Department of Biomedical Engineering, Tufts University, Medford, MA 02155, USA.
Research and Business Development Division, CYBERDYNE INC, 3013 AK Rotterdam, The Netherlands.
Sensors (Basel). 2020 Jul 6;20(13):3789. doi: 10.3390/s20133789.
Photoacoustic (PA) imaging-a technique combining the ability of optical imaging to probe functional properties of the tissue and deep structural imaging ability of ultrasound-has gained significant popularity in the past two decades for its utility in several biomedical applications. More recently, light-emitting diodes (LED) are being explored as an alternative to bulky and expensive laser systems used in PA imaging for their portability and low-cost. Due to the large beam divergence of LEDs compared to traditional laser beams, it is imperative to quantify the angular dependence of LED-based illumination and optimize its performance for imaging superficial or deep-seated lesions. A custom-built modular 3-D printed hinge system and tissue-mimicking phantoms with various absorption and scattering properties were used in this study to quantify the angular dependence of LED-based illumination. We also experimentally calculated the source divergence of the pulsed-LED arrays to be 58° ± 8°. Our results from point sources (pencil lead phantom) in non-scattering medium obey the cotangential relationship between the angle of irradiation and maximum PA intensity obtained at various imaging depths, as expected. Strong dependence on the angle of illumination at superficial depths (-5°/mm at 10 mm) was observed that becomes weaker at intermediate depths (-2.5°/mm at 20 mm) and negligible at deeper locations (-1.1°/mm at 30 mm). The results from the tissue-mimicking phantom in scattering media indicate that angles between 30-75° could be used for imaging lesions at various depths (12 mm-28 mm) where lower LED illumination angles (closer to being parallel to the imaging plane) are preferable for deep tissue imaging and superficial lesion imaging is possible with higher LED illumination angles (closer to being perpendicular to the imaging plane). Our results can serve as a priori knowledge for the future LED-based PA system designs employed for both preclinical and clinical applications.
光声（PA）成像是一种将光学成像探测组织功能特性的能力与超声的深层结构成像能力相结合的技术，在过去二十年中，由于其在多种生物医学应用中的实用性，已经得到了广泛的关注。最近，发光二极管（LED）作为一种替代笨重昂贵的激光系统的方法，在 PA 成像中得到了探索，因为它们具有便携性和低成本。由于与传统激光束相比，LED 的光束发散角较大，因此必须量化基于 LED 的照明的角度依赖性，并优化其对浅层或深层病变的成像性能。本研究使用定制的模块化 3D 打印铰链系统和具有各种吸收和散射特性的组织模拟体模来量化基于 LED 的照明的角度依赖性。我们还通过实验计算出脉冲 LED 阵列的源发散角为 58°±8°。我们在无散射介质中的点源（铅笔芯体模）的结果遵循在各种成像深度处获得的辐照角度和最大 PA 强度之间的余切关系，这是预期的。在浅层深度（10mm 处为-5°/mm）处观察到对照明角度的强烈依赖性，在中间深度（20mm 处为-2.5°/mm）处减弱，在更深的位置（30mm 处为-1.1°/mm）则可以忽略不计。在散射介质中的组织模拟体模的结果表明，可以在各种深度（12mm-28mm）处使用 30-75°的角度来对病变进行成像，其中较低的 LED 照明角度（更接近平行于成像平面）更适合深层组织成像，而较高的 LED 照明角度（更接近垂直于成像平面）则可以对浅层病变进行成像。我们的结果可以作为未来用于临床前和临床应用的基于 LED 的 PA 系统设计的先验知识。
