Flap surgery consists of the transplantation of healthy tissue from a donor site to a wounded recipient area affected by loss of tissue due of burn, trauma or cancer removal. The transplanted tissue usually comprises skin and fatty tissue, but it can also include muscular tissue. When possible, the skin graft is transplanted from a nearby area without disconnecting the vascular network; however, in certain cases the tissue must be transplanted from a different area of the body (free flap), and the vascular network is reconnected to the blood vessels adjacent to the wounded area. After detachment from the donor site, it is crucial to re-establish blood perfusion throughout the transplanted tissue in timely manner and with high accuracy to guarantee a successful long-term outcome. During the procedure, surgeons use a Doppler ultrasound pencil probe to assess if blood flow is re-established in the vessels underneath the transplanted skin. Although of some value, this method only allows very coarse assessment of blood flow in major vessels by providing qualitative auditory feedback to the surgeon. The proposed technology consists of a non-invasive imaging system that provides real-time, dynamic, quantifiable and clinically-relevant information about blood perfusion within the skin graft during and after transplantation. The proposed methodology is based on an optical technique called Near-lnfraRed Spectroscopy (NIRS) which measures oxygenated hemoglobin (Hb02) and deoxygenated hemoglobin (HHb) in tissues. NIRS exploits the semi-transparency of human tissues to near-infrared light (650+1000 nm) to investigate properties up to several centimeters in depth. This disclosure describes a skin-contact optical system able to reconstruct a tridimensional color-coded image that is correlated to the presence of Hb02 and HHb in the tissue, thus providing quantitative information about the tissue oxygenation at any given time. The main advantages of this system over the Doppler ultrasound pencil are represented by: a. a much more granular investigation over a much wider area, allowing the monitoring of tissue perfusion and oxygenation provided by both major vessels and capillary networks; b. a more intuitive visual information that requires lesser interpretation by the clinician; c. a technique-independent usage that does not require the clinician to locate and hold the probe to obtain perfusion readings; d. a continuous real-time oxygenation monitoring during and after surgery; e. the ability to monitor graft health even after the patient has been sent home. Variants of this technology could be used in other forms of surgery and veterinary medicine. For example, a cardiovascular surgeon might apply an epicardial sensing array on the outside of the heart after coronary bypass surgery to assess cardiac muscle reperfusion. Other large organ procedures that involve temporary occlusion of blood supply might similarly benefit from this technology. It can also be envisioned that such sensing systems could be left within the body following surgery, allowing continuous or periodic monitoring of tissue health, with transmission to a transceiver outside of the body.