Submitted on April 20, 2004
Accepted on October 5, 2005
Non-invasive in vivo Monitoring of Methemoglobin Formation and Reduction with Broadband Diffuse Optical Spectroscopy
Jangwoen Lee1, Naglaa El-Abaddi2, Andrew Duke2, Albert E Cerussi1, Matthew Brenner3, and Bruce J Tromberg1*
1 Laser Microbeam and Medical Program, Beckman Laser Institute, University of California, Irvine, Irvine, CA, USA
2 Division of Pulmonary Medicine, Department of Medicine, University of California, Irvine, Irvine, CA, USA
3 Laser Microbeam and Medical Program, Beckman Laser Institute, University of California, Irvine, Irvine, CA, USA; Division of Pulmonary Medicine, Department of Medicine, University of California, Irvine, Irvine, CA, USA
* To whom correspondence should be addressed. E-mail: tromberg{at}bli.uci.edu.
We present non-invasive quantitative in vivo measurements of methemoglobin formation and reduction in a rabbit model using broadband diffuse optical spectroscopy (DOS). Broadband DOS combines multi-frequency frequency domain photon migration (FDPM) with time-independent near infrared (NIR) spectroscopy to quantitatively measure bulk tissue absorption and scattering spectra between 600 nm and 1000 nm. Tissue concentrations of methemoglobin [MetHb], deoxyhemoglobin [Hb-R], and oxyhemoglobin [Hb-O2] were determined from absorption spectra acquired in "real-time" during nitrite infusions in nine pathogen free New Zealand white rabbits. As little as 30 nM [MetHb] changes were detected for levels of [MetHb] that ranged from 0.80 to 5.72 µM, representing 2.2 to 14.9 % of the total hemoglobin content (% MetHb). These values agreed well with on-site ex vivo co-oximetry data ( r2 = 0.902, p<0.0001, n = 4). The reduction of MetHb to functional hemoglobins was also carried out with intravenous injections of Methylene Blue (MB). As little as 10 nM changes in [MB] were detectable at levels of up to 150 nM in tissue. Our results demonstrate, for the first time, the ability of broadband DOS to non-invasively quantify real-time changes in [MetHb] and four additional chromophore concentrations ([Hb-R], [Hb-O2], [H2O], and [MB]) despite significant overlapping spectral features. These techniques are expected to be useful in evaluating dynamics of drug delivery and therapeutic efficacy in blood chemistry, human, and pre-clinical animal models.
