Shortwave infrared detection of medical radioisotope Cerenkov luminescence.

Rationale: Cerenkov luminescence (CL) is produced by medical radioisotopes when charged particles (β+/-) travel faster than light in a dielectric medium (e.g. tissue). CLs blue-weighted luminescence is continuous and decreases proportional to wavelength. CL imaging (CLI) is an economical PET alternative, but heavily limited by the optical properties (scattering, absorption and special setup requirements). Shortwave infrared (SWIR, 900 – 1700 nm) CL has been detected from linear accelerators operating at MeV ranges but not from from medical radioisotopes. Methods: Indium gallium arsenide (InGaAs) focal plane arrays and SWIR lenses were mounted onto a ambient light excluding preclinical enclosure. A suitable exposure and processing pipeline were developed with SWIR CLI then performed across a variety of medical radioisotopes at in vitro and in vivo conditions. Results: SWIR CL was detected from the clinical radioisotopes: ⁹⁰Y, ⁶⁸Ga, ¹⁸F, ⁸⁹Zr, ¹³¹I and ³²P, used in biomedical research. SWIR CLIs advantage over conventional CLI is shown in terms with increased light penetration and decreased scattering at depth, in line with fluorescent SWIR imaging. The radioisotope SWIR spectrum is reported, the sensitivity limit (0.23 µCi/µl of ⁶⁸Ga) and SWIR CLIs preclinical feasibility is shown with ex vivo and in vivo preclinical examples. Conclusion: This work is the first to show that radioisotope SWIR CLI can be performed with commerical components. SWIR CL has significant advanatges over VIS CL and behaves in a similar manner. Further improvements in SWIR optics and technology are required to enable widespread adoption.