Mapping Microvasculature with Acoustic Angiography Yields Quantifiable Differences between Healthy and Tumor-bearing Tissue Volumes in a Rodent Model

Abstract

Purpose:To determine if the morphologies of microvessels could be extracted from contrast material-enhanced acoustic angiographic ultrasonographic (US) images and used as a quantitative basis for distinguishing healthy from diseased tissue. Materials and Methods:All studies were institutional animal care and use committee approved. Three-dimensional contrast-enhanced acoustic angiographic images were acquired in both healthy (n = 7) and tumor-bearing (n = 10) rats. High-spatial-resolution and high signal-to-noise acquisition was enabled by using a prototype dual-frequency US transducer (transmit at 4 MHz, receive at 30 MHz). A segmentation algorithm was utilized to extract microvessel structure from image data, and the distance metric (DM) and the sum of angles metric (SOAM), designed to distinguish different types of tortuosity, were applied to image data. The vessel populations extracted from tumor-bearing tissue volumes were compared against vessels extracted from tissue volumes in the same anatomic location within healthy control animals by using the two-sided Student t test. Results:Metrics of microvascular tortuosity were significantly higher in the tumor population. The average DM of the tumor population (1.34 6 0.40 [standard deviation]) was 23.76% higher than that of the control population (1.08 6 0.08) (P , .0001), while the average SOAM (22.53 6 7.82) was 50.73% higher than that of the control population (14.95 6 4.83) (P , .0001). The DM and SOAM metrics for the control and tumor populations were significantly different when all vessels were pooled between the two animal populations. In addition, each animal in the tumor population had significantly different DM and SOAM metrics relative to the control population (P , .05 for all; P value ranges for DM, 3.89 3 10 27 to 5.63 3 10 23 ; and those for SOAM, 2.42 3 10 212 to 1.57 3 10 23). Conclusion:Vascular network quantification by using high-spatialresolution acoustic angiographic images is feasible. Data suggest that the angiogenic processes associated with tumor development in the models studied result in higher instances of vessel tortuosity near the tumor site. Kruse and Ferrara (16), and the design of the prototype imaging transducer has been previously presented by Gessner et al (17). The purpose of this analysis was to test our hypothesis that the morphologies of microvessels could be extracted from US images and used as a quantitative basis for distinguishing healthy from diseased tissue volumes in a rat model. Materials and Methods Animal and Contrast Agent PreparationAll animal protocols used in this prospective study were approved by our institutional animal care and use committee. Animals used in this prospective study were female Fischer 344 rats (approximately 250 g, Charles River Laboratories, Durham, NC). A fibrosarcoma tumor model was established through the implantation of a 1-mm 3 sample of tissue in the right flank region of the animals as previously described (18). Animals were imaged after the tumor had grown larger than 0.5 cm ...

Early Assessment of Tumor Response to Radiation Therapy Using High-Resolution Quantitative Microvascular Ultrasound Imaging

“…tortuosity, density) that allow us to discern cancerous tissue from normal tissue [31,32]. Based on previous research that has demonstrated that microvascular remodeling occurs within days after radiation exposure using optical imaging, we hypothesized that quantification of microvascular changes using acoustic angiography may indicate response to therapy sooner than using tumor volume alone, the current clinical standard for assessing response to treatment [9].…”

A preliminary engineering design of intravascular dual-frequency transducers for contrast-enhanced acoustic angiography and molecular imaging

“…7, the response of the low-frequency transducer was nearly linear at excitation voltages lower than 70 V, having an average transmitting sensitivity of 14.5 kPa/V. nonlinearities showed up when the input was higher than 70 V. at about 100 V, more than 1.2 MPa rarefractional pressure (MI: 0.48) was generated, which was sufficient to produce a high-frequency broadband response from microbubbles imaged in tissue in prior studies [16], [17].…”

“…additionally, a new high-frequency contrast imaging technique, acoustic angiography [16], takes advantage of exciting microbubbles near resonance and detecting their high-frequency, broadband harmonics with sufficient bandwidth separation to achieve both high resolution and high contrast-to-noise ratio (cnr). data has shown that acoustic angiography enables detailed visualization and analysis of microvascular structure [16], [17], and will likely be applicable to vasa vasorum imaging. Thus, we hypothesize that there is a role for contrastenhanced ultrasound imaging in the assessment of atherosclerosis.…”

“…Kruse et al also utilized a dual-frequency transducer arrangement and demonstrated that substantial scattered energy from microbubbles excited near 2 MHz could be detected at a frequency as high as 45 MHz. More recently, Gessner et al [16], [17], [25] utilized mechanically-scanned dual-frequency transducers (transmit at 2 or 4 MHz; receive at 30 MHz) on the Visualsonics Vevo770 (Visualsonics Inc., Toronto, on, canada) to perform high-frequency 3-d contrast imaging of in vivo microvasculature and achieved resolution on the order of 100 μm with a cTr high enough that microvessels could be readily segmented from the images and their morphology analyzed.…”

Dual-frequency IVUS array for contrast enhanced intravascular ultrasound imaging

“…Microvascular images obtained with such 2 MHz transmission and 30 MHz receiving approach were demonstrated to have very high resolution and contrast to tissue ratios (CTR), producing high quality images similar to x-ray angiography, and thus dual frequency ultra-broadband contrast imaging approach is referred to as "acoustic angiography" [13][14][15].…”