Which type of implant poses a thermal risk to patients during MRI?

The correlation between long linear conductive objects and thermal risks during an MRI arises primarily from how these materials interact with radiofrequency (RF) fields. Long linear conductive objects, such as certain types of electrodes or wires, can act as antennas. When exposed to the RF energy during the MRI, these antennas can absorb and dissipate energy, leading to localized heating. This heating effect is what poses a thermal risk to patients, as it can potentially cause burns or overheating in sensitive tissue areas.

In contrast, the other options do not adequately represent a direct thermal risk. For example, saying that all can present thermal risk lacks specificity, as not all implants affect MRI safety in the same way. Objects outside the RF field typically do not interact with the RF energy and therefore would not create a thermal risk. Additionally, smaller objects, like those less than 2 cm, generally do not present significant heating effects simply due to their size and because they are often less conductive in a manner that contributes to thermal induction.

Thus, long linear conductive objects specifically present a unique risk due to their ability to enhance energy deposition during MRI, leading to overheating and possible thermal injury.