METHODS: The European Association of Nuclear Medicine (EANM) procedure guidelines version 2.0 for FDG-PET tumor imaging has adhered for this purpose. A NEMA2012/IEC2008 phantom was filled with tumor to background ratio of 10:1 with the activity concentration of 30 kBq/ml ± 10 and 3 kBq/ml ± 10% for each radioisotope. The phantom was scanned using different acquisition times per bed position (1, 5, 7, 10 and 15 min) to determine the Tmin. The definition of Tmin was performed using an image coefficient of variations (COV) of 15%.
RESULTS: Tmin obtained for 18F, 68Ga and 124I were 3.08, 3.24 and 32.93 min, respectively. Quantitative analyses among 18F, 68Ga and 124I images were performed. Signal-to-noise ratio (SNR), contrast recovery coefficients (CRC), and visibility (VH) are the image quality parameters analysed in this study. Generally, 68Ga and 18F gave better image quality as compared to 124I for all the parameters studied.
CONCLUSION: We have defined Tmin for 18F, 68Ga and 124I SPECT CT imaging based on NEMA2012/IEC2008 phantom imaging. Despite the long scanning time suggested by Tmin, improvement in the image quality is acquired especially for 124I. In clinical practice, the long acquisition time, nevertheless, may cause patient discomfort and motion artifact.
MATERIALS AND METHODS: This study was conducted based on the guideline published by the European Association of Nuclear Medicine (EANM) version 2.0 FDG-PET/CT and conducted in two phases. Firstly, 100 whole-body scan 18FFDG PET/CT images were selected for the average coefficient of variation (COV) analysis in the liver region. Second, a NEMA 2012/IEC2008 phantom was used to obtain the relationship between the COVphantom and the scanning time. Finally, the images acquired using the two Tmin were quantitatively compared using contrast recovery coefficient (QH), signal to noise ratio (SNR), and visibility (VH). Independent t-test between each image quality parameter performed with p-value <0.05 considered significant.
RESULTS: The average COV of the liver was 17.7%. Currently, this value was clinically accepted to produce appropriate image quality at IKN. Interpolation at COV=17.7% gave a Tmin value of 2.9 minutes. Comparisons show that the two Tmin yielded equivalent PET/CT image quality (p-value of QH=0.774, SNR=0.780 and VH=0.915).
CONCLUSION: The optimal Tmin defined in this study was 2.9 minutes, 27.6% shorter than the Tmin previously defined based on COV=15%. Despite the higher average COV, the shorter Tmin beneficial in the lower total 18F-FDG activity administered, reduce the internal dose to the patient while producing equivalent image quality.