Smartphone Thermal Imaging as an Adjunct to Identify Free Flap Perforators and Assisting Flap Design: A Pilot Study

Background: The main technique for identification of free flap perforator vessels is Doppler sonography, which is not always accurate, user dependent and affected by the patient's body habitus.

Methods: Adult patients undergoing head and neck resection and free flap reconstruction at two academic institutions were enrolled. Doppler sonography was used to identify perforators, and were marked using a skin marker. The donor site was cooled down for 3 min using a sterile iced saline bag. FLIR-ONE (FLIR Systems Inc., Wilsonville, OR) camera was used to assess for "hot spots" during a 3-5 min period of re-warming as a surrogate for cutaneous blood flow. The distance between the Doppler signal location, and the "hot spot" was recorded. The position of the perforator was then identified intraoperatively and the distances between the surgical position, the Doppler and "hot spot" were recorded.

Results: A total of 28 patients were included. For all flap types, FLIR thermal imaging measurements consistently tended to be closer to the surgical site compared to Doppler ultrasound. In anterolateral thigh flaps (n = 20), thoracodorsal artery perforator flaps (n = 5), and fibula osteocutaneous flaps (n = 3), absolute mean differences ranged from 0.62 to 1.33 cm, with trends favoring FLIR. While paired t-tests did not reach statistical significance, both methods correlated with intraoperatively identified skin perforators, and distances generally ranged between 0 and 2 cm.

Conclusion: We demonstrate that a smartphone-based thermal imaging system has the potential to serve as an adjunct for identifying flap perforators, with the possibility of reducing operative times and minimizing patient morbidity.

Level of evidence: Level 3.