High-frequency Ultrasound Imaging of Mouse Cervical Lymph Nodes

Abstract

High-frequency ultrasound (HFUS) is widely employed as a non-invasive method for imaging internal anatomic structures in experimental small animal systems. HFUS has the ability to detect structures as small as 30 µm, a property that has been utilized for visualizing superficial lymph nodes in rodents in brightness (B)-mode. Combining power Doppler with B-mode imaging allows for measuring circulatory blood flow within lymph nodes and other organs. While HFUS has been utilized for lymph node imaging in a number of mouse model systems, a detailed protocol describing HFUS imaging and characterization of the cervical lymph nodes in mice has not been reported. Here, we show that HFUS can be adapted to detect and characterize cervical lymph nodes in mice. Combined B-mode and power Doppler imaging can be used to detect increases in blood flow in immunologically-enlarged cervical nodes. We also describe the use of B-mode imaging to conduct fine needle biopsies of cervical lymph nodes to retrieve lymph tissue for histological analysis. Finally, software-aided steps are described to calculate changes in lymph node volume and to visualize changes in lymph node morphology following image reconstruction. The ability to visually monitor changes in cervical lymph node biology over time provides a simple and powerful technique for the non-invasive monitoring of cervical lymph node alterations in preclinical mouse models of oral cavity disease.

Development of Preclinical Ultrasound Imaging Techniques to Identify and Image Sentinel Lymph Nodes in a Cancerous Animal Model

“…Limiting surgical resection would significantly reduce surgical complications and consequently result in an improved quality of life for the patient. Grey scale ultrasound imaging (US) has previously been used to identify and characterize the LNs adjacent to the primary tumor [4,[6][7][8]. Specifically with respect to rectal cancer, a meta-analysis of clinical studies undertaken between 1985 and 2005 demonstrated that endoluminal ultrasound was at least as good as MRI or CT for identification of nodal disease and that no significant difference between imaging modalities was measured with respect to the staging of nodal status [4].…”

“…Lin et al demonstrated that quantitative parameters such as short axis length, echogenicity, shape, and how distinct the lymph node margin were independent features capable of predicting lymph node metastasis in lung cancer patients [7]. In a highly detailed paper, Walk et al demonstrated the efficacy of high-resolution ultrasound for imaging and accurately reconstructing small structures such as mouse cervical lymph nodes in 3D [6].…”

“…Combined with color Doppler and ultrasonic contrast agents, it can help determine the vascularization and the shape of superficial LNs [9]. Unlike CT and MRI, US provides real-time images and can therefore be utilized for fine-needle aspiration biopsies [6,10]. Despite promising findings, EFSUMB guidelines do not recommend the use of US or CEUS for the characterization of LN for clinical use; however, they encourage research in this field [11].…”

Lymph node expansion predicts magnitude of vaccine immune response

“…In this work, we assessed the cellular and tissue-scale LN responses to 'strong' and 'weak' vaccines with distinct therapeutic outcomes. Vaccine-draining LNs (dLNs) were imaged longitudinally using high frequency ultrasound (HFUS), a simple, noninvasive technique for visualizing superficial internal structures with high (~20μm) axial resolution, to establish the magnitude and kinetics of LN response [14]. Gross LN expansion was then analyzed in comparison to outcomes of immunization (i.e.…”