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

The 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 1μg of iron oxide cannot be detected by sensors with a diameter larger than 15mm. To detect a spot with MNPs at 5cm depth in tissue, it should contain at least 325μg 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. •Compensation accuracy of the magnetic tissue response limits detection of MNPs.•With larger detection coils the tissue response dominates over the MNP response.•The use of MNPs' nonlinearity is crucial for high-sensitive clinical application.