It is possible to distinguish between papillary carcinomas and other lesions with the thyroid stiffness index calculated from US elastography using carotid arterial pulsation.

Objective. The purpose of this study was to evaluate the feasibility of ultrasound thyroid elastography using carotid artery pulsation as the compression source and its potential for differential diagnosis of thyroid nodules. Methods. Baseband sonographic data were acquired for 16 thyroid nodules from 12 patients. The natural pulsation of the carotid artery was used as the compression source, and thyroid strain was estimated offline. For quantitative assessment of thyroid tissue stiffness, a new metric called the thyroid stiffness index (TSI) was computed as the ratio of strain near the carotid artery (high-strain region) to that of a stiff region (low-strain region) inside a thyroid nodule. The stiffness information from elastography was correlated with histopathologic findings. Results. The TSI for papillary carcinoma (n = 9) was higher than the TSI for a benign nodular goiter (n = 6), indicating that papillary carcinoma is stiffer than a benign nodular goiter (P < .05). In 1 patient, we were able to distinguish a papillary carcinoma nodule and a benign nodular goiter located in the same thyroid lobe based on the stiffness information obtained from elastography. This suggests that elastography could be used for guiding fine-needle aspiration biopsy to a thyroid nodule with a high probability of cancer. Conclusions.The results from this preliminary study indicate the feasibility of the pulsation-induced thyroid elastography. Ultrasound thyroid elastography using carotid artery pulsation appears to have the potential for noninvasively differentiating papillary carcinoma from benign nodular goiter. Future studies are needed to evaluate the efficacy of elastography in detecting thyroid cancer and guiding thyroid biopsies. Key words: carotid artery pulsation; elastography; thyroid; thyroid stiffness index; ultrasound.Received February 5, 2007,

For ultrasound thyroid elastography, hand-induced freehand compression is typically applied on the neck area to induce strain in the thyroid. In contrast to this conventional approach, we have utilized natural pulsation of the carotid artery as the compression source for thyroid elastography. We have developed strain processing techniques to aid interpretation of strain induced by internal compression. Furthermore, we have developed a metric called thyroid stiffness index (TSI) to provide a more quantitative measure of thyroid tissue stiffness. From 18 patients with thyroid nodules and 5 healthy volunteers, the pulsation-induced thyroid strain was estimated and analyzed. We have found that pulsation of the carotid artery can serve as a repeatable and operator-independent compression source for thyroid elastography. TSI results from 23 subjects indicate that papillary carcinoma is stiffer than other thyroid lesions and normal thyroid glands (p<0.001), thus TSI may be useful in differentiating papillary carcinoma, the most prevalent thyroid cancer, from other lesions. With high quality strain images and a quantitative stiffness measure, thyroid elastography using natural carotid artery pulsation has good potential to provide non-invasive differential diagnosis of thyroid nodules.

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