Circular small FOV magnetic resonance three-dimensional real-time imaging method applying dynamic keyhole method

Abstract

The invention discloses a circular small FOV magnetic resonance three-dimensional real-time imaging method applying a dynamic keyhole method, and the method comprises the steps: S1, selecting an out-of-region suppression pulse 2DRF and a 180-degree selection layer refocusing pulse 3D coding sequence as an imaging sequence, and achieving the imaging of a circular small FOV; s2, determining a scanning positioning line of an intervention process according to the intervention program, and obtaining pre-scanned reference image data; s3, a dynamic keyhole method is applied to two phase codes of the three-dimensional image, the number of phase codes in a keyhole is calculated according to reference image data, the phase codes of the sequence are modified accordingly, and keyhole data scanning is achieved; s4, performing registration on reference data and keyhole data obtained by real-time scanning by utilizing an image similarity function and a respiration monitoring method; and S5, performing rapid image reconstruction according to the registered data, and performing real-time imaging display on a display of the interventional image. The magnetic resonance real-time imaging method can give consideration to both the imaging quality and the imaging speed during interventional application.

Description

Technical Field

[0001] The invention relates to magnetic resonance imaging (MRI) technology, and in particular to a circular small FOV magnetic resonance three-dimensional real-time imaging method using a two-dimensional dynamic keyhole method. Background Art

[0002] At present, interventional therapy has become one of the commonly used methods in clinical treatment. Traditional interventional therapy mainly relies on X-ray fluoroscopy and auxiliary ultrasound imaging, but X-ray transmission imaging only provides rough details of human tissues, poor contrast of soft tissues, and ionizing radiation from X-rays can harm patients and staff. Ultrasound imaging has limited soft tissue contrast, acoustic shadow effect, and limited field of view, which cannot guide complex interventions.

[0003] MRI is an advanced medical imaging technology that has the advantages of no radiation, flexible soft tissue contrast, high resolution, providing auxiliary hemodynamic data, and three-dimensional (3D) visualization of human tissue or structure, which can provide greater advantages in interventional treatment.

[0004] These advantages of MRI help in equipment and blood vessel navigation, making it one of the technologies for image-guided human interventional treatment. However, there are still problems with magnetic field interference, imaging speed and magnetic resonance compatibility of interventional equipment. However, many scholars and engineers have conducted a lot of research, which has greatly promoted the gradual large-scale application of magnetic resonance interventional imaging.

[0005] At present, MRI interventional real-time imaging mainly uses 2D fast imaging sequences, but there are no examples of its application in 3D imaging. In addition, some fast reconstruction methods also combine fast pulse sequences to improve the temporal resolution of real-time imaging. Currently, the commonly used methods include parallel imaging technology, compressed sensing technology, and nonlinear inversion reconstruction methods. However, these technologies all have limitations in different aspects.

[0006] For parallel imaging technology, the acceleration factor of k-space data for Cartesian trajectories is usually 2-3 times, providing limited time resolution for real-time imaging. Too high an acceleration factor will significantly reduce the signal-to-noise ratio of the image. When using non-Cartesian trajectories, the acceleration factor is usually limited to 3-4 times, but in order to use the fast Fourier transform method (FFT), the k-space data needs to be resampled to the Cartesian network, which obviously increases the time cost of reconstruction. For methods such as compressed sensing and nonlinear inversion reconstruction, although higher acceleration factors can be achieved, the images of such methods need to be continuously reconstructed and iterated nonlinearly, resulting in a long image reconstruction time, and the image delay displayed by real-time imaging is huge.

[0007] Therefore, it is necessary to provide a real-time magnetic resonance imaging method for interventional applications that can balance imaging quality and imaging speed. Summary of the invention

[0008] The purpose of the present invention is to provide a new circular small FOV three-dimensional MRI fast imaging method using out-of-region suppression technology to improve the image quality of real-time imaging to meet clinical reference requirements. Secondly, it is proposed to apply the dynamic keyhole method to the two phase encoding directions of three-dimensional imaging and the corresponding accelerated data acquisition, registration and image reconstruction method, which can greatly improve the imaging speed of MRI during the intervention process with little impact on image quality.

[0009] To this end, the present invention provides a circular small FOV magnetic resonance three-dimensional real-time imaging method using a dynamic keyhole method, comprising: S1, selecting an out-of-region suppression pulse 2DRF and a 180-degree layer selection refocusing pulse 3D coding sequence as an imaging sequence, that is, adding a corresponding external volume suppression pulse as a preparation pulse before the coding excitation pulse to achieve circular small FOV imaging; S2, determining the scanning positioning line of the intervention process according to the intervention procedure, and obtaining pre-scanned reference image data; S3, applying the dynamic keyhole method to two phase encodings of the three-dimensional image, calculating the number of phase encodings in the keyhole according to the reference image data, and modifying the phase encoding of the sequence accordingly to achieve keyhole data scanning; S4, using an image similarity function and a respiratory monitoring method to align the reference data and the keyhole data obtained by real-time scanning; S5, quickly reconstructing the image according to the aligned data, and displaying it in real time on a display of the intervention image.

[0010] The present invention also provides a circular small FOV magnetic resonance three-dimensional real-time imaging system using a dynamic keyhole method, comprising: a sequence processing module, used to select an out-of-region suppression pulse 2DRF and a 180-degree layer selection refocusing pulse 3D coding sequence as an imaging sequence, and to modify and improve the pulse sequence, wherein a corresponding external volume suppression pulse is added as a preparation pulse before the coding excitation pulse to achieve circular small FOV imaging; a pre-scanning parameter determination module, used to determine the scanning positioning line of the intervention process according to the intervention procedure, completely obtain the entire magnetic resonance imaging original k-space data, use it as reference data, and calculate the number of keyholes of the dynamic keyhole method based on this, and modify the phase encoding corresponding to the sequence according to the number; a data alignment module, used to receive the k-space data obtained by the modified sequence scan, and align the reference data and the keyhole data according to the image similarity function and the respiratory monitoring method; a real-time imaging display module, used to receive the aligned k-space data for rapid reconstruction, and display the reconstructed image data on the corresponding display screen.

[0011] The present invention has the following technical advantages / effects:

[0012] 1. Compared with traditional MRI large FOV imaging, circular small FOV imaging achieved by out-of-region suppression technology has more advantages. Small FOV imaging means a smaller imaging area. Therefore, the corresponding MRI images can provide higher spatial resolution, only need to collect data in a smaller area, have faster imaging speed, save imaging time and resources, and only collect signals in the local area, which can reduce artifacts and image distortion. In addition, small FOV imaging can provide more accurate positioning and navigation information, which helps to accurately locate and navigate specific anatomical parts in interventional procedures, thereby ensuring the accuracy and safety of the operation.

[0013] 2. The dynamic keyhole method is used in two phase encoding directions of the three-dimensional image at the same time, so it is necessary to determine the number of phase encodings in the keyholes in the two directions. The dynamic keyhole method is used in two phase encoding directions at the same time, which greatly improves the speed of magnetic resonance imaging and is conducive to real-time imaging.

[0014] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0016] Figure 1 The relevant parameter description of magnetic resonance three-dimensional imaging is shown;

[0017] Figure 2 It is a schematic diagram of the process of real-time MRI acquisition imaging of the present invention;

[0018] Figure 3 This is a schematic diagram of a circular small FOV signal achieved by the out-of-area suppression technology;

[0019] Figure 4 It is a module diagram of a circular small FOV magnetic resonance three-dimensional real-time imaging system of the present invention;

[0020] Figure 5 It is a flow chart of a circular small FOV magnetic resonance three-dimensional real-time imaging method using a dynamic keyhole method of the present invention;

[0021] Figure 6 2DRF imaging effect diagrams used in the present invention, wherein (a), (b), (c), and (d) are excitation effect diagrams under different excitation diameters. DETAILED DESCRIPTION

[0022] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0023] Explanation of terms

[0024] Interventional therapy: A general term for a series of techniques that use puncture needles, catheters and other interventional equipment to introduce specific instruments into the diseased parts of the human body through natural channels or tiny incisions under the guidance and monitoring of medical imaging equipment for minimally invasive treatment.

[0025] Real-time magnetic resonance imaging (RT-MRI): Capable of acquiring data in rapid succession in real time, with the delay between acquisition and image display short enough to allow interactivity.

[0026] Magnetic resonance three-dimensional (3D) imaging: k-space data is collected along three directions (lateral, longitudinal and axial) through a magnetic resonance sequence to obtain images containing three-dimensional spatial information.

[0027] k-space data: The raw data collected by the magnetic resonance device represents the frequency and phase information of the MRI signal, including two-dimensional (2D) k-space and three-dimensional (3D) k-space. Two-dimensional k-space is a data matrix composed of two dimensions, which are called "frequency encoding" and "phase encoding". Usually, frequency encoding corresponds to the spatial position along the horizontal direction, while phase encoding corresponds to the spatial position along the vertical direction. Three-dimensional k-space is similar to two-dimensional k-space, but it contains three dimensions, one frequency encoding and two phase encoding data dimensions.

[0028] Keyhole method: A method that speeds up imaging by using extensive matrix reduction on the k-space data, thereby preventing image blur by merging the acquired low-frequency data with high-frequency data borrowed from a reference image, obtaining an image that attempts to view all the k-space data by peering through the keyhole.

[0029] Magnetic resonance pulse sequence: It consists of a series of gradient pulses and radio frequency (RF) pulses, including specific pulse design and parameter settings. It is used to produce different types of images in MRI scans and to perform specific imaging and evaluation of different tissues and lesions.

[0030] Imaging sequence: 2DRF excitation pulse is used as preparation pulse to realize circular small FOV, and then 180 degree pulse is added in the other direction for 3D imaging with layer selection and refocusing. 2DRF pulse: Compared with the traditional one-dimensional excitation pulse, 2DRF emits two selection gradient waveforms on two independent gradient axes to realize selective excitation in 2D space, and uses two oscillating gradients to cover the two-dimensional RF k space to realize circular small FOV.

[0031] Magnetic resonance imaging (MRI) outer-volume suppression technology OVS (outer-volume suppression) is an important MRI imaging technology that suppresses human tissue or organs by adding additional pulse waveforms in the magnetic resonance sequence. This technology aims to suppress signals around the region of interest, thereby highlighting the details and structures within the region of interest on the image.

[0032] FOV (Field of View): refers to the size of the imaging area selected on the imaging plane (the field of view of the MRI image), that is, the range of the physical area covered in the MRI image. Larger FOV images cover a wider area of ​​the human body, and small FOV images cover a local range of the human body.

[0033] Temporal resolution: In MRI, temporal resolution refers to the time interval between adjacent displayed images in the scanning sequence, usually measured in ms. If measured in frames, it indicates the number of times the magnetic resonance image is updated within 1 second.

[0034] Spatial resolution: Spatial resolution refers to the size of the smallest structure or feature that can be distinguished in an MRI image.

[0035] For a description of the parameters related to 3D MRI, see Figure 1 .

[0036] In view of the requirements of interventional therapy for real-time imaging technology, combined with reference Figures 1 to 6 The present invention selects a 2DRF excitation pulse as a preparation pulse to realize a circular small FOV, and then follows multiple imaging excitation pulses to achieve the acquisition of multiple lines of k-space data. First, since the circular small FOV is realized by the out-of-region suppression technology, a 40mm-150mm (preferably 40mm-80mm, more preferably 40mm-50mm) circular diameter field of view image is selected as the circular small FOV imaging.

[0037] Compared with traditional large FOV imaging methods, it can achieve higher resolution while greatly reducing the number of phase encodings required, reducing scanning time, and by combining multiple 180-degree pulses, it can quickly acquire multiple lines of k-space data.

[0038] In order to further speed up MRI imaging, some scholars have proposed the traditional keyhole method and the improved dynamic keyhole method. However, up to now, the keyhole method has only been used in combination with a two-dimensional (2D) imaging pulse sequence, and the keyhole method is applied in the phase encoding direction of two-dimensional (2D) imaging for acceleration.

[0039] The present invention combines the keyhole method with a three-dimensional (3D) imaging pulse sequence for the first time. By applying an out-of-region suppression pulse (2DRF) and a 180-degree selective layer refocusing pulse 3D encoding sequence, the image intensity tolerance of the pre-scanned image data is used to determine the number of phase encodings collected in the keyhole. It should be ensured that the pre-scanned reference data and the keyhole data have the same positioning line when scanned.

[0040] Then, for the first time, the dynamic keyhole method was applied in two phase encoding directions of three-dimensional (3D) imaging, which greatly improved the imaging speed of 3D imaging. The keyhole data and reference data were aligned for images of different levels and different respiratory states through image similarity function and respiratory detection.

[0041] In addition, traditional real-time imaging uses a large FOV for imaging, so there are problems such as low spatial resolution and long scanning time. The present invention proposes the application of out-of-region suppression technology to achieve precise imaging of a circular small FOV area. By modifying or adding additional pulses in the imaging sequence, the out-of-region suppression technology is realized, further improving the MRI imaging speed and image quality.

[0042] The schematic diagram of the MRI real-time acquisition imaging process of the present invention is as follows Figure 2 shown.

[0043] Currently, MRI interventional real-time imaging mainly uses MRI two-dimensional (2D) rapid imaging sequences combined with reconstruction acceleration algorithms to increase the temporal resolution of real-time imaging.

[0044] The commonly used methods at present mainly include parallel imaging technology, compressed sensing technology and nonlinear inversion reconstruction method, but these technologies all have limitations in different aspects. The present invention adopts dynamic keyhole method for real-time imaging, and applies dynamic keyhole method to two phase encoding directions of three-dimensional imaging for the first time. The image intensity tolerance of pre-scanned image data is used to determine the number of phase encodings collected in the keyhole, and it should be ensured that the pre-scanned reference data and keyhole data have the same positioning line when scanning. Then the keyhole data and reference data are matched by image similarity function (SSIM) and respiratory monitoring. It is found through testing that this method can significantly reduce the number of central k-space data lines required to obtain sufficient image quality, can achieve 4-5 times acceleration for magnetic resonance imaging, and the reconstruction time of the image is short, which can achieve low-latency display.

[0045] In order to further meet the requirements of interventional therapy for real-time imaging, this patent applies the circular small FOV imaging technology realized by the magnetic resonance out-of-region suppression technology. The MRI out-of-region suppression technology is designed to suppress the signal of the surrounding tissue, highlight the signal of the area of ​​interest, and reduce the impact of the surrounding tissue on the image quality. The out-of-region suppression technology can improve the contrast of the image, reduce the interference and artifacts in the image, and highlight the specific anatomical details, thereby improving the quality and readability of MR images and enhancing the accuracy and practicality of imaging.

[0046] Compared with traditional MRI large FOV imaging, circular small FOV imaging has more advantages. Circular small FOV imaging means a smaller imaging area. Therefore, the corresponding MRI images can provide higher spatial resolution and only need to collect data in a smaller area. It has a faster imaging speed, saves imaging time and resources, and only collects signals in the local area, which can reduce artifacts and image distortion. In addition, small FOV imaging can provide more accurate positioning and navigation information, which helps to accurately locate and navigate specific anatomical parts during interventional procedures, thereby ensuring the accuracy and safety of the operation. The excitation signal image achieved by magnetic resonance imaging through out-of-region suppression technology is shown in the figure. Figure 3 shown.

[0047] The circular small FOV magnetic resonance three-dimensional real-time imaging method of the present invention comprises the following steps:

[0048] S1, select the out-of-region suppression pulse 2DRF and the 180-degree layer-selective refocusing pulse 3D coding sequence as the imaging sequence, that is, add the corresponding external volume suppression pulse as the preparation pulse before the coding excitation pulse to achieve circular small FOV imaging;

[0049] S2, determining a scanning positioning line for the intervention process according to the intervention procedure, and acquiring pre-scanned reference image data;

[0050] S3, applying a dynamic keyhole method on two phase encodings of a three-dimensional (3D) image, i.e., using the image intensity tolerance of the pre-scanned image data to determine the number of phase encodings in the keyhole, and modifying the phase encoding of the sequence according to the result to achieve keyhole data scanning;

[0051] S4, using an image similarity function and a breathing monitoring method to perform registration of the reference data and the keyhole data obtained by real-time scanning;

[0052] S5. Rapidly reconstruct the image according to the registered data, and display the image in real time on the interventional image display.

[0053] In step S1, an out-of-region suppression pulse 2DRF and a 180-degree selected-slice refocusing pulse 3D coding sequence are implemented on the magnetic resonance spectrometer software of the three-dimensional magnetic resonance imaging system; an out-of-region suppression technique is used outside the predetermined anatomical structure, that is, a corresponding external volume suppression pulse is added before the coding excitation pulse to achieve circular small FOV imaging. For example, the circular small FOV is a circular field of view with a diameter of 50 mm.

[0054] In step S2, the imaging sequence of step S1 is used for pre-scanning. In this step, the entire magnetic resonance imaging raw k-space data is completely acquired in strict accordance with the standard interventional procedure determined by the interventional physician and used as reference data. This process does not involve interventional surgery, but only pre-collection of k-space data.

[0055] In step S3, the data is input into a defined program to obtain the phase encoding number of the dynamic keyhole method, and the phase encoding corresponding to the sequence is modified according to the number.

[0056] In step S4, the k-space data obtained by the modified sequence scan is input into a defined program, and the reference data and the keyhole data are registered according to the image similarity function and the respiratory monitoring method.

[0057] Image similarity function registration: By comparing the image reconstructed from the keyhole data with the image reconstructed from the pre-scanned reference data, the k-space data of the image with the highest similarity is selected for registration with the keyhole data scanned in real time. Respiration detection method registration: Breathing causes the movement of organs in the body, so manual registration is performed based on the organ positions of the keyhole reconstructed image and the pre-scanned reference image.

[0058] The present invention also provides a circular small FOV magnetic resonance three-dimensional real-time imaging system, comprising: a sequence processing module, a pre-scanning parameter determination module, a data registration module, and a real-time imaging display module.

[0059] The sequence processing module is mainly responsible for the realization of the out-of-region suppression pulse 2DRF and the 180-degree selected layer refocusing pulse 3D coding sequence, as well as the modification and improvement of the pulse sequence to realize the out-of-region suppression technology, thereby realizing the circular small FOV imaging of the sequence. The FOV position in this process should be updated according to the change of the position of the interventional device.

[0060] The pre-scan parameter determination module is to obtain the entire magnetic resonance imaging raw k-space data strictly in accordance with the standard interventional procedure determined by the interventional physician, and use it as reference data. This process does not perform interventional surgery, but only collects k-space data in advance. The data is input into the defined program to obtain the number of keyholes in the dynamic keyhole method, and the phase encoding corresponding to the sequence is modified according to the number. That is, the pre-scan parameter determination module is used to implement the functions of steps S2 and S3.

[0061] The data registration module receives the k-space data obtained by the modified sequence scan, and inputs the defined program to perform registration of the reference data and the keyhole data according to the image similarity function and the respiratory monitoring method.

[0062] The real-time imaging display module receives the registered k-space data for rapid reconstruction and displays the displayed image data on the corresponding display screen.

[0063] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A circular small FOV magnetic resonance three-dimensional real-time imaging method using a dynamic keyhole method, characterized in that: include: S1, select the out-of-region suppression pulse 2DRF and the 180-degree layer-selective refocusing pulse 3D coding sequence as the imaging sequence, that is, add the corresponding external volume suppression pulse as the preparation pulse before the coding excitation pulse to achieve circular small FOV imaging; S2, determining a scanning positioning line for the intervention process according to the intervention procedure, and acquiring pre-scanned reference image data; S3, applying the dynamic keyhole method on two phase encodings of the three-dimensional image, calculating the number of phase encodings in the keyhole according to the reference image data, and modifying the phase encoding of the sequence accordingly to realize keyhole data scanning; S4, using an image similarity function and a breathing monitoring method to perform registration of the reference data and the keyhole data obtained by real-time scanning; S5. Rapidly reconstruct the image according to the registered data, and display the image in real time on the interventional image display.

2. The circular small FOV magnetic resonance three-dimensional real-time imaging method according to claim 1, characterized in that: The circular small FOV imaging is imaging of a circular diameter field of view of 40mm-150mm.

3. The circular small FOV magnetic resonance three-dimensional real-time imaging method according to claim 1, characterized in that: The image intensity tolerance of the pre-scanned image data is used to determine the amount of phase encoding within the keyhole.

4. The circular small FOV magnetic resonance three-dimensional real-time imaging method according to claim 1, characterized in that: In step S1 , the FOV position is updated according to the change in the position of the interventional instrument.

5. A circular small FOV magnetic resonance three-dimensional real-time imaging system using a dynamic keyhole method, characterized in that: include: The sequence processing module is used to select the out-of-region suppression pulse 2DRF and the 180-degree layer selection refocusing pulse 3D coding sequence as the imaging sequence, and to modify and improve the pulse sequence, wherein the corresponding external volume suppression pulse is added as a preparation pulse before the coding excitation pulse to achieve circular small FOV imaging; The pre-scan parameter determination module is used to determine the scanning positioning line of the intervention process according to the intervention procedure, completely obtain the original k-space data of the entire magnetic resonance imaging, use it as reference data, and calculate the number of keyholes of the dynamic keyhole method based on it, and modify the phase encoding corresponding to the sequence according to the number; A data registration module, for receiving the k-space data obtained by the modified sequence scan, and registering the reference data and the keyhole data according to the image similarity function and the respiratory monitoring method; The real-time imaging display module is used to receive the registered k-space data for rapid reconstruction and display the reconstructed image data on the corresponding display screen.

6. The circular small FOV magnetic resonance three-dimensional real-time imaging method according to claim 5, characterized in that: The sequence processing module selects a 40mm-150mm circular diameter field of view image as the circular small FOV imaging.

7. The circular small FOV magnetic resonance three-dimensional real-time imaging method according to claim 5, characterized in that: The pre-scan determination parameter module determines the amount of phase encoding within the keyhole using an image intensity tolerance of the pre-scanned image data.

8. The circular small FOV magnetic resonance three-dimensional real-time imaging method according to claim 5, characterized in that: In the sequence processing module, the FOV position is updated according to the change of the position of the interventional instrument.

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