OPTICAL PATHLENGTH MEASUREMENTS ON ADULT HEAD, CALF AND FOREARM AND THE HEAD OF THE NEWBORN-INFANT USING PHASE-RESOLVED OPTICAL SPECTROSCOPY

We have used an intensity modulated optical spectrometer, which measur es the phase shift across tissue experienced by intensity modulated ne ar-infrared light, to determine the absolute optical pathlength throug h tissue. The instrument is portable and takes only 5 s to record path length at four wavelengths (690 nm, 744 nm, 807 nm and 832 nm). The ab solute pathlength divided by the known spacing between the light sourc e and detector on the skin is the differential pathlength factor (DPF) which previous studies have shown is approximately constant for spaci ngs greater than 2.5 cm. DPF results are presented for measurements on 100 adults and 35 newborn infants to determine the statistical variat ion on the DPF. All measurements were made at a frequency of 200 MHz w ith source-detector spacings of > 4 cm. Results at 807 nm show a DPF o f 4.16 (+/-18.8%) for adult arm, 5.51(+/-18%) for adult leg, 6.26(+/-1 4.1%) for adult head and 4.99(+/-19%) for the head of a newborn infant . A wavelength dependence was obtained for DPF On all tissues and a di fference in DPF between male and female was observed for both the adul t arm and leg. The results can be used to improve the quantitation of chromophore concentration changes in adults and newborn infants.