- #1
alanesq
- 11
- 0
Hi,
I have been trying to figure out how MRI scanners work but am getting a bit confused and wondered if someone could put me straight on this ?
I am just interested as they strike me as being amazing machines (possibly one of human kinds greatest inventions?) and the way they work is truly amazing (but pretty difficult to understand)
I am not interested in the maths of it, just a general lay persons understanding of the basics
BTW - If I ever manage to get some kind of understanding I may try to create a layman's explanation web page as I am sure a lot of people would be very interested in this
I have watched these videos many times over (which are very good) - http://www.magritek.com/videos.html#01
What I am stuck on at the moment is how it scans the patient (i.e. traverses K space ?)
I keep thinking I am close to getting it then realize there is something I don't understand
looking at the pulse sequence example on Wikipedia - http://en.wikipedia.org/wiki/Mri#Example_of_a_pulse_sequence
This is what I think is going on:
SS - puts a gradient on the patient (head to foot) and by careful selection of radio frequency only a thin slice through the patient at a specific point receives the 90 degree tilt (i.e. a slice is selected)
So now any signal received will only be from this slice
PE - puts a gradient across this slice for a set period of time to causes a phase shift across it
(this seems to be suggested that its selecting a line but I don't understand how?)
SS - Now a gradient is put across the slice in the other plane and again through careful selection of radio frequency only a thin line of the slice is given a 180 degree flip (to create a spin echo)
So now any signal received is only going to be from this line through the patient
FE - a gradient is then put across so giving a range of frequencies across this line relative to its location (readout gradient)
the resulting signal is recorded forming a single line in K space?
What I don't understand here is what is the phase needed for ?
as the signals location seems to be given by its frequence so it is not needed
I have been trying to figure out how MRI scanners work but am getting a bit confused and wondered if someone could put me straight on this ?
I am just interested as they strike me as being amazing machines (possibly one of human kinds greatest inventions?) and the way they work is truly amazing (but pretty difficult to understand)
I am not interested in the maths of it, just a general lay persons understanding of the basics
BTW - If I ever manage to get some kind of understanding I may try to create a layman's explanation web page as I am sure a lot of people would be very interested in this
I have watched these videos many times over (which are very good) - http://www.magritek.com/videos.html#01
What I am stuck on at the moment is how it scans the patient (i.e. traverses K space ?)
I keep thinking I am close to getting it then realize there is something I don't understand
looking at the pulse sequence example on Wikipedia - http://en.wikipedia.org/wiki/Mri#Example_of_a_pulse_sequence
This is what I think is going on:
SS - puts a gradient on the patient (head to foot) and by careful selection of radio frequency only a thin slice through the patient at a specific point receives the 90 degree tilt (i.e. a slice is selected)
So now any signal received will only be from this slice
PE - puts a gradient across this slice for a set period of time to causes a phase shift across it
(this seems to be suggested that its selecting a line but I don't understand how?)
SS - Now a gradient is put across the slice in the other plane and again through careful selection of radio frequency only a thin line of the slice is given a 180 degree flip (to create a spin echo)
So now any signal received is only going to be from this line through the patient
FE - a gradient is then put across so giving a range of frequencies across this line relative to its location (readout gradient)
the resulting signal is recorded forming a single line in K space?
What I don't understand here is what is the phase needed for ?
as the signals location seems to be given by its frequence so it is not needed
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