Systematic evaluation of phantom fluids for simultaneous PET/MR hybrid imaging

Area of Science:

• Medical Imaging Physics
• Radiochemistry
• Biomedical Engineering

Background:

• Integrated PET/MR systems require specialized phantom fluids for simultaneous measurements.
• Standard MR phantom fluids may not be suitable for PET imaging, and vice versa, especially at high magnetic field strengths.
• Systematic evaluation of phantom fluid usability for simultaneous PET/MR imaging is needed.

Purpose of the Study:

• To evaluate different phantom fluid approaches for simultaneous PET/MR phantom imaging.
• To identify optimal fluids for specific PET tracers and MR conditions.
• To assess the applicability of novel PET tracers in combined imaging scenarios.

Main Methods:

• Investigated demineralized water, conductive water, water-oil emulsion, monoethylene glycol, and triethylene glycol.
• Utilized the common PET tracer (18)F-FDG and an alternative (18)F-fluoride Kryptofix 222 complex.
• Performed measurements on a 3.0 T integrated PET/MR whole-body system using a NEMA quality-standard phantom.

Main Results:

• All tested fluids homogeneously dissolved (18)F-FDG.
• Tested fluids significantly improved MR homogeneity (excitation flip angle increase by 2.0x) compared to pure water.
• Triethylene glycol provided the best compromise for (18)F-FDG (flip angle increase by 1.13x).
• The alternative tracer dissolved in oil but showed accumulation issues.

Conclusions:

• A systematic approach for phantom fluid selection in 3.0 T simultaneous PET/MR imaging is presented.
• Triethylene glycol is a viable option for simultaneous PET/MR scans using (18)F-FDG.
• Methods to improve MR homogeneity with water-based phantoms are discussed.
• Alternative PET tracers show potential for oil-based phantoms but require further optimization.