A patient with a ferromagnetic aneurysm clip is scheduled for MRI. Which of the following is the PRIMARY safety concern?

Explanation

## Ferromagnetic Objects in MRI: Safety Hazards **Key Point:** Ferromagnetic objects (iron, cobalt, nickel) experience both **torque** (rotational force) and **translational force** (linear attraction) in the strong static magnetic field of an MRI scanner. For aneurysm clips, this poses a catastrophic risk of clip displacement or aneurysm rupture. ### Mechanism of Ferromagnetic Hazard 1. **Static field interaction:** The B₀ field exerts a force on ferromagnetic materials proportional to the field gradient and the object's magnetic susceptibility. 2. **Torque:** Ferromagnetic objects align with B₀, creating a rotational moment that can twist the clip. 3. **Translational force:** The field gradient pulls ferromagnetic objects toward the magnet bore (higher field region). 4. **Clinical consequence:** In an aneurysm clip, even small displacement can tear the vessel wall, causing catastrophic hemorrhage. ### Classification of Aneurysm Clips | Clip Type | Ferromagnetism | MRI Safe? | Notes | |-----------|----------------|-----------|-------| | **Titanium alloy** | Non-ferromagnetic | Yes | Preferred for MRI-compatible patients | | **Stainless steel (older)** | Ferromagnetic | No | Absolute contraindication | | **Cobalt-chromium** | Weakly ferromagnetic | Conditional | Depends on specific alloy and field strength | | **Platinum** | Non-ferromagnetic | Yes | Safe but less commonly used | **High-Yield:** Always obtain clip documentation (manufacturer, model, year) before MRI. If history is unknown, a non-contrast head CT or skull X-ray may help identify the clip type. ### Why Other Options Are Wrong - **RF heating:** While RF energy can cause heating, the primary acute danger is mechanical displacement. - **Electrical currents:** Ferromagnetic clips do not conduct electricity in a way that causes seizures; the mechanical force is the dominant hazard. - **Gadolinium toxicity:** Gadolinium does not accumulate preferentially in ferromagnetic clips. **Clinical Pearl:** Modern aneurysm clips are increasingly made of non-ferromagnetic titanium alloy, but older patients may have ferromagnetic stainless steel clips. Always verify clip safety status before proceeding with MRI.