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Acute Increases in Murine Tumor Echogenicity After Antivascular Ultrasound Therapy

A Pilot Preclinical Study

Department of Clinical Studies, School of Veterinary Medicine (A.K.W.W.), University Laboratory Animal Resources (R.M.B.), and Department of Radiology (S.M.S., C.M.S.), University of Pennsylvania, Philadelphia, Pennsylvania USA.

Address correspondence to Chandra M. Sehgal, PhD, Department of Radiology, University of Pennsylvania Medical Center, 3400 Spruce St, Philadelphia, PA 19104 USA. E-mail: sehgalc{at}uphs.upenn.edu

Objective. This study was designed to determine whether the echogenicity of neoplastic tissues changed as a result of low-intensity insonation and whether such alterations were related to an anti-vascular effect. Methods. In 21 mice, implanted melanomas were insonated at either 1, 2, or 3 MHz using low-intensity ultrasound (spatial-average temporal-average intensity, 2.1 W/cm²). B-mode (mean gray scale) and contrast-enhanced power Doppler (percentage area of flow) measurements were made on each tumor before and after therapy. Results. There was an increase in the echogenicity of the tumors with the increase in the frequency of the therapy beam and an accompanying decrease in tumor vascularity. Conclusions. Although the mechanisms responsible for the echogenicity change are not fully understood, it appears that an increase in the tumor mean gray scale was, at least in part, related to tissue inhomogeneities formed after disruption of the tumor neovasculature.

Key Words: antivascular ultrasound therapy • B-mode gray scale • vascular disrupting agent

Abbreviations: PAF, percentage area of flow