Near-infrared fluorescence spectroscopy detects Alzheimer's disease in vitro

The purpose of this study was to investigate whether near-infrared (NIR) fl uorescence spectroscopy could be used to detect Alzheimer's disease (AD) by brain tissue autofluorescence. Unfixed temporal cortex specimens from AD c ases and age-matched, non-AD controls were frozen at autopsy and then thawe d just prior to spectral measurement. Spectra of intrinsic tissue fluoresce nce induced by 647 nm light were recorded from 650 to 850 nm. We used princ ipal component analysis of the tissue spectra from 17 AD cases and 5 non-AD control cases in a calibration study to establish a diagnostic algorithm. Retrospectively applied to the calibration set, the algorithm correctly cla ssified 23 of 24 specimens. In a prospective study of 19 specimens from 5 A D brains and 2 non-AD control brains, 3 of the 4 control specimens and all AD specimens were correctly diagnosed. Both the excitation light used and t he measured brain tissue autofluorescence are at NIR wavelengths that can p ropagate through skull and overlying tissue. Therefore, our results demonst rate an optical spectroscopic technique that carries direct molecular level information about disease. This is the first step toward a clinical tool t hat has the potential to be applied to the noninvasive diagnosis of AD in l iving patients.