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

描述（由申请人提供）：局部氧浓度（血氧测定法）和pH成像是肿瘤放射治疗的时机和造型、伤口愈合的改善、外周血管疾病治疗设计和药物设计的关键。使用三苯甲基或氮氧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。脉冲方法已被用于改善信噪比和减少时间，以获取图像与三苯甲基自由基。氮氧自由基具有优于三苯甲基自由基的优势，因为它们可以用促进穿过血脑屏障或靶向细胞内空间的结构制备。氮氧自由基还可以被设计用于监测局部pH值，这对肿瘤的治疗干预具有显著影响。用目前的EPR方法很难将脉冲方法应用于氮氧自由基，因为这些自由基的电子自旋弛豫时间比三苯甲基短。在目标1中，提出了一种新的方法来提高氮氧化物脉冲成像的信噪比，这将增强pO2的测量。它是基于一个双峰谐振器的设计，其中激励和检测谐振器通过调谐到不同的频率去耦。将使用快速正弦扫描来允许在谐振器1的频率处激发自旋并在谐振器2的频率处检测双脉冲回波。该方法将在丹佛大学的幻影上进行测试。在目标2中，所提出的方法将在芝加哥大学EPR中心与共同导师Halpern教授合作实施，用于小鼠肿瘤的体内血氧测定。将提出的新方法与目前使用的方法进行定量比较。PI在芝加哥的时间也将用于获得动物处理和设计体内实验的实践技能。在目标3中，PI将设计并实施快速扫描EPR成像实验，以使用氮氧自由基测量pH值，氮氧自由基的光谱具有pH值依赖性，可以靶向细胞外或细胞内结构域。补充MRI扫描将用于解剖特征的配准以及PI培训目的。这项工作不取决于目标1和2的结果，因此可以并行进行。在整个资助期间，PI将参加生物学，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，并使他能够设计和解释肿瘤生理学成像实验，并作为独立的PI评估药物和放射疗法。目标1、2和3的工作将在三年的奖励期内越来越独立地进行。这项工作将提供编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.