1. A method comprising: obtaining a plurality of images of a measured fluorescence intensity decay for a sample having been exposed to an excitation pulse generated by an excitation light source, the measured fluorescence intensity decay being associated with a fluorescence impulse response function; deconvolving the excitation pulse from the measured images; estimating a first expansion coefficient (C 0 ); generating a map of higher expansion coefficients (“{c j }”); expanding the fluorescence impulse response function on a Laguerre basis; and computing a map of average lifetimes by constructing an impulse response function (“IRF”) at every pixel for a predetermined number of time instances (“S”) and interpolating a time point at which the IRF becomes 1/e of its maximum value, wherein the IRF is represented by the equation: h ⁡ ( r , n ) = ∑ j = 0 L - 1 ⁢ c j ⁢ ⁢ ( r ) · b j α ⁡ ( n ) , n = 0 , 1 , … ⁢ , S - 1.