Determining biological tissue type

A method of determining if a biological tissue region of interest includes intraneural tissue based on a complex impedance spectra that has been obtained from a probe with a conducting part adjacent the tissue region of interest, wherein the impedance spectra includes data from a plurality of frequencies, the method comprising:

• obtaining, from the complex impedance spectra, a first data set representative of impedance modulus values, or equivalent admittance values, at one or more frequencies;
• obtaining, from the complex impedance spectra, a second data set representative of impedance phase angle values, or equivalent admittance values, at one or more different frequencies;
• applying a first discrimination criterion to the first data set to determine whether or not the impedance modulus is below a value known to exclude subcutaneous fat tissue;
• applying a second discrimination criterion to the second data set to determine if the phase angle at a set frequency is above a threshold level that is known to exclude at least one of muscle tissue and perineural tissue;
• applying a third discrimination criterion to the second data set to determine if a gradient of the phase angle at a set frequency is larger than 3/126 degrees per kHz at a set frequency that is above 10 kHz and below 400 kHz;
• and
• thereby determining if the tissue region of interest includes intraneural tissue.