Straightforward PET phantom preparation using ⁶⁸Gallium diluted with acid

Area of Science:

• Nuclear Medicine
• Radiochemistry
• Medical Imaging

Background:

• Quantitative Positron Emission Tomography (PET) relies on accurate phantom preparations for quality assurance and calibration.
• Gallium-68 (68Ga) is a widely used PET radionuclide, necessitating practical methods for phantom creation.
• Ensuring spatial uniformity and stability in 68Ga PET phantoms is crucial for reliable quantitative imaging.

Purpose of the Study:

• To develop a user-friendly and practical method for preparing phantoms for routine quantitative 68Gallium (68Ga) PET imaging.
• To evaluate different methods of preparing 68Ga phantoms regarding their spatial uniformity and image noise characteristics.
• To establish reliable phantom preparation techniques for quality assurance and cross-calibration in 68Ga PET.

Main Methods:

• Produced gallium ions from a 68Ge/68Ga generator in 0.05 M HCl.
• Prepared phantoms by direct dilution of 68Ga3+ in water, neutralization then dilution, radiolabeling with PSMA-617 then dilution, direct addition to 0.05 M HCl, or 0.1 M citric acid.
• Scanned cylindrical phantoms for 60 minutes, reconstructing images into 5-minute frames to assess temporal changes in uniformity and noise using SD, CV, SUVmean, and pixel-wise analysis.

Main Results:

• Phantom preparation via neutralization in NaOH resulted in non-uniform activity distribution and deteriorating spatial uniformity over time.
• Methods involving direct dilution in 0.05 M HCl or 0.1 M citric acid, and radiolabeling with PSMA-617, yielded visually homogeneous images with stable spatial uniformity.
• Quantitative analysis indicated that acidic dilutions (HCl, citric acid) provided more stable uniformity compared to direct water dilution, despite visual homogeneity in the latter.

Conclusions:

• Diluting 68Ga3+ in 0.05 M HCl or 0.1 M citric acid provides a reliable method for preparing uniform 68Ga PET phantoms.
• These acidic dilution methods offer spatial uniformity comparable to radiolabeling techniques, suitable for quality assurance and cross-calibration.
• The developed approaches are practical and user-friendly for routine quantitative 68Ga PET applications.