Imaging and sensing of pH and chemical state with nuclear-spin-correlated cascade gamma rays via radioactive tracer

Abstract

Single-photon-emission computed tomography (SPECT) and positron-emission tomography (PET) are highly sensitive molecular detection and imaging techniques that generally measure accumulation of radio-labeled molecules by detecting gamma rays. Quantum sensing of local molecular environment via spin, such as nitrogen vacancy (NV) centers, has also been reported. Here, we describe quantum sensing and imaging using nuclear-spin time-space correlated cascade gamma-rays via a radioactive tracer. Indium-111 (111In) is widely used in SPECT to detect accumulation using a single gamma-ray photon. The time-space distribution of two successive cascade gamma-rays emitted from an 111In atom carries significant information on the chemical and physical state surrounding molecules with double photon coincidence detection. We propose and demonstrate quantum sensing capability of local micro-environment (pH and chelating molecule) in solution along with radioactive tracer accumulation imaging, by using multiple gamma-rays time-and-energy detection. Local molecular environment is extracted through electric quadrupole hyperfine interaction in the intermediate nuclear spin state by the explicit distribution of sub-MeV gamma rays. This work demonstrates a proof of concept, and further work is necessary to increase the sensitivity of the technique for in vivo imaging and to study the effect of scattered radiation for possible application in nuclear medicine.

A double photon coincidence detection method for medical gamma-ray imaging

“…Cascade nuclides not only improve gamma-ray imaging, but also have the potential to provide more advanced information. The chemical state of the cascade nuclide can be extracted using the angular correlation of cascade photons, which are perturbed by external electric and magnetic fields [44,45]. We succeeded in simultaneous chemical sensing and accumulation imaging of 111In solutions [44].…”

“…The chemical state of the cascade nuclide can be extracted using the angular correlation of cascade photons, which are perturbed by external electric and magnetic fields [44,45]. We succeeded in simultaneous chemical sensing and accumulation imaging of 111In solutions [44]. Recently, Moskal et al have proposed a positronium imaging, which can sense the chemical environment of a radionuclide [46,47].…”

Improvement of double photon emission Compton imaging using angular and polarization correlations in cascade photons

“…The angular correlation is attenuated by the environment. The external magnetic field, pH, and electric quadrupole interactions cause this attenuation [7,8,12]. Therefore, the application of the measured angular correlation has the potential to improve the image further.…”

Multi-molecule imaging and inter-molecular imaging in nuclear medicine

“…The pH information can be extracted through the hyperfine interaction between the 111 In nucleus and the external electric field gradient, especially the change around pH 3-5. Moreover, by combining the DPEI method with chemical sensing, we can simultaneously visualize the accumulation of radioactive sources and their surrounding environment, such as pH in the pico-mole concentration range [51].…”

“…Therefore, chemical sensing in nuclear medicine still requires further improvement, such as the dedicated design of molecules. Another possibility is to use the chelating state detection demonstrated in the [51].…”