Summary

集成光声、超声和血管造影断层扫描 (PAUSAT) 用于缺血性卒中的无创全脑成像

Published: June 02, 2023
doi:

Summary

这项工作展示了使用基于多模态超声的成像平台对缺血性中风进行无创成像。该系统允许通过光声成像量化血液氧合,并通过声学血管造影在大脑中受损灌注。

Abstract

这里介绍的是使用我们新开发的无创成像系统进行的实验性缺血性卒中研究,该系统集成了三种基于声学的成像技术:光声、超声和血管造影断层扫描 (PAUSAT)。结合这三种模式有助于获得脑血氧合的多光谱光声断层扫描 (PAT)、脑组织的高频超声成像和脑血灌注的声学血管造影。多模态成像平台可以研究中风后整个小鼠大脑的脑灌注和氧合变化。评估了两种常用的缺血性脑卒中模型:永久性大脑中动脉闭塞(pMCAO)模型和光血栓(PT)模型。PAUSAT用于对中风前后的相同小鼠大脑进行成像,并定量分析两种中风模型。该成像系统能够清楚地显示缺血性中风后的脑血管变化,包括与未受伤组织(对侧)相比,中风梗死区域(同侧)的血液灌注和氧合显着减少。激光散斑对比成像和三苯基氯化四唑(TTC)染色证实了结果。此外,两种卒中模型中的脑卒中梗死体积均通过TTC染色作为基本事实进行测量和验证。通过这项研究,我们已经证明PAUSAT可以成为缺血性中风无创和纵向临床前研究的有力工具。

Introduction

血液将氧气(通过血红蛋白和其他重要营养素输送到我们体内的组织。当血液流经组织中断(缺血)时,可能会对组织造成严重损害,其最直接的影响是由于缺氧(缺氧)。缺血性中风是流向大脑某个区域的血流中断的结果。缺血性中风引起的脑损伤可在血管阻塞后几分钟内发生,并且通常具有使人衰弱和持久的影响1,2。评估缺血性中风后生理病理学以及识别和测试新疗法的一种非常有价值的策略是在实验室中使用小动物模型。实验室中发现的治疗方法旨在转化为临床应用并改善患者的生活。然而,动物在生物医学研究中的使用需要根据Russell和Burch的3R原则进行仔细评估:替换,减少和改进3。减少部分的目标是在不影响数据收集的情况下减少动物数量。考虑到这一点,能够通过无创成像纵向评估病变演变,在减少所需动物数量以及最大化从每只动物获得的信息方面具有很大的优势4。

光声断层扫描 (PAT) 是一种混合成像方式,将光学吸收对比与超声成像空间分辨率相结合5。PAT的成像机制如下。激发激光脉冲照射在被成像的目标上。假设目标吸收激发激光波长的光,它将温度升高。温度的快速升高导致目标的热弹性膨胀。膨胀导致超声波从目标传播出去。通过检测多个位置的超声波,可以使用波从目标传播到探测器所需的时间,通过重建算法创建图像。PAT检测深层组织区域的光吸收的能力将PAT与超声成像区分开来,超声成像可检测组织不同声阻抗的边界5。在可见光和近红外光谱中,生物体中丰富的主要高吸收生物分子是血红蛋白、脂质、黑色素和水7。中风研究中特别感兴趣的是血红蛋白。由于氧合血红蛋白和脱氧血红蛋白具有不同的光吸收光谱,PAT可以与多个激发激光波长一起使用,以确定蛋白质两种状态的相对浓度。这允许在梗死区域内外量化血红蛋白 (sO2) 的氧饱和度或血液氧合 8,9。这是缺血性卒中的重要指标,因为它可以指示缺血后受损脑组织中的氧气水平。

声波血管造影(AA)是一种对比增强超声成像方法,特别适用于体内脉管系统的形态成像10。该方法依赖于使用双晶摆动换能器(低频元件和高频元件)与注入成像对象循环系统的微气泡结合使用。换能器的低频元件用于以微气泡的谐振频率(例如2 MHz)传输,而高频元件用于接收微气泡的超谐波信号(例如,26 MHz)。当以共振频率激发时,微气泡具有很强的非线性响应,导致产生周围身体组织不产生的超谐波信号11。通过使用高频元件接收,这确保了仅检测到微气泡信号。由于微气泡仅限于血管,因此结果是血管形态的血管造影图像。AA是缺血性中风成像的有力方法,因为流经循环系统的微气泡不能流过阻塞的血管。这允许AA检测由于缺血性中风而未灌注的大脑区域,这表明梗死区域。

临床前缺血性卒中研究通常依赖于使用组织学和行为学测试来评估卒中的位置和严重程度。三苯基氯化四唑 (TTC) 染色是用于确定卒中梗死体积的常见组织学分析。但是,它只能在终点使用,因为它需要对动物实施安乐死12。行为测试可用于确定多个时间点的运动功能障碍,但它们不能提供定量的解剖学或生理学值13。生物医学成像提供了一种更定量的方法来研究缺血性中风的无创和纵向影响9,14,15。然而,现有的成像技术(如小动物磁共振成像[MRI])的成本可能很高,无法同时提供结构和功能信息,或者穿透深度有限(如大多数光学成像技术)。

在这里,我们结合了光声,超声和血管造影断层扫描(PAUSAT;参见图1中的系统 ),这允许缺血性中风16后血液灌注和氧合的互补结构和功能信息。这是评估损伤严重程度和监测恢复或对治疗反应的两个重要方面。使用这些综合成像方法可以增加每只动物获得的信息量,减少所需的动物数量,并在研究缺血性中风的潜在治疗方法方面提供更多信息。

Figure 1
1:PAUSAT图。 (A)PAUSAT系统的完整原理图,包括用于PAT的激光器和OPO。 (B)PAUSAT系统的内部视图,包括两个超声换能器。双晶摆动探头用于B型超声和AA,线性阵列探头用于PAT。两个传感器都安装在同一个2D电动载物台上,允许扫描以生成体积数据。这一数字已从16修改而来。请点击此处查看此图的大图。

Protocol

所有动物程序均由杜克大学医学中心动物护理和使用委员会批准,并按照美国公共卫生署的《实验动物人道护理和使用政策》进行。雄性和雌性C57BL / 6J小鼠(见 材料表)用于这些研究。每个中风模型组至少对三只动物进行成像。有关此协议中遵循的工作流程,请参见 图 2 。 <img alt="Figure 2" class="xfigimg" src="/fi…

Representative Results

大脑血管形态成像AA通过激发循环系统中的微气泡在其共振频率下并接收微泡的超谐波响应来生成血管形态图像。通过使用连接到手动可调载物台的定制斜坡(图2C),我们可以在两个不同的焦深下以AA模式对小鼠大脑进行成像。当针对更深的区域时,更浅的区域(如大脑皮层)显示出较差的分辨率和信号强度(图3A),反之亦然(<strong …

Discussion

这种方法有几个重要方面,如果操作不正确,可能会导致图像质量和定量分析显着下降。PAUSAT图像中最常见的用户错误结果是信号不足或信号强度非常低,这两种原因都可能由于各种原因而发生。其中一个原因是声耦合的问题。在成像过程中,小鼠头部周围水中的大气泡通常会阻止超声波往返换能器,从而导致系统所有三种模态的结果图像中出现阴影区域。这可以通过确保系统膜和待成像样品之?…

Disclosures

The authors have nothing to disclose.

Acknowledgements

作者要感谢SonoVol Inc.的工程团队的技术支持。这项工作部分由美国心脏协会合作科学奖(18CSA34080277)赞助,授予J. Yao和W. Yang;美国国立卫生研究院(NIH)拨款R21EB027981,R21 EB027304,RF1 NS115581(BRAIN倡议),R01 NS111039,R01 EB028143;美国国家科学基金会(NSF)职业奖2144788;陈·扎克伯格倡议拨款(2020-226178),授予J. Yao;美国国立卫生研究院向W. Yang授予R21NS127163和R01NS099590。

Materials

20 GA catheter BD Insyte Autoguard Winged 381534 For mouse intubation
2,3,5-Triphenyltetrazolium chloride Sigma T8877 Necessary for TTC-staining brain for validation
532nm Laser Quantel Q-smart 850 Laser used to pump the OPO for PAT
Automatic Ventilator Rovent Jr. Kent Scientific RV-JR To keep mice under anesthesia during surgical procedure
Black braided silk 4-0 USP Surgical Specialties SP116 Used for sutures on the neck for pMCAO surgery
Bupivacaine Hospira 0409-1159-18 Used prior to closing wounds during surgical procedure
C57BL/6 Mice Jackson Lab #000664 Mice used for studying ischemic stroke (2-6 month old male/female)
Clear suture Ethicon 8606 Used for closing wound (PT stroke and pMCAO). A clear suture won't interfere with PAT
Cold Light LED Schott KL 1600 Needed to create PT stroke
Disposable Razor Blade Accutec Blades 74-0002 For sectioning mouse brain
Electric drill JSDA JD-700 Used to expose MCA during pMCAO procedure
Electrocauterization tool Wet-Field Wet-Field Bipolar-RG Stops blood flow after drilling during pMCAO procedure
Hair removal gel Veet 8282651 Used to remove hair from mouse prior to imaging
High Temperature Cautery Loop Tip BOVIE Medical Corporation REF AA03 Used to avoid bleeding when separating the temporal muscle from the skull
IR Detector Card Thorlabs VRC5 Used to ensure light path is aligned
Laser Power Meter Ophir StarBright, P/N 7Z01580 Can be used to calibrate the laser energy prior to imaging
Laser Speckle Imaging System RWD Life Science Co. RFLSI-III Can be used to validate stroke surgery success
Lubricant Eye Ointment Soothe AB31336 Can be used to avoid drying of the eyes
Manually adjustable stage Thorlabs L490 Used with custom ramp for multiple focal depth AA imaging
Modified Vega Imaging System Perkin Elmer LLA00061 System containing both B-mode/AA and PAT transducers
Optical Parametric Oscillator Quantel versaScan-L532 Allows for tuning of excitation wavelength in a large range
Programmable Ultrasound System Verasonics Vantage 256 Used for PAT part of system
Rose Bengal Sigma 330000 Necessary to induce PT stroke
Suture LOOK SP116 Used for permanent ligation of CCA
Temperature Contoller Physitemp TCAT-2 Used to maintain stable body temperature of mice during procedures
VesselVue Microbubbles Perkin Elmer P-4007001 Used for acoustic angiography (2.43 × 10^9 microbubbles/mL)

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Cite This Article
Menozzi, L., del Águila, Á., Vu, T., Ma, C., Yang, W., Yao, J. Integrated Photoacoustic, Ultrasound, and Angiographic Tomography (PAUSAT) for NonInvasive Whole-Brain Imaging of Ischemic Stroke. J. Vis. Exp. (196), e65319, doi:10.3791/65319 (2023).

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