title: Phantom study quantifying the depth performance of a handheld magnetometer for sentinel lymph node biopsy.
abstract: OBJECTIVE
  The use of a magnetic nanoparticle tracer and handheld magnetometer for sentinel lymph node biopsy (SLNB) was recently introduced to overcome drawbacks associated with the use of radioisotope tracers. Unlike the gamma probe, the used magnetometers are not only sensitive to the tracer, but also the diamagnetic human body. This potentially limits the performance of the magnetometer when used clinically.
  
  
  METHODS
  A phantom, mimicking the magnetic and mechanical properties of the human axilla, was constructed. The depth performance of two current generation magnetometers was evaluated in this phantom. LN-phantoms with tracer uptake ranging from 5 to 500μg iron were placed at clinically relevant depths of 2.5, 4 and 5.5cm. Distance-response curves were obtained to quantify the depth performance of the probes.
  
  
  RESULTS
  The depth performance of both probes was limited. In the absence of diamagnetic material and forces on the probe (ideal conditions) a LN-phantom with high uptake (500μg iron) could first be detected at 3.75cm distance. In the phantom, only superficially placed LNs (2.5cm) with high uptake (500μg iron) could be detected from the surface. The penetration depth was insufficient to detect LNs with lower uptake, or which were located deeper.
  
  
  CONCLUSIONS
  The detection distance of the current generation magnetometers is limited, and does not meet the demands formulated by the European Association for Nuclear Medicine for successful transcutaneous SLN localization. Future clinical trials should evaluate whether the limited depth sensitivity is of influence to the clinical outcome of the SLNB procedure.
authors.affiliation: MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, P.O. Box 217, 7500AE, Enschede, The Netherlands. Electronic address: J.J.Pouw@utwente.nl.
authors.forename: Joost J
authors.initials: JJ
authors.lastname: Pouw
authors.affiliation: MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, P.O. Box 217, 7500AE, Enschede, The Netherlands. Electronic address: DanielBastiaan@gmail.com.
authors.forename: Daniel M C
authors.initials: DM
authors.lastname: Bastiaan
authors.affiliation: Department of Surgery, Medisch Spectrum Twente, P.O. Box 50.000, 7500KA, Enschede, The Netherlands. Electronic address: J.Klaase@mst.nl.
authors.forename: Joost M
authors.initials: JM
authors.lastname: Klaase
authors.affiliation: MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, P.O. Box 217, 7500AE, Enschede, The Netherlands. Electronic address: B.tenHaken@utwente.nl.
authors.forename: Bennie
authors.initials: B
authors.lastname: Ten Haken
mesh_terms: D006801:Humans; D060328:Magnetic Phenomena; D060306:Magnetometry / Q000295:instrumentation*; D019047:Phantoms, Imaging; D021701:Sentinel Lymph Node Biopsy / Q000295:instrumentation*
keywords: Magnetic tracer; Magnetometer; Penetration depth; Phantom; Sentimag; Sentinel lymph node biopsy