A cooling failure often goes unnoticed at first — and without early detection, can quickly turn into a costly problem. How high the costs climb depends on how fast you react.
The cooling system fails. As a result, the magnet may lose helium. No critical damage yet, but immediate action is required.
A cooling failure doesn't start inside the magnet — it usually starts on the roof. The external AC unit that supplies cold water to the MRI cooling circuit fails. The water in the circuit warms up. Once the water temperature exceeds a defined threshold, the helium compressor shuts itself down automatically — as a self-protection measure.
The AC unit is the most common cause — but not the only one. Clogged filters in the water cooling circuit, a power outage, or a faulty compressor itself can all lead to insufficient cooling of the magnet. In every case, the result is the same: the cold head stops, the helium warms up.
Without the compressor, the cold head also stops. It can no longer keep the helium in the magnet at temperature. The liquid helium begins to warm up slowly — and gradually evaporates. Pressure builds inside the magnet and is relieved through a pressure relief valve. The escaped helium is gone for good.
At this stage, the magnetic field is still intact. The MRI is still running — but the silent loss has already begun. The earlier the failure is detected, the lower the damage. If action is taken within a few hours, simply refilling the helium is often enough. If the failure goes unnoticed, the situation escalates — stage by stage.
Mag-Guard detects the failure immediately — the moment the compressor stops.
Usually the result of a prolonged cooling failure. A quench occurs: the magnet abruptly collapses its magnetic field. A significant amount of helium is lost. On 3T systems, all the helium is lost — regardless of the fill level beforehand.
The powerful magnetic field of an MRI is generated by coils inside the magnet. Electric current circulates in these coils — and moving electrons create a magnetic field. The stronger the current, the stronger the field. The key advantage: the coils are superconducting, meaning that at the right temperature they have zero electrical resistance. The current flows without any losses — indefinitely.
This temperature — −269 °C (4 Kelvin) — is maintained by the liquid helium inside the magnet. If the cooling fails, the helium gradually warms up. Eventually, the coils reach a point at which they lose their superconductivity.
Now a chain reaction sets in: the sudden electrical resistance generates heat. This heat transfers to the liquid helium — which instantaneously changes state from liquid to gas. In doing so, it expands by a factor of 700: one litre of liquid helium becomes 700 litres of helium gas in fractions of a second.
What happens here follows the law of conservation of energy: the energy contained in the coils converts into heat and is transferred to the surrounding helium. The helium is not just a coolant here, but also a buffer: it absorbs this energy and evaporates in a controlled manner through the quench pipe.
This is also one of the reasons why a magnet must always contain a minimum amount of helium. Without this buffer, the released energy would remain directly in the coils — they would burn out, and the magnet would be lost for good.
This gas forces its way out — through the dedicated quench pipe on the outside of the building. Visible as the white cloud of vapour it produces. In 3T systems, 100% of the helium is lost this way — gone for good.
If the quench goes unnoticed — at night or over the weekend — the magnet begins to warm up without helium. The next scenario then looms: the thermocycle.
Mag-Guard detects the quench immediately and alerts you — before the magnet gets too warm.
The quench goes unnoticed. Without helium, the magnet warms up — the critical temperature can be exceeded in as little as 2 hours. A thermocycle then becomes necessary: a long process in which the magnet is cooled back down over several weeks. The system is out of service for weeks.
Depending on the magnet type and age, the critical temperature can be reached within just a few hours without cooling — in some cases as soon as 2 hours. The critical threshold is around −200 °C. Beyond this point, normal refilling with liquid helium is no longer possible: any helium added would immediately evaporate and escape through the quench pipe.
From this point, a special procedure is required: the thermocycle. The magnet is first allowed to warm up completely to room temperature. During this process, the outer walls of the helium vessel become extremely cold — the gradient coil is at risk of damage and typically must be removed.
Once room temperature is reached, the vacuum can be re-established. The vacuum sits in a layer between the inner helium vessel and the outer magnet housing — it thermally insulates the magnet from the outside world and is essential for an efficient cool-down.
Then the cool-down begins: multiple cold heads are used in parallel. Helium is filled into the magnet, evaporates, is captured, re-liquefied and fed back in — a closed loop that gradually brings the magnet back to −269 °C (4 Kelvin). The magnet can then be refilled with liquid helium and brought back to field.
The entire process takes at least 4 weeks. During this time, no examinations are possible. Due to the complexity, the specialised equipment required, and the need for a technician permanently on site, a thermocycle is an extraordinarily costly undertaking.
Mag-Guard helps you avoid this scenario.
Weekend. The rooftop air conditioning unit fails. By chance, a caretaker notices the acoustic alarm on Saturday and informs the radiologist — even so, a quench could not be prevented.
Repair costs: €88,000 — plus downtime.
Without the caretaker's fast response, the quench would have gone unnoticed and led to the magnet warming up — a thermocycle.
As soon as the cooling system fails, you're alerted by SMS and email — day or night, weekday or weekend. Before stage 1 becomes stage 3.
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