Performance of a Nonlinear Magnetic Handheld Probe for Intraoperative Sentinel Lymph Node Detection: A Phantom Study

Abstract

Objective: This study investigates the performance of the DiffMag handheld probe (nonlinear magnetometry), to be used for sentinel lymph node detection. Furthermore, the performance of DiffMag is compared with a gamma probe and a first-order magnetometer (Sentimag^®, linear magnetometry).

Methods: The performance of all three probes was evaluated based on longitudinal distance, transverse distance, and resolving power for two tracer volumes. A phantom was developed to investigate the performance of the probes for a clinically relevant situation in the floor of the mouth (FOM).

Results: Considering the longitudinal distance, both DiffMag handheld and Sentimag^® probe had comparable performance, while the gamma probe was able to detect at least a factor of 10 deeper. Transverse distances of 13, 11, and 51 mm were measured for the small tracer volume by the DiffMag handheld, Sentimag^®, and the gamma probe, respectively. For the large tracer volume this was 21, 18, and 55 mm, respectively. The full width at half maximum, at 7 mm probe height from the phantom surface, was 14, 12, and 18 mm for the small tracer volume and 15, 18, and 25 mm for the large tracer volume with the DiffMag handheld, Sentimag^®, and gamma probe, respectively.

Conclusions: With a high resolving power but limited longitudinal distance, the DiffMag handheld probe seems suitable for detecting SLNs which are in close proximity to the primary tumor. In this study, comparable results were shown using linear magnetometry. The gamma probe reached 10 times deeper, but has a lower resolving power compared with the DiffMag handheld probe.

Keywords: Detection; Gamma probe; Magnetic handheld probe; Sentinel lymph node; Superparamagnetic iron oxide nanoparticle.

Fig. 1

Schematic representation of setup, measuring a tracer sample. a Magnetic probe setup. b Gamma probe setup. Black dots between the phantom and polymethyl-methacrylate (PMMA) sheet represent PMMA supports, preventing the PMMA from touching the radioisotope sample. c Schematic representation of phantom with axis orientation

Fig. 2

a Longitudinal distance evaluation, a.1 measurement of an SLN and a.2 of an injection spot. b Transverse measurements of individual tracer volumes for full width at half maximum (FWHM) calculation, and maximum transverse distance, b.1 measurement of an SLN and b.2 of an injection spot. c Transverse measurements for resolving power evaluation (c.1, two adjacent samples)

Fig. 3

Longitudinal distance (mm) measured for 140 µg Fe (a) and 2800 µg Fe (b) Magtrace using DiffMag and Sentimag probes, and for ≈ 5.75 MBq (a) and ≈ 23 MBq (b) ^99mTc using gamma probe

Fig. 4

Transverse distance for DiffMag handheld, Sentimag, and gamma probe at 140 µg Fe/≈ 5.75 MBq (a) and 2800 µg Fe/≈ 23 MBq (b)

Fig. 5

a Application of Gaussian mixture model on results of two adjacent small tracer volumes 16 mm apart, the different probes at 7 mm height from the phantom surface. b For the DiffMag handheld probe, two adjacent small tracer volumes 16 mm apart, measured at 1 mm and 7 mm height above the phantom surface

Fig. 6

A Delrin^® phantom shows within each column one big pit (capacity 500 µl) representing one injection spot and two small pits (capacity 5 µl) representing the SLNs