Photoacoustic imaging modality detects ultrasound signals generated through transient thermal expansion of tissues after optical absorbers are illuminated by pulsed light. Only a shallow depth of less than 1 mm can be viewed with optical imaging, whereas photoacoustic imaging can reconstruct several centimeters of human tissue.
However, conventional ultrasound or photoacoustic imaging assumes a representative SoS value such as 1,540 meter per second which may cause aberrations. It was sometimes necessary to view the images without obtaining a sufficient signal due to the limitations in the imaging system. In this case, artifacts appeared in the image and interfered with its interpretation.
To overcome this issue, the researchers produced a distorted photoacoustic image by arbitrarily setting the medium's SoS and an actual undistorted photoacoustic image from an acoustic wave simulation. The AI was trained accordingly and its effectiveness was confirmed by applying it to simulated trained images and PA images of humans.
As a result, the distortions that occurred in conventional PA images were reduced, the intensity of the streak artifacts near the main signal was reduced by up to 5 percent, and the signal-to-noise ratio (SNR) was increased to about 25 decibels (dB) at maximum. Even when only 64 data acquisition channels of the total 128 channels in the imaging system were used, AI helped to produce a PA image with almost the same quality.
Specifically, SoS aberrations in the PA images of blood vessels in healthy human limbs and melanoma patients were alleviated and the resolution was improved. Major diagnostic information such as oxygen saturation only showed a difference of about 5 percent, proving that it was superior to AI models such as U-net or Segnet. This technique can be used in actual clinical conditions where the medium has a heterogeneous SoS distribution or the data sampling is sparse.
"We can obtain high-resolution images fairly quickly using this technique," explained Professor Kim. "It is anticipated to be applicable in various clinical studies in the future, such as diagnosing vascular diseases in extremities of the human body, determining the stage of a cancer, and setting precise boundaries for resection."
MEDICA-tradefair.com; Source: Pohang University of Science & Technology (POSTECH)
