Abstract
The study aimed to assess a hypothetical minimum activity with regard to agreement of 124Iodine uptake (124I-RAIU) measured by positron emission tomography/computed-tomography (PET/CT) with 131Iodine uptake (131I-RAIU) determined by probe measurement which is considered clinical standard. Moreover, the impact of different reconstruction algorithms on 124I-RAIU and the evaluation of pixel noise as parameter for image quality were investigated. Methods: Different scan durations were simulated by different reconstruction intervals of 600-second-list-mode PET data sets (including 15 intervals up to 600 seconds and five different reconstruction algorithms; filtered-back projection and four iterative techniques) acquired 30 hours after administration of 1MBq 124I. The Bland-Altman method was used to compare mean 124I-RAIU levels versus mean 3MBq 131I-RAIU levels (clinical standard). The data of 37 patients with benign thyroid diseases were assessed. The impact of different reconstruction lengths on pixel noise was investigated for all five 124I-PET reconstruction algorithms. A hypothetical minimum activity was sought by means of a proportion equation, considering that the length of a reconstruction interval is equitable to a hypothetical activity. Results: Mean 124I-RAIU and 131I-RAIU showed high levels of agreement already for reconstruction intervals as short as 10 seconds, corresponding to a hypothetical minimum activity of 0.017MBq 124I. The iterative algorithms proved generally superior to the filtered-back projection. 124I-RAIU showed a trend to higher levels compared to 131I-RAIU if the influence of retrosternal tissue was not considered which was proven to be the cause of a slight overestimation by 124I-RAIU measurement. A hypothetical minimum activity of 0.5MBq 124I obtained with the iterative reconstruction appeared sufficient with regard to pixel noise as well as visually. Conclusion: This study confirms the potential of 124I-RAIU measurement as alternative method for 131I-RAIU measurement in benign thyroid disease and suggests the option to reduce administered activity. CT information is particularly important in case of retrosternal expansion. The results are relevant because 124I-PET/CT allows additional diagnostic means, i.e., possibility to perform fusion imaging with ultrasound. 124I-PET/CT might be an alternative especially when hybrid 123I-single photon emission computed-tomography (SPECT)/CT is not available.
- Endocrine
- Image Reconstruction
- PET
- 124Iodine
- 124Iodine-PET
- Benign thyroid diseases
- Pre-therapeutic uptake measurement
- Reconstruction parameters
- Copyright © 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.