Quantum Entanglement in PET: A New Era of Medical Imaging ✛ ✦
Context
Modern positron emission tomography (PET) is based on detecting two 511 keV gamma rays from positron annihilation. Until recently, however, the quantum properties of these photons, such as the superposition of polarization states and their decoherence, were ignored. Fundamental research by Einstein, Bell, and Bohm showed that Bell's theorem makes it possible to experimentally distinguish quantum entanglement from classical correlations. In the context of PET, this opens the opportunity not only to improve image quality but also to obtain new physiological information.
Methods
To measure the degree of entanglement, polarimetric methods based on Compton scattering of photons are used. Detectors made of plastic scintillators or semiconductors (CZT) register both the initial hit of annihilation photons and subsequent scattering. The azimuthal distribution of the angle φ between the scattering planes of the two photons is analyzed, described by the function F(φ) = F₀[1 - CQE·A(θ₁)A(θ₂)cos(2φ)]. This allows calculating the parameter CQE — the degree of quantum entanglement, independent of scattering angles. Experiments are conducted on prototypes such as the modular J-PET with plastic strips, GAGG and LYSO crystal matrices, and hybrid Compton-PET systems.
Results
Key results were obtained in 2023–2025: (i) entanglement is not destroyed by Compton scattering of one photon at angles θS < 36°, as confirmed by decoherence measurements; (ii) the degree of entanglement is not maximal for annihilation in a porous polymer (CQE < 1), indicating dependence on tissue type; (iii) the measured asymmetry factor R at scattering angles of 81.7° was 2.00 ± 0.03 (for a maximally entangled state, R = 2.84 is predicted, and for a separable one, 1.63). This opens the possibility of using CQE as a biomarker of hypoxia: for adipose tissue CQE ≈ 0.89, for water 0.82, and when the partial pressure of oxygen changes from 50 to 10 mmHg, CQE changes by 0.0019.
Implications
These results mean that quantum entanglement could become a new dimension in PET, allowing not only improved signal-to-noise ratio through suppression of random coincidences but also visualization of tissue microenvironment. In particular, entanglement degree maps can reflect oxygenation level, which has direct relevance to cancer diagnosis. This also stimulates the development of multi-channel detector systems and machine learning algorithms for processing multiple scatterings.
Future development
Further development of QE-PET involves building full total-body systems with high sensitivity, such as the planned TB J-PET with an axial field of view of 2.43 m. Theoretical models of multiple Compton scattering (3-Compton) will be integrated into Geant4 simulations. Work is underway to adapt iterative reconstruction methods for simultaneous recovery of activity distribution and CQE parameter. Three-photon entanglement from ortho-positronium decay is also being investigated, potentially leading to new imaging types.
Impact
QE-PET technology will impact nuclear medicine by enabling multiparametric imaging within a single scan, as well as quantum informatics by providing a platform for studying decoherence in the high-energy regime. Moreover, the development of hybrid Compton-PET systems will contribute to the advancement of radiotheragnostics.
Next steps
Next steps include clinical validation of CQE as a biomarker on large patient cohorts, improving the timing and energy resolution of detectors to levels < 100 ps and < 1%, and developing standardized imaging and reconstruction protocols for QE-PET.
Key open problems
QE-PET touches upon the fundamental problem of quantum decoherence in macroscopic systems and the question of the limits of quantum mechanics at the mesoscale. Measuring the degree of entanglement of annihilation photons may shed light on the nature of wave function collapse and testing Bell inequalities in a new energy range.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The study explores the possibility of using quantum entanglement of annihilation photons in PET to obtain new diagnostic information. The authors measure the degree of entanglement through the CQE parameter and demonstrate its dependence on tissue type and oxygenation, opening the way to imaging the microenvironment.
Where its strength is
Concrete experimental confirmation of the link between the degree of entanglement and physiological parameters (tissue type, oxygen level) — this is a measurable quantity that can be integrated into existing PET systems as an additional biomarker.
Where it could go next
- It might be interesting to see how CQE contrast changes when using quantum eraser methods to separate entangled and random events — in our archive there is a nearby experiment with two-frame imaging.based on: Quantum Eraser Captures Two Pictures in One Snap arXiv:2606.03914
- There is a related work on entangled photons as a tool for imaging the invisible — perhaps their approach to background suppression could help improve the signal-to-noise ratio in polarimetric PET.based on: Entangled Photons: A New Way to See the Invisible arXiv:2603.22547
Worth trying
- Test suppression of random coincidences using a quantum eraser scheme on a Compton-PET prototype.
- Assess whether CQE can be used not only for hypoxia but also for distinguishing soft tissue types in vivo, relying on data from porous media.
Why this may matter
If CQE becomes a routine measurement in PET, it will add functional contrast without additional injections of radiopharmaceuticals, which is especially valuable for follow-up scans and therapy monitoring.
Nearby works in our archive
- Positronium and Quantum Hide-and-Seek: How to 'Push' a Photon to Uncover the Mysterysimilarity 0.67
- Entangled Photons: A New Way to See the Invisiblesimilarity 0.66
- Sunlight Creates Quantum Entanglementsimilarity 0.63
- Quantum Eraser Captures Two Pictures in One Snapsimilarity 0.62
- Two Quantum Sensors Peek Inside a Living Cellsimilarity 0.62
- Thermometers in Plasma Lie in Unisonsimilarity 0.61
The closest work in the archive sits at 0.67 by meaning — the usual level for our corpus.
Original abstract
as written by the authors arXiv:2607.12182
Annihilation photons are quantum entangled in their polarization, a property that is not accessible in state-of-the-art clinical Positron Emission Tomography (PET). This roadmap describes the current status of research in the emerging field of quantum entanglement applications involving these photons for medical diagnosis. It outlines the underlying physics phenomena and the development of detector systems that can serve as a foundation for future Quantum Entanglement PET (QE-PET) scanners. These scanners will be capable of utilizing the entanglement between annihilation photons by measuring their Compton scattering on electrons. This roadmap comprises up-to-date experimental results on the study of quantum entanglement and the decoherence of annihilation photons, alongside the current theoretical understanding of these phenomena. The methods and detector technologies described herein are being developed (i) in order to enhance standard PET imaging by suppressing random coincidences in the reconstruction of annihilation site density distributions, (ii) in order to establish the degree of quantum entanglement as a diagnostic biomarker for tissue pathology and oxygenation, and (iii) in order to elaborate a method for pH imaging. Whether entanglement-based imaging and pH mapping can be successfully translated into clinical practice remains an open question and a subject of exciting ongoing research. This roadmap serves as an invitation to the scientific community to join this burgeoning field.
Historically, the first experimental confirmation of polarization correlation of annihilation photons was obtained by Wu and Shaknov in 1950, but only in 2025 did the J-PET group discover that entanglement is not maximal and depends on the material. And the survival of entanglement after scattering, contrary to expectations, came as a surprise, explained only in 2024.
The idea of quantum entanglement as 'spooky action at a distance' is depicted in many science fiction works, such as 'The Quantum Thief' by Hannu Rajaniemi, where entanglement is used for instantaneous communication. QE-PET, by detecting real entangled photon pairs within a patient's body, resembles a medical 'quantum communicator'.
Key numbers
- Maximum R ratio for entangled photons: 2.84
- R ratio for separable photons: 1.63
- Scattering angle for maximum correlation: 81.7°
- Threshold scattering angle in tissue for entanglement preservation: 36°
- QE-PET sensitivity for fourfold coincidences (TB J-PET): ~3 cps/kBq