Temporal vs Spatial Contrast in Speckle Contrast Imaging

Question

I have been reading about Speckle Contrast Imaging recently. Its quite an interesting topic given that it should be possible with relatively inexpensive equipment. The basic premise from what I gathered is as follows:

1. A laser beam forms a "speckle" pattern when shined on a surface due to random interference
2. Motion of the scattering species e.g. blood cells can cause these speckles to "blur"
3. The blurring of these speckles can be used to highlight the motion of the scattering species

The contrast ratio $K = \frac {\sigma}{<I>}$ quantifies the blurring of the speckles. $\sigma$ is the standard deviation of an $N\times N$ cluster of pixels while $<I>$ is the mean intensity. Iterating over an entire image (e.g. $1024\times 1280$ pixels) would yield a value of $K$ for each pixel which can be used to "construct" a new image, highlighting the scattering species.

Now there is some terminology related to the topic which I'm not sure about. Many of the sources I have seen mention "Spatial Contrast" and "Temporal Contrast".

An example source: Laser speckle contrast imaging in biomedical optics

Could someone explain the differences between these and what they would mean from a practical point of view? Thanks!

Answer 1

Spatial would mean that we have one image, smooth areas are where there was motion and the image looked smooth/constant value .... rough spots are observed where motion is less, i.e the area shows lots of variation/contrast in intensity.

Temporial would require video or a changing of signal with time, like looking at a whole surface that started or stopped moving.

With a video you could do both spatial and temporal at the same time. Watching blood cells move under a smooth surface.