Currently, the evaluation of thyroid cancer relies on the use of fine needle aspiration biopsy as non-invasive imaging methods do not provide sufficient levels of accuracy for the diagnosis of this disease. In this study, the potential of quantitative ultrasound methods for characterizing thyroid tissues was studied using a rodent model ex vivo. A high-frequency ultrasonic scanning system (40 MHz) was used to scan thyroids extracted from mice that had spontaneously developed thyroid lesions (cancerous or benign). Three sets of mice were acquired having different predispositions to developing thyroid anomalies (a C-cell adenoma, a papillary thyroid carcinoma (PTC), and a follicular variant papillary thyroid carcinoma (FV-PTC)). A fourth set of mice did not develop thyroid anomalies (normal mice) and were used as controls. The backscatter coefficient was estimated from excised thyroid lobes for the different mice. From the backscatter coefficient versus frequency (25 to 45 MHz), the effective scatterer diameter (ESD) and effective acoustic concentration (EAC) were estimated. From the envelope of the backscattered signal, the homodyned K distribution was used to estimate the k parameter (ratio of coherent to incoherent signal energy) and the μ parameter (number of scatterers per resolution cell). Statistically significant differences were observed between the malignant thyroids and the normal thyroids based on the ESD, EAC and μ parameters. The mean values of the ESDs were 18.0 ± 0.92, 15.9 ± 0.81, and 21.5 ± 1.80 µm for the PTC, FV-PTC and the normal thyroids, respectively. The mean values of the EACs were 59.4 ± 1.74, 62.7 ± 1.61, and 52.9 ± 3.42 dB (mm−3) for the PTC, FV-PTC and the normal thyroids, respectively. The mean values of the μ parameters were 2.55 ± 0.37, 2.59 ± 0.43, and 1.56 ± 0.99 for the PTC, FV-PTC and the normal thyroids, respectively. Statistically significant differences were observed between the malignant thyroids and the C-cell adenomas based on the ESD and EAC parameters with estimated values for the ESD of 21.3 ± 1.50 µm and EAC of 54.7 ± 2.24 dB (mm−3) for the C-cell adenomas. These results suggest that high frequency quantitative ultrasound may enhance the ability to detect and classify diseased thyroid tissues.

The incidence of diagnosed thyroid cancer has increased significantly over the last decades. Although advances in ultrasonic imaging have increased the malignancy detection rate, current ultrasonic imaging markers do not provide a sufficient level of diagnostic accuracy to replace biopsy. Recent studies suggest that ultrasound parameters derived from backscatter coefficients may allow differentiating among different types of thyroid tumors and normal tissues in a rodent model ex vivo. In this work, the potential use of attenuation coefficient (AC) estimates for the same purpose was explored. A sample set of 24 excised mice thyroids were scanned using a 40-MHz, f/3 single element transducer. The experimental dataset contained six animals that developed papillary thyroid carcinoma (PTC), five that developed follicular variant papillary thyroid carcinoma (FV-PTC), five that developed c-Cell adenoma (c-Cell) and eight that did not develop thyroid abnormalities (control). AC slope maps were generated with a spectral log difference method using 0.5mm by 0.5mm data blocks. Outliers of each slice due to artifacts in AC estimation were discarded using the Thompson Tau method. Finally, a Kruskal-Wallis test was conducted to analyze if statistically significant differences in the mean AC slope among the four groups existed. The median and interquartile range for each group were 1.29 and 0.22 dB/cmMHz for the control group, 1.64 and 0.09 dB/cm-MHz for c-Cell, 1.16 and 0.12 dB/cm-MHz for PTC and 1.33 and 0.08 dB/cmMHz for FV-PTC, respectively. These values are consistent with previous reports of attenuation in thyroid tissues. The KruskalWallis test reported statistically significant differences between the c-Cell group and the other groups of study and between the PTC and FV-PTC groups (p<0.05). These preliminary results suggest that the AC may be used to characterize thyroid tissues.

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