From Lab to Clinic: Making Heart Scans as Simple as Blood Tests

In our previous posts, we introduced two ideas: first, that there is a missing cardiac test in your annual check-up; second, that magnetocardiography (MCG) — measuring the heart's magnetic field — could fill that gap with a 5-minute, non-contact, zero-radiation screening test.

But if MCG has such clear advantages, why isn't it already in every hospital and clinic? The answer is a story about physics, engineering, and a technology barrier that has only recently been broken.

The old way: liquid helium and shielded rooms

MCG was first demonstrated in the 1960s. The sensors used were called SQUIDs — superconducting quantum interference devices. SQUIDs are fantastically sensitive magnetometers, capable of detecting fields as small as a few femtotesla (a femtotesla is one millionth of one billionth of a tesla). They remain the most sensitive magnetic field detectors ever built.

But SQUIDs come with a crippling practical problem: they only work when cooled to near absolute zero. Specifically, they require liquid helium at 4.2 Kelvin (−269°C). This means a SQUID-based MCG system needs a cryogenic dewar that must be continuously refilled with liquid helium — an expensive, logistically complex, and increasingly scarce resource.

That's not all. The heart's magnetic field (~50 picotesla) is about a billion times weaker than Earth's ambient magnetic field (~50 microtesla). To detect such a tiny signal, SQUID systems traditionally required a magnetically shielded room — a specially constructed enclosure lined with layers of mu-metal and aluminium that blocks external magnetic fields. These rooms cost ₹5–15 crores to build and occupy hundreds of square feet of hospital floor space.

The result? Despite decades of published clinical evidence showing that MCG works — that it can detect coronary artery disease, arrhythmia risk, and other cardiac conditions — fewer than a handful of hospitals worldwide have ever had an MCG system. The technology was proven but impractical. The science was right; the engineering wasn't ready.

The breakthrough: atomic magnetometers

The technology that changes everything is the optically pumped magnetometer, or OPM. Instead of a superconducting circuit, an OPM uses a small glass cell filled with an alkali metal vapour — in our case, rubidium-87 atoms. A laser beam is used to "pump" these atoms into a quantum spin-polarised state, and then "probe" how that spin state evolves in the presence of a magnetic field.

The key physics is this: when rubidium atoms are spin-polarised and placed in a magnetic field, they precess (rotate) around the field direction at a very precise frequency — the Larmor frequency — which is directly proportional to the field strength. By measuring this precession frequency with extreme precision, you can measure the magnetic field with extreme precision.

The critical advantage: this entire process happens at room temperature. No cryogenics. No liquid helium. No expensive dewar. The sensor is a small glass cell, a laser, and a photodetector. It can be made compact, lightweight, and — with continued engineering — affordable.

The real innovation: no shielded room

Making the sensor room-temperature is necessary but not sufficient. The bigger challenge is operating without a magnetically shielded room. Remember, the heart's magnetic field is about a billion times weaker than the environment. How do you detect it without blocking out the environment?

The answer is a technique called gradiometry. Instead of using a single magnetometer, you use two — one positioned close to the chest (measuring heart signal + environment) and one positioned a few centimetres further away (measuring mostly environment). By subtracting the two readings, the common environmental noise cancels out, and what remains is predominantly the cardiac signal.

This works because the heart's magnetic field falls off steeply with distance (approximately as 1/r³ for a dipole source), while distant environmental noise is nearly the same at both sensor positions. The subtraction preferentially preserves the nearby cardiac source and rejects the distant noise.

Using a gradiometric configuration of two scalar FID-OPM sensors, our team at GDQLabs has detected human cardiac magnetic fields with a sensitivity of 2.6 pT/√Hz in a completely unshielded environment — no magnetic shielding of any kind. The QRS complex of the cardiac cycle was clearly visible with a peak-to-peak amplitude of approximately 20 picotesla.

This is the result that changes the equation. It means MCG can be performed in a normal room — a doctor's consultation room, a diagnostic clinic, a mobile health unit. The requirement for a magnetically shielded room, which was the single biggest barrier to clinical adoption of MCG for 50 years, has been eliminated.

Who would benefit?

If MCG becomes a routine clinical tool — a 5-minute, non-contact test costing less than ₹8,000 — the potential impact is enormous. The populations who stand to benefit the most are:

What GDQLabs is building

At GDQLabs, we are developing a portable, magnetic-shield-free MCG system based on scalar free-induction-decay optically pumped magnetometers. Our system uses rubidium-87 vapour cells operating at room temperature, in the Earth's ambient magnetic field, without any magnetic shielding.

We have already demonstrated human MCG recordings in a completely unshielded laboratory at IISER Pune, detecting QRS complexes across multiple chest positions with clear polarity reversal — confirming that the system has genuine spatial sensitivity to the cardiac source.

The roadmap ahead involves scaling from a single gradiometric sensor pair to a multi-channel array, developing machine-learning-powered diagnostic software, pursuing regulatory clearance, and conducting clinical validation studies. The goal is a system that can be deployed in hospitals and clinics as a routine cardiac screening platform — making MCG as accessible and routine as a blood test.

For fifty years, MCG has been a technology that works but couldn't scale. The physics was proven. The clinical evidence was strong. But the engineering demanded liquid helium, shielded rooms, and million-dollar budgets.

That era is ending. Room-temperature quantum sensors, operating in Earth's ambient field without shielding, are making MCG practical for the first time. The science finally has the engineering it deserves.

The missing test in your annual check-up may not be missing for much longer.