Detection of Shortwave-Infrared Cerenkov Luminescence from Medical Isotopes

Medical radioisotopes produce Cerenkov luminescence (CL) from charged subatomic particles (β^+/−) traveling faster than light in dielectric media (e.g., tissue). CL is a blue-weighted and continuous emission, decreasing proportionally to increasing wavelength. CL imaging (CLI) provides an economic PET alternative with the advantage of also being able to image β⁻ and α emitters. Like any optical modality, CLI is limited by the optical properties of tissue (scattering, absorption, and ambient photon removal). Shortwave-infrared (SWIR, 900–1700 nm) CL has been detected from MeV linear accelerators but not yet from keV medical radioisotopes. 

Methods: Indium-gallium-arsenide sensors and SWIR lenses were mounted onto an ambient light-excluding preclinical enclosure. An exposure and processing pipeline was developed for SWIR CLI and then performed across 6 radioisotopes at in vitro and in vivo conditions.

Results: SWIR CL was detected from the clinical radioisotopes ⁹⁰Y, ⁶⁸Ga, ¹⁸F, ⁸⁹Zr, ¹³¹I, and ³²P (biomedical research). SWIR CLI’s advantage over visible-wavelength (VIS) CLI (400–900 nm) was shown via increased light penetration and decreased scattering at depth. The SWIR CLI radioisotope sensitivity limit (8.51 kBq/μL for ⁶⁸Ga), emission spectrum, and ex vivo and in vivo examples are reported.

Conclusion: This work shows that radioisotope SWIR CLI can be performed with unmodified commercially available components. SWIR CLI has significant advantages over VIS CLI, with preserved VIS CLI features such as radioisotope radiance levels and dose response linearity. Further improvements in SWIR optics and technology are required to enable widespread adoption.