[Insight-users] Behaviour of DICOM images with ConnectedThresholdImageFilter

Tue Nov 12 07:29:59 EST 2013

Dear ITK community,
I'm doing some segmentation tests over a set of CT DICOM images, but I've some difficulties with the configuration of the thresholds. If I convert the images to .png format, I don't have this problem, because the threshold definition is quite straightforward when the images are in the range 0-255.
If I analyse one of the Dicom images with Matlab or using the StatisticsImageFilter I see that it has values between 0 and 946. Then, if I call the ConnectedThresholdImageFilter example using as lowerThreshold 0 and upperThreshold 946 (just to check the validity of these ranges), I don't obtain a totally white image as expected. Doing some tests, I've discovered that in order to obtain the white image, the range has to be [-4,897], and I don't understand why. I've also observed that the ranges are different in each Dicom image and especially when they belong to different CT phases.
(I send you an image attached so you can see what I mean).
Having said this, my question is:
Is it necessary to make any pre-processing of the DICOM images? Or ... Does the ConnectedThresholdImageFilter treats these images in a special way?

Thanks a lot in advance for your support!!! (This problem is driving me crazy...)

Regards,
Cristina

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