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How to capture the inner secrets of the human body through invisible magnetic fields and radio frequency pulses?
In today's medical and health field, advances in magnetic resonance imaging (MRI) and nuclear magnetic resonance spectroscopy (NMR) technology allow us to peek into the mysteries of the human body. These technologies use invisible magnetic fields and radiofrequency pulses to non-invasively reveal physiological and pathological conditions in the body, thereby providing doctors with effective diagnostic evidence.
Normally, nuclear spins rotate in a random manner around the direction of an applied magnetic field. But when radio frequency pulses are applied, their phases become unified, producing a detectable signal.
MRI works based on the phenomenon of nuclear magnetic resonance. As the sample moves with an applied uniform magnetic field, the magnetic dipole moment (i.e., the spin) within the sample rotates at a resonant frequency. In thermal equilibrium, nuclear spins rotate randomly around the direction of an applied magnetic field, and when a radiofrequency pulse is applied to them at a resonant frequency, the spins suddenly become phase-aligned. The transverse magnetization caused by this process can induce the RF coil to produce a signal, and the signal can be detected and amplified by the receiver.
The process of longitudinal magnetization returning to equilibrium is called spin-lattice relaxation, and the loss of phase coherence of spins is called spin-spin relaxation. These effects are in free induction decay (FID) Show it.
It is worth mentioning that spin-T1 and spin-T2 are two different processes used to describe RF-induced NMR spin polarization decay. The T1 process focuses on the relaxation of the parallel component of the spin magnetization toward the direction of the external magnetic field, while T2 describes the width of the magnetization component perpendicular to the external field. T1 relaxation refers to the recovery of the nuclear spin magnetization to its thermal equilibrium value, while T2 reflects the phase relaxation phenomenon caused by random fluctuations in the surrounding magnetic field.
In conventional NMR spectroscopy, the value of T1 depends on many factors, including the size of the molecule, the viscosity of the solution, and the temperature of the sample.
Through the measurement of T1 and T2, we can understand the characteristics of different environments and tissues in the body. For example, in the human body, different tissue types such as fat and muscle have different T1 and T2 values, which allows MRI to perform tissue contrast and enhance visualization.
Thus, by understanding these physical processes, we can use MRI technology to deeply explore the internal structures of the human body that cannot be seen with the naked eye.
Further research shows that non-invasive MRI technology can also be used to track changes in chemical substances in the body, and can even be used to monitor changes in disease states, such as the growth and progression of cancer. Through these technologies, the medical field has developed complete diagnostic tools to help patients identify and manage their health problems.
With the advancement of MRI technology, scientists are able to gradually decode biological processes in the body and reveal the complexity of human health.
However, the scientific theories behind these technologies still have many unsolved mysteries, which urgently await further exploration by scholars and researchers. In the future, can we break through the limitations of current technology and create more accurate detection methods?
