Perfusion imaging of free flaps with contrast harmonic ultrasound imaging, laser-induced indocyanine green fluorescence angiography and magnetic resonance imaging

Currently there is no image-guided modality which is sufficient and exact enough to evaluate the perfusion of tissue in its different layers after transplantation of microvascular flaps. Examination of capillary filling after compression (refill) allows merely a vague estimation. The cutaneous blood flow can be shown with different methods of fluoroscopy, but the perfusion of deeper tissue layers is not detectable with these methods. To a certain degree indocyanin green fluoroscene angiography can help to measure the cutaneous perfusion semi-quantitatively. To assess the perfusion in deeper tissue layers with high spatial (and temporal) resolution there are basically two methods available: dynamic MRI techniques and contrast enhanced ultrasound with high-resolution linear probes using the contrast harmonic imaging (CHI) technique. Therefore, the aim of this study was to evaluate post surgery tissue perfusion of free flaps with contrast enhanced harmonic ultrasound (CHI), laser-induced indocyanine green (ICG) fluorescence angiography and dynamic susceptibility contrast perfusion weighted (PW) MRI.