How to deal with DICOM images while creating classifier?

I am started to create classifier of DICOM images. In each set I have about 100 DICOM images and few GPEG(that I inserted for testing only). When I create sets, the program counts GPEG images, but not DICOM images.

My code is as follows:

rootFolder = fullfile('C:\Documents and Settings\x\Desktop\Medical Imaging\MyProject');

imgSets = [ imageSet(fullfile(rootFolder, 'ast')), ...
            imageSet(fullfile(rootFolder, 'gbm')), ...
            imageSet(fullfile(rootFolder, 'oligl')) ];

>> [imgSets.Count]

ans = 3  3  2

How should I modify the code to get correct results?