Quantification of radioactivity by planar gamma-camera images, a promoted method of absorbed dose in the thyroid after iodine-131 treatment

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.

Quantifying partial volume effect in SPECT and planar imaging: optimizing region of interest for activity concentration estimation in different sphere sizes

“…In recent years, with the advancement of the image processing field, a more precise ROI and background regions might be obtained, leading to more accurately quantifying planar imaging as well as reducing PVE. For example, [42] proposed a new technique to define the ROI boundary according to the upper limit window level and a ring-like shape of the background to correct ROI counts and obtain 131 I activity quantification in rat thyroid. The results were promising and revealed that using the above-mentioned method can lead to a more accurate 131 I quantification of thyroid uptake by SPECT planar imaging in an in-vivo rat study [42].…”

“…For example, [42] proposed a new technique to define the ROI boundary according to the upper limit window level and a ring-like shape of the background to correct ROI counts and obtain 131 I activity quantification in rat thyroid. The results were promising and revealed that using the above-mentioned method can lead to a more accurate 131 I quantification of thyroid uptake by SPECT planar imaging in an in-vivo rat study [42]. Regarding the great importance of choosing appropriate ROI in activity estimation, the values of ROI/size can be helpful for reducing PVE and consequently more accurate activity quantification in patient organs with different sizes, especially small organs.…”