Time Domian Electron Paramagnetic Resonance Imaging

项目概要： 当前的电子顺磁共振成像系统被开发为体内氧气成像扫描仪的原型，具有从传统磁共振成像（MRI）获得的解剖相关性和血管密度等附加信息，利用两种模式的组合谐振器，允许可靠地配准来自两种成像的空间信息扫描。随后的发展侧重于提高空间和时间分辨率。在过去一年中开发的EPR成像系统现在具有以下能力：A）可以在2分钟内获得图像数据集，允许在单次团注示踪剂Oxo 63后收集约8 - 10个图像，允许评估肿瘤氧状态的时间变化。B）在几天-几周的时间内纵向监测肿瘤氧状态的变化，以评估药物诱导的氧状态变化并与治疗功效相关。通过这些改进，我们已经利用该系统来纵向监测肿瘤氧状态、血管密度以及响应于用影响肿瘤氧状态和血管密度的化疗药物治疗的相应变化。根据这些能力，正在进行以下三项试验： 1)肿瘤中循环（急性）缺氧的评估：肿瘤由于其异常血管系统而具有慢性（扩散限制）和循环（急性）缺氧。虽然慢性缺氧是扩散限制的，但急性缺氧已被证明可转化为表现出对治疗的抗性的表型以及更恶性的表型。虽然已经使用侵入性方法（例如插入氧感测电极）或实验性地实施的这种模式来研究这种现象，但是成像技术迄今为止还不能研究和区分这两种类型的缺氧。在一项旨在使用EPR检查这种现象的研究中，研究了植入小鼠的两种肿瘤模型（SCC VII和HT 29），以评估慢性和循环缺氧的水平。MRI研究依次进行，以获得解剖相关以及血管密度。还评价了肿瘤切片的血管密度和血管完整性的组织学相关性。还通过呼吸施加空气-碳水化合物-空气挑战以检查对肿瘤氧的时空响应，以区分慢性低氧区域与循环低氧区域。研究表明，研究的两种肿瘤类型都表现出循环缺氧，与HT 29肿瘤相比，SCC VII移植物表现出大幅度的波动。HT 29肿瘤血管系统中相对较强的周细胞覆盖是观察到的差异的原因。 2)抗血管生成药物舒尼替尼对肿瘤氧合和血管密度的影响：抗血管生成药物已被证明在治疗开始后通过称为血管再正常化的过程短暂增加肿瘤氧水平。随后是由于血管损失导致的氧气稳定减少。血管重整期是与放疗或化疗协同作用的时间窗口。我们评估了舒尼替尼（一种抗血管生成药物）在C3 H小鼠中的作用，该小鼠在后腿上植入鳞状细胞癌（SCC），并在治疗开始后几天监测氧和血管密度的变化，并与对照未治疗的荷瘤小鼠进行比较。这些研究表明：a）可以纵向监测肿瘤氧和血管密度的变化; B）舒尼替尼治疗后血管密度降低;和d）舒尼替尼治疗后肿瘤氧合短暂增加。这些数据与血管密度标记物的免疫组织化学数据一致。一个重要的发现是，EPR成像研究可以确定肿瘤中的血管重整期，在此期间，我们发现放射治疗时有显着的协同作用。另一个发现是，在血管再正常化期间，氧气的波动最小化。 3)mTOR抑制剂雷帕霉素对肿瘤氧合和血管密度的影响：雷帕霉素在人类许多肿瘤类型中处于积极研究中。它对肿瘤的一些影响包括自噬和肿瘤血管损伤。在用雷帕霉素治疗期间，对带有SCC肿瘤的小鼠进行EPR成像和MRI研究。研究表明，早在治疗开始后一天，雷帕霉素就对肿瘤血管损伤具有显著影响。然而，肿瘤血管减少与肿瘤氧合的短暂但显著增加相关，这与表明肿瘤血管系统正常化增加肿瘤氧合的结果一致。

Project Summary: The current Electron Paramagnetic Resonance imaging system developed as a prototype in vivo oxygen imaging scanner with anatomic correlates obtained from conventional Magnetic Resonance Imaging (MRI) and additional information such as blood vessel density makes use of a combined resonator for both the modalities allowing reliable coregistration of spatial information from both imaging scans. Subsequent developments focused on improving the spatial and temporal resolutions. The EPR imaging system with the developments during the last year now has the following capabilities: A) An image data set can be obtained in 2 minutes permitting the collection of about 8-10 images after a single bolus injection of the tracer Oxo63, allowing the assessment of temporal changes in tumor oxygen status. B) monitoring changes in tumor oxygen status longitudinally over a period of several days-weeks to assess drug induced changes in oxygen status and correlate with treatment efficacy. With these improvements, w have utilized the system for longitudinal monitoring of tumor oxygen status, blood vessel density and the corresponding changes in response to treatment with chemotherapeutic drugs which impact tumor oxygen status and blood vessel density. Based on these capabilities, the following three experiments are being pursued: 1) Assessment of cycling (acute) hypoxia in tumors: Tumors, as a result of their aberrant vasculature have both chronic (diffusion limited) and cycling (acute) hypoxia. While chronic hypoxia is diffusion limited, acute hypoxia has been shown to coner phenotypes which display resistance to treatment and also a more malignant phenotype. While this phenomenon has either been studied using invasive approaches such as insertion of oxygen sensing electrodes or such a pattern enforced experimentally, imaging techniques so far have not been able to study and distinguish the two types of hypoxia. In a study designed to examine this phenomenon using EPR, two tumor models (SCC VII and HT 29) implanted in mice were studied to assess the levels of both chronic and cycling hypoxia. MRI studies were sequentially carried out to obtain anatomic correlates as well as blood vessel density. Histological correlates from tumor sections were also evaluated for blood vessel density and vascular integrity. Air-Carbogen-Air challenge via respiration was also imposed to examine the spatio-temporal responses to tumor oxygen to distinguish chronic vs cycling hypoxic regions. The studies reveal that both tumor types studied exhibited cycling hypoxia, withtyhe SCC VII transplant exhibiting fluctuations to a large magnitude compared to HT 29 tumors. The relatively stronger pericyte coverage in HT 29 tumor vasculature was accounted for the observed differences. 2) Effect of the anti-angiogenic drug, sunitinib on tumor oxygenation and blood vessel density: Ant-angiogenic drugs have been shown to transiently increase tumor oxygen levels after treatment initiation through a process called vascular re-normalization. This is followed by a steady decrease in oxygen resulting from loss of blood vessels. The vascular renormalization period is a window in time for synergy with radiotherapy or chemotherapy. We have evaluated the effect of sunitinib, an anti-angiogenic drug in C3H mice implanted with squamous cell carcinoma (SCC) on the hind leg and monitored changes in oxygen and blood vessel density on several days after treatment initiation and compared with control untreated tumor bearing mice. These studies showed: a) it is possible to longitudinally monitor changes in tumor oxygen and blood vessel density; b) blood vessel density decreases after treatment with sunitinib; and d) there is a transient increase in tumor oxygenation after sunitinib treatment. These data are in agreement with the immunohistochemical data obtained on the markers for blood vessel density. An important finding is that EPR imaging studies can identify the vascular renormalization period in tumors during which time we find that there is a significant synergy when radiotherapy is administered. Another finding is that fluctuations in oxygen are minimized during the period of vascular re-normalization. 3) Effect of the mTOR inhibitor, rapamycin on tumor oxygenation and blood vessel density: Rapamycin is in active investigation in many tumor types in humans. Some of its effects on tumors include autophagy and tumor vessel damage. EPR imaging and MRI studies were conducted on SCC tumor bearing mice during treatment with rapamycin. The studies show that rapamycin has significant influence in tumor vessel damage as early as one day after treatment initiation. However, the tumor vessel decrease was associated with a transient but significant increase in tumor oxygenation in agreement with results which suggest that there is a normalization of tumor vasculature which increases tumor oxygenation.