Categories: MRI Techs

The Deep Chill: Why MRI Machines Need Liquid Helium

When you walk into an MRI suite, you’re not just looking at a medical camera—you’re looking at one of the most incredible engineering feats in a modern hospital. At the heart of every MRI is a magnet so powerful it could easily lift a car, but keeping that magnet running requires a temperature colder than the surface of Pluto.

This is where liquid helium comes in. To keep the machine functioning, the magnet must stay in a state of superconductivity. Here is a look behind the scenes at the fascinating relationship between extreme cold and life-saving technology.

1. The “Thermos within a Thermos” (The Cryostat)

You might imagine helium floating around the room, but it is actually sealed away in a very specific place. The magnetic coils are housed inside a massive, vacuum-sealed, multi-layered stainless steel container called a cryostat.

Submerged Science: The magnet doesn’t just sit near the helium; it is directly submerged in it.
Extreme Insulation: The cryostat acts like a high-tech thermos. It uses multiple vacuum layers to prevent even a tiny bit of outside heat from reaching the liquid inside.

2. The Great Expansion: From Liquid to Gas

Helium is used because it has the lowest boiling point of any element on Earth. However, it is very “restless”—it wants to turn back into a gas the moment it warms up even slightly.

The 700-to-1 Rule: When helium warms up and turns to gas, it expands at a staggering ratio of 700 to 1. One liter of liquid helium suddenly becomes 700 liters of gas.
The Quench Pipe: This is why MRI rooms have massive pipes leading through the ceiling to the roof. If the magnet ever loses its chill, these “quench pipes” safely vent the rapidly expanding gas outside the building.

3. “Zero Boil-Off” Magic

In the early days of MRI technology, hospitals had to refill their helium constantly as it slowly evaporated. Modern machines have solved this with a piece of tech called a “cold head.”

The Mechanical Refrigerator: This specialized chiller sits on top of the scanner. It catches any helium that starts to turn into gas, re-chills it back into a liquid, and drops it back into the tank.
Sustainability: Because of this “zero boil-off” technology, modern scanners rarely need to be “refueled,” making them much more efficient than older models.

4. The Magnet That Never Sleeps

Perhaps the most surprising fact about an MRI is that the magnet is permanently on. Because the coils are submerged in that freezing helium, there is zero electrical resistance.

Unplugged Power: Once the initial electricity is fed into the coils (a process called “ramping up”), it keeps flowing in a perfect loop. You could actually unplug the machine from the wall, and the magnet would stay at full strength indefinitely, as long as it stays submerged in that -452°F helium.

Why Does the MRI Chirp?

If you’ve ever stood in an MRI room and heard a distinct “chirping” or “knocking” sound—even when the machine isn’t scanning a patient—you’re hearing the cooling system at work. That sound is the “cold head” pumping away to ensure the helium stays liquid, keeping the world’s most powerful medical magnet ready for the next patient.

The next time you see an MRI machine, remember: it’s not just a scanner. It’s a multi-layered, superconducting “thermos” that uses the coldest liquid in the universe to help doctors see the invisible.

Explore Medical Imaging Programs at MCC

If the technology and clinical work of medical imaging interest you, Midwest Career College offers specialized Associate of Applied Science (AAS) programs designed to get you started in these vital healthcare roles. Explore our programs below to find the right fit for your career goals:

Imaging Career Path	Program Information
MRI Technology	AAS in Magnetic Resonance Imaging (MRI) Technology
Radiography / X-Ray	AAS in Diagnostic Medical Imaging Radiography
Ultrasound / Sonography	AAS in Diagnostic Medical Sonography
Cardiovascular Sonography	AAS in Noninvasive Cardiovascular Sonography (NICVS)