Three-dimensional positron emission tomography imaging with 124I and 86Y

Area of Science:

• Nuclear medicine
• Medical imaging
• Radiochemistry

Background:

• Impure positron emitters (e.g., 124I, 86Y) present image quality challenges in Positron Emission Tomography (PET) compared to conventional isotopes like 18F.
• These challenges stem from physical characteristics such as larger positron range and associated decay modes.
• Quantifying these effects is crucial for optimizing their clinical application.

Purpose of the Study:

• To quantify the image quality degradation caused by impure positron emitters (124I and 86Y) in a human 3-D PET system.
• To determine an optimized acquisition protocol using Monte Carlo simulations to achieve image quality comparable to 18F.
• To evaluate the impact of various physical factors on image quality and identify mitigation strategies.

Main Methods:

• Extensive Monte Carlo simulations of the Allegro PET scanner were performed to assess the effects of positron range, associated singles, and other decay modes.
• Spatial resolution was evaluated for 124I and 86Y and compared to 18F.
• Noise Equivalent Count (NEC) analysis was used to study scanner performance at low count rates, incorporating spurious coincidences and optimizing energy thresholds.

Main Results:

• Spatial resolution degradation was observed: ~0.5 mm for 86Y and ~1 mm for 124I compared to 18F.
• Associated singles and scattered coincidences contribute to image background, with scatter being more significant.
• Optimal energy threshold (600 keV for Allegro) minimized spurious coincidences, resulting in ~2.5% extra contamination for 124I and ~5.5% for 86Y.

Conclusions:

• 3-D PET imaging with 124I and 86Y results in lower spatial resolution, though less critical for human scanners than animal scanners.
• Increased imaging time (3-5x) can compensate for the limited positron decay fraction.
• Optimized energy window settings and short coincidence windows are essential for minimizing artifacts and achieving good image quality efficiently.