High-frequency Ultrasound Imaging of the Abdominal Aorta

Overview

Source: Amelia R. Adelsperger, Evan H. Phillips, and Craig J. Goergen, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana

High-frequency ultrasound systems are used to acquire high resolution images. Here, the use of a state-of-the-art system will be demonstrated to image the morphology and hemodynamics of small pulsatile arteries and veins found in mice and rats. Ultrasound is a relatively inexpensive, portable, and versatile method for the noninvasive assessment of vessels in humans as well as large and small animals. These are several key advantages that ultraound offers compared to other techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), and near-infrared fluorescence tomography (NIRF). CT requires ionizing radiation and MRI can be prohibitively expensive and even impractical in some scenarios. NIRF, on the other hand, is limited by the penetration depth of light required to excite the fluorescent contrast agents.

Ultrasound has limitations in terms of imaging depth; however, this may be overcome by sacrificing resolution and using a lower frequency transducer. Abdominal gas and excess body weight can severely diminish image quality. In the first case, the propagation of sound waves is limited, while in the latter case, they are attenuated by overlying tissues, such as fat and connective tissue. As a result, no contrast or faint contrast may be observed. Finally, ultrasound is a highly user-dependent technique, requiring the sonographer to be familiar with anatomy and to be able to work around issues, such as the appearance of imaging artifacts or acoustic interference.

Procedure

1. Image setup

Turn the ultrasound system on using the switch on the back. Turn the monitor on.
Plug in the physiological monitoring unit and turn on heart rate and temperature monitoring. Turn on the gel warmer and ensure the light is on.
Check the isoflurane level in the anesthetic vaporizer and refill if necessary.
Turn on your O₂ tank or filtered air source and adjust the air flow on the vaporizer to approximately 1 L/min.
Attach the mouse or rat stage, a

Results

This procedure allowed the anatomical and functional imaging of the abdominal aorta. Acquiring real-time images in short-axis and long-axis by B-mode, M-mode, and Doppler ultrasound takes at least thirty minutes and therefore requires careful monitoring of the anesthetized animal. Some data are readily analyzed on-the-fly, such as two-dimensional B-mode scans (Fig. 1). These data can provide aortic diameter or cross-sectional area measurements. Other data, such as three-dimensional B-mode (Fig. 2), M-mode (Fig. 3), Color

Application and Summary

Recently developed high-frequency ultrasound transducers are well suited for visualizing small structures to a depth of up to 3 cm. Here the versatility of a small animal ultrasound system was demonstrated to acquire in vivo imaging data of the dynamics of the mouse aorta. This technique requires practice and recognition of common difficulties, such as abdominal shadows and Doppler scan alignment. Despite these limitations, it is a powerful and versatile technique for quickly obtaining non-invasive imaging data.