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Oliver Lyttelton

Mon. 1 Mar.10,
13:39

[Reply (8 of 12) to:
'90 excitation pulse vs 180 inversion pulse'
started by: 'Bjorn Redfors'
on Sat. 27 Jun.09]


 
  Category: 
Basics and Physics

 
90 excitation pulse vs 180 inversion pulse
Okay, so this thread is answering close to a question I had, which is how to conceptually understand what happens with alpha>90 degrees excitation pulses.
I can imagine spinning tops, precessing at the Larmor frequency, I can imagine that as you apply the excitation pulse which is always in the transverse plane to the main magnet, you start to pull the tops further away from the B0 axis and bring them into coherence so like lots of little lighthouses they are all bright/dark in phase with each other. I can imagine a 90 degree pulse bring the spins completely into the transverse plane. I can imagine them relaxing, dephasing quickly and then slowly reducing their angle of precession back up towards initial state close to direction B0.

But what I can't understand in my (rather newtonian) model, is what happens as you continue to excite beyond the 90 degree transverse plane. I sort of get that somehow the spins continue to rotate in some (weird) dimension, and that they have to come back through that (weird) dimension first before returning from 90 degrees back to the relaxed state. But what happens in "weird" dimension is beyond my conceptual model. Can someone extend my model for me, preferrably without signal equations?

tar muchly,

Oliver
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alex dacles

Sat. 27 Feb.10,
23:17

[Reply (2 of 4) to:
'ARRT vs.ARMRIT exams'
started by: 'Reader Mail'
on Fri. 22 Jan.10]


 
  Category: 
Organisations

 
ARRT vs.ARMRIT exams
Thanks Sunny for your reply it means that I need to abandon my plan to set an exam for arrt registry I am graduated from Philippines actively practising as MRI Radiographer here in United kingdom. i'm not quite sure if they are open for foreigner Radiographer as our curriculum based on american standard i'm trying to read the requirements to set an exam I didn't spot any article for foreign graduate who wants to practise in USA.
I tried to inquired in ARMRIT they are pretty helpful I'm not 100% convinced to set an exam as it seems difficult and complicated to start my career again in US.


Thanks again

Alex


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George LoGuirato

Thu. 18 Feb.10,
16:26

[Reply (1 of 2) to:
'bandwidth'
started by: 'Stephen Roberts'
on Mon. 15 Feb.10]


 
  Category: 
Devices, Scanner, Machines

 
bandwidth
Quite possible. Manufactures like their own designations for bandwidth for ??? reasons. GE uses true bandwidth in KHz. Siemens uses Hz/PIXEL. Not sure what Toshiba uses. Contact Toshiba applications for designator and conversion factor.
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sivagami samy

Sun. 14 Feb.10,
04:53

[Reply (2 of 3) to:
'EPILEPSY -MRI'
started by: 'sivagami samy'
on Thu. 26 Nov.09]


 
  Category: 
Applications and Examinations

 
EPILEPSY -MRI
thanks for your reply sir.rnrni got one patient image from scan center. but i need lot of images for to improve my result efficiency. still i am trying to get more ,but here limited hospitals having MRI.in some hospitals they are not willing to give . rnrnif you know any website or if you are having the images . please send me.rnrnThanks in advance .. Bye...
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Osvaldo Pino

Thu. 11 Feb.10,
10:47

[Start of:
'echo spacing'
0 Reply]


 
  Category: 
Basics and Physics

 
echo spacing
how can I increase echo spacing without modifying the bandwith in a Siemens Trio?
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