Intraoperative Tissue Perfusion Measurement by Laser Speckle Imaging: A Potential Aid for Reducing Postoperative Complications in Free Flap Breast Reconstruction

Validity of laser speckle contrast imaging for predicting wound healing potential in burns: A critical examination

BACKGROUND

Accurate assessment of burn depth is imperative for the efficacious management of burns. Although clinical assessment is commonly used, its accuracy ranges only between 50 % and 70 %. Laser Doppler imaging (LDI) is considered as a gold standard - with an accuracy exceeding 95 %, - for the objective measurement of Healing Potential (HP), HP being the output of the LDI device, as colour-coded on LDI blood flow images. Despite its proven efficacy, widespread adoption is impeded by practical challenges. Laser Speckle Contrast Imaging (LSCI) emerges as a possible alternative. This study investigated the performance and accuracy of LSCI in comparison with LDI for predicting the HP of burns; LDI was assumed to provide 'ground truth' for the assessment of HP.

METHODS

Hospitalized burn patients underwent LDI and LSCI scans between day 2 and day 5 postburn. Analysis involved selecting corresponding regions of interest (ROI) in target wounds prioritized by LDI and LSCI perspectives.

RESULTS

In 19 patients, 112 ROI within LDI-priority ranges were collected from 50 target wounds. 130 ROI within LSCI-priority ranges were collected from 52 target wounds. Positive predictive values (PPV) were low, at only 50.8 % and 68.2 % for HP14-21 and HP21, respectively, and 86.9 % for HP14.

CONCLUSION

Objective assessment by LSCI for burns is not recommended, as it fails to detect deep dermal blood flow, leading to an overestimation of burn severity and potential inadequacies in therapy.

Mitigation of Motion Artifacts in Handheld Laser Speckle Contrast Imaging Illustrated on Psoriasis Lesions

BACKGROUND

Handheld laser speckle contrast imaging (LSCI) is crucial in clinical settings, but motion artifacts (MA) can compromise perfusion image reliability. Current prevention and suppression methods are often impractical or complex. Machine vision techniques, promising in medical imaging, could improve signal quality, but their use in suppressing MA is still unexplored.

OBJECTIVE

We propose an innovative method based on linear regression for MA correction (MAC) in LSCI and validate it in vivo.

METHODS

We performed paired handheld and mounted LSCI measurements on 14 subjects with psoriasis using the previously validated handheld perfusion imager (HAPI). By marking lesion boundaries for clinical purposes, the HAPI used a monochromatic camera for both speckle imaging and motion detection, simplifying hardware requirements. Accurate estimation of relative displacements between the test object and LSCI probe allowed us to apply MAC to the perfusion images.

RESULTS

Local perfusion values correlated with applied speed were used to calculate and correct MA. The difference between mean perfusion in handheld and mounted modes after MAC significantly decreased (median error 14.2 perfusion units (p.u.) on lesions before correction (p 0.0005) and 0.5 p.u. after correction (p=0.2)).

CONCLUSION

The findings provide evidence for robust handheld LSCI and validate the MA technique in psoriasis case. Of the two causes of MA-on-surface speeds and wavefront tilt-we address the former and correct mean perfusion, assuming constant temporal perfusion at each location.

SIGNIFICANCE

We describe a practical, non-contact, marker-free technique for reliable handheld perfusion imaging, supporting further clinical translation in plastic surgery and burns.

In vivo laser speckle contrast imaging of microvascular blood perfusion using a chip-on-tip camera

Laser speckle contrast imaging (LSCI) is an important non-invasive capability for real-time imaging for tissue-perfusion assessment. Yet, the size and weight of current clinical standard LSCI instrumentation restricts usage to mainly peripheral skin perfusion. Miniaturization of LSCI could enable hand-held instrumentation to image internal organ/tissue to produce accurate speckle-perfusion maps. We characterized a 1mm2 chip-on-tip camera for LSCI of blood perfusion in vivo and with a flow model. A dedicated optical setup was built to compare chip-on-tip camera to a high specification reference camera (GS3) for LSCI. We compared LSCI performance using a calibration standard and a flow phantom. Subsequently the camera assessed placenta perfusion in a small animal model. Lastly, a human study was conducted on the perfusion in fingertips of 13-volunteers. We demonstrate that the chip-on-tip camera can perform wide-field, in vivo, LSCI of tissue perfusion with the ability to measure physiological blood flow changes comparable with a standard reference camera.

Hyperspectral Imaging Allows Evaluation of Free Flaps in Craniomaxillofacial Reconstruction

INTRODUCTION

Treatment of extended defects after tumor resection in oral, maxillofacial, and facial surgery (craniomaxillofacial) is usually performed by free microvascular flaps. Evaluation of flap survival is crucial, especially in the first hours after insertion and connection. For flap evaluation various invasive and noninvasive methods have been developed. This retrospective clinical study examined the ability of a hyperspectral imaging (HSI) camera (Tivita, Diaspective Vision, Germany) to assess postoperative flap properties in comparison to established clinical parameters.

MATERIALS AND METHODS

Thirteen patients with tumor resection and free flap reconstruction were included for camera analysis and another 10 patients as control group. For this purpose, at defined time intervals and under standardized conditions, recordings of transplants 3 to 100 hours postoperatively were performed. Images were used to examine oxygenation (StO 2 %), tissue hemoglobin index, tissue water index, near infrared range perfusion index of free flaps quantitatively and qualitatively.

RESULTS

HSI provides values differing between patients observed with no intraindividual significant difference. After 24 hours a mean reduction of 16.77% for StO 2 %, 9.16% for tissue hemoglobin index and 8.46% was observed, going in line with no loss of flap was noted in the observation period.

CONCLUSION

HSI is suitable as a noninvasive measure for the evaluation of free flaps in craniomaxillofacial surgery in case of stable imaging conditions with respect to light, surrounding and position of the camera. However, clinical measurements are still the method of choice.

[New Technologies in Microsurgery: Potential, Indications and Economical Aspects - Report of the Consensus Workshop of the German-Speaking Society for Microsurgery of Peripheral Nerves and Vessels (DAM)]

Recently, several new technologies to support microsurgeons have received European market approval. This article summarizes and discusses the impressions of an expert panel to classify the potential of new technologies in terms of benefits for the surgeon, specific indications and economic aspects during the 42nd Annual Meeting of the German-speaking Working Group for Microsurgery of Peripheral Nerves and Vessels (DAM) in Graz, Austria. In general, the expert panel addressed the principles and prerequisite for the successful establishment of new technologies and, in particular, novel optical and robotic systems. For this purpose, the current scientific literature was reviewed and initial clinical experience in the context of case series and retrospective studies was presented by the members of the expert panel. In the ensuing discussion, it was pointed out that it will first be necessary to identify patient subgroups in which the use of the new technologies is most likely to achieve a clinical benefit. Since clinical approval has already been granted for some systems, an approach can be developed for immediate clinical application from the simplest possible use to ever finer applications, i. e. from microsurgery to supermicrosurgery. Initially, funding for cost-intensive systems would presumably not be possible through revenue from standard care, but only through grants or subsidized clinical trials. In a final survey, the majority of meeting participants see the need for a price reduction of both visualization and surgical robotics technologies to enable widespread clinical establishment. Likewise, a majority of participants would prefer a combination of an exoscope or robotic microscope and a surgical robot for clinical use. The present consensus work addresses the development of a strategy for the effective establishment of new technologies, which should further increase the surgical quality of selected interventions.

Intraoperative Optical and Fluorescence Imaging of Blood Flow Distributions in Mastectomy Skin Flaps for Identifying Ischemic Tissues

SUMMARY

Insufficient blood flow causes mastectomy skin flap necrosis in 5 to 30 percent of cases. Fluorescence angiography with the injection of indocyanine green dye has shown high sensitivities (90 to 100 percent) but moderate specificities (72 to 50 percent) in predicting mastectomy skin flap necrosis. However, a number of challenging issues limit its wide acceptance in clinical settings, including allergic reaction, short time-window for observation, and high cost for equipment and supplies. An emerging inexpensive speckle contrast diffuse correlation tomography technology enables noninvasive, noncontact, and continuous three-dimensional imaging of blood flow distributions in deep tissues. This preliminary study tested the hypothesis that speckle contrast diffuse correlation tomography and indocyanine green-fluorescence angiography measurements of blood flow distributions in mastectomy skin flaps are consistent. Eleven female patients undergoing skin-sparing or nipple-sparing mastectomies were imaged sequentially by the dye-free speckle contrast diffuse correlation tomography and dye-based commercial fluorescence angiography (SPY-PHI). Resulting images from these two imaging modalities were co-registered based on the ischemic areas with the lowest blood flow values. Because the ischemic areas have irregular shapes, a novel contour-based algorithm was used to compare three-dimensional images of blood flow distribution and two-dimensional maps of indocyanine green perfusion. Significant correlations were observed between the two measurements in all contours from a selected area of 10 × 10 mm 2 with the lowest blood flow ( r ≥ 0.78; p < 0.004), suggesting that speckle contrast diffuse correlation tomography provides the information for identifying ischemic tissues in mastectomy skin flaps. With further optimization and validation in large populations, speckle contrast diffuse correlation tomography may ultimately be used as a noninvasive and inexpensive imaging tool for intraoperative assessment of skin flap viability to predict mastectomy skin flap necrosis.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Diagnostic, II.

Ex Vivo Thrombolysis to Salvage Free Flaps Using Machine Perfusion: A Pilot Study in a Porcine Model

BACKGROUND

 Mechanical evacuation of capillary thrombi in free flaps is difficult, and often requires thrombolytic therapy. Utilizing machine perfusion systems, the possibility rises to salvage free flaps ex vivo by administering high doses of thrombolytic agents. The primary aim of this pilot study in a porcine model is to investigate the feasibility of ex vivo thrombolysis using an extracorporeal perfusion machine.

METHODS

 A model of stasis-induced thrombosis was used in 12 free rectus abdominis flaps harvested from six Dutch Landrace pigs. Compromised flaps were ex vivo perfused with University of Wisconsin preservation solution and treated according to the following study groups: (1) 1 mg of tissue plasminogen activator (t-PA) as additive, (2) 3 mg of t-PA as an additive, and (3) no thrombolytic additive. Microcirculation was assessed using near-infrared fluorescence angiography.

RESULTS

 Pedicled abdominal flaps were created and thrombus formation was successfully induced. Eleven abdominal flaps were perfused using the modified heart-lung machine setup. Near-infrared fluorescence angiography showed delayed or no filling was noted in the control group. In comparison, the flaps which were perfused with 1 mg t-PA or 3 mg t-PA as additive showed increased fluorescence intensity curves.

CONCLUSION

 This pilot study in a porcine model presents a reliable and reproductive stasis-induced thrombosis model in free flaps. By adding t-PA to a custom-made extracorporeal perfusion system, the indocyanine green fluorescence intensity curves increased of all flaps that were perfused with different dosages of t-PA as additives, indicating restoration of capillary pressure and microcirculatory inflow.

Inhibition of microRNA-29b suppresses oxidative stress and reduces apoptosis in ischemic stroke

MicroRNAs (miRNAs) regulate protein expression by antagonizing the translation of mRNAs and are effective regulators of normal nervous system development, function, and disease. MicroRNA-29b (miR-29b) plays a broad and critical role in brain homeostasis. In this study, we tested the function of miR-29b in animal and cell models by inhibiting miR-29b expression. Mouse models of middle cerebral artery occlusion were established using the modified Zea-Longa suture method. Prior to modeling, 50 nmol/kg miR-29b antagomir was injected via the tail vein. MiR-29b expression was found to be abnormally increased in ischemic brain tissue. The inhibition of miR-29b expression decreased the neurological function score and reduced the cerebral infarction volume and cell apoptosis. In addition, the inhibition of miR-29b significantly decreased the malondialdehyde level, increased superoxide dismutase activity, and Bcl-2 expression, and inhibited Bax and Caspase3 expression. PC12 cells were treated with glutamate for 12 hours to establish in vitro cell models of ischemic stroke and then treated with the miR-29 antagomir for 48 hours. The results revealed that miR-29b inhibition in PC12 cells increased Bcl-2 expression and inhibited cell apoptosis and oxidative damage. These findings suggest that the inhibition of miR-29b inhibits oxidative stress and cell apoptosis in ischemic stroke, producing therapeutic effects in ischemic stroke. This study was approved by the Laboratory Animal Care and Use Committee of the First Affiliated Hospital of Zhengzhou University (approval No. 201709276S) on September 27, 2017.

Flap Monitoring Using Transcutaneous Oxygen or Carbon Dioxide Measurements

Free tissue transfer is a cornerstone of complex reconstruction. In many cases, it represents the last option available for a patient and their reconstruction. At high-volume centers, the risk of free flap failure is low but its occurrence can be devastating. Currently, the mainstay for flap monitoring is the clinical examination. Though reliable when performed by experienced clinicians, the flap exam is largely subjective, is performed discontinuously, and often results in significant time delay between detection of flap compromise and intervention. Among emerging flap monitoring technologies, the most promising appear to be those that rely on noninvasive transcutaneous oxygen and carbon dioxide measurements, which provide information regarding flap perfusion. In this article, we review and summarize the literature on various techniques but primarily emphasizing those technologies that rely on transcutaneous gas measurements. We also define characteristics for the ideal flap monitoring tool and discuss critical barriers, predominantly cost, preventing more widespread utilization of adjunct monitoring technologies, and their implications.

Current and novel mapping substances in gynecologic cancer care

Many tracers have been introduced into current medical practice with the purpose of improving lymphatic mapping techniques, anatomic visualization, and organ/tissue perfusion assessment. Among them, three tracers have dominated the field: indocyanine green, technetium-99m radiocolloid (Tc99m), and blue dye. Tc99m and blue dye are used individually or in combination; however, given particular challenges with these tracers, such as the need for a preoperative procedure by nuclear medicine and cost, other options have been sought. Indocyanine green has proven to be a promising alternative for certain procedures, as it is easy to use and has quick uptake. Its use in the management of gynecologic cancers was first described for sentinel lymph node mapping in cervical cancer, and later for endometrial and vulvar cancers. This review provides an in-depth look at these mapping substances, their uses, and the potential for new discoveries.

Intraoperative Laser Speckle Contrast Imaging in DIEP Breast Reconstruction: A Prospective Case Series Study

Introduction:

Laser speckle contrast imaging (LSCI) is a laser-based perfusion imaging technique that recently has been shown to predict ischemic necrosis in an experimental flap model and predicting healing time of scald burns. The aims were to investigate perfusion in relation to the selected perforator during deep inferior epigastric artery perforator (DIEP) flap surgery, and to evaluate LSCI in assisting of prediction of postoperative complications.

Methods:

Twenty-three patients who underwent DIEP-procedures for breast reconstruction at 2 centers were included. Perfusion was measured in 4 zones at baseline, after raising, after anastomosis, and after shaping the flap. The perfusion in relation to the selected perforator and the accuracy of LSCI in predicting complications were analyzed.

Results:

After raising the flap, zone I showed the highest perfusion (65 ± 10 perfusion units, PU), followed by zone II (58 ± 12 PU), zone III (53 ± 10 PU), and zone IV (45 ± 10 PU). The perfusion in zone I was higher than zone III (P = 0.002) and zone IV (P < 0.001). After anastomosis, zone IV had lower perfusion than zone I (P < 0.001), zone II (P = 0.01), and zone III (P = 0.02). Flaps with areas <30 PU after surgery had partial necrosis postoperatively (n = 4).

Conclusions:

Perfusion is highest in zone I. No perfusion difference was found between zones II and III. Perfusion <30 PU after surgery was correlated with partial necrosis. LSCI is a promising tool for measurement of flap perfusion and assessment of risk of postoperative ischemic complications.