Application of Photoacoustic Imaging for Lymphedema Treatment

Abstract

Background Lymphatic vessels are difficult to identify using existing modalities as because of their small diameter and the transparency of the lymph fluid flowing through them. Methods Here, we introduce photoacoustic lymphangiography (PAL), a new modality widely used for lymphedema treatment, to observe limb lymphatic vessels. The photoacoustic imaging system used in this study can simultaneously visualize lymphatic vessels and veins with a high resolution (0.2 mm) and can also observe their three-dimensional relationship with each other. Results High-resolution images of the lymphatic vessels, detailed structure of the dermal back flow, and the three-dimensional positional relationship between the lymphatic vessels and veins were observed by PAL. Conclusion The clear image provided by PAL could have a major application in pre- and postoperative use during lymphaticovenular anastomosis for lymphedema treatment.

The Lymphatic System—A Surgeon’s Point of View

“…Ultra-high frequency ultrasound (UHF-US) with a frequency range of 48-70 MHz provides an improved resolution compared to conventional ultrasound (15)(16)(17)(18)(19)(20)(21)(22)(23)(24). It enables the accurate, real-time visualization of the lymphatic vessels, even those with diameters smaller than 0.3 mm, and allows operators to distinguish them from the subcutaneous veins or the nerves [20].…”

“…Photoacoustic imaging is a novel technique that utilizes the photoacoustic effect to visualize the lymphatic and vascular systems in three dimensions with a high resolution. This imaging modality, known as PA lymphangiography, involves the absorption of a specific wavelength of light by chromophores such as melanin, hemoglobin, or ICG, leading to thermoelastic expansion and the production of acoustic waves that are detected using an ultrasound transducer [23,24]. Unlike ICG-L, which also relies on ICG to identify lymphatic vessels, PA imaging can accurately differentiate between veins and lymphatic vessels, asses the three-dimensional relationship between them, and is less influenced by dermal backflow [23].…”

“…This imaging modality, known as PA lymphangiography, involves the absorption of a specific wavelength of light by chromophores such as melanin, hemoglobin, or ICG, leading to thermoelastic expansion and the production of acoustic waves that are detected using an ultrasound transducer [23,24]. Unlike ICG-L, which also relies on ICG to identify lymphatic vessels, PA imaging can accurately differentiate between veins and lymphatic vessels, asses the three-dimensional relationship between them, and is less influenced by dermal backflow [23]. Consequently, using PA imaging intraoperatively enables the rapid identification of optimal sites for LVA and the assessment of anastomosis patency.…”

“…However, it is still a developing technology, and handheld PA imaging devices are limited to a depth of 1 cm. Additionally, accurately adjusting the positions of the PA lymphangiography figures and the patient's limb for clinical application remains challenging [23,24]. Despite these challenges, PA lymphangiography shows great promise as a valuable tool in lymphatic surgery.…”

Comparative Analysis of Preoperative High Frequency Color Doppler Ultrasound versus MR Lymphangiography versus ICG Lymphography of Lymphatic Vessels in Lymphovenous Anastomosis

“…In addition to the various imaging modalities that are available to detect lymphatic vessels, newer modalities are continuously being introduced today. [8][9][10][11] Currently, the most commonly used diagnostic tool for lymphedema is lymphoscintigraphy but gives little information regarding the actual lymphatic vessels that can be targets for physiologic surgery. Therefore, other imaging techniques have been utilized for planning lymphovenous anastomosis.…”