Rapid vs. delayed infrared responses after ischemia reveal recruitment of different vascular beds

Role of Infrared Thermography in Planning and Monitoring of Head and Neck Microvascular Flap Reconstruction

Background

Reconstruction using microvascular free flaps has become the standard of care in head and neck cancer surgery, and their success lies in appropriate planning, adequate revascularization, and early detection of flap compromise so that prompt salvage is possible. This study evaluates the role of infrared thermography in the planning, execution, and postoperative monitoring of microvascular flaps in head and neck reconstructions.

Methods

This is a single institutional, prospective observational study conducted at a tertiary care hospital in South India for 13 months. Twenty patients were included, and their thermographic images were captured in the preoperative, intraoperative, and postoperative settings using the infrared camera FLIR T400. These images were analyzed along with the Doppler, and clinical monitoring findings in all the settings and the temperature difference were calculated postoperatively.

Results

Hotspot perforator marking was made using infrared camera, and perforator marking was made using hand-held Doppler preoperatively, which correlated in 93% of cases. Intraoperatively, flap rewarming was successfully demonstrated in 19 of 20 cases. Postoperatively, flap compromise was observed on infrared thermography during the first 24 hours but not on clinical monitoring in three cases. The temperature difference values recorded were 5.4°C, 2.4°C, and 4.9°C. The mean of temperature difference of the healthy flaps was 1.0°C (range 0.1°C-1.8°C).

Conclusion

Infrared thermography provides simple and reliable imaging, which can be used in perforator marking and flap designing preoperatively and checking the flap perfusion and vascular anastomosis patency intra- and postoperatively.

Automatic detection of perforator vessels using infrared thermography in reconstructive surgery

PURPOSE

Knowing the location of the blood vessels supplying the skin and subcutaneous tissue is a requirement during the planning of tissue transfer in reconstructive surgery. Commonly used imaging techniques such as computed tomography angiography and indocyanine green angiography expose the patient to radiation or a contrast agent, respectively. Infrared thermal imaging was evaluated with success as a non-invasive alternative. To support the interpretation of thermograms, a method to automatically detect the perforators was developed and evaluated.

METHODS

A system consisting of a thermal camera, a PC and custom software was developed. The temperature variations of the skin surface were analysed to extract the perforator locations. A study was conducted to assess the performance of the algorithm by comparing the detection results of the algorithm with manually labelled thermal images by two clinicians of the deep inferior epigastric perforator flap of 20 healthy volunteers.

RESULTS

The F measure, precision and recall were used to evaluate the system performance. The median F measure is 0.833, the median precision is 0.80, and the median recall is 0.907.

CONCLUSION

The results of this study showed that it is possible to automatically and reliably detect the skin perforators in thermograms despite their weak temperature signature. Infrared thermal imaging is a non-invasive and contactless approach suitable for intraoperative use. Combined with a computer-assisted tool for the automatic detection of perforator vessels, it is a relevant alternative intraoperative imaging method to the standard indocyanine green angiography.