Ultrasonic spectroscopy at 20–80 MHz to evaluate lymph node status during breast conserving surgery

Abstract

High-frequency (20–80 MHz) ultrasound was used to evaluate 77 lymph nodes from 38 patients to identify metastatic breast cancer. Lymph nodes were resected during routine breast conserving surgery. Through-transmission point measurements were collected from the resected nodes immediately following surgery using two single-element transducers (50-MHz center frequency, 6.35-mm diameter), a high-frequency ultrasonic pulser-receiver,and a 1-GHz digital oscilloscope. Attenuation and two spectral parameters—peak density and tortuosity—were calculated from the ultrasonic waveforms and power spectra, respectively. Fisher’s exact test was used to optimize the sensitivity and specificity for each parameter separately and for multivariate analyses. A multivariate analysis of peak density versus tortuosity with a cube-root decision boundary produced the most significant results, with an 89.6% accuracy, 100% sensitivity, 88.4% specificity, and p-value of 6.12 × 10−7. Computer simulations and phantom experiments showed that the sensitivity of the spectral parameters to tissue malignancy arises from ultrasonic Mie scattering from cell nuclei and nuclear pleomorphism. The results demonstrate that ultrasonic spectroscopy at 20–80 MHz provides high sensitivity and specificity for malignant lymph nodes in the breast, and has promise as a rapid, intraoperative, and potentially in vivo diagnostic tool for surgeons and a wide range of soft tissue cancers.