Laser Speckle Contrast Imaging Measurements Research Articles

Dynamic light scattering and laser speckle contrast imaging of the brain: theory of the spatial and temporal statistics of speckle pattern evolution.

Dynamic light scattering (DLS) and laser speckle contrast imaging (LSCI) are closely related techniques that exploit the statistics of speckle patterns, which can be utilized to measure cerebral blood flow (CBF). Conventionally, the temporal speckle intensity auto-correlation function is calculated in DLS, while the spatial speckle contrast Ks is calculated in LSCI measurements. Due to the rapid development of CMOS detection technology with increased camera frame rates while still maintaining a large number of pixels, the ensemble or spatial average of as well as the temporal contrast Kt can be easily calculated and utilized to quantify CBF. Although many models have been established, a proper summary is still lacking to fully characterize DLS and LSCI measurements for spatial and temporal statistics, laser coherence properties, various motion types, etc. As a result, there are many instances where theoretical models are misused. For instance, mathematical formulas derived in the diffusive regime or for ergodic systems are sometimes applied to small animal brain measurements, e.g., mice brains, where the assumptions are not valid. Therefore, we aim to provide a review of the speckle theory for both DLS and LSCI measurements with detailed derivations from first principles, taking into account non-ergodicity, spatial and temporal statistics of speckles, scatterer motion types, and laser coherence properties. From these calculations, we elaborate on the differences between spatial and temporal averaging for DLS and LSCI measurements that are typically ignored but can result in inaccurate measurements of blood flow, particularly the spatially varying nature of the static component in and Kt. We also obtained maps in in vivo mouse brain measurements using high frame rate CMOS cameras which have not been demonstrated before, and compared with and Ks,t. This work provides a useful guide for choosing the correct model to analyze spatial and temporal speckle statistics in in-vivo DLS and LSCI measurements.

Laser speckle contrast imaging for intraoperative assessment of intestinal microcirculation in normo- and hypovolemic circulation in a porcine model

Introduction: Healing is essential for successful colorectal surgery. Optimal microcirculation is needed to ensure this; however, this is only subjectively assessed by the surgeon. Laser Speckle Contrast Imaging (LSCI) is an objective non-contact, image-based method to quantify microcirculation in bowel ends. This study aimed to evaluate the application of LSCI in an open surgery porcine model, determine differences between normal and impaired microcirculation, and test the LSCI applicability to repeated measurements. Method: A midline laparotomy was made in ten healthy female pigs to expose the colon and small intestine. Subsequently, baseline measurements were conducted. A local arteria supplying the colonic or small intestine mesentery was clamped for 5 min. and LSCI measures were made again. After an hour’s rest, LSCI measurements were done in two unaffected areas on the colon and the small intestine, and baseline values were recorded. Hypotension was induced with rapid bleeding and LSCI measurements were done. After the mean arterial blood pressure (MAP) dropped to 50-60 mmHg, norepinephrine infusion was started. At a stable MAP of 85-100 mmHg, LSCI measurements were repeated at 0 min. and 30 min. during continuous norepinephrine infusion. Results: Cross-clamping caused LSCI levels to drop equally in both the colon and small intestine by 60% in the entire the clamped zone. Compared to baseline, the microcirculation measured by LSCI in the unclamped adjacent transition zone was diminished by 33% and 40%, colon and small intestines, respectively. During hypotension due to bleeding, LSCI decreased as expected. When MAP was stabilized by norepinephrine infusion, LSCI values dropped further: compared to baseline, measurements decreased with 24% and 20% in colon and small intestines, respectively. Conclusion: LSCI can be used as a quantitative, real-time, non-contact method to detect changes in the microcirculation during open intestinal surgery with large changes in microcirculation due to e.g., hypovolemic and norepinephrine infusion. It is simple to use and in contrast to the existing intraoperative microcirculation assessment techniques, LSCI stands out primarily for its elimination of the requirement for a dye. As our study has shown, this feature allows us to perform time-independent measurements and repeat them indefinitely in nearby regions without compromising the effectiveness of the method.

Renal cortex microperfusion evaluated by laser speckle contrast imaging in an exvivo perfused kidney model-A proof-of-concept study.

Validated quantitative biomarkers for assessment of renal graft function during normothermic machine perfusion (NMP) conditions are lacking. The aim of this project was to quantify cortex microperfusion during exvivo kidney perfusion using laser speckle contrast imaging (LSCI), and to evaluate the sensitivity of LSCI when measuring different levels of renal perfusion. Furthermore, we aimed to introduce LSCI measurements during NMP in differentially damaged kidneys. Eleven porcine kidneys were nephrectomized and perfused exvivo. Cortex microperfusion was simultaneously monitored using LSCI. First, a flow experiment examined the relationship between changes in delivered renal flow and corresponding changes in LSCI-derived cortex microperfusion. Second, renal cortical perfusion was reduced stepwise by introducing a microembolization model. Finally, LSCI was applied for measuring renal cortex microperfusion in kidneys exposed to minimal damage or 2 h warm ischemia (WI). Cortex microperfusion was calculated from the LSCI-obtained data. The flow experiment resulted in relatively minor changes in cortex microperfusion compared to the pump-induced changes in total renal flow. Based on stepwise injections of microspheres, we observed different levels of cortex microperfusion that correlated with administrated microsphere dosages (r2 = 0.95-0.99). We found no difference in LSCI measured cortex microperfusion between the kidneys exposed to minimal damage (renal cortex blood flow index, rcBFI = 2090-2600) and 2 h WI (rcBFI = 2189-2540). Based on this preliminary study, we demonstrated the feasibility of LSCI in quantifying cortex microperfusion during exvivo perfusion. Furthermore, based on LSCI-measurements, cortical microperfusion was similar in kidneys exposed to minimal and 2 h WI.

Optimizing the precision of laser speckle contrast imaging

Laser speckle contrast imaging (LSCI) is a rapidly developing technology broadly applied for the full-field characterization of tissue perfusion. Over the recent years, significant advancements have been made in interpreting LSCI measurements and improving the technique’s accuracy. On the other hand, the method’s precision has yet to be studied in detail, despite being as important as accuracy for many biomedical applications. Here we combine simulation, theory and animal experiments to systematically evaluate and re-analyze the role of key factors defining LSCI precision—speckle-to-pixel size ratio, polarisation, exposure time and camera-related noise. We show that contrary to the established assumptions, smaller speckle size and shorter exposure time can improve the precision, while the camera choice is less critical and does not affect the signal-to-noise ratio significantly.

Real-time laser speckle contrast imaging measurement during normothermic machine perfusion in pretransplant kidney assessment.

Normothermic machine perfusion (NMP) provides a platform for pre-transplant kidney quality assessment that is essential for the use of marginal donor kidneys. Laser speckle contrast imaging (LSCI) presents distinct advantages as a real-time and noncontact imaging technique for measuring microcirculation. In this study, we aimed to assess the value of LSCI in visualizing renal cortical perfusion and investigate the additional value of dual-side LSCI measurements compared to single aspect measurement during NMP. Porcine kidneys were obtained from a slaughterhouse and then underwent NMP. LSCI was used to measure one-sided cortical perfusion in the first 100 min of NMP. Thereafter, the inferior renal artery branch was occluded to induce partial ischemia and LSCI measurements on both ventral and dorsal sides were performed. LSCI fluxes correlated linearly with the renal blood flow (R2  = 0.90, p < 0.001). After renal artery branch occlusion, absence of renal cortical perfusion could be visualized and semiquantified by LSCI. The overall ischemic area percentage of the ventral and dorsal sides was comparable (medianinterquartile range[IQR], 38 [24-43]% vs. 29 [17-46]%, p = 0.43), but heterogenous patterns between the two aspects were observed. There was a significant difference in oxygen consumption (mean ± standard deviation [SD], 2.57 ± 0.63 vs. 1.83 ± 0.49 mLO2 /min/100 g, p < 0.001), urine output (median [IQR], 1.3 [1.1-1.7] vs. 0.8 [0.6-1.3] mL/min, p < 0.05), lactate dehydrogenase (mean ± SD, 768 ± 370 vs. 905 ± 401 U/L, p < 0.05) and AST (mean ± SD, 352 ± 285 vs. 462 ± 383 U/L, p < 0.01) before and after renal artery occlusion, while no significant difference was found in creatinine clearance, fractional excretion of sodium, total sodium reabsorption and histological damage. LSCI fluxes correlated linearly with renal blood flow during NMP. Renal cortical microcirculation and absent perfusion can be visualized and semiquantified by LSCI. It provides a relative understanding of perfusion levels, allowing for a qualitative comparison between regions in the kidney. Dual-side LSCI measurements are of added value compared to single aspect measurement and renal function markers.

Monitoring Muscle Perfusion in Rodents During Short-Term Ischemia Using Power Doppler Ultrasound

The aim of this work was to evaluate the reliability of power Doppler ultrasound (PD-US) measurements made without contrast enhancement to monitor temporal changes in peripheral blood perfusion. On the basis of pre-clinical rodent studies, we found that combinations of spatial registration and clutter filtering techniques applied to PD-US signals reproducibly tracked blood perfusion in skeletal muscle. Perfusion is monitored while modulating hindlimb blood flow. First, in invasive studies, PD-US measurements in deep muscle with laser speckle contrast imaging (LSCI) of superficial tissues made before, during and after short-term arterial clamping were compared. Then, in non-invasive studies, a pressure cuff was employed to generate longer-duration hindlimb ischemia. Here, B-mode imaging was also applied to measure flow-mediated dilation of the femoral artery while, simultaneously, PD-US was used to monitor downstream muscle perfusion to quantify reactive hyperemia. Measurements in adult male and female mice and rats, some with exercise conditioning, were included to explore biological variables. PD-US methods are validated through comparisons with LSCI measurements. As expected, no significant differences were found between sexes or fitness levels in flow-mediated dilation or reactive hyperemia estimates, although post-ischemic perfusion was enhanced with exercise conditioning, suggesting there could be differences between the hyperemic responses of conduit and resistive vessels. Overall, we found non-contrast PD-US imaging can reliably monitor relative spatiotemporal changes in muscle perfusion. This study supports the development of PD-US methods for monitoring perfusion changes in patients at risk for peripheral artery disease.

A robust quantitative approach for laser speckle contrast imaging perfusion analysis revealed anomalies in the brain blood flow in offspring mice of preeclampsia.

Microcirculation analysis of the brain cortex is challenging because surface perfusion varies rapidly in small space-time regions and is bone protected. The laser speckle contrast imaging (LSCI) technique allows analyzing in vivo brain vascular perfusion generating a large amount of data that requires sophisticated data analytics, making researchers invest much effort in processing. Our research question was whether the reduced placental perfusion model (RUPP) of preeclampsia (PE) was associated with impaired blood perfusion in the offspring's brains. We aimed to develop a robust numerical approach that mainly consisted of applying a signal-processing tool for calculating optimal segmentation and piece-wise fits of the offspring's brain perfusion signals obtained from the LSCI technique. We combined this tool with the usual statistical analysis, implementing both in Matlab software. We performed brain perfusion measurements from offspring (five days postnatal, P5) of control pregnant dams (sham, n=13) and of RUPP dams (RUPP, n=7) using the Pericam® PSI-HR system at a basal condition and after thermal stimuli (warm and cold). We found that pups of RUPP mice exhibited significant differences in perfusion and vascular response to thermal stimuli compared to the sham mice. These differences were associated with high data variability in the Sham group, while in the RUPP group, perfusion looks "stiffer." Data also suggest sex-dimorphism in the vascular response since female pups in the Sham group but not male pups showed statistically significant differences in response to the warm stimulus. Again, this sex-related difference was absent in pups of RUPP mice. In conclusion, we present a robust quantitative approach for LSCI measurements that revealed anomalies in the brain blood flow in offspring of the RUPP model of PE.

Movement correction method for laser speckle contrast imaging of cerebral blood flow in cranial windows in rodents.

Laser speckle contrast imaging (LSCI) is used in clinical research to dynamically image blood flow. One drawback is its susceptibility to movement artifacts. We demonstrate a new, simple method to correct motion artifacts in LSCI signals measured in awake mice with cranial windows during sensory stimulation. The principle is to identify a region in the image in which speckle contrast (SC) is independent of blood flow and only varies with animal movement, then to regress out this signal from the data. We show that (1) the regressed signal correlates well with mouse head movement, (2) the corrected signal correlates better with independently measured blood volume and (3) it has a (59 ± 6)% higher signal-to-noise ratio. Compared to three alternative correction methods, ours has the best performance. Regressing out flow-independent global variations in SC is a simple and accessible way to improve the quality of LSCI measurements.

The Association between Foot and Ulcer Microcirculation Measured with Laser Speckle Contrast Imaging and Healing of Diabetic Foot Ulcers.

Diagnosis of peripheral artery disease in people with diabetes and a foot ulcer using current non-invasive blood pressure measurements is challenging. Laser speckle contrast imaging (LSCI) is a promising non-invasive technique to measure cutaneous microcirculation. This study investigated the association between microcirculation (measured with both LSCI and non-invasive blood pressure measurement) and healing of diabetic foot ulcers 12 and 26 weeks after measurement. We included sixty-one patients with a diabetic foot ulcer in this prospective, single-center, observational cohort-study. LSCI scans of the foot, ulcer, and ulcer edge were conducted, during baseline and post-occlusion hyperemia. Non-invasive blood pressure measurement included arm, foot, and toe pressures and associated indices. Healing was defined as complete re-epithelialization and scored at 12 and 26 weeks. We found no significant difference between patients with healed or non-healed foot ulcers for both types of measurements (p = 0.135–0.989). ROC curves demonstrated moderate sensitivity (range of 0.636–0.971) and specificity (range of 0.464–0.889), for LSCI and non-invasive blood pressure measurements. Therefore, no association between diabetic foot ulcer healing and LSCI-measured microcirculation or non-invasive blood pressure measurements was found. The healing tendency of diabetic foot ulcers is difficult to predict based on single measurements using current blood pressure measurements or LSCI.

Assessing Intraoperative Laser Speckle Contrast Imaging of Parathyroid Glands in Relation to Total Thyroidectomy Patient Outcomes.

Background: Accurate assessment of parathyroid gland vascularity is important during thyroidectomy to preserve the function of parathyroid glands and to prevent postoperative hypocalcemia. Laser speckle contrast imaging (LSCI) has been shown to be accurate in detecting differences in parathyroid vascularity. In this surgeon-blinded prognostic study, we evaluate the relationship between intraoperative LSCI measurements and postoperative outcomes of total thyroidectomy patients. Methods: Seventy-two thyroidectomy patients were included in this study. After thyroid resection, an LSCI device was used to image all parathyroid glands identified, and a speckle contrast value was calculated for each. An average value was calculated for each patient, and the data were grouped according to whether the patient had normal (16-77 pg/mL) or low levels of parathyroid hormone (PTH) measured on postoperative day 1 (POD1). The aim of this study was to establish a speckle contrast threshold for classifying a parathyroid gland as adequately perfused and to determine how many such glands are required for normal postoperative parathyroid function. Results: A speckle contrast limit of 0.186 separated the normoparathyroid and hypoparathyroid groups with 87.5% sensitivity and 84.4% specificity: 7 of 8 patients with low PTH on POD1 had an average parathyroid speckle contrast above this limit, while 54 of 64 patients with normal postoperative PTH had an average parathyroid speckle contrast below this limit. Taking this value as the threshold for adequate parathyroid perfusion, it was determined that only one vascularized gland was needed for normal postoperative parathyroid function: 64 of 69 patients (92.8%) with at least one vascularized gland (determined by LSCI) had normal postoperative PTH, while all 3 patients (100%) with no vascularized glands had low postoperative PTH. Overall, the rates of temporary and permanent hypoparathyroidism in this study were 8.3% and 1.4%, respectively. Conclusions: LSCI is a promising technique for assessing parathyroid gland vascularity. It has the potential to help reduce the incidence of hypocalcemia after thyroidectomy by providing surgeons with additional information during surgery to aid in the preservation of parathyroid function.

Development of a Preclinical Laser Speckle Contrast Imaging Instrument for Assessing Systemic and Retinal Vascular Function in Small Rodents.

PurposeTo develop and test a non-contact, contrast-free, retinal laser speckle contrast imaging (LSCI) instrument for use in small rodents to assess vascular anatomy, quantify hemodynamics, and measure physiological changes in response to retinal vascular dysfunction over a wide field of view (FOV).MethodsA custom LSCI instrument capable of wide-field and non-contact imaging in small rodents was constructed. The effect of camera gain, laser power, and exposure duration on speckle contrast variance was standardized before the repeatability of LSCI measurements was determined in vivo. Finally, the ability of LSCI to detect alterations in local and systemic vascular function was evaluated using a laser-induced branch retinal vein occlusion and isoflurane anesthesia model, respectively.ResultsThe LSCI system generates contrast-free maps of retinal blood flow with a 50° FOV at >376 frames per second (fps) and under a short exposure duration (>50 µs) with high reliability (intraclass correlation R = 0.946). LSCI was utilized to characterize retinal vascular anatomy affected by laser injury and longitudinally measure alterations in perfusion and blood flow profile. Under varied doses of isoflurane, LSCI could assess cardiac and systemic vascular function, including heart rate, peripheral resistance, contractility, and pulse propagation.ConclusionsWe present a LSCI system for detecting anatomical and physiological changes in retinal and systemic vascular health and function in small rodents.Translational RelevanceDetecting and quantifying early anatomical and physiological changes in vascular function in animal models of retinal, systemic, and neurodegenerative diseases could strengthen our understanding of disease progression and enable the identification of new prognostic and diagnostic biomarkers for disease management and for assessing treatment efficacies.

Blood Perfusion of Random Skin Flaps in Humans-In Vivo Assessment by Laser Speckle Contrast Imaging.

The viability of random skin flaps (RSFs) depends on an adequate perfusion pressure to avoid necrosis. Laser speckle contrast imaging is a new method to monitor skin flap microcirculation. The authors aimed to use laser speckle contrast imaging in evaluating the correlation between the perfusion pressure and the length-to-width ratio (LTWR) of RSFs. Sixty patients submitted to flaps were included: 20 advancement, 20 rotation, and 20 transposition flaps. Laser speckle contrast imaging measurements of perfusion were obtained-after the flaps were planned, dissected, and sutured-from the base to the tip of the flaps, allowing the creation of plot charts and calculation of linear regression equations. Perfusion consistently and significantly decreased with the dissection of all flaps. A significant correlation between LTWR and perfusion was observed in undermined and sutured stages; a mathematical model was then delineated, explaining objectively the drop of perfusion along LTWR, with statistical significance, in all flaps. Laser speckle contrast imaging allows accurate, rapid, reproducible, and noncontact measurements of skin blood perfusion over RSF, ultimately leading to an optimization of skin flap planning. This study proves that variation of perfusion pressure along the flap is dependent on the LTWR in a linear decreasing function.

P.320 Risk/benefit balance of antipsychotics in the treatment of adult patients with major depressive disorder: a systematic review and meta-analysis

To explore the feasibility of a new quantitative method for microvascular function: non-invasive retinal function imaging (RFI). in sickle cell disease (SCD) patients and healthy controls and have it benchmarked against Laser Speckle Contrast Imaging (LSCI) measurements.The variability of Microvascular measurements was assessed in 8 SCD patients and 8 healthy matched controls. Measurements were conducted twice on two different study days. RFI was performed for assessment of arterial and venous retinal blood flow. LSCI measurements included post occlusive reactive hyperemia and IBH challenges. Measured variables included basal flow, flow upon occlusion-reperfusion and flow during an IBH.RFI arterial flow and venous flow and LSCI basal flow and peak flow showed excellent intra subject repeatability between days (CVC of 8.5% 9.5%, 7.6% and 7.7% respectively) and between measurements on one day (CVC of 7.0%, 7.7%, 7.6% and 4.7% respectively). RFI arterial flow (p < 0.002), and RFI venous flow (p = 0.007) differed significantly between SCD patients and controls in as did LSCI basal flow, maximal flow and delta flow during IBH (p < 0.0001).RFI showed low variability for all readout measures, comparable with most microvascular measures from LSCI. The discriminating power of the RFI between SCD patients and controls demonstrate the feasibility of this device for quantitative assessment of the microcirculation in clinical research.

Laser speckle contrast imaging, the future DBF imaging technique for TRP target engagement biomarker assays

A comparison was made between the established laser Doppler imaging (LDI) technique and the more recently developed laser speckle contrast imaging (LSCI) method to measure changes in capsaicin- and cinnamaldehyde-induced dermal blood flow (DBF) as an indicator of TRPV1 and TRPA1 activation, respectively. MethodsCapsaicin (1000 μg/20 μl) and cinnamaldehyde (10%) solutions were applied on the forearm of 16 healthy male volunteers, alongside their corresponding vehicle solutions. Pre challenge and 10, 20, 30, 40 and 60 min post challenge application, changes in DBF were assessed with the LSCI technique, followed by LDI. The area under the curve from 0 to 60 min (AUC0–60) post capsaicin and cinnamaldehyde application was calculated as a summary measure of the response. Correlation between the LDI and LSCI instrument was assessed using a simple linear regression analysis. Sample size calculations (SSC) were performed for future studies using either the LDI or LSCI technique. ResultsHigher arbitrary perfusion values were obtained with LDI compared to LSCI, yet a complete discrimination between the challenge and vehicle responses was achieved with both techniques. A strong degree of correlation was observed between LDI and LSCI measurements of the capsaicin- (R = 0.84 at Tmax and R = 0.92 for AUC0–60) and cinnamaldehyde-induced (R = 0.78 at Tmax and R = 0.81 for AUC0–60) increase in DBF. SSC revealed that LSCI requires considerably less subjects to obtain a power of 80% (about 15 versus 27 subjects in case of capsaicin and 7 versus 13 for cinnamaladehyde). ConclusionsThe LSCI technique was identified as the preferred method to capture capsaicin- and cinnamaldehyde-induced changes in DBF. Besides its reduced variability, the shorter scan time provides a major advantage, allowing real-time DBF measurements.

Comparison of laser speckle contrast imaging and laser-Doppler fluxmetry in boys and men

ObjectiveWe compare microvascular reactivity assessed by laser-Doppler fluxmetry (LDF) and laser speckle contrast imaging (LSCI) of boys and men during rest, post-occlusive reactive hyperaemia (PORH), and cycling exercise. Methods19 boys (9 ± 1 y) and 18 men (22 ± 2 y) participated. LDF and LSCI measures were taken of the forearm during rest, PORH, and exercise. ResultsFor all 3 assessments, the LSCI presented with higher flux values than the LDF for both boys and men (p < 0.001). Bland-Altman analyses indicated that there was a positive linear bias between LSCI and LDF measurements in both boys and men. Regression analyses showed that the responses for the two methods were variable, depending on the particular assessment. For instance, at rest in boys there was no relationship between LDF and LSCI (r2 = 0.002), while in men there was a strong relationship (r2 = 0.86). ConclusionsLSCI presented with higher values than LDF during rest, PORH, and exercise; the disparity between the two measures was larger as blood flow increased. The assessments were generally consistent, both methods appear to provide usable data for the assessment of microvascular reactivity in both boys and men. There are biases to each method and the data are not interchangeable between LDF and LSCI.

Robust quantitative single-exposure laser speckle imaging with true flow speckle contrast in the temporal and spatial domains.

A systematic and robust laser speckle contrast imaging (LSCI) method and procedure is presented covering the LSCI system calibration, static scattering removal, and measurement noise estimation and correction to obtain a true flow speckle contrast and the flow speed from single-exposure LSCI measurements. We advocate the use of as the speckle contrast instead of the conventional contrast K, as the former relates simply to the flow velocity and is with additive noise alone. We demonstrate the efficacy of the proposed true flow speckle contrast by imaging phantom flow at varying speeds, showing that (1) the proposed recipe greatly enhances the linear sensitivity of the flow index (inverse decorrelation time) and the linearity covers the full span of flow speeds from 0 to 40 mm/s; and (2) the true flow speed can be recovered regardless of the overlying static scattering layers and the type of speckle statistics (temporal or spatial). The fundamental difference between the apparent temporal and spatial speckle contrasts is further revealed. The flow index recovered in the spatial domain is much more susceptible to static scattering and exhibit a shorter linearity range than that obtained in the temporal domain. The proposed LSCI analysis framework paves the way to estimate the true flow speed in the wide array of laser speckle contrast imaging applications.

Reliability of vulvar blood perfusion in women with provoked vestibulodynia using laser Doppler perfusion imaging and laser speckle imaging

BackgroundMicrovascular assessment has become increasingly used in gynecology to better understand the pathophysiology of various vulvar conditions and to study sexual function. Alteration in blood perfusion of the vulvar area has been observed using laser technologies in women with provoked vestibulodynia (PVD), the leading cause of vulvar pain. However, no studies have thus far investigated the reliability of and agreement between lasers for evaluating vulvar blood perfusion. ObjectivesThe main objective was to investigate the between-session reliability of the laser Doppler perfusion imaging (LDPI) and laser speckle contrast imaging (LSCI) for assessing blood perfusion of the vulvar vestibule in women with PVD. Secondary aims were to evaluate the association and agreement between the two laser technologies. MethodsTwenty-six women with PVD participated in the study. Blood perfusion of the vulvar vestibule was assessed with LDPI and LSCI during two sessions 2 to 4 weeks apart. Blood perfusion was analyzed in five specific areas of the vulvar vestibule: 1) 3 o'clock site, 2) 6 o'clock site, 3) 9 o'clock site, 4) central area (delimited by areas 1, 2 and 3), and 5) posterior fourchette. The reliability of the measurements of the two instruments was calculated with intraclass correlation coefficients (ICCs), standard errors of measurement (SEMs) and coefficients of variation (CVs). Paired t-tests were also computed to compare the CVs of each laser technology. The association and agreement between LDPI and LSCI measurements were evaluated by Pearson's correlation coefficients and Bland-Altman plots, respectively. ResultsExcellent reliability was found for LDPI (ICCs = 0.78–0.80, p < 0.001, SEMs = 16.1–47.9) and LSCI measurements (ICCs = 0.75–0.81, p ≤ 0.001, SEMs = 17.0–52.2) for all vulvar vestibule areas. However, CVs were significantly higher using LDPI (CVs = 15.1–19.8) when compared to LSCI (CVs = 7.0–11.6) for all areas (p ≤ 0.031), except for area 4 (p = 0.079). Significant correlations were found between LDPI and LSCI for all areas (r = 0.58–0.89, p ≤ 0.003). Bland-Altman plots revealed a systematic difference between LDPI and LSCI measurements. ConclusionFindings show that both LDPI and LSCI measurements are reliable for assessing blood perfusion of the vulvar vestibule in women with PVD. The LSCI appears to be a more reliable measurement as it presents less variation than LDPI. Finally, although LDPI and LSCI measurements are related, the systematic difference observed between them makes it impossible to compare absolute units.

Retinal microcirculation imaging in sickle cell disease patients

ObjectivesTo explore the feasibility of a new quantitative method for microvascular function: non-invasive retinal function imaging (RFI). in sickle cell disease (SCD) patients and healthy controls and have it benchmarked against Laser Speckle Contrast Imaging (LSCI) measurements. MethodsThe variability of Microvascular measurements was assessed in 8 SCD patients and 8 healthy matched controls. Measurements were conducted twice on two different study days. RFI was performed for assessment of arterial and venous retinal blood flow. LSCI measurements included post occlusive reactive hyperemia and IBH challenges. Measured variables included basal flow, flow upon occlusion-reperfusion and flow during an IBH. ResultsRFI arterial flow and venous flow and LSCI basal flow and peak flow showed excellent intra subject repeatability between days (CVC of 8.5% 9.5%, 7.6% and 7.7% respectively) and between measurements on one day (CVC of 7.0%, 7.7%, 7.6% and 4.7% respectively). RFI arterial flow (p<0.002), and RFI venous flow (p=0.007) differed significantly between SCD patients and controls in as did LSCI basal flow, maximal flow and delta flow during IBH (p<0.0001). ConclusionsRFI showed low variability for all readout measures, comparable with most microvascular measures from LSCI. The discriminating power of the RFI between SCD patients and controls demonstrate the feasibility of this device for quantitative assessment of the microcirculation in clinical research.

Ergodic and non-ergodic regimes in temporal laser speckle imaging.

The non-ergodicity problem of temporal averaging in the laser speckle contrast imaging (LSCI) is discussed both theoretically and numerically. We demonstrate that temporal speckle statistics assessed within a finite time window might differ from the statistics of the speckle ensemble. The dependence of temporal speckle contrast on sample dynamics is non-monotonic and demonstrates regimes of negative (ergodic), as well as positive correlations with dynamics (non-ergodic). The ergodic regime is similar to an ensemble (spatial) averaging case and is typically assumed for interpretation of LSCI measurements. The positive relation in the non-ergodic regime is an artifact of temporal statistics which we further quantify and describe the transition between two regimes.

Laser Speckle Contrast Imaging for Monitoring Changes in Microvascular Blood Flow

Background/Aims: Microvascular blood flow is essential for healing and predicts surgical outcome. The aim of the current study was to investigate the relation between fluxes measured with the laser speckle contrast imaging (LSCI) technique and changes in absolute blood flow. In addition, we studied the reproducibility of the LSCI technique when assessing the intra-abdominal microcirculation of the pig. Methods: During trial 1, a fish gill arch was mechanically perfused with heparinized fish blood under controlled stepwise-altered flow rates alongside mechanically induced movement artefacts. The microcirculation of the fish gill was simultaneously assessed with the LSCI technique. In trial 2, microcirculation was measured in the stomach, liver, and small intestine of 10 pigs by two observers. Results: A linear correlation was observed between flux and volumetric flow. During conditions of no volumetric flow, the high recording speed with the LSCI technique registered the movement artefacts as flow signals. The LSCI measurements showed good correlation and agreement between the two observers when assessing microcirculation in the stomach, liver, and small intestine (r² = 0.857, 0.956, and 0.946; coefficients of variation = 6.0, 3.2, and 6.4%, respectively). Conclusion: Due to the non-contact and real-time assessment over large areas, LSCI is a promising technique for the intraoperative assessment of intra-abdominal microcirculation. A linear correlation between flux and volumetric flow was found, in accordance with previous experimental studies. However, movement artefacts affect flux measurements, and the choice of the sampling speed must be made with care, depending on the given setting.