Perbandingan Jarak Kolimator Terhadap Nilai Thyroid Uptake Pada Pemeriksaan Uji Tangkap Thyroid Menggunakan Kamera Gamma

The accuracy of thyroid uptake quantification using a gamma camera with Tc-99m pertechnetate is influenced by acquisition geometry parameters, particularly the distance between the collimator and the patient. This study aimed to evaluate the effect of collimator distances of 5 cm and 20 cm on thyroid uptake percentage values in patients with normal thyroid function. A quantitative analytical study with a within-subject paired design was conducted among 12 patients with normal thyroid function at Santosa Kopo Hospital, Bandung, during June–August 2026. Each patient was scanned at collimator distances of 5 cm and 20 cm using a planar anterior acquisition with an LEHR collimator (128 × 128 matrix, zoom 4, 10-minute acquisition). Differences in uptake values were analyzed using a paired t-test (α = 0.05), Bland–Altman bias analysis, and Spearman rank correlation. All subjects demonstrated higher thyroid uptake values at a 5 cm distance (* ) compared with 20 cm ( ). Increasing the collimator distance reduced the uptake value by a mean difference of * * percentage points, corresponding to a relative reduction of 36.46% ( *; * *; Cohen’s * ). Bland–Altman analysis confirmed a positive mean bias of 0.32% (95% LoA: 0.10–0.54%). Patient characteristics, including age, body weight, and radiopharmaceutical dose, were not significantly correlated with the reduction in uptake ( *). Variation in collimator distance significantly affects the percentage thyroid uptake values obtained during thyroid uptake examinations. Increasing the scanning distance reduces the measured uptake due to degradation of spatial resolution and count loss outside the ROI. Standardization of the collimator distance as close as possible to the patient’s neck (5 cm) is recommended for clinical protocols