Depth limitations for in vivo magnetic nanoparticle detection with a compact handheld device

Abstract

a b s t r a c tThe increasing interest for local detection of magnetic nanoparticles (MNPs) during clinical interventions requires the development of suitable probes that unambiguously detect the MNPs at a depth of several centimeters in the body. The present study quantitatively evaluates the limitations of a conventional magnetometry method using a sinusoidal alternating field. This method is limited by the variability of the magnetic susceptibility of the surrounding diamagnetic tissue. Two different sensors are evaluated in a theoretical model of MNP detection in a tissue volume. For a coil that completely encloses the sample volume, the MNPs can be detected if the total mass contributing to the signal is larger than 4.1 10 7 × − times the tissue mass. For a handheld surface coil, intended to search for the MNPs in a larger tissue volume, an amount of 1 μg of iron oxide cannot be detected by sensors with a diameter larger than 15 mm. To detect a spot with MNPs at 5 cm depth in tissue, it should contain at least 325 μg iron oxide.Therefore, for high-sensitive clinical MNP detection in surgical interventions, techniques with increased specificity for the nonlinear magnetic properties of MNPs are indispensable.

Novel Handheld Magnetometer Probe Based on Magnetic Tunnelling Junction Sensors for Intraoperative Sentinel Lymph Node Identification

“…The presence of tissue in the vicinity of the probe tip introduces a secondary effect: reduction in the magnetic signal in vivo due to the negative susceptibility (and hence diamagnetic nature) of surrounding tissue. Using a simple mathematical approximation, more than 0.4 μg of iron oxide nanoparticles would be required per 1.0 cm 3 of tissue to counteract this diamagnetic effect and be measured by a coil or induction-based magnetometer 21 . However, the impact of diamagnetic tissue on overall signal strength is expected to be low for the MTJ magnetometer probe, given the large dependence of signal strength on distance from the probe tip.…”

Phantom study quantifying the depth performance of a handheld magnetometer for sentinel lymph node biopsy

“…Unlike the gamma probe, the used magnetometers are not only sensitive to the tracer, but also to the diamagnetic human body. The tissue contribution limits the sensitivity of the devices [11]. This study is the first to quantify the depth performance of the current generation magnetometers, using a tissue mimicking phantom.…”

“…Therefore the positive signal from the tracer can be 'obscured' by the negative signal from the tissue, potentially resulting in failed sentinel lymph node detection. Since the response of this magnetometer is highly distance dependent, this poses a fundamental limitation for the detection of deeply located sentinel nodes with low tracer uptake [11].…”

A handheld SPIO-based sentinel lymph node mapping device using differential magnetometry

“…At this point, it becomes hard to localize the particles because of the low signal to noise ratio (SNR). This means that the maximum attainable sensitivity of such a probe is not limited by the hardware or noise performance of the probe itself, but rather by the tissue under investigation, which is a limitation that cannot be alleviated without obtaining a specific contrast between the SPIONs and the tissue sample (Visscher et al 2015).…”