Ata Chizari

Objective: Advancing microcirculatory perfusion assessment methods is crucial for evaluating organ status during ex-vivo organ preservation and expanding the donor pool. This study demonstrates the feasibility of microcirculatory perfusion imaging in an ex-vivo liver model under normothermic machine perfusion, using two non-contact imaging techniques: laser Doppler perfusion imaging (LDPI) and laser speckle contrast imaging (LSCI). Methods and procedures: An ex-vivo porcine liver was perfused with oxygenated blood for 3 hours. Blood samples were collected every 30 minutes from the hepatic artery and portal vein to evaluate the liver’s overall status. Each of the five liver lobes was imaged every 15 minutes using both the in-house developed LDPI and wireless LSCI devices. Temporally averaged perfusion maps were analyzed to assess spatiotemporal blood flow. Then, correlations between LDPI and LSCI perfusion indices were evaluated. Results: Spatiotemporal perfusion images showed detailed superficial microcirculatory perfusion across five imaged lobes. High correlations between LDPI and LSCI indices were observed in lobes 3−5 (R² = 0.81), which were well-perfused. Blood lactate levels increased over time, indicating a shift in metabolic activity due to ischemia. Also, correlation of LSCI perfusion indices with pH (R²_max. = 0.95) was observed. Conclusion: The ex-vivo liver model mimics in-vivo perfusion under controlled experimental conditions. LDPI and LSCI provide rapid, independent assessments of local microcirculatory blood flow, demonstrate a high inter-technique correlation, and reflect the overall deterioration of liver status, as evidenced by blood gas parameters. Significance: A compact, wireless LSCI system—validated against LDPI—enables non-invasive evaluation of microcirculatory status and serves as a complementary tool for assessing deep tissue viability. Clinical and Translational Impact Statement: We introduce a wireless, compact, and non-contact LSCI system (validated by LDPI) enabling microcirculatory assessment during machine perfusion, complementing deep tissue medical imaging methods and blood gas analysis to enhance organ viability evaluation and support pre-transplantation treatment decisions (Category: Pre-Clinical Research).

Background : Handheld laser speckle contrast imaging (LSCI) is crucial in clinical settings, but motion artifacts (MA) can compromise perfusion image reliability. Current prevention and suppression methods are often impractical or complex. Machine vision techniques, promising in medical imaging, could improve signal quality, but their use in suppressing MA is still unexplored. Objective : We propose an innovative method based on linear regression for MA correction (MAC) in LSCI and validate it in vivo. Methods : We performed paired handheld and mounted LSCI measurements on 14 subjects with psoriasis using the previously validated handheld perfusion imager (HAPI). By marking lesion boundaries for clinical purposes, the HAPI used a monochromatic camera for both speckle imaging and motion detection, simplifying hardware requirements. Accurate estimation of relative displacements between the test object and LSCI probe allowed us to apply MAC to the perfusion images. Results : Local perfusion values correlated with applied speed were used to calculate and correct MA. The difference between mean perfusion in handheld and mounted modes after MAC significantly decreased (median error 14.2 perfusion units (p.u.) on lesions before correction ( $p< 0.0005$ ) and 0.5 p.u. after correction ( $p=0.2$ )). Conclusion : The findings provide evidence for robust handheld LSCI and validate the MA technique in psoriasis case. Of the two causes of MA-onsurface speeds and wavefront tilt-we address the former and correct mean perfusion, assuming constant temporal perfusion at each location. Significance : We describe a practical, non-contact, marker-free technique for reliable handheld perfusion imaging, supporting further clinical translation in plastic surgery and burns.

Perfusion of the flap is essential in Deep Inferior Epigastric Perforator (DIEP) flap breast reconstruction surgery for flap survival, yet perioperative assessment of flap perfusion to detect perfusion-related problems is challenging. Laser Speckle Contrast Imaging (LSCI) is an optical technique for quantitative microcirculation assessment. Mounted LSCI devices are bulky and impractical to use during surgery, or in other clinical settings where investigation of microcirculation is needed. Therefore, a handheld wireless perfusion imager (WIPI) was developed including a 660 nm laser and an RGB camera for image registration. With this device, flap perfusion during surgery (at baseline, after fully raising the flap, and during ischemia) was compared for different Hartrampf zones. The results indicate that poorly perfused DIEP flap zones may be detected in an early stage using a handheld LSCI device. More r

Laser Speckle Contrast Imaging (LSCI) is an optical technique for noninvasive assessment of microcirculatory blood flow. LSCI has a broad application in medicine including dermatology. Since laser speckles are the basis for this imaging modality, any external motions during a measurement from both patient and operator affect the blood flow images. This challenge is called Motion Artefacts (MA). Here, we propose a complete procedure for analysis of speckles, that is, pre-segmentation, segmentation, motion detection, spatial alignment, perfusion map calculation and MA suppression. The Handheld Perfusion Imager (HAPI) operated in both handheld and mounted schemes, has been used for measurements on 14 psoriasis subjects. The advantage of HAPI is use of a single monochromatic camera for both speckle imaging and motion detection. We make use of the black marker dots (made by the clinical investigator to determine visual psoriasis lesion boundary) for calculation of two-dimensional displacements of HAPI during each measurement (i.e. on-surface displacements). These on-surface displacements are integrated to translate each speckle image back to the initial position at the start of the measurement (i.e. spatial alignment). Furthermore, in handheld measurements, MA corrected blood flow maps (also called perfusion maps) are formed by extrapolation of a linear fit from local perfusion versus detected speed to the zero speed, that is, a value ideally always lower than the local mean perfusion. We show that our MA suppression technique makes handheld perfusion maps more similar to the associated mounted perfusion maps in term image histograms and mean values.

Four decades ago, a technique was developed for the measurement of spatiotemporal blood flow variations in the microcirculation by the analysis of laser speckle.¹ Since then, this technique, known as laser speckle contrast imaging (LSCI),^{2 – 5} has advanced in different aspects, such as enhancement of spatial resolution,⁶ processing time,⁷ and quantitative prediction of blood flow.^{8 – 11} When coherent light encounters an optically rough surface or propagates through a scattering medium such as tissue, an interference pattern called speckle is observed on an image screen. Movements of the medium or scattering particles inside it cause formation of dynamic speckles. Imaging of dynamic speckles with a limited exposure time results in speckle pattern images of reduced contrast. The speckle contrast is a measure of motion on or inside the illuminated target: lower speckle contrast corresponds to higher movement.³

Progress has been made in laser speckle contrast imaging (LSCI) of microcirculatory blood flow for biology and medicine. However, the underlying reason for occurrence of movement artefacts (MA) that compromises effective use of LSCI remains largely unexplored. Here, employing a dual-camera setup for both speckle imaging and movement tracking, we validate our analytical model that is based on optical Doppler effect for predication of speckle contrast drop as a function of applied translational speed. We perform both motorized and handheld experiments where planar and scrambled wave illumination schemes have been examined. Experimental data points fairly match the theoretical predictions. These findings indicate that the vision-based movement detection during handheld LSCI is a preferable option. Moreover, the proposed analytical model is promising for further exploration of MA in order to realize a reliable handheld LSCI.

Background: Skin microvasculature changes are crucial in psoriasis development and correlate with perfusion. The noninvasive Handheld Perfusion Imager (HAPI) examines microvascular skin perfusion in large body areas using laser speckle contrast imaging (LSCI).Objectives: To (i) assess whether increased perilesional perfusion and perfusion inhomogeneity are predictors for expansion of psoriasis lesions and (ii) assess feasibility of the HAPI system in a mounted modality.Methods: In this interventional pilot study in adults with unstable plaque psoriasis, HAPI measurements and color photographs were performed for lesions present on one body region at week 0, 2, 4, 6 and 8. The presence of increased perilesional perfusion and perfusion inhomogeneity was determined. Clinical outcome was categorized as increased, stable or decreased lesion surface between visits. Patient feedback was collected on a 10‐point scale.Results: In total, 110 lesions with a median follow‐up of 6 (IQR 6.0) weeks were assessed in 6 patients with unstable plaque psoriasis. Perfusion data was matched to 281 clinical outcomes after two weeks. A mixed multinomial logistic regression model revealed a predictive value of perilesional increased perfusion (OR 9.90; p < 0.001) and perfusion inhomogeneity (OR 2.39; p = 0.027) on lesion expansion after two weeks compared to lesion stability. HAPI measurements were considered fast, patient‐friendly and important by patients.Conclusion: Visualization of increased perilesional perfusion and perfusion inhomogeneity by noninvasive whole field LSCI holds potential for prediction of psoriatic lesion expansion. Furthermore, the HAPI is a feasible and patient‐friendly tool.

Laser speckle contrast imaging (LSCI) is a non-invasive and affordable technique to visualize skin perfusion. Handheld use of the system facilitates measurements on various skin areas in a flexible manner. However, movement artefacts caused by handheld operation or test subject movements hamper its performance. In this work, we study the influence of the laser beam type in handheld-LSCI by evaluating the speckle contrast on static objects for beams with planar, spherical or scrambled wavefronts, and for movement artefacts caused by tilting or translation of wavefronts. We show that the scrambled waves made by often-used engineered diffusers lead to significantly larger movement artefacts than planar or spherical waves.