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Introduction
Protocol
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医学

小动物高分辨率心脏正电子发射断层扫描/计算机断层扫描

Published: December 16, 2022
doi:
10.3791/64066
, , , , , ,
1CNR Institute of Clinical Physiology, 2Sant’Anna School of Advanced Studies, 3Fondazione Regione Toscana/CNR “G. Monasterio”

Summary

在这里，我们提出了一种实验成像协议，用于使用高分辨率正电子发射断层扫描/计算机断层扫描来量化小动物的心脏功能和形态。考虑小鼠和大鼠，讨论计算机断层扫描造影剂对两个物种的不同要求。

Abstract

正电子发射断层扫描（PET）和计算机断层扫描（CT）是最常用的诊断成像技术之一，两者都有助于了解心脏功能和代谢。在临床前研究中，采用具有高灵敏度和高时空分辨率的专用扫描仪，旨在应对小鼠和大鼠的小心脏尺寸和非常高的心率所带来的苛刻技术要求。本文描述了一种用于实验小鼠和/或大鼠心脏病模型的双模心脏PET / CT成像方案，从动物制备和图像采集和重建到图像处理和可视化。

特别是， 18F标记的氟脱氧葡萄糖（[18F]FDG）-PET扫描允许测量和可视化左心室（LV）不同部分的葡萄糖代谢。极地地图是显示此信息的便捷工具。CT 部分包括使用无心电图 （ECG） 导联的回顾性门控对整个心脏 （4D-CT） 进行时间分辨 3D 重建，从而可以对左心室进行形态功能评估，并随后量化最重要的心脏功能参数，例如射血分数 （EF） 和每搏输出量 （SV）。使用集成的PET / CT扫描仪，该协议可以在同一麻醉诱导内执行，而无需在不同的扫描仪之间重新定位动物。因此，PET / CT可以被视为几种心脏病小动物模型中心脏形态功能和代谢评估的综合工具。

Introduction

小动物模型对于促进对心血管疾病的认识极为重要1，2。在过去的几十年里，非侵入性诊断成像工具彻底改变了我们在临床和临床前环境中看待心脏功能的方式。就心脏病的小动物模型而言，已经开发出具有非常高时空分辨率的特定成像工具。因此，此类仪器可以满足在特定疾病模型中（例如心力衰竭（HF）3或心肌梗塞（MI）4）中对小鼠和大鼠非常小且非常快速移动的心脏进行相关代谢和动力学心肌参数的准确定量的需求。为此目的有几种方式，每种方式都有自己的优点和缺点。超声（英文）成像是使用最广泛的方式，因为它具有极大的灵活性、非常高的时间分辨率和相对较低的成本。自从使用超高频5，6探头的系统出现以来，美国心脏成像在小动物中的采用已经大大增加，其空间分辨率低于50μm。

US 用于全 3D 心脏成像的主要缺点之一是需要沿心脏轴进行线性扫描，方法是将探头安装在电动平移台上，以创建整个心脏的完整动态 B 模式图像7。最终，该过程产生（在每个探头位置获取的图像进行准确的空间和时间配准后）在面内和面外方向之间具有不同空间分辨率的4D图像。心脏MR（CMR）8也存在空间分辨率不均匀的问题，这 仍然是心脏功能成像的黄金标准。可以使用计算机断层扫描（CT）和正电子发射断层扫描（PET）9来获得真正的各向同性3D成像。PET在每注射探针量（在纳摩尔范围内）的图像信号方面提供了一种非常灵敏的工具，尽管与CT，MR或US相比，它的空间分辨率降低。PET的主要优点是它能够显示器官病理生理学背后的细胞和分子机制。例如，注射[18F]FDG后的PET扫描可以重建体内葡萄糖代谢的3D图。通过将其与动态（即时间分辨）数据采集相结合，示踪动力学建模可用于计算葡萄糖摄取代谢率（MRGlu）的参数图，这将提供有关心肌活力的重要信息10。

CT需要大量高浓度的外部造影剂（CA）（每毫升高达400毫克碘），以提供相关组织成分（例如，血液与肌肉）的可测量增强，但它在空间和时间分辨率方面表现出色，特别是在使用专为小动物成像设计的最先进的微型CT扫描仪时。11 可以应用心脏PET / CT的典型疾病模型是心肌梗塞和心力衰竭的实验评估以及对治疗的相关反应。在小动物中诱导心肌梗死的常见方法是手术结扎左前降（LAD）冠状动脉12，13 ，然后在随后的几天纵向评估疾病的进展和心脏重塑4。然而，小动物心脏的定量形态功能评估在很大程度上也适用于其他疾病模型，例如评估衰老对心脏功能的影响14 或肥胖模型中受体表达的改变15。所提出的成像方案不限于任何给定的疾病模型，因此，在小型啮齿动物临床前研究的几种背景下可能是最广泛的兴趣。

在本文中，我们提出了一种使用小动物集成PET / CT进行心脏成像的从头到尾实验方案。尽管所提出的协议是为特定的双峰集成扫描仪设计的，但所述程序的PET和CT部分可以在来自不同制造商的单独扫描仪上独立执行。在使用中的PET/CT扫描仪中，操作顺序在预编程的工作流程中组织。每个工作流程的主要分支是一个或多个采集协议;每个采集协议可以有一个或多个用于特定预处理协议的分支，反过来，每个预处理协议可以有一个或多个用于特定重建协议的分支。描述了在成像床上制备动物和在成像过程中要注射的外部试剂的制备。图像采集程序完成后，提供了基于常用软件工具的定量图像分析示例程序。主协议专为鼠标模型设计;尽管小鼠仍然是该领域最常用的物种，但我们在主协议结束时也展示了对大鼠成像协议的改编。显示了小鼠和大鼠的代表性结果，展示了所描述程序可能预期的输出类型。本文最后进行了彻底的讨论，以强调该技术的优缺点、关键点以及如何使用不同的PET放射性示踪剂，而几乎不修改准备和采集/重建步骤。

Protocol

动物实验是根据欧洲指令（1986年第86/609/EEC号指令和2010/63/UE指令）和意大利法律（D.Lgs.26/2014）要求的《国际实验动物处理指南》中的建议进行的。 1. PET/CT 成像方案和工作流程的设置 注意：此处介绍的方案是专门为小鼠模型的心脏成像而设计的。与大鼠一起工作可能意味着对实际方案进行一些修改，主要是因为动物的体型更大（大约重10倍）?…

Representative Results

在本节中，显示了按照目前描述的程序进行PET和CT分析的典型结果。 图6 显示了对照（健康）CD-1小鼠的[18F]FDG PET扫描的自动心肌和左心室腔分割的结果。尽管右心室在重建的图像中并不总是可见，但基于DICOM接头的方向轴可用于正确区分室间隔与其他左心室壁，这是按照美国心脏协会（AHA）建议25可靠识别标准扇区所必需的。.在心肌缺血的情况下，…

Discussion

本文提出的协议侧重于通过使用高分辨率PET / CT成像对心脏损伤小动物模型进行转化心血管研究的典型实验程序。所呈现的结果表明PET和Cine-CT图像具有很高的定量和定性价值，提供了整个心脏关于其葡萄糖代谢，形状和收缩动力学的功能和结构信息。此外，获得的所有图像都是3D的，时间分辨的，并且呈现各向同性的像素间距;从图像处理的角度来看，这是有益的，因为它不需要预扫描操作员依赖?…

Disclosures

The authors have nothing to disclose.

Acknowledgements

这项研究得到了JPI-HDHL-INTIMIC “GUTMOM”项目的部分支持：后代的母亲肥胖和认知功能障碍：肠道微生物的因果作用和早期饮食预防（项目编号INTIMIC-085，意大利教育部，大学和研究部第946/2019号法令）。

Materials

0.9% sterile saline Fresenius Kabi 0.9% sodium chloride for injection
1025L Physiological Monitoring Small Animal Instruments Physiological monitoring system for small animal imaging
5 mL syringes Artsana Syringes with needle for injection of PET tracer
Atomlab 500 Else Nuclear PET Dose calibrator
Atrium software Inviscan Version 1.5.5 PET/CT operating software
Butterfly catheters Delta Med 27.5 G needle
Carimas software Turku PET Center Version 2.10 Image analysis software
Fenestra VC Medilumine Lipid emulsion iodinated contrast agent for small animals
Heat lamp Heat lamp with clamp and switch
Insulin syringes Artsana Syringes with needle for injection of CT CA
Iomeron 400 mgI/mL Bracco Iomeprol, vascular contrast agent
IRIS PET/CT Inviscan PET/CT scanner for small animals
Isoflurane Zoetis Inhalation anesthetic, 250 mL
OneTouch Glucometer Johnson&Johnson Medical Glucose meter kit
Osirix MD software Pixmeo Version 11 Image analysis software
Oxygen Air liquide Compressed gas
Rectal probe for 1025L Small Animal Instruments Rectal probe with cable for SAII 1025L systems
Respiratory sensor for 1025L Small Animal Instruments Respiratory pillow with tubings for SAII 1025L systems
TJ-3A syringe pump Longer Motorized syringe pump for CT CA injection
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Tags

Keywords: Cardiac PET/CTSmall Animal ImagingMyocardial InfarctionCardiometabolic DiseasesCardiac MetabolismCardiac FunctionF-18 FDGIomeprolCaudal Vein CannulationBlood SamplingAnesthesiaTemperature MonitoringRespiration MonitoringMotion Artifacts
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Panetta, D., Guzzardi, M. A., La Rosa, F., Granziera, F., Terlizzi, D., Kusmic, C., Iozzo, P. High-Resolution Cardiac Positron Emission Tomography/Computed Tomography for Small Animals. J. Vis. Exp. (190), e64066, doi:10.3791/64066 (2022).
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