Studies on measurement of thyroid uptake rate on 131I scintigraphy images

2626 Objectives It is important to evaluate accurately 131I uptake in the thyroid gland before the internal 131I therapy for patients with Graves’ disease. The purpose of this study was to compare measurements of 131I thyroid uptake rate (TUR) before and after 131I therapy by using thyroid phantom and clinical data. Methods An original thyroid phantom was designed and the 131I solutions were enclosed into the phantoms. In the phantom study, TUR was calculated with the data acquired from planar and SPECT images and the TUR measurement system (AZ-800, Anzai Medical). The TUR values obtained by these three kinds of methods were compared with that measured by the automatic well counter (ACCUFLEXγ 7001, Hitachi-Aloka Medical) as the standard. In the clinical study, the equation for expressing the relationship between the 131I radioactivity and the counts on the planar images was established using the 131I capsule and planar images. The TUR values in clinical cases were measured and compared with those measured by the TUR measurement system before 131I therapy. Results In the phantom studies, the maximum errors of the TUR values obtained using planar and SPECT images, and the TUR measurement system were 4.79, 4.91, and 9.86%, respectively. The results show that the TUR values with errors less than 5% can be obtained by planar and SPECT images. In the human studies, there was a close correlation between the TUR values measured by the TUR measurement system before 131I therapy and those measured on planar images after 131I therapy. There was up to 25% differences between the TUR values measured before 131I therapy and those after therapy. Conclusions The phantom studies show that TUR can be measured on planar and SPECT images with errors less than 5%. The human studies show that the TUR values measured on planar images after 131I therapy correlate closely with those measured before the therapy, although there are differences up to 25% between them.