Independent first and second information signals are transmitted over separate independent physical channels to a receiving location. Therefore a first set of parallel saturation planes is obtained by applying a first nonselective RF pulse with a flip angle of 90, an intermediate magnetic field gradient pulse in direction of the spatial modulation, and a second nonselective RF pulse with a flip angle of 90. The filter can be removed and replaced by simply rotating the grill member to an open position to thereby disengage the extended arm from the filter and allow it to be removed. An apparatus maintains a valid volume table of contents written to in a fast replication relationship.