PA22 A simple budget-friendly technique in infrared skin photography for the rapid differentiation of deep dermal pigmentation from bruising

Abstract Infrared (IR) photography is long established as an art form, allowing images to be created using light outside the visible spectrum. Professional and amateur photographers have developed several ways of seeing the world through this hidden light. These include IR film, filters and specialized cameras. One method is converting an old digital camera to IR by removing its internal IR filter from the existing sensor, resulting in a cheap but effective way of capturing IR photographs. The use of infrared photography in medicine has been documented in forensic pathology, where it helps document post mortem findings, including gunpowder traces, victim identification via tattoos, and detection of external signs of blunt force trauma such as bruises (Rost T, Kalberer N, Scheurer E. A user-friendly technical set-up for infrared photography of forensic findings. Forensic Sci Int 2017; 278: 148–55). In living patients, differentiating between deep dermal pigmentation, such as lumbosacral dermal melanocytosis, and contusions from nonaccidental injury has proven challenging in the busy environment of the emergency department. We aimed to find out whether this IR photographic technique could be an easy way to rapidly tell the difference. We collected photographs from a series of patients with either bruising or haematomas as a result of trauma or deep dermal pigmentation using conventional visible light photography and an IR-converted digital SLR camera (IR-converted Nikon D50 with Nikon AF 35–80 mm F/4–5.6 lens) with a mounted IR torch. All IR photographs were colour corrected using open-source image editing software. We demonstrated enhanced visualization of bruising and blood-containing structures through the sharper contrast under IR photography. In comparison, melanin sources of pigmentation, such as deep dermal pigmentation, were less obvious if not invisible when photographed in IR. Our examples included photographs of lumbosacral dermal melanocytosis and oculodermal melanocytosis (naevus of Ota). IR photography using a modified digital camera may be a simple, cheap and effective technique allowing the rapid and noninvasive identification of skin bruising, differentiating it from deep dermal pigmentation. This is particularly important in the setting of the emergency department, where confusion has occurred, particularly in patients with skin of colour.