Non-Invasive Imaging Technology Probes Deeper Into Tissue

Photoacoustic tomography image showing mouse fat deposits around blood vessels, distinct from fat under the skin. Click on image for full-size view. (Purdue University)

29 August 2018. An imaging process that combines ultrasound and lasers is shown in tests with lab samples and in animals to provide clearer and more detailed images of tissue deeper in the body. An engineering team from Purdue University in West Lafayette, Indiana describes the technology in the 22 August issue of the journal Photoacoustics.

Researchers from the Cardiovascular Imaging Research Lab in Purdue’s biomedical engineering school are seeking better tools for diagnosing serious non-communicable diseases affecting large segments of the population, such as heart disease, cancer, and complications from diabetes. In many of these cases, the disease can be prevented or better managed if caught early, and the team led by biomedical engineering professor Craig Goergen studies imaging techniques to make early diagnostics easier and more readily available.

“That means there will be a great need for medical imaging,” says Goergen in a university statement. “Trying to diagnose these diseases at an earlier time can lead to improved patient care.”

One of those technologies is photoacoustic tomography that uses both sound and light waves to return images from inside the body. The technique sends laser beams through the skin, which absorbs the energy and heats the tissue below. The heated tissue expands, which can be detected and measured with ultrasound waves, also sent from outside the skin. The ultrasound device then receives and assembles the signals into visual images highlighting differences in absorption of the laser beams to show details of the underlying tissue.

While photoacoustic tomography is considered an important advance in medical imaging, it still does not provide sufficient detail and resolution for some applications. One of those potential uses is imaging fat deposits around arteries, a condition known as atherosclerosis, or hardening of the arteries, a risk factor of heart disease. Among the problems with detecting these deposits are the presence of fat under the skin that also absorbs laser beams, as well as properties of fat tissue that diffuse light waves and weaken the returned signals.

Goergen and colleagues identified techniques for fine-tuning photoacoustic tomography to better penetrate the light and sound waves into tissue and better capture the signals reflected back. The techniques include more precise angles for aiming the laser and ultrasound beams, and more sensitive methods for processing the returned signals to separate out the noise from the desired data. The researchers also designed a motorized device to house and direct the photoacoustic transmitters and receivers.

The Purdue team tested their system first in lab tissue specimens, then in mice. Their results identify the optimal orientation and settings for maximizing image quality with photoacoustic tomography that provide higher percentages of imaging fat deposits around arteries deeper into mouse tissue separate from fat under the skin. The researchers also devised techniques for redirecting surface skin reflections that interrupt signals from deeper into tissue.

Purdue University filed for a provisional patent on the technology. Goergen tells more about the techniques and the study in the following video.

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