Backward active noise reduction circuit for gradient coil

Abstract

A backward active noise reduction circuit for a gradient coil belongs to the technical field of MRI (magnetic resonance imaging) equipment and solves the problem of how to reduce electromagnetic noise in gradient coil current and improve imaging quality. One end of the gradient coil is connected with one end of a secondary side of a current transformer Tc1, and the other end of the secondary side of the current transformer Tc1 is connected with an output end of an amplifier PA1; the other end of the gradient coil is connected with the grounding end of the amplifier PA1; effective components in driving current of the gradient coil are eliminated through the subtracter, the current transformer is coupled to the output end of the gradient power amplifier, noise components in the driving current are counteracted in the output end of the power amplifier and an output loop, noise reduction and suppression are carried out on the gradient coil, and the signal purity is improved. The system is suitable for mobile and portable MRI (Magnetic Resonance Imaging) systems, and has the advantages of small size and low cost.

Description

Technical Field

[0001] This utility model belongs to the field of MRI equipment technology and relates to a backward active noise reduction circuit for gradient coils. Background Technology

[0002] The gradient system plays a crucial role in MRI equipment. It consists of several key components working together, including a gradient waveform generator, a gradient controller, a gradient amplifier, and a gradient coil. The gradient coil is the core component of MRI spatial coding, achieving spatial coding by generating a magnetic field gradient.

[0003] According to the principle of electromagnetic induction, when a rapidly changing current is applied to a gradient coil placed in a strong static magnetic field, it experiences a Lorentz force, causing minute mechanical deformation and high-speed vibration in the coil structure. These vibrations are transmitted through the coil fixing device and equipment structure, ultimately radiating out as sound waves, forming the main noise heard during the examination. For example, utility model patent CN213758224U discloses a medical MRI noise reduction structure that uses a first buffer layer to buffer the vibration of the gradient coil, reducing the noise generated by the gradient coil during vibration. The first noise reduction layer weakens the noise, reducing the intensity of the noise transmitted from the inner shell layer and minimizing noise interference to the patient. Existing noise reduction methods for gradient systems mainly reduce the mechanical vibration generated by the equipment by setting sound insulation layers, buffer layers, or sound-absorbing holes. However, these methods do not consider the electromagnetic noise contained in the driving current of the gradient coil inside the gradient system. This electromagnetic noise can couple into the radio frequency coil through the gradient coil, leading to degradation of MRI image quality and poor equipment imaging quality. Utility Model Content

[0004] The technical solution of this utility model is used to solve the problem of how to reduce electromagnetic noise in gradient coil current and improve imaging quality.

[0005] This utility model solves the above-mentioned technical problems through the following technical solution:

[0006] A backward active noise reduction circuit for a gradient coil includes a backward active noise reduction unit and a gradient coil; the input terminal of the backward active noise reduction unit receives an input signal, and the output terminal of the backward active noise reduction unit is connected to the gradient coil.

[0007] The backward active noise reduction unit includes amplifier PA1, amplifier PA2, current transformer Tc1, current transformer Tc2, resistor R1, and subtractor; one end of the gradient coil is connected to one end of the secondary side of current transformer Tc1, the other end of the secondary side of current transformer Tc1 is connected to the output terminal of amplifier PA1, and the other end of the gradient coil is connected to the ground terminal of amplifier PA1.

[0008] The primary side of the current transformer Tc1 is connected in parallel with resistor R1. One end of resistor R1 is connected to reference ground, and the other end of resistor R1 is connected to the positive input terminal of the subtractor. The input terminal of amplifier PA1 is connected to the negative input terminal of the subtractor. The output terminal of the subtractor is connected to the input terminal of amplifier PA2. The output terminal of amplifier PA2 is connected to one end of the primary side of current transformer Tc2. The other end of the primary side of current transformer Tc2 is connected to reference ground. One end of the secondary side of current transformer Tc2 is connected to the output terminal of amplifier PA1. The other end of the secondary side of current transformer Tc2 is connected to the ground terminal of amplifier PA1.

[0009] Furthermore, the amplifier PA2 includes an error amplifier and a current power amplifier; the input terminal of the error amplifier is connected to the output terminal of the subtractor, the output terminal of the error amplifier is connected to the input terminal of the current power amplifier, and the output terminal of the current power amplifier is connected to one end of the primary side of the current transformer Tc2.

[0010] Furthermore, the amplifier PA1 is a gradient power amplifier.

[0011] The advantages of this utility model are:

[0012] This invention eliminates the effective component of the drive current of the gradient coil using a subtractor, and combines this with a current transformer coupled to the output of the gradient power amplifier. This cancels out the noise component in the drive current at the power amplifier output and in the output circuit, thus suppressing noise in the gradient coil and improving signal purity. This, in turn, improves imaging resolution and system reliability. It is suitable for mobile and portable MRI systems and has the advantages of small size and low cost. Attached Figure Description

[0013] Figure 1 This is a circuit structure diagram of a backward active noise reduction circuit for a gradient coil according to Embodiment 1 of this utility model. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below in conjunction with the embodiments of this utility model. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0015] The technical solution of this utility model will be further described below with reference to the accompanying drawings and specific embodiments:

[0016] Example 1

[0017] like Figure 1 As shown, specifically, a backward active noise reduction circuit for a gradient coil is disclosed, including a backward active noise reduction unit and a gradient coil; the input terminal of the backward active noise reduction unit receives an input signal, and the output terminal of the backward active noise reduction unit is connected to the gradient coil.

[0018] The backward active noise reduction unit includes amplifier PA1, amplifier PA2, current transformer Tc1, current transformer Tc2, resistor R1, and subtractor; one end of the gradient coil is connected to one end of the primary side of the current transformer Tc1, the other end of the primary side of the current transformer Tc1 is connected to the output terminal of amplifier PA1, and the other end of the gradient coil is connected to the ground terminal of amplifier PA1.

[0019] The secondary side of the current transformer Tc1 is connected in parallel with resistor R1. One end of resistor R1 is connected to reference ground, and the other end of resistor R1 is connected to the positive input terminal of the subtractor. The input terminal of amplifier PA1 is connected to the negative input terminal of the subtractor. The output terminal of the subtractor is connected to the input terminal of amplifier PA2. The output terminal of amplifier PA2 is connected to one end of the primary side of current transformer Tc2. The other end of the primary side of current transformer Tc2 is connected to reference ground. One end of the secondary side of current transformer Tc2 is connected to the output terminal of amplifier PA1. The other end of the secondary side of current transformer Tc2 is connected to the ground terminal of amplifier PA1.

[0020] Furthermore, the amplifier PA1 is a gradient power amplifier. Amplifier PA1 amplifies the voltage input signal received at its input terminal and outputs a power current signal to drive the gradient coil. , It includes the effective drive current component and the noise current component of the gradient power amplifier output.

[0021] Furthermore, the current transformer Tc1 picks up the drive current signal from one side of the gradient coil on its primary side, isolates and outputs it to the secondary side of the current transformer Tc1, and converts it into a voltage signal through resistor R1. .

[0022] Furthermore, the positive input terminal of the subtractor receives a voltage signal. The negative input terminal samples the input terminal of amplifier PA1 to receive the voltage input signal. In this embodiment, the subtraction circuit performs the operation. Eliminated The effective drive current component contained therein leaves a voltage signal that reflects the noise current component. .

[0023] Furthermore, the amplifier PA2 includes an error amplifier and a current power amplifier (not shown in the figure); the input terminal of the error amplifier is connected to the output terminal of the subtractor, the output terminal of the error amplifier is connected to the input terminal of the current power amplifier, and the output terminal of the current power amplifier is connected to one end of the primary side of the current transformer Tc2.

[0024] In this embodiment, the error amplifier converts the voltage signal containing noise current components into voltage signals. Amplified, and then output as a drive current through a current power amplifier, this drive current is related to... The noise current component is out of phase.

[0025] Furthermore, the current transformer Tc2 is used to convert the large current signal into a smaller, measurable current signal while providing electrical isolation. The current transformer Tc2 isolates the current output from amplifier PA2 and couples it to the gradient coil, which in turn couples it to the power current signal output from amplifier PA1. Equal amplitude and opposite direction will cancel each other out. Noise current in the middle.

[0026] Working principle:

[0027] First, amplifier PA1 amplifies the voltage input signal received at its input terminal and outputs the power current signal that drives the gradient coil. , The mixed signal, containing both effective current and noise current, is directly detected by the current transformer Tc1 on the output gradient coil side, and converted into a voltage signal on the secondary side. Secondly, a subtractor is used to compare the mixed signal containing both effective current components and noise current. Sampling of voltage input signal The effective components are eliminated by a subtractor to extract the pure noise signal. The error amplification stage of amplifier PA2 will convert the pure noise signal The signal is amplified to enhance the amplification accuracy of the noise signal. Then, a reverse compensation current is generated through a current amplifier to output a current signal that is out of phase with the original noise. Finally, the signal is coupled to the output of amplifier PA1 through current transformer Tc2 to cancel the noise component in the output current of PA1.

[0028] Active noise reduction is a technique that reduces or eliminates noise by generating a signal wave with the opposite phase and equal amplitude to the noise. Since the gradient coil is only a component that converts current into a magnetic field, it cannot reduce noise on its own. Most of the noise comes from the gradient power amplifier itself, and the noise and distortion generated by the gradient power amplifier are random or complex. Therefore, by acquiring noise and distortion in real time and using another low-power, low-noise, low-distortion auxiliary power amplifier to cancel these noise and distortion, this invention uses a subtraction circuit combined with a current transformer to cancel the noise component in the current, thereby achieving active noise reduction. It eliminates electromagnetic noise at the power amplifier output and in the output circuit, effectively improving signal purity, and thus improving the performance of the gradient system and the imaging quality of the equipment.

[0029] Traditional gradient systems often rely on filters for noise isolation. However, filters are bulky, heavy, and expensive. Furthermore, filters can only filter out noise in specific frequency bands, limiting their noise suppression capabilities. Excessive filtering can also distort the gradient signal. The backward active noise reduction circuit provided in this invention, on the other hand, essentially performs further cancellation and correction based on the residual error after cancellation. Theoretically, it can eliminate all noise and distortion, making it suitable for mobile and portable MRI systems. It also boasts advantages such as small size and low cost.

[0030] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A backward active noise reduction circuit for gradient coils, characterized in that, It includes a backward active noise reduction unit and a gradient coil; the input terminal of the backward active noise reduction unit receives the input signal, and the output terminal of the backward active noise reduction unit is connected to the gradient coil. The backward active noise reduction unit includes amplifier PA1, amplifier PA2, current transformer Tc1, current transformer Tc2, resistor R1, and subtractor; one end of the gradient coil is connected to one end of the secondary side of current transformer Tc1, the other end of the secondary side of current transformer Tc1 is connected to the output terminal of amplifier PA1, and the other end of the gradient coil is connected to the ground terminal of amplifier PA1. The primary side of the current transformer Tc1 is connected in parallel with resistor R1. One end of resistor R1 is connected to reference ground, and the other end of resistor R1 is connected to the positive input terminal of the subtractor. The input terminal of amplifier PA1 is connected to the negative input terminal of the subtractor. The output terminal of the subtractor is connected to the input terminal of amplifier PA2. The output terminal of amplifier PA2 is connected to one end of the primary side of current transformer Tc2. The other end of the primary side of current transformer Tc2 is connected to reference ground. One end of the secondary side of current transformer Tc2 is connected to the output terminal of amplifier PA1. The other end of the secondary side of current transformer Tc2 is connected to the ground terminal of amplifier PA1.

2. The backward active noise reduction circuit for gradient coils according to claim 1, characterized in that, The amplifier PA2 includes an error amplifier and a current power amplifier; the input terminal of the error amplifier is connected to the output terminal of the subtractor, the output terminal of the error amplifier is connected to the input terminal of the current power amplifier, and the output terminal of the current power amplifier is connected to one end of the primary side of the current transformer Tc2.

3. The backward active noise reduction circuit for gradient coils according to claim 1, characterized in that, The amplifier PA1 is a gradient power amplifier.

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