Abstract
Three-dimensional imaging is valuable to noninvasively assess angiogenesis given the complex 3-D architecture of vascular networks. The emergence of high frame rate (HFR) ultrasound, which can produce thousands of images per second, has inspired novel signal processing techniques and their applications in structural and functional imaging of blood vessels. Although highly sensitive vascular mapping has been demonstrated using ultrafast Doppler, the detectability of microvasculature from the background noise may be hindered by the low signal-to-noise ratio (SNR) particularly in the deeper region and without the use of contrast agents. We have recently demonstrated a coherence-based technique, acoustic subaperture imaging (ASAP), for super-contrast vascular imaging and illustrated the contrast improvement using HFR contrast-enhanced ultrasound. In this work, we provide a feasibility study for microvascular imaging using ASAP without contrast agents, and extend its capability from 2-D to volumetric vascular mapping. Using an ultrasound research system and a preclinical probe, we demonstrated the improved visibility of microvascular mapping using ASAP in comparison to ultrafast power Doppler (PD) on a mouse kidney, liver, and tumor without contrast agent injection. The SNR of ASAP images improves in average by 10 dB when compared to PD. In addition, directional velocity mappings were also demonstrated by combining ASAP with the phase information extracted from lag-1 autocorrelation. The 3-D vascular and velocity mapping of the mouse kidney, liver, and tumor were demonstrated by stacking the ASAP images acquired using 2-D ultrasound imaging and a trigger-controlled linear translation stage. The 3-D results depicted clear microvasculature morphologies and functional information in terms of flow direction and velocity in two nontumor models and a tumor model. In conclusion, we have demonstrated a new 3-D in vivo ultrasound microvascular imaging technique with significantly improved SNR over existing ultrafast Doppler.
Highlights
A NGIOGENESIS is an important predictor of both normal physiological processes and biological behavior of many diseases [1]–[3]
Existing flow imaging modalities that are able to visualize tumor vascular environment include computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound imaging. Both CT and MRI have the advantages of full-3-D volumetric imaging and reasonable spatial resolution, the long acquisition time and relatively high cost result in a lack of accessibility
Starting from the channel data acquired from an high frame rate (HFR) ultrasound system, an ultrasound image can be reconstructed by delay-and-sum (DAS) applied to the radio frequency (RF) signal across the receive aperture with M elements
Summary
A NGIOGENESIS is an important predictor of both normal physiological processes and biological behavior of many diseases [1]–[3]. Existing flow imaging modalities that are able to visualize tumor vascular environment include computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound imaging. Both CT and MRI have the advantages of full-3-D volumetric imaging and reasonable spatial resolution, the long acquisition time and relatively high cost result in a lack of accessibility. Ultrasound, on the other hand, is portable and affordable. It has the highest temporal resolution among these modalities, high and scalable spatial resolution, and the capability for real-time imaging making ultrasound an indispensable tool for frontline clinical use
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