C-13
In Vivo Spectroscopy
Carbon is the basis for the chemistry of the body, and the C-14 radionuclide has been extensively used in biochemical and medical research. The short lived beta emitter C-11 radionuclide is used for PET imaging. The C-13 nucleus is a stable isotope which is a dilute spin in nature. Hence, its use in MR imaging is currently very difficult. However, C-13 has been used for many years in analytical spectroscopy, and does have all the correct NMR properties to make it a favorable nucleus for medical spectroscopy:
Stable isotope
1.1% Natural abundance
Spin 1/2
Gyromagnetic ratio of 10.7MHz/T (25% of H-1)
Sensitivity 1.59% of H-1 at constant field
Chemical shift range 300 ppm
The dilute spin of C-13 eliminates C-13{C-13} coupling, but C-13{H-1} coupling does reduce the signal intensity by producing multiplets. H-1 decoupling is useful to collapse the resonances into singlets, and (possibly) generate some NOE (Nuclear Overhauser Effect) enhancement.
C-13 Natural Abundance Lipids
The C-13 WALTZ-8 decoupled spectrum of a human calf muscle (Siemens Medical Systems data). Note the well defined -CH2- resonances. This resolution is not much different than early 60 MHz (H-1) FT instruments of complex mixtures, or organic lab student data!
C-13 Field Differences in Resolution and S/N
Both C-13 spectra are of human muscle tissue (Siemens Medical Systems data). Note the peak separation at 4T, and the S/N improvement with less aquisitions!
C-13 REFERENCES
Last real update for this page: 13-Mar-98
(WIP - works in progress)
