Lock-in Amplifier-Based Impedance Detection of Tissue Type Using a Monopolar Injection Needle

Abstract

For successful intra-articular injection therapy, it is essential to accurately position the tip of the injection needle into the target joint area while administering the drug into the affected tissue. In this study, we investigated the feasibility of a monopolar injection needle and lock-in amplifier (LIA)-based impedance measurement system for detecting the tissue type where the needle tip is located. After positioning the monopolar injection needle tip into the dermis, hypodermis, or muscle layer of pork tissue, the electrical impedance was measured in the frequency range of 10 Hz to 10 kHz. We observed a difference in the results based on the tissue type where the needle was positioned (p-value < 0.01). Therefore, the monopolar injection needle with electrical impedance measurement can be used to improve intra-articular injection therapy through non-destructive and real-time monitoring of the needle position in the tissues.

Keywords: bio-impedance; intra-articular injection therapy; lock-in amplifier; monopolar injection needle; porcine tissue.

Figure 1

Experimental setup of the lock-in amplifier (LIA)-based impedance measurement system for detection of the tip position of the monopolar injection needle in the tissue layers with Ag/AgCl counter electrode and saline injection with the syringe pump and ultrasound (US) device.

Figure 2

(a) Electrical impedance magnitude and (b) phase of the resistors (100 Ω to 1 MΩ) or the (c) impedance magnitude and (d) phase of capacitors (1 nF to 1 μF) measured by the developed impedance measurement system (symbols) and commercialized product (PalmSens4, lines) in the frequency range of 10 Hz to 10 kHz.

Figure 2

(a) Electrical impedance magnitude and (b) phase of the resistors (100 Ω to 1 MΩ) or the (c) impedance magnitude and (d) phase of capacitors (1 nF to 1 μF) measured by the developed impedance measurement system (symbols) and commercialized product (PalmSens4, lines) in the frequency range of 10 Hz to 10 kHz.

Figure 3

Ultrasound image of the needle insertion in the tissue layer.

Figure 4

(a) Real and (b) imaginary part of the impedance spectra measured at different depths of the needle in the dermis, hypodermis, or muscle tissue; and normalized (c) real and (d) imaginary part of the impedance spectra to the data of the saline (0.9% NaCl) solution.

Figure 5

(a) Real and imaginary part of the impedance of the tissue layer measured at 2.15 kHz. (b) Difference of the average of the real part of the impedance at 2.15 kHz between the tissue layers (n = 3, bar: Standard error) evaluated by the Student’s t-test. (c) Monitoring of the real part of the impedance at 2.15 kHz, while the monopolar injection needle is moved to a different tissue layer. (d) Monitoring of the real part of impedance at 2.15 kHz during the saline injection process at different tissue layers.