Slicer 4.10.1 Interpolation/Slicing Issue with Segmentation on MRI Dicom files

I have imported dicom (.dcm) files of MRI data which has a slice thickness of 3 millimeters between slices. I am attempting to segment a region within the MRI data but am seeing distortion of the area I am segmenting in which there are regions on slices I did not select which are appearing to have been automatically segmented. Furthermore, there are regions I would like to segment on other slices that will not allow me to apply the segmentation. If any of you have had similar issues with this any help would be much appreciated.