Original ContributionShear Wave Elasticity Imaging of Cervical Lymph Nodes
Introduction
Ultrasound shear wave elastography (SWE) is a comparatively new development in elasticity imaging and has only recently been available on commercial clinical ultrasound (US) systems. Such systems generate acoustic radiation force impulses using specialized transducers, measure the speed of induced shear waves using ultrafast US tracking techniques, and from this data estimate tissue elastic modulus (stiffness) (Bercoff et al. 2004). At present, in systems using real-time SWE, this information can be displayed continually using a colour-coded overlay onto gray-scale images, while absolute measurements can be obtained within static elasticity image frames. As SWE permits absolute quantification of tissue stiffness, it represents a significant advance over conventional US (strain) elastography that at best produces semiquantitative estimates corresponding to relative tissue strain. Furthermore, by utilizing acoustic radiation to stimulate tissues, modern systems using SWE circumvent the requirement for manual tissue compression and, hence, may be less operator-dependent than conventional elastography. A handful of preliminary studies evaluating conventional strain elastography have documented moderate to high accuracies for differentiating benign and malignant cervical lymph nodes (73%–95%)(Alam et al., 2008, Aoyagi et al., 2009, Bhatia et al., 2010, Lyshchik et al., 2007, Saftoiu et al., 2006). The aim of this pilot study was to document our preliminary experience of performing SWE in the neck for cervical lymph nodes in routine clinical practice and, in particular, investigate its utility in identifying malignancy. It was not the purpose of this study to document the accuracy of conventional sonographic criteria for malignancy as this has been well documented in the medical literature.
Section snippets
Patient selection
Between January and June 2011, 46 patients with 55 neck lymph nodes undergoing US guided fine needle aspiration for cytology (FNAC) in a routine head and neck US clinic were enrolled into this prospective pilot study. Conventional sonography using a 5–12 MHz linear array transducer (Philips iU22; Philips Healthcare Nederland, Eindhoven, The Netherlands) had been performed by experienced head and neck radiologists (A.T.A and E.H-Y.Y) and nodes were selected for FNAC based on well-documented
Results
Of 55 lymph nodes, 31 were malignant (11 squamous cell carcinoma, 5 nasopharyngeal cancer, 4 non Hodgkin’s lymphoma, 5 adenocarcinoma of the lung, 5 papillary thyroid cancer, 1 poorly differentiated cancer) and 24 were benign (23 reactive, 1 tuberculous node). The mean short axis diameter ± 1 standard deviation of benign nodes was 8.8 ± 3.4 mm (range 3–30 mm) and malignant nodes was 11.4 ± 6.8 mm (range 4–30 mm), which were not significantly different (p = 0.26, Mann Whitney U test). No nodes
Discussion
Previously published pilot studies of US elastography for cervical lymph nodes have utilized conventional strain elastography with a variety of methods for strain measurement. These include visual or software-assisted grading of colour-coded strain elastograms or semiquantitative strain indices whereby strain in lymph nodes is compared to a reference tissue such as muscle (Alam et al., 2008, Aoyagi et al., 2009, Bhatia et al., 2010, Lyshchik et al., 2007, Saftoiu et al., 2006). The present
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