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CN-121978601-A - Method and device for measuring and correcting rapid vortex field

CN121978601ACN 121978601 ACN121978601 ACN 121978601ACN-121978601-A

Abstract

The invention discloses a method for measuring and correcting a rapid vortex field, which comprises the steps of preliminarily designing the size of a probe according to a probe signal-to-noise ratio formula, calculating a corresponding signal-to-noise ratio, guiding parameter design of a subsequent vortex measuring sequence, ensuring that the interval of each sampling window in the subsequent vortex measuring sequence is larger than T1 and the length of each sampling window is smaller than T2 through relaxation information corresponding to a T1 and T2 quantitative image test solution, designing a positioning sequence, positioning the probe, measuring vortex by using the vortex field measuring sequence, fitting data by using a composite model, reconstructing the vortex field, and transmitting the data to a spectrometer system for compensation. The invention also discloses a device for measuring and correcting the rapid vortex field. The method greatly improves the eddy current measurement efficiency and the eddy current measurement accuracy, and provides a stable and effective method for rapid eddy current correction after the portable magnetic resonance reaches different scenes.

Inventors

  • DANG ZHAOZHAO
  • Chen Suen
  • YANG SHIWEI
  • LAI HAIFENG

Assignees

  • 上海智像医疗科技有限公司

Dates

Publication Date
20260505
Application Date
20260319

Claims (10)

  1. 1. A method for rapid vortex field measurement and correction comprising the steps of: Step 1, preliminarily designing the probe size according to a probe signal-to-noise ratio formula, calculating a corresponding signal-to-noise ratio, and guiding parameter design of a subsequent vortex measurement sequence, wherein through relaxation information corresponding to a T1 and T2 quantitative image test solution, the interval of each sampling window in the subsequent vortex measurement sequence is ensured to be larger than T1, and the length of the sampling window is smaller than T2; Step 2, designing a positioning sequence, and positioning the probe; step3, measuring vortex by using a vortex field measurement sequence; and 4, fitting the data through the composite model, reconstructing a vortex field, and sending the vortex field to a spectrometer system for compensation.
  2. 2. A rapid vortex field measurement and correction method according to claim 1 wherein the probe diameter size in step 1 covers 1mm to 10 mm in a portable low field.
  3. 3. A method for measuring and correcting a rapid vortex field according to claim 2, wherein the probe in the step 1 is spherical or cylindrical in shape, and is filled with a test solution without bubbles.
  4. 4. A rapid vortex field measurement and correction method according to claim 1, characterized in that step 2 comprises in particular the steps of: Sequentially climbing X, Y, Z gradients to a known non-zero gradient value, maintaining the length of 2-4 s, collecting probe signals at a time point after the gradients are stable, and converting the position of a field probe by using a formula (1) of the phase and the gradients; the method comprises the steps that a signal acquisition module without gradient is additionally added before each gradient, the phase of the signal acquisition module without gradient is subtracted from the phase obtained through calculation in the formula (1), and finally accurate probe position information of removing background phases containing non-uniform field information is obtained; (1) wherein phi represents the probe phase, gamma represents the magnetic rotation ratio, G represents the non-zero gradient value, R represents the probe position, t represents the probe receiving opening and gradient acting time, Representing a background field containing non-uniform field information.
  5. 5. The method of claim 4, wherein the eddy current measuring sequence in step 3 is composed of a large gradient of induced eddy current followed by a series of probe signal acquisition modules composed of excitation pulses and spectrometer receiving modules, and the time from the probe signal acquisition module to the introduction of the large gradient of eddy current is sequentially changed.
  6. 6. A rapid vortex field measurement and correction method according to claim 5 wherein the probe signal acquisition module time to the large gradient of induced vortex is varied with linear time intervals or with exponential time intervals, covering any time from 0.5 ms to 10 s.
  7. 7. A method of measuring and correcting a fast vortex field as defined in claim 6 wherein the large gradient of induced vortex flow includes three combinations, one positive gradient and one zero gradient, two positive polarity different magnitude gradients and two negative polarity different magnitude gradients.
  8. 8. A rapid vortex field measurement and correction method according to claim 7, characterized in that step 4 comprises in particular the steps of: step 4.1, calculating the position information of the probe according to the corresponding basis of the spherical harmonic space function by using a formula (2) to obtain corresponding parameters; (2) Wherein R is the coordinate of each probe corresponding to the spherical harmonic space base, R' represents the total position matrix of the probe, x, y, z, m represents the coordinate of the probe in x, y and z axes and the number of the probes respectively; Step 4.2, solving the relation between the phase information phi of each probe and the vortex field by utilizing formulas (3) to (5), wherein the phase phi of each probe comprises position and time information, dividing the field generating probe signals into a zero-order vortex field B e and first-order and higher-order vortex fields R.K, K which are first-order and higher-order spatial distribution coefficients representing the vortex fields, deriving the phase information, fitting by adopting an exponential model in a short-time vortex part, fitting by adopting a linear model in a long-time vortex part larger than 1s, improving the calculation efficiency, and obtaining a time-varying model of the spatial distribution coefficients of the vortex fields; (3) (4) (5) Where τ represents time, Φ + is the phase information generated by the first gradient in the large gradient of the introduced vortex, Φ ref is the phase information generated by the second gradient in the large gradient of the introduced vortex, Φ R is the phase information at the probe placement position; Step 4.3, calculating a vortex field by using the formula (6) and combining the probe position R; (6) Wherein G e represents the vortex field; Step 4.4, fitting the obtained amplitude and time constant into a spectrometer by using a formula (7) vortex field to form an exponential sum; (7) y denotes the vortex field, τ i denotes the vortex time constant, and a i denotes the amplitude corresponding to each vortex time constant.
  9. 9. The rapid vortex field measurement and correction device is characterized by comprising a radio frequency power amplifier, a power divider, a control module or spectrometer containing an FPGA, a transceiver switch, a low noise amplifier and a field probe array consisting of a plurality of probes, wherein the radio frequency power amplifier is configured to amplify a transmission pulse to a required power value, an output pulse signal is connected to the power divider, and the power divider equally divides excitation pulse power into the transceiver switches corresponding to the probes; the size of the probe is optimized by combining the measured vortex field size under the guidance of a signal-to-noise ratio and field measurement resolution formula (8); (8) where SNR represents the signal-to-noise ratio, V sample represents the volume of solution inside the probe, B 0 represents the main magnetic field, and BW represents the sequence receiving bandwidth.
  10. 10. The rapid vortex field measurement and correction device according to claim 9, further comprising a probe positioning module and a vortex generation module, wherein the probe positioning module comprises a B0 field reference module without gradient and with only a sampling window, the reference module outputs background phase information including B0 field, the vortex generation module comprises a gradient module with same polarity, and the gradient module with same polarity comprises three combination modes, namely a combination of positive gradient and zero gradient, a combination of two gradients with different magnitudes with same positive polarity, and a combination of two gradients with different magnitudes with same negative polarity.

Description

Method and device for measuring and correcting rapid vortex field Technical Field The invention relates to the technical field of low-field magnetic resonance imaging, in particular to a method and a device for measuring and correcting a rapid vortex field. Background Magnetic resonance imaging (Magnetic Resonance Imaging, MRI) is a non-contact, noninvasive, non-radiative medical imaging technique capable of providing high-resolution soft tissue images, and can provide a multi-contrast structure through various sequence designs and parameter selections, thereby providing a more accurate and rich basis for clinical disease diagnosis. With the development of magnetic resonance technology, portable low-field MRI apparatuses based on smaller volumes of permanent magnets and lower costs are getting more attention from researchers with related technologies. The MRI device has the characteristics of low cost and convenient use, and promotes the popularization and development of MRI equipment to basic medical institutions and more flexible and diverse application scenes. However, permanent magnet-based portable low-field MRI systems are more susceptible to interference from eddy current artifacts, mainly due to the large amount of conductive material in the permanent magnet MRI system that approximates the imaging region. Meanwhile, since the portable magnetic resonance has various application scenes and it may be required to rapidly complete correction and scanning in one scene. Therefore, the search for a rapid and effective eddy current measurement and correction method is of great significance in improving image quality and diagnostic accuracy. Currently, eddy current measurement methods can be largely divided into three types of methods, artifact-mitigating imaging sequence design, image phase measurement-based and external sensor-based methods. The artifact mitigation sequence reduces the accumulated additional eddy current phase or measures the corresponding eddy current phase to compensate by optimizing the gradient design or adding a phase navigation module, but often at the cost of reducing the time resolution, and possibly introducing new artifact types. Phase measurement based on images is a relatively easy way to implement, often requiring only one uniform spherical water mold to start eddy current measurement. However, this approach requires high signal-to-noise ratio and field uniformity. There are limitations in the application of portable permanent magnet low-field MRI in that the measurement time is long and the effectiveness of the result is reduced. External sensor based approaches often require additional spatial registration and high requirements for magnetic compatibility, long installation times and cumbersome use. In 2008, de Zanche et al proposed a field probe technique based on nuclear magnetic resonance (Nuclear Magnetic Resonance, NMR). By means of the miniature field probe array with miniature coil and water model, and combining with eddy current measuring sequence, fast eddy current field distribution measurement can be realized. Compared with the traditional vortex measuring method, the method has the advantages of time synchronization and quick positioning, and has high vortex measuring efficiency. Meanwhile, the related technology can be expanded to high-order vortex field measurement and real-time phase monitoring, and has high application expansibility. The application of the method in low fields is helpful for improving the efficiency of vortex field measurement and provides a brand new idea for solving the problem of low field correction slowness. The prior art mainly has the following problems: 1. The existing portable low-field MRI system based on the permanent magnet is easy to be interfered by a larger vortex field, the generated artifact seriously reduces the image quality, and an advanced functional MRI sequence such as a rapid Diffusion WEIGHTED IMAGING, DWI cannot be realized, so that the clinical application value of the system is reduced. Whereas the most commonly used image phase based eddy current measurements in low fields tend to take up to several hours due to limitations in signal-to-noise ratio and the need for assisted localization of the encoding gradient. However, since portable MRI is not equipped with a temperature control system, long scans can cause changes in magnet temperature, which in turn affects the main magnetic field frequency and eddy current fields in the system. In addition, the accuracy of the eddy current measurement results is reduced and the eddy current correction effect is reduced due to the influence of extra eddy currents introduced by the encoding gradients in the eddy current scanning sequence. 2. Current field probes are designed for low temperature superconducting high field magnetic resonance systems and cannot work in low field MRI. 3. The current field probe measurement method is not suitable for the characteristics of non-unifo