Why EMC is a Core Technology for MRI Scanners

First, Advancing Towards High Reliability

The EMC application challenges of MRI scanners. As a core device in modern medical diagnostics, the internal electromagnetic environment of a Magnetic Resonance Imaging (MRI) scanner is far more complex than that of ordinary electronic equipment. The system integrates a high-power RF transmission chain, a high-sensitivity reception chain, a high-current gradient coil driver, and a precise superconducting magnet control system. These subsystems operate in synergy within a confined space, each acting as both a potent source of electromagnetic interference and a highly susceptible unit. For instance, transient magnetic field changes generated by the rapid switching of gradient coils can interfere with the preamplifiers of adjacent receiver coils via spatial coupling or conduction paths, leading to a decrease in image signal-to-noise ratio or even the appearance of artifacts. Simultaneously, MRI equipment must comply with stringent medical safety and electromagnetic compatibility standards, such as IEC 60601-1-2, which imposes rigorous requirements on the radiated emissions and immunity of medical devices. Therefore, the EMC design of an MRI scanner is not merely a compliance test; it is a core technical barrier directly related to the device's imaging quality, operational stability, and patient safety.

Second, EMC/ESD Challenges Faced by R&D Engineers

The EMC challenges of an MRI system are multidimensional and intertwined. In the transmission chain, harmonics and spurious signals generated by high-power RF amplifiers can interfere with the device's own reception channels and even affect other electronic equipment in the same medical environment. In the reception chain, the front-end low-noise amplifier (LNA) amplifies microvolt-level nuclear magnetic resonance signals; any noise coupling from the power supply, digital circuits, or space can lead to signal distortion. The fast dV/dt and dI/dt generated by the gradient driver power supply can cause severe conducted and radiated emission issues. More critically, the device contains various interfaces, such as coil connectors, control signal interfaces, sensor interfaces, and DC/AC power lines supplying the submodules. These interfaces are vulnerable points for the intrusion of transient disturbances like ESD (electrostatic discharge) and surges. An inadvertent ESD event, coupled through data or power lines, can damage sensitive ADCs (analog-to-digital converters) or control logic chips, leading to system crashes or performance degradation. Furthermore, the signal integrity of safety-critical circuits, such as quench detection for the superconducting magnet and liquid helium level/temperature monitoring, must be absolutely guaranteed. Any interference may trigger false alarms or mask real faults, posing safety risks.

Third, Designing Efficient Circuit Protection Solutions

Given the specificities of MRI systems, their EMC protection must adopt a systematic, layered, and zoned strategy. The core concept is to insert protective devices at key nodes along the interference propagation path, establishing a defense-in-depth system from the port to the chip level. For the RF transmission and reception channels, the focus is on selecting protection devices with ultra-low capacitance and high power handling capacity. These must shunt transient high currents while minimizing impact on GHz-level operating signals to ensure signal integrity. For high-power analog circuits like gradient coil drivers and magnet power supplies, the protection focus shifts to suppressing their generated conducted noise and protecting their control ends from back-fed interference. This typically involves deploying surge protection devices (TVS or GDT) with high energy absorption capabilities at the power entry points. For various low-frequency control, sensing, and data interfaces—such as quench detection, temperature monitoring, and CAN bus communication—it is necessary to carefully select ESD protection devices with low clamping voltage based on signal voltage, speed, and wiring environment. This ensures fast response and precise clamping to prevent overvoltage damage to downstream ICs. Reasonable PCB layout and grounding design, combined with appropriate filtering and shielding, form the foundation for effective protection. The selection of protection devices must be co-optimized with the circuit topology and component layout to form a complete noise suppression and energy discharge path.

Fourth, Practical Selection Guide

Based on the aforementioned protection strategies, YINT Electronics provides validated, high-reliability solutions for several typical and critical protection scenarios within MRI systems. These solutions precisely match the medical equipment industry's demand for long-term stability and ultimate safety. For the widely present CAN bus network within the system, used for transmitting control commands and status information, YINT Electronics recommends the CML4532A-510T common mode choke paired with the ESDLC3V3D3B TVS array. This combination effectively suppresses common-mode noise on the bus and provides symmetrical ESD protection with less than 5pF capacitance for the CAN-H and CAN-L line pair, ensuring reliable communication even in complex electromagnetic environments. For the 24V DC power ports supplying gradient amplifiers and electronic modules within the control cabinet, which face dual surge threats from the grid and the load side, it is recommended to use a protection combination consisting of the PBZ series (e.g., PBZ2012E600Z0T) high-current power bead and the 5.0SMDJ24CA TVS diode. The bead filters high-frequency noise on the power line, while the TVS diode can absorb surge energy up to several thousand joules, clamping the voltage to a safe range and protecting the expensive downstream power devices and controllers. For potential USB Type-C interfaces on the device used for data transfer or debugging, whose high-speed data lines have stringent signal integrity requirements, the recommendation is to use the CMZ20212A-900T ultra-miniature common mode choke and the ESDLC5V0D3B multi-channel TVS protector. This common mode choke maintains excellent common-mode rejection characteristics up to 10GHz, while the TVS protector features an extremely low load capacitance of only 0.5pF, ensuring unimpeded data transmission at USB 3.0 and higher speeds while providing contact discharge protection capability up to 30kV. Additionally, for lightning surge protection at the AC 220V main power input, YINT Electronics offers solutions such as a combination of a 14D101K Gas Discharge Tube (GDT) and a Metal Oxide Varistor (MOV), capable of withstanding standard-defined differential-mode and common-mode surge impacts, laying the foundation for the power supply safety of the entire MRI system.

Fifth, Summary and Recommendations

The electromagnetic compatibility design of a Magnetic Resonance Imaging (MRI) scanner is a systematic engineering task that runs throughout the entire device development process. Engineers need to fully consider EMC issues from the initial architectural design phase, adopting a "combination of blocking and channeling" approach: suppressing interference sources, cutting off propagation paths, and protecting sensitive circuits. In component selection, priority should be given to brands like YINT Electronics, which specialize in the circuit protection field, offer a complete product line, and whose parameters are validated in harsh medical environments. Their comprehensive range of protection devices—covering signals to power, low frequency to RF, and ESD to surges—can help R&D teams quickly establish a robust protection network. Ultimately, an excellent MRI EMC design achieves the optimal balance between image quality, system stability, and long-term operational reliability while meeting mandatory standards like IEC 60601-1-2. This requires hardware engineers to not only have a deep understanding of circuit principles but also to master the coupling mechanisms of electromagnetic interference and the characteristics of protection devices, thereby making precise design decisions.

References: IEC 60601-1, IEC 60601-1-2