Illumination dependency in dynamic laser speckle analysis

Rivera, Fernando Pujaico

doi:10.1016/j.optlastec.2020.106221

Cited by 2 publications

(1 citation statement)

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“…In recent sCMOS cameras, it is carefully corrected 15 similarly to DSNU avoiding unwanted spatial patterns that could bias the speckle images in the synthetic exposure mode. Another issue, not specific to synthetic acquisition, is the importance of homogeneous illumination for speckle contrast calculation, as inhomogeneous illumination leads to biased flow maps due to inhomogeneous shot noise contributions within the field of view 19 , 20 . Although calculating speckle contrast in the temporal dimension solves this issue 21 , 22 , in the current implementation of the synthetic exposure mode, the speckle contrast is calculated using spatial kernels and the non-uniformity of field illumination should be minimized or corrected as differences add with the sum of frames.…”

Section: Discussionmentioning

confidence: 99%

Synthetic exposure with a CMOS camera for multiple exposure speckle imaging of blood flow

Chammas

Pain

2022

Sci Rep

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Speckle contrast imaging is an established technique to obtain relative blood flow maps over wide fields of view. A major improvement of the method relies on the acquisition of raw speckle images at different exposure times but requires simultaneous modulation of a laser pulse in duration and intensity and precise synchronization with a camera. This complex instrumentation has limited the use of multiple exposure speckle imaging. We evaluate here the use of a CMOS camera for a simplified approach based on synthetic exposure images created from the sum of successive frames acquired at a 1 ms exposure time. Both methods have been applied to evaluate controlled flows in micro-channels. The contribution of noises to the speckle contrast have been quantified and compared. Dark, readout and shot noise contributions to the total contrast remain constant for modulated exposure, while all these contributions decrease with increasing exposure time for synthetic exposure. The relative contribution of noises to speckle contrast depends on the level of illumination and the exposure time. Guidelines for flow measurements and limitations of the use of a CMOS camera with a limited frame rate for synthetic exposure acquisition scheme are discussed. The synthetic exposure method is simple to implement and should facilitate the translation of multiple exposure speckle imaging to clinical set-ups.

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