Wavelength dependence of the precision of noninvasive optical measurement of oxy-, deoxy-, and total-hemoglobin concentration

The precision of noninvasive optical measurement of the concentration chang es in oxy-, deoxy-, and total-hemoglobin depends on wavelength. For estimat ing the precision, we calculated the noise level of the concentration chang es as the uncertainty in measurements using several wavelength pairs of lig ht. Seven laser diodes (664-848 nm) were used simultaneously for spectrosco pic measurement of brain activity during finger motor stimulation. We also used the analysis of error propagation from the uncertainty in direct measu rements of absorbance changes to estimate indirectly the uncertainty of con centration changes. The measurement of the concentration changes made using an 830/664-nm pair are two times (oxy-Hb) and six times (deoxy-Hb) more pr ecise than those made using an 830/782-nm pair. (C) 2001 American Associati on of Physicists in Medicine.