I think you could use just
:mri1dt_0 | :ct1dt_0 | :us1dt_0
but to be a bit more sure I would add Is Missing there. With that you can then do many different types of comparisons, below is one using ! (not) and & (and)
!(Is Missing(:mri1dt_0) & Is Missing(:ct1dt_0) & Is Missing(:us1dt_0))
If you want to have Yes / No, you could use If statement OR value labels column property
-Jarmo