Highlights
- •Two radionuclides included in the studies, Ga-66 and F-18 as a reference.
- •High energy positrons in lower density materials produce extended distributions.
- •NEMA NU 4-2008 image quality phantom with Ga-66 produced blurred images.
- •Quantitative PET imaging with Ga-66 is hampered due to high-energy positrons.
- •Both spatial resolution and activity concentration quantification are affected.
Abstract
Purpose
Gallium-66 is a non-conventional positron emitter that stands out not only for its
high potential to label peptides, proteins and antibodies, but also because it can
provide spatio-temporal information of relatively slow physiological processes in
the body due to its conveniently long half-life of 9.5 h. However, 66Ga emits the most energetic positrons for PET imaging. The lack of information of
the positron range effect on spatial resolution for this positron emitter is an issue,
particularly in preclinical imaging.
Methods
The line spread function (LSF) in tissue-equivalent materials with densities between
0.2 and 1.93 g/cm3 was obtained with 66Ga and 18F. A complementary study with the NEMA NU 4-2008 image quality phantom is also included.
Results
High-energy positrons moving in lower density materials produce far-reaching activity
distributions. The LSFs were characterized with Lorentzian-Gaussian fits, with spatial
resolution (FWHM) in the 2.14–3.2 mm range, and long tails extending a few tens of
mm depending on the material type and density. A narrowing of the LSF was observed
for lung-equivalent materials, indicating the lack of enough material for the positron
annihilation to take place. The NEMA NU 4-2008 image quality phantom produced blurred
images, notoriously observed in the hot and cold cylinders used for evaluation of
recovery coefficients (RC) and spill-over ratios (SOR), producing very low RC and
very large SOR.
Conclusions
Quantitative PET imaging with the non-conventional 66Ga is hampered due to the large range of its high-energy positrons affecting both
spatial resolution and activity concentration quantification.
Keywords
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Article info
Publication history
Published online: October 24, 2019
Accepted:
October 9,
2019
Received in revised form:
September 25,
2019
Received:
April 29,
2019
Identification
Copyright
© 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
