Language
Country/Area
No result found
The mystery of Z spectrum: How to reveal subtle changes in the body through frequency?
In the field of medical imaging, magnetization transfer technology (MT) is gradually showing its importance, especially in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI).Through this technology, we can deeply understand the subtle changes inside cells and further reveal the deep principles of life's operation.Magnetization transfer not only involves the polarization of nuclear spins and the energy transfer between different nuclear groups, but also adds the concept of chemical exchange, making it more widely used in biomedical science.
Magnetization transfer technology can detect dynamic relationships between different nuclear groups, which represents chemical reactions and biological processes at the microscopic level.
The core of magnetization transfer lies in the energy coupling between NMR active nuclei.This process can be achieved through a series of mechanisms, including angular momentum coupling, magnetic dipole-dipole interaction, and nuclear Overhauser effect.Under the influence of these phenomena, medical imaging scholars can detect changes in tumors or tissues more accurately.The magnetization transfer technology is not only a simple image display, but also a dynamic analysis experiment.
Chemical exchange magnetization transfer
In studying NMR or MRI of macromolecular samples, especially protein solutions, it is common to see two types of water molecules: free water (bulk) and bound water (hydration).Free water molecules have many mechanical degrees of freedom, and their movement behavior thus exhibits statistical average characteristics.In an ideal NMR spectrum, the resonance frequency of free water protons is almost close to the average Larmor frequency of all protons, thus presenting a narrow Lorentzian line (located at 4.8 ppm, 20 degrees Celsius).
Free water protons experience slower lateral magnetization and phase removal in a uniform magnetic field, so their T2 value is relatively long; in contrast, bound water protons are restricted by local macromolecules, causing uneven magnetic field, resulting in Faster phase removal.
Because the T2 value of bound water protons is very short, its NMR signal is usually not observed in MRI.However, irradiating bound water protons through saturation pulses not at the resonant frequency can have a measurable impact on the NMR signal of free water protons.When a group of spins is saturated so that the size of the macroscopic magnetization vector is close to zero, an NMR signal cannot be generated at this time.
Longitudinal relaxation (T1) refers to the process of longitudinal spin polarization recovery, the rate of which is described by T1.Although the number of bound water molecules may not be enough to generate an observable signal, the exchange of water molecules between bound and free water populations is still able to characterize bound water populations.In this regard, magnetization transfer technology provides an alternative comparison method that reflects the structural integrity of the tissue in addition to differences in T1, T2 and proton density.
The magnetization transfer ratio (MTR) of extended magnetization transfer technology has been used in neuroradiology to highlight abnormalities in brain structures.
The MTR calculation formula is (Mo-Mt)/Mo, which can display the tissue characteristics under certain conditions.When we systematically adjust the frequency offset of the saturated pulse and draw a graph relative to the free water signal, we can form what is called a "Z spectra".This technique is also often referred to as "Z-Spectroscopy", which helps diagnose different pathological changes in clinical practice.
Conclusion
Overall, magnetization transfer is not only part of imaging technology, but also a key tool for exploring internal changes.The Z-spectrum technology further expands our understanding of life activities, but what new possibilities can such technology open up for future medical research?
