Magnetic induction spectroscopy (MIS)-probe design for cervical tissue measurements.

OBJECTIVE: Gradiometers have the advantage of increasing measuring sensitivity, which is particularly useful in magnetic induction spectroscopy (MIS) for bio-impedance measurements. Traditional gradiometers use a pair of field sensing coils equally distant and on opposite sides of a drive coil, which provides high immunity to interference. In this paper, a ferrite-cored coaxial gradiometer probe of 29 mm diameter has been developed for measuring the impedance spectra of cervical tissues in vivo. APPROACH: It consists of a ferrite rod with outer ferrite confinement screening in order to eliminate the signals from surrounding tissue. The magnetic screening efficiency was compared with an air-cored gradiometer probe. For both gradiometer probes, a drive coil and two sensing coils were wound on a borosilicate glass former aligned coaxially with two sensing coils equidistant from the drive coil. The signal sensitivity of those two MIS gradiometers has been measured using saline samples with a conductivity range between 0.1 and 1.1 S m-1. Finite element methods using COMSOL Multiphysics have been used to simulate the distribution of sensitivity to conductivity over the face of each probe and with depth. MAIN RESULTS: The ferrite-cored probe has a sensitivity confined to the volume defined by the gap between the ferrite core and outer tube of ferrite while the air-cored probe without any magnetic shielding had a wide sensitivity over the face and the side of the probe. Four saline samples and one of distilled water with conductivities from 0.1 to 1.1 S m-1 have been used to make conductivity measurements at frequencies of 50 kHz, 100 kHz, and 300 kHz. The measurement accuracy of the air-cored MIS probe was 0.09 S m-1 at 50 kHz, improving to 0.05 S m-1 at 300 kHz. For the ferrite-cored MIS probe, the measurement accuracy was 0.28 S m-1 at 50 kHz, improving to 0.04 S m-1 at 300 kHz. SIGNIFICANCE: In vivo measurements on human hand have been performed using both types of gradiometers and the conductivity is consistent with reported data.

Young's modulus measurement on pig trachea and bronchial airways.

Young's Modulus was measured on the trachea and first three generations of pig airways by compression. A simple and low-cost system for measuring the elastic properties of small bio-materials is presented. The force-displacement measurements have been undertaken on dissected cartilage and trachea mucosa from pig trachea and bronchial segments. Young's Modulus of trachea wall, 1.78 ± 0.51 MPa, is found to be dominated by the trachea cartilage of value 1.74 ± 0.85 MPa while the modulus for trachea mucosa was 0.15 ± 0.03 MPa. The Young's Modulus of the airway wall from the first three generations of bronchi decreases from 1.35 ± 0.17 to 0.35 ± 0.10 MPa which is also found to be dominated by the airway cartilage. Airway mucosa is found to have similar Young's modulus of 0.036 ± 0.005 MPa for the first three generations of bronchial airways.