Applying the following logic in a computed field will allow you to access MRI.PAT last (most recent) visit information from a report written in MRI.DRC.  You can then use this computed field for display, sorting and selecting:

DAT=FREE
JFY=L
LEN=10
VAL=IF{""^MRI.PAT.visit.subscript,@Next(MRI.PAT.visit.subscript),
VAL=@MRI.PAT.visit.type}

Since both MRI.DRC & MRI.PAT have medical.record as the primary subscript it is not necessary to enter that reference into the computed field.  We assign nil to the visit.subscript and then get the next available value.  This field logic will display the most recent visit's visit.type but you can substitute this with any of the fields from the MRI.PAT detail segment mri.pat.visits.