Re: Reverse FFT ?

["Jonas" <jonas_2(at)hotmail.com>]

Hi Rich

If the image data you have is not complex, then it is not possible to
retrieve the correct k-space data by doing an FFT. A reconstructed MR image
is always in complex form (to be represented by a mgnitude and a phase
angle, or by a real and an imaginary number), but the image shown on the
screen is the magnitude of each complex number. If you only have the
magnitude data, you have "thrown away" some important information, and will
not be able to get a correct k-space. k-space is by definition filled with
complex data.

Furthermore, if I remember my MR physics correct, you are supposed to do a
forward transform when going from image space to k-space, but I am not
sure...


However, if you just want to have a look at a "general k-space", you might
take a look at the magnitude of a FFT of a magnitude image... don't forget
to shift the transformed data so that the lowest frequency is centered in
the image....

regards
Jonas


--
====================================
Jonas Svensson, MSc
Medical Physicist, MRI
Department of Radiation Physics
Malmö University Hospital
SE-205 02 Malmö, SWEDEN
+46 40 331021 (phone), +46 40 963185 (FAX)



Richard Tyc <richt@sbrc.umanitoba.ca> skrev i
diskussionsgruppsmeddelandet:8mpv4l$rtl$1@canopus.cc.umanitoba.ca...
> Can you do a reverse FFT in IDL and how is it implemented  ?
> ie. FFT provides a complex array - How do you get the original Time domain
> back from the complex series.
>
> I am trying to retrieve "k" space data back from real/imaginary MRI data.
I
> would like to see how time consuming this really is.
>
> Thanks
> Rich
>
>