We present a 4-dimensional (4D) fluorescence imaging
system in
which each of the 65,536 pixels in the image array contains an excitation-emission-matrix
spectrum with 31 excitation wavelengths and 8 emission wavelengths
(x, y, λexc, λem). Hadamard-transform multiplexing of the excitation light
from a 31-channel programmable light source allows for an increase
in the data acquisition rate so that each 65,536-pixel image can be
obtained within 8 s. The system is demonstrated and characterized
using, first, a 4D image of 10 capillaries filled with four dye solutions
and their binary and ternary mixtures, and, second, using a sequence
of about 100 images of layered fluorescent dye solutions and their
changing fluorescence as a function of temperature. Multivariate analysis
using parallel factor analysis produces images of the spatial distribution
of the fluorophores together with their relative intensity as a function
of time.