Design of a Phantom Mimicking Rectal Lymph Nodes for Magnetomotive Ultrasound

Durable and stable phantoms for verifying and validating the new magnetomotive ultrasound technique are lacking. Here we propose a phantom design to address this need.

A mixture of styrene-butylene/ethylene-styrene (SEBS) in mineral oil and glass beads as a scattering material acted as a bulk material, in which a polyvinyl alcohol (PVA) inclusion containing magnetic nanoparticles in water solution and graphite was embedded. The design mimics nanoparticle-laden lymph nodes embedded in mesorectal fat, as would be the clinical scenario for diagnostic support of staging rectal cancer using magnetomotive ultrasound.

The estimated reflection between the insert and bulk material was 10%, matching the clinical case of a lymph node within fat (9%). Speed of sound, attenuation, and Young's modulus of the bulk material were matched with those of body fat. The insert also matched the acoustic and elastic properties of lymph node tissue except for attenuation, which was lower than that given in the literature. Glass beads and graphite were used to control backscatter levels in the respective tissue mimics, providing a contrast of -3.8 dB that was consistent with clinical image appearance. The magnitude of magnetomotion remained stable in three separate samples over the course of 3 weeks.

We have developed a phantom for magnetomotive ultrasound that combines the stability of an oil-based bulk material with the necessity of using a water-based material for the insert. The production procedure may be applied to other phantoms where one tissue type needs to be embedded within another.