Hi Kana,<br><br>You need to arrange the lambda values in the order of decreasing magnitudes. So based on your convention:<br>lambda1 = 12.2557<br>lambda2 = - 560.862<br>lambda3 = - 1022.66<br><br>You may want to use the filter developed in:<span lang="EN-GB"> "Generalizing
vesselness with respect to dimensionality and shape", </span><a href="http://www.insight-journal.org/browse/publication/175" target="_blank"><span lang="EN-GB">http://www.insight-journal.org/browse/publication/175</span></a><span lang="EN-GB"></span>
<br>The basic work consist of Frangi's measures and it is mentioned in the references of the above article. Specifically, the above paper implements the filter proposed by Manniesingh et al.:<br>"Vessel enhancing diffusion: A scale space representation of vessel structures "<br>
<br>This filter will allow you to first preprocess your images and enhance tubes.<br><br><br>For your second question, you can follow the center line by looking for the eigen-vector whose corresponding eigen value has a value closest to 0. The reason is that along the center-line, there is no gradient in intensity and hence the lambda1~0. So, you will go in the direction [-0.120 0.010 0.992]<br>
<br><br><br>Kishore<br><br><br><br><div class="gmail_quote">On Wed, Mar 10, 2010 at 11:31 AM, Arunachalam Kana <span dir="ltr"><<a href="mailto:Kana.Arunachalam@fh-wels.at">Kana.Arunachalam@fh-wels.at</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div link="blue" vlink="purple" lang="DE-AT">
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<p class="MsoNormal"><span lang="EN-GB">Hi itk users,</span></p>
<p class="MsoNormal"><span lang="EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB">I am trying to write an algorithm to trace
centre line of a tube shape in 3D CT image.</span></p>
<p class="MsoNormal"><span lang="EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB">I am using the hessian matrix to get the
direction of the tube shape.</span></p>
<p class="MsoNormal"><span lang="EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB">The Eigen values and vector of hessian
matrix for coordinate [9,5,2]:</span></p>
<p class="MsoNormal"><span lang="EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB">Eigen value: -560.862 -1022.66
12.2557 (not in any order)</span></p>
<p class="MsoNormal"><span lang="EN-GB"> </span></p>
<p class="MsoNormal">Eigen vectors: 0.701 0.708 0.078</p>
<p class="MsoNormal">
-0.702 0.705 -0.092</p>
<p class="MsoNormal"> -0.120 0.010 0.992</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span lang="EN-GB">When arranged in |Lambda1| < |Lambda2|
< |Lambda3| , i get 12.2557 as Lambda1.</span></p>
<p class="MsoNormal"><span lang="EN-GB">If my understanding of literature is right,
then the direction of the tube centre line will</span></p>
<p class="MsoNormal"><span lang="EN-GB">point in the direction of eigenvector corresponding
to 12.2557 which is 0.992.</span></p>
<p class="MsoNormal"><span lang="EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB">If i am right so far, then my question is :</span></p>
<p><span lang="EN-GB"><span>1.<span style="font-family: "Times New Roman"; font-style: normal; font-variant: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">
</span></span></span><span lang="EN-GB">how to calculate the next coordinate
to which i have to move from [9,5,2]?</span></p>
<p><span lang="EN-GB"><span>2.<span style="font-family: "Times New Roman"; font-style: normal; font-variant: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">
</span></span></span><span lang="EN-GB">Is there any literature to
refer to ?</span></p>
<p class="MsoNormal"><span lang="EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB">Help to solve this problem will be highly
appreciated.</span></p>
<p class="MsoNormal"><span lang="EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB">Thank you,</span></p>
<p class="MsoNormal"><span lang="EN-GB">Regards,</span></p>
<p class="MsoNormal">Kana</p>
<p class="MsoNormal"> </p>
</div>
</div>
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