Access VB.Net structure element by variable name

Ok, some inherited code: I have a struct with a whole load of permissions:

public structure Perms
    dim writeStaff as Boolean
    dim readStaff as Boolean
    dim writeSupervisor as Boolean
    dim readSuperVisor as Boolean
    ' ... and many more
End Structure

And I want a function canDo which I created like so:

public function canDo(p as Perms, whichOne as String) as boolean
    Dim b as System.Reflection.FieldInfo
    b = p.GetType().GetField(whichOne)
    return b
end function

and I call canDo with pre-filled structure and "writeSupervisor" parameters

In debug, b appears as {Boolean writeSupervisor}, but when I try to return b as a Boolean, I get error: Value of type 'System.Reflection.FieldInfo' cannot be converted to 'Boolean'.

Any ideas how I can "index" into a struct by element name and test / compare / return values?