Is the Image Quality of I-124-PET Impaired by an Automatic Correction of Prompt Gammas?

Abstract

ObjectivesThe aim of this study is to evaluate the quality of I-124 PET images with and without prompt gamma compensation (PGC) by comparing the recovery coefficients (RC), the signal to noise ratios (SNR) and the contrast to F-18 and Ga-68. Furthermore, the influence of the PGC on the quantification and image quality is evaluated.MethodsFor measuring the image quality the NEMA NU2-2001 PET/SPECT-Phantom was used containing 6 spheres with a diameter between 10 mm and 37 mm placed in water with different levels of background activity. Each sphere was filled with the same activity concentration measured by an independently cross-calibrated dose calibrator. The “hot” sources were acquired with a full 3D PET/CT (Biograph mCT®, Siemens Medical USA). Acquisition times were 2 min for F-18 and Ga-68, and 10 min for I-124. For reconstruction an OSEM algorithm was applied. For I-124 the images were reconstructed with and without PGC. For the calculation of the RCs the activity concentrations in each sphere were determined; in addition, the influence of the background correction was studied.ResultsThe RCs of Ga-68 are the smallest (79%). I-124 reaches similar RCs (87% with PGC, 84% without PGC) as F-18 (84%). showing that the quantification of I-124 images is similar to F-18 and slightly better than Ga-68. With background activity the contrast of the I-124 PGC images is similar to Ga-68 and F-18 scans. There was lower background activity in the I-124 images without PGC, which probably originates from an overcorrection of the scatter contribution. Consequently, the contrast without PGC was much higher than with PGC. As a consequence PGC should be used for I-124.ConclusionsFor I-124 there is only a slight influence on the quantification depending on the use of the PGC. However, there are considerable differences with respect to I-124 image quality.

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

“…On the other hand, the measured background variability for 124 I was still limited to about 3%-4%, compared with 2%-3% for the other isotopes, and no image artifacts were visually detected. Other studies also demonstrate good quantification of 124 I distribution when proper prompt g correction is applied (29). 90 Y is a challenging isotope, as we confirmed by the lower contrast recovery measured (Figs.…”

Biodistribution and Radiation Dosimetry for a Probe Targeting Prostate-Specific Membrane Antigen for Imaging and Therapy

“…Data on the partial-volume effect for 68 Ga and small volumes are shown by, for example, Preylowski et al (32). …”

The Relevance of Dosimetry in Precision Medicine

“…Quantification using this radionuclide is, however, hampered by the presence of a prompt g-emission that could potentially lead to false coincidences. Some manufacturers have a built-in prompt g-correction, which, for 124 I, leads to acceptable image quantification (18). Other nuclides that could potentially be used for pretherapeutic PET-based dose planning are 44 Sc, 68 Ga, and 86 Y (19).…”