Photoacoustic imaging, which uses optical contrast for ultrasound detection, is currently the fastest-growing field in the area of biomedical imaging research. While endogenous contrasts like hemoglobin can be easily detected at certain wavelengths, in order to specifically image a particular area, we still need exogenous contrasts. This has kicked off research in the field of developing contrast agents that are safe and target specific. Contrast agents, in order to be approved for human use, need to go through extensive screening in terms of safety and usability.
For our research, we thought of considering different foodstuffs that are already consumed by many, and therefore, are quite safe. After painstakingly imaging over 200 foodstuffs, we arrived at a particular version of roasted barley as the winner. In our recently published work , after eliminating most of the foodstuffs, we have performed several experiments in mice and humans to show the usefulness of roasted barley in imaging the gastrointestinal tract.
To begin with, we focused on dark foods and beverages that would absorb better from laser light to give strong image intensity. We used a control NIR (near infrared) dye and measured the photoacoustic signal intensity of various foods with respect to the dye. The foodstuffs with higher absorbance than the dye were identified to be types of roasted barley. Further, we imaged 20 different types of commercially available roasted barley to identify the one with the highest signal. Finally, MTS barley emerged to be the one exhibiting highest photoacoustic signal. In order to identify the depth of imaging possible, we used chicken breast tissue layer by layer on top of the MTS roasted barley grains. We could see a depth of 3.5 cm using our PACT system. We then went on to image under 2.5 cm of human palm, and we could see a very strong signal from the grain. In order to see the usefulness of barley as a contrast agent for the gastrointestinal tract, we imaged mice that were fed the MTS roasted barley. With our linear array based photoacoustic computed tomography system, we could track the dynamic motion of mice intestines and their peristaltic rate, details of which are discussed in our paper.
Furthermore, we checked the photoacoustic signal generated by the liquid part of boiled barley tea. After imaging this under a 2.5 cm of chicken breast tissue, it was clear to us that the tea generated a high photoacoustic signal. Therefore, we could comfortably use it as a contrast agent in real-time photoacoustic imaging to detect the human swallowing process. Dysphagia or swallowing disorder can be an indicator for various diseases. The standard procedure to test for this is by orally administering the patient with a Barium drink. This is usually followed by X-ray or MRI for imaging the throat with Barium as a contrast agent.
We used the same concept but replaced Barium with liquid part of boiled barley tea for photoacoustic imaging. The volunteer was asked to take a sip of the tea and the swallowing process was imaged using a transducer and laser light. The results clearly showed the photoacoustic signal from the bolus and its movement through the oral cavity. Therefore, we have identified a new and safe photoacoustic contrast agent, MTS roasted barley, in order to detect disorders of the gastrointestinal tract in humans.
These findings are described in the article entitled Ingestible roasted barley for contrast-enhanced photoacoustic imaging in animal and human subjects, recently published in the journal Biomaterials. This work was conducted by Depeng Wang, Dong Hyeun Lee, Haoyuan Huang, Tri Vu, Rachel Su Ann Lim, Nikhila Nyayapathi, Upendra Chitgupi, Maggie Liu, Jumin Geng, Jun Xia, and Jonathan F. Lovell from the University at Buffalo. The research was supported by grants from the National Institutes of Health, the Clinical and Translational Science Institute at UB, and the UB Office of the Vice President for Research and Economic Development.
- D. Wang et al., “Ingestible roasted barley for contrast-enhanced photoacoustic imaging in animal and human subjects,” Biomaterials, vol. 175, pp. 72-81, 2018.