IN-VITRO DIAGNOSIS OF AXILLARY LYMPH-NODE METASTASES IN BREAST-CANCERBY SPECTRUM ANALYSIS OF RADIO-FREQUENCY ECHO SIGNALS

Axillary lymph node status is of particular importance for staging and managing breast cancer. Currently, axillary lymph node dissection is performed routinely in cases of invasive breast cancer because of the lack of accurate noninvasive methods for diagnosing lymph node metasta sis. We investigated the diagnostic ability of ultrasonic tissue chara cterization based on spectrum analysis of backscattered echo signals t o detect axillary lymph node metastasis in breast cancer in vitro comp ared with in vitro B-mode imaging. Immediately after surgery, individu al lymph nodes were isolated from axillary tissue. Each lymph node was scanned in a water bath using a 10-MHz instrument, and radio frequenc y data and B-mode images were acquired. Spectral parameter values were calculated, and discriminant analysis was performed to classify metas tatic and nonmetastatic lymph nodes. Forty histologically characterize d axillary lymph nodes were enrolled in this study, including 25 nonme tastatic and 15 metastatic lymph nodes. A significant difference exist ed in the spectral parameter values (slope and intercept) for metastat ic and nonmetastatic lymph nodes. Spectral parameter-based discriminan t function classification of metastatic vs. nonmetastatic lymph nodes provided a sensitivity of 93.3%, specificity of 92.0%, and overall acc uracy of 92.5%. In comparison, B-mode ultrasound images of in vitro ly mph nodes provided a sensitivity of 73.3%, specificity of 84.0%, and o verall accuracy of 80.0%. Receiver operating characteristic (ROC) anal ysis comparing the efficacy of both methods gave an ROC curve area of 0.9888 for spectral methods, which was greater than the area of 0.8980 for B-mode ultrasound. Hence, this in vitro study suggests that the d iagnostic ability of spectrum analysis may prove to be markedly superi or to that of B-mode ultrasound in detecting axillary lymph node metas tasis in breast cancer. Because of these encouraging results, we inten d to conduct an investigation of the ability of spectral methods to cl assify metastatic axillary lymph nodes in vivo. (C) 1998 World Federat ion for Ultrasound in Medicine & Biology.