Influence of PET reconstruction parameters on the TrueX algorithm. A combined phantom and patient study

Area of Science:

• Medical Imaging
• Radiotherapy Physics
• Nuclear Medicine

Background:

• Functional imaging, particularly Positron Emission Tomography (PET), is increasingly vital in modern radiotherapy (RT).
• Automated integration of PET into target definition necessitates reliable PET quantification.
• New PET scanners utilize point-spread-function (PSF) based resolution recovery, but its impact on quantification needs investigation.

Purpose of the Study:

• To investigate the impact of PSF-based reconstruction algorithms on PET quantification.
• To compare the performance of OSEM and PSF TrueX algorithms in PET imaging.
• To determine appropriate thresholds for accurate tumor delineation with PSF reconstruction.

Main Methods:

• Siemens PET/CT phantom measurements with varying activity.
• Reconstruction using OSEM (Gauss filter) and PSF TrueX (Gauss/Allpass filters) with varied iterations (i) and subsets (ss).
• Comparison of recovery coefficient (RC) and volume threshold; analysis of eight lung patient scans.

Main Results:

• PSF TrueX demonstrated lower thresholds (up to 40%) than OSEM for defining real sphere volumes.
• TrueX showed higher sensitivity to iteration/subset variations; OSEM's RC stabilized with increasing iterations.
• Adapted thresholds and activity correction reduced volume and activity differences between TrueX and OSEM in patient scans.

Conclusions:

• PSF TrueX offers excellent diagnostic image quality but requires extended guidelines for PSF-based methods.
• A lower threshold than the 42% for OSEM is necessary for TrueX to ensure appropriate tumor delineation.
• Filter-dependent thresholds for TrueX must be verified on different scanners before multicenter trial implementation.