B-11 NMR OF BOROCAPTATE - RELAXATION AND IN-VIVO DETECTION IN MELANOMA-BEARING MICE

Longitudinal and transverse relaxation rates for the B-11 resonances i n sodium borocaptate (BSH) at varying concentrations were measured in undiluted horse serum in a 4.7 Tesla field, The results could be fit b y a model that assumes fast exchange of the BSH molecule between a fre e and a bound state, using values of 0.77 +/- 0.7 MHz for the B-11 qua drupole coupling constant and (6.3 +/- 0.9) x 10(-9) s for the rotatio nal correlation time in the bound state, These results were used as a basis for assessing the requirements and limitations of quantitative d etermination of BSH concentrations in vivo, using B-11 NMR, Surface co il B-11 NMR spectroscopy was performed on a total of 14 mice injected with BSH, Some of the animals (n = 9) had implanted M2R melanoma tumor s grown to various sizes in the rear thigh, in which case the surface coil was placed against the tumor, whereas for the other animals (with out tumor), the coil was placed against the rear thigh muscle. NMR spe ctra were acquired under fully relaxed conditions, The spectra were qu antitated by peak integration; apparent absolute BSH concentrations we re derived by comparison with spectra from a phantom with known BSH co ncentration, using extrapolation of the time-domain data to zero preac quisition delay, The results indicate significantly higher B-11 BSH si gnal intensities in tumors, compared with muscle tissue, whereas the u ptake and clearance kinetics were similar.