As a radiology student or practitioner you must often have felt intrigued about MRI. And always wanted to start learning mri interpretation at some point.So this is a small step towards it.
THE PRINCIPLE........
Just trying to make things too simple....
Xray, USG or CT scans seem much more simpler since they have one or only few different methods of looking at things.Like USG means grey scale... doppler , CT--plain, contrast.
MRI however seems to be more complex since there are various ways you are looking at the same anatomy and at times different ways of looking at different structures ..where starts all the PROBLEMS and COMPLEXITY. It is just like looking at same thing with different coloured glasses causing all the confusion.
THE PHYSICS
Hearing about it you will often feel like losing the race before you have started it....It is like an ocean. But still u cant escape physics.It makes sense to know at least some basics whats happening in MRI.
In most simple way-
Everything boils down to PROTONS (H) which is there in abundance in body.This is where the MAGNETISM starts off....... becos these every individual protons also are tiny magnets. They get aligned some thing like...... straight when placed in a magnet i.e. the huge round machine you see with restricted entry and large CAUTION board on the door.
There is another thing here which is called the RADIOFREQUENCY waves.It comes from an external source which is transmitted to body. What do they do after all ? They bring about SOME change in the magnetic field in these PROTONS.
This SOME change gives out what is called a SIGNAL. This SIGNAL is captured by the receiver coils which you see wrapped around the body part being scanned..
This SIGNAL then undergoes what is called as FOURIER TRANSFORMATION......... some complex mathematics (dont worry abt it for now) which gives the final image which we see on the screen. The entire thing is much more complex though.
Feels like some WONDER or MAGIC...Interactions of magnets and radiofrequency one is able to see in great detail the internal human anatomy.
After a short cut through PHYSICS lets get into looking into MRI proper.....
T1,T2,STIR,PD,CISS,SPGR,FLAIR,GRE. ??? ##^^%!!@@%%%
....................oops looks like suddenly in the middle of a sea.
At this point forget the rest and just hold on to T1 and T2 so that u dont drown down... and if u have some more strength also hold on to FLAIR and STIR.......these are supposedly very basic things.......getting u just above water.
Now this comes with a price...the TR and TE which are fundamental. These are which make the SEQUENCES. You can get away without these but better to know these becos sooner or later u r going to get stumped by them. Earlier you learnt that RF is transmitted to body which then gives out a SIGNAL. So....
TR is time between two RF pulses.
TE time between RF pulse and signal.
In simple terms manipulation of these parameters gives different sequences.like...
T1- short TR short TE
T2- long TR long TE
Another one add here...........PD (proton density)-long TR and short TE.
A typical spin echo sequence would look like
90 180 echo 90
Now along with TR and TE, there is also TI (time to inversion). TI comes into play in inversion recovery sequences like FLAIR and STIR.It is time between 180 pulse and 90.
What do the Inversion recovery seqs do ?
In simple words it is suppression of some things to be able to make other things more prominent.Example Fat is nulled in STIR and CSF is nulled in FLAIR.
Inversion recovery would look like
180 90 180
TI
Its quite interesting to see that different type of images are obtained by changing TR and TE which are like the backbone these pulse sequences.
A WORD ABOUT GRADIENT SEQUENCES
In simple words traditional spin echo is time consuming. Rephasing of magnetisation is by RF. Whereas Gradient seqs are fast ! and rephasing is done by gradients.
THE CORE PHYSICS
This sequence of events are seen in a typical spin echo sequence.
THE PRINCIPLE........
Just trying to make things too simple....
Xray, USG or CT scans seem much more simpler since they have one or only few different methods of looking at things.Like USG means grey scale... doppler , CT--plain, contrast.
MRI however seems to be more complex since there are various ways you are looking at the same anatomy and at times different ways of looking at different structures ..where starts all the PROBLEMS and COMPLEXITY. It is just like looking at same thing with different coloured glasses causing all the confusion.
THE PHYSICS
Hearing about it you will often feel like losing the race before you have started it....It is like an ocean. But still u cant escape physics.It makes sense to know at least some basics whats happening in MRI.
In most simple way-
Everything boils down to PROTONS (H) which is there in abundance in body.This is where the MAGNETISM starts off....... becos these every individual protons also are tiny magnets. They get aligned some thing like...... straight when placed in a magnet i.e. the huge round machine you see with restricted entry and large CAUTION board on the door.
There is another thing here which is called the RADIOFREQUENCY waves.It comes from an external source which is transmitted to body. What do they do after all ? They bring about SOME change in the magnetic field in these PROTONS.
This SOME change gives out what is called a SIGNAL. This SIGNAL is captured by the receiver coils which you see wrapped around the body part being scanned..
This SIGNAL then undergoes what is called as FOURIER TRANSFORMATION......... some complex mathematics (dont worry abt it for now) which gives the final image which we see on the screen. The entire thing is much more complex though.
Feels like some WONDER or MAGIC...Interactions of magnets and radiofrequency one is able to see in great detail the internal human anatomy.
SOME MORE BASICS
After a short cut through PHYSICS lets get into looking into MRI proper.....
T1,T2,STIR,PD,CISS,SPGR,FLAIR,GRE. ??? ##^^%!!@@%%%
....................oops looks like suddenly in the middle of a sea.
At this point forget the rest and just hold on to T1 and T2 so that u dont drown down... and if u have some more strength also hold on to FLAIR and STIR.......these are supposedly very basic things.......getting u just above water.
Now this comes with a price...the TR and TE which are fundamental. These are which make the SEQUENCES. You can get away without these but better to know these becos sooner or later u r going to get stumped by them. Earlier you learnt that RF is transmitted to body which then gives out a SIGNAL. So....
TR is time between two RF pulses.
TE time between RF pulse and signal.
In simple terms manipulation of these parameters gives different sequences.like...
T1- short TR short TE
T2- long TR long TE
Another one add here...........PD (proton density)-long TR and short TE.
A typical spin echo sequence would look like
90 180 echo 90
Now along with TR and TE, there is also TI (time to inversion). TI comes into play in inversion recovery sequences like FLAIR and STIR.It is time between 180 pulse and 90.
What do the Inversion recovery seqs do ?
In simple words it is suppression of some things to be able to make other things more prominent.Example Fat is nulled in STIR and CSF is nulled in FLAIR.
Inversion recovery would look like
180 90 180
TI
Its quite interesting to see that different type of images are obtained by changing TR and TE which are like the backbone these pulse sequences.
A WORD ABOUT GRADIENT SEQUENCES
In simple words traditional spin echo is time consuming. Rephasing of magnetisation is by RF. Whereas Gradient seqs are fast ! and rephasing is done by gradients.
THE CORE PHYSICS
This sequence of events are seen in a typical spin echo sequence.
