MRI MEASUREMENTS OF CEREBRAL DEOXYHEMOGLOBIN CONCENTRATION [DHB] - CORRELATION WITH NEAR-INFRARED SPECTROSCOPY (NIRS)

Changes in physiological parameters such as cerebral blood flow, cereb ral blood volume, oxygen extraction, and the size and distribution of cerebral bleed vessels, result in changes in the local concentration o f deoxyhaemoglobin ([dHb]). The purpose of this study was to quantitat ively investigate the dependence of the R-2 relaxation rate upon the [dHb] per voxel. Five neonatal piglets were studied in a 7 T/20 cm bor e magnet. MRI was conducted using a 2.5 cm diameter surface coil place d over the parietal lobes. Four progressively T-2-weighted images wer e acquired, allowing the absolute quantitation of R-2. Simultaneous n ear infrared spectroscopy (NIRS) measurements were made from an area e ncompassing the MR imaging slice, and allowed the absolute quantitatio n of [dHb]. The arterial oxygen saturation (SaO(2)) of the piglet was lowered stepwise by decreasing the fractional inspired oxygen concentr ation (FiO(2)), which precipitated a change in [dHb]. NIRS and MRI mea surements were made at each FiO(2) step. The results demonstrate an ex tremely strong, linear relationship between R2 as determined by MRI a nd [dHb], as measured by NIRS. Whereas NIRS can only give us a global measure of [dHb], the results suggest the future use of MRI in produci ng high resolution relaxation rate maps related to the [dHb] distribut ion of the brain. (C) 1998 John Wiley & Sons, Ltd.