects the PSF based on the difference obtained in step 504 (initially the initial value of the PSF in step 501), and returns to step 503 to perform the deconvolution operation of the PSF and the degraded image again.

[0130] Repeat steps 503-506 until the difference between the degraded image (MRI image) and the image that underwent high-resolution processing in step 503 becomes less than a threshold. Thus, with each repetition, the accuracy of the PSF improves, resulting in higher-resolution images.

[0131] (Step 305)

[0132] The super-resolution processing unit 223 displays the high-resolution image obtained by repeating steps 503 to 506 on the display 169.

[0133] As described above, according to the first embodiment, by acquiring the MRI signal from the subject without assigning frequency encoding and phase encoding, and performing a Fourier transform on the acquired MRI signal, the resulting signal is used as a PSF, thereby obtaining a PSF that well reflects the characteristics of the MRI device in a short time.

[0134] Therefore, by using this PSF to perform super-resolution processing on MRI images, higher-resolution MRI images with higher accuracy can be obtained.

[0135] <<<Second Implementation Method>>>

[0136] Furthermore, in the first embodiment, the subject 10, which is used for formal imaging, is also used in obtaining the PSF in step 301. However, considering the size of the subject 10, the PSF has an amplitude in the frequency direction due to the influence of the static magnetic field uniformity. Therefore, in the second embodiment, to avoid the influence of the non-uniformity of the static magnetic field strength, a sufficiently small phantom (described later) is used to perform step 301 (steps 401-405) of the first embodiment to obtain the PSF. The device structure and operation of each part of the MRI apparatus in the second embodiment are the same as those in the first embodiment, except that a sufficiently small phantom is used, so the description is omitted.

[0137] The PSF signal of the second embodiment will be further explained. In this embodiment, the NMR signal is acquired without position encoding (frequency encoding and phase encoding) and used as the PSF. In this structure, the magnetic field strength at different object placement locations is not entirely uniform. Figure 6 The frequency of the NMR signal obtained in (b-2) has an amplitude that depends on the magnetic field inhomogeneity. Since the magnetic field inhomogeneity varies depending on the location, it is not appropriate to apply the obtained PSF to the entire image.

[0138] Therefore, by placing a suitable phantom, large enough to obtain a signal and small enough to ignore magnetic field inhomogeneity, in the imaging space, and then obtaining the NMR signal without omitting position coding, a suitable PSF reflecting the signal transmission system of the MRI device can be obtained without being affected by magnetic field inhomogeneity.

[0139] Furthermore, as the phantom size decreases, the signal strength decreases proportionally to its volume, while the signal-to-noise ratio increases proportionally to the static magnetic field strength. Therefore, while a completely small phantom cannot be universally defined, a phantom of approximately 3 cm square in a 1.5T apparatus is sufficient for acquiring NMR signals for PSF. Moreover, a 3 cm square phantom effectively avoids the influence of magnetic field inhomogeneities.

[0140] <<<Third Implementation Method>>>

[0141] In the second embodiment, the influence of static magnetic field inhomogeneity is avoided by using a small phantom. However, in the third embodiment, when a high-frequency magnetic field pulse is applied to the subject 10 or the phantom in step 402, PSF can also be obtained while avoiding the influence of static magnetic field inhomogeneity by selectively exciting only a very narrow range of atomic nuclei spins.

[0142] Specifically, as methods for selectively exciting atomic nuclei spin, there are methods that achieve this by emitting a pre-saturation pulse that suppresses signals from the unselected portion, and methods that use two-dimensional selective RF pulses to excite only the desired portion.

[0143] In embodiments 1 to 3, the case where the NMR signal is one-dimensional data was described, but it can also be applied to two-dimensional and three-dimensional MRI images.

[0144] Furthermore, the algorithm used for super-resolution image processing with PSF is not limited to the algorithms mentioned above; various well-known algorithms can be used. That is, the method of using PSF is not particularly restricted, and higher-precision techniques can be employed for high-resolution processing.

Claims

1. A magnetic resonance imaging device, characterized in that, have: A static magnetic field generating device applies a static magnetic field to the shooting space; A high-frequency magnetic field irradiation device irradiates the spins of the atomic nuclei of the subject disposed in the imaging space with a high-frequency magnetic field. A tilting magnetic field generating device applies tilting magnetic fields in two given directions to assign frequency and phase encoding to the spin of the atomic nucleus. A receiving device that receives nuclear magnetic resonance signals generated by the spins of the atomic nuclei; The image reconstruction unit performs a two-dimensional Fourier transform on the plurality of nuclear magnetic resonance signals arranged in the measurement space to reconstruct an image of the subject. and The image processing unit performs processing on the reconstructed image to improve its resolution using a point intensity distribution function. The image processing unit includes: The part obtains the intensity distribution function of the point image; and The storage unit stores the acquired point image intensity distribution function. After the acquisition unit irradiates the phantom or subject disposed in the imaging space with the high-frequency magnetic field from the high-frequency magnetic field irradiation device, it enables the receiving device to acquire the nuclear magnetic resonance signal from the phantom or the subject without assigning the frequency encoding and phase encoding by not applying the tilted magnetic field for frequency encoding and the tilted magnetic field for phase encoding by the tilted magnetic field generating device. The acquisition unit performs a Fourier transform on the acquired nuclear magnetic resonance signal and stores the obtained signal as the point image intensity distribution function in the storage unit.

2. The magnetic resonance imaging device according to claim 1, characterized in that, The image processing unit generates an image with improved resolution by performing a deconvolution operation on the image of the subject and the point image intensity distribution function.

3. The magnetic resonance imaging device according to claim 1, characterized in that, The phantom body is 1cc or more but less than 30cc.

4. The magnetic resonance imaging device according to claim 1, characterized in that, The acquisition unit selectively excites only a portion of the atomic nuclei spins of the phantom or the subject using the high-frequency magnetic field.

5. An image processing method for improving the resolution of images captured by a magnetic resonance imaging device using a pre-calculated point image intensity distribution function. The image processing method is characterized in that... The point image intensity distribution function is a signal as follows: after irradiating a phantom or subject arranged in the imaging space of the magnetic resonance imaging device with a high-frequency magnetic field, the nuclear magnetic resonance signal from the phantom is obtained without frequency encoding and phase encoding by not applying a tilted magnetic field for frequency encoding and a tilted magnetic field for phase encoding, and the obtained nuclear magnetic resonance signal is Fourier transformed to obtain the signal.

Images