Journal of Biomedical OpticsNear-infrared fluorescence contrast-enhanced imaging with intensified charge-coupled device homodyne detection: measurement precision and accuracy
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Fluorescence frequency-domain photon migration (FDPM) through tissue refers to the propagation of intensity-modulated fluorescent light that originates from tissue-laden fluorophores following illumination with an intensity-modulated excitation light source. FDPM measurements of modulation amplitude and phase are ultimately employed in an inversion algorithm for tomographic reconstruction of interior optical and fluorescent property maps that delineate disease enhanced with fluorescent contrast agent. Because the inverse problem is underdetermined, measurement precision and accuracy crucially impact its solution. Reported here are the precision and accuracy of FDPM measurements acquired using an intensified CCD homodyne detection system. By introducing 32 phase delays between the oscillators used to modulate the intensifier gain and light source intensity at 100 MHz, mean precision is maximized at ∓0.46% and ∓0.26 deg for measurements of modulation amplitude and phase, respectively. Measurement precision improves when the number of phase delays increases. Measurements of fluorescence modulation amplitude and phase, acquired from the surface of a tissue phantom at distances ranging between 0.71 and 3.6 cm from an incident excitation point source, exhibit a mean accuracy of 17% and 1.9 deg, respectively. Measurement accuracy deteriorates with increasing distance from the point source, but for distances up to 1.0 cm from the point source, measurements of fluorescence modulation amplitude and phase exhibit a mean accuracy of 5.4% and 0.30 deg, respectively.