The acousto-optic-tunable-filter-based (AOTF-based) spectral imaging systems for non-invasive photoluminescence diagnostics are discussed. The problem of image distortion caused by AO interaction which causes the inaccuracy of spectral measurements is considered. The existing methods of AOTF calibration do not provide the full information about the image structure and the individual aberrations. It is proposed to reconstruct the optical path difference (OPD) caused by AOTF. For this purpose the experimental setup based on Shack-Hartmann sensor was assembled. It is shown that it allows defining the magnitude of the main aberrations of double AOTF are meridional and sagittal coma and some high-order components. Spectral dependence of OPD and its components is rather weak and shows a small chromatic image distortion. The obtained data is in good correspondence with the results of the theoretical studies of the double AOTFs. Wave front measurement may be effectively used for the study and optimization of existing AOTF-based spectral imagers. The effectiveness of this technique is demonstrated on the measurement of the spectrums of real biomedical tissues obtained by the endoscopic AOTF-based imager.