text: In general, we can use the either Rb or Cs alkali metal atoms with inert nitrogen gas. However, we are using Cs atoms with nitrogen to make the spin exchange with Xe for number of advantages:
  * Cs has natural perfect abundance while rubidium has two (Rb and Rb) isotopes. Abstraction of one isotope separately from these two (Rb and Rb) is difficult compare to collect the Cs isotope. Abstraction of Cs is convenient.
  * Optical pumping cell normally is operated at lower temperature to avoid chemically breakdown issue. SEOP is using Cs at low temperature and hence it has fewer chemical corrosion with SEOP cell wall glass.
  * Cs-Xe couple have spin exchange rate about 10% that is more compare to the Rb-Xe couple have.
  Although Xe has a bunch of preferable characteristic applications in NMR technique, Kr can also be used since it has a lot of advantages in NMR techniques in different ways than Xe.
  * Kr stable isotope has spin I=9/2 and has larger Van der Waals size 2.02A. It has quadrupolar effect can be diffuse to nearby environment shortly & distinctively (polar to nonpolar media in vivo system).
  * Chemical composition of materials can influence the longitudinal relaxation of hyperpolarized Kr.
  * The relaxation can distinguish among the hydrophobic and hydrophilic substrate. Although He and Xe have spin half but they are not quadrupolar active.
  * However, the Ne (I=3/2), Kr(I=9/2) and Xe (I=3/2) have Quadrupolar moment. Quadrupolar interactions make these isotopes having spin relaxation.
  * Due to this spin relaxation and evolution, these isotopes can be used as contrasting agents to say about the probe can determine the structural feature and chemical compositions of the surfaces for a permeable media.
  * SEOP can calculate the relaxation of spin T by using the equation nonlinear least-squares fitting for Kr signal as a function of time as well as experimental number of media flip angle (≈12°) for NMR experimenting radio frequency pulses.
  * Hyperpolarized Kr is being separated from Rb gases after spin exchanging in the optical pumping process and then used in variety of in vivo system to get MRI signal. This is the first isotope showed lots of applicability for MRI technique even though has the spin is 9½.
  * During experiment of canine lung tissue, the using magnet was 9.4 T, media was porous and similar porosity to alveolar dimensions which is disseminated at atmospheric pressure. Spin lattice relaxation was reasonably long enough so it is applicable in vivo system although the oxygen level could be 20%.
  * As Kr contrasting agent is promising to develop pristine in vivo MRI methodology to identify the lung diseases epically those effect have been caused in parenchyma surface due to the surfactant concentration.
  * Boyed the boundary this particular contrasting agent can work to figure out the size of pour of porous media in materials science.
  * In addition, this technique can take us about to prepare the surface coating, spatial fluctuations of surfaces. Eventually, never ending the good sign of this contrasting agent like natural abundance (11.5% of Kr) makes it easy to get with reasonable price $5/L.