Patent Application
20220011393
The present disclosure generally relates to magnetic resonance imaging (“MRI”) and, more specifically to systems and methods for improving MRI image quality in instances where a subject undergoing MRI moves during acquisition of an MRI image.
MRI is a non-invasive imaging technology that creates detailed images of organs and tissues in the body. MRI may be used as a tool to diagnose and/or monitor a variety of health conditions. An MRI device includes a primary magnet which generates a strong primary magnetic field (B0) that causes the magnetic moments of the protons of the hydrogen atoms in the body to align parallel or antiparallel to the direction of the primary magnetic field, creating a net magnetic vector in the direction of the primary magnetic field. Application of a radiofrequency excitation pulse deflects the net magnetic vector toward a traverse plane perpendicular to the primary magnetic field. When the radiofrequency source is switched off, the protons relax to their resting state and release radiofrequency signals that are detected as data by the MRI device and used to create the MRI image. Proton relaxation may be measured by both T1 relaxation (the time for the net magnetic vector to return to the resting state) and T2 relaxation (the time for the proton axial spins to return to their resting state). Gradient coils may be used to generate gradients of the primary magnetic field, and allow the MRI device to image body parts in selected slices such as selected axial, sagittal, and coronal slices. The data used to create MRI image may be collected row by row in k-space, which is a data grid or matrix where the data is stored prior to application of the Fourier Transform to generate the final image. Each MRI image may be generated by averaging the data from two or more consecutive MRI scans in order to improve the signal-to-noise ratio and image quality.
Movement of or by the patient during acquisition of the MRI image may compromise image quality and resolution. For instance, patient movement due to respiration, heart muscle motion, or even larger body movements may result in undesirable motion artifacts in the resulting MRI image such as ghosting, blurring, or streaking. To avoid these artifacts, some current methods for MRI may discard the data for an entire scan during which the patient movement occurred, and average the data for the remaining scans prior to MRI image generation.
However, it would be desirable to minimize the amount of data that is discarded during MRI. In addition, certain MRI protocols, such as those applied on neonates, may average only two consecutive scans in order to reduce the imaging time. In such situations, discarding all of the data for one of the two scans might substantially reduce the signal-to-noise ratio and quality of the image. Thus, there is a need for improved systems and methods that generate high quality MRI images, even where a patient undergoing MRI moves during image acquisition.
In an embodiment, the disclosure describes a computer-implemented method for generating an MRI image of a subject. The computer-implemented method may include performing, using an MRI device, at least two consecutive MRI scans of a subject, a first MRI scan and a second MRI scan. The computer-implemented method may further include obtaining first k-space grid data for the first MRI scan and second k-space grid data for the second MRI scan, comparing the first k-space grid data to the second k-space grid data (e.g., by subtraction on a point by point basis) to obtain delta k-space grid data, and using the delta k-space grid data to determine, on a scan line by scan line basis, if the subject undergoing MRI moved during acquisition of any given scan line either during the first MRI scan or the second MRI scan. If it is determined that the subject moved during acquisition of any given scan line, then the computer-implemented method further includes determining whether the specific scan line movement occurred during the first MRI scan or the second MRI scan using a motion detector. If the movement occurred during the first MRI scan, then the applicable scan line data (i.e., the particular scan line associated with movement) for first k-space grid data is replaced with the same scan line data for the second k-space grid data. Conversely, if the movement occurred during the second MRI scan, then the applicable scan line data for the second k-space grid data is replaced with the same scan line data for the first k-space grid data. The computer-implemented method may further include averaging the resultant first k-space grid data with the resultant second k-space grid and generating an MRI image using the Fourier Transform. By replacing scan line data as described above, the generated MRI image is corrected for motion artifacts.
In another embodiment, the disclosure describes an MRI system that includes an MRI device. The MRI device may include a body defining a bore into which a subject (or portion thereof) is inserted for acquisition of an MRI image, one or more primary magnets configured to generate a primary magnetic field, one or more gradient coils configured to generate gradients of the primary magnetic field, and one or more radiofrequency coils configured to transmit radiofrequency pulses to the subject in the bore of the MRI device and receive radiofrequency signals from the subject in the bore of the MRI device. The MRI system may further include a computer device coupled to the MRI device and including a processor configured according to computer executable instructions. The processor may include an acquisition module configured to cause the MRI device to perform at least two consecutive MRI scans of a subject. The at least two consecutive MRI scans may include a first MRI scan and a second MRI scan. The acquisition module may be further configured to obtain corresponding first k-space grid data and second k-space grid data. The processor may further include a motion correction module in communication with the acquisition module and configured to generate an MRI image in accordance with the computer-implemented method described above.
The disclosure may be better understood by reference to the detailed description when considered in conjunction with the accompanying drawings. The components and figures are not necessarily drawn to scale, emphasis being placed instead upon illustrating the principles of the disclosure.
The present description now will be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of illustration, specific exemplary embodiments by which the description may be practiced. This description may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the description to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense.
As used herein, an “MRI image” may be an image generated from data signals collected from one or more Mill scans, and an “Mill scan” may be an Mill pulse sequence used for the collection of the data signals to generate the Mill image. In addition, as used herein, “motion artifacts” may refer to artifacts such as blurring, streaking, or ghosting in the Mill image that result from movement of the subject undergoing MRI scanning.
Referring now to the drawings and with specific reference to
The MRI system 10 may further include a computer device 28 coupled to the MRI device 12 for control thereof. The computer device 28 may include one or more processors 30, at least one non-transitory computer readable medium (e.g., memory) (not illustrated) containing computer-executable instructions stored thereon. The one or more processors 30 may be configured to execute or carry out computer-executable instructions for running a selected MRI protocol (or set of pulse sequences), acquiring k-space grid data, and generating an MRI image, as explained in further detail below. The computer device 28 may also include a display interface 32 allowing an operator to input or alter the MRI protocol, and view the MRI images.
The MRI system 10 may further include a motion sensor 34 in electrical or wireless communication with the computer device 28, and positioned with respect to the subject 18 to detect movement of the subject 18 during acquisition of the MRI image (e.g., during an MRI scan). The motion sensor 34 may be placed proximate a region of interest that is imaged, such as a specific body part. For example, if the head of the subject 18 is imaged, the motion sensor 34 may be placed beneath the head while the image is acquired. In one exemplary embodiment, the motion sensor 34 is a respiration sensor, such as a Graseby Respiration Sensor. The motion sensor 34 may be other types of motion sensors in alternative embodiments.
An exemplary computer device 28 of the MRI system 10 is schematically depicted in
The one or more processors 30 may, when executing certain computer readable instructions, operate as an acquisition module 40 that instructs the MRI device 12 to acquire an MRI image according to a selected MRI protocol, and collects MRI image data during acquisition of the MRI image. More specifically, the acquisition module 40 may cause (e.g., control) the MRI device 12 to perform at least two MRI scans (at least a first MRI scan and a second MRI scan) during acquisition of the MRI image of the subject 18. In an embodiment, the first and second MRI scans may be consecutive. Further, the acquisition module 40 may obtain MRI image data in k-space (e.g., that reflect the proton relaxation signals during each of the first and second MRI scans). The k-space data may be obtained scan line by scan line or row by row for each of the first and second MRI scans, thereby generating first k-space grid data and second k-space grid data, respectively.
The processor(s) 30 may further, when executing certain other computer readable instructions, operate as a motion correction module 42 in communication with the acquisition module 40 and motion sensor 34 for collection of data therefrom. As explained more specifically below, the motion correction module 42 collects the data from the acquisition module 40 and data from the motion sensor 34, and provides MRI motion correction during MRI image acquisition.
In one embodiment, acquisition module 40 and motion correction module 42 may be implemented as any other single or collection of circuit(s), integrated circuit(s), processor(s), processing device(s), transistor(s), memory(s), storage(s), computer readable medium(s), combination logic circuit(s), or any combination of the above that is capable of providing a desired operation(s) or function(s). “Memory,” “computer-readable media,” and “storage” may refer to any suitable internal or external volatile or non-volatile, memory device, memory chip(s), or storage device or chip(s) such as, but not limited to system memory, frame buffer memory, flash memory, random access memory (RAM), read only memory (ROM), a register, a latch, or any combination of the above. A “processor” may refer to one or more dedicated or non-dedicated: micro-processors, micro-controllers, sequencers, micro-sequencers, digital signal processors, processing engines, hardware accelerators, applications specific circuits (ASICs), state machines, programmable logic arrays, any integrated circuit(s), discreet circuit(s), etc. that is/are capable of processing data or information, or any suitable combination(s) thereof. “Executable instructions” may refer to software, firmware, programs, instructions or any other suitable instructions or commands capable of being processed by a suitable processor.
A method for acquiring an MRI image and providing MRI motion correction during MRI image acquisition, as performed by the one or more processors 30 of the computer device 28 is illustrated in
After block 54, an MRI motion correction method 56 is applied. In one embodiment, the image correction method 56 is performed by the motion correction module 42 upon receipt of the first and second k-space grid data from the acquisition module 40. At block 58 of the image correction method 56, the first k-space grid data and second k-space grid data is compared (e.g., point by point via subtraction) to generate a delta k-space grid data where each point represents the difference between corresponding points in the first k-space grid data and the second k-space grid data. The method then, based on the delta k-space grid data, determines whether the subject undergoing MRI moved during acquisition of any given scan line in either the first or second MM scan, at block 60. In one example, the method makes such determination by determining the standard deviation of the values of any given row of the delta k-space grid data difference between the data along each row number of the k-space subtraction is then determined. If the standard deviation for any row in the delta k-space data files is greater than a threshold value, then it is determined that there was movement of the subject during acquisition of that scan line in either the first or second MRI scan. Notably, the identification of one or more rows having a standard deviation above the threshold may indicate movement of the subject occurred during acquisition of the data in that row, but may not provide information as to whether the movement occurred during acquisition of the row number in the first MRI scan or the second MRI scan. The threshold may be predetermined and chosen by the operator of the MRI device 12, or may be a default value that varies depending on the pulse sequence.
If at least one of the row numbers in the k-space subtraction has a standard deviation above the threshold indicating movement of the subject occurred, the MRI image is “corrected” for motion artifacts according to the following description. At block 62, it is determined whether the specific movement of the subject 18 occurred during the first MRI scan or the second MRI scan based on data collected from the motion sensor 34. Specifically, block 62 may involve determining a time of the movement based on data collected from the motion sensor 34, and determining whether the time of the movement occurred during acquisition of the specific scan line where movement was determined to have occurred. If the movement occurred during the first MRI scan, then the applicable scan line data for the first k-space grid data associated with movement is replaced with the same scan line data from the second k-space grid data to “correct” the data of the first MRI scan (block 64). Conversely, if the movement occurred during the second MRI scan, then the applicable scan line data for the second k-space grid data associated with movement is replaced with the same scan line data from the first k-space grid data, Such replacement may be performed for each scan line of the delta k-space grid data having a standard deviation above the threshold. An MRI image is then generated at block 66. Block 66 may include averaging corrected first k-space grid data and/or corrected second k-space grid data and performing a Fourier Transition on the averaged data to generate an MRI image from the first and second MRI scans.
If none of the row numbers have a standard deviation above the threshold indicating that the subject did not move during either of the first or second MRI scans, then the MRI image can be generated (block 66), using for example the first and second k-space grid data. It will be understood that the image correction method 56 described above may be adapted for image correction when more than two MRI scans are performed. For instance, the image correction method 56 may involve repeating the method as additional k-space grid data are collected with each additional scan.
For comparison,
As a result of the system and method described herein, a technical problem of retaining meaningful Mill scan data is addressed. By replacing only scan lines in k-space associated with movement, the present system and method improves computers and processors controlling MRI systems and improves signal to noise and image quality.
This application claims priority to U.S. Provisional Patent Application No. 62/751,035, filed on Oct. 26, 2018, which is herein incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IL2019/051156 | 10/27/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62751035 | Oct 2018 | US |
