Injections of anaesthetics into the epidural space are widely performed to relieve pain. Here, for the first time, we investigated the use of photoacoustic imaging to identify the epidural space using an interventional multispectral photoacoustic (IMPA) imaging system. Excitation light was delivered through an optical fibre positioned within a needle to illuminate the epidural space in a swine model. Spectral unmixing of the images revealed prominent distributions of lipids and haemoglobin in the epidural space at a depth of 35 mm. We conclude that IMPA could be a useful imaging modality to guide placement of needles into the epidural space
