In vivo multipinhole helical SPECT of a mouse thyroid

Radioiodine imaging using I for single photon emission computed tomography (SPECT) is particularly suitable for studies of the mouse thyroid gland based upon the ability to detect and track emitted gamma radiation. However, the resolution available with parallel-hole SPECT limits the extraction of fine detail in the bilobal structure of a mouse thyroid gland. Though high-resolution single-pinhole imaging is a promising tool, high administered radioactivity is usually required in order to compensate for its low sensitivity without compromising the quality of image reconstruction. Consequentially one must consider the potential high-dose effects on small animals such as mice. Herein we applied multipinhole helical SPECT to address the issues related to in vivo imaging of the mouse thyroid. We have carried out "proof-of-concept" studies using both phantoms and mice and further validated the efficacy of multipinhole helical SPECT by monitoring molecular expression of a transmembrane ion channel called the sodium iodide symporter (NIS) responsible for ¹²⁵I metabolism. In vivo two-pinhole helical SPECT of the mouse thyroid has been successfully achieved with a dose of 200 muCi Na¹²⁵I. The reconstructed images clearly delineated the bilobal structure of the thyroid region. Complementary results from immunohistochemistry and reverse transcriptase polymerase chain reaction (RT-PCR) verified that radioiodine incorporation in the thyroid gland reflects NIS expression. The present studies demonstrate that multipinhole helical SPECT is suitable for in vivo analysis of the mouse thyroid at the molecular level, suggesting potential molecular imaging applications for a variety of biological studies of NIS-expressing tissues in mice such as stomach or mammary tumors.