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*Subject*: Re: Reverse FFT ?*From*: "Richard Tyc" <richt(at)sbrc.umanitoba.ca>*Date*: Wed, 9 Aug 2000 09:00:39 -0500*Newsgroups*: comp.lang.idl-pvwave*Organization*: The University of Manitoba*References*: <8mpv4l$rtl$1@canopus.cc.umanitoba.ca> <8mrhpq$hkk$1@news.lth.se>*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:20736

Thanks Jonas, I do retain the phase and magnitude image (from which I can find the Real and Imaginary Data). So, from Craig's reply, I should be able to find "k" space by doing a reverse FFT on the Real/Imaginary image date right ? Would the real part of this reverse FFT solution be true k space ? ie. setting the second term to a negative number Also, would I have to do a 1D FFT Row by Row on my data or can it be done as a 2D FFT. Rich Jonas <jonas_2@hotmail.com> wrote in message 8mrhpq$hkk$1@news.lth.se">news:8mrhpq$hkk$1@news.lth.se... > 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) > >

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