https://www.na-mic.org/w/index.php?action=history&feed=atom&title=July31T-con%2FPlayingWithTheDiffusionData 2026-04-06T15:33:42Z Revision history for this page on the wiki MediaWiki 1.33.0 https://www.na-mic.org/w/index.php?title=July31T-con/PlayingWithTheDiffusionData&diff=14156&oldid=prev 2007-08-03T15:58:09Z

<p></p> <table class="diff diff-contentalign-left" data-mw="interface"> <col class="diff-marker" /> <col class="diff-content" /> <col class="diff-marker" /> <col class="diff-content" /> <tr class="diff-title" lang="en"> <td colspan="2" style="background-color: #fff; color: #222; text-align: center;">← Older revision</td> <td colspan="2" style="background-color: #fff; color: #222; text-align: center;">Revision as of 15:58, 3 August 2007</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l14" >Line 14:</td> <td colspan="2" class="diff-lineno">Line 14:</td></tr> <tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Image:logfouriermagnitude.png|500px]]</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Image:logfouriermagnitude.png|500px]]</div></td></tr> <tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Image:logfouriermagnitude-centered.png|500px]]</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Image:logfouriermagnitude-centered.png|500px]]</div></td></tr> <tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr> <tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">Unfortunately, we don't see nice blue regions that we would have expected from ideal zero-padding.</ins></div></td></tr> <tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">Instead it looks a little &quot;salt-and-peppery.&quot; Is this a scanner discretization effect?</ins></div></td></tr> <tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr> <tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Cutting away everything that should ideally be zero gives this Fourier log-image:</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Cutting away everything that should ideally be zero gives this Fourier log-image:</div></td></tr> </table>

Niethammer https://www.na-mic.org/w/index.php?title=July31T-con/PlayingWithTheDiffusionData&diff=14155&oldid=prev 2007-08-03T15:56:10Z

<p>diffusion data downsampling test</p> <p><b>New page</b></p><div>== Exploring the Upsampling of the BWH Diffusion Data ==<br /> <br /> Extracting one a slice for one of the gradient directions of the diffusion data results in an image like this: &lt;br&gt;<br /> <br /> [[Image:original.png|500px]]<br /> <br /> A two-dimensional Fourier transform leads the following magnitude images (uncentered and centered):<br /> <br /> [[Image:fouriermagnitude.png|500px]]<br /> [[Image:fouriermagnitude-centered.png|500px]]<br /> <br /> Representing this in the log-domain results in<br /> <br /> [[Image:logfouriermagnitude.png|500px]]<br /> [[Image:logfouriermagnitude-centered.png|500px]]<br /> <br /> Cutting away everything that should ideally be zero gives this Fourier log-image:<br /> <br /> [[Image:Logfouriermagnitude-centered-and-cut.png|500px]]<br /> <br /> An inverse Fourier transform followed by discretization results in:<br /> <br /> [[Image:reconstructed.png|500px]]<br /> <br /> The result is slighly smoother than the original, which is sensible since we essentially low-pass<br /> filtered the result.<br /> <br /> The difference between original and reconstruction is not great, but still shows a little bit of structure:<br /> <br /> [[Image:reconstruction-diffference.png|500px]]<br /> <br /> <br /> In case you want to recreate the results. Here is the matlab script [[media:dwiTstScript.m|dwiTstScript.m]]. And here is the data [[media:SampleDWIDataSlice.tar.gz|SampleDWIDataSlice.tar.gz]].</div>

Niethammer