Mean flow rate and integrated perfusion estimates obtained with contrast-assisted ultrasound

In this paper, we detail blood flow studies in a rat mammary adenocarcinoma model using contrast-enhanced ultrasound. Imaging was implemented on a Siemens Elegra, and utilized the subharmonic phase-inversion detection scheme introduced last year by Chomas, et al. Parameters used in these studies include a transmission frequency of 6 MHz, receive center frequency of 3 MHz, and transmitted pressures ranging from 800 kPa -2.2 MPa. A base study was completed to observe normal tumor growth over a five-week period. Measures of mean replenishment time and integrated enhancement were evaluated and compared to the percentage of viable tumor observed with histology. Results obtained for replenishment measures in tumors were also compared with those obtained in the normal kidney cortex. Mean replenishment time intervals of 6-14 seconds were observed in the tumors. The histogram of replenishment times within a given tumor plane has a wide distribution. We hypothesize this may be due to variably and poorly perfused tissue, abnormal vascular architecture, and tortuosity. The zeroth and first moments of the histograms of integrated enhancement provided an additional method of analysis.