Ultra-high energy spectral prompt PET

Objective.Utilizing prompt gammas in preclinical pinhole-collimated positron emission tomography (PET) avoids image degradation due to positron range blurring and photon down scatter, enables multi-isotope PET and can improve counting statistics for low-abundance positron emitters. This was earlier reported for¹²⁴I,⁸⁹Zr and simultaneous¹²⁴I -¹⁸F PET using the VECTor scanner (MILabs, The Netherlands), demonstrating sub-mm resolution despite long positron ranges. The aim of the present study is to investigate if such sub-mm PET imaging is also feasible for a large variety of other isotopes including those with extremely high energy prompt gammas (>1 MeV) or with complex emission spectra of prompt gammas.Approach.We use Monte Carlo simulations to assess achievable image resolutions and uniformity across a broad range of spectrum types and emitted prompt gamma energies (603 keV-2.2 MeV), using⁵²Mn,⁹⁴Tc,⁸⁹Zr,⁴⁴Sc,⁸⁶Y,⁷²As,¹²⁴I,³⁸K, and⁶⁶Ga.Main results.Our results indicate that sub-millimeter resolution imaging may be feasible for almost all isotopes investigated, with the currently used cluster pinhole collimators. At prompt gamma energies of 603 keV of¹²⁴I, an image resolution of ∼0.65 mm was achieved, while for emissions at 703, 744, 834, and 909 keV of⁹⁴Tc,⁵²Mn,⁷²As, and⁸⁹Zr, respectively, ∼0.7 mm resolution was obtained. Finally, at ultra-high energies of 1.2 (⁴⁴Sc) and 1.4 MeV (⁵²Mn) resolutions of ∼0.75 mm and ∼0.8 mm could still be achieved although ring artifacts were observed at the highest energies (1.4 MeV). For³⁸K (2.2 MeV), an image resolution of 1.2 mm was achieved utilizing its 2.2 MeV prompt emission.Significance.This work shows that current cluster pinhole collimators are suitable for sub-mm resolution prompt PET up till at least 1.4 MeV. This may open up new avenues to developing new tracer applications and therapies utilizing these PET isotopes.