Abstract
Iodine-131 (131I) is an essential and widely used radioisotope in thyroid diseases and animal experiments. Planar imaging has been considered the most popular method for 131I thyroid uptake radioactive activity quantification. The ROI defining section is essential and can affect the accuracy of quantitative results. However, a consistent method has not been proposed. In this study, a UC-ROI defining method based on ULWL setting and colour display grade was applied. Three steps were performed: image acquisition of five standard activity models and obtaining the exact value that the counts per radioactive activity contributes to the ROI; image acquisition of 20 rat thyroids and obtaining the counts of the ROI (thyroid); and calculating the rat thyroid radioactive activity and comparing these values with the true values. The accuracy of quantification activity of 131I in rat thyroid reached 2.62% ± 0.41%. The mean quantification within 5% could be achieved in 19 of 20 rat thyroids. No significant difference existed between calculated thyroid 131I activity and true values with a paired matched-test (t = −0.384, P = 0.706 > 0.05). The results indicated that with the UC-ROI defining method, more accurate thyroid uptake 131I radioactive activity quantification by SPECT planar imaging can be achieved in vivo rat study.
Highlights
With the increasing use of radiopharmaceuticals both in clinics and animal experiments, precise estimation of the absorbed dose in patients is crucially required to evaluate the prognosis and side effects[1]
All the images of five standard activity models were processed by drawing a UC-region of interest (ROI) and a circle background ROI (Fig. 5a)
Results of deviation for UC-ROI defining method is listed as a contrast
Summary
With the increasing use of radiopharmaceuticals both in clinics and animal experiments, precise estimation of the absorbed dose in patients is crucially required to evaluate the prognosis and side effects[1]. For clinical practice and animal researches, a simple, accurate, easy-to-reach quantitative method of planar imaging is desired. With the development of image data processing workstations, a more accurate ROI and background regions can be defined, which has made the exact quantification of planar imaging possible. We adopted a new method for defining the ROI border based on the upper limit window level (ULWL) and a ring-like shape of the background to obtain corrected ROI counts and achieve quantification of thyroid uptake 131I activity. Three steps were performed to derive absolute values for radioactive activity in Bq (1 μCi = 3.7 × 104 Bq) from planar images and verify accuracy[5,13]: image acquisition of standard activity models and obtaining the exact value that the counts per radioactive activity contribute to the ROI; image acquisition of rat thyroids and obtaining the counts of the ROI (thyroid); and calculating the rat thyroid radioactive activity and comparing these values with the true values. We tried to verify the accuracy of the quantification in rats experiments
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