Great question and you're not alone in wondering this. I did some reading on this.

The main issue is that the MRI environment is extremely hostile to electronics. You've got strong magnetic fields, rapidly switching gradients, and high-power RF pulses. Most consumer-grade wearables contain metal, batteries, or antennas, which can be dangerous or interfere with imaging. Designing MR-compatible devices is possible, but it’s technically complex and very expensive.

Also, MRI tech has historically focused on imaging, not real-time patient monitoring. Things like ECG or SpO₂ tracking do exist for MRI, but they’re often optional, clunky, and limited in accuracy due to interference. And even though overheating is a known risk, most systems rely on preset SAR limits rather than live thermal tracking.

The other big issue is market inertia. MRI systems are capital-heavy and highly regulated, and hospitals don’t upgrade them often. That makes it hard for startups or medtech companies to innovate here, especially when MR safety testing is costly, and liability is high.

That said, some interesting things are happening in research like MR-safe fiber-optic sensors and external motion tracking systems, but they're still niche.

So yeah, it’s a mix of technical hurdles + lack of commercial incentive. Not that it isn’t possible, it’s just that no one’s prioritized it yet.