In vivo optical/near-infrared spectroscopy and imaging of metalloproteins

A number of medical applications of near-infrared spectroscopy are growing closer to clinical acceptance, and new techniques involving both spectroscopy and imaging are evolving rapidly. In vivo spectroscopy and, more recently, imaging techniques are largely based upon optical electronic transitions involving the metal centers of hemoglobin (blood), myoglobin (muscle) and cytochrome aa3 (mitochondria). The wide variety of near-IR based applications includes heart and stroke research, monitoring cerebral oxygenation of premature babies, and 'functional activation' (response of brain to mental tasks). All of these applications are founded upon changes in hemoglobin O2 saturation; these changes are monitored by following trends in the near-infrared absorptions of deoxyhemoglobin (760 nm) and oxyhemoglobin (920 nm). The same absorptions provide a basis for imaging regional variations in blood oxygenation. This report presents and discusses examples, both from the literature and from our recent work, of near-infrared spectroscopy and imaging in medical applications.