Hyperpolarized Nuclear Singlet States

核磁共振是一种技术，它利用许多原子核充当微小的无线电发射器的事实，以精确定义的频率发射无线电信号，可以由仔细调整的探测器检测到。信号的频率和强度取决于样品所在的磁场：磁场越高，频率越高，信号越强。在核磁共振实验中，首先通过将样品置于强磁场中一段时间来磁化原子核。然后，一系列射频脉冲被施加到样本上，然后样本发出无线电波，可以在无线电接收器中检测到。发射波的模式取决于原子核在脉冲序列中经历了什么。一个有用的特征是，原子核可以在无线电信号发出前几秒钟“记住”发生在他们身上的事情。这种“记忆”特性使人们能够通过核磁共振跟踪运动，如化学反应、分子的随机置换以及血液和其他液体的流动。直到最近，原子核的“记忆时间”还被认为是被研究物质的一种固定性质，不能通过实验的方式来显著改变。然而，我们的团队在2004年表明，对于某些物质，通过使用特殊的非磁性量子态，即单重态，可以将记忆时间延长10倍或更多。大约在同一时间，瑞典的一组研究人员，包括我们的项目合作伙伴Jan-Henrik Ardenkjaer-Larsen，开发了一种革命性的方法，将核磁共振信号的幅度增加1万倍甚至更多。这种方法被称为溶解DNP，英国牛津仪器公司制造并销售了一种实现这一方法的工具。然而，这项技术的一个缺点是大大增强的极化(称为超极化)很快就消失了。在这个项目中，我们将结合这两个发展，使用溶解-DNP产生超极化，然后将超极化物质转换为具有更长寿命的单重态。我们将合成具有维持长寿命单重态的正确性质的分子，并进行超极化核磁共振成像实验，绘制出扩散和流动等缓慢过程。我们还希望开发出一种方法，使人们能够构建血液等流体的含氧量地图。通过这种方式，我们将开发和展示一系列在医学、化学工程和材料科学中广泛应用的新的磁共振方法。

Nuclear Magnetic Resonance (NMR) is a technique which uses the fact that the nuclei of many atoms act as tinyradiotransmitters, emitting radio signals at precisely-defined frequencies, which can be detected by a carefully-tuned detector. The frequencies and strengths of the signals depend on the magnetic field in which the sample is placed: the higher field, the higher the frequency, and the stronger the signals. In an NMR experiment, the nuclei are first magnetized by placing a sample in a strong magnetic field for some time. A sequence of radiofrequency pulses is then applied to the sample, which then emits radiowaves which can be detected in the radio receiver. The pattern of emitted waves depends on what the nuclei experienced during the pulse sequence.One useful feature is that the nuclei can "remember" what happened to them some seconds before the radiosignals are emitted. This "memory" property allows one to track movements such as chemical reactions, the random displacement of molecules, and the flow of blood and other fluids by NMR. Until recently, the "memory time" of the atomic nuclei was thought to be a fixed property of the substance under study, which could not be changed significantly by the way one does the experiment. However, our group showed in 2004 that for some substances the memory time could be extended by a factor of 10 or more by using special quantum states which are non-magnetic, called singlet states.At roughly the same time, a group of researchers in Sweden, including our project partner Jan-Henrik Ardenkjaer-Larsen, developed a revolutionary method for increasing the amplitude of NMR signals by a factor of ten thousand or even more. This method is called dissolution-DNP and an instrument to implement this is built and marketed by the British company Oxford Instruments. However a drawback of the technique is that the greatly enhanced polarization (called hyperpolarization) dies out quickly. In this project we will combine these two developments by using dissolution-DNP to generate hyperpolarization and then convert the hyperpolarized substances into singlet states, which have a much longer lifetime. We will synthesize molecules which have the right properties to sustain the long-lived singlet states and perform hyperpolarized NMR imaging experiments, mapping out slow processes such as diffusion and flow. We also expect to develop methods that allow one to construct a map of the oxygen content of fluids such as blood. In this way we will develop and demonstrate a range of new magnetic resonance methods with a wide range of applications in medicine, chemical engineering and materials science.