Enhancing in vivo EPR imaging using spin probes with short relaxation times

描述(申请人提供)：局部氧浓度(血氧计)和pH值的成像是肿瘤放射治疗的时机和形状、改善伤口愈合、设计外周血管疾病的治疗方法和药物设计的关键。使用三苯基或氮氧化物自由基探针的电子顺磁共振(EPR)成像正在开发中，用于临床前和临床血氧测定。脉冲方法已经被用来改善信噪比并减少获取带有三苯基基的图像的时间。与三苯基相比，氮氧自由基具有优势，因为它们可以被制备成有利于跨越血脑屏障或靶向细胞内空间的结构。氮氧化物也可以被设计来监测局部的PH值，这对肿瘤的治疗干预有很大的影响。在目前的EPR方法中，很难将脉冲方法应用于氮氧化物，因为这些自由基的电子自旋弛豫时间比三苯基短。在目标1中，提出了一种新的方法来改善氮氧化物脉冲成像的信噪比，从而提高pO2的测量。它基于双模谐振器设计，其中激励和检测谐振器通过调谐到不同的频率来解耦。快速正弦扫描将被用来在谐振器1的频率上激发自旋，并在谐振器2的频率上检测到双脉冲回波。该方法将在丹佛大学的模体上进行测试。在目标2中，建议的方法将在芝加哥大学EPR中心与共同导师Halpern教授合作，在小鼠肿瘤中实施体内血氧测定。建议的新方法将与目前使用的方法进行定量比较。PI在芝加哥花费的时间还将用于获得动物处理和设计活体实验的实用技能。在目标3中，PI将设计和实施快速扫描EPR成像实验，以使用氮氧自由基来测量pH，其光谱与pH有关，可以针对细胞外或细胞内区域。互补的MRI扫描将用于解剖特征的联合配准，以及用于PI训练目的。这项工作将不依赖于目标1和目标2的结果，因此可以并行完成。在整个授权期内，PI将学习生物、化学和医学基础课程，以补充他在数学和物理方面的强大背景，并将他带到一个水平，使他能够设计和解释肿瘤生理学成像实验，并将药物和放射疗法作为独立的PI进行评估。在三年的获奖期内，目标1、目标2和目标3的工作将越来越独立地进行。这项工作将提供撰写与大脑成像相关的R01提案所需的初步结果。

DESCRIPTION (provided by applicant): Imaging of localized oxygen concentration (oximetry) and pH are key to the timing and sculpting of radiation treatment of tumors, improvement of wound healing, and design of therapy for peripheral vascular disease and for drug design. Electron paramagnetic resonance (EPR) imaging using trityl or nitroxide radical probes is under development for pre-clinical and clinical oximetry. Pulsed methods have been used to improve signal-to-noise and reduce the time to acquire an image with trityl radicals. Nitroxide radicals have advantages over trityl radicals because they can be prepared with structures that facilitate crossing the blood-brain barrier or targeting of intracellular spaces. Nitroxides also can be designed to monitor local pH, which has dramatic impact on therapeutic interventions for tumors. With current EPR methodology it is difficult to apply pulse methods to nitroxides because these radicals have shorter electron spin relaxation times than trityls. In Aim 1 a new method is proposed to improve the signal-to-noise in pulsed imaging of nitroxides which will enhance measurement of pO2. It is based on a bimodal resonator design where excitation and detection resonators are decoupled by tuning to different frequencies. Rapid sinusoidal scans will be used to permit excitation of the spins at the frequency of resonator 1 and detection of a two-pulse echo at the frequency of resonator 2. The method will be tested on phantoms at the University of Denver. In Aim 2 the proposed method will be implemented for in vivo oximetry in mouse tumors at the University of Chicago EPR Center, working collaboratively with co- mentor Prof. Halpern. The proposed new method will be quantitatively compared with the currently used methods. The time spent by the PI in Chicago will also be used to acquire practical skills in animal handling and designing in vivo experiments. In Aim 3 the PI will design and implement rapid scan EPR imaging experiments to measure pH using nitroxide radicals for which spectra are pH-dependent which can be targeted for either extracellular or intracellular domains. Complementary MRI scans will be used for co-registration of anatomical features, as well as for PI training purposes. This work will not be dependent on the outcome of Aims 1 and 2, so it can be done in parallel. Throughout the grant period the PI will take courses in biology, chemistry, and fundamentals of medicine to complement his strong background in mathematics and physics and bring him to a level where he can design and interpret tumor physiology imaging experiments, and evaluate drug and radiation therapies as an independent PI. The work on Aims 1, 2, and 3 will be performed increasingly independently during the three year award period. The work will provide the preliminary results needed to write an R01 proposal related to imaging in brain.