A circular small FOV MRI three-dimensional real-time imaging method using the dynamic keyhole method

Abstract

The present invention discloses a circular small FOV 3D real-time magnetic resonance imaging method using a dynamic keyhole method, comprising: S1, selecting an out-of-region suppression pulse 2DRF and a 180-degree slice-selective refocusing pulse 3D encoding sequence as an imaging sequence to achieve circular small FOV imaging; S2, determining a scanning positioning line for the interventional process according to the interventional procedure, and obtaining pre-scanned reference image data; S3, applying the dynamic keyhole method to two phase encodings of the 3D image, calculating the number of phase encodings within the keyhole based on the reference image data, and modifying the phase encoding of the sequence accordingly to achieve keyhole data scanning; S4, registering the reference data with the keyhole data obtained by real-time scanning using an image similarity function and a respiratory monitoring method; S5, rapidly reconstructing the image based on the registered data, and displaying the image in real time on a display of the interventional image. The present invention's real-time magnetic resonance imaging method can balance imaging quality and imaging speed in interventional applications.

Description

Technical Field

[0001] The present 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] Interventional therapy has become a common approach in clinical treatment. Traditional interventional therapies rely primarily on X-ray fluoroscopy and ultrasound imaging. However, X-ray fluoroscopy provides only general details of human tissue and poor soft tissue contrast. Furthermore, X-rays emit ionizing radiation, which can harm patients and staff. Ultrasound imaging, with its limited soft tissue contrast, acoustic shadowing, and restricted field of view, is not suitable for guiding complex interventions.

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

[0004] These advantages of MRI facilitate device and vascular 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 extensive research, which has greatly promoted the gradual and large-scale application of magnetic resonance interventional imaging.

[0005] Currently, real-time MRI interventional imaging primarily utilizes rapid two-dimensional (2D) imaging sequences, but their application in 3D imaging is unknown. Furthermore, some rapid reconstruction methods, combined with rapid pulse sequences, aim to improve the temporal resolution of real-time imaging. Commonly used methods include parallel imaging, compressed sensing, and nonlinear inversion reconstruction. However, these techniques all have various limitations.

[0006] For parallel imaging techniques, the acceleration factor for k-space data using Cartesian trajectories is typically 2-3 times, which limits the temporal resolution of real-time imaging. Excessively high acceleration factors can significantly reduce the signal-to-noise ratio of the image. When using non-Cartesian trajectories, the acceleration factor is typically limited to 3-4 times. However, in order to use the fast Fourier transform (FFT), the k-space data must be resampled onto a Cartesian network, which significantly increases the time cost of reconstruction. Although methods such as compressed sensing and nonlinear inversion reconstruction can achieve higher acceleration factors, the images produced by these methods require continuous nonlinear reconstruction iterations, resulting in long reconstruction times and significant image delays in real-time imaging.

[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 this invention is to provide a novel fast imaging method for circular small FOV three-dimensional MRI using out-of-field suppression technology, improving the image quality of real-time imaging to meet clinical application requirements. Secondly, a dynamic keyhole method is proposed for applying it to two phase encoding directions of three-dimensional imaging, along with corresponding accelerated data acquisition, registration, and image reconstruction methods. This method can significantly improve MRI imaging speed during interventional procedures with minimal impact on image quality.

[0009] To this end, the present invention provides a circular small FOV three-dimensional magnetic resonance real-time imaging method using a dynamic keyhole method, comprising: S1, selecting an out-of-region suppression pulse 2DRF and a 180-degree slice 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 within 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 the image in real time on a display of the intervention image.

[0010] The present invention also provides a circular small FOV 3D magnetic resonance real-time imaging system using a dynamic keyhole method, comprising: a sequence processing module for selecting an out-of-region suppression pulse 2DRF and a 180-degree slice selection refocusing pulse 3D coding sequence as an imaging sequence, and modifying and improving 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-scan parameter determination module for determining a scanning positioning line for the interventional process according to the interventional procedure, completely acquiring the entire magnetic resonance imaging original k-space data, using it as reference data, and calculating the number of keyholes of the dynamic keyhole method based on the data, and modifying the phase encoding corresponding to the sequence according to the number; a data alignment module for receiving the k-space data obtained by the modified sequence scan, and performing alignment between the reference data and the keyhole data according to the image similarity function and the respiratory monitoring method; a real-time imaging display module for receiving the aligned k-space data for rapid reconstruction, and displaying the reconstructed image data on a corresponding display screen.

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

[0012] 1. Compared to traditional MRI large FOV imaging, circular small FOV imaging achieved with out-of-region suppression technology offers advantages. Small FOV imaging means a smaller imaging area, resulting in higher spatial resolution and faster imaging speeds. Data acquisition only requires a smaller area, saving imaging time and resources. By capturing signals only within a localized area, artifacts and image distortion can be reduced. Furthermore, small FOV imaging can provide more precise positioning and navigation information, facilitating precise positioning and navigation of specific anatomical sites during interventional procedures, thereby ensuring accuracy and safety.

[0013] 2. The dynamic keyhole method is used simultaneously in both phase encoding directions of the 3D image, so the number of phase encodings in the keyholes in both directions needs to be determined. Using the dynamic keyhole method in both phase encoding directions simultaneously greatly improves the speed of MRI and facilitates real-time imaging.

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

[0015] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying 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 imaging acquisition of the present invention;

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

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

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

[0021] Figure 6 2DRF imaging results used in the present invention, wherein (a) (b) (c) (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 is a general term for a series of minimally invasive treatment techniques that use puncture needles, catheters and other interventional equipment to introduce specific instruments into the body's diseased areas through natural channels or tiny incisions under the guidance and monitoring of medical imaging equipment.

[0025] Real-time magnetic resonance imaging (RT-MRI): It is 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: Magnetic resonance sequences are used to collect k-space data along three directions (transverse, longitudinal, and axial) to obtain images containing three-dimensional spatial information.

[0027] K-space data: The raw data collected by the magnetic resonance imaging device represents the frequency and phase information of the MRI signal, and includes two-dimensional (2D) k-space and three-dimensional (3D) k-space. Two-dimensional k-space is a data matrix consisting of two dimensions, called "frequency encoding" and "phase encoding." Typically, frequency encoding corresponds to spatial position along the transverse direction, while phase encoding corresponds to spatial position along the longitudinal 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 and obtaining an image by merging the acquired low-frequency data with high-frequency data borrowed from a reference image, attempting to view all k-space data by peering through the keyhole.

[0029] Magnetic resonance pulse sequence: Consists of a series of gradient pulses and radio frequency (RF) pulses with specific pulse designs and parameter settings. It is used to produce different types of images during MRI scans and to perform specific imaging and assessment of different tissues and lesions.

[0030] Imaging sequence: A 2DRF excitation pulse serves as a preparatory pulse to achieve a small circular FOV, followed by an additional 180-degree pulse in the opposite direction for slice selection and refocusing in 3D imaging. 2DRF pulses: Compared to traditional one-dimensional excitation pulses, 2DRF emits two selection gradient waveforms along two independent gradient axes, enabling selective excitation in 2D space. Two oscillating gradients cover the two-dimensional RF k-space to achieve a small circular 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 to the magnetic resonance sequence. This technology aims to suppress the signal around the region of interest, thereby highlighting the details and structures within the region of interest on the image.

[0032] FOV (Field of View): This 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, while smaller FOV images cover a smaller area 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 milliseconds. 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 uses a 2DRF excitation pulse as a preparatory pulse to achieve a circular small FOV. This pulse is followed by multiple imaging excitation pulses, enabling the acquisition of multiple lines of k-space data. First, because the circular small FOV is achieved through out-of-area suppression, a circular field of view image with a diameter of 40mm-150mm (preferably 40mm-80mm, and more preferably 40mm-50mm) 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] To further accelerate MRI imaging, some scholars have proposed the traditional keyhole method and the improved dynamic keyhole method. However, to date, 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 layer-selective 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 of images at different levels and in different respiratory states were aligned 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 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 the dynamic keyhole method for real-time imaging. It applies the dynamic keyhole method to the two phase encoding directions of three-dimensional imaging for the first time, and uses the image intensity tolerance of the pre-scanned image data 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 scanning. The keyhole data and the reference data are then matched by the image similarity function (SSIM) and respiratory monitoring. Through testing, it was found 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 has a short image reconstruction time, which can achieve low-latency display.

[0045] To further meet the real-time imaging requirements of interventional therapy, this patent applies circular small FOV imaging technology achieved through MRI out-of-area suppression. MRI out-of-area suppression technology is designed to suppress signals from surrounding tissue, highlight signals in the region of interest, and reduce the impact of surrounding tissue on image quality. Out-of-area suppression technology can enhance image contrast, reduce interference and artifacts, and highlight specific anatomical details, thereby improving the quality and readability of MR images and enhancing imaging accuracy and practicality.

[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 diagram of magnetic resonance imaging achieved through out-of-region suppression technology is shown below. 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 180-degree slice-selective refocusing pulse 3D coding sequence as the imaging sequence, that is, add the corresponding external volume suppression pulse as a preparation pulse before the coding excitation pulse to achieve circular small FOV imaging;

[0049] S2. Determine a scanning positioning line for the interventional process according to the interventional procedure and obtain pre-scanned reference image data;

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

[0051] S4, using an image similarity function and a respiratory monitoring method to register the reference data with 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 encoding sequence) are implemented in the MRI spectrometer software of the 3D MRI system. Outside the predetermined anatomical structure, out-of-region suppression technology is used, i.e., a corresponding external volume suppression pulse is added before the encoding excitation pulse to achieve circular small FOV imaging. For example, the circular small FOV is a 50 mm diameter circular field of view.

[0054] In step S2, a pre-scan is performed using the imaging sequence from step S1. In this step, the entire MRI raw k-space data is acquired strictly according to the standard interventional procedure determined by the interventional physician and used as reference data. This process does not involve any interventional surgery, but only pre-collects 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 reconstructed keyhole data with the image reconstructed from pre-scanned reference data, the k-space data of the image with the highest similarity is selected for registration with the real-time keyhole data. Respiration detection registration: Breathing causes organ movement in the body, so manual registration is performed based on the organ positions in 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-scan parameter determination module, a data registration module, and a real-time imaging display module.

[0059] The sequence processing module primarily implements out-of-region suppression pulse 2DRF and 180-degree selected slice refocusing pulse 3D encoding sequences, as well as modifies and improves these pulse sequences to implement out-of-region suppression technology, thereby achieving circular small FOV imaging. The FOV position during this process should be updated based on the position of the interventional device.

[0060] The pre-scan parameter determination module strictly follows the standard interventional procedures determined by the interventional physician to fully acquire the entire MRI raw k-space data, which serves as reference data. This process does not involve any surgical intervention; it merely collects k-space data in advance. This data is input into a defined program to determine the number of keyholes in the dynamic keyhole method, and the corresponding phase encoding is modified accordingly. The pre-scan parameter determination module implements 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 a defined program to perform registration between 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 foregoing description is merely an embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection 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 180-degree slice-selective refocusing pulse 3D coding sequence as the imaging sequence, that is, add the corresponding external volume suppression pulse as a preparation pulse before the coding excitation pulse to achieve circular small FOV imaging; S2. Determine a scanning positioning line for the interventional process according to the interventional procedure and obtain pre-scanned reference image data; S3. Applying a dynamic keyhole method to two phase codes of a three-dimensional image, calculating the number of phase codes within the keyhole based on the reference image data, and modifying the phase code of the sequence accordingly to achieve keyhole data scanning; S4, using an image similarity function and a respiratory monitoring method to register the reference data with 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 3D magnetic resonance real-time imaging method according to claim 1, characterized in that: The circular small FOV imaging is imaging of a circular field of view of 40mm-150mm in diameter.

3. The circular small FOV 3D magnetic resonance 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 3D magnetic resonance 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 slice-selective refocusing pulse 3D coding sequence as the imaging sequence, and to modify and improve the pulse sequence. In particular, 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 scan positioning line of the intervention process according to the intervention procedure, completely obtain the entire magnetic resonance imaging raw k-space data, use it as reference data, and calculate the number of keyholes in the dynamic keyhole method based on this data, 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 performing registration between 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 3D real-time magnetic resonance imaging system 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 3D real-time magnetic resonance imaging system according to claim 5, characterized in that: The pre-scan parameter determination module determines the amount of phase encoding within the keyhole using an image intensity tolerance of pre-scanned image data.

8. The circular small FOV 3D real-time magnetic resonance imaging system 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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