2.1. MESI set-up and speckle contrast images database building

The imaging set-up is showed in Fig. 1. A 633 nm laser diode (SGL, Shanghai, China) is used. Images were acquired with a sCMOS camera (Orca Flash 2.8, Hamamatsu, Japan) through a stereomicroscope (Leica MZ16). Images are composed of 1920 × 1440 square pixels. MESI data were obtained for the following exposure times: 1, 2, 5, 10, 15, and 25 and 50 ms and for two magnification levels of the optics (×2.5 and ×6) corresponding to fields of view of 3 × 2.1 mm² and 1.1 × 0.9 mm² respectively. For all conditions, speckle contrast images K at different exposure times were generated using the MESI synthetic exposure technique as detailed in [11] with a 5 × 5 sliding window and Eq. (1).

MESI synthetic exposure imaging set-up. A speckle contrast images database was acquired for different exposure times, flows and channels diameter using a microfluidic system (pressure flow control, flowmeter, and a microfluidic chip) with 2%-intralipid as flowing media. Insert: microfluidic chip including 40, 60, 80, 100, 300 and 500 µm diameter channels.

The microfluidic set-up was described in detail previously [9]. Speckle contrast images were obtained for various flows in microfluidic channels with diameters of 40, 60, 80, 100, 300 and 500 µm. We used 2%-intralipid as flowing media as it provides a reduced scattering optical coefficient close to that of flowing blood [20,21]. For the database construction, flows of 1, 2, 3, 4, 5, 6, 7 and 8 µl/min have been used. These flows are representative of microcirculation blood velocities in the mice brain (speed ranging from 0.5 to 30 mm/s) [7,22]. All flow values have been used to generate the database except for the 40 µm channel where the highest achievable flow with reliable stability was 5 µl/min. Representative speckle contrast images from the database are shown in Fig. 2. The complete dataset is available on an institutional repository and referenced as Dataset 1 [23].

Speckle contrast database sample images. Representative speckle contrast images are shown for Q = 2 µl/min and Q = 5 µl/min), 2 different channels diameters Φ = 100 µm and Φ = 300 µm and two magnification levels (×2.5 and ×6). In each case, contrast images are shown for three exposure times (T = 1 ms, T = 5 ms and T = 15 ms).