Walther Andreas, Rippe Lars, Wang Lihong V, Andersson-Engels Stefan, Kröll Stefan
Department of Physics, Lund University, 221 00 Lund, Sweden.
California Institute of Technology, 1200 E California Blvd., MC 138-78, Pasadena CA 91125, USA.
Biomed Opt Express. 2017 Sep 19;8(10):4523-4536. doi: 10.1364/BOE.8.004523. eCollection 2017 Oct 1.
Despite the important medical implications, it is currently an open task to find optical non-invasive techniques that can image deep organs in humans. Addressing this, photo-acoustic tomography (PAT) has received a great deal of attention in the past decade, owing to favorable properties like high contrast and high spatial resolution. However, even with optimal components PAT cannot penetrate beyond a few centimeters, which still presents an important limitation of the technique. Here, we calculate the absorption contrast levels for PAT and for ultrasound optical tomography (UOT) and compare them to their relevant noise sources as a function of imaging depth. The results indicate that a new development in optical filters, based on rare-earth-ion crystals, can push the UOT technique significantly ahead of PAT. Such filters allow the contrast-to-noise ratio for UOT to be up to three orders of magnitude better than for PAT at depths of a few cm into the tissue. It also translates into a significant increase of the image depth of UOT compared to PAT, enabling deep organs to be imaged in humans in real time. Furthermore, such spectral holeburning filters are not sensitive to speckle decorrelation from the tissue and can operate at nearly any angle of incident light, allowing good light collection. We theoretically demonstrate the improved performance in the medically important case of non-invasive optical imaging of the oxygenation level of the frontal part of the human myocardial tissue. Our results indicate that further studies on UOT are of interest and that the technique may have large impact on future directions of biomedical optics.
尽管具有重要的医学意义，但目前寻找能够对人体深部器官进行成像的光学非侵入性技术仍是一项尚未完成的任务。为了解决这一问题，光声断层扫描（PAT）在过去十年中受到了广泛关注，这得益于其高对比度和高空间分辨率等优良特性。然而，即使使用最佳组件，PAT也无法穿透超过几厘米的深度，这仍然是该技术的一个重要限制。在此，我们计算了PAT和超声光学断层扫描（UOT）的吸收对比度水平，并将它们与其相关噪声源作为成像深度的函数进行比较。结果表明，基于稀土离子晶体的光学滤波器的新发展可以使UOT技术显著领先于PAT。这种滤波器使UOT在进入组织几厘米深度时的对比度噪声比比PAT高出多达三个数量级。这也意味着与PAT相比，UOT的图像深度显著增加，能够实时对人体深部器官进行成像。此外，这种光谱烧孔滤波器对组织中的散斑去相关不敏感，并且可以在几乎任何入射光角度下工作，从而实现良好的光收集。我们从理论上证明了在对人体心肌组织前部氧合水平进行非侵入性光学成像这一医学重要案例中的性能提升。我们的结果表明，对UOT的进一步研究具有重要意义，并且该技术可能会对生物医学光学的未来发展方向产生重大影响。
