firasm / CEST

Analysis of studies
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Effect of RF Spoiling #17

Closed firasm closed 9 years ago

firasm commented 9 years ago

Did a quick experiment today with various acceleration factors and RF Spoiling on and off.

I think I have some SNR issues at high acceleration

cest 001 cest 002

Some conclusions:

- Cannot reproduce the second peak, with or without RF spoiling
- Noise increases with increased acceleration
- RF spoling reduces noise in the spectrum
- Peak height decreases with increased acceleration
- Line width increases with increased acceleration
- Where the hell is that second peak when you scan without alternating frequencies !?
DrSAR commented 9 years ago

What are you talking about when you say 'Cannot reproduce the second peak, with or without RF spoiling'. I see it in the alternating offset scan. In fact your water peak is split because you are off resonance and hence you have two water peaks. It's not as obvious in the linear offset version although fast acceleration will probably smear peaks out across several frequencies. Hence broader peaks for So I think a clear conclusion is that the second peak is an artifact of insufficient spoiling or, at the least, saturation effects lingering for longer than one shot. I wonder whether shorter T1 can make this go away (unfortunately hard to test without affecting T2s as well).

Time to get the saturation dynamics simulation going so we can develop an intuitive understanding of these relationship.

firasm commented 9 years ago

I think we've solved this issue in #18 - it sounds like RF spoiling was never an issue, but now that we have it, I think we'll just leave it on always. It only costs us 1 ms to do and doesn't seem to have any effect on SNR.

We (Scott) will repeat the Acceleration experiment when he gets back on Monday, and I'll get him to spot-check the effect of RF spoiling.

DrSAR commented 9 years ago

also, the 1ms (default) can be shortened to say 200us without too much problem if required