# US 2021/0333347 A1 · Magnetic resonance imaging apparatus and image processing method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0333347 A1 - Document ID: US20210333347A1 - Status: Published application - Kind: A1 - Application number: 17/205,238 - Filed: 2021-03-18 - Published: 2021-10-28 - Earliest claimed: 2020-04-28 - Assignees: Hitachi, Ltd. - Applicants: Hitachi, Ltd. - Inventors: Hiroki SHOJI; Toru SHIRAI; Shinji KUROKAWA - Web page: https://patentgrep.com/patent/US20210333347A1 ## CPC - G01R 33/5608: {Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels (image data processing or generation, in general G06T)} - G01R 33/5602: {by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse} - G06T 3/4084: in the transform domain, e.g. fast Fourier transform [FFT] domain scaling - G16H 30/20: for handling medical images, e.g. DICOM, HL7 or PACS - G16H 30/40: for processing medical images, e.g. editing - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL - G16H: HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA ## Abstract Provided is a magnetic resonance imaging apparatus with no occurrence of artifacts, even after noise removal by applying Wavelet transform to a zero-fill reconstructed image. Nuclear magnetic resonance signals acquired by the magnetic resonance imaging apparatus are processed to perform reconstruction with a reconstruction matrix extended by zero-filling an acquisition matrix, and then a zero-fill reconstructed image is produced. This reconstructed image is subjected to an iterative operation combining the Wavelet transform and L1 norm minimization to remove noise. Before the noise removal, a pre-processing is performed to change the reconstruction matrix size so that an artifact does not occur in the image after noise removal, an artifact portion appears outside the reconstruction matrix after the noise removal, or cutting out is performed so that no artifact appears after the noise removal. The matrix size is restored to its original size in the post-processing after the noise removal. ## Claims ### Claim 1 A magnetic resonance imaging apparatus comprising, a measuring unit having a transmission unit configured to transmit an RF magnetic field pulse to a subject disposed in a static magnetic field, a receiving unit configured to receive a nuclear magnetic resonance signal generated by the subject, and a gradient magnetic field generator for providing a gradient magnetic field to the static magnetic field, and a computer configured to perform an operation on the nuclear magnetic resonance signal received by the receiving unit, wherein the computer comprises an image generator configured to process the nuclear magnetic resonance signal being received to generate a reconstructed image with a reconstruction matrix obtained by extending an acquisition matrix by zero-filling, and a noise remover configured to remove noise from the reconstructed image, wherein the noise remover performs noise removal after changing the size of a matrix of the reconstructed image, and performs a process of restoring the matrix of the reconstructed image after the noise removal, to the reconstruction matrix. ### Claim 2 (depends on 1) The magnetic resonance imaging apparatus according to claim 1, wherein, the noise remover transforms the matrix of the reconstructed image to a matrix larger than the reconstruction matrix. ### Claim 3 (depends on 2) The magnetic resonance imaging apparatus according to claim 2, wherein the noise remover extends the matrix of the reconstructed image to the matrix larger than the reconstruction matrix, by zero-filling. ### Claim 4 (depends on 2) The magnetic resonance imaging apparatus according to claim 2, wherein the noise remover extends the matrix of the reconstructed image to be four times larger than the acquisition matrix. ### Claim 5 (depends on 1) The magnetic resonance imaging apparatus according to claim 1, wherein, the noise remover performs noise removal after changing the matrix of the reconstructed image to be smaller than the reconstruction matrix, and restores the matrix of the reconstructed image after the noise removal to the reconstruction matrix. ### Claim 6 (depends on 5) The magnetic resonance imaging apparatus according to claim 5, wherein, the noise remover uses the size of the acquisition matrix, as the size of the matrix smaller than the reconstruction matrix. ### Claim 7 (depends on 5) The magnetic resonance imaging apparatus according to claim 5, wherein, the noise remover uses as the size of the matrix smaller than the reconstruction matrix, a value of power of two in a size equal to or larger than the acquisition matrix and smaller than the reconstruction matrix. ### Claim 8 A magnetic resonance imaging apparatus comprising, a measuring unit having a transmission unit configured to transmit an RF magnetic field pulse to a subject disposed in a static magnetic field, a receiving unit configured to receive a nuclear magnetic resonance signal generated by the subject, and a gradient magnetic field generator for providing a gradient magnetic field to the static magnetic field, and a computer configured to perform an operation on the nuclear magnetic resonance signal received by the receiving unit, wherein the computer comprises an image generator configured to process the nuclear magnetic resonance signal being received to generate a reconstructed image with a reconstruction matrix obtained by extending an acquisition matrix by zero-filling, and a noise remover configured to remove noise from the reconstructed image, wherein the noise remover comprises an artifact prediction unit configured to predict a characteristic of an artifact caused by generating the reconstructed image in the image generator and by removing noise, and a window function creating unit configured to create a window function for eliminating the predicted artifact, and the artifact is eliminated by using the window function. ### Claim 9 (depends on 8) The magnetic resonance imaging apparatus according to claim 8, wherein, the artifact prediction unit obtains the characteristic of the artifact from a storage means where behaviors of artifacts relative to a ratio between the reconstruction matrix and the acquisition matrix are empirically databased and stored. ### Claim 10 (depends on 8) The magnetic resonance imaging apparatus according to claim 8, wherein, the artifact prediction unit extracts an artifact signal from k-space data of an image for noise removal to predict the artifact. ### Claim 11 (depends on 10) The magnetic resonance imaging apparatus according to claim 10, wherein, the artifact prediction unit considers as the artifact, a signal outside the acquisition matrix and larger than any threshold value in the k-space, or a signal outside the acquisition matrix. ### Claim 12 An image processing method for noise removal in an image acquired by a magnetic resonance imaging apparatus, the image being a reconstructed image obtained with a reconstruction matrix extended by zero-filling an acquisition matrix of nuclear magnetic resonance signals, wherein the noise removal comprises a process of subjecting the reconstructed image to Wavelet transform and L1 norm minimization process, and the noise removal further comprises a process of changing a matrix size of the reconstructed image prior to the Wavelet transform, and a process of restoring the matrix size of the reconstructed image after the noise removal to an original size. ### Claim 13 An image processing method for noise removal in an image acquired by a magnetic resonance imaging apparatus, the image being a reconstructed image obtained with a reconstruction matrix extended by zero-filling an acquisition matrix of nuclear magnetic resonance signals, wherein the noise removal comprises a process of subjecting the reconstructed image to Wavelet transform and L1 norm minimization process, and the noise removal further comprises, a process of predicting a characteristic of an artifact caused by reconstruction and noise removal, a process of creating a window function for eliminating the artifact being predicted, and a process of applying the created window function to the image after the L1 norm minimization.