Comparison of image quality with ⁶²Cu and ⁶⁴Cu-labeled radiotracers in positron emission tomography whole-body phantom imaging

Objective: PET imaging is possible with copper (Cu) isotopes, ⁶⁰Cu, ⁶¹Cu, ⁶²Cu and ⁶⁴Cu. Although ⁶²Cu- and ⁶⁴Cu-labeled radiotracers are often used for preclinical and clinical PET studies, we do not know which radiotracers have better image quality for tumor imaging. In this study, we compare image quality between ⁶²Cu and ⁶⁴Cu imaging with a different acquisition mode and reconstruction algorithm using a whole-body phantom for tumor imaging. Methods: In a National Electrical Manufacturers Association (NEMA) 2001 whole-body phantom, the concentration of ⁶²Cu-ATSM and ⁶⁴Cu-ATSM was, respectively, approximately 2.7 and 1.8MBq/mL in all the spheres and approximately 0.9 and 0.6MBq/mL in the background. After adjustment for true coincidence events between ⁶²Cu and ⁶⁴Cu, two-dimensional (2D) and three-dimensional (3D) PET scan data were acquired for 10min. The data were reconstructed using filtered back projection (FBP) and the ordered subset expectation maximization (OSEM) algorithm. Image quality of ⁶²Cu and ⁶⁴Cu was compared using recovery coefficient (RC), sphere-to-background ratio (SBR) and coefficient of variation (%COV). Results: There were little significant differences between ⁶²Cu and ⁶⁴Cu imaging, visually. Recovery coefficients of ⁶⁴Cu images were higher than those of ⁶²Cu images. The RC of ⁶⁴Cu images with 3D acquisition mode and OSEM was the highest in all experiments. No SBR values were significantly different from the true value of 3.0 in 37mm sphere diameters, but 3D acquisition and OSE-Myielded slight overestimations compared with 2D acquisition and FBP, the gold standard for quantification in PET studies. Percentage COV values of ⁶⁴Cu with OSEM were significantly lower than those of ⁶²Cu. Conclusions: Copper-64 radiotracers provide higher image quality than ⁶²Cu-radiotracers in whole-body tumor imaging only when the 3D acquisition mode and OSEM algorithm are applied. However, the quantitative values for smaller tumors may be slightly overestimated.