Dynamic Infrared Thermography (DIRT) in DIEP flap breast reconstruction: A clinical study with a standardized measurement setup

[Using a smartphone-compatible thermal camera (FLIR One) for preoperative mapping of DIEP perforators]

INTRODUCTION

The success of surgeries involving free flaps largely depends on accurate preoperative mapping of perforator arteries. Various imaging techniques, such as Doppler ultrasound and CT angiography, are typically used, each having its advantages and disadvantages in terms of cost, accuracy, and patient risk. The main objective of our study is to compare the effectiveness of the FLIR One device for detecting these arteries compared with traditional methods. Thermal imaging appears to be a simpler, less expensive, and less invasive alternative for surgical planning.

MATERIAL AND METHOD

The study, conducted at the Regional Hospital Center of Nancy, included 25 free flaps (DIEP) on an exclusively female cohort of 22 patients, with follow-up from 2022 to 2023. Before the procedure, an abdominal-pelvic CT angiography was performed, followed by additional evaluation with thermal imaging using FLIR One and acoustic Doppler examination on the eve of the operation. This approach aimed to provide precise mapping of vascular perforators for each patient. Three different operators performed these markings, and the results were then compared with intraoperative observations. The imaging protocol also included a Doppler examination to validate the results of the thermal imaging. Statistical analyses with intraclass correlation coefficients (ICC) were performed to evaluate the correlation between different preoperative localization methods of perforating vessels.

RESULTS

In 22 patients undergoing 25 DIEP flaps for breast reconstructions, three imaging techniques were used to identify vascular perforators: thermal imaging with FLIR, acoustic Doppler, and CT angiography. FLIR identified the most perforators (n=137), followed by acoustic Doppler (n=128) and CT angiography (n=126). Comparing these with intraoperative results, 66% of perforators identified by FLIR were confirmed, 70% for acoustic Doppler, and 95% for CT angiography. The ICCs shows a significant correlation between these imaging techniques and intraoperative results. FLIR demonstrated a strong correlation with intraoperative observations (ICC of 0.74, P<0.001), followed by a moderate correlation with acoustic Doppler (ICC of 0.56, P<0.03) and CT angiography (ICC of 0.52, P<0.006).

CONCLUSION

The study concludes that thermal imaging with FLIR is a reliable and effective tool for locating vascular perforators. Although the study and FLIR have their own limitations, the tool presents several advantages such as ease of use, speed, and affordability. These characteristics make FLIR particularly attractive as a complement to traditional detection methods, such as acoustic Doppler and CT angiography.

Thermal Changes During Clavicle Fracture Healing in Children

Introduction: Clavicle fractures are among the most common in children, typically treated conservatively, with standard radiographs used to diagnose and monitor healing. Recently, infrared thermography (IRT) has been proposed as an alternative method for fracture detection, but no study has correlated the temperature changes during callus formation. Materials and Methods: Children aged 4-18 with X-ray-diagnosed clavicle fractures were included in the study. IRT measured temperatures above the fracture and contralateral healthy side on the 1st, 4th, 8th, 15th, and 22nd day after the injury. Along with IRT, an ultrasound was used to assess callus formation. Results: The study included 27 patients with an average age of 12.4 years, mostly boys. The left side was more often affected than the right side (33%). We found a correlation between callus formation and the ∆T. A maximum temperature difference of an average of 0.7 °C was noted during the proliferative phase of callus formation. After the formation of the fibrocartilaginous callus (4th to 8th day), the temperature above the fracture declined until it was equal (22nd day) to that of the healthy side. The average temperature difference between the broken and the healthy sides was statistically significant on the 4th and 8th days (during callus formation). Conclusions: The increased skin temperature above the fracture correlates with the inflammatory phase of bone healing. After the callus is visible on ultrasound, the temperature linearly drops with no statistical difference between the injured and the healthy sides. The standard protocol for clavicle fracture treatment typically involves using X-rays to assess callus formation during follow-up. IRT has shown potential in diagnosing callus formation in children with clavicle fractures, potentially reducing the need for traditional X-rays.

The Role of Computed Tomography Angiography in Perforator Flap Planning

Preoperative computed tomography angiography (CTA) for perforator free flaps is accurate, precise, and reliable in mapping perforator anatomy that can be used in the intraoperative domain. CTA holds important clinical value as a tool in surgical decision making and surgical innovation, enabling reconstructive surgeons to tailor complex flap designs for extensive defects. Integration into existing infrastructure for virtual surgical planning is feasible, and future efforts to characterize the association of preoperative CTA with postoperative outcomes and cost-analyses for perforator flaps are warranted.

The Precision of Colour Doppler Ultrasonography Combined with Dynamic Infrared Thermography in Perforator Mapping for Deep Inferior Epigastric Perforator Flap Breast Reconstruction

Background: Perforator mapping is a mandatory tool for the preoperative planning of a microsurgical free flap, especially in breast reconstruction. Numerous methods for mapping have been described. In this study, we investigate the combined use of Dynamic Infrared Thermography (DIRT) and Colour Doppler Ultrasonography (CDUS) only to see whether it can eliminate the need for Computed Tomography Angiography (CTA). Methods: A prospective study was conducted on 33 patients with deep inferior epigastric perforator (DIEP) flaps for breast reconstruction. DIRT, followed by CDUS and CTA, was performed preoperatively and perforators were confirmed intraoperatively. Results: From 135 hot spots found on DIRT, 123 perforators were confirmed by CDUS (91.11%). A total of 86.66% of the perforator vessels detected on CTA have their correspondent on DIRT, while 95.12% have their correspondent on CDUS. No statistically significant difference (p > 0.05) was found comparing DIRT vs. CTA and CDU vs. CTA. The average DIRT time was 121.54 s and CDUS 232.09 s. The mean sensitivity for DIRT was 95.72% and 93.16% for CDUS. Conclusion: DIRT combined with CDUS can precisely and efficiently identify suitable perforators without the need for CTA in DIEP breast reconstruction.

Automated thermographic detection of blood vessels for DIEP flap reconstructive surgery

PURPOSE

Inadequate perfusion is the most common cause of partial flap loss in tissue transfer for post-mastectomy breast reconstruction. The current state-of-the-art uses computed tomography angiography (CTA) to locate the best perforators. Unfortunately, these techniques are expensive and time-consuming and not performed during surgery. Dynamic infrared thermography (DIRT) can offer a solution for these disadvantages.

METHODS

The research presented couples thermographic examination during DIEP flap breast reconstruction with automatic segmentation approach using a convolutional neural network. Traditional segmentation techniques and annotations by surgeons are used to create automatic labels for the training.

RESULTS

The network used for image annotation is able to label in real-time on minimal hardware and the labels created can be used to locate and quantify perforator candidates for selection with a dice score accuracy of 0.8 after 2 min and 0.9 after 4 min.

CONCLUSIONS

These results allow for a computational system that can be used in place during surgery to improve surgical success. The ability to track and measure perforators and their perfused area allows for less subjective results and helps the surgeon to select the most suitable perforator for DIEP flap breast reconstruction.

Advancing DIEP Flap Monitoring with Optical Imaging Techniques: A Narrative Review

OBJECTIVES

This review aims to explore recent advancements in optical imaging techniques for monitoring the viability of Deep Inferior Epigastric Perforator (DIEP) flap reconstruction. The objectives include highlighting the principles, applications, and clinical utility of optical imaging modalities such as near-infrared spectroscopy (NIRS), indocyanine green (ICG) fluorescence angiography, laser speckle contrast imaging (LSCI), hyperspectral imaging (HSI), dynamic infrared thermography (DIRT), and short-wave infrared thermography (SWIR) in assessing tissue perfusion and oxygenation. Additionally, this review aims to discuss the potential of these techniques in enhancing surgical outcomes by enabling timely intervention in cases of compromised flap perfusion.

MATERIALS AND METHODS

A comprehensive literature review was conducted to identify studies focusing on optical imaging techniques for monitoring DIEP flap viability. We searched PubMed, MEDLINE, and relevant databases, including Google Scholar, Web of Science, Scopus, PsycINFO, IEEE Xplore, and ProQuest Dissertations & Theses, among others, using specific keywords related to optical imaging, DIEP flap reconstruction, tissue perfusion, and surgical outcomes. This extensive search ensured we gathered comprehensive data for our analysis. Articles discussing the principles, applications, and clinical use of NIRS, ICG fluorescence angiography, LSCI, HSI, DIRT, and SWIR in DIEP flap monitoring were selected for inclusion. Data regarding the techniques' effectiveness, advantages, limitations, and potential impact on surgical decision-making were extracted and synthesized.

RESULTS

Optical imaging modalities, including NIRS, ICG fluorescence angiography, LSCI, HSI, DIRT, and SWIR offer a non- or minimal-invasive, real-time assessment of tissue perfusion and oxygenation in DIEP flap reconstruction. These techniques provide objective and quantitative data, enabling surgeons to monitor flap viability accurately. Studies have demonstrated the effectiveness of optical imaging in detecting compromised perfusion and facilitating timely intervention, thereby reducing the risk of flap complications such as partial or total loss. Furthermore, optical imaging modalities have shown promise in improving surgical outcomes by guiding intraoperative decision-making and optimizing patient care.

CONCLUSIONS

Recent advancements in optical imaging techniques present valuable tools for monitoring the viability of DIEP flap reconstruction. NIRS, ICG fluorescence angiography, LSCI, HSI, DIRT, and SWIR offer a non- or minimal-invasive, real-time assessment of tissue perfusion and oxygenation, enabling accurate evaluation of flap viability. These modalities have the potential to enhance surgical outcomes by facilitating timely intervention in cases of compromised perfusion, thereby reducing the risk of flap complications. Incorporating optical imaging into clinical practice can provide surgeons with objective and quantitative data, assisting in informed decision-making for optimal patient care in DIEP flap reconstruction surgeries.

Projected augmented reality in DIEP flap breast reconstruction: Projecting perforators on the skin using dynamic infrared thermography

BACKGROUND

Dynamic infrared thermography (DIRT) is a quick and non-invasive technique for perforator mapping in free flaps that provides real-time information. After a cold challenge, areas best supplied with blood become visible hotspots on color-coded maps, indicating perforators. This study presents a proof of principle for a new and innovative feature of DIRT, where projected augmented reality is used to directly display thermal images on the patient's abdomen prior to the deep inferior epigastric artery perforator (DIEP) flap breast reconstruction.

METHODS

A self-aligning projection device prototype (Anatomy Projector) equipped with an integrated thermal camera was used to obtain thermal information and project the color-coded map directly on the patient's abdomen before DIEP flap breast reconstruction. Projected DIRT hotspots were verified using a hand-held Doppler, and compared to the vascularity on computed tomography angiography (CTA), and intraoperative perforator measurements following a Cartesian grid.

RESULTS

A total of 514 DIRT hotspots were projected in 50 patients, among them 97.3% could be verified using Doppler. The positive predictive value for CTA was 74.5%. Intraoperative measurements yielded 132 perforators in 71 flaps, among them 75 perforators (56.8%) correlated with projected DIRT hotspots, and half of them (54.7%) appeared within the first 5 emerging hotspots.

CONCLUSION

This study showed that real-time display of thermal data in DIEP flap breast reconstruction is feasible via projected augmented reality. Projection facilitates convenient marking of hotspots, and a high resemblance to Doppler and CTA data was observed. Further research should assess the added value of projecting thermal images intraoperatively and in other fields of plastic surgery.

Smartphone-based thermography in flap surgery: A systematic review and meta-analysis of perforator identification

Background

Thermography can be used in pre-operative planning of free perforator flap surgeries. Thermography assesses skin temperature by measuring the quantity of infrared radiation observed. In this meta-analysis, authors assess the sensitivity of smartphone-based thermal imaging (SBTI) in the detection of perforators and analyze the difference between static and dynamic imaging.

Materials and methods

Authors followed the PRISMA guidelines for systematic reviews and meta-analyses. The meta package in R was used to conduct the meta-analysis. The "metaprop" function was used to calculate the overall sensitivity estimate and 95% confidence interval. The "metaprop.one" function was used to calculate subgroup estimates for static and dynamic study types. The "metareg" function was used to conduct meta-regression analyses to explore sources of heterogeneity.

Results

This study includes seven articles with 1429 perforators being evaluated. The overall proportion of the sensitivities was estimated to be 0.8754 (95% CI: 0.7542; 0.9414) using a random effects model. The heterogeneity of the studies was high, as indicated by the tau^2 value of 1.2500 (95% CI: 0.4497; 8.4060) and the I^2 value of 92.6% (95% CI: 88.1%; 95.4%). The pooled sensitivity for static imaging was 0.8636 (95%CI: 0.6238-0.9603) with a tau^2 of 2.0661 and a tau of 1.4374, while the pooled sensitivity for dynamic imaging was slightly higher (p = 0.7016) at 0.8993 (95%CI: 0.7412-0.9653) with a smaller tau^2 of 0.8403 and a tau of 0.9167.

Conclusion

Further studies need to confirm that SBTI is a reliable and convenient technique for detecting perforators for the pre-operative planning of free perforator flap surgeries.

Uses of Smartphone Thermal Imaging in Perforator Flaps as a Versatile Intraoperative Tool: The Microsurgeon's Third Eye

Introduction

In this study, we evaluate the versatility of smartphone thermal imaging technology as a valuable intraoperative modality in different stages of perforator flap surgery aiming to minimize the complications and achieve the best postoperative outcome.

Patients and methods

Thermography was performed in 20 perforator flaps in 20 patients at different surgical stages in three different ways to identify the most dominant perforator: first, by measuring the surface temperature of the skin; second, by using the dynamic infrared thermography technique; and third, by assessing the perfusion pattern when the flap was supplied by each perforator separately. Thermography was used to help in discarding the least perfused area of the flap. After microvascular anastomosis, the flap reheating pattern was evaluated.

Results

Seventeen free and three pedicled perforator flaps were included. Intraoperatively, each of the selected perforators had a corresponding hotspot. The perforator with the hottest hotpot, best rewarming, and provision of best flap perfusion on thermography was found clinically dominant. After microvascular anastomosis in free flaps, rapid rewarming was recorded in 15 cases. In two deep inferior epigastric perforator flaps, no rapid rewarming was observed. The pedicle was kinked in one case and there was a venous insufficiency in another case that required a cephalic turndown. All flaps showed good perfusion on thermography after inset.

Conclusion

Smartphone thermography has proven to be a valuable, cheap, rapidly employed, and objective tool not only for the design of perforator flaps, but also for the decision making intraoperatively to achieve the best surgical outcome.

Reliability of Postoperative Free Flap Monitoring with a Novel Prediction Model Based on Supervised Machine Learning

BACKGROUND

Postoperative free flap monitoring is a critical part of reconstructive microsurgery. Postoperative clinical assessments rely heavily on specialty-trained staff. Therefore, in regions with limited specialist availability, the feasibility of performing microsurgery is restricted. This study aimed to apply artificial intelligence in postoperative free flap monitoring and validate the ability of machine learning in predicting and differentiating types of postoperative free flap circulation.

METHODS

Postoperative data from 176 patients who received free flap surgery were prospectively collected, including free flap photographs and clinical evaluation measures. Flap circulation outcome variables included normal, arterial insufficiency, and venous insufficiency. The Synthetic Minority Oversampling Technique plus Tomek Links (SMOTE-Tomek) was applied for data balance. Data were divided into 80%:20% for model training and validation. Shapley Additive Explanations were used for prediction interpretations of the model.

RESULTS

Of 805 total included flaps, 555 (69%) were normal, 97 (12%) had arterial insufficiency, and 153 (19%) had venous insufficiency. The most effective prediction model was developed based on random forest, with an accuracy of 98.4%. Temperature and color differences between the flap and the surrounding skin were the most significant contributing factors to predict a vascular compromised flap.

CONCLUSIONS

This study demonstrated the reliability of a machine-learning model in differentiating various types of postoperative flap circulation. This novel technique may reduce the burden of free flap monitoring and encourage the broader use of reconstructive microsurgery in regions with a limited number of staff specialists.

The Utility of Smartphone-Based Thermal Imaging in the Management and Monitoring of Microvascular Flap Procedures: A Systematic Review and Meta-Analysis

BACKGROUND

Smartphone-based thermal imaging (SBTI) has been reported in the literature to be an easy-to-use, contactless, cost-friendly alternative to standard imaging modalities in identifying flap perforators, monitoring flap perfusion, and detecting flap failure. Our systematic review and meta-analysis aimed to evaluate SBTI's accuracy in perforator identification and secondarily evaluate SBTI's utility in flap perfusion monitoring as well as ability to predict flap compromise, failure, and survival.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines, a systematic review was performed using PubMed from inception to 2021. Articles were uploaded into Covidence and, following duplicate deletion, were initially screened for use of SBTI in flap procedures through title and abstract screening followed by full-text review. The following data points, if provided, were extracted from each included study: study design, number of patients, patient demographics, perforator number and location, flap number and location, room temperature, cooling method, imaging distance, time from cloth removal, primary (SBTI's accuracy in perforator identification), and secondary outcomes (prediction of flap compromise/failure/survival and cost analysis). Meta-analysis was performed using RevMan v.5.

RESULTS

The initial search yielded 153 articles. Eleven applicable studies with a total of 430 flaps from 416 patients were ultimately included. The SBTI device assessed in all included studies was FLIR ONE. Four studies assessed the SBTI's perforated detection ability and were included in meta-analysis. Smartphone-based thermal imaging correctly identified 378 (93.3%; n = 405) perforators, and computed tomography angiography (CTA) correctly identified 402 (99.2%; n = 402), although in one study SBTI found additional perforators not detected on CTA. A random-effects model was used (I2 = 65%), and no significant difference in perforator detection ability was found between SBTI and CTA (P = 0.27).

CONCLUSIONS

This systematic review and meta-analysis supports SBTI as user- and cost-friendly ($229.99), contactless imaging modality with perforator detection ability comparable to current criterion-standard CTA. Postoperatively, SBTI outperformed Doppler ultrasound in early detection of microvascular changes causing flap compromise, allowing for prompt tissue salvage. With a minimal learning curve, SBTI seems to be a promising method of postoperative flap perfusion monitoring able to be used by all hospital ranks. Smartphone-based thermal imaging could thus increase flap monitoring frequency and lower complication rates, although further study is warranted.

Value of the combination of a smartphone-compatible infrared camera and a hand-held doppler ultrasound in preoperative localization of perforators in flaps

This study was conducted to evaluate the effectiveness of the FLIR ONE PRO, a thermal imaging camera for smartphones, combined with handheld Doppler (HHD) in the localization of perforator arteries and to assess the efficacy of the FLIR ONE PRO in distinguishing perforators of the descending branch of the lateral circumflex femoral artery (LCFA) from other perforators of the anterolateral thigh perforator (ALTP) flap. We enrolled 29 free perforator flaps from 22 patients in our study. Before surgery, dynamic infrared thermography was performed using a FLIR ONE PRO to visualize hotspots on the flaps. Subsequently, HHD was used to further determine the perforators under the hotspots, which were ultimately identified and confirmed through intraoperative findings. Additionally, infrared images of the ALTP flap were analyzed using FLIR Tools. The performances of the FLIR ONE PRO and FLIR ONE PRO + HHD groups were evaluated by comparing the intraoperative findings. Using FLIR ONE PRO + HHD, 119 hotspots and 106 perforators were identified during surgery. Using FLIR ONE PRO + HHD, sensitivity and positive predictive value were 97.87% and 88.46%, respectively, in the young (age≤45 years). In the elderly group (age>45 years), these percentages were 93.22% and 82.09%, respectively. In addition, we found that the FLIR ONE PRO could be useful for differentiating perforators in the descending branch of the LCFA from other perforators within 5 min. The results showed a sensitivity of 96.15%, a specificity of 98.9%, a positive predictive value of 96.15%, and a negative predictive value of 98.9%. Compared to using FLIR ONE PRO alone, the combined application of HHD and FLIR ONE PRO had a higher value in perforator localization by increasing the positive predictive value. The FLIR ONE PRO may have significance in the rapid prediction of perforators deriving from the descending branch of the LCFA.

Operative Efficiency in Deep Inferior Epigastric Perforator Flap Reconstruction: Key Concepts and Implementation

The deep inferior epigastric perforator flap has become one of the most popular approaches for autologous breast reconstruction after mastectomy. As much of health care has moved to a value-based approach, reducing complications, operative time, and length of stay in deep inferior flap reconstruction is becoming increasingly important. In this article, we discuss important preoperative, intraoperative, and postoperative considerations to maximize efficiency when performing autologous breast reconstruction and offer tips on how to handle certain challenges.

Skin Cancer Detection Using Infrared Thermography: Measurement Setup, Procedure and Equipment

Infrared thermography technology has improved dramatically in recent years and is gaining renewed interest in the medical community for applications in skin tissue identification applications. However, there is still a need for an optimized measurement setup and protocol to obtain the most appropriate images for decision making and further processing. Nowadays, various cooling methods, measurement setups and cameras are used, but a general optimized cooling and measurement protocol has not been defined yet. In this literature review, an overview of different measurement setups, thermal excitation techniques and infrared camera equipment is given. It is possible to improve thermal images of skin lesions by choosing an appropriate cooling method, infrared camera and optimized measurement setup.

Performance of infrared thermography and thermal stress test in perforator mapping and flap monitoring: A meta-analysis of diagnostic accuracy

BACKGROUND

Accurate mapping of perforators prior to flap reconstruction and early detection of poor flap perfusion reduces the risk of flap failure. Infrared thermography (IRT) has recently regained popularity within reconstructive surgery to aid flap design, reduce operative time and assess flap viability based on surface temperature changes. The aim of this review is to quantify the diagnostic ability of IRT in perforator mapping preoperatively and monitor flap perfusion perioperatively.

METHODS

We conducted a systematic review of literature and included all studies that evaluated the use of IRT for perforator mapping and flap perfusion monitoring. We used a mixed-effects logistic regression bivariate model to estimate the summary sensitivity and specificity and constructed hierarchical summary receiver operative characteristic (HSROC) curves.

OUTCOME

We identified 18 studies and observed IRT to have sensitivities of 99.6% and 89.6% with specificities of 99.9% and 96.0% for perforator mapping and flap monitoring, respectively. Moreover, IRT recognises patterns of perfusion within interperforator zones through visualisation of angiosomal rewarming and may improve flap outcomes.