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Initial Clinical Experience Imaging Scatterer Size and Strain in Thyroid Nodules

Department of Radiology, University of Tennessee, Memphis, Tennessee USA (T.W., L.V.); and Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin USA (Q.C., J.A.Z., T.V.).

Address correspondence to Thaddeus Wilson, PhD, Department of Radiology, University of Tennessee, 865 Jefferson Ave, Memphis, TN 38163 USA. E-mail: tawilson{at}utmem.edu

Objective. This article describes a new research ultrasound scanner that can be programmed to produce elastograms and backscatter parametric images in real time. Its performance was evaluated in a clinical setting. Methods. Radio frequency data were acquired from 13 patients with thyroid nodules and from 4 normal thyroids, along with reference phantom data. Scatterer size was deduced by measuring the backscatter versus frequency and fitting data to a model. Strain was obtained by a cross-correlation method, comparing precompression and postcompression radio frequency signals. Scatterer size contrast was defined as the observed contrast between the "normal" and "abnormal" tissue in the same gland or, when considering diffuse conditions, by comparing with normal values. Strain contrast was estimated if abnormal and normal tissue was captured in the same palpation, that is, excluding diffuse disease, which was the case for 9 subjects. Results. On scatterer size images, 4 nodules exhibited positive contrast versus the adjacent normal parenchyma, indicating larger scatterers. Five nodules were isoechoic, and 4 had negative contrast. Four nodules exhibited positive strain contrast, indicating that they were softer than the normal parenchyma. Two nodules had the same brightness, and 3 were darker than the background thyroid tissue on strain images. Conclusions. Contrast was observed between nodules and thyroid parenchymal tissue for both types of parametric images. Further work is needed to determine whether the diagnostic importance of these parameters in characterizing thyroid nodules might be worthwhile. Both modes must be of a sufficient frame rate to provide real-time feedback to operators, which will require further work.

Key Words: acoustic backscatter coefficient • elastography • frequency-dependent backscatter • quantitative imaging • sonographic tissue characterization • thyroid

Abbreviations: FNA, fine-needle aspiration • RF, radio frequency • TSH, thyrotropin

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