Three-dimensional detection of metastases in freshly excised human lymph nodes using quantitative ultrasound backscatter and envelope parameters.

Abstract

High-frequency quantitative ultrasound (QUS) may offer a reliable means of identifying tumor foci in dissected lymph nodes. Detection of metastases is essential for staging and treatment planning. Conventional histopathology methods do not allow nodes to be examined over their entire volume. Therefore, our objective is to develop QUS methods to improve detection of clinically significant lymph-node metastases. A single-element 26-MHz ultrasound transducer was used to scan and digitally acquire rf echo-signal data in three-dimensional (3D) from more than 200 lymph nodes. Thirteen QUS estimates based on backscatter spectra and envelope statistics were computed in 3D. Serial-sectioning histology was performed at 50-μm intervals to depict cancer foci in 3D. Classification based on QUS estimates was performed using linear-discriminant analyzes; areas under ROC curves (AUCs) were computed. The most-significant QUS estimates for metastases detection were identified. Comparison of the 3D QUS results and 3D histology showed promising classification results. The AUC for the linear combination of four QUS estimates was 0.91 for a dataset of 73 breast-cancer nodes. Similarly, using only two QUS estimates, an AUC of 0.97 was obtained for a dataset of 143 colorectal-cancer nodes. These results suggest that QUS may be effective in distinguishing metastatic nodes from normal nodes.