Development of New Gradient System – For Seamless Hardware Development

Motohiro Miura

Canon Medical Systems Corporation has recently developed a new in-house magnet, making it possible to produce the entire imaging system core components, including the gradient magnetic field and RF system. Therefore, we took this opportunity to review and redesign the architecture of the gradient magnetic field and static magnetic field.
In MRI systems, gradient coils are placed in an extremely large static magnetic field of 3T. Then, images with various contrasts can be obtained by switching several hundred amperes of current flowing through the gradient coils in several hundred microseconds based on pulse sequences for imaging.
As is known from the principle of a motor, when current is passed through a wire placed in a magnetic field, force is applied to the wire. If this force causes the wires to move, the movement will disrupt the gradient magnetic field and give damage to image quality. MRI systems have a gradient coil structure that eliminates this movement of the wires, but as can be observed from the acoustic noise during scanning, small movements still occur in the entire gradient coils. When this movement is transmitted to the magnet, it causes mechanical resonance, which leads to increased oscillation and acoustic noise in the entire magnetic system. The oscillation of the entire magnetic system causes a loss of image quality, especially for fast scanning sequences, and the increased acoustic noise directly impacts to patient comfort. Therefore, by reconsidering the support system for the gradient coil, we developed a new gradient magnetic field system called Cross-pattern Supported Gradient Coil (CSGC) that reduces the mechanical connection between the gradient coil and the magnet.

CSGC made it possible to reduce the transmission of oscillation to the magnet, and as a result, it suppressed the transmission of oscillation to the patient table. In addition, by optimizing the oscillation transmission to the magnet, the noise generated by the oscillation of the gradient coil being transmitted to the magnet was reduced, making it possible to reduce the scanning acoustic noise of the entire system. This new gradient system not only reduces oscillation and acoustic noise, but also improves the current sensitivity and reduces heat generation in the gradient coil, thereby improving the effective Gmax and effective slew rate (SR). Therefore, it is possible to realize sequences with shorter TE, resulting in improved image quality and an increase in the number of imaging slices for the same TR.
In addition, the effective Gmax and effective SR have also been improved by improving the gradient coil itself. Moreover, various other innovations have been added through collaboration between the gradient system engineers and magnet system engineers. This is because all of the main hardware is now collaboratively designed and developed in-house. Furthermore, we have worked closely with the magnetic field hardware team, RF hardware team, software team, and sequence development team, and we are proud to have created a 3T system that has been optimized for image quality, patient comfort, and various other aspects. Canon's engineers will continue to work collaboratively as one to provide systems that deliver satisfaction to staff and patients. //