Sentinel Node Detection Using Contrast-Enhanced Power Doppler Ultrasound Lymphography

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Abstract
To establish the feasibility of using contrast-enhanced interstitial ultrasound (US) lymphography as an alternative to current sentinel node detection methods. Aqueous US contrast microbubble suspensions of varying diameter were evaluated in vitro to characterize response to insonation. Contrast media were then injected subcutaneously into the distal extremities of 11 normal dogs to target the cervical and popliteal lymph nodes (nodes, n = 40). First-order (sentinel) lymph nodes and second-order sublumbar nodes were imaged intermittently from 0 to at least 120 minutes following contrast injection using continuous power Doppler mode. Lymphoscintigraphy studies were performed on 4 dogs to verify lymphatic drainage patterns and sentinel lymph nodes. Contrast enhancement occurred in 34/40 (85%) sentinel nodes overall and in 30/32 (94%) nodes when submicron or near-micron diameter bubble formulations were used. In many instances, enhancement persisted throughout the imaging period. Contrast response was most pronounced using a high mechanical index and tissue artifact was reduced or eliminated when using a high pulse repetition frequency. Contrast-enhanced interstitial US lymphography could serve as an alternative to current sentinel node detection methods. Preliminary findings suggest that submicron or near-micron-diameter bubbles may be suitable for lymphatic imaging applications.