Morphological ultrasound micro-imaging of thyroid in living mice.

To explore high-frequency ultrasound (HFUS) for non-invasive micro-imaging of thyroid in living mice. Thyroid examination was performed by HFUS in 10 normal C57BL/6 mice, 8 mice treated by propil-thyouracil (PTU), and 22 Tg-TRK-T1 transgenic mice. The dimension of the gland and the presence of nodules were evaluated. Nodules were classified as malignant (hypoechogenicity, poorly defined margins, internal microcalcification, irregular shapes and extra glandular extension) or not and the findings were compared to histological data. Thyroid images were successfully obtained in all the animals analyzed. Normal thyroid reached a volume of 4.92 microl (range 2.11-4.92 microl). Mice with PTU-induced goiter showed diffuse thyroid enlargement (median volume 6.67 microl, range 4.09-8.82 microl). In 19 of 22 (86%) Tg-TRK-T1 mice, HFUS identified a nodular process (the smallest detected nodule had a diameter of 0.46 mm). Eleven nodules were classified as malignant and 8 as benign. Compared to histological analysis, HFUS showed a sensitivity of 100% in the detection of thyroid nodules and a specificity of 60% (2 of the nodules identified by HFUS were not confirmed at the histology). The specificity and sensitivity of HFUS in predicting the malignancy of the thyroid nodules were 83% and 91%, respectively. Thus, HFUS is an accurate imaging modality that can potentially replace more invasive techniques, and, therefore, it represents a significant advancement in phenotypic assessment of mouse models of thyroid cancer.