Thyroid Ultrasound > New Horizons

New Horizons

As it appears in Ultrasound Clinics April 2009 issue, "Ultrasound of Thyroid Nodules" by Desser TS and Kamay A.

Three-dimensional (3D) ultrasound, in which a free-hand or automated sweep of the transducer generates an image volume that can be displayed in axial, coronal, or sagittal planes, can generate good-quality images of multinodular thyroids. 

Compound imaging is a signal-averaging technique designed to reduce speckle noise and improve contrast resolution, and has been shown to increase contrast-to-noise ratio in clinical thyroid images. 

Tissue harmonic imaging (THI) uses the first harmonic of the transmitted frequency for image formation and results in images with less noise. THI appears to improve lesion conspicuity and gray-scale contrast between lesions. 

Sonographic contrast agents have been used in other organ systems, but to date have not had a significant role in thyroid nodule imaging.

Elastography is an evolving technology with early reported promise of differentiating benign nodules from malignant nodules with 96% specificity and 82% specificity. Similar to palpation, the rationale behind elastography is that a cancerous nodule is stiffer, with less elastic deformation compared with muscle or a benign thyroid nodule. Ultrasound elastography is a dynamic method in which an external compressive force is applied during scanning and the degree of distortion used to estimate the stiffness of the tissue of interest. Ultrasound elastography has already been used to differentiate cancer from benign lesions in the prostate, breast, pancreas, and lymph nodes. Different methods of identifying a stiff thyroid nodule are currently being studied, including manual compression with comparison of the lesion during a cine loop using speckle tracking in two and three dimensions, or with evaluation of the nodule under normal respiratory and cardiac pulsations. Although promising, elastography needs further study to determine whether the method will prove as robust when used on a larger scale.

It is of note that Cronan JJ (Radiology June 2008), raises the question of whether it is wise to continue performing thyroid ultrasounds at the current rate considering the significant overlap of benign and malignant appearances, cost, increasing incidental detection and the low rate of malignancy and its slow-growing nature: "Thyroid Nodules: Is It Time to Turn Off the US Machines?" by Cronan JJ.

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