Magnetic induction spectroscopy: non-contact measurement of the electrical conductivity spectra of biological samples

Abstract

Measurement of the electrical conductivity of biological tissues as a function of frequency, often termed 'bioelectrical impedance spectroscopy (BIS)', provides valuable information on tissue structure and composition. In implementing BIS though, there can be significant practical difficulties arising from the electrode-sample interface which have likely limited its deployment in industrial applications. In magnetic induction spectroscopy (MIS) these difficulties are eliminated through the use of fully non-contacting inductive coupling between the sensors and sample. However, inductive coupling introduces its own set of technical difficulties, primarily related to the small magnitudes of the induced currents and their proportionality with frequency. This paper describes the design of a practical MIS system incorporating new, highly-phase-stable electronics and compares its performance with that of electrode-based BIS in measurements on biological samples including yeast suspensions in saline (concentration 50-400 g l −1 ) and solid samples of potato, cucumber, tomato, banana and porcine liver. The shapes of the MIS spectra were in good agreement with those for electrode-based BIS, with a residual maximum discrepancy of 28%. The measurement precision of the MIS was 0.05 S m −1 at 200 kHz, improving to 0.01 S m −1 at a frequency of 20 MHz, for a sample volume of 80 ml. The data-acquisition time for each MIS measurement was 52 s. Given the value of spectroscopic conductivity information and the many advantages of obtaining these data in a non-contacting manner, even through electrically-insulating packaging materials if necessary, it is concluded that MIS is a technique with considerable potential for monitoring bio-industrial processes and product quality.

Twenty-Four-Hour Real-Time Continuous Monitoring of Cerebral Edema in Rabbits Based on a Noninvasive and Noncontact System of Magnetic Induction

“…In addition to the MIPS data obtained in the frequency range of 300 kHz to 200 MHz, a magnetic induction amplitude in the same frequency range was obtained. The greater the amplitude of the frequency, the higher the MIPS detection sensitivity and the better the consistency among samples [15,16,20]. Therefore, the software automatically defaults the detection frequency to the frequency with the highest amplitude.…”

“…Different biological tissues have different electromagnetic properties and therefore can be differentiated on the basis of these features [10]. Currently this method has been applied to study the moisture content of the brain, brain hematoma, dielectric constant and cardiopulmonary activities [11,12,13,14,15,16]. Therefore, we assume that measuring the change in the MIPS could be a noncontact method for the bedside monitoring of cerebral edema to show its development.…”

Inductive phase shift as a future cost effective diagnostic tool in breast cancer localization: A prologue study

“…The EMIS was particularly very useful in detecting buried landmines and unexploded ordnance (Won, Keiswetter, & Novikova, 1998). The non-contacting magnetic induction technologies was then evolved and adapted to measure bio-impedance level [2][3] [4] and dielectrical properties in biological sample [5] [6][7][8]. H. Scharfetter et al mentioned that apart from the common PEPs, which is the conductivity and permittivity values, magnetic permeability can also be useful for medical diagnostic purposes.…”

Wideband microwave imaging system for brain injury diagnosis

“…Because of the reduced computational complexity, the image reconstruction with proposed algorithm takes 7-10 seconds, which is less than the time required by existing algorithms [20,21]. Other reported low-cost and portable imaging technologies (e.g., EIT [27], MIT [28], MIS [29], PSSMI [30]) demonstrate advantages in either simulations or on simple phantoms without much realistic demonstration.…”

“…Several medical imaging modalities, like electrical impedance tomography (EIT) [27], magnetic induction tomography (MIT) [28], magnetic induction spectroscopy (MIS) [29], or phase shift spectroscopy of magnetic induction (PSSMI) [30] are recently explored by the researchers. However, these technologies are either invasive or cannot detect ICH in a realistic environment; hence their practical demonstration is scarce.…”