LED-based photoacoustic imaging of the lymphatic vessels in patients with secondary lymphedema

Abstract

Lymphedema is characterized by the accumulation of protein-rich fluid in the intersitium (i.e., dermal backflow (DBF)), causing swelling. It is commonly seen due to iatrogenic damage to the lymphatics after surgical and radiotherapeutic treatment of cancer. An important microsurgical treatment is lymphovenous bypass (LVB) surgery, during which a lymphatic vessel is anastomosed to a vein to bypass the site of lymphatic flow obstruction. Pre-operative imaging of the lymphatic vessels is a prerequisite for surgical planning. Photoacoustic imaging (PAI) can potentially visualize both lymphatic vessels (with the aid of indocyanine green; ICG) and the receiving veins, with high resolution, in depth, in the presence of superficial DBF. We investigated lymphatic vessel imaging using light emitting diode (LED) based PAI (Acoustic X, Cyberdyne Inc., Tsukuba, Japan) in patients with secondary limb lymphedema. Ten patients were enrolled in the study. ICG-mediated near-infrared fluorescence lymphography (NIRF-L) revealed multiple locations of lymphatic vessels on the healthy and affected limb, with and without the presence DBF in various stages. Subsequently, interleaved PAI (820 and 940 nm) and ultrasound images were acquired in these locations and successful vessel depiction was determined. The ratio between the PA signal at 940 and 820 nm was used to differentiate between ICG-labelled lymphatics and blood vessels. We demonstrated that dual-wavelength, LED-based PAI can visualize lymphatic and blood vessels even in the presence of DBF. These findings suggest that LED-based PAI has potential for pre-operative lymphedema assessment, especially in cases with extensive DBF pattern hindering adequate assessment with NIRF-L.