Nagarajan Vivek Krishna, Yu Bing
Department of Biomedical Engineering, The University of Akron, Auburn Science and Engineering Center (ASEC) 275, West Tower, Akron, Ohio, 44325-0302.
Lasers Surg Med. 2016 Sep;48(7):686-94. doi: 10.1002/lsm.22541. Epub 2016 Jun 1.
Real-time monitoring of tissue status during thermal ablation of tumors is critical to ensure complete destruction of tumor mass, while avoiding tissue charring and excessive damage to normal tissues. Currently, magnetic resonance thermometry (MRT), along with magnetic resonance imaging (MRI), is the most commonly used technique for monitoring and assessing thermal ablation process in soft tissues. MRT/MRI is very expensive, bulky, and often subject to motion artifacts. On the other hand, light propagation within tissue is sensitive to changes in tissue microstructure and physiology which could be used to directly quantify the extent of tissue damage. Furthermore, optical monitoring can be a portable, and cost-effective alternative for monitoring a thermal ablation process. The main objective of this study, is to establish a correlation between changes in tissue optical properties and the status of tissue coagulation/damage during heating of ex vivo tissues.
A portable diffuse reflectance spectroscopy system and a side-firing fiber-optic probe were developed to study the absorption (μa (λ)), and reduced scattering coefficients (μ's (λ)) of native and coagulated ex vivo porcine, and chicken breast tissues. In the first experiment, both porcine and chicken breast tissues were heated at discrete temperature points between 24 and 140°C for 2 minutes. Diffuse reflectance spectra (430-630 nm) of native and coagulated tissues were recorded prior to, and post heating. In a second experiment, porcine tissue samples were heated at 70°C and diffuse reflectance spectra were recorded continuously during heating. The μa (λ) and μ's (λ) of the tissues were extracted from the measured diffuse reflectance spectra using an inverse Monte-Carlo model of diffuse reflectance. Tissue heating was stopped when the wavelength-averaged scattering plateaued.
The wavelength-averaged optical properties, <μ's (λ)> and <μa (λ)>, for native porcine tissues (n = 66) at room temperature, were 5.4 ± 0.3 cm(-1) and 0.780 ± 0.008 cm(-1) (SD), respectively. The <μ's (λ)> and <μa (λ)> for native chicken breast tissues (n = 66) at room temperature, were 2.69 ± 0.08 cm(-1) and 0.29 ± 0.01 cm(-1) (SD), respectively. In the first experiment, the <μ's (λ)> of coagulated porcine and chicken breast tissue rose to 56.4 ± 3.6 cm(-1) at 68.7 ± 1.7°C (SD), and 52.8 ± 1 cm(-1) at 57.1 ± 1.5°C (SD), respectively. Correspondingly, the <μa (λ)> of coagulated porcine (140.6°C), and chicken breast tissues (130°C) were 0.75 ± 0.05 cm(-1) and 0.263 ± 0.004 cm(-1) (SD). For both tissues, charring was observed at temperatures above 80°C. During continuous monitoring of porcine tissue (with connective tissues) heating, the <μ's (λ)> started to rise rapidly from 13.7 ± 1.5 minutes and plateaued at 19 ± 2.5 (SD) minutes. The <μ's (λ)> plateaued at 11.7 ± 3 (SD) minutes for porcine tissue devoid of connective tissue between probe and tissue surface. No charring was observed during continuous monitoring of thermal ablation process.
The changes in optical absorption and scattering properties can be continuously quantified, which could be used as a diagnostic biomarker for assessing tissue coagulation/damage during thermal ablation. Lasers Surg. Med. 48:686-694, 2016. © 2016 Wiley Periodicals, Inc.
在肿瘤热消融过程中实时监测组织状态对于确保肿瘤组织完全被破坏至关重要，同时要避免组织炭化以及对正常组织造成过度损伤。目前，磁共振测温法（MRT）与磁共振成像（MRI）一起，是监测和评估软组织热消融过程最常用的技术。MRT/MRI非常昂贵、体积庞大，且经常受到运动伪影的影响。另一方面，光在组织内的传播对组织微观结构和生理变化敏感，这可用于直接量化组织损伤程度。此外，光学监测可以成为一种用于监测热消融过程的便携且经济高效的替代方法。本研究的主要目的是建立组织光学特性变化与离体组织加热过程中组织凝固/损伤状态之间的相关性。
开发了一种便携式漫反射光谱系统和一个侧射光纤探头，用于研究离体猪和鸡胸组织在天然状态及凝固状态下的吸收系数（μa(λ)）和约化散射系数（μ's(λ)）。在第一个实验中，猪和鸡胸组织均在24至140°C的离散温度点加热2分钟。在加热前和加热后记录天然组织和凝固组织的漫反射光谱（430 - 630nm）。在第二个实验中，将猪组织样本加热至70°C，并在加热过程中连续记录漫反射光谱。使用漫反射的逆蒙特卡罗模型从测量的漫反射光谱中提取组织的μa(λ)和μ's(λ)。当波长平均散射达到平稳时停止组织加热。
室温下天然猪组织（n = 66）的波长平均光学特性<μ's(λ)>和<μa(λ)>分别为5.4±0.3cm⁻¹和0.780±0.008cm⁻¹（标准差）。室温下天然鸡胸组织（n = 66）的<μ's(λ)>和<μa(λ)>分别为2.69±0.08cm⁻¹和0.29±0.01cm⁻¹（标准差）。在第一个实验中，凝固猪和鸡胸组织的<μ's(λ)>在68.7±1.7°C（标准差）时升至56.4±3.6cm⁻¹，在57.1±1.5°C（标准差）时升至52.8±1cm⁻¹。相应地，凝固猪组织（140°C）和鸡胸组织（130°C）的<μa(λ)>分别为0.75±0.05cm⁻¹和0.263±0.004cm⁻¹（标准差）。对于两种组织，在温度高于80°C时均观察到炭化现象。在对猪组织（带有结缔组织）加热的连续监测过程中，<μ's(λ)>在13.7±1.5分钟时开始迅速上升，并在19±2.5（标准差）分钟时达到平稳。对于探头与组织表面之间没有结缔组织的猪组织，<μ's(λ)>在11.7±3（标准差）分钟时达到平稳。在热消融过程的连续监测中未观察到炭化现象。
光学吸收和散射特性的变化可以被连续量化，这可作为评估热消融过程中组织凝固/损伤的诊断生物标志物。《激光外科与医学》48:686 - 694，2016年。©2016威利期刊公司
