Lead filter effects to improve image quality in ¹³¹I Whole-body SPECT/CT of high uptake thyroid cancer patient

Objectives In order to reduce artifacts caused by high uptake tumor in ¹³¹I whole-body scan of thyroid cancer patients, B-filter is used. However, SPECT/CT has a limitation not to use B-filter due to the detector rotation in spite of the advantage of CT scan. Therefore, the lead filter was invented which could be applied to ¹³¹I whole-body SPECT/CT to reduce artifacts and improve overall image quality.

Methods After injecting ¹³¹I (solution), manufacturing IEC (international electro-technical commission) phantom and wrapping the whole 360° of phantom with lead (8mm thickness, 15cm width) was experimented using SPECT/CT (GE, USA) scanner (6° angle/view, 40 sec/view, 360° total angular range, step and shoot mode), After adding one hot sphere in the middle of phantom, 5 sphere except largest sphere and smallest sphere were assumed as metastasis focus. When using lead filter, only virtual thyroid cancer parts made filtered after making hot region (diameter 10mm, length 30mm) at the upper part of 5cm. And, after reorganizing the acquired data of before-and-after using lead filter with OSEM (ordered Subset expectation maximization) method (2 iteration, 10 subset), data were analyzed with the blind-tests by 10 nuclear medicine reading doctors.

Results In the evaluation of 9 reading doctors out of 10, hot sphere was not almost seen when setting the density in the images before using lead filter to virtual thyroid cancer, and when setting the density to hot sphere, virtual thyroid cancer was expanded than actual size and artifacts greatly occurred. In the images using lead filter, artifacts decreased around virtual thyroid cancer and virtual thyroid cancer could be examined well even when the density was set to hot sphere.

Conclusions If ¹³¹I whole-body SPECT/CT is executed using 360° 3D lead filter in case of high uptake thyroid cancer patient, artifacts decreased and image quality is improved and CT image scan information could be obtained, and therefore, the quantity of image information is more excellent that plane scan information.