title: Tissue type determination by impedance measurement: A bipolar and monopolar comparison.
abstract: BACKGROUND
  In certain medical applications, it is necessary to be able to determine the position of a needle inside the body, specifically with regards to identifying certain tissue types. By measuring the electrical impedance of specific tissue types, it is possible to determine the type of tissue the tip of the needle (or probe) is at.
  
  
  METHODS
  Two methods have been investigated for electric impedance detection; bipolar and monopolar. Commercially available needle electrodes are of a monopolar type. Although many patents exist on the bipolar setups, these have not as yet been commercialized. This paper reports a comparison of monopolar and bipolar setups for tissue type determination.In vitroexperiments were carried out on pork to compare this investigation with other investigations in this field.
  
  
  RESULTS
  The results show that both monopolar and bipolar setups are capable of determining tissue type. However, the bipolar setup showed slightly better results; the difference between the different soft tissue type impedances was greater compared to the monopolar method.
  
  
  CONCLUSIONS
  Both monopolar and bipolar electrical impedance setups work very similarly in inhomogeneous volumes such as biological tissue. There is a clear potential for clinical applications with impedance-based needle guidance, with both the monopolar and bipolar setups. It is, however, worth noting that the bipolar setup is more versatile.
authors.affiliation: Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK.
authors.forename: Jack
authors.initials: J
authors.lastname: Sharp
authors.affiliation: Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK.
authors.forename: Kaddour
authors.initials: K
authors.lastname: Bouazza-Marouf
authors.affiliation: Department of Anaesthesia, University Hospitals of Leicester NHS Trust, Leicester, Leicestershire LE1 5WW, UK.
authors.forename: Dorita
authors.initials: D
authors.lastname: Noronha
authors.affiliation: Department of Anaesthesia, University Hospitals of Leicester NHS Trust, Leicester, Leicestershire LE1 5WW, UK.
authors.forename: Atul
authors.initials: A
authors.lastname: Gaur
keywords: Anesthesia interventions; bipolar; impedance; monopolar; soft tissue