Currently, the Dicom Decoder will decode the full size image then resize it into the thumbnail control.  There might be some optimizations we can make in the future for faster thumbnail loading.  We'll look into it.

We can't share the DICOM images we have, but there are websites out there with some test images.  If you download the latest version of DotImage, it will now support DicomWorks images.

Indeed, the images you refer to don't open in DotImage.  Not sure why, but now we have them to test so I'm sure we'll be able to resolve it soon.  Please try the viewer on other DICOM images, we've tested quite a few without this problem.