# Line Scan Spatial Speckle Contrast Imaging and Its Application in Blood Flow Imaging
## 1 Introduction  
Laser speckle contrast imaging (LSCI) has been broadly applied to visualize blood flow imaging in living tissues, such as the retina [1, 2, 3, 4], skin [5, 6, 7, 8, 9], and brain [10, 11, 12, 13, 14, 15, 16] since it was first introduced in the 1980s [1]. It can monitor the dynamic blood flow response and relative changes in values. A few reviews have summarized the recent technological advancements and some practical challenges of LSCI [17, 18, 19, 20, 21]. [PERSON] and [PERSON] firstly studied the quantitative relationship between the contrast of speckle pattern and the velocity of the flow, and assumed a Lorentzian distribution for Brownian motion (unordered flow) of the scatterers [1]. In fact, some research groups demonstrated that the Lorentzian model is suitable for Brownian motion [1, 22, 23, 24]. The Gaussian model is generally considered more suitable for ordered flow [23, 25, 26]. Many researchers often discuss which model is more appropriate [22, 26, 27, 28, 29, 30]. [PERSON] et al. [31] analyzed the influence of the assumptions in the LSCI theory on the accuracy of blood flow estimation. They proved that the blood flow changes are severely underestimated by the most commonly used LSCI model under ischemic conditions, and proposed an alternative model that can measure blood flow changes more accurately. [PERSON] et al. [32] demonstrated that the influence of anti-aging or anti-AD treatments on cerebral micro vascular health can be evaluated by LSCI. [PERSON] et al. [33] developed a dual-display laparoscopic vision system, which combines LSCI with a commercially rigid laparoscope. The standard color vision, unlabeled vasculature imaging, and fusion display modes are available. They found that the integrated system can detect early changes in bowel perfusion that areinvisible with standard color imaging. [PERSON] et al. [34] proved that LSCI is capable of generating real-time full field cerebral blood flow images with high spatial resolution, while minimizing damage to the surgical process during neurosurgeries.  
However, conventional LSCI is based on wide-field optical imaging, which suffers from deteriorated spatial resolution and contrast when the sample is optically thick. In a previous paper, line scan laser speckle contrast imaging (LS-LSCI) was proven with good experimental results with higher spatial resolution than conventional laser speckle contrast imaging [35; 36]. In this paper, we further compared the performance of spatial and temporal speckle contrast-based image acquisition approaches, and verified the flow quantification capability of our speckle imaging system, which features confocal illumination and detection. The system can be configured with three imaging modes. The first one is surface illumination laser speckle contrast imaging (SI-LSCI), and the other two are line scan temporal speckle contrast imaging (LS-TSCI) and line scan spatial speckle contrast imaging (LS-SSCI). The Materials and Method section discloses the imaging setup, theoretical models, data processing, and sample preparation details. The Results and Discussion section presents the experimental images obtained from chick embryos, and compared and fully discussed the performance of various imaging modes.