Ultrasonographic, thermographic and histologic evaluation of MNU-induced mammary tumors in female Sprague-Dawley rats

Abstract

Background: As the worldwide breast cancer burden increases, non-invasive tools, such as ultrasonography and thermography are being increasingly sought after. N-methyl-N-nitrosourea-induced rat mammary tumors are important tools to investigate the usefulness of such imaging techniques.

Objective: This study aimed to integrate both ultrasonographic and thermographic approaches to the vascularization and the superficial temperature of chemically-induced rat mammary tumors.

Materials and methods: Twenty-five female Sprague-Dawley rats were divided into two groups: group I (intraperitoneally administered with N-methyl-N-nitrosourea) and group II (control group). Thirty-five weeks after the administration of the carcinogen, mammary tumors were evaluated using Power Doppler, B Flow and Contrast-enhanced ultrasound, thermography and histology analyses.

Results: Group I animals showed an average of 2.5 mammary tumors per animal, mostly papillary and cribriform non-invasive carcinomas. B Flow detected higher counts of colour pixels than Power Doppler. Contrast-enhanced ultrasound analysis showed a centripetal enhancement order of contrast agent and clear margins. Maximum tumor temperature and thermal amplitude determined by thermography were significantly correlated with tumor volume and with color pixel density, determined by Power Doppler.

Conclusion: B Flow was more sensitive than Power Doppler in detecting tumor vessels, but Power Doppler correlates with thermographic data concerning superficial temperature and may reflect tumor angiogenesis.

Keywords: Mammary tumors; Rat; Vascularization.