Overhauser Enhanced Magnetic Resonance Imaging (OMRI)

奥豪瑟增强磁共振成像 (OMRI)

• 批准号: 7292183
• 负责人: murali cherukuri
• 金额: --
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/7292183
• 关键词: Overhauser; Enhanced; Magnetic; Resonance; Imaging; Overhauser; Enhanced; Magnetic; Resonance; Imaging

Project 2: Overhauser enhanced Magnetic Resonance Imaging. (OMRI)This methodology provides anatomically co-registered pO2 images by combining the sensitivity of EPR detection at low fields and the dynamic nuclear polarization (DNP) to enhance the MR image intensity significantly at low magnetic fields. Therefore, the scanner is a combination of EPR Imaging and MR imaging and we use a contrast agent whose relaxation properties are linearly dependent on pO2. Earlier studies demonstrated the quantitative pO2 imaging capabilities of this technique. However, two aspects needed to be addressed for this technique to progress for in vivo imaging applications with minimal artifacts.pO2 images normalized for changes in proton T1. The enhancement of the water 1H based MR images from OMRI studies depends upon: a) concentration of the contrast agent; b) RF power deposited to excite the contrast agent; c) tissue pO2; and d) intrinsic 1H T1 relaxation times. Of these, the T1 of the protons in tissue varies with the regions examined and hence may lead to significant errors in estimating pO2. We have developed image data collection strategies to correct for this artifact by using novel pulse sequences from which the changes in the tissue based T1 values can be independently estimated.Use of Inductive loop for RF Focusing in OMRI: One unique feature in OMRI imaging is that the irradiation of the unpaired spin to generate the required Ovehauser enhancement uses high RF power at a duty cycle of nearly 50% of the total measurement time. This leads to a high SAR (Specific Absorption Rate) well above the one prescribed for human use by the FDA. Any prospective human application therefore necessitates efforts to reduce SAR in OMRI. Among several strategies that we are planning, the one we have recently successfully tested is the use of local inductive loop, which is a passive tuned resonator (such as a surface loop) that is tuned to the same frequency as the main volume resonator, kept close to the region of interest (ROI). Such a passive tuned element draws RF flux close to itself at the expense of RF flux elsewhere, and produces enhanced image intensity compared to locations which are outside the loop. This strategy has been tested both on phantoms and in vivo, and produces RF focusing leading to improved image sensitivity at the localized region. This will allow the use of significantly lower RF power than normal, and yet produce enhanced image intensity at the ROI. Such a focusing effect of RF will allow effective OMRI imaging and oxymetry of topical tumors in animal models at much reduced SAR. We are also experimenting on the use of quadrature transmit and receive coils to reduce the power requirements further by factor of 2, and bring the effective SAR well under FDA limits.

项目2：大关增强的磁共振成像。 （OMRI）该方法通过将EPR检测的敏感性和动态核极化（DNP）结合起来，从而提供了解剖共同注册的PO2图像，从而在低磁场下显着增强了MR图像强度。因此，扫描仪是EPR成像和MR成像的组合，我们使用了造影剂，其弛豫特性线性依赖于PO2。较早的研究证明了该技术的定量PO2成像能力。但是，对于此技术，需要解决两个方面，以进行最小伪像的体内成像应用程序。来自OMRI研究的基于水1H的MR图像的增强取决于：a）对比剂的浓度； b）沉积以激发对比剂的RF功率； c）Tissue PO2; d）内在的1H T1松弛时间。其中，组织中质子的T1随检查的区域而变化，因此可能导致估计PO2的重大错误。我们已经开发了图像数据收集策略，通过使用新型的脉冲序列来纠正此伪像，从中可以独立估计基于组织的T1值的变化。使用OMRI中的RF归纳环的使用：OMRI成像中的一个独特功能是，不归档的旋转的辐射以产生所需的Ovehauser增强量的iSATER量表，该效率是高RF的50％。这导致较高的SAR（特定吸收率）远高于FDA为人类使用的规定。因此，任何潜在的人类应用都必须努力减少OMRI中的SAR。在我们计划的几种策略中，我们最近成功测试的一种策略是使用局部电感环，这是一种被动调谐的谐振器（例如表面环），该谐振器与主体积谐振器的调谐频率相同，它保持接近兴趣区域（ROI）。这样的被动调谐元件以其他地方的RF磁通量为代价，将RF通量与自身接近，并与循环外部的位置相比产生增强的图像强度。该策略已在幻象和体内进行了测试，并产生了RF的重点，从而提高了局部区域的图像灵敏度。这将允许使用明显低于正常的RF功率，但在ROI处产生增强的图像强度。 RF的这种聚焦效果将允许在大量降低的SAR中有效的OMRI成像和局部肿瘤的氧对象。我们还在尝试使用正交传输和接收线圈以将功率要求进一步降低2倍，并在FDA限制下使有效的SAR很好地降低功率要求。