Regsitration is done in physical space, So it does take into account the spacing. (This allows a high resolution image of a patient to be registered to a low res image).<br><br>As a starting point, you might want to simply omit the registration step. Resample the moving image to the fixed, with an "InitialTransform" and see how they overlay with each other. Figure out a good "InitialTransform" . And then start off with trying to register them, with this initial transform. My guess is that in manually changing the spacing, you're initial transform (which is in physical space) places you elsewhere.
<br><br>--<br>karthik<br><br><div><span class="gmail_quote">On 2/16/07, <b class="gmail_sendername">Sims Richard (RKB) Clinical Scientist</b> <<a href="mailto:Richard.Sims@uhcw.nhs.uk">Richard.Sims@uhcw.nhs.uk</a>> wrote:
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<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">Hi all</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">I have ammended one of the example codes provided with ITK
to perform rigid registration using a Centered Rigid 2D Transform with a Mattes
Mutual Information Metric. My fixed and moving images are both bitmaps which of
512x512 size but have different pixel spacing, 0.898mm/pixel for the fixed
image and 0.527mm/pixel for the moving image. I have successfully registered
these images using a Similarity 2D Rigid Transform (the moving image being
re-scaled to the fixed image), but would like to rigidly register them without
scaling by accouting for their different pixel spacing. I've tried to explicitly
define the spacing of the pixels using the following code:</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">FixedImageType::SpacingType spf;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">MovingImageType::SpacingType spm;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">FixedImageType::PointType orf;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">MovingImageType::PointType orm;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">spm[0]=0.527344;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">spm[1]=0.527344;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">//spf[2]=1.000000;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">orf[0]=0.0;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">orf[1]=0.0;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">//orf[2]=0.0;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">spf[0]=0.898438;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">spf[1]=0.898438;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">//spm[2]=1.000000;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">orm[0]=0.0;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">orm[1]=0.0;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">//orm[2]=0.0;</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">fixedImage->SetSpacing(spf);</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">fixedImage->SetOrigin(orf);</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">movingImage->SetSpacing(spm);</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">movingImage->SetOrigin(orm);</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">But it doesn't seem to have an effect... I'm
guessing it has something to do with the resample image filter, but have
reached a stumbling block... could anyone give me a pointer in the right
direction?</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">Many thanks,</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">Richard.</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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