We have designed and built a small-animal single-photon emission computed tomography (SPECT) imaging system equipped with parallel-hole and multipinhole collimators and capable of circular or helical SPECT. Copper–beryllium parallel-hole collimators suitable for imaging the ∼35keV photons from the decay of 125I have been built and installed to achieve useful spatial resolution over a range of object–detector distances and to reduce imaging time on our dual-detector array. To address the resolution limitations in the parallel-hole SPECT and the sensitivity and limited field of view of single-pinhole SPECT, we have incorporated multipinhole circular and helical SPECT in addition to expanding the parallel-hole SPECT capabilities. The pinhole SPECT system is based on a 110mm diameter circular detector equipped with a pixellated NaI(Tl) scintillator array (1×1×5mm3/pixel). The helical trajectory is accomplished by two stepping motors controlling the rotation of the detector-support gantry and displacement of the animal bed along the axis of rotation of the gantry. Results obtained in SPECT studies of various phantoms show an enlarged field of view, very good resolution and improved sensitivity using multipinhole circular or helical SPECT. Collimators with one, three and five, 1-mm-diameter pinholes have been implemented and compared in these tests. Our objective is to develop a system on which one may readily select a suitable mode of either parallel-hole SPECT or pinhole circular or helical SPECT for a variety of small animal imaging applications.

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.

The protection of the thyroid against radioiodine uptake has been an important safety concern for decades. After several studies examined potassium iodide blockade efficacy in the 1960's and 1970's, a standard dosage was prescribed by both the World Health Organization and the U.S. Food and Drug Administration. In this paper, we tested the effectiveness of a scaled version of that standard dosage in comparison to higher doses in mice. A novel gamma camera was employed with a high spatial resolution for precisely quantifying activity within the thyroid and a field of view large enough to image the entire mouse body. Thyroid and whole-body 125I biodistribution was analyzed immediately after exposure and 1 and 7 days later. It was found that 1 h after exposure five times the scaled human dose blocked thyroid uptake about 40% more effectively than the 1X scaled dose. Even after 1 d and 7 d, five times the recommended scaled human dose blocked approximately 10% more effectively than the 1X dose. These data suggest the need for continued evaluation of the effectiveness of KI as a blocking agent and the application of novel, non-invasive technologies to this important human health issue.

O has a half life of only 2minutes [2]. This presents great difficulties since most laboratories do not havecyclotrons capable of producing such short-lived isotopes.Magnetic Resonance Imaging is a technique that uses a strong magnetic field toalign the magnetic moments of the nuclei of the specimen with the field. Radiofrequencypulses are applied on the specimen, which causes the spins to flip. This allows themeasurement of the time it takes for the magnetic moments to realign with the magnetic