Biomedical Instrumentation and Imaging Laboratory (BIIL), School of Physics (SoP), Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Thiruvananthapuram 695551, India.
Scanning Probe Microscopy and Plasmonics Lab, School of Physics (SoP), Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Thiruvananthapuram 695551, India.
Sensors (Basel). 2021 Feb 8;21(4):1190. doi: 10.3390/s21041190.
Use of portable and affordable pulse light sources (light emitting diodes (LED) and laser diodes) for tissue illumination offers an opportunity to accelerate the clinical translation of photoacoustic imaging (PAI) technology. However, imaging depth in this case is limited because of low output (optical) power of these light sources. In this work, we developed a noninvasive technique for enhancing strength (amplitude) of photoacoustic (PA) signal. This is a photothermal-based technique in which a continuous wave (CW) optical beam, in addition to short-pulse ~ nsec laser beam, is employed to irradiate and, thus, raise the temperature of sample material selectively over a pre-specified region of interest (we call the process as pre-illumination). The increase in temperature, in turn enhances the PA-signal strength. Experiments were conducted in methylene blue, which is one of the commonly used contrast agents in laboratory research studies, to validate change in temperature and subsequent enhancement of PA-signal strength for the following cases: (1) concentration or optical absorption coefficient of sample, (2) optical power of CW-optical beam, and (3) time duration of pre-illumination. A theoretical hypothesis, being validated by numerical simulation, is presented. To validate the proposed technique for clinical and/or pre-clinical applications (diagnosis and treatments of cancer, pressure ulcers, and minimally invasive procedures including vascular access and fetal surgery), experiments were conducted in tissue-mimicking Agar phantom and ex-vivo animal tissue (chicken breast). Results demonstrate that pre-illumination significantly enhances PA-signal strength (up to ~70% (methylene blue), ~48% (Agar phantom), and ~40% (chicken tissue)). The proposed technique addresses one of the primary challenges in the clinical translation of LED-based PAI systems (more specifically, to obtain a detectable PA-signal from deep-seated tissue targets).
使用便携式、价格合理的脉冲光源（发光二极管 (LED) 和激光二极管）进行组织照明为加速光声成象 (PAI) 技术的临床转化提供了机会。然而，由于这些光源的输出 (光学) 功率较低，因此成像深度受到限制。在这项工作中，我们开发了一种用于增强光声 (PA) 信号强度（幅度）的非侵入性技术。这是一种基于光热的技术，其中连续波 (CW) 光束与短脉冲 nsec 激光束一起用于选择性地辐照并因此升高样品材料的温度，超过预定的感兴趣区域（我们称该过程为预照明）。温度的升高反过来又增强了 PA 信号强度。在亚甲蓝中进行了实验，亚甲蓝是实验室研究中常用的对比剂之一，以验证以下情况的温度变化和随后的 PA 信号强度增强：(1) 样品的浓度或光吸收系数，(2) CW-光光束的光功率，和 (3) 预照明的持续时间。提出了一个经过数值模拟验证的理论假设。为了验证该技术在临床和/或临床前应用（癌症、压疮的诊断和治疗，以及包括血管通路和胎儿手术在内的微创程序）中的可行性，在组织模拟琼脂体和离体动物组织（鸡胸肉）中进行了实验。结果表明，预照明可显著增强 PA 信号强度（高达 ~70%（亚甲蓝），48%（琼脂体）和 ~40%（鸡胸肉））。该技术解决了基于 LED 的 PAI 系统临床转化中的一个主要挑战（更具体地说，从深部组织靶标获得可检测的 PA 信号）。
