BOLD MRI vs. NIR spectrophotometry. Will the best technique come forward?

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.