Quantitative Analysis of Superparamagnetic Contrast Agent in Sentinel Lymph Nodes Using Ex Vivo Vibrating Sample Magnetometry

Abstract

As the first step in developing a new clinical technique for the magnetic detection of colorectal sentinel lymph nodes (SLNs), a method is developed to measure the magnetic content in intact, formalin fixated lymph nodes using a vibrating sample magnetometer (VSM). A suspension of superparamagnetic nanoparticles is injected ex vivo around the tumor in the resected colon segments. A selection of three lymph nodes is excised from the region around the tumor and is separately measured in the VSM. The iron content in the lymph nodes is quantified from the magnetic moment curve using the Langevin model for superparamagnetism and a bimodal particle size distribution. Adverse, parasitic movements of the sample were successfully reduced by tight fixation of the soft tissue and using a small vibration amplitude. Iron content in the lymph nodes is detected with 0.5 μg accuracy and ranged from 1 to 51 μg. Histological staining confirmed iron presence. The current method of measuring intact biological tissue in a VSM is suitable to show the feasibility and merit of magnetic detection of SLNs in colorectal cancer. For clinical validation of magnetic SLN selection in colorectal cancer, a new magnetometer with high specificity for superparamagnetic nanoparticles is required.

Comparison of three magnetic nanoparticle tracers for sentinel lymph node biopsy in an in vivo porcine model

“…VSM allows quantification with 0.5 μg Fe accuracy and is nondestructive, which allows subsequent histopathological analysis of the same samples. 22 …”

Ex vivo sentinel lymph node mapping in colorectal cancer using a magnetic nanoparticle tracer to improve staging accuracy: a pilot study

“…Magnetic tracers have several advantages for use in SLNM in CRC. We previously demonstrated that they accumulate in the LNs in CRC after ex vivo administration using nonclinical laboratory equipment [16].…”

“…Magnetic tracers have several advantages for use in SLNM in CRC. We previously demonstrated that they accumulate in the LNs in CRC after ex vivo administration using nonclinical laboratory equipment . Recently the use of magnetic tracers was also evaluated for SLN biopsy in patients with breast cancer .…”

Magnetic nanoparticle imaging using multiple electron paramagnetic resonance activation sequences

“…4,5 To generate the correct temperatures, accurate knowledge of the spatial MNP distribution is of critical importance. Other MNP-based applications such as drug targeting 5,6 and detection 7,8 also require this knowledge. In this paper, Electron Paramagnetic Resonance (EPR) is employed for recovering the MNP distribution.…”