USE OF COMPUTER-SIMULATIONS FOR QUANTITATION OF P-31 ISIS MRS RESULTS

The difficulties in quantitation of in vivo P-31 spectra are exacerbat ed by the fact that, in general, coils with inhomogeneous B1 fields ar e used with in vivo samples. A general method for quantitation of in v ivo P-31 MRS results obtained with the ISIS localization method was de veloped using computer simulations. The simulation calculates the prep aration of the sample magnetization throughout the sample by the ISIS pulse sequence, as well as the sensitivity of signal reception. The ca lculation accounts for both the B1 field and the B0 gradients applied to the sample. The sensitivity of the experiment is expressed by integ ration of the simulated signal over the sample, assuming a homogeneous sample. The primary advantage of this approach is that a separate loc alization experiment on a phantom of known concentration is not requir ed each time parameters of the localization experiment, such as dimens ions or location of the localized volume, are altered. In addition, th e simulations indicate the degree of contamination (signal from outsid e of the localized volume) that occurs, and provide a means of compari ng different executions of the ISIS experiment. Experiments were perfo rmed on phantoms to verify the simulations, and experimental results o n human brain and liver are reproduced to show that this approach prov ides reasonable estimates of metabolite levels in terms of molar conce ntrations.