Fig. 12.

(A) Photograph of a sample containing 1.0 mm glass beads with a siliconized, hydrophobic surface in compartment (i) and an untreated, hydrophilic surface in compartment (ii). (B) MRI of gas phase hp ⁸³Kr shortly after transfer into the sample. (C) Hp ⁸³Kr MRI as in (B) but after additional 6 s delay time, showing a surface sensitive MRI contrast. The ⁸³Kr quadrupolar relaxation caused by surface interactions leads to T₁ = 9 s in the hydrophobic region (i) and to T₁ = 35 s in the hydrophilic region (ii). Adapted figure, printed with permission from Pavlovskaya et al. P. Ntl. Acad. Sci. USA 2005; 102:18278 © 2005 National Academy of Sciences, USA.