<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Wes,<br>Yes, 650 HU is much better for all datasets for a starting point and I see that it is nearly impossible to find optimal value without human interaction. <br><br>Chasan KIOUTSOUKMOUSTAFA<br><br>--- On <b>Thu, 8/26/10, Wes Turner <i><wes.turner@kitware.com></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From: Wes Turner <wes.turner@kitware.com><br>Subject: Re: [vtkusers] Hounsfield Units of Human body part<br>To: "Chasan KIOUTSOUKMOUSTAFA" <chasank@yahoo.com><br>Cc: "vtk mailList" <vtkusers@vtk.org><br>Date: Thursday, August 26, 2010, 9:28 PM<br><br><div id="yiv514007402">Chasan,<div><br></div><div>Marching Cubes looks for the boundary where the voxel value goes from below the threshold value to above the threshold value. CT is a noisy modality
and you should not expect that all the bone voxels will be at the optimal bone value. Assuming that 1250 is the average value for bone, then one half of the bone voxels will be at or below 1250. So setting the Marching Cubes threshold to that level will give a very poor segmentation.</div>
<div><br></div><div>You should set the Marching Cubes threshold at somewhere between the value outside of the bone vs the value of the bone. Based on your numbers, I would probably go with around 650 as a starting point and then adjust up or down based on image characteristics and the quality of the output segmentation until I reach a suitable value. The noise level of the image, patient age, surrounding material (i.e. in vivo or ex vivo), and age of the bones (for ex vivo) will all have an impact on the determining the proper threshold.</div>
<div><br></div><div>- Wes<br><br><div class="yiv514007402gmail_quote">On Thu, Aug 26, 2010 at 2:13 PM, Chasan KIOUTSOUKMOUSTAFA <span dir="ltr"><<a rel="nofollow" ymailto="mailto:chasank@yahoo.com" target="_blank" href="/mc/compose?to=chasank@yahoo.com">chasank@yahoo.com</a>></span> wrote:<br><blockquote class="yiv514007402gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<table border="0" cellpadding="0" cellspacing="0"><tbody><tr><td style="font: inherit;" valign="top">I'm using vtkDICOMImageReader class for reading the images, if i give the exact HU values for example;<br><br>boneExtractor->SetInputConnection(reader->GetOutputPort());<br>
boneExtractor->SetValue(0, HUofBone); // HUofBone is 1250<br><br>it does not give optimal solution...<br>boneExtractor is vtkMarchingCubes object<br><br><br>Chasan KIOUTSOUKMOUSTAFA<br><br>--- On <b>Thu, 8/26/10, John Drescher <i><<a rel="nofollow" ymailto="mailto:drescherjm@gmail.com" target="_blank" href="/mc/compose?to=drescherjm@gmail.com">drescherjm@gmail.com</a>></i></b> wrote:<br>
<blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From: John Drescher <<a rel="nofollow" ymailto="mailto:drescherjm@gmail.com" target="_blank" href="/mc/compose?to=drescherjm@gmail.com">drescherjm@gmail.com</a>><br>Subject: Re: [vtkusers] Hounsfield Units of Human body part<br>
To: "Chasan KIOUTSOUKMOUSTAFA" <<a rel="nofollow" ymailto="mailto:chasank@yahoo.com" target="_blank" href="/mc/compose?to=chasank@yahoo.com">chasank@yahoo.com</a>><br>Cc: "vtk mailList" <<a rel="nofollow" ymailto="mailto:vtkusers@vtk.org" target="_blank" href="/mc/compose?to=vtkusers@vtk.org">vtkusers@vtk.org</a>><br>
Date: Thursday, August 26, 2010, 9:06 PM<br><br><div>On Thu, Aug 26,
2010 at 1:59 PM, Chasan KIOUTSOUKMOUSTAFA<br><<a rel="nofollow" target="_blank" href="http://mc/compose?to=chasank@yahoo.com">chasank@yahoo.com</a>> wrote:<br>><br>> HUofAir = (double)(reader->GetPixelRepresentation() * reader->GetRescaleSlope()) + (double) reader->GetRescaleOffset();<br>
> // HuofAir represents -1000 HU<br>> HUofBone = HUofAir + 2250.0; // 1250 HU for Bone<br>> HUofMuscle = HUofAir + 1050.0; // 50 HU for Muscle<br>> HUofFat = HUofAir + 880; // -120 HU for Fat<br>><br><br>
How are you reading your images? They already should be in Hounsfield<br>
( no no calculation is needed) if you use the vtk image readers and<br>use signed short images.<br><br>John<br></div></blockquote></td></tr></tbody></table><br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>Wesley D. Turner, Ph.D.<br>Kitware, Inc.<br>Technical Leader<br>28 Corporate Drive<br>Clifton Park, NY 12065-8662<br>Phone: 518-881-4920<br>
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