Behavior of contrast in MRI
Strength OF MRI is Multi-parametric Images
In MRI each nuclei in the sample or subject under examination participate in signal generation. The signal varies due to many reasons like density, local environment around nuclei, flow etc. This gives strength to MRI as compared to other modality like x-ray CT, ultrasound where attenuation of tissue is the only factor due which the contrast changes.
T1 relaxation time
The spin-lattice relaxation time, also known as the T1 relaxation time, is a measure of how rapidly the net magnetization vector (NMV) returns to its ground state in the direction of B0. The loss of energy to the surrounding nuclei is connected with the return of excited nuclei from the high energy state to the low energy or ground state. The name “spin-lattice” relaxation comes from the fact that nuclear magnetic resonance was first used to study materials in the form of lattices. Where M is the magnetization at time = t, the time after the 90o pulse, Mo is the maximum magnetization at full recovery.
T1 weighted image
T1 weighted image (also known as T1WI or “spin-lattice” relaxation time) is one of the most basic MRI pulse sequences that shows differences in tissue T1 relaxation times. The longitudinal relaxation of a tissue’s net magnetization vector is used in a T1WI (NMV).
T2 relaxation
T2 relaxation, also known as spin-spin relaxation or transverse relaxation, is the gradual dephasing of spinning dipoles that results in a decrease in transverse magnetization (Mxy). This type of relaxation happens with the time constant T2, where T2 is the time it takes for the transverse magnetization vector to decline to 1/e, or 37 percent of its initial magnitude, following a radiofrequency pulse. T2 relaxation occurs as a result of tissue-specific properties, primarily those that affect the rate of movement of protons, which are found in water molecules for the most part.
T2-weighted image
A T2-weighted picture is a basic magnetic resonance (MR) imaging pulse sequence that reveals differences in T2 relaxation time of distinct tissues. Because most tissues implicated in a pathologic process have a higher water content than usual, and fluid (e.g., cerebrospinal fluid, vitreous humour) causes affected areas to appear bright on T2-weighted images, T2-weighted pictures provide the greatest clinical portrayal of disease.
Figure showing T1 relaxation time
Figure showing T1 weighted image
Figure showing T2 relaxation time
