T2relaksaatioon

T2 relaxation, also known as spin-spin relaxation, is a fundamental process in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) that describes the decay of transverse magnetization. Following excitation by a radiofrequency pulse, nuclear spins align in a transverse plane and begin to precess. T2 relaxation occurs as these spins interact with each other through magnetic dipole-dipole couplings and also with their surrounding molecular environment. These interactions cause the spins to dephase, meaning they lose their synchronized precession. This loss of coherence leads to a decrease in the net transverse magnetization over time.

The rate of T2 relaxation is characterized by the T2 relaxation time constant, which is the time it takes for the transverse magnetization to decay to approximately 37% (1/e) of its initial value. T2 values are highly dependent on the physical and chemical properties of the substance being studied, including its molecular structure, viscosity, and temperature. Molecules that move rapidly tend to have longer T2 times as their interactions are averaged out. Conversely, molecules with restricted motion or strong interactions experience faster dephasing and thus shorter T2 times.

In NMR spectroscopy, T2 relaxation influences the linewidth of spectral peaks. Broader peaks indicate faster T2 relaxation. In MRI, T2-weighted images are generated by exploiting differences in T2 relaxation times between tissues, allowing for the visualization of various anatomical structures and the detection of pathological changes. Tissues with high water content, such as cerebrospinal fluid, generally have longer T2 values compared to tissues like muscle or fat.