Laser Speckle Perfusion Imaging Research Articles

Renal autoregulation dynamics monitored across the renal surface

We extended dynamic analysis of renal autoregulation across a spatial surface using laser speckle perfusion imaging (LSPI) of an area of the renal cortex. Anaesthetized (isoflurane) male Long‐Evans rats (N=8) had left kidneys exposed and an occluder placed around the renal artery. Monitoring included LSPI of the renal cortex, renal blood flow (RBF) and blood pressure (BP) under BP forcing during NOS inhibition by intrarenal infusion of L‐NAME (10 μg/min × 20 min then 3 μg/min i.r.a.) followed by rho‐kinase inhibition by intrarenal infusion of Y‐27632 (to achieve 10 μmol/L in RBF). Transfer function analysis was performed with either RBF or LSPI as output signals and BP as the input. Using both pairs of transfer functions, we found a significant increase in coherence (0.05 – 0.08 Hz) and a significant decrease in gain slope (0.05 – 0.15 Hz) and phase (0.1 Hz) from L‐NAME to Y‐27632. These results indicate LSPI detected decreased tubuloglomerular feedback and myogenic activity during rho‐kinase inhibition. Additionally, using LSPI we were able to identify changes at all locations within the imaging window, and using time‐varying analysis we were able to identify them temporally. We conclude that transfer function analysis of LSPI can be used to monitor renal autoregulation across spatial and temporal dimensions. This work was performed under CIHR Grant MOP‐102694, and CS was supported by an AHA predoctoral fellowship.

Internephron synchronization is modulated by nitric oxide (NO) but not increased renal perfusion pressure (RPP) or reduced renal vascular conductance

Renal autoregulation is synchronized among nearby nephrons. Synchronization comes from vasomotion conducted upstream through endothelial gap junctions. NO modulates autoregulation and the conductance of arteriolar gap junctions. We tested the role of NO in the regulation of the radius and strength of internephron synchronization. Male Long‐Evans rats (N=14) were anaesthetized (isoflurane) and their left kidneys were exposed. Cortical perfusion during control and NOS inhibition (L‐NAME, 10mg/kg i.v.) was monitored by laser speckle perfusion imaging. Clusters of synchronized nephrons were identified based on phase coherence in the myogenic and tubuloglomerular feedback operating frequencies. L‐NAME increased blood pressure and decreased renal vascular conductance. After L‐NAME clusters were smaller and more strongly synchronized. When phenylephrine (PE) was used to increase blood pressure, the number of clusters did not change from control. PE infused directly into the kidney reduced renal vascular conductance but the number of clusters and the synchronization strength also did not change. The radius of spontaneous clusters was 2.3mm (myogenic) and 1.8mm (TGF). We conclude that NO modulates internephron synchronization and that this modulation is mediated by either the effect of NO on blood flow dynamics or the effect of NO to reduce gap junction conductance. Supported by CIHR MOP‐102694.

Monitoring Microcirculation Changes in Port Wine Stains During Vascular Targeted Photodynamic Therapy by Laser Speckle Imaging

This study was conducted to test laser speckle perfusion imaging (LSPI) for imaging microcirculation and monitoring microcirculatory changes of port wine stains (PWS) during vascular targeted photodynamic therapy (V-PDT). Before and 5 min after V-PDT, PWS lesions and the corresponding contralateral healthy skins of 24 PWS patients were scanned, whereas seven PWS patients were scanned throughout V-PDT. V-PDT was conducted immediately after intravenous injection of photocarcinorin (4-5 mg kg(-1)). A 532 nm laser was used for irradiation (power density: 80-100 mW cm(-2), exposure time: 20-50 min). Before V-PDT, all 24 PWS patients demonstrated a significant difference in perfusion between the PWS lesion and the contralateral healthy control skin (1132 ± 724 and 619 ± 478 PU, respectively, P < 0.01). Five minutes after V-PDT, the mean perfusion value of the 24 PWS lesions was 1246 ± 754 PU. There was no significant difference compared to the perfusion before V-PDT (P > 0.05). During V-PDT, the perfusion of seven PWS patients increased rapidly after initiation of V-PDT, reached a maximum within 10 min, lasted for several minutes, and slowly returned to a relatively lower level at the end of V-PDT. On the basis of these results, LSPI is capable of imaging PWS microvasculature and monitoring microvascular reactivity to V-PDT.

Angiotensin II (ANG II), renal perfusion pressure (RPP) and synchronization of cortical blood flow studied using laser speckle perfusion imaging (LSPI)

Renal autoregulatory mechanisms, myogenic (MR) and tubuloglomerular feedback (TGF), are synchronized among neighboring nephrons. Using LSP I (Moor FLPI) we examined on a physiologically relevant scale the contribution of this synchronization, or coupling, to regulation and autoregulation of renal blood flow. In particular we explore the roles of RPP and ANG II on synchronization at the surface of the kidney cortex. A circular spatial filter (r=562±87 μm) was applied to each frame. Time‐frequency spectra were computed for each pixel and synchronization was assessed by frequency locking within MR and TGF bands. Five male Long Evans rats were studied during spontaneous pressure (SPN, 110±13 mmHg), reduced RPP (LP, 61±2), captopril (1 mg/kg, CAP, 89±12), and LP+CAP, 61±2 mmHg. Surface flux was 1679+227, 1386+172, 2076+126 and 1807+156 units, respectively. Synchronization occurred in both MR and TGF frequency bands at SPN. As expected power in these bands was markedly reduced at LP as was synchronization. Instead, a single dominant frequency developed and was widely synchronized. LP+CAP also showed reduced MR and TGF power, but neither a single dominant frequency nor wide synchronization. The data show that reduced RPP during ACE inhibition reduces synchronization of MR and TGF and suggest that ANG II is a major regulator of the radius of synchronization. Funded by CIHR MOP‐102694

Spatiotemporal analysis of renal autoregulation

Laser speckle perfusion imaging was used to study vascular interactions among nephrons in relation to renal autoregulation on physiologically relevant spatial and temporal scales. Surface images of stabilized rat kidneys were collected with a moorFLPI imager (Moor Instruments, UK) at a sampling rate of 1 Hz. High resolution time‐frequency spectra (TFS) were generated for each pixel after application of a 2D spatial filter. The maximum amplitude from each TFS within the two autoregulation frequency ranges (tubuloglomerular feedback: 0.02 – 0.05 Hz and the myogenic mechanism: 0.1 – 0.3 Hz) were found at each time point, and the corresponding instantaneous frequency and phase were extracted. Frequency maps at each time point were constructed to visualize how autoregulation is organized across the kidney surface. Time‐varying, wide‐radius synchronization in the form of frequency‐locked pixels was observed. The reported methods can be used to study the synchronization of nephrons and the autoregulatory components involved. It can also be used to study pathophysiological consequences of loss of synchronization. This research was supported by CIHR MOP‐102694 and the Intramural Research Program of the National Institute of Biomedical Imaging and Bioengineering, NIH.

Immediate ACL reconstruction prevents microvascular pathophysiology in the Uninjured MCL that is not fully reversed by delayed ACL reconstruction

Anterior cruciate ligament (ACL) injury induces maladaptive vascular responses that degrade medial collateral ligament (MCL) function. The purpose of this study was to determine if early or delayed ACL reconstruction can prevent or reverse the abnormal changes in vascular function that occur in the uninjured MCL after ACL injury. Twenty-four rabbits were divided into four groups (n = 6); control, ACL-deficient (ACL-X), immediate ACL reconstructed (ACL-IR) and delayed ACL reconstructed (ACL-DR). After 8 weeks, MCLs were assessed for blood flow, responses to acetylcholine (ACh) and phenylephrine (Phe) and autoregulatory responses, using laser speckle perfusion imaging. In ACL-X knees, blood flow in the MCL increased by 2.5-fold compared to control. MCL hyperemia was diminished in ACL-DR knees and was unaltered in ACL-IR knees. MCL vasculature was unresponsive to ACh and Phe in ACL-X. These responses were partially restored by ACL reconstruction. Autoregulatory responses were not significantly different between groups. ACL-DR decreased hyperemia in the MCL and partially attenuated abnormal MCL vascular responses. ACL-IR was more effective at preventing MCL hyperemia and preserving vascular responsiveness to ACh and Phe. This suggests that the vascular alterations in the uninjured rabbit MCL are largely caused by abnormal mechanical loading resulting from ACL deficiency and can be prevented through early reconstruction. Early ACL reconstruction could limit the progression of microvascular dysfunction of the MCL, and preserve physiological joint homeostasis. This might prevent joint degeneration and delay the progression of osteoarthritis.

A transmissive laser speckle imaging technique for measuring deep tissue blood flow: An example application in finger joints

Laser speckle perfusion imaging (LSPI) is a minimally invasive optical measure of relative changes in blood flow, providing real-time, high resolution, two-dimensional maps of vascular structure. Standard LSI imaging uses a light-reflective geometry that limits the measurement to a thin surface layer of 0.2-1 mm. The objective of this study was to test a new LSI instrument geometry with the laser source opposed to the image capture plane (light transmissive). Captured light then travels the entire tissue thickness (10-15 mm), sampling much deeper regions of interest than conventional optical imaging techniques. Reflective-light (conventional) and transmissive-light LSI modes were used to measure finger joint blood flow during a timed tourniquet occlusion of the brachial artery in volunteer participants. There was greatly increased visibility of vessels underlying the skin in the light-transmissive mode LSI mode. Established LSI algorithms were shown to still work in the light-transmissive mode, despite decorrelation due to finite laser coherence length and the light passing through a tissue thickness of 10-15 mm. Transmissive LSI can be used to measure blood flow deep (10-15 mm) into tissues. This could be useful for non-invasive measurements of finger joint synovial blood flow in diagnosing and treating peripheral vascular disorders, such as rheumatoid arthritis.

Biophotonics Modalities for High-Resolution Imaging of Microcirculatory Tissue Beds Using Endogenous Contrast: A Review on Present Scenario and Prospects

The microcirculation is a complex system, and the visualization of microcirculation has great significance in improving our understanding of pathophysiological processes in various disease conditions, in both clinical and fundamental studies. A range of techniques are available or emerging for investigating different aspect of the microcirculation in animals and humans. This paper reviews the recent developments in the field of high-resolution and high-sensitive optical imaging of microcirculatory tissue beds, emphasizing technologies that utilize the endogenous contrast mechanism. Optical imaging techniques such as intravital microscopy, Capillaroscopy, laser Doppler perfusion imaging, laser speckle perfusion imaging, polarization spectroscopy, photo-acoustic tomography, and various implementations of optical coherence tomography based on Doppler and speckle contrast imaging are presented together with their prospectives and challenges.

Portable laser speckle perfusion imaging system based on digital signal processor

The ability to monitor blood flow in vivo is of major importance in clinical diagnosis and in basic researches of life science. As a noninvasive full-field technique without the need of scanning, laser speckle contrast imaging (LSCI) is widely used to study blood flow with high spatial and temporal resolution. Current LSCI systems are based on personal computers for image processing with large size, which potentially limit the widespread clinical utility. The need for portable laser speckle contrast imaging system that does not compromise processing efficiency is crucial in clinical diagnosis. However, the processing of laser speckle contrast images is time-consuming due to the heavy calculation for enormous high-resolution image data. To address this problem, a portable laser speckle perfusion imaging system based on digital signal processor (DSP) and the algorithm which is suitable for DSP is described. With highly integrated DSP and the algorithm, we have markedly reduced the size and weight of the system as well as its energy consumption while preserving the high processing speed. In vivo experiments demonstrate that our portable laser speckle perfusion imaging system can obtain blood flow images at 25 frames per second with the resolution of 640 × 480 pixels. The portable and lightweight features make it capable of being adapted to a wide variety of application areas such as research laboratory, operating room, ambulance, and even disaster site.

What is the optimal anesthetic protocol for measurements of cerebral autoregulation in spontaneously breathing mice?

Autoregulation, an important feature of the cerebral circulation, is affected in many diseases. Since genetically modified mice are a fundamental tool in biomedical research, including neuro(bio)logy also in this specie measurements of cerebral autoregulation (CA) are mandatory. However, this requires anesthesia that unfortunately significantly impacts cerebral perfusion and consequently might distort CA measurements directly or by altering arterial pCO(2). The latter can be avoided by artificial ventilation but requires several control measurements of blood gases, each consuming at least 100 μl of blood or 5% of a mouse's blood volume. To avoid such diagnostic hemorrhage, we systematically analyzed the effect of different common anesthetic protocols used for rodents in spontaneously breathing mice on CA measured with Laser speckle perfusion imaging. Halothane, Isoflurane and Pentobarbital abrogated CA and Ketamin/Xylazine as well as Chloralose had a moderate reproducibility. In contrast, the rather rarely used anesthetic Ethomidate applied in low doses combined with local anesthetics had the best reproducibility. Although with this anesthesia the lower CA limit was lower than with Ketamin/Xylazine and Chloralose as reported in the handful of papers so far dealing with CA in mice, we suggest Ethomidate as the anesthetic of choice for CA measurements in spontaneously breathing mice.

Early Protective Effect of Bone Marrow Mononuclear Cells Against Ischemic White Matter Damage Through Augmentation of Cerebral Blood Flow

To investigate the efficacy of bone marrow mononuclear cell (BMMNC) treatment against ischemic white matter (WM) damage in a hypoperfused brain. Mice were administered intravenous treatment of vehicle, spleen-derived marrow mononuclear cells (MNCs), or BMMNCs (5 × 10⁶ cells) obtained from enhanced green fluorescent protein transgenic mice 24 hours after bilateral common carotid artery stenosis (BCAS), and then euthanized at either 1 day or 30 days after treatment. Laser speckle perfusion imaging analyses revealed marked recovery of cerebral blood flow (CBF) in the early phase after BMMNC treatment (6 hours after administration), before histological evidence of angiogenesis was assessed by fluorescein-isothiocyanate-dextran perfusion assay. BMMNC treatment induced an increase in vascular endothelial growth factor and Ser1177 phosphorylated endothelial nitric oxide synthase levels in the BCAS-induced mouse brains at 1 day after the treatment. BCAS-induced ischemic WM lesions were significantly improved 30 days after BMMNC treatment despite any evidence of direct structural incorporation of donor BMMNCs into endothelial cells and oligodendrocytes. Instead, enhanced green fluorescent protein-positive donor cells with morphological features of pericytes were observed in the vessel walls. Post-BMMNC administration of an NOS inhibitor abolished early CBF recovery and produced protective effects against ischemic WM damage. BMMNC treatment provides marked protection against ischemic WM damage, enhancing CBF in the early phase and in subsequent angiogenesis, both of which involve nitric oxide synthase activation. These findings suggest promise for the application of BMMNCs for subcortical ischemic vascular dementia.

The Importance of Engraftment in Flap Revascularization: Confirmation by Laser Speckle Perfusion Imaging

The delivery of proangiogenic agents in clinical trials of wound healing has produced equivocal results, the lack of real-time assessment of vascular growth is a major weakness in monitoring the efficacy of therapeutic angiogenesis, and surgical solutions fall short in addressing the deficiency in microvascular blood supply to ischemic wounds. Therefore, elucidation of the mechanisms involved in ischemia-induced blood vessel growth has potential diagnostic and therapeutic implications in wound healing. Three surgical models of wound ischemia, a cranial-based myocutaneous flap, an identical flap with underlying silicone sheeting to prevent engraftment, and a complete incisional flap without circulation were created on C57BL6 transgenic mice. Laser speckle contrast imaging was utilized to study the pattern of ischemia and return of revascularization. Simultaneous analysis of wound histology and microvascular density provided correlation of wound perfusion and morphology. Creation of the peninsular-shaped flap produced a gradient of ischemia. Laser speckle contrast imaging accurately predicted the spatial and temporal pattern of ischemia, the return of functional revascularization, and the importance of engraftment in distal flap perfusion and survival. Histologic analysis demonstrated engraftment resulted in flap revascularization by new blood vessel growth from the recipient bed and dilatation of pre-existing flap vasculature. Further research utilizing this model of graded wound ischemia and the technology of laser speckle perfusion imaging will allow monitoring of the real-time restitution of blood flow for correlation with molecular biomarkers of revascularization in an attempt to gain further understanding of wound microvascular biology.

Neural stimulation does not mediate attenuated vascular response in ACL‐deficient knees: Potential role of local inflammatory mediators

Chronic inflammation associated with osteoarthritis (OA) alters normal responses and modifies the functionality of the articular vasculature. Altered responsiveness of the vasculature may be due to excessive neural activity associated with chronic pain and inflammation, or from the production of inflammatory mediators which induce vasodilation. Using laser speckle perfusion imaging (LSPI), blood flow to the medial collateral ligament (MCL) of adult rabbits was measured in denervated ACL transected knees (n = 6) and compared to unoperated control (n = 6) and 6-week anterial cruciate ligament (ACL)-transected knees (n = 6). Phenylephrine and neuropeptide Y were applied to the MCL vasculature in topical boluses of 100 microL (dose range 10(-14) to 10(-8) mol and 10(-14) to 10(-9) mol, respectively). Denervation diminished vasoconstrictive responsiveness to phenylephrine compared to both control and ACL-transected knees. Denervation minimally enhanced vascular responses to neuropeptide Y (NPY) compared to ACL deficiency alone, which nevertheless remained significantly diminished from control responses. To evaluate the potential role of inflammatory dilators in the diminished contractile responses, phenylephrine was coadministered with histamine, substance P, and prostaglandin E(2). High-dose histamine, and low-dose substance P and PGE(2) were able to inhibit contractile responses in the MCL of control knees. Excessive neural input does not mediate diminished vasoconstrictive responses in the ACL transected knee; inflammatory mediators may play a role in the deficient vascular responsiveness of the ACL transected knee.

Comparison of instruments for investigation of microcirculatory blood flow and red blood cell concentration

The use of laser Doppler perfusion imaging (LDPI) and laser speckle perfusion imaging (LSPI) is well known in the noninvasive investigation of microcirculatory blood flow. This work compares the two techniques with the recently developed tissue viability (TiVi) imaging system, which is proposed as a useful tool to quantify red blood cell concentration in microcirculation. Three systems are evaluated with common skin tests such as the use of vasodilating and vasoconstricting drugs (methlynicotinate and clobetasol, respectively) and a reactive hyperaemia maneuver (using a sphygmomanometer). The devices investigated are the laser Doppler line scanner (LDLS), the laser speckle perfusion imager (FLPI)-both from Moor Instruments (Axminster, United Kingdom)-and the TiVi imaging system (WheelsBridge AB, Linkoping, Sweden). Both imaging and point scanning by the devices are used to quantify the provoked reactions. Perfusion images of vasodilatation and vasoconstriction are acquired with both LDLS and FLPI, while TiVi images are acquired with the TiVi imager. Time acquisitions of an averaged region of interest are acquired for temporal studies such as the reactive hyperaemia. In contrast to the change in perfusion over time with pressure, the TiVi imager shows a different response due its measurement of blood concentration rather than perfusion. The responses can be explained by physiological understanding. Although the three devices sample different compartments of tissue, and output essentially different variables, comparisons can be seen between the three systems. The LDLS system proves to be suited to measurement of perfusion in deeper vessels, while FLPI and TiVi showed sensitivity to more superficial nutritional supply. LDLS and FLPI are insensitive to the action of the vasoconstrictor, while TiVi shows the clear boundaries of the reaction. Assessment of the resolution, penetration depth, and acquisition rate of each instrument show complimentary features that should be taken into account when choosing a system for a particular clinical measurement.

121 Laser Speckle Perfusion Imaging of Wound Healing in a Porcine Model

A Laser Speckle Perfusion Imaging (LSPI) system has been developed to achieve rapid, high-resolution, noninvasive imaging of tissue blood flow. This study was designed to evaluate LSPI for monitoring dermal blood flow during the wound healing process in a well-established porcine model. Full-thickness excisional wounds (2 × 2 cm) were created on the dorsal skin of 11 juvenile female red Duroc pigs. The skin wounds were imaged weekly with the LSPI system until day 49 postwounding. Blood flow values for the wounds were normalized using the values from the surrounding healthy skin to account for variations in systemic perfusion from one scan date to the next. An average normalized perfusion value was obtained from the scans of all animals for each time point. Wound perfusion at the time of reepithelialization reached ∼165% of the surrounding skin (p < 0.001). This elevation in wound perfusion slowly and steadily decreased over time, until day 49 postwounding, at which time the values returned to normal. This trend toward decreased wound perfusion over time has previously been reported in human burn wounds using the LSPI instrument. Further, the LSPI data from this study and from other human studies correlates well with data generated using the more widely established Laser Doppler Imaging (LDI) technique. The faster scan time and higher resolution of the LSPI method provides a distinct clinical advantage, both in terms of patient comfort and for reliably matching perfusion characteristics to their associated anatomical features. The fast temporal response of the LSPI instrument could be used to monitor vascular responses to mechanical or pharmacological interventions to study dynamic vascular changes to damaged tissues. This study validates LSPI as a tool to measure blood flow in skin wounds and further supports the use of the juvenile female pig as a model of excisional wound healing, yielding results comparable to healing in humans. Acknowledgments: Funding provided by CIHR, AHFMR, and NSERC

Nerve growth factor improves ligament healing

Previous work has shown that innervation participates in normal ligament healing. The present study was performed to determine if exogenous nerve growth factor (NGF) would improve the healing of injured ligament by promoting reinnervation, blood flow, and angiogenesis. Two groups of 30 Sprague-Dawley rats underwent unilateral medial collateral ligament transection (MCL). One group was given 10 microg NGF and the other was given PBS via osmotic pump over 7 days after injury. After 7, 14, and 42 days, in vivo blood flow was measured using laser speckle perfusion imaging (LSPI). Morphologic assessments of nerve density, vascularity, and angiogenesis inhibitor production were done in three animals at each time point by immunohistochemical staining for the pan-neuronal marker PGP9.5, the endothelial marker vWF, and the angiogenesis inhibitor thrombospondin-2 (TSP-2). Ligament scar material and structural mechanical properties were assessed in seven rats at each time point. Increased nerve density was promoted by NGF at both 14 and 42 days. Exposure to NGF also led to increased ligament vascularity, as measured by histologic assessment of vWF immunohistochemistry, although LSPI-measured blood flow was not significantly different from controls. NGF treatment also led to decreased expression of TSP-2 at 14 days. Mechanical testing revealed that exposure to NGF increased failure load by 40%, ultimate tensile strength by 55%, and stiffness by 30% at 42 days. There were no detectable differences between groups in creep properties. The results suggest that local application of NGF can improve ligament healing by promoting both reinnervation and angiogenesis, and results in scars with enhanced mechanical properties.

Endothelial dysfunction and decreased vascular responsiveness in the anterior cruciate ligament-deficient model of osteoarthritis

Chronic inflammation associated with osteoarthritis (OA) may alter normal vascular responses and contribute to joint degradation. Vascular responses to vasoactive mediators were evaluated in the medial collateral ligament (MCL) of the anterior cruciate ligament (ACL)-deficient knee. Chronic joint instability and progressive OA were induced in rabbit knees by surgical transection of the ACL. Under halothane anesthesia, laser speckle perfusion imaging (LSPI) was used to measure MCL blood flow in unoperated control (n = 12) and 6-wk ACL-transected knees (n = 12). ACh, bradykinin, histamine, substance P (SP), and prostaglandin E(2) (PGE(2)) were applied to the MCL vasculature in topical boluses of 100 microl (dose range 10(-14) to 10(-8) mol). In normal joints, ACh, bradykinin, histamine, and PGE(2) evoked a dilatory response. Substance P caused a biphasic response that was dilatory from 10(-14) to 10(-11) mol and constricting at higher doses. In ACL-deficient knees, ACh, bradykinin, histamine, and SP decreased perfusion, whereas PGE(2) had a biphasic response that decreased perfusion at 10(-14) to 10(-11) mol and was dilatory at higher concentrations. Sodium nitroprusside increased perfusion in resting and phenylephrine-precontracted vessels with no significant differences between ACL-transected and control knees. Femoral artery occlusion and release increased perfusion by 74.3 +/- 11.1% in control knees but only by 25.8 +/- 4.4% in ACL-deficient knees. The altered responsiveness of the MCL vasculature to these inflammatory mediators may indicate endothelial dysfunction in the MCL, which may contribute to the progression and severity of OA and to the adaptation of the joint in an altered mechanical environment.

Kinetics of blood flow during healing of excisional full‐thickness skin wounds in pigs as monitored by laser speckle perfusion imaging

The laser speckle perfusion imaging (LSPI) system is a new, non-invasive technique for rapidly and reproducibly measuring tissue perfusion. The high resolution and frame rate of the LSPI overcome many of the limitations of traditional laser Doppler imaging techniques. Therefore, LSPI is a useful means for evaluating blood flow in a variety of situations. The present study investigates the ability of the LSPI system to detect temporal changes in blood flow during the healing of cutaneous wounds in a well-characterized animal model. Full-thickness excisional skin wounds (2 x 2 cm) were created on the backs of juvenile female red Duroc pigs. Every week post-injury, the wounds were measured and photographed, and normalized blood flow values were determined using the LSPI system. Tissue perfusion values were available after complete re-epithelialization and removal of the eschar, at day 21. At this point, wound blood flow was significantly elevated as compared with the surrounding, uninvolved skin. Wound blood flow declined steadily during healing, and approached normal values by day 35 post-injury. The kinetics of blood flow during excisional wound healing in the red Duroc model are comparable with that previously observed in laser Doppler imaging of healing human skin wounds and hypertrophic scars. These results therefore confirm that the red Duroc is a good model of human wound healing, and further indicates that the LSPI is an excellent technique for evaluating angiogenesis and neovascularization during healing in this and other models.

A comparison of two laser-based methods for determination of burn scar perfusion: Laser Doppler versus laser speckle imaging

Laser Doppler perfusion imaging (LDI) is an established technique for early assessment of burn depth to help determine a course of treatment. Laser speckle perfusion imaging (LSPI) is an alternative laser based, non-invasive perfusion monitoring technique that offers rapid and high resolution images of tissue. We have evaluated the ability of the LSPI instrument in determining and monitoring burn scar perfusion over time and compared it with the LDI instrument as a standard. Methods: Ten patients with hypertrophic burn scars (time since injury: 1–8 months) were recruited. Burn scars were scanned with both instruments (LSPI and LDI) monthly over a period of 11 months. Clinical grading of the burn scars was assessed on every scan date using the Vancouver burn scar scale. Results: Comparison of the perfusion values determined by each instrument shows a strong positive correlation, r 2 = 0.86 ( n = 63). Each instrument's output also correlated significantly with the clinical grading of the scar, indicating the expected decrease in perfusion as the clinical condition of the scars improved with time. Significance: The new LSPI instrument compared favorably with the established LDI instrument, yielding similar results. The considerably faster scan time and higher resolution of the LSPI method provides a distinct clinical advantage, both in terms of patient comfort and for reliably matching perfusion characteristics to their associated anatomical features. The fast temporal response of the LSPI instrument could be used to monitor near real-time responses to mechanical or pharmacological interventions to study dynamic vascular changes to burn damaged tissues.

A Laser Speckle Imaging Technique for Measuring Tissue Perfusion

Laser Doppler imaging (LDI) has become a standard method for optical measurement of tissue perfusion, but is limited by low resolution and long measurement times. We have developed an analysis technique based on a laser speckle imaging method that generates rapid, high-resolution perfusion images. We have called it laser speckle perfusion imaging (LSPI). This paper investigates LSPI output and compares it to LDI using blood flow models designed to simulate human skin at various levels of pigmentation. Results show that LSPI parameters can be chosen such that the instrumentation exhibits a similar response to changes in red blood cell concentration (0.1%-5%, 200 microL/min) and velocity (0-800 microL/min, 1% concentration) and, given its higher resolution and quicker response time, could provide a significant advantage over LDI for some applications. Differences were observed in the LDI and LSPI response to tissue optical properties. LDI perfusion values increased with increasing tissue absorption, while LSPI perfusion values showed a slight decrease. This dependence is predictable, owing to the perfusion algorithms specific to each instrument, and, if properly compensated for, should not influence each instrument's ability to measure relative changes in tissue perfusion.