Forward active noise reduction circuit for gradient coil

Abstract

A forward 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. An input end of an amplifier PA1 receives an input signal, an output end of the amplifier PA1 is connected with one end of a secondary side of a current transformer Tc1, and an output end of the current transformer Tc1 is connected with the other end of the secondary side of the current transformer Tc1; the other end of the secondary side of the current transformer Tc1 is connected with one end of the gradient coil, and the other end of the gradient coil is connected with the grounding end of the amplifier PA1; effective components in driving current output by the gradient power amplifier are eliminated through the subtracter, the current transformer is coupled to the gradient coil, noise components in the driving current are counteracted, electromagnetic noise generated when the gradient power amplifier drives a high load is eliminated, noise reduction and suppression are carried out on the gradient coil, and the signal purity is improved. Therefore, the imaging resolution and the system reliability are improved.

Description

A forward active noise reduction circuit for gradient coils Technical Field

[0001] This utility model belongs to the field of MRI equipment technology and relates to a forward 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 gradient coils. The gradient coil is the core component of MRI spatial coding, achieving spatial coding by generating magnetic field gradients.

[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. Summary of the Invention

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

[0007] The forward active noise reduction unit includes amplifier PA1, amplifier PA2, current transformer Tc1, current transformer Tc2, resistor R1, and subtractor; the input terminal of amplifier PA1 receives the input signal, the output terminal of amplifier PA1 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 one end of gradient coil, and the other end of 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. The secondary side of current transformer Tc2 is connected in parallel with gradient coil.

[0009] Furthermore, the amplifier PA1 is a gradient power amplifier.

[0010] Furthermore, the amplifier PA2 is a current power amplifier.

[0011] The advantages of this utility model are:

[0012] This invention eliminates the effective component of the drive current output by the gradient power amplifier using a subtractor, and combines this with a current transformer coupled to the gradient coil to cancel out the noise component in the drive current. This eliminates the electromagnetic noise generated by the gradient power amplifier when driving high loads (such as gradient coils), thus reducing noise in the gradient coil and improving signal purity. This, in turn, improves imaging resolution and system reliability. Attached Figure Description

[0013] Figure 1 is a circuit structure diagram of a forward active noise reduction circuit for gradient coils 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] As shown in Figure 1, a forward active noise reduction circuit for a gradient coil is disclosed, including a forward active noise reduction unit and a gradient coil; the input terminal of the forward active noise reduction unit receives an input signal, and the output terminal of the forward active noise reduction unit is connected to the gradient coil.

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

[0019] 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. The secondary side of current transformer Tc2 is connected in parallel with gradient coil.

[0020] Furthermore, the amplifier PA1 is a gradient power amplifier. The amplifier PA1 amplifies the voltage input signal received at the input terminal and outputs a power current signal i1 that drives the gradient coil. i1 includes the effective driving current component and the noise current component output by the gradient power amplifier.

[0021] Furthermore, the current transformer Tc1 picks up the current signal i1 output by the primary side amplifier PA1, isolates it, and outputs it to the secondary side of the current transformer Tc1, where it is converted into a voltage signal v1 through resistor R1.

[0022] Furthermore, the positive input terminal of the subtractor receives the voltage signal v1, and the negative input terminal samples the input terminal of the amplifier PA1 to receive the voltage input signal v2. In this embodiment, through the operation v3 = v1 - v2 of the subtraction circuit, the effective driving current component contained in v1 is eliminated, leaving the voltage signal v3 that reflects the noise current component.

[0023] Furthermore, the amplifier PA2 is a current power amplifier. Amplifier PA2 amplifies the voltage signal v3 and outputs a drive current through amplifier PA2. This drive current is out of phase with the noise current component of i1.

[0024] 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 of amplifier PA2 and couples it to the gradient coil, which is equal in amplitude and opposite in direction to the power current signal i1 output by amplifier PA1, thus canceling out the noise current in i1.

[0025] Working principle:

[0026] First, amplifier PA1 amplifies the voltage input signal received at its input terminal and outputs a power current signal i1 that drives the gradient coil. i1 contains a mixed signal of effective current component and noise current. Current transformer Tc1 detects the output current of amplifier PA1 and converts it into a voltage signal v1 on the secondary side. Second, a subtractor is used to compare the mixed signal v1 containing effective current component and noise current with the sampled voltage input signal v2. The effective component is eliminated by the subtractor, and the pure noise signal v3 is extracted. Amplifier PA2 amplifies the pure noise signal v3 and outputs a current signal that is out of phase with the original noise. Finally, the current transformer Tc2 couples to the gradient coil to cancel the noise component in the output current of PA1.

[0027] 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, eliminating the electromagnetic noise generated by the gradient power amplifier when driving a high load (such as a gradient coil), effectively improving signal purity, and thus improving the performance of the gradient system and the imaging quality of the equipment.

[0028] 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. In contrast, the forward active noise reduction circuit provided in this invention can theoretically eliminate all noise and distortion. It is suitable for mobile and portable MRI systems and boasts advantages such as small size and low cost.

[0029] 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 forward active noise reduction circuit for gradient coils, characterized in that, The system includes a forward active noise cancellation unit and a gradient coil. The input terminal of the forward active noise cancellation unit receives the input signal, and its output terminal is connected to the gradient coil. The forward active noise cancellation unit includes amplifiers PA1 and PA2, a current transformer Tc1, a current transformer Tc2, a resistor R1, and a subtractor. The input terminal of amplifier PA1 receives the input signal, and its output terminal is connected to one end of the secondary winding of the current transformer Tc1. The other end of the secondary winding of the current transformer Tc1 is connected to one end of the gradient coil. The other end is connected to the ground terminal of amplifier PA1; the two ends of the primary side of the current transformer Tc1 are connected in parallel with resistor R1, one end of resistor R1 is connected to reference ground, the other end of resistor R1 is connected to the positive input terminal of subtractor, the input terminal of amplifier PA1 is connected to the negative input terminal of subtractor, the output terminal of 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, and the two ends of the secondary side of current transformer Tc2 are connected in parallel with gradient coil.

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

3. The forward active noise reduction circuit for gradient coils according to claim 1, characterized in that, The amplifier PA2 is a current power amplifier.

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