Investigating the feasibility of a hand-held photoacoustic imaging probe for margin assessment during breast conserving surgery

Abstract

Approximately 19% of breast cancer patients undergoing breast conserving surgery (BCS) must return for a secondary surgery due to incomplete tumour removal. We propose a single sensor, low-frequency hand-held photoacoustic imaging (PAI) probe for detection of residual cancer tissue during BCS within the surgical cavity and on the excised specimen based on lipid content differences. The probe incorporated a single polyvinylidene fluoride acoustic sensor, a 1-to-4 optical fibre bundle and a polycarbonate axicon lens for light delivery. A phantom consisting of nylon strings was imaged to find an optimal scanning geometry and resolution of the probe. The effect of limited angular coverage was evaluated by comparing the PAI results of a phantom mimicking an ex-vivo breast cancer specimen obtained with the hand-held probe and near-full view PAI system. Translation of the probe with 4 mm steps and rotation over 6° steps resulted in lateral and axial resolution of 1.8 mm and 1 mm, respectively. Experiments with the prototype hand-held PAI probe at 930 nm resulted in excellent image contrast exclusively from lipids. Lipid-free gaps mimicking positive margins were clearly visible in the images. Compared to images from the near full-view PAI system, the hand-held PAI probe had a higher signal-to-noise ratio but suffered from more negativity image artefacts. Taken together, the results show that PAI with the hand-held probe has the potential for detection of residual breast cancer tissue during BCS.