Quantitative imaging of 124I and 86Y with PET

Abstract

The quantitative accuracy and image quality of positron emission tomography (PET) measurements with 124I and 86Y is affected by the prompt emission of gamma radiation and positrons in their decays, as well as the higher energy of the emitted positrons compared to those emitted by 18F. PET scanners cannot distinguish between true coincidences, involving two 511-keV annihilation photons, and coincidences involving one annihilation photon and a prompt gamma, if the energy of this prompt gamma is within the energy window of the scanner. The current review deals with a number of aspects of the challenge this poses for quantitative PET imaging. First, the effect of prompt gamma coincidences on quantitative accuracy of PET images is discussed and a number of suggested corrections are described. Then, the effect of prompt gamma coincidences and the increased singles count rates due to gamma radiation on the count rate performance of PET is addressed, as well as possible improvements based on modification of the scanner’s energy windows. Finally, the effect of positron energy on spatial resolution and recovery is assessed. The methods presented in this overview aim to overcome the challenges associated with the decay characteristics of 124I and 86Y. Careful application of the presented correction methods can allow for quantitatively accurate images with improved image contrast.

Beyond 18F-FDG: Characterization of PET/CT and PET/MR Scanners for a Comprehensive Set of Positron Emitters of Growing Application—18F, 11C, 89Zr, 124I, 68Ga, and 90Y

“…The performance of clinical PET scanners using 18 F is routinely presented (17,18 (19,20). The performance of small-animal and high-resolution PET scanners with 18 F, 68 Ga, 124 I, and 89 Zr have, however, been investigated (24,25).…”

Recovery and normalization of triple coincidences in PET

“…7,8 In some special preclinical scan-ners with single-crystal read-out like the MADPET-II (Ref. 9) 14 the additional prompt γ-rays emitted with posit-rons also generate triple and higher-order coincidence events 8 that can be recovered to enhance the photon sensitivity. 15 Finally, there are other processes which can also yield tri-ple coincidences, like random triple events caused by three different decays, or positron annihilations generating three γ-rays via the formation of orthopositronium.…”

Matched pairs for radionuclide-based imaging and therapy

“…The quantification of 86 Y PET investigations is more of a challenge than that of 124 I investigations because of the higher number of disturbing gamma rays per β-decay [13].…”

“…This is a challenge for quantitative measurements with 86 Y even more than with 124 I [10][11][12]. The paper from Lubberink and Herzog is dedicated to this aspect [13]. Other important aspects of quantification, which is essential for dosimetry, are discussed by Sgouros et al [9].…”