[Insight-users] Obtaining Real Result from Inverse Fourier Transform

[DVigneault]

All--

I have a magnitude MRI image with vertical stripes, which produce harmonics
in the spectral domain.  I've isolated one of those harmonics and used the
VnlInferseFFTImageFilter to produce a spatial image from the isolated
harmonic.  I'd now like to do an operation on that image, which requires
that I access both the imaginary and real components of the output in the
spatial domain.  However, I've only been able to access one component of the
result.

The code I'm using for performing the inverse transform is:

typedef itk::VnlInverseFFTImageFilter< ComplexImageType > 
FFTInverseFilterType;
typedef FFTInverseFilterType::OutputImageType SpatialImageType;
    FFTInverseFilterType::Pointer fftInverseFilter =
FFTInverseFilterType::New();
    fftInverseFilter->SetInput( maskedShiftFilter->GetOutput() );
    try {
        fftInverseFilter->Update();
        std::cerr << "fftInverseFilter->Update() excecuted successfully." <<
std::endl; }
    catch( itk::ExceptionObject & excp ) {
        std::cerr << "Error during fftInverseFilter->Update(): " <<
std::endl;
        std::cerr << excp << std::endl;
        return EXIT_FAILURE; }

I'm using this function to view the pixel values:

typedef FFTInverseFilterType::OutputImageType SpatialImageType;

void OutputImage( SpatialImageType::Pointer image )
{
    itk::ImageRegionConstIterator< SpatialImageType >
imageIterator(image,image->GetLargestPossibleRegion());
    
    while(!imageIterator.IsAtEnd())
    {
        // Get the value of the current pixel
        SpatialImageType::PixelType val = imageIterator.Get();
        std::cout << val << std::endl;
        
        ++imageIterator;
    }
}

The values I'm getting from this function look like this:

-0.354988
-0.43072
-0.519287
-0.615867
-0.714985
-0.810802
...

I've used a very similar function on the spectral image to get out complex
values, which come out like this:

(102.69,143.811)
(-490.191,-181.034)
(-290.731,-346.93)
(17.2402,-449.111)
(-247.687,-201.641)
...

Any idea what I'm doing wrong?

Best, and thanks,

--Davis



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