Impact of high (131)I-activities on quantitative (124)I-PET

Area of Science:

• Nuclear Medicine
• Medical Imaging
• Radiopharmaceutical Therapy

Background:

• Peri-therapeutic Iodine-124 Positron Emission Tomography/Computed Tomography (PET/CT) is valuable for guiding radioiodine therapy.
• High Iodine-131 activities used in therapy can degrade Iodine-124 PET/CT image quality due to dead time and random coincidences.

Purpose of the Study:

• To evaluate the feasibility and image quality of Iodine-124 PET/CT during high Iodine-131 activity for radioiodine therapy guidance.
• To assess the impact of varying Iodine-131 activities on quantitative accuracy and image noise in Iodine-124 PET/CT.

Main Methods:

• Phantom experiments using a clinical PET/CT system with clinically relevant Iodine-124 and Iodine-131 activities.
• Noise Equivalent Count Rate (NECR) measurements and quantitative accuracy assessments using NEMA NU-2 phantoms.
• Evaluation of contrast recovery, background variability, and scatter/attenuation corrections at different sphere-to-background activity ratios.

Main Results:

• Iodine-124 PET/CT image quality was good in the presence of high Iodine-131 activities, with unaffected quantification below 1000 MBq.
• Image noise increased slightly at higher Iodine-131 activities, and NECR peaked at 550 MBq, showing a 2.8-fold reduction.
• Scatter and attenuation corrections remained accurate, and contrast recovery was well-preserved.

Conclusions:

• Quantitative peri-therapeutic Iodine-124 PET/CT is feasible for guiding radioiodine therapy, even with concurrent high Iodine-131 activities.
• The method provides reliable imaging and quantification, supporting its clinical application in treatment planning and monitoring.