Near Infrared Imaging and Flap Necrosis

Background of the study:

There are commercial medical devices that measure the spectrum of near infrared light reflected from at a single location of tissue. These non-imaging devices are also called point NIR spectroscopy devices. Point NIR spectroscopy devices have been used to monitor blood perfusion to free flaps and mastectomy flaps. The unit of measurement is StO2; StO2 is a measure of hemoglobin oxygen saturation weighted towards the saturation in the microvascular bed as opposed to SaO2 or SvO2 which correspond to the arterial and venous hemoglobin saturation respectively. StO2 is mixed arterial - venous measure of hemoglobin oxygen saturation. Point devices use a light delivery and collection probe that needs to be in contact with tissue. They can measure on the order of ~10mm deep over an area of approximately 1cm by 1cm depending on the configuration of the device. Some studies using point devices have shown significant differences in StO2 values in flaps that became necrotic versus flaps that remained viable. NIR point systems however are not widely used intraoperatively because they need to be brought in contact with the tissue being measured. They also measure small areas thereby necessitating measurements over many spatially distinct points on the flap to get a comprehensive measurement of flap oxygenation.

Rationale for this study A new commercially available imaging technology uses NIR spectroscopy to measure regional tissue hemoglobin oxygenation, StO2. The device is based on the same principles as point NIR spectroscopy devices but instead of contacting the skin a set of images are taken 12 inches away from the patient. These images are processed to produce a colour coded StO2 image of a large tissue area (~6" by 4"). Since the image device doesn't contact the skin the depth of measurement is ~2mm instead of ~10mm with a point system. Compared to dye based angiography methods, StO2 NIR imaging does not require the injection of a dye. The advantage of the NIR imaging device over point NIR systems is a lack of patient contact. Thus StO2 NIR imaging is completely non-invasive, non-contact. Images can be captured and displayed in less than 5 seconds therefore imaging can be repeated as needed with no risk to the patient and no cost for disposables. Preclinical data shows that NIR can predict necrosis in flaps but clinical data is needed to characterize and assess the value of the technology in plastic and reconstructive surgery.

Study hypotheses or research questions This study will explore the ability of NIR imaging to predict of tissue viability in immediate breast reconstruction procedures. Necrosis will be scored using the SKIN score.

Primary objectives and secondary objectives:

Aim 1: To establish the NIR parameters that are consistent with flap viability. Aim 1: To develop parameters to predict flap viability intraoperatively. Aim 3: To determine if NIR values correspond to SKIN scores

Significance of the study The Innovation is a non-contact, non-invasive means to map/image the oxygen available to an area of tissue. It requires no setup time and there are no consumables associated with its measurement method. As cellular respiration in tissue requires an adequate supply of oxygen, the tissue hemoglobin oxygen saturation image provided by the Innovation can detect areas of tissue that are threatened by a poor oxygen supply. The oxygenation measures provided by the device give surgeons insight into the healing potential of skin flaps in procedures such as mastectomies. Skin flaps that are not sufficiently oxygenated are at risk for necrosis which can be costly to the hospital systems and affect the patient quality of life. The Innovation's oxygenation image assists surgeons in identifying areas of flap ischemia intra-operatively and can be used to monitor flaps post-operatively. With early identification of ischemic areas surgeons can intervene earlier to reduce the risk of flap necrosis.