Thermal, Hyperspectral, and Laser Doppler Imaging: Non-Invasive Tools for Detection of The Deep Inferior Epigastric Artery Perforators-A Prospective Comparison Study

Smartphone-based thermal imaging for pedicled skin flaps: a pilot study toward objective perfusion assessment in facial, head, and neck reconstruction

PURPOSE

This study aims to develop a practical algorithm for utilizing smartphone-based thermal imaging (SBTI) in the perioperative setting and to establish a standardized evaluation method for objectively assessing SBTI images for cutaneous perfusion of pedicled flaps in the face, head, and neck.

METHODS

This prospective conducted study, integrated SBTI into the assessment of 16 patients undergoing reconstructive surgery for face and neck defects. Thermal images were captured at four timepoints: after marking (T1), after flap elevation (T2), upon completion of surgery (T3), and 24 h postoperatively (T4). The flap areas were divided into three flap zones and graded based on temperature differences (ΔT), with a grading system where grade 1 indicated perfect perfusion and grades 2 to 5 indicated increasing perfusion impairment.

RESULTS

6 male and 10 female patients aged 64-93 years (mean 78.5 years) undergoing reconstructive pedicled skin flap surgery for facial and neck defects (1 × 1 cm to 11 × 8 cm) due to diagnoses of malignant cutaneous lesions were investigated. Intraoperative assessments indicated good perfusion across flaps. One postoperative dehiscence occurred in an 83-year-old male with a cervical advancement flap, correlated with a significant temperature difference (ΔT > 4 °C) intraoperatively. Statistical analysis revealed a strong positive correlation (p = 0.0003) between clinical assessment grades and ΔT values between specific flap zones at T3.

CONCLUSION

SBTI is an easy-to-apply, low-cost, real-time and reproducible technique for indirect perfusion assessment in pedicled skin flaps of the head and neck region. Further studies are needed implementing this methodology in large and free flaps.

Perfusion in Pedicled Skin Flaps: Initial Insights from Smartphone-Based Thermal Imaging Protocol

OBJECTIVE

Successful outcomes in head and neck surgery rely on maintaining perfusion in pedicled skin flaps. Thermal imaging offers a noninvasive means to assess tissue perfusion, potentially aiding in predicting flap viability. This pilot study explores the utility of SBTI (smartphone-based thermal imaging) for predicting flap vitality and monitoring during surgery.

METHODS

Thermal imaging was employed using the FLIR One System. An imaging protocol was established, defining points of interest (T1-T4) on pedicled skin flaps. Conducted over four months, the study integrated SBTI into reconstructive surgery for the face, head and neck defects post-tumor resections. SBTI's effectiveness was assessed with n = 11 pedicled flaps, capturing images at key stages and correlating them with clinical flap assessment. Thermal images were retrospectively graded by two surgeons, evaluating flap perfusion on a scale from 1 to 5, based on temperature differences (1 = ΔT < 2 °C, 2 = ΔT ≥ 2 °C, 3 = ΔT ≥ 4 °C, 4 = ΔT ≥ 6 °C, and 5 = ΔT ≥ 8 °C), with assessments averaged for consensus and compared with the clinical assessment control group.

RESULTS

The study encountered challenges during implementation, leading to the exclusion of six patients. Patient data included 11 cases with n = 44 SBTI images. Intraoperative assessments consistently showed good perfusion. One postoperative dehiscence was noted, which retrospectively coincided with intraoperative SBTI grading, but not with clinical assessment. Statistical analysis indicated consistent outcomes following clinical and SBTI assessments. Thermal imaging accurately predicted flap viability, although it had limitations with small flaps.

CONCLUSION

SBTI proved effective, inexpensive, and noninvasive for assessing tissue perfusion, showing promise for predicting flap viability and intraoperative monitoring in head and neck surgery.

An overview of current assessment techniques for evaluating cutaneous perfusion in reconstructive surgery

This article provides a comprehensive analysis of modern techniques used in the assessment of cutaneous flaps in reconstructive surgery. It emphasizes the importance of preoperative planning and intra- and perioperative assessment of flap perfusion to ensure successful outcomes. Despite technological advancements, direct clinical assessment remains the gold standard. We categorized assessment techniques into non-invasive and invasive modalities, discussing their strengths and weaknesses. Non-invasive methods, such as acoustic Doppler sonography, near-infrared spectroscopy, hyperspectral imaging thermal imaging, and remote-photoplethysmography, offer accessibility and safety but may sacrifice specificity. Invasive techniques, including contrast-enhanced ultrasound, computed tomography angiography, near-infrared fluorescence angiography with indocyanine green, and implantable Doppler probe, provide high accuracy but introduce additional risks. We emphasize the need for a tailored decision-making process based on specific clinical scenarios, patient characteristics, procedural requirements, and surgeon expertise. It also discusses potential future advancements in flap assessment, including the integration of artificial intelligence and emerging technologies.

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.

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.

Special Issue "Plastic and Reconstructive Surgery in Personalized Medicine"

With an ever-growing knowledge in various disciplines of medicine and with rapidly evolving new techniques and operative methods in plastic surgery, it is obvious that it becomes more and more difficult to keep up with all the developments in this field at any time [...].

[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.

Evaluation of the Influence of Short Tourniquet Ischemia on Tissue Oxygen Saturation and Skin Temperature Using Two Portable Imaging Modalities

BACKGROUND

The exact influence of tourniquet ischemia on a treated extremity remains unclear.

METHODS

Twenty patients received an operation on one hand under tourniquet ischemia. Twenty healthy volunteers received 10 min of tourniquet ischemia on one of their arms. Measurements of tissue oxygen saturation using near-infrared reflectance-based imaging and skin temperature of the dorsum of the hand were performed at five different timepoints (t0 was performed just before the application of the tourniquet ischemia, t1 directly after the application of the tourniquet ischemia, t2 before the release of the ischemia, t3 directly after the release of the ischemia, and t4 on the following day).

RESULTS

In both groups, tissue oxygen saturation dropped after the application of the tourniquet ischemia compared to t0 and increased after the release of the tourniquet ischemia. In the patient group, tissue oxygen saturation at t4 was higher compared to t0; in contrast, the level of tissue oxygen saturation in the participant group dropped slightly at t4 compared to t0. The measured skin temperature in the patient group showed an increase during the observation period, while it continuously decreased in the group of healthy participants.

CONCLUSIONS

Short-term ischemia did not appear to permanently restrict perfusion in this study design. The non-invasive imaging modalities used were easy to handle and allowed repetitive measurement.

Assessment of Mastectomy Skin Flaps for Immediate Reconstruction with Implants via Thermal Imaging-A Suitable, Personalized Approach?

BACKGROUND

Impaired perfusion of the remaining skin flap after subcutaneous mastectomy can cause wound-healing disorders and consecutive necrosis. Personalized intraoperative imaging, possibly performed via the FLIR ONE thermal-imaging device, may assist in flap assessment and detect areas at risk for postoperative complications.

METHODS

Fifteen female patients undergoing elective subcutaneous mastectomy and immediate breast reconstruction with implants were enrolled. Pre-, intra- and postoperative thermal imaging was performed via FLIR ONE. Potential patient-, surgery- and environment-related risk factors were acquired and correlated with the occurrence of postoperative complications.

RESULTS

Wound-healing disorders and mastectomy-skin-flap necrosis occurred in 26.7%, whereby areas expressing intraoperative temperatures less than 26 °C were mainly affected. These complications were associated with a statistically significantly higher BMI, longer surgery duration, lower body and room temperature and a trend towards larger implant sizes.

CONCLUSION

Impaired skin-flap perfusion may be multifactorially conditioned. Preoperative screening for risk factors and intraoperative skin-perfusion assessment via FLIR ONE thermal-imaging device is recommendable to reduce postoperative complications. Intraoperative detectable areas with a temperature of lower than 26 °C are highly likely to develop mastectomy-skin-flap necrosis and early detection allows individual treatment concept adaption, ultimately improving the patient's outcome.