You can find the full list of these prefixes in Windows Internals. In edition 5, it's page 72-73 (I don't have a copy of edition 6 on me, but it's presumably similar)
Anyway, if you look at the list, you'll see Lsa (Local Security Authority); Mm (Memory manager); Nt (Nt system services).
But no Mi. Why? You'll need to read the previous paragraph:
"...either the first letter of the prefix followed by an i "for internal", or the full prefix followed by a p (for private)."
So, Mi should be an internal Memory Manager function.