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Introduction
Reconstruction influences the quantitative results in PET imaging. The aim of this
study was the evaluation of different image reconstruction parameters and their impact
on quantification for F-FDG PET of the brain. The reconstruction parameters studied were the number of iterations,
smoothing levels (relaxation parameter lambda), and the use of time of flight (TOF)
information. In addition, we investigated the effect of signal-to-noise ratio on each
of these reconstructed brain images, as well as the effect of scan duration on image
quality.
Materials and Methods
A Philips® Gemini-TF Big bore PET/CT was used for acquiring data of a 3D Hoffman Brain
phantom. Data was acquired for 25 minutes in list mode format after injection of 40
MBq FDG, and reconstructed with a voxel size of 2 × 2 × 2 using two different iterative reconstruction algorithms: LOR-RAMLA and BLOB-OS. The
number of iterations and subsets was varied successive from 3/33 (vendor default)
to 30/33, acquisition scan duration from 1 to 25 minutes, lambda was selected as smooth
(0.7) and normal (1.0), and TOF was switched on and off for BLOB-OS. The impact on
image quality was analyzed in 15 cortical and subcortical brain regions (volumes of
interest, VOIs) and for grey and white matter.
Results
Contrast increased for all regions of the brain and for grey matter/white matter (GM/WM)
ratio if the number of iterations increased. Image convergence was reached after fifteen
iterations for all different algorithms. When varying the smoothing filter it was
found that lambda 1.0 resulted in a faster convergence than 0.7. The coefficient of
variation (COV) for all VOIs showed BLOB-OS with TOF to be superior to the other algorithms.
The COV results for different scan durations showed only a minimal improvement after
5 minutes in high-activity regions (GM), and after 10 minutes in low-activity regions
(WM).
Conclusion
Based on phantom data F-FDG brain imaging for 10 minutes and reconstructed with the BLOB-OS algorithm including
TOF information with 15 iterations is optimal on the Philips Gemini TF Big bore PET/CT.
Further analyses is planned using patient data to verify if these findings remain
valid in a clinical setting.
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