Magnetic induction tomography: hardware for multi-frequency measurements in biological tissues.
Magnetic induction tomography (MIT) is a contactless method for mapping the electrical conductivity of tissue. MIT is based on the perturbation of an alternating magnetic field by a conducting object. The perturbation is detected by a voltage change in a receivercoil. At physiologically interesting frequencies (10 kHz-10 MHz) and conductivities (< 2 S m(-1)) the lower limit for the relative voltage change (signal/carrier ratio = SCR) to be resolved is 10(-7)-10(-10). A new MIT hardware has been developed consisting of a coil system with planar gradiometers and a high-resolution phase detector (PD). The gradiometer together with the PD resolves an SCR of 2.5 x 10(-5) (SNR = 20 dB at 150 kHz, acquisition speed: 100 ms). The system operates between 20 and 370 kHz with the possibility of extending the range up to 1 MHz. The feasibility of measuring conductivity spectra in the beta-dispersion range of biological tissues is experimentally demonstrated. An improvement of the resolution towards SCR = 10(-7) with an SNR of > or = 20 dB at frequencies > 100 kHz is possible. On-line spectroscopy of tissue conductivity with low spatial resolution appears feasible, thus enabling applications such as non-invasive monitoring of brain oedema.
Institute for Biomedical Engineering, Technical University of Graz, Austria. scharfetter@bmt.tu-graz.ac.at
H
H
Scharfetter
H K
HK
Lackner
J
J
Rosell
D001929:Brain Edema / Q000175:diagnosis; D004553:Electric Conductivity; D004867:Equipment Design; D006801:Humans; D008280:Magnetics; D012680:Sensitivity and Specificity; D014054:Tomography / Q000295:instrumentation* / Q000706:statistics & numerical data