APPLICATION

Magnetic Resonance Imaging (MRI) Equipment

The output feedback of high-precision current transducer in MRI imaging equipment can control the precise phase of the gradient amplifier in real time, which is the basis of the whole system.


Magnetic resonance imaging is a relatively new medical imaging technology, and it was officially used clinically since 1982. It uses a static magnetic field and a radio frequency magnetic field to image human tissues. In the imaging process, high-contrast, clear images can be obtained without using electron-emitting radiation or contrast agents. It can reflect the abnormalities and early lesions of human organs from the inside of human molecules.


In an MRI system, a gradient amplifier unit refers to all circuit units associated with a gradient magnetic field. It is used to provide the system with a gradient field which meet the linear requirements and can be quickly switched.


The linearity of the gradient coil is an indicator of the gradient field stability. The better the linearity, the more accurate the gradient field is, and the better the image quality is. If the gradient field is not linear, the spatial and intensity distortions may appear on the edge of the image. Therefore, the gradient amplifier unit is one of the core components of the MRI apparatus.

Gradient magnetic field is generated by the gradient current along the axial direction, and its performance indicators are mainly effective solution, linearity, gradient field strength, gradient field rate, gradient field crawl time and so on. In order to generate gradient signals along the axial direction, the system requires several pairs of current coils. Current direction is reversed in each pair of coils, as shown in the following figure:  


In fact, three pairs of gradient coils are located inside the cavity of an MRI device to generate three orthogonal magnetic fields. Therefore, the magnetic field can be adjusted anywhere in the wall. A gradient amplifier operating in a closed servo loop drives the current in the gradient coil (as shown below). Therefore, three such current control loops are required for each MRI.



Gradient coil current control loop


The output feedback from the current transducer can control the precise phase of the gradient amplifier in real time, which is the basis of the entire system. From the MRI principle outlined in the figure above, it can be seen that the quality, sharpness and resolution of the image are directly related to the magnetic field generated by the current through the gradient coil. Therefore, the accuracy of the current transducer is one of the most critical factors in determining the current control loop.

It is particularly important to note that the following key parameters must be met when using current transducers:
· 1ppm non-linear error
· -40 - 85°C Operating Temperature Range
 ·  <<0.1ppm / K temperature drift
· Very high time stability (caused by the duration of the MRI scan, which may last for tens of minutes)
· Up to 1000A peak current
 · 3dB bandwidth above 400KHz

OurAIT1000-SGhigh-precision current transducer is a multi-point zero flux closed loop transducer, which can perfectly meet the above requirements of these performance indicators.


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