RUS-PAT ultrasound approach produces 3D vascular images

An imaging system that combines rotational ultrasound (RUS) with photoacoustic tomography (PAT) could help produce 3D whole-body images, according to a proof-of-concept study published January 16 in Nature Biomedical Engineering. 

This approach led to both tissue structure and blood vessels being captured across a region up to 10 cm wide in about 10 seconds, wrote a team of researchers led by Charles Liu, MD, PhD, from the University of Southern California in Los Angeles, in collaboration with the California Institute of Technology in Pasadena. 

“3D RUS-PAT is a powerful tool for high-speed, dual-contrast imaging of the human body with potential for rapid clinical translation,” Liu and colleagues wrote. 

While ultrasound has important applications for imaging many parts of the body, its limited field of view negatively affects its capabilities compared with other imaging modalities such as MRI, CT, and x-ray. However, each of the latter modalities has its share of limitations as well, including higher costs, contraindications, accessibility, and the use of ionizing radiation, among others. 

RUS-PAT uses a single source for ultrasound transmission and a rotating array module for detection. This allows for images of 3D structures to be obtained with a larger field of view. The approach generates wide-field acoustic waves using a single-element ultrasound transducer and co-axially rotates the arc-shaped detection ultrasonic transducer array to achieve 3D panoramic hemispherical ultrasonic detection. RUS is fully compatible with PAT. This combination makes way for more comprehensive imaging at meaningful depths, the team noted. 

“By switching the acoustic source to a light source, the system is conveniently converted to PAT mode to acquire angiographic images in the same region,” the team added. 

Liu and co-authors explored applications for RUS-PAT, including using the system to image multiple regions of the human body, such as the brain, breasts, hands, and feet. The team performed brain imaging in patients with traumatic brain injury undergoing surgery, who had portions of their skull temporarily removed. 

The system achieved a field of view of 10 cm and an isotropic spatial resolution of about 400 μm for both RUS and PAT. The field of view is decided by the region of the source acoustic field and the light illumination, which the researchers noted is smaller than the diameter of the arc-shaped arrays.  

The total scanning time to acquire each volumetric image was 10 seconds, the team also reported. It also observed comparable structures and the width of the object, about 1.5 mm with RUS and PAT. 

The researchers reported maximal signal-to-noise ratio (SNR) percentage changes of 55% for RUS and 58% for PAT from an acoustic perspective. However, for PAT when considering both light and acoustic attenuation in soft tissue, the distribution of SNR in the field of view showed a drop of about 50 decibels with a 4 cm penetration depth. 

The study authors suggested that, among other applications, RUS-PAT could provide rapid, low-cost imaging of the foot, useful for managing care for people living with diabetic foot complications, venous disease, and other vascular diseases and conditions. 

In a prepared statement, Liu said this “early but important proof-of-concept study” shows that RUS-PAT can create medically meaningful images across multiple parts of the body.  

“We’re now continuing to refine the system as we move toward future clinical use,” Liu said. 

Read the full study here.