Update MR_Physics.md

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@@ -12,49 +12,49 @@ modalities. MRI enables to perform dynamic studies due to it's speed of acquisit
 ## Basic Physics
 
 Any atomic nucleous with an odd numer of nucleons has spin different from zero and so, a magnetic moment (magnetic dipole). 
-In the body, we can find several atoms with magnetic moment such as H, P, C, F, Na. Around 60% of the human body is made up
-of water that contains hydrogen, which is also present in proteins and lipids. For this reason, hydrogen is very sensitive
-to magnetic fields and MRI takes advantage of this phenomenom. 
+In the body, we can find several atoms with magnetic moment such as H, P, C, F, Na, which are sensitive to magnetic resonance.
+Around 60% of the human body is made up of water that contains hydrogen, which is also present in proteins and lipids. 
+For this reason, hydrogen is the most widely used in MRI.
 
- atoms with magnetic dipole
 
 MRI bore contains a powerful magnet which generates an uniform magnetic field B0. Patiens are introduced in this magnetic field
-and hydrogen atoms align to the magnetic field. According to Larmour's law,a magnetic dipole inside a magnetic field 
+and hydrogen atoms align to the magnetic field. According to Larmour's law, a magnetic dipole inside a magnetic field 
 precesses (spins) arround the magnetic field with a frequency proportional to the magnetic field strength. Hence, hydrogen atoms
-precess arround the magnetic field generated by the MR. 
+precess arround the magnetic field generated by the MR with a frequency (Larmour frequency) that follows the equation:
 
 w =  γ B0
 
+![](https://www.frontiersin.org/files/Articles/427144/frym-07-00023-HTML-r2/image_m/figure-2.jpg)
 This precession can be parallel or antiparallel to B0. In the body the number of atoms that precess parallel is different to 
-the ones that precess antiparallel inducing an small magnetic field which is proportional to B0 and also depends on the density 
-od hydrogen nuclei. To sum up, static magnetic field (B0) induces a slight magnetization of tissues. 
+the ones that precess antiparallel producing an small magnetic field which is proportional to B0 and also depends on the density 
+of hydrogen nuclei. So, the static magnetic field (B0) induces a slight magnetization of tissues. 
 
----- (induced magnetization inside the bore)
-
-(Mx, My, Mz)
 
 Then, a radiofrequency pulse is emitted perpendicular to B0 with the same frequency that the spin precession frequency.Hydrogen atoms 
-abrosrb energy and spin out of equilibrium.Then, when the RF dissapears, the magnetic momentum gradually goes back to te minimum 
+abrosrb energy and spin out of equilibrium. Longitudinal magnetization (Mz) of protons in a parallel direction to B0 decreases, and a
+transverse magnetization (Mx, My) appears.
+
+Then, when the RF dissapears, the magnetic momentum gradually goes back to te minimum 
 energy position (magnetic relaxation) while releasing energy. This emited signals are measured into the k-space which is an array 
-of numbers representing spatial frequencies in the MR image. Each k-space point contains spatial frequency and phase information
-about every pixel in the final image. Fourier transformed is performed to the k-space to obtain the final image. By varying the 
+of numbers representing spatial frequencies in the MR image. (Each k-space point contains spatial frequency and phase information
+about every pixel in the final image). Fourier transforme is performed to the k-space to obtain the final image. By varying the 
 sequence of RF pulses applied & collected, different types of images are created.
 
--TR
--TE
-The angle the magnetization is shifted, is a parameter to be defined 
-(Flip angle) and depends on the intensity and duration of the RF pulse.
 
 ### MRI Sequences 
 
-The most common sequences are T1-weighted and T2-weighted images. In neuroimaging, T1-weighted images are commonly used in anatomical
-related studies, they are based in longitudinal relaxation and are produced with short TR and TE. 
-(explicar longitudinal relaxation My, T1).(...) 
+It's important to understand the meaning of **repetition time (TR)** and **echo time (TE)** in order to comprehend the main
+MRI sequences. Time to Echo (TE) is the time between the delivery of the RF pulse and the receipt of the echo signal and 
+the interval between subsequent pulse sequences delivered to the same slice is known as the repetition time (TR).
 
+The most common sequences are T1-weighted and T2-weighted images. In neuroimaging, **T1-weighted** images are commonly used in anatomical
+related studies, they are based on the study of the relaxation of the nuclei in the longitudinal component (Mz) of the magnetization
+vector and are produced with short TR and TE.**T2-weighted** images are produced with longer TR and TE. They are based on study of the 
+variations of the component on the transverse plane of the magnetization during the relaxation, known as transverse relaxation (Mxy).
 
-T2-weighted images are produced with longer TR and TE. They are based on study of the variations of the component on the transverse 
-plane of the magnetization during the relaxation, known as transverse relaxation (Mxy).
+There are many sequences that can be used depending on the objective. T
 
+## Multi-echo
 
 
 ## Bibliography