Hi; Not sure what you mean? Isn't a slice width typically 4 mm?
True. But there is also a gap between the slices. I looked at my own images. There wasn't anything that told me the width of the slices but I was able to figure out the width of the gaps (3.2mm).
My AN is shaped like a baked bean (4mm x 4mm x 12mm).
Imagine an egg slicer slicing my baked bean.
If a slicing wire parallel to the length of the bean were to slice the bean right down the middle you would see that the 2 dimensional image of the bean was 4mm x 12 mm.
If the wire was off center, the 2 dimensional image would be smaller and smaller as the wire moved further from the center.
If 2 wires came down on the bean and were equidistant from the center of the bean they would each slice off an edge of the bean and the 2 dimensional image of those images would be smaller than the center image.
So, if one MRI happened to slice right down the middle and the next MRI had the wire a little off center, it could make a 1mm (or more) difference in measurement even though the tumor was the same size.
I don't think it matters much how wide the slice is (the narrower the slice the clearer the image - is what I have read). I think that the gap is what makes the difference.
Try slicing hard boiled eggs with an egg slicer and you'll get the idea.
Of course, the above are the ramblings of a layman, but I think that's a reasonable explanation. There may be other responders that know more about it.
