Acoustic radiation force impulse imaging for evaluation of the thyroid gland.

OBJECTIVES: To study acoustic radiation force impulse (ARFI) imaging as a new quantitative and noninvasive tool for evaluating thyroid nodules and to compare ARFI imaging with other tools for studying thyroid nodules: sonography, real-time elastography, and fine-needle aspiration biopsy.

METHODS: We conducted a prospective study from June 2011 to June 2012, which analyzed 157 thyroid nodules (129 benign and 28 malignant) using the ARFI technique and a 9-MHz probe. Shear wave velocities (SWVs) were obtained while the patients held their breath to avoid respiratory movement artifacts. All nodules underwent conventional sonography and real-time elastography of the thyroid gland. All patients received either a cytologic examination using fine-needle aspiration biopsy or a histologic examination from thyroid surgery to verify the diagnosis (reference standard).

RESULTS: The mean SWV ± SD on ARFI imaging in healthy, nodule-free thyroid glands was 2.04 ± 0.51 m/s (range, 0.76-3.63 m/s). The mean SWV in benign thyroid nodules was 1.70 ± 0.55 m/s (range, 0.50-2.80 m/s), and the mean SWV in malignant nodules was 3.39 ± 1.15 m/s (range, 1.50-6.08 m/s). When we used an SWV greater than 2.50 m/s for the diagnosis of malignant nodules and less than 2.50 m/s for the diagnosis of benign nodules, the sensitivity and specificity of ARFI imaging were 85.7% and 96.0%, respectively.

CONCLUSIONS: We found that SWVs were substantially higher in malignant nodules than benign ones. Perhaps if ARFI imaging is used in conjunction with sonographic findings and patient demographics, it will be possible to find a combination of factors that would yield a negative predictive value high enough to distinguish benign from malignant nodules with confidence, which may lead to a decrease in the biopsy rate for benign nodules.