Spanish term (edited): t�cnica de efecto T1 y T2

2. The biological parameters T1 and T2 in resonance


--------------------------------------------------------------------------------


The relaxation process in resonance is controlled by the biological parameters T1 and T2. These parameters are tissue dependent, introducing the possibility to separate different tissue types in the human body. T2 - named the spin-spin relaxation time - is the time constant for the relaxation process in the xy-plane, where as T1 - named spin-lattice relaxation time - is the time constant in the z-direction. T1 and T2 are related to physical interaction phenomenums in the tissue.

T2 effect
The T2 effect in the relaxation proces is due to dephasing of the individuel protons MDM because of the existence of a non-stationary magnetic field. Each proton will experience the external, stationary magnetic field B0 along with the self generated magnetic field of the neighbouring protons. Since the angular frequency of a proton is propertional to the experienced magnetic field, the protons will precess at different frequencies, depending on the actual field. When the protons precess at different frequencies, some MDM's will be ahead and other behind compared to the ideal frequency - the Larmor frequency, resulting in a net decrease of magnetic moment in the xy-plane as time goes on. At some point the magnetic moment will become zero, when all the MDM's equalize one another. The time period from maximum value to zero is characterized by T2. The value of T2 depends on the mobility of the protons, since a large mobility results in an average magnetic field variation of zero, resulting in a long T2 period.

T1 effect
The T1 effect in the relaxation process is due to the return of the high state protons to the low energy state. Over the time period T1 the high state protons exchange the "extra" energy with the neighbouring protons, resulting in heat and thermal energy. The value of T1 is dependent of the protons ability to exchange the energy.

Examples of T1 and T2 values of different tissues in the brain are listed in Table 2.1 below.


--------------------------------------------------
Note added at 24 mins (2006-01-27 18:50:38 GMT)
--------------------------------------------------

Technique, perdón

Spanish term (edited): t�cnica de efecto T1 y T2

Check the following URL (or any of the other 301,999 you get if you type "T1-weighted MRI in Google):

A retrospective analysis of 158 T1-weighted and T2-weighted MRI scans of normal
brains at 0.5 and 1....
www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve& db=PubMed&list_uids=8574041&dopt=Abstract

--------------------------------------------------
Note added at 43 mins (2006-01-27 19:09:47 GMT)
--------------------------------------------------

Dear spanruss:

You can also use "Tx-effect technique", as shown in the following URL from the same source (NIH); but Tx-weighted is much more widely used.

PURPOSE: Evaluation of the diagnostic usefulness of the T1-effect of Resovist (SPIO)
for dynamic MRI...
www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve& db=PubMed&list_uids=9551108&dopt=Abstract