What factors determine the T1 and T2 relaxation time of a tissue?

Factors affecting T1 and T2 relaxation times of different tissues are generally based on molecular motion, size and interactions.

What are T1 and T2 relaxation times?

The approach of the system to thermal equilibrium is known as relaxation and T1 and T2 are relaxation times (relaxation rates R1(2)=1/T1(2) are also used). Both relaxation times are time constants used to characterize what are assumed to be first order rate processes.

What are the causes of T1 and T2 relaxation relaxation mechanisms?

Molecular motion of each spin near the Larmor frequency causes local magnetic field fluctuations with both T1 and T2 relaxation. The effectiveness of a dipole-dipole interaction at producing relaxation depends on 1) the types of spins; 2) their spatial relationship; and 3) their relative motion.

What is the difference between T2 * and T2 relaxation?

T2* can be considered an “observed” or “effective” T2, whereas the first T2 can be considered the “natural” or “true” T2 of the tissue being imaged. T2* is always less than or equal to T2. T2* results principally from inhomogeneities in the main magnetic field.

What is the effect of MRI contrast agents on the tissue relaxation times T1 and T2?

Although, both T1 and T2 relaxation efficiency are improved, T1 effects predominate, in most situations. Most MRI contrast agents are chelates of the rare-earth element gadolinium and produce an increased signal (“positive contrast”) on T1-weighted images (the effect on T2-weighted images is generally negligible).

What causes T2 relaxation?

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.

What happens in T1 relaxation?

T1 relaxation is the process by which the net magnetization (M) grows/returns to its initial maximum value (Mo) parallel to Bo. Synonyms for T1 relaxation include longitudinal relaxation, thermal relaxation and spin-lattice relaxation.

What is T2 relaxation process?

T2 relaxation, also known as spin-spin relaxation or transverse relaxation, refers to the progressive dephasing of spinning dipoles resulting in decay in the magnetization in the transverse plane (Mxy).

What is a T1 and T2?

T1 and T2 are technical terms applied to different MRI methods used to generate magnetic resonance images. Specifically, T1 and T2 refers to the time taken between magnetic pulses and the image is taken. These different methods are used to detect different structures or chemicals in the central nervous system.

What is T2 relaxation time in MRI?

T2 Relaxation: Definition Thus T2 is the time required for the transverse magnetization to fall to approximately 37% (1/e) of its initial value. Synonyms for T2 relaxation are transverse relaxation and spin-spin relaxation.

What is T1 and T2 in MRI?

T1 images – 1 tissue type is bright – FAT. T2 images – 2 tissue types are bright – FAT and WATER.

What affects T1 relaxation?

T1 relaxation is fastest when the motion of the nucleus (rotations and translations or “tumbling rate”) matches that of the Larmor frequency. As a result, T1 relaxation is dependent on the main magnetic field strength that specifies the Larmor frequency. Higher magnetic fields are associated with longer T1 times.