Research Summary: Detection of magnetic nanoparticles in tissue using magneto-motive ultrasound

The purpose of this study was to demonstrate the magneto-motive ultrasonic detection of superparamagnetic iron oxide (SPIO) nanoparticles as a marker of macrophage recruitment in tissue. The capability of ultrasound to detect SPIO nanoparticles (core diameter ∼20 nm) taken up by murine liver macrophages was investigated. Eight mice were sacrificed two days after the intravenous administration of four SPIO doses (1.5, 1.0, 0.5, and 0.1 mmol Fe/kg body weight). In the iron-laden livers, ultrasound Doppler measurements showed a frequency shift in response to an applied time-varying magnetic field. M-mode scan and colour power Doppler images of the iron-laden livers also demonstrated nanoparticle movement under focused magnetic field excitation. In the livers of two saline injected control mice, no movement was observed using any ultrasound imaging modes. The results of our experiments indicate that ultrasound imaging of magneto-motive excitation is a candidate imaging modality to identify tissue-based macrophages containing SPIO nanoparticles.

Nanotechnology 17 (2006) 4183–4190

Ultrasound greyscale ((a)–(e)), colour power Doppler ((f)–(j)) and M-mode (k–o) images of livers with different SPIO doses (1.5, 1.0, 0.5, and 0.1 mmol Fe/kg and control liver). Conventional B-scan images were obtained prior to applying the magnetic field. In colour power Doppler mode, a focused magnetic field (2 T) was applied. The liver with high dose administration of SPIO (f) shows significant increasing colour Doppler signal while the normal liver (j) does not exhibit any appreciable colour Doppler signal. The M-mode signal intensity and displacement are proportional to the concentration of SPIO dose. The M-mode signal obtained from a high dose specimen (k) clearly demonstrates a sinusoidal pattern of the displacement once the magnetic field is turned on.

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