含有宏观结构的光学组织幻影的制备与表征
Summary
光学组织幽灵是光学成像系统标定、表征和理论模型验证的基本工具。本文详细介绍了一种幻像制作方法, 包括组织光学特性和三维组织结构的复制。
Abstract
新的光学成像技术的迅速发展取决于低成本、可定制和易于重现的标准的可用性。通过复制成像环境, 可以规避昂贵的动物实验来验证技术。预测和优化体内和前体成像技术的性能需要对与感兴趣的组织光学相似的样本进行测试。组织模仿光学幽灵为光学系统的评估、表征或校准提供了标准。均匀聚合物光学组织幽灵被广泛地用于模仿一个特定组织类型的光学性质在狭窄的光谱范围之内。层状组织, 如表皮和真皮, 可以通过简单地堆叠这些均质板幽灵来模拟。然而, 许多体内成像技术被应用于空间更复杂的组织, 如血管、呼吸道或组织缺损等三维结构会影响成像系统的性能。
本协议描述了一种组织模拟幻影的制作, 该幻像采用具有组织光学性质的材料的三维结构复杂度。查找表提供印度墨水和二氧化钛配方的光学吸收和散射目标。介绍了材料光学特性的表征和调优方法。本文详述的幻像制造有一个内部分支模拟气道空隙;然而, 该技术可以广泛应用于其他组织或器官结构。
Introduction
组织幽灵广泛用于光学成像和光谱学仪器的系统表征和校准, 包括包含超声波或核模式的综合系统1,2,3 ,4。幽灵为多种生物成像技术的系统表征和质量控制提供了受控光学环境。组织仿幽灵是预测系统性能和优化系统设计的重要工具, 在手头的生理任务;例如, 预测用于评估肿瘤边缘的光谱探针的探测深度5。幽灵的光学特性和结构设计可以被调谐来模拟使用该仪器的特定生理环境, 因此既允许可行性研究, 也可验证系统性能3, 6,7。在进入临床前或临床试验之前, 用逼真的光学幽灵验证成像系统的性能, 可以减少在体内研究期间出现故障或无法获取数据的风险。光学幽灵的重现性和稳定性使它们可定制光学技术的校准标准, 以监测内部和仪器间的变异性, 特别是在多中心临床试验中使用不同的仪器,运算符和环境条件8,9。
组织模拟幽灵也作为可调谐和可重现的物理模型, 用于验证理论光学模型。模拟有助于设计和优化在体内光学仪器, 同时减少对动物实验的需要10,11。光学模拟的发展和验证, 以准确地表示在体内环境可以由复杂的组织结构, 生物化学的内容, 以及目标或组织的位置在体内。不同学科之间的变异性使验证的理论模型具有挑战性的使用动物或人类的测量。聚合物光学组织幽灵允许通过提供已知和可再生的光学环境来验证理论模型, 研究光子迁移12,13,14,15。
在系统标定的目的, 固体光学幽灵可能包括一个单一的均匀板的固化聚合物与光学散射, 吸收, 或荧光调谐波长的兴趣。层状聚合物幽灵经常用于模拟上皮组织模型中组织光学特性的深度方差16,17。这些幻像结构是足够的上皮成像和建模, 因为组织结构是相当均匀, 通过每一层。然而, 更大的规模和更复杂的结构影响辐射运输在其他器官。为模拟皮下血管的光学环境, 建立了更复杂的幽灵的方法18,19甚至整个器官, 如膀胱20。由于空气组织界面的分支结构, 肺中光传输的建模提供了一个独特的问题;固体幻影不可能准确地在器官中复制辐射传输21。为了描述一种将复杂结构并入光学幻像的方法, 我们描述了一种方法, 用于创建一个表示气道三维 (3D) 宏观结构的内部可重现分形树 void (图 1)。
在过去的几十年中, 3D 打印已成为一个主要的方法, 快速原型医疗设备和模型22, 和光学组织幽灵也不例外。3D 印刷作为一种添加剂制造工具, 用于制作具有通道23、血管网络24和全身小动物模型25的光学幽灵。这些方法使用一个或两个具有独特光学性质的印刷材料。还开发了一些方法来调整印刷材料的光学特性, 以模拟一般的, 混浊的生物组织25,26。然而, 可实现光学性能的范围受到印刷材料的限制, 通常是聚合物, 如丙烯腈丁二烯苯乙烯 (ABS)26, 所以这种方法不适合所有的生物组织。烷 () 是一种光学上清晰的聚合物, 可以很容易地与散射和吸收粒子混合, 具有较高水平的调谐27,28。此外, 在为部署栓塞设备29、30的动脉瘤模型中, 还使用了用于建模的幽灵。这些幽灵还利用了一个可溶性的3D 打印部分, 但保持光学清晰, 以可视化设备部署。本文将该方法与调谐散射和吸收粒子的光学性质结合起来, 制备了小鼠肺组织和气道的初步模型。
虽然这里所呈现的幻影是特定于肺部, 这个过程可以应用到各种其他器官。3D. 幻影的内部结构的打印允许设计可以为任何目的和可打印的规模, 无论是血液或淋巴血管网络, 骨髓, 甚至心脏的四腔结构31。因为我们对肺的光学成像和建模有兴趣32,33,34, 我们选择使用四代分形树作为内部结构在聚合物幻影内复制。该结构的设计, 以近似的分支结构的气道和有突破支持材料的3D 印刷过程。如果不需要防断支架材料, 可以打印出更具解剖学上正确的气道。虽然这个特定的模型代表一个气道, 但幻影的内部结构并不需要保持物质的空隙。一旦周围的聚合物固化, 3D 印刷部分被溶解, 内部结构可以作为一个流动路径或作为一个二级模具的材料具有自己独特的吸收和散射特性。例如, 如果该协议的内部结构被设计成数字骨而不是气道, 则骨骼结构可以是3D 打印, 用与该手指的光学特性进行模压, 然后从幻影中溶解出来。然后, 可以用不同光学性质的混合材料填充该空隙。此外, 每个模具不限于一个单一的可溶性部分。手指的幻像可以被创造, 包括骨骼, 静脉, 动脉和一般的软组织层, 每个都有自己独特的光学特性。
Protocol
Representative Results
Discussion
我们已经展示了一种制造光学幽灵的方法, 用来代表小鼠肺, 用内部分支结构模拟内部空气组织界面。小鼠肺组织的光学特性是通过将独特的光学散射浓度和吸收粒子分布在 homogenously 内的聚合物来实现的。这些光学特性可以在不同状态 (即健康与病态组织) 的不同光谱范围内模拟生理值。光学特性取决于感兴趣的波长、基材和幻像内粒子的浓度。然而, 对于多个粒子, 散射和吸收之间的关系?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
这项工作得到国家科学基金会职业奖的支持。CBET-1254767 和国家过敏和传染性疾病研究所授予 no。R01 AI104960。我们感激地承认帕特里克格里芬和丹为他们的协助与定性测量和得克萨斯 A & M 心血管病理学实验室为微 CT 成像。
Materials
| Dow Corning Sylgard 184 Silicone Encapsulant Clear 0.5 kg Kit | Ellsworth Adhesives | 184 SIL ELAST KIT 0.5KG | Polydimethylsiloxane: polymer base for optical phantoms |
| White Rutile Titanium Dioxide powder | Atlantic Equipment Engineers | TI-602 | Scattering particles for optical phantoms |
| Higgins Fountain Pen India Ink | Michaels Craft Stores | 10015483 | Absorbing particles for optical phantom |
| Heat Resistant tape | Uline | S-7595 | Heat resistant tape for polymer molds |
| Fortus 360mc 3D printer | Stratasys | N/A | Able to switch build and support material with this model printer |
| ABS Ivory Model Material | Stratasys | SDS-000001 | Material for printing mold parts and/or using as support for printing internal structure |
| SR-30 Soluble Support | Stratasys | 400638-0001 | Base soluble support material for printing internal structure |
| Flacktek Speedmixer | Flacktek Inc. | DAC 150.1 FV | For efficient mixing of polymer and particles |
| Integrating sphere | Edmund Optics | 58-585 | For measuring optical properties |
| Polycarbonate build plates (1 mm) | Stratasys | N/A | Used polycarbonate build plates from Stratasys printer can also be used |
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