text: The sensitivity of NMR signal detection depends on the gyromagnetic ratio (γ) of the nucleus.  In general, the signal intensity produced from a nucleus with a gyromagnetic ratio of γ is proportional to γ because the magnetic moment, the Boltzmann populations, and the nuclear precession frequency all increase in proportion to the gyromagnetic ratio γ.  For example, the gyromagnetic ratio of C is 4 times lower than that of H, so the signal intensity it produces will be 64 times lower than one produced by a proton. However, since noise also increases as the square root of the frequency, the sensitivity is roughly proportional to γ.  A C nucleus would be 32 times less sensitive than a proton, and N around 300 times less sensitive.  Sensitivity enhancement techniques are therefore desirable when recording an NMR signal from an insensitive nucleus.
  The sensitivity can be enhanced artificially by increasing the Boltzmann factors. One method may be through NOE; for example, for C signal, the signal-to-noise ratio can be improved three-fold when the attached protons are saturated.  However, for NOE, a negative value of K, the ratio of gyromagnetic ratios of the nuclei, may result in a reduction in signal intensity. SinceN has a negative gyromagnetic ratio, the observed N signal can be near zero if the dipolar relaxation has to compete with other mechanisms. Alternative methods are therefore necessary for nuclei with a negative gyromagnetic ratio. One such method using the INEPT pulse sequence was proposed by Ray Freeman in 1979, which  became widely adopted.