Detection of magnetomotive ultrasound signals from human tissue

Rectal cancer is a common cancer, with presently a 5-year survival of 67 %. Treatment is based on tumor stage, but current staging methods, such as magnetic resonance imaging (MRI) or ultrasound, are limited in the ability to correctly stage the disease. Magnetomotive ultrasound is a developing modality that has a potential to improve rectal cancer staging. Magnetic nanoparticles are set in motion by an external magnetic field, and the resulting motion signature is detected by ultrasound. Here, we report on magnetomotive images of magnetic nanoparticles in human tissue, using a prototype system where a rotating permanent magnet provides the varying magnetic field, and an ultrasound transducer array encircling the magnet, detects the induced motion. Prior to surgery, a patient with a low rectal tumor was injected at three sites close to the tumor with magnetic nanoparticles. Postsurgical magnetomotive ultrasound scanning revealed the three injection sites, with no obvious artefactual signals. A phantom study showed detection of nanoparticles beyond 40 mm, where 30 mm is the expected maximum distance to mesorectal lymph nodes.

Magnetomotive ultrasound image of iron oxide nanoparticles in human tissue. Prior to surgery a patient was injected with nanoparticles, and the excised tissue specimen was imaged with a prototype magnetomotive ultrasound system. The three colored areas overlaid on the standard B-mode greyscale image, correspond to the three injection sites.