OCR Physics A G485 - Frontiers of Physics - 18th June 2015

So why do we need to change it as we go down the body?

I write the answers and get the marks, but I don't understand why we want different larmor frequencies

Wouldn't that just flip different protons idk

It's so the detectors can identify which part of the body the emitted radio waves when the proton returns to parallel alignment after the relaxation time came from.

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It's so the detectors can identify which part of the body the emitted radio waves when the proton returns to parallel alignment after the relaxation time came from.

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Yes and no because if the larmor frequency is the same at two parts of the body then it would cause confusion so main reason larmor frequency varies from proton to proton is because of tissue. Larmor frequency cant be changed its independent and is based on the area the proton is in.

Yes and no because if the larmor frequency is the same at two parts of the body then it would cause confusion so main reason larmor frequency varies from proton to proton is because of tissue. Larmor frequency cant be changed its independent and is based on the area the proton is in.

That's incorrect. It only depends on the magnetic field strength it's in. The relaxation time is what depends on the tissue.

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Okay this makes sense to me

So say near the bottom of the patient where the magnetic field is weaker, a lower frequency can be used

And when the proton relaxes, it sends out a lower frequency photon of radio wave, and the frequency of it tells us what slice it's from, and the relaxation time will tell us where the proton is within that slave based on tissues and such

That's incorrect. It only depends on the magnetic field strength it's in. The relaxation time is what depends on the tissue. H

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Ok sure have it your way, my answer is based on research and tutoring and teachers. How on earth is relaxation time (a unit ot time) based on tissue? Im sorry but thats really stupid. Relaxation time is based on the energy it absorbs and how much of it. Consider a tumour, you may have read or teacher must have told you that inorder to destroy a tumour 20% more energy needs to be provided because it absorbs it. So it has more energy provided than normal tissue therefore it has a longer relaxation time..

Ok sure have it your way, my answer is based on research and tutoring and teachers. How on earth is relaxation time (a unit ot time) based on tissue? Im sorry but thats really stupid. Relaxation time is based on the energy it absorbs and how much of it. Consider a tumour, you may have read or teacher must have told you that inorder to destroy a tumour 20% more energy needs to be provided because it absorbs it. So it has more energy provided than normal tissue therefore it has a longer relaxation time..

I just did an exam question and the mark scheme said "relaxation time varies in different tissues"

Obviously the more complex answer may be something to do with energy and absorption but ocr doesn't care ahha

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Lol, it is definitely dependent on tissues the relaxation times

In fats it is shorter apparently

Lol I asked my teacher and it turns out that we are all correct because he said, that dependant on the tissue the amount of energy absorbed by the proton determines the relaxation time. I said that the energy absorbed by the proton determines the relaxation time and Elcor said relaxation time depends on tissue. Gg guys we both missed out a bit of detail :P

Think you might owe that guy an apology

I've got no chance in this exam, we barely got taught any of the medical section and I keep missing lessons on the universe section because of exams

No? it doesn't mean I'm wrong? Neither is he, i was right but I just said the same thing in a more complex way. I'm sorry I don't remember asking you anyhting.

You post on a public forum, what do you expect.....?

People answering and asking question rather than ordering me to do something.