Comparison of PSF and Non PSF BLOB based reconstructed image in Time-of-Flight PET/CT
Main Article Content
Abstract
Hybrid PET/CT imaging with the use of 18F FDG is a widely used imaging technique with major indications in oncology for staging, re-staging and monitoring response to therapy. There is a major issue of partial volume effect in PET images which affects image quality as well as quantitative accuracy in small lesions. Multiple attempts have been made to resolve these issues. The aim of our study was to look into impact of Point‐spread-function (PSF) on reconstructed attenuation corrected (AC) images of PET/CT and to find out best combination of the number of PSF iterations with regularization level while applying PSF.
Methods
We performed phantom study before performing patient study with similar algorithm on a time of flight (TOF) PET/CT system. We used NEMA IEC body phantom filled with appropriate activity in spheres and background area. After acquisition, data reconstructed three times, non PSF, 2PSF and 4PSF. We measured noise, CRC and SNR in all 3 sets of reconstructed phantom image. We selected 96 patients for our study and acquisition was performed similar to phantom study followed by data reconstruction. In all three sets of data reconstruction we measured SUVmax, SUVmean and lesion volume for both phantom and patient study. All quantitative data and lesion detectability in 2PSF and 4PSF images were visually assessed by two nuclear medicine physicians.
Results
The measured background noise, CRCmax and CRCmean were significantly increased in 2PSF and 4PSF images as compared to non PSF. The SNRmax relatively increased in 2PSF as compared to non PSF and decreased in 4PSF as compared to 2PSF for lesions <2cm. In lesions >2cm SNRmax was not much significantly increased as compared to small lesions (<2cm). The SUVmax was increased in 2PSF & 4PSF as compare to non PSF while in SUVmean, values were not significantly increased as compared to SUVmax.
Conclusion
2PSF iterations combined with the 6 regularization level reconstructed PET image play a significant role in the accuracy of the SUVmax determination. SUVmean tends to be more accurate at relatively higher PSF iteration (4PSF) with smoothing levels. It gives acceptable noise and good image quality which leads to improved small lesion detection and well defined margin of the lesion.
Article Details
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