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KMID : 0861420120160010102
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Korean Journal of Nuclear Medicine Technology
2012 Volume.16 No. 1 p.102 ~ p.107
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The Evaluation of Difference according to Image Scan Duration in PET Scan using Short Half-Lived Radionuclide
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Hong Gun-Chul
Cha Eun-Sun
Kwak In-Suk
Lee Hyuk
Park Hoon
Choi Choon-Ki
Seok Jae-Dong
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Abstract
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Purpose: Because of the rapid physical decay of the short half-lived radionuclide, counting of event for image is very limited. In this reason, long scan duration is applied for more accurate quantitative analysis in the relatively low sensitive examination. The aim of this study was to evaluate the difference according to scan duration and investigate the resonable scan duration using the radionuclide of 11C and 18F in PET scan.
Materials and Methods: 1994-NEMA Phantom was filled with 11C of 30.08±4.22 M㏃ and 18F of 40.08±8.29 M㏃ diluted with distilled water. Dynamic images were acquired 20frames/1minute and static image was acquired for 20minutes with 11C. And dynamic images were acquired 20frames/2.5minutes and static image was acquired for 50minutes with 18F. All of data were applied with same reconstruction method and time decay correction. Region of interest (ROI) was set on the image, maximum radioactivity concentration (maxRC, k㏃ /mL) was compared. We compared maxRC with acquired dynamic image which was summed one bye one to increase the total scan duration.
Results: maxRC over time of 11C was 3.85±0.45 ~ 5.15±0.50 k㏃/mL in dynamic image, and static image was 2.15±0.26 k㏃/mL. In case of 18F, the maxRC was 9.09±0.42 ~ 9.48±0.31 k㏃/mL in dynamic image and 7.24±0.14 k㏃/mL in static. In summed image of 11C, as total scan duration was increased to 5, 10, 15, 20minutes, the maxRC were 2.47±0.4, 2.22±0.37, 2.08±0.42, 1.95±0.55 k㏃/mL respectively. In case of 18F, the total scan duration was increased to 12.5, 25, 37.5, and 50minutes, the maxRC were 7.89±0.27, 7.61±0.23, 7.36±0.21, 7.31±0.23 k㏃/mL.
Conclusion: As elapsed time was increased after completion of injection, the maxRC was increased by 33% and 4% in dynamic study of 11C and 18F respectively. Also the total scan duration was increased, the maxRC was reduced by 50% and 20% in summed image of 11C and 18F respectively. The percentage difference of each result is more larger in study using relatively shorter half-lived radionuclide. It appears that the accuracy of decay correction declined not only increment of scan duration but also increment of elapsed time from a starting point of acquisition. In study using 18F, there was no big difference so it’s not necessary to consider error of quantitative evaluation according to elapsed time. It’s recommended to apply additional decay correction method considering decay correction the error concerning elapsed time or to set the scan duration of static image less than 5minutes corresponding 25% of half life in study using shorter half-lived radionuclide as 11C.
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KEYWORD
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Radio activity concentrations, Image summation, Decay correction
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