[Insight-users] Need help resizing/resampling PET image

[Abhik Datta]

Hi All,

I am new to ITK and I am working on PET-CT registration. I have a PET image
dataset which has a very low resolution, whereas my CT image dataset is of
very high resolution. Before I run my registration algorithm, I want to
resample/resize my PET images to match the resolution of the CT images.
However, any resizing of the PET image is bringing in excessive noise in the
image, even with BSpline interpolation. Also, I notice that if I don't
resize the image at all, the output image still has significant noise.
Therefore I think I must be missing something in my code. I have tried
the Similarity2DTransform, the AffineTransform. My code goes somewhat like
this:

                typedef itk::ResampleImageFilter <InputImageType,
OutputImageType> FilterType;
FilterType::Pointer filter = FilterType::New();

typedef itk::AffineTransform <double, Dimension>  TransformType;
TransformType::Pointer transform = TransformType::New();
 filter->SetTransform(transform);

typedef itk::BSplineInterpolateImageFunction <InputImageType, double>
InterpolatorType;
 InterpolatorType::Pointer interpolator = InterpolatorType::New();
filter->SetInterpolator ( interpolator );

 double spacing[Dimension];
spacing[0] = 1.0; // pixel spacing in millimeters along X
spacing[1] = 1.0; // pixel spacing in millimeters along Y
 filter->SetOutputSpacing ( spacing );

double origin[Dimension];
origin[0] = -500; // X space coordinate of origin
 origin[1] = -500; // Y space coordinate of origin
filter->SetOutputOrigin ( origin );

InputImageType::DirectionType direction;
 direction.SetIdentity();
direction = inputImage->GetDirection();

InputImageType::SizeType size;

size[0] = 1000;  // number of pixels along X
size[1] = 1000;  // number of pixels along Y

 filter->SetSize(size);

What I am looking to do is get the PET image to look like when we zoom into
the image using a image viewer like IrfanView.

Any suggestions will be of great help.

Thanks,
Abhik Datta.
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