A multi-element focused ultrasound focus shifting method, system and storage medium

Abstract

The present invention belongs to the field of medical data processing technology, and specifically relates to a multi-element focused ultrasound focus shifting method, system and storage medium. The method and system of the present invention use the focus shift test results of the reference positioning point to predict the actual phase difference of the skull, and then perform focus correction based on the obtained phase difference. Focus correction according to the present invention has the advantages of reducing the radiation exposure received by the patient, shortening the treatment process and eliminating the positional offset of the patient's head movement. Therefore, the present invention has a good application prospect in neuroregulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical data processing, and in particular relates to a multi-element focused ultrasound focus shifting method, system and storage medium. Background Art

[0002] Transcranial magnetic resonance guided focused ultrasound is an emerging neuromodulation technology. Different from previous invasive stimulation, it can use phased array ultrasound to focus non-invasively on the cortex or deep brain, and its spatial resolution can reach several cubic millimeters. However, in the actual treatment process, due to the huge difference in sound speed between the skull and brain tissue, and the skull's absorption of ultrasound energy, the phase of the sound beam after entering the brain is severely distorted, eventually resulting in speckle, focus shift, and insufficient temperature rise.

[0003] Therefore, during transcranial magnetic resonance-guided focused ultrasound, the focus of ultrasound needs to be corrected. The existing correction methods are mainly divided into two types:

[0004] One is the "energy-based adaptive focusing technology" that uses the magnetic resonance acoustic radiation force sequence to obtain the corresponding displacement map by inputting different coding modes, thereby achieving the purpose of compensating for the skull difference. However, due to the inherent limitations of the algorithm and hardware, the calibration time is too long and the risk of energy deposition in the subject's skull is increased, so this method has always been in the theoretical stage.

[0005] The other is to use computed tomography (CT) scanning to obtain skull acoustic information and achieve transcranial focusing through numerical simulation. This technology is currently the only method used in actual treatment, but because it requires CT scanning, it will cause radiation exposure to patients.

[0006] Therefore, there is an urgent need in this field to develop a new transcranial magnetic resonance-guided focused ultrasound focus correction method that does not use CT scan information, so as to shorten the treatment process and reduce radiation. Summary of the invention

[0007] In view of the problems in the prior art, the present invention provides a multi-element focused ultrasound focus shifting method, system and storage medium.

[0008] A multi-element focused ultrasound focus shifting method comprises the following steps:

[0009] Step 1, in a pure water environment, measuring the time delay of the input signal when the ultrasonic probe is focused at the center position and the boundary position, and obtaining the maximum effective range for linear focus shifting and the maximum time delay of the control pulse signal corresponding to the boundary position;

[0010] Step 2, collecting three-dimensional magnetic resonance structural imaging data, determining the target stimulation area and the initial placement coordinates of the ultrasound probe;

[0011] Step 3, synchronously performing magnetic resonance acoustic radiation force imaging sequence scanning and ultrasound signal transmission, wherein the phase of each channel of the ultrasound signal is transmitted in sequence according to the maximum time delay of the control pulse signal corresponding to the boundary position;

[0012] Step 4, recording the focus deviation between the actual focus position and the theoretical focus position when focusing at the center position and the boundary position;

[0013] Step 5, based on the phase difference of the focus deviation, taking the center position as the origin, estimating the phase difference caused by the skull in the area covered by the ultrasound probe, and adjusting the input of the ultrasound phase according to the estimated phase difference;

[0014] Step 6, using a magnetic resonance acoustic radiation force imaging sequence to detect the focus position of the ultrasound signal and determine whether it is focused on the target stimulation area;

[0015] Step 7: if the focus position is focused on the target stimulation area, end the focus shift; if the focus position is not focused on the target stimulation area, repeat steps 5-6 for iteration.

[0016] Preferably, in step 1, the boundary position includes four points selected respectively on the boundaries of the range capable of achieving focusing in four directions: up, down, left, and right.

[0017] Preferably, in step 2, the specific parameters of the three-dimensional magnetic resonance structural imaging data are set as: 3DT1 sequence, repetition time of 5~8ms, echo time of 2.5~4.5ms, flip time of 900 ms, flip angle of 10°, acquisition matrix of (225~256)×(225~256), number of layers of 160~256, intra-layer resolution of (0.8~1.2)mm×(0.8~1.2)mm, layer thickness of 0.8~1.2 mm, and sequence scanning time of 7~8 minutes.

[0018] Preferably, in step 3, the specific parameters of the ultrasonic signal emission are set as follows: ultrasonic fundamental frequency is 0.2-0.8 MHz, pulse time is 16-25 ms, pulse period is 0.8-1.2 s, stimulation duration is 0.8-5 s, stimulation interval is 0.8-5 s, sound pressure is ≤ 2 MPa, spatial peak pulse average sound intensity is ≤ 35 W, and spatial peak time average sound intensity is ≤ 700 mW / cm 2 , mechanical index ≤ 1.5;

[0019] The specific parameters of the MRI sequence scanning were set as follows: repetition time of 800-1200 ms, echo time of 40-50 ms, bandwidth of 120-150 Hz, flip angle of 90°, MEG of 65-85 mT, MEG duration of 12-17 ms, imaging field of view of (125-200) mm×(125-200) mm, scanning matrix of (64-96)×(64-96), intra-slice resolution of (2-3) mm×(2-3) mm, slice thickness of 3-6 mm, and sequence scanning time of 4-6 minutes.

[0020] Preferably, in step 3, the specific parameters of the ultrasonic signal emission are set as follows: ultrasonic fundamental frequency is 0.5 MHz, pulse time is 21.76 ms, pulse period is 1 s, stimulation duration is 1 s, stimulation interval is 1 s, sound pressure ≤ 2MPa, spatial peak pulse average sound intensity ≤ 35 W, empty peak time average sound intensity ≤ 700 mW / cm 2 , mechanical index ≤1.5;

[0021] The specific parameters of the MRI sequence scanning were set as follows: repetition time of 1000 ms, echo time of 45 ms, bandwidth of 130 Hz, flip angle of 90°, MEG of 75 mT, MEG duration of 15 ms, imaging field of view of 156 mm×156 mm, scanning matrix of 64×64, intra-slice resolution of 2.5 mm×2.5 mm, slice thickness of 5 mm, and sequence scanning time of 4 to 5 minutes.

[0022] Preferably, in step 3, the phase of each channel is determined in the following manner: the acoustic path difference from each array element of the ultrasound probe to a preset focus is calculated, and the emission delay time of each array element is determined according to the acoustic path difference and the speed of ultrasound in the tissue.

[0023] Preferably, in step 5, an inverse affine transformation is used to estimate the phase difference caused by the skull in the area covered by the ultrasound probe.

[0024] The present invention also provides a system for implementing the above-mentioned multi-element focused ultrasound focus shifting method, comprising:

[0025] An ultrasonic probe, used for transmitting ultrasonic signals;

[0026] A magnetic resonance acoustic radiation force imaging module, used for performing magnetic resonance acoustic radiation force imaging sequence scanning;

[0027] The focus correction module is used to adjust the input of the ultrasonic phase according to the above-mentioned multi-element focused ultrasonic focus shifting method to achieve focus correction.

[0028] Preferably, the ultrasound probe is selected from a 32-channel circular concave ultrasound probe.

[0029] The present invention also provides a computer-readable storage medium, on which is stored: a computer program for implementing the above-mentioned multi-element focused ultrasound focus shifting method, or a computer program for implementing the above-mentioned system.

[0030] The present invention constructs a new skull phase difference compensation technology in the field of transcranial focusing. The technology uses reference positioning points (i.e., center position and boundary position) to predict the actual skull phase difference to achieve the purpose of focus correction. The technology has fewer calibration times and does not require the participation of CT scanning. The entire process of ultrasound focus calibration is implemented in a magnetic resonance environment, thereby reducing the patient's radiation exposure and shortening the treatment process. In addition, the present invention uses iterative technology to achieve ultrasound calibration, which naturally has the disadvantage of compensating for the position offset caused by the patient's head movement during treatment. Therefore, the present invention has a good application prospect.

[0031] Obviously, according to the above contents of the present invention, in accordance with common technical knowledge and customary means in the art, without departing from the above basic technical ideas of the present invention, other various forms of modification, replacement or change may be made.

[0032] The above contents of the present invention are further described in detail below through specific implementation methods in the form of embodiments. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples. All technologies realized based on the above contents of the present invention belong to the scope of the present invention. DETAILED DESCRIPTION

[0033] It should be noted that the algorithms of data collection, transmission, storage and processing steps not specifically described in the embodiments, as well as the hardware structure, circuit connection, etc. not specifically described can all be implemented through the contents disclosed in the prior art.

[0034] Example 1 Multi-element focused ultrasound focus shifting method and system for neural regulation

[0035] The system of this embodiment is integrated into the existing transcranial magnetic resonance guided focused ultrasound device, which includes:

[0036] An ultrasonic probe, used for transmitting ultrasonic signals;

[0037] A magnetic resonance acoustic radiation force imaging module, used for performing magnetic resonance acoustic radiation force imaging sequence scanning;

[0038] The focus correction module is used to execute the multi-element focused ultrasound focus shifting method, adjust the ultrasound phase input, and realize focus correction.

[0039] In this embodiment, the ultrasonic probe is selected from a 32-channel circular concave ultrasonic probe.

[0040] The multi-element focused ultrasound focus shifting method comprises the following steps:

[0041] Step 1: In a pure water environment, measure the time delay of the input signal when the ultrasonic probe is focused at the center position and the boundary position, as the reference in the water environment, repeat 3 times for each reference point, and take the average value. In this way, the maximum effective range for linear focus shifting and the maximum time delay of the control pulse signal corresponding to the boundary position are obtained; as a preferred method, in this embodiment, the boundary position includes four points selected on the boundaries of the range that can achieve focusing in the four directions of up, down, left, and right.

[0042] In step 2, the subject lies flat on the MRI scanning bed with the RF receiving coil fixed on the outside of the head. The subject is sent into the center area of ​​the magnet to acquire three-dimensional MRI structural imaging data, determine the target stimulation area and the initial placement coordinates of the ultrasound probe; the specific parameters of the three-dimensional MRI structural imaging data are set as follows: 3DT1 sequence, repetition time of 7.2 ms, echo time of 3.1 ms, flip time of 900 ms, flip angle of 10°, acquisition matrix of 230×256, number of layers of 176, intra-layer resolution of 1 mm×1 mm, layer thickness of 1 mm, and sequence scanning time of 7 to 8 minutes.

[0043] Step 3, exit the magnetic resonance scanning bed, fix the ultrasound probe according to the marked position, and send the subject into the center area of ​​the magnet again. Perform magnetic resonance acoustic radiation force imaging sequence scanning and ultrasound signal emission simultaneously, in which the phase of each channel is emitted in sequence according to the maximum time delay of the control pulse signal corresponding to the boundary position determined in step 1; the phase of each channel is determined in the following manner: calculate the acoustic path difference from each array element of the ultrasound probe to the preset focus, and determine the emission delay time of each array element according to the acoustic path difference and the sound speed of ultrasound in the tissue.

[0044] The specific parameters of the transmitted ultrasonic signal were set as follows: ultrasonic fundamental frequency was 0.5 MHz, pulse time was 21.76 ms, pulse period was 1 s, stimulation duration was 1 s, stimulation interval was 1 s, sound pressure was ≤ 2 MPa, spatial peak pulse average sound intensity was ≤ 35 W, and spatial peak time average sound intensity was ≤ 700 mW / cm 2 , mechanical index ≤ 1.5;

[0045] The specific parameters of the MRI sequence scanning were set as follows: repetition time of 1000 ms, echo time of 45 ms, bandwidth of 130 Hz, flip angle of 90°, MEG of 75 mT, MEG duration of 15 ms, imaging field of view of 156 mm×156 mm, scanning matrix of 64×64, intra-slice resolution of 2.5 mm×2.5 mm, slice thickness of 5 mm, and sequence scanning time of 4 to 5 minutes.

[0046] Step 4, recording the focus deviation between the actual focus position and the theoretical focus position when focusing at the center position and the boundary position;

[0047] Step 5: Based on the phase difference caused by the focus deviation, taking the center position as the origin, an inverse affine transformation method is used to estimate the phase difference caused by the skull in the area covered by the ultrasound probe, and the ultrasound phase input is adjusted based on the estimated phase difference.

[0048] Specifically, the focus at the posterior center position and the boundary position (up, down, left, and right) of the skull may deviate. The five newly focused points generated by this deviation are in a linear affine transformation relationship with the five preset focuses in the uniform medium water. The so-called focus deviation (deviation in spatial position) can be obtained based on magnetic resonance acoustic radiation force imaging. According to the linear relationship, the target point is multiplied by the inverse matrix of the affine transformation to obtain the focus coordinates of the corresponding point when no distortion occurs. According to the acoustic path difference of the focus point of each array element and the sound speed of ultrasound in the tissue, the phase deviation is obtained. This phase deviation can be used to calculate the transmission delay time of each array element.

[0049] Step 6, using a magnetic resonance acoustic radiation force imaging sequence to detect the focal position of the ultrasound signal and determine whether it is focused on the target stimulation area;

[0050] Step 7, if the focus position is focused on the target stimulation area, end the focus shift; if the focus position is not focused on the target stimulation area, correct the affine transformation matrix according to the actual focus position, and repeat steps 5-6 for iteration.

[0051] By using the above method and system, the process of performing ultrasound focus correction in this embodiment has the following advantages:

[0052] 1. The purpose of focus correction is achieved without CT scanning, reducing the radiation exposure of patients;

[0053] 2. The whole process is carried out in a magnetic resonance environment, with fewer calibration times, thus shortening the treatment process;

[0054] 3. Step 7 is an iterative process that can eliminate positional deviations caused by patient head movement during long-term treatment.

[0055] Therefore, the multi-element focused ultrasound focus shifting method and system provided by the present invention have good application prospects in neural regulation.

Claims

1. A multi-element focused ultrasound focus shifting method, characterized in that: The steps include: Step 1, in a pure water environment, measuring the time delay of the input signal when the ultrasonic probe is focused at the center position and the boundary position, and obtaining the maximum effective range for linear focus shifting and the maximum time delay of the control pulse signal corresponding to the boundary position; Step 2, collecting three-dimensional magnetic resonance structural imaging data, determining the target stimulation area and the initial placement coordinates of the ultrasound probe; Step 3, synchronously performing magnetic resonance acoustic radiation force imaging sequence scanning and ultrasound signal transmission, wherein the phase of each channel of the ultrasound signal is transmitted in sequence according to the maximum time delay of the control pulse signal corresponding to the boundary position; Step 4, recording the focus deviation between the actual focus position and the theoretical focus position when focusing at the center position and the boundary position; Step 5, based on the phase difference of the focus deviation, taking the center position as the origin, estimating the phase difference caused by the skull in the area covered by the ultrasound probe, and adjusting the input of the ultrasound phase according to the estimated phase difference; Step 6, using a magnetic resonance acoustic radiation force imaging sequence to detect the focus position of the ultrasound signal and determine whether it is focused on the target stimulation area; Step 7, if the focus position is focused on the target stimulation area, the focus shifting is ended; If the focal position is not focused on the target stimulation area, repeat steps 5-6 for iteration; In step 5, an inverse affine transformation is used to estimate the phase difference caused by the skull in the area covered by the ultrasound probe; the inverse affine transformation specifically includes: the focus at the center position and the boundary position after the skull may deviate, and the five newly focused points generated by this deviation are in a linear affine transformation relationship with the five preset focal points in the uniform medium water; The focal deviation is obtained based on magnetic resonance acoustic radiation force imaging; based on the linear relationship, the target point is multiplied by the inverse matrix of the affine transformation to obtain the focal coordinates of the corresponding point when no distortion occurs; the phase deviation is obtained based on the acoustic path difference of the focal point of each array element and the sound speed of ultrasound in the tissue; this phase deviation is used to calculate the emission delay time of each array element to obtain the input of the adjusted ultrasound phase.

2. The multi-element focused ultrasound focus shifting method according to claim 1, characterized in that: In step 1, the boundary position includes four points selected respectively on the boundaries of the range in which focusing can be achieved in four directions: up, down, left, and right.

3. The multi-element focused ultrasound focus shifting method according to claim 1, characterized in that: In step 2, the specific parameters of the three-dimensional magnetic resonance structural imaging data were set as follows: 3DT1 sequence, repetition time of 5-8 ms, echo time of 2.5-4.5 ms, flip time of 900 ms, flip angle of 10°, acquisition matrix of (225-256) × (225-256), number of layers of 160-256, intra-layer resolution of (0.8-1.2) mm × (0.8-1.2) mm, layer thickness of 0.8-1.2 mm, and sequence scanning time of 7-8 minutes.

4. The multi-element focused ultrasound focus shifting method according to claim 1, characterized in that: In step 3, the specific parameters of the ultrasonic signal emission are set as follows: ultrasonic fundamental frequency is 0.2-0.8 MHz, pulse time is 16-25 ms, pulse period is 0.8-1.2 s, stimulation duration is 0.8-5 s, stimulation interval is 0.8-5 s, sound pressure is ≤ 2 MPa, spatial peak pulse average sound intensity is ≤ 35 W, and spatial peak time average sound intensity is ≤ 700 mW / cm 2 , mechanical index ≤ 1.5; The specific parameters of MR ARF sequence scanning were set as follows: repetition time of 800-1200 ms, echo time of 40-50 ms, bandwidth of 120-150 Hz, flip angle of 90°, MEG of 65-85 mT, MEG duration of 12-17 ms, imaging field of view of (125-200) mm×(125-200) mm, scanning matrix of (64-96)×(64-96), intra-slice resolution of (2-3) mm×(2-3) mm, slice thickness of 3-6 mm, and sequence scanning time of 4-6 minutes.

5. The multi-element focused ultrasound focus shifting method according to claim 1 or 4, characterized in that: In step 3, the specific parameters of the ultrasonic signal are set as follows: ultrasonic fundamental frequency is 0.5 MHz, pulse time is 21.76 ms, pulse period is 1 s, stimulation duration is 1 s, stimulation interval is 1 s, sound pressure ≤ 2 MPa, spatial peak pulse average sound intensity ≤ 35 W, and spatial peak time average sound intensity ≤ 700 mW / cm 2 , mechanical index ≤ 1.5; The specific parameters of the magnetic resonance acoustic radiation force imaging sequence scanning were set as follows: repetition time of 1000 ms, echo time of 45 ms, bandwidth of 130 Hz, flip angle of 90°, MEG of 75 mT, MEG duration of 15 ms, imaging field of view of 156 mm × 156 mm, scanning matrix of 64 × 64, intra-slice resolution of 2.5 mm × 2.5 mm, slice thickness of 5 mm, and sequence scanning time of 4 to 5 minutes.

6. The multi-element focused ultrasound focus shifting method according to claim 1, characterized in that: In step 3, the phase of each channel is determined in the following manner: the acoustic path difference from each array element of the ultrasound probe to the preset focus is calculated, and the transmission delay time of each array element is determined according to the acoustic path difference and the speed of ultrasound in the tissue.

7. A system for implementing the multi-element focused ultrasound focus shifting method according to any one of claims 1 to 6, characterized in that: include: An ultrasonic probe, used for transmitting ultrasonic signals; A magnetic resonance acoustic radiation force imaging module, used for performing magnetic resonance acoustic radiation force imaging sequence scanning; A focus correction module is used to adjust the input of the ultrasonic phase according to the multi-element focused ultrasound focus shifting method described in any one of claims 1 to 6 to achieve focus correction.

8. The system according to claim 7, characterized in that The ultrasonic probe is selected from a 32-channel circular concave ultrasonic probe.

9. A computer-readable storage medium, characterized in that: Stored thereon is: a computer program for implementing the multi-element focused ultrasound focus shifting method described in any one of claims 1-6, or a computer program for implementing the system described in claim 7 or 8.