A method and apparatus for the accumulation of hyperpolarized 129Xe is described. The process comprises a two-stage roasting process comprising a first roasting step and a second roasting step. The two circular holes are coaxial and have different diameters. The detecting step may be performed by delivering a series of acoustic pulses at the free surface and detecting acoustic reflections from the free surface as the oscillating free surface relaxes. The process comprises: flowing a first liquid through a process microchannel, the process microchannel having a wall with an apertured section; flowing a second liquid through the apertured section into the process microchannel in contact with the first liquid, the first liquid forming a continuous phase, the second liquid forming a discontinuous phase dispersed in the continuous phase. The guidance application may determine a user’s identity from a voice command and provide personalized guidance features.