Reconstructive Surgery

Knowledge of how blood perfusion is affected during and after reconstructive surgery is of great importance to predict the survival of grafts and flaps. When commonly used reconstructive procedures were developed a century ago, they were based on empirical observations of clinical outcome. However, today modern, non-invasive techniques are available to monitor perfusion during and after surgery.

An adequate blood supply is important for the success of skin flap or free skin grafts in plastic reconstructive surgery, and oculoplastic surgeons must therefore have considerable knowledge on the perfusion in the periorbital area. However, the clinical rules of thumb concerning the design of flaps are mostly based on empirical observations and beliefs, rather than actual knowledge of blood perfusion. Several imaging techniques have been developed during the past decades offering high-resolution images of the structure and function of tissue. Peroperative monitoring can improve our understanding of how blood perfusion is affected by surgical interventions, and will hopefully allow surgical techniques to be improved, resulting in better clinical outcome.

Perfusion monitoring using laser speckle contrast imaging (LSCI)

Our research has implemented laser speckle contrast imaging (LSCI) for perfusion monitoring in the oculoplastic area. Laser-based techniques are today the most frequently used, and clinically most applicable to assess the microcirculation. However, LSCI is hampered by movement artifacts, and does not inform about the oxygenation in the tissue, which is crucial for the survival of flaps and grafts.

Oxygenation mapping in 2D using hyperspectral imaging (HIS)

Spectroscopic techniques such as near-infrared spectroscopy, as well as pulse oximetry, is the most common technique used to monitor oxygenation non-invasively, but hitherto lack the spatial resolution needed to identify heterogeneous tissue oxygenation for mapping e.g. a reconstructive surgical area. Hyperspectral imaging (HSI) encompasses provide both spatial and spectral information, however, HIS has not yet been implemented clinically, but there are a few experimental studies demonstrating its applicability in monitoring sO2 in in humans, whereof only one in reconstructive surgery[MM1] . The aim of our research is to develop and implement HSI for mapping sO2 in reconstructive surgery.

Oxygenation mapping in 3D using photoacoustic imaging (PAI)

A limitation with HSI is that it is an imaging modality that relies on light diffusely reflecting back out of the tissue. HSI is therefore only reliably monitored in the outermost layers of the skin, with a limited interrogation depth of less than 1 mm. Despite the interrogation depth being low, HSI is still not capable of providing depth resolved information and only yields detailed surface details.

Photoacoustic imaging (PAI) is currently one of the most promising imaging techniques for clinical applications, as it provides high-resolution 3D images down to a depth of several centimeters non-invasively.. It is a novel hybrid imaging technology that combines the strengths of optical and ultrasound imaging, to reveal the molecular composition of tissue at high resolution. The tissue is irradiated with pulsed laser light, which causes so-called thermoelastic expansion, which in turn generates mechanical waves that can be detected by the ultrahigh-frequency ultrasound scanner. The technique provides a spectral signature of the tissue with spatial resolution. The detection of small variations in tissue composition by photoacoustics is hence superior to that possible with other methods. PAI thus has the potential for non-invasive mapping of oxygenation in deeper tissue. In our first studies we show the applicability of using PAI to r monitoring of local changes in oxygen saturation following adrenaline injection in human forearm skin.