In a proof-of-concept study funded by the National Institutes of Health, researchers from the Keck School of Medicine of USC and the California Institute of Technology (Caltech) have shown that an innovative, noninvasive technique can be used to quickly collect 3D images of the human body, from head to foot. The technology combines ultrasound and photoacoustic imaging, which detects sound waves generated by light, to simultaneously collect images of both tissue and blood vessels. The findings, just published in the journal Nature Biomedical Engineering , have the potential to address current gaps in medical imaging.
Imaging is a critical part of modern medicine, informing care across injury, infection, cancer, chronic disease and more. But today's gold standard techniques—ultrasound, X-ray, computed tomography (CT) and magnetic resonance imaging (MRI)—each have their limitations. These include cost and time required for each scan, as well as what the images can capture—how much of the body can be seen at once, how deep images can reach and how much detail they provide.
"You cannot understate the importance of medical imaging for clinical practice. Our team has identified key limitations of existing techniques and developed a novel approach to address them," said Charles Liu, MD, PhD , professor of clinical neurological surgery, urology and surgery at the Keck School of Medicine, director of the USC Neurorestoration Center and co-senior author of the new research.
To show how broadly the technology can be applied, the researchers used the system to image multiple regions of the human body: the brain, breast, hand and foot. Brain imaging was done in patients with traumatic brain injury undergoing surgery, who had portions of their skull temporarily removed. The results show that the technology can capture both tissue structure and blood vessels across a region up to 10 centimeters wide, all in about 10 seconds.
"We've devised a novel method that changes how ultrasound and photoacoustic imaging systems work together, which allows us to achieve far more comprehensive imaging at meaningful depths. It's an exciting step forward in noninvasive diagnostics that doesn't use ionizing radiation or strong magnets," said co-senior author Lihong Wang, PhD, the Bren Professor of Medical Engineering and Electrical Engineering and Andrew and Peggy Cherng Medical Engineering Leadership Chair at Caltech.
A new imaging platform
For the first time in humans, the research team combined two imaging methods, rotational ultrasound tomography (RUST) and photoacoustic tomography (PAT), to create what they call RUS-PAT.
Similar to a standard ultrasound, RUST directs sound waves at an area being imaged. But instead of using a single detector to create a 2D image, it uses an arc of detectors to recreate a 3D volumetric image of the body's tissues. PAT directs a beam of laser light at the same area, which is absorbed by hemoglobin molecules in the blood. These molecules vibrate and give off ultrasonic frequencies, which are measured by the same detectors to create 3D images of blood vessels.
The RUS-PAT system builds on earlier work by the USC-Caltech team , which showed that PAT can also be used to collect images of brain activity.
RUS-PAT offers several potential benefits over existing medical imaging tools. It is less expensive to build than an MRI scanner, avoids the radiation needed for X-ray and CT scans and provides more sophisticated images than conventional ultrasound.
"When we think about the critical limitations of current medical imaging, including expense, field of view, spatial resolution and time to scan, this platform addresses many of them," Liu said.
Broad clinical potential
By imaging the brain, breast, hand and foot, the researchers have shown RUS-PAT's potential across a wide range of health care applications. Brain imaging plays a central role in the diagnosis and treatment of stroke, traumatic brain injury and neurological disease, while breast imaging supports care for one of the most common cancers worldwide.
"Photoacoustics opens up a new frontier of human study, and we believe this technology will be critical for the development of new diagnostics and patient-specific therapies," said Jonathan Russin, MD, co-first author of the study and professor and chief of neurosurgery at the University of Vermont.
Rapid, low-cost imaging of the foot could also aid millions of people living with diabetic foot complications and venous disease.
"This approach clearly has the potential to help clinicians identify at-risk limbs and inform interventions to preserve function in diabetic foot disease and other vascular conditions," said Tze-Woei Tan, MD , coauthor and associate professor of clinical surgery and director of the Limb Salvage Research Program at the Keck School of Medicine.
More work is needed before RUS-PAT is ready for clinical use. One major challenge for brain application remains that the human skull distorts the system's signals, making it hard to collect clear images of the brain. The Caltech team is exploring novel approaches to solve this problem, including adjustments to ultrasound frequency. Further improvements are also needed to ensure consistent image quality across scans.
"This is an early but important proof-of-concept study, showing 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.
About this study
In addition to Liu, Wang, Russin and Tan, the study's other authors are Yang Zhang, Shuai Na, Karteekeya Sastry, Li Lin, Junfu Zheng, Yilin Luo, Xin Tong, Yujin An, Peng Hu and Konstantin Maslov from Caltech Optical Imaging Laboratory, Andrew and Peggy Cherng Department of Medical Engineering, California Institute of Technology.
This work was supported by the National Institutes of Health [R01 CA282505, U01 EB029823 (BRAIN Initiative) and R35 CA220436 (Outstanding Investigator Award)].
