Statistical characterization of Ultrasound-Contrast-agent velocity fields for prostate cancer localization

Prostate cancer (PCa) is the second leading cause of cancer mortality in men. Visualization of angiogenic vascularization associated with the development of tumors is of particular interest for PCa detection. For this purpose, Dynamic Contrast Enhanced Ultrasound (DCE-US) is a widely used noninvasive imaging modality. The passage of ultrasound contrast agents through the prostate is usually analyzed for the assessment of tissue perfusion. However, the well-known heterogeneous nature of blood flow in angiogenic vasculature hampers the effectiveness of perfusion based parameters. In this regard, quantification of the flow heterogeneity may provide a relevant additional feature for localizing angiogenesis. Statistics based on flow magnitude, as well as its orientation, can be exploited for this purpose. The objective of this study is to estimate the microbubble velocity fields from a standard bolus injection, and to provide a first statistical characterization by performing a spatial entropy analysis. By testing the method on 12 patients with biopsy-proven prostate cancer, we show that the proposed method can be applied effectively to clinically acquired DCE-US data. The method permits estimation of the in-plane flow vector fields and their local heterogeneity, yielding promising results (receiver-operating-characteristic curve area of 0.82) for the detection of prostate cancer.