## 1 Introduction  
Intra-articular injection therapy is used for the treatment of adhesive capsulitis [1] and joint diseases, including rheumatoid arthritis and osteoarthritis [2]. In contrast to blind injections, imaging-guided (ultrasnography or fluoroscopy) injections ensure better needle insertion and placement of injections at target sites, thereby minimizing injection-induced adverse effects [3]. Ultrasound-guided injections are a rapid and radiation-free technique; however, limited resolution in deep structures reduces the accuracy of this modality. Additionally, greater operator effort is required to skillfully maneuver and coordinate the movements of the probe held in one hand with the needle in the other [1]. Fluoroscopy guided injections are associated with radiation exposure, and visualization of soft tissue structures (particularly nerves and blood vessels) is limited with this modality [2]. Due to the limitations of imaging-guided injections described above, the development of complementary methods for precise needle positioning and effective drug administration in the pathological tissues is still required. To accurately detect the needle position _in vivo_, electrical impedance characterization of tissues can be applied, which non-destructively measures in real-time the electrical properties of the tissue by using a weak alternating electric field [4; 5]. [PERSON] et al. reported the feasibility of the needle guidance in clinical applications using the finite element method (FEM) simulation of electric fields to the electrical impedance (EI) measurement on tissues [6]. The type of tissue can be characterized by analyzing the electrical properties of the biological tissue determined by its morphological structure and physiological condition, such as water contents, fat, consecutive tissue [7]. According to [PERSON] et al., it is possible to detect the needle position from extraneural to intranural compartments in human peripheral nerves by measuring a significant difference in EI [8]. Biological tissues structure shows two conducting sections, the extra- and intercellular area is separated by insulating membranes. Both conductivity and permittivity differ extensively between different biological tissues, and these factors also vary with the frequency [9]. A dielectric property is, therefore, associated with biological tissue wherein the relative permittivity reduces with increasing frequency [10]. Previous studies reported the monopolar, bipolar, or quadripolar microelectrode integrated needle using impedance measurement for the tissue characterization [3; 11; 12; 13; 14; 15; 16]. The microelectrode based impedance measurement showed the possibility of tissue discrimination with needle guidance [3; 13; 14]. [PERSON] et al. presented the impedimetric sensor based biopsy needle for the detection and extraction of suspected cancerous tissues [15]. [PERSON] et al. introduced the novel Injeq IQ-Biopsy needle for real-time tissue identification and discrimination by FEM simulation and biopsy experiment with 21 punctures in five tissue types [17]. [PERSON] et al. introduced the catheter needle mounted by the electrical impedance sensor to improve the success rate of intravenous catheter insertion [14]. Therefore, the utilization of the electrical impedance measurement using the microelectrode integrated needles for diverse clinical applications is increasingly extended. The monopolar injection needle is preferred rather than other electrode configurations when aiming for intra-articular injection therapy since the sensing area of the needle tip is where the drug is administered into the tissue. For the fast detection of the needle position in tissue, in this study, a discrete Fourier transform (DFT)-based impedance monitoring system was developed and evaluated. Since the electrical properties (conductivity, dielectric constant) of porcine tissues are similar to those of human counterparts [18], the pork tissue was used for the impedance measurement using the monopolar injection needle.