Development of a Combined MRI-PET System for Contemporaneous Functional Imaging

描述（由申请人提供）：小动物成像系统正迅速成为许多生物医学研究项目的组成部分，允许对许多疾病的动物模型进行详细研究。近年来，多模成像技术最初是为临床应用而开发的，现已应用于临床前。在这个项目中，我们建议创建一个联合MRI- pet成像插入，设计用于使用3T临床MRI对小动物进行定量同期成像。因此，MRI- pet成像可以提供给那些无法使用当前一代专为专门的高场小动物MRI系统设计的MRI- pet插入物的研究人员，该系统针对小鼠成像进行了优化。该系统的核磁共振兼容PET组件将利用连续的闪烁体块，通过短光纤光导连接到位于核磁共振系统孔外的微通道板、位置敏感光电倍增管（MCP- PSPMTs）。光导的使用使我们能够使用高增益，大面积光电倍增管，这将最大化PET的视场（FOV），以促进比小鼠（大鼠到兔子）更大的动物物种的快速成像。这种能力在不久的将来可能是非常重要的，因为在这些物种中已经开发了许多重要的疾病模型，并且可能比一些小鼠模型更可取。此外，由于在MRI扫描仪的成像区域内没有敏感的电气元件，因此不需要电屏蔽。因此，在MRI视场中不会有可能产生涡流的导电材料，涡流已被证明会影响MRI信噪比。由于光导中信号衰减引起的某些PET成像性能指标的退化将通过使用高光输出闪烁体（LaBr3）的连续块来抵消。连续块闪烁体的应用使我们能够利用光脉冲的形状来测量光子相互作用的深度。此外，我们的系统将在其设计中包括一个旋转光子源，这将有助于校正光子衰减效应。如果PET图像用于放射性示踪剂浓度的定量，这种能力是至关重要的。同时，将开发和测试两个定制的发送/接收MRI线圈组。一组线圈是为大鼠的最佳磁共振成像而设计的，而另一组线圈是为兔子大小的动物设计的。用于获取解剖、功能和光谱MR数据的MRI方法将适用于我们的新系统。此外，技术将实现分割MRI图像和共同注册MRI， fMRI和PET图像。最后，除了最初的幻影测试外，还将对少量大鼠和兔子进行成像，以展示新系统的成像能力。该设备的新颖方面包括使用LaBr3连续块，应用mcp - pspmt创建大视场MRI-PET系统，获取传输扫描以进行衰减校正，实现PET图像重建方法，利用MRI图像的结构信息以及开发可互换的MRI- rf线圈以适应所调查动物物种的大小。在该项目完成后，我们将建造并初步测试用于临床MRI 3T扫描仪的大型FOV MRI- pet插入物，使这项最先进的技术可供更多的研究人员使用临床前成像技术。公共卫生相关性：本申请提出了一种大视场联合MRI-PET动物成像系统的开发。这种装置可能有助于发现新的药物和方法，以帮助诊断和治疗许多疾病。

DESCRIPTION (provided by applicant): Small animal imaging systems are rapidly becoming integral elements of many biomedical research programs, allowing the detailed study of animal models of a number of diseases. Recently, the multimodality imaging techniques originally developed for clinical use have been applied to pre-clinical applications. In this project we propose to create a combined MRI-PET imaging insert designed for quantitative contemporaneous imaging of small animals using a 3T clinical MRI. Thus, MRI-PET imaging can be made available to researchers who do not have access to the current generation of MRI-PET inserts designed for specialized high field, small animal MRI systems optimized for the imaging of mice. The MR-compatible PET component of the system will utilize continuous blocks of scintillator, coupled to microchannel plate, position-sensitive photomultiplier tubes (MCP- PSPMTs) located outside the bore of the MRI system via short fiber optic light guides. The use of light guides allows us to use high gain, large area photomultiplier tubes, which will maximize the field-of-view (FOV) of the PET to facilitate rapid imaging of animal species larger than mice (rats to rabbits). This capability is likely to be very important in the near future since a number of important disease models in these species have been developed and may be preferable to some mouse models. In addition, since there are no sensitive electrical components in the imaging area of the MRI scanner, no electrical shielding is required. Thus, there will be no conductive material in the MRI FOV that may produce eddy currents, which have been shown to affect MRI SNR. Degradation in some PET imaging performance metrics caused by attenuation of signal in the light guides will be offset by the use continuous blocks of a very high light output scintillator (LaBr3). Application of continuous block scintillator permits us to measure depth of photon interaction by using the shape of the light pulses. Furthermore, our system will include a rotating photon source in its design that will facilitate correction of photon attenuation effects. This capability is critical if the PET images are to be used for quantification of radiotracer concentration. In parallel, two custom transmit/receive MRI coil sets will be developed and tested. One coil set is designed for optimal MR imaging of rats, while the other is intended for animals up to the size of rabbits. MRI methods for acquiring anatomical, functional and spectroscopic MR data will be adapted for use with our new system. In addition, techniques will be implemented for segmenting the MRI images and co- registering the MRI, fMRI, and PET images. Finally, in addition to initial phantom testing, a small number of rats and rabbits will be imaged to demonstrate the imaging capabilities of the new system. The novel aspects of this device include the use continuous blocks of LaBr3, application of MCP-PSPMTs to create a large FOV MRI-PET system, acquisition of transmission scans for attenuation correction, implementation of PET image reconstruction methods that utilize structural information from MRI images and the development of interchangeable MRI-RF coils to fit the size of the animal species under investigation. At the completion of this project we will have built and initially tested a large FOV MRI-PET insert for use in clinical MRI 3T scanners, making this state-of-the-art technology available to an expanded number of researchers utilizing pre-clinical imaging techniques. PUBLIC HEALTH RELEVANCE: This application proposes the development of a large field-of-view combined MRI-PET animal imaging system. This device could be instrumental in the discovery of new drugs and methods to aid in the diagnosis and treatment of a large number of diseases.