Each positron annihilation is like the birth of a pair of dancers, connected by an invisible thread of polarization. Two gamma quanta fly apart, but their states remain entangled: measuring one instantly determines the other — as if one partner senses every movement of the other, no matter the distance. Einstein himself called it 'spooky action at a distance,' and today it opens a window into diagnostics.

Standard PET simply registers coincidence — two photons, therefore an annihilation. QE-PET, however, listens in on their polarization duet. The photons pass through the body, sometimes experiencing Compton scattering — as if a dancer brushes against a branch. But here's the surprise: if the scattering angle is less than 36°, decoherence does not occur, and the pair continues to move in sync. This effect, confirmed in recent measurements, is what makes the technology feasible.

To decode the message, they use a polarimetric method. Scintillation detectors register the azimuthal scattering angles of each photon, and then a function is constructed: F(φ) = F₀[1 – CQE·A(θ₁)A(θ₂)cos(2φ)]. Here, CQE is the degree of quantum entanglement, and the modulation factors A(θ) are known from Compton theory. The depth of modulation directly indicates the strength of correlation: for a fully entangled state, the cosine is maximally pronounced; for a separable state, it fades. Experiments from 2023–2025 at the J-PET facilities showed something surprising: CQE differs in different materials. For fat tissue, CQE ≈ 0.89; for water, 0.82; and a change in oxygen partial pressure shifts this value by fractions of a percent — enough to become a biomarker for hypoxia.

It seems the environment where the positron annihilates leaves its imprint on the quantum connection — like the dance pattern depends on the floor surface. This yields not just an anatomical image, but a spectral-polarization portrait of the tissue, where QE-PET combines polarimetry with Compton scattering spectroscopy. The TB J-PET project — a total-body scanner with a 2.43-meter axial field — will be able to reconstruct a three-dimensional map of entanglement distribution throughout the body. Such multiparameter imaging will allow simultaneous visualization of tumors, oxygenation levels, and perhaps therapy efficacy. This is a step toward turning superposition and quantum measurement into routine clinical tools. Physicists will gain a playground for studying decoherence in a high-energy regime, while doctors get a way to peer into the world of antimatter inside us.