In-Vivo Polarized Nuclear Imaging

摘要 磁共振成像(MRI)提供精致的空间分辨率、光谱敏感性和丰富的种类 用于诊断医学应用的对比剂机制。使用伽马相机的核成像提供了 使用少量放射性示踪剂寻找体内感兴趣的特定目标的好处。我们 已经开发出一种新的成像和光谱模式，最近发表在《自然》杂志上，它 利用了这两种方法的优点。空间信息被编码成微小的自旋方向 使用两种射频电磁辐射(RF)脉冲的偏振放射性示踪剂的量 和磁场梯度，就像核磁共振一样。而不是检测固有的微弱电磁信号 然而，根据进动磁化，通过检测伽马来获得成像信息 从极化的原子核发出的射线。与核成像不同，甚至可以使用单个伽马射线探测器 获取图像；不需要伽马相机。我们的新模式利用了这样一个事实 具有自旋的偏振核以相对于方向的空间各向异性方式发射伽马射线 它们所指向的方向。我们把我们的新技术称为偏振核成像(PNI)。尽管我们 尽管成功进行了概念验证演示，但在转移到体内应用方面仍存在重大挑战。这个 我们研究的长期目标是将PNI建立为一种实用的医学成像技术，以解决 未得到满足的医疗诊断需求。我们在此应用程序中解决的短期目标是演示 在活体内使用的可行性，通过在活体动物中产生第一个偏振核图像。我们的具体目标 (1)建立一种适合于体内应用的PNI脉冲序列策略，并演示 通过在玻璃细胞模体中获取二维图像来实现其功效；以及(2)演示偏振 首次在活体动物身上进行核成像，通过获取吸入131mXe的一维图像 兔肺。这些目标的成功完成将为PNI成为实用的新成像奠定基础 并将展示PNI创造一类新的医学示踪剂的潜力。

ABSTRACT Magnetic resonance imaging (MRI) provides exquisite spatial resolution, spectral sensitivity, and a rich variety of contrast mechanisms for diagnostic medical applications. Nuclear imaging using gamma cameras offers the benefits of using small quantities of radioactive tracers that seek specific targets of interest within the body. We have developed a new imaging and spectroscopic modality, recently published in the journal Nature, which utilizes favorable aspects of both approaches. Spatial information is encoded into the spin orientations of tiny amounts of a polarized radioactive tracer using pulses of both radio-frequency electromagnetic radiation (RF) and magnetic-field gradients, as in MRI. Rather than detecting the inherently weak electromagnetic signals from the precessing magnetization, however, imaging information is obtained through the detection of gamma rays emitted from the polarized nuclei. Unlike nuclear imaging, even a single gamma-ray detector can be used to acquire an image; no gamma camera is needed. Our new modality takes advantage of the fact that polarized nuclei with spin > ½ emit gamma rays in a spatially anisotropic fashion with respect to the direction along which they are oriented. We refer to our new technique as Polarized Nuclear Imaging (PNI). Despite our successful proof-of-concept demonstration, significant challenges remain in moving to in vivo applications. The long-term goal of our research is to establish PNI as a practical medical imaging technology that addresses unmet medical diagnostic needs. Our short-term goal addressed in this application is to demonstrate the feasibility of in vivo use, by producing the first polarized nuclear images in a living animal. Our specific aims are: (1) to develop a pulse sequence strategy for PNI that is suitable for in-vivo application, and to demonstrate its efficacy by acquiring two-dimensional images in glass-cell phantoms; and (2) to demonstrate polarized nuclear imaging for the first time in a living animal, by acquiring one-dimensional images of inhaled 131mXe in rabbit lungs. Successful completion of these aims will lay the basis for PNI to become a practical new imaging modality, and will demonstrate the potential of PNI to create a new class of medical tracers.