We report on imaging of microcirculation by calculating the speckle variance of optical coherence tomography (OCT) structural images acquired using a Fourier domain mode-locked swept-wavelength laser. The algorithm calculates interframe speckle variance in two-dimensional and three-dimensional OCT data sets and shows little dependence to the Doppler angle ranging from 75 degrees to 90 degrees . We demonstrate in vivo detection of blood flow in vessels as small as 25 microm in diameter in a dorsal skinfold window chamber model with direct comparison with intravital fluorescence confocal microscopy. This technique can visualize vessel-size-dependent vascular shutdown and transient vascular occlusion during Visudyne photodynamic therapy and may provide opportunities for studying therapeutic effects of antivascular treatments without on exogenous contrast agent.

The spatial control of optical absorption provided by twophoton excitation (TPE) has led to tremendous advances in microscopy 1 and microfabrication 2 . Medical applications of TPE in photodynamic therapy (PDT) 3,4 have often been suggested 5-18 , but have been made impractical by the low twophoton cross-sections of photosensitiser drugs (i.e. compounds taken up by living tissues that become toxic on absorption of light). The invention of efficient two-photon activated drugs will allow precise manipulation of treatment volumes in three dimensions, to a level unattainable with current techniques. Here we present a new family of PDT drugs designed for efficient TPE, and use one of them to demonstrate selective closure of blood vessels via TPE-PDT in vivo. These conjugated porphyrin dimers have two-photon cross-sections that are more than two orders of magnitude greater than those of clinical photosensitisers 17 . This is the first demonstration of in vivo PDT using a photosensitiser engineered for efficient two-photon excitation.Photodynamic therapy is used to treat diseases characterised by neoplastic growth including various cancers, age-related macular degeneration (AMD) and actinic keratosis 3,4 . Cell death is induced by photoexcitation of a sensitiser, generally via production of singlet oxygen. In the absence of light the photosensitiser is benign, so systemic toxicity is rare and treatment may be repeated without acquired resistance. Two-photon excitation of the photosensitiser should allow greater precision than is attainable by conventional one-photon excitation, as a consequence of the quadratic dependence of TPE on the local light intensity -the amount of TPE is inversely proportional to the fourth power of the distance from the focus. In addition, the longer wavelengths associated with TPE allow treatment deeper into tissue, by minimising absorption from endogenous chromophores.High instantaneous photon densities are essential for two-photon excitation. Early TPE-PDT studies used nanosecond lasers, but the dominant effect was photothermal damage [5][6][7] . The advent of commercial femtosecond tuneable Ti:sapphire lasers has greatly facilitated the investigation of TPE-PDT, and the limiting factor has become the availability of suitable photosensitisers. The majority of chromophores possess low two-photon cross-sections, of the order of 1-100 Goeppert-Mayer units (1 GM = 10 -50 cm 4 s photon -1 ). For example, the two FDA-approved PDT photosensitisers, verteporfin and Photofrin (cross sections 50 GM and 10 GM respectively) 17 , are unlikely to be suitable for TPE-PDT, as the high light intensities needed to achieve a therapeutic effect are close to the thresholds for photothermal or photomechanical damage 18 .Several design strategies for TPE-PDT photosensitisers have been reported recently [11][12][13][14][15][16] , but few of these compounds have yet been studied in vitro 15 , and, to date, none have progressed to in vivo testing. Porphyrin derivatives are often effective PDT agents, as exemplified ...

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Campbell, B. C.V. et al. (2019) Penumbral imaging and functional outcome in patients with anterior circulation ischaemic stroke treated with endovascular thrombectomy versus medical therapy: a meta-analysis of individual patient-level data.ABSTRACT Background: CT-perfusion (CTP) and MRI may assist patient selection for endovascular thrombectomy. We aimed to establish whether imaging assessments of ischaemic core and penumbra volumes were associated with functional outcomes and treatment effect.

We optimize speckle variance optical coherence tomography (svOCT) imaging of microvasculature in high and low bulk tissue motion scenarios. To achieve a significant level of image contrast, frame rates must be optimized such that tissue displacement between frames is less than the beam radius. We demonstrate that higher accuracy estimates of speckle variance can enhance the detection of capillaries. These findings are illustrated in vivo by imaging the dorsal window chamber model (low bulk motion). We also show svOCT imaging of the nonstabilized finger (high bulk motion), using optimized imaging parameters, demonstrating better vessel detection than Doppler OCT.

Improvements in real-time Doppler optical coherence tomography (DOCT), acquiring up to 32 frames per second at 250 x 512 pixels per image, are reported using signal processing techniques commonly employed in Doppler ultrasound imaging. The ability to measure a wide range of flow velocities, ranging from less than 20 microm/s to more than 10 cm/s, is demonstrated using an 1.3 microm DOCT system with flow phantoms in steady and pulsatile flow conditions. Based on full implementation of a coherent demodulator, four different modes of flow visualization are demonstrated: color Doppler, velocity variance, Doppler spectrum, and power Doppler. The performance of the former two, which are computationally suitable for real-time imaging, are analyzed in detail under various signal-to-noise and frame-rate conditions. The results serve as a guideline for choosing appropriate imaging parameters for detecting in vivo blood flow.

Campbell, B. C. V. et al. (2018) Effect of general anaesthesia on functional outcome in patients with anterior circulation ischaemic stroke having endovascular thrombectomy versus standard care: a meta-analysis of individual patient data. Lancet Neurology, 17(1), pp. 47-53. (doi:10.1016/S1474-4422(17)30407-6) This is the author's final accepted version.There may be differences between this version and the published version. You are advised to consult the publisher's version if you wish to cite from it.http://eprints.gla.ac.uk/149670/ variables. An alternative approach using propensity-score stratification was also used. To account for between-trial variance we used mixed-effects modeling with a random effect for trial incorporated in all models. Bias was assessed using the Cochrane tool.Findings: Of 1764 patients in 7 trials, 871 were allocated to endovascular thrombectomy. After exclusion of 74 patients (72 who did not undergo the procedure and 2 with missing data on anaesthetic strategy), 236/797 (30%) of endovascular patients were treated under GA. At baseline, GA patients were younger and had shorter time to randomisation but similar pre-treatment clinical severity compared to non-GA. Endovascular thrombectomy improved functional outcome at 3 months versus standard care in both GA (adjusted common odds ratio (cOR) 1·52, 95%CI 1·09-2·11, p=0·014) and non-GA (adjusted cOR 2·33, 95%CI 1·75-3·10, p<0·001) patients. However, outcomes were significantly better for those treated under non-GA versus GA (covariate-adjusted cOR 1·53, 95%CI 1·14-2·04, p=0·004; propensitystratified cOR 1·44 95%CI 1·08-1·92, p=0·012). The risk of bias and variability among studies was assessed to be low.Interpretation: Worse outcomes after endovascular thrombectomy were associated with GA, after adjustment for baseline prognostic variables. These data support avoidance of GA whenever possible. The procedure did, however, remain effective versus standard care in patients treated under GA, indicating that treatment should not be withheld in those who require anaesthesia for medical reasons. Funding:The HERMES collaboration was funded by an unrestricted grant from Medtronic to the University of Calgary. Research in contextEvidence before this study between abolition of the thrombectomy treatment effect in MR CLEAN and no effect in THRACE. Three single-centre randomised trials of general anaesthesia versus conscious sedation found either no difference in functional outcome between groups or a slight benefit of general anaesthesia. Added value of this studyThese data from contemporary, high quality randomised trials form the largest study to date of the association between general anesthesia and the benefit of endovascular thrombectomy versus standard care. We used two different approaches to adjust for baseline imbalances (multivariable logistic regression and propensity-score stratification). We found that GA for endovascular thrombectomy, as practiced in contemporary clinical care across a wide range of expert centres during the rand...

Abstract. High-resolution mapping of microvasculature has been applied to diverse body systems, including the retinal and choroidal vasculature, cardiac vasculature, the central nervous system, and various tumor models. Many imaging techniques have been developed to address specific research questions, and each has its own merits and drawbacks. Understanding, optimization, and proper implementation of these imaging techniques can significantly improve the data obtained along the spectrum of unique research projects to obtain diagnostic clinical information. We describe the recently developed algorithms and applications of two general classes of microvascular imaging techniques: speckle-variance and phase-variance optical coherence tomography (OCT). We compare and contrast their performance with Doppler OCT and optical microangiography. In addition, we highlight ongoing work in the development of variance-based techniques to further refine the characterization of microvascular networks. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.