"Each magnetic dipole exists in a microenvironment unique to the tissue where it belongs. In all tissues, there exist tiny magnetic fields (~1mT) generated by the spinning hydrogen nuclei (protons). T2 relaxation occurs in a varying local magnetic field when there is transfer of energy between dipoles facing parallel and antiparallel to the external magnetic field, flipping each other in opposite directions. This rate of flipping or transfer of energy between spins or dipoles increases as the frequency of the variation of the local magnetic field approaches the Larmor frequency. This is related to the rate of rotation and translation of the water molecule or adjacent dipoles. The dipole-dipole interaction is also increased the strength of the local field which is dependent on the proximity of the adjacent dipoles."
"Note: T2 relaxation is not to be confused with T2*, which is a broader phenomenon and includes static magnetic field effects in addition to the tissue-characteristic T2 relaxation."
"Factors affecting T2 relaxation"
"Note: T2 relaxation is not to be confused with T2*, which is a broader phenomenon and includes static magnetic field effects in addition to the tissue-characteristic T2 relaxation."
Expected headings
"Discussion"
"Factors affecting T2 relaxation"
"In solutions of macromolecules and tissues the relaxation rate is much faster, i.e., the T2 time is shorter. This is related in part to the slower motion of protons both in macromolecules as well as water molecules attracted to the surface of the macromolecule. This slower motion is closer to the Larmor frequency. Examples of T1 and T2 in biological tissues include: CSF, T1=1.9 seconds and T2=0.25 seconds; brain white matter, T1=0.5 seconds and T2=0.07 seconds (70 msec)."
"Loss of signal and darkness on T2-weighted images in cortical bone, teeth, calculi is primarily a result of little water (low proton density) unlike tendons and ligaments 4. The water that is in bone, teeth, and calculi would mostly be bound as to collagen and would have a very short T2 time constant and appear dark. There is also mild susceptibility differences between bone and soft tissue that could contribute to a dark appearance at interfaces, as between marrow and bone trabecula. This is seen in particular on gradient echo images."