Evaluation of the vascular integrity of free flaps based on microcirculation imaging techniques

A free-flap graft refers to the free transfer of tissue to cover tissue defects caused by trauma or malperfusion in plastic surgery. The basic principle, which makes a free flap working is an adequate blood flow. We applied new techniques which are able to detect the blood flow of the anastomosis and of dermal and subdermal tissue layers in a reliable way.

To this end we applied innovative Ultrasound-techniques (contrast enhanced high resolution Ultrasound (US), color coded Doppler sonography (CCDS), Cross Beamtrade mark, Power Doppler, Tissue Harmonic Imagingtrade mark (THI), Speckle Reduction Imagingtrade mark (SRI)), as well as the Indocyanine Green (ICG) fluorescence angiography to evaluate the vascular integrity of 15 parascapular flaps implanted to the fore foot over a period of four years. The age of the subjects ranged from 16 to 60 years. The US machine (GE Logiq 9) was equipped with a Logiq 9L transducer (6-9 MHz) and the modalities of CHI (Contrast Harmonic Imaging) and True Agent Detection (dual view of B-Mode and contrast mode).

The borders of the investigated flaps could be best detected using Cross Beamtrade mark Technology with SRItrade mark and THItrade mark. Power Doppler was able to detect anastomotic vessels even if they were twisted or elongated. Reduced perfusion curves were seen in cases with low anastomotic flow in CCDS. The CHItrade mark allowed dynamic flow detection of the microcirculation of the tissue graft over a depth of up to 3 cm including quantitative perfusion curves of tissue microcirculation by using TICtrade mark analysis. There is a strong correlation between the perfusion indices measured by ICG fluorescence angiography and CHItrade mark. Furthermore the ICG showed a remarkable enhancement of fluorescence in the flap borders, which need to be explored in future investigations.

These new applications provide useful and effective methods for improved postoperative monitoring of free flaps in plastic surgery and can lead to substantial reduction in the overall risk of flap failure.