Multispectral photoacoustic assessment of thyroid cancer nodules in vivo

Thyroid cancer is one of the most commonly diagnosed cancers in the world. Ultrasonography and fine-needle aspiration biopsy are the typical standard-of-care method for diagnosing thyroid nodules. However, about 20% of fine-needle aspiration biopsies generate undeterminable results, which can lead to overdiagnosis and overtreatment. In this study, we propose photoacoustic imaging as an additional triaging tool for identifying cancerous nodules in vivo. We enrolled and photoacoustically imaged 28 patients (19 malignant and 9 benign) who have thyroid nodules. To perform multispectral analysis, we used a series of 5 different wavelengths (i.e., 700, 756, 796, 866, and 900 nm), which were selected based on the optical absorption property of oxy-and deoxy-hemoglobin. All the raw data were automatically stored for further off-line processing, while the corresponding images were visualized on the clinical ultrasound machine in real-time. By using the multispectral photoacoustic data, we calculated the oxygen saturation values of the nodule areas. The result showed that the oxygen saturation level of malignant nodules was lower than that of benign nodules (p < 0.005), which matched with the well-known property of cancerous nodules. Based on the oxygen saturation value, malignant and benign nodules were differentiable with a sensitivity of 80% and specificity of 89%. The result showed the great potential of multispectral photoacoustic analysis as a novel method to identify malignancy of thyroid nodules in vivo. We also verified the robustness of the result by testing reproducibility and comparing inter-physician interpretation.