<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css" style="display:none;"> P {margin-top:0;margin-bottom:0;} </style>
</head>
<body dir="ltr">
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Hello fellow CASToR users,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Have you ever experienced visible differences in reconstructed images depending on the type of data format you used? Indeed, for the same simulation of a Derenzo type phantom made in GATE, I obtain different reconstructed images whether I converted the data
in histogram or list-mode format using the "castor-GATERootToCastor" utility. This seems to happen only when I use the multiSiddon projector though. Since the sampling with this projector is random, I set the seed with "-rng-seed 0" to ensure the differences
do not come from a different LOR sub-sampling. I would expect the images to be, within numerical errors, identical since they come from the same information, just formatted differently... I am currently using CASToR v2.0.2.</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Here is an example using the Siddon projector, that gives almost identical images, as expected. The top image is list-mode, the middle one is histogram mode, and the bottom one is the subtraction. The command lines used to reconstruct both images are :</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
List-mode : "castor-recon -df data.lm_CstrProj.Cdh -dout image.lm.siddon.15mmAx -it 32:1 -dim 100,100,50 -vox 0.3,0.3,0.3 -vb 1 -th 4"<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Histogram mode : "castor-recon -df data.hm_CstrProj.Cdh -dout image.hm.siddon.15mmAx -it 32:1 -dim 100,100,50 -vox 0.3,0.3,0.3 -vb 1 -th 4"<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<img size="313083" contenttype="image/png" unselectable="on" tabindex="-1" style="max-width: 100%; user-select: none;" data-outlook-trace="F:1|T:1" src="cid:f7922b70-f2fc-4938-9e82-bc3f6750a2a2"><br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Here is the same example using the mutliSiddon projector, that gives different images. Again, the top image is list-mode, the middle one is histogram mode, and the bottom one is the subtraction. The command lines used to reconstruct both images are :<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
List-mode : "castor-recon -df data.lm_CstrProj.Cdh -dout image.lm.multiSiddon_25.15mmAx -it 32:1 -dim 100,100,50 -vox 0.3,0.3,0.3 -vb 1 -th 4 -proj multiSiddon,25 -rng-seed 0 -oit -1"<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Histogram mode : "castor-recon -df data.hm_CstrProj.Cdh -dout image.hm.multiSiddon_25.15mmAx -it 32:1 -dim 100,100,50 -vox 0.3,0.3,0.3 -vb 1 -th 4 -proj multiSiddon,25 -rng-seed 0 -oit -1"<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<img size="296591" contenttype="image/png" unselectable="on" tabindex="-1" style="max-width: 100%; user-select: none;" data-outlook-trace="F:1|T:1" src="cid:e4e2fdd6-ff58-48a1-a2e1-2f0c491fceda"><br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
In addition to the white spots appearing in list-mode at axial extremities, the histogram version looks "smoother".</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Thank you to provide me an explanation if you understand what is going on!</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Étienne</div>
</body>
</html>