Where is the likelihood of PNS highest?

The likelihood of peripheral nerve stimulation (PNS) is highest near the individual gradient coil of wire that is activated due to the way gradient systems work in magnetic resonance imaging (MRI). When the gradients are engaged, they generate rapidly changing magnetic fields. These changing fields induce electrical currents in nearby conductive tissues, including peripheral nerves.

As the gradient coils are positioned around the area being imaged, the strongest changes in the magnetic field and, consequently, the highest potential for induced currents are found directly near these coils. Therefore, when specific coils are activated, they can produce enough magnetic field strength rapidly enough to stimulate nearby nerves, which can lead to sensations such as tingling or warmth.

In contrast, locations such as the control room or areas outside the gantry experience significantly weaker magnetic fields as the distance from the source increases. The isocenter, while crucial for imaging, is typically a point where the gradients are balanced, meaning the PNS risk would not be as high as it would be near the active coils.