Faculty Bibliography

This paper will discuss the assumptions, strengths and weaknesses of both BOLD imaging and NIR spectrophotometry with respect to monitoring tissue oxygenation. BOLD, or blood oxygen level dependent MRI, is an imaging protocol that is sensitive to specific relaxation rates which are influenced by deoxyhemoglobin. NIRS is capable of providing information on oxyhemoglobin, deoxyhemoglobin and total hemoglobin. Both techniques have inherent assumptions, strengths and weaknesses. NIRS has not been able to provide the spatial sensitivity of BOLD. BOLD may be more difficult to quantify. Currently, these two methods are complementary, providing data that strengthens the interpretation of results from each modality. Recent data indicate that relaxation rates can be used to quantify deoxyhemoglobin in isolated blood and, under specific conditions, there is a strong correlation between deoxyhemoglobin content measured by NIRS and changes in relaxation rates measured by MRI. These data indicate that BOLD imaging has the potential to become an attractive alternative to NIRS

Improvements of the Cadzow enhancement procedure (EP) are reported. A numerical study showed that once EP has properly converged, it results in a near-optimum signal fitting the noisy data in the least-squares sense. At convergence, the estimated signal involves purely exponentially damped sinusoids; then any linear-prediction methods can be used indifferently in the subsequent quantitation step. Moreover, this final step needs only a few samples. Amplitude estimates have negligible bias even for low SNR and their standard deviations are nearly equal to their Cramer-Rao lower bounds. This is illustrated in a Monte Carlo simulation and an in vitro study using three different SVD-based quantitation methods (LPSVD, HSVD, TLS). EP used prior to any linear-prediction methods leads to an important reduction of the threshold SNR and results in near-optimal automatic quantitation methods. (C) 1994 Academic Press, Inc.

To obtain reliable NMR quantitation, experimental cautions concerning data acquisition must be taken when using automatic predictive calculations. For this study, 2000 31P in vitro and in vivo spectra were processed, using the enhancement procedure with linear prediction using singular value decomposition (EPLPSVD) method, and analyzed. The effects of quadrature detection modes (simultaneous or sequential), of the number of time-domain samples used are investigated and experimental conditions such as sample motions and spectral width are discussed