Relationship between the blood perfusion values determined by laser speckle imaging and laser Doppler imaging in normal skin and port wine stains

Non-invasive efficacy assessment of pulsed dye laser and photodynamic therapy for port-wine stain

Port wine stain (PWS) is a congenital vascular malformation that commonly occurs on the face and neck. Currently, the main treatments for port wine stain are pulsed dye laser (PDL) and photodynamic therapy (PDT). However, the efficacy evaluation of PWS mostly relies on the subjective judgement of clinicians, and it is difficult to accurately respond to many small changes after treatment. Therefore, some non-invasive and efficient efficacy assessment methods are also needed. With the continuous development of technology, there are currently many visualisation instruments to evaluate PWS, including dermoscopy, VISIA-CR™ system, reflectance confocal microscopy (RCM), high-frequency ultrasound (HFUS), optical coherence tomography (OCT), Photoacoustic imaging (PAI), laser speckle imaging (LSI) and laser Doppler imaging (LDI). Among them, there are simple and low-cost technologies such as dermoscopy and the VISIA-CR™ system, but they may not be able to observe the deeper structures of PWS. At this time, combining techniques such as HFUS and OCT to increase penetration depth is crucial to evaluate PWS. In the future, the combination of these different technologies could help overcome the limitations of a single technology. This article provides a systematic overview of non-invasive methods for evaluating treatment efficacy in port wine stains and summarises their advantages and disadvantages.

Multi-level optical angiography for photodynamic therapy

Blood flow imaging is widely applied in photodynamic therapy (PDT) to provide vascular morphological and statistical parameters. This approach relies on the intensity of time-domain signal differences between blood vessels and background tissues; therefore, it often ignores differences within the vasculature and cannot accommodate abundant structural information. This study proposes a multi-level optical angiography (MOA) method for PDT. It can enhance capillaries and image vessels at different levels by measuring the signal frequency shift associated with red blood cell motion. The experimental results regarding the PDT-induced chorioallantoic membrane model showed that the proposed method could not only perform multi-level angiography but also provide more accurate quantitative information regarding various vascular parameters. This MOA method has potential applications in PDT studies.

Multi-step deep neural network for identifying subfascial vessels in a dorsal skinfold window chamber model

Automatic segmentation of blood vessels in the dorsal skinfold window chamber (DWSC) model is a prerequisite for the evaluation of vascular-targeted photodynamic therapy (V-PDT) biological response. Recently, deep learning methods have been widely applied in blood vessel segmentation, but they have difficulty precisely identifying the subfascial vessels. This study proposed a multi-step deep neural network, named the global attention-Xnet (GA-Xnet) model, to precisely segment subfascial vessels in the DSWC model. We first used Hough transform combined with a U-Net model to extract circular regions of interest for image processing. GA step was then employed to obtain global feature learning followed by coarse segmentation for the entire blood vessel image. Secondly, the coarse segmentation of blood vessel images from the GA step and the same number of retinal images from the DRIVE datasets were combined as the mixing sample, inputted into the Xnet step to learn the multiscale feature predicting fine segmentation maps of blood vessels. The data show that the accuracy, sensitivity, and specificity for the segmentation of multiscale blood vessels in the DSWC model are 96.00%, 86.27%, 96.47%, respectively. As a result, the subfascial vessels could be accurately identified, and the connectedness of the vessel skeleton is well preserved. These findings suggest that the proposed multi-step deep neural network helps evaluate the short-term vascular responses in V-PDT.

Combined Fluorescence and Optoacoustic Imaging for Monitoring Treatments against CT26 Tumors with Photoactivatable Liposomes

The newly developed multimodal imaging system combining raster-scan optoacoustic (OA) microscopy and fluorescence (FL) wide-field imaging was used for characterizing the tumor vascular structure with 38/50 μm axial/transverse resolution and assessment of photosensitizer fluorescence kinetics during treatment with novel theranostic agents. A multifunctional photoactivatable multi-inhibitor liposomal (PMILs) nano platform was engineered here, containing a clinically approved photosensitizer, Benzoporphyrin derivative (BPD) in the bilayer, and topoisomerase I inhibitor, Irinotecan (IRI) in its inner core, for a synergetic therapeutic impact. The optimized PMIL was anionic, with the hydrodynamic diameter of 131.6 ± 2.1 nm and polydispersity index (PDI) of 0.05 ± 0.01, and the zeta potential between -14.9 ± 1.04 to -16.9 ± 0.92 mV. In the in vivo studies on BALB/c mice with CT26 tumors were performed to evaluate PMILs' therapeutic efficacy. PMILs demonstrated the best inhibitory effect of 97% on tumor growth compared to the treatment with BPD-PC containing liposomes (PALs), 81%, or IRI containing liposomes (L-[IRI]) alone, 50%. This confirms the release of IRI within the tumor cells upon PMILs triggering by NIR light, which is additionally illustrated by FL monitoring demonstrating enhancement of drug accumulation in tumor initiated by PDT in 24 h after the treatment. OA monitoring revealed the largest alterations of the tumor vascular structure in the PMILs treated mice as compared to BPD-PC or IRI treated mice. The results were further corroborated with histological data that also showed a 5-fold higher percentage of hemorrhages in PMIL treated mice compared to the control groups. Overall, these results suggest that multifunctional PMILs simultaneously delivering PDT and chemotherapy agents along with OA and FL multi-modal imaging offers an efficient and personalized image-guided platform to improve cancer treatment outcomes.

Monitoring perfusion and oxygen saturation in port-wine stains during vascular targeted photodynamic therapy

Background

Vascular targeted photodynamic therapy (V-PDT) is a safe and effective therapeutic modality for port-wine stains (PWS) by targetedly damaging the dilated and malformed blood vessels. This study aims to monitor and quantify the changes in oxygen saturation (StO₂), blood volume fraction (BVF) and perfusion in PWS lesions before and during V-PDT.

Methods

Microvascular parameters (i.e., StO₂ and BVF) and skin perfusion were measured noninvasively by using diffuse reflectance spectroscopy (DRS) and laser Doppler imaging (LDI), respectively. The change in StO₂, BVF and perfusion that occurred in the PWS lesions of 26 patients were monitored and investigated before and during V-PDT in vivo with the systematic administration of the porphyrin-based photosensitizer HiPorfin.

Results

The mean StO₂ (P<0.05), BVF (P<0.05), and perfusion (P<0.001) in PWS lesions of all subjects significantly increased by 6%, 34%, and 113%, respectively, 3 min after the initiation of V-PDT. The StO₂ increased first and fluctuated during V-PDT. The overall trend of BVF change was consistent with the perfusion change. The BVF and the perfusion of PWS lesions increased after the initiation of V-PDT, and then gradually decreased.

Conclusions

V-PDT is an effective therapeutic modality in treating PWS. Results showed that LDI and DRS permitted the noninvasive monitoring of the changes in StO₂, BVF, and perfusion in PWS lesions during V-PDT, and these methods can be useful in facilitating our understanding of the basic physiological mechanisms during V-PDT.

Removing Subcutaneous Microvessels Using Photo-Mediated Ultrasound Therapy

BACKGROUND AND OBJECTIVES

We have developed a novel anti-vascular technique, termed photo-mediated ultrasound therapy (PUT), which utilizes nanosecond duration laser pulses synchronized with ultrasound bursts to remove the microvasculature through cavitation. The objective of the current study is to explore the potential of PUT in removing subcutaneous microvessels.

STUDY DESIGN/MATERIALS AND METHODS

The auricular blood vessels of two New Zealand white rabbits were treated by PUT with a peak negative ultrasound pressure of 0.45 MPa at 0.5 MHz, and a laser fluence of 0.056 J/cm2 at 1064 nm for 10 minutes. Blood perfusion in the treated area was measured by a commercial laser speckle imaging (LSI) system before and immediately after treatment, as well as at 1 hour, 3 days, 2 weeks, and 4 weeks post-treatment. Perfusion rates of 38 individual vessels from four rabbit ears were tracked during this time period for longitudinal assessment.

RESULTS

The measured perfusion rates of the vessels in the treated areas, as quantified by the relative change in perfusion rate, showed a statistically significant decrease for all time points post-treatment (P < 0.001). The mean decrease in perfusion is 50.79% immediately after treatment and is 32.14% at 4 weeks post-treatment. Immediately after treatment, the perfusion rate decreased rapidly. Following this, there was a partial recovery in perfusion rate up to 3 days post-treatment, followed by a plateau in the perfusion from 3 days to 4 weeks.

CONCLUSIONS

This study demonstrated that a single PUT treatment could significantly reduce blood perfusion by 32.14% in the skin for up to 4 weeks. With unique advantages such as low laser fluence as compared with photothermolysis and agent-free treatment as compared with photodynamic therapy, PUT holds the potential to be developed into a new tool for the treatment of cutaneous vascular lesions. Lasers Surg. Med. © 2020 Wiley Periodicals, LLC.

In vivo assessment of vascular-targeted photodynamic therapy effects on tumor microvasculature using ultrahigh-resolution functional optical coherence tomography

Vascular-targeted photodynamic therapy (VTP) is an emerging treatment for tumors. The change of tumor vasculatures, including a newly-formed microvascular, in response to VTP, is a key assessment parameter for optimizing the treatment effect. However, an accurate assessment of vasculature, particularly the microvasculature's changes in vivo, remains challenging due to the limited resolution afforded by existing imaging modalities. In this study, we demonstrated the in vivo imaging of VTP effects on an A431 tumor-bearing window chamber model of a mouse with an 800-nm ultrahigh-resolution functional optical coherence tomography (UHR-FOCT). We further quantitatively demonstrated the effects of VTP on the size and density of tumor microvasculature before, during, and after the treatment. Our results suggest the promising potential of UHR-FOCT for assessing the tumor treatment with VTP in vivo and in real time to achieve an optimal outcome.

Automatic protocol for quantifying the vasoconstriction in blood vessel images

Vascular targeted photodynamic therapy (V-PDT) has been successfully utilized for various vascular-related diseases. To optimize the PDT dose and treatment protocols for clinical treatments and to elucidate the biological mechanisms for V-PDT, blood vessels in the dorsal skin-fold window chamber (DSWC) of nude mice are often chosen to perform in vivo studies. In this study, a new automatic protocol to quantify the vasoconstriction of blood vessels in the DSWC model is proposed, which focused on tracking the pixels of blood vessels in pre- V-PDT images that disappear after V-PDT. The disappearing pixels indicate that the blood vessels were constricted, and thus, the vasoconstriction image for pixel distribution can be constructed. For this, the image of the circular region of interest was automatically extracted using the Hough transform. In addition, the U-Net model is employed to segment the image, and the Speeded-Up Robust Features algorithm to automatically register the segmented pre- and post- V-PDT images. The vasoconstriction of blood vessels in the DSWC model after V-PDT is directly quantified, which can avoid by the potential of generating new capillaries. The accuracy, sensitivity and specificity of the U-Net model for image segmentation are 90.64%, 80.12% and 92.83%, respectively. A significant difference in vasoconstriction between a control and a V-PDT group was observed. This new automatic protocol is well suitable for quantifying vasoconstriction in blood vessel image, which holds the potential application in V-PDT studies.

Blood flow index as an indicator of successful sciatic nerve block: a prospective observational study using laser speckle contrast imaging

BACKGROUND

Laser speckle contrast imaging allows real-time, non-invasive, quantitative measurements of regional blood flow. The objectives of this prospective observational study were to use laser speckle contrast imaging to evaluate blood flow changes after sciatic nerve block, and to determine whether this novel optical technique can evaluate block success.

METHODS

This observational study included 63 adult patients undergoing elective lower limb surgery with sciatic nerve block. Blood flow images and blood flow index (BFI) values of toes were recorded using laser speckle contrast imaging 5 min before nerve block and at 5 min intervals until 30 min after sciatic block. The sensitivity, specificity, and cut-off value of laser speckle contrast imaging for predicting successful sciatic block were determined by receiver operator characteristic (ROC) curve analysis.

RESULTS

The BFI values of toes were significantly increased at each time point after successful sciatic block, compared with the baseline value obtained 5 min before nerve block; in failed sciatic block, there were no significant differences. For successful sciatic block, the highest increase of BFI value was at the big toe. BFI increase of the big toe at 10 min after sciatic block has great potential as an indicator of block success. The area under the ROC curve was 0.954 at a cut-off value of 8.48 perfusion units (PU) with a sensitivity of 89% and a specificity of 100%.

CONCLUSIONS

Laser speckle contrast imaging might be an early, objective, quantitative, and reliable indicator of successful sciatic block. BFI increase of the big toe not reaching 8.48 PU within 10 min after sciatic block indicates block failure.

CLINICAL TRIAL REGISTRATION

NCT03169517.

Laser Doppler: A Tool for Measuring Pancreatic Islet Microvascular Vasomotion In Vivo

As a functional status of microcirculation, microvascular vasomotion is important for the delivery of oxygen and nutrients and the removal of carbon dioxide and waste products. The impairment of microvascular vasomotion might be a crucial step in the development of microcirculation-related diseases. In addition, the highly vascularized pancreatic islet is adapted to support endocrine function. In this respect, it seems possible to infer that the functional status of pancreatic islet microvascular vasomotion might affect pancreatic islet function. Analyzing the pathological changes of the functional status of pancreatic islet microvascular vasomotion may be a feasible strategy to determine contributions that pancreatic islet microcirculation makes to related diseases, such as diabetes mellitus, pancreatitis, etc. Therefore, this protocol describes using a laser Doppler blood flow monitor to determine the functional status of pancreatic islet microvascular vasomotion, and to establish parameters (including average blood perfusion, amplitude, frequency, and relative velocity of pancreatic islet microvascular vasomotion) for evaluation of the microcirculatory functional status. In a streptozotocin-induced diabetic mouse model, we observed an impaired functional status of pancreatic islet microvascular vasomotion. In conclusion, this approach for assessing pancreatic islet microvascular vasomotion in vivo may reveal mechanisms relating to pancreatic islet diseases.

Estimation of vessel diameter and blood flow dynamics from laser speckle images

Laser speckle imaging is a rapidly developing method to study changes of blood velocity in the vascular networks. However, to assess blood flow and vascular responses it is crucial to measure vessel diameter in addition to blood velocity dynamics. We suggest an algorithm that allows for dynamical masking of a vessel position and measurements of it's diameter from laser speckle images. This approach demonstrates high reliability and stability.

Intraoperative monitoring of blood perfusion in port wine stains by laser Doppler imaging during vascular targeted photodynamic therapy: A preliminary study

OBJECTIVE

The objective of this study was to monitor blood perfusion dynamics of port wine stains (PWS) during vascular targeted photodynamic therapy (V-PDT) with laser Doppler imaging (LDI).

METHODS

The PWS lesions of 30 facial PWS patients received V-PDT, while the normal skins on the forearm of 5 healthy subjects were treated as light-only controls for comparison. Furthermore, two different PWS lesions in the same individual from each of 3 PWS patients successively received laser irradiation only and V-PDT, respectively. LDI was used to monitor intraoperative blood perfusion dynamics.

RESULTS

During V-PDT, the blood perfusion (278±96 PU) in PWS lesions for 31 of 33 PWS patients significantly increased after the initiation of V-PDT treatment, then reached a peak (638±105 PU) within 10min, followed by a slow decrease to a relatively lower level (515±100 PU). Furthermore, the time for reaching peak and the subsequent magnitude of decrease in blood perfusion varied with different patients. For light-only controls, an initial perfusion peak at 3min followed by a nadir and a secondary increase were found not only in normal skin, but also in PWS lesions.

CONCLUSION

The preliminary results showed that the LDI permits non-invasive monitoring blood perfusion changes of PWS lesions during V-PDT. There was a clear trend in blood perfusion responses during V-PDT and laser irradiation. The blood perfusion changes during treatment were due to V-PDT effects as well as local temperature increase induced by laser irradiation.