Time Domian Electron Paramagnetic Resonance Imaging

项目概述：目前的电子顺磁共振成像系统是作为活体氧气成像扫描仪的原型开发的，它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，为这两种模式使用了一个组合谐振器，允许可靠地配准来自两种成像扫描的空间信息。随后的发展侧重于提高空间和时间分辨率。EPR成像系统在过去一年中的发展现在具有以下能力：a)在单次注射示踪剂Oxo63后，可以在2分钟内获得图像数据集，允许收集大约8-10个图像，从而能够评估肿瘤氧气状态的时间变化。B)在几天至几周的时间内纵向监测肿瘤氧状态的变化，以评估药物引起的氧状态变化并与治疗效果相关。通过这些改进，我们利用该系统对肿瘤氧状态、血管密度以及化疗药物治疗后影响肿瘤氧状态和血管密度的相应变化进行了纵向监测。基于这些能力，正在进行以下三个实验：1)评估肿瘤中的循环(急性)缺氧：由于其异常的血管系统，肿瘤同时具有慢性(扩散受限)和循环(急性)缺氧。虽然慢性缺氧是扩散受限的，但急性缺氧被证明是耐药的表型，也是更恶性的表型。虽然这一现象要么是通过插入氧气传感电极等侵入性方法进行研究，要么是通过实验强制实施这种模式，但到目前为止，成像技术还无法研究和区分这两种类型的缺氧。在一项旨在利用EPR检查这一现象的研究中，对两种移植到小鼠体内的肿瘤模型(SCC VII和HT29)进行了研究，以评估慢性和循环缺氧的水平。随后进行MRI研究，以获得解剖相关性和血管密度。肿瘤切片的组织学相关性也被评估为血管密度和血管完整性。通过呼吸施加空气-碳氧-空气激发，以检查肿瘤氧气的时空反应，以区分慢性和循环缺氧区。研究表明，这两种类型的肿瘤都表现出周期性低氧，与HT29肿瘤相比，SCC VII移植瘤表现出较大幅度的波动。观察到的差异是HT29肿瘤血管中较强的周细胞覆盖所致。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：已有证据表明，抗血管生成药物在治疗开始后通过一种称为血管重新正常化的过程短暂地增加肿瘤的氧气水平。紧随其后的是由于血管丧失而导致的氧气的稳定减少。血管重整化期是与放疗或化疗协同的时间窗口。我们评价了抗血管生成药物舒尼替尼对C3H小鼠后腿种植鳞状细胞癌(SCC)的影响，并监测了治疗开始后几天氧和血管密度的变化，并与未治疗的荷瘤小鼠进行了比较。这些研究表明：a)可以纵向监测肿瘤氧气和血管密度的变化；b)舒尼替尼治疗后血管密度降低；d)舒尼替尼治疗后肿瘤氧合一过性增加。这些数据与血管密度标记物上获得的免疫组织化学数据一致。一个重要的发现是，EPR成像研究可以识别肿瘤中的血管重整化期，在此期间，我们发现在进行放射治疗时存在显着的协同作用。另一个发现是，在血管重新正常化期间，氧气的波动最小。3)mTOR抑制剂雷帕霉素对肿瘤氧合和血管密度的影响：雷帕霉素在人类多种肿瘤类型中处于活跃状态。它对肿瘤的一些影响包括自噬和肿瘤血管损伤。在雷帕霉素治疗过程中，对荷鳞癌小鼠进行了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有显著影响。然而，肿瘤血管减少与一过性但显著的肿瘤氧合增加有关，这与提示肿瘤血管正常化从而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.