Variation Of Electrical Impedance Research Articles

Engineering Biomedical Problems to Detect Carcinomas: A Tomographic Impedance Approach

Computed tomography (CT), magnetic resonance imaging (MRI), and radiography expose patients to electromagnetic fields (EMFs) and ionizing radiation. As an alternative, Electrical Impedance Tomography (EIT) offers a less EMF-influenced method for imaging by measuring superficial skin currents to provide a map of the body’s conductivity. EIT allows for functional monitoring of anatomical regions using low electromagnetic fields and minimal exposure times. This paper investigates the application of EIT for the morphological and functional assessment of tissues. Using the Finite Element Method (FEM) (Comsol 5.2), both two-dimensional and three-dimensional models and simulations of physiological and pathological tissues were developed to replicate EIT operations. The primary objective is to detect carcinoma by analysing the electrical impedance response to externally applied excitations. An eight-electrode tomograph was utilised for this purpose, specifically targeting epithelial tissue. The study allowed the characterisation of tomographs of any size and, therefore, the possibility to verify both their geometric profile and the ideal value of the excitation current to be delivered per second of the type of tissue to be analysed. Simulations were conducted to observe electrical impedance variations within a homogeneously modelled tissue and a carcinoma characterized by regular geometry. The outcomes demonstrated the potential of EIT as a viable technique for carcinoma detection, emphasizing its utility in medical diagnostics with reduced EMF exposure.

Variation of electrical impedance over 5 years post-implantation and relationship with the maximum comfort level (MCL) in adults with cochlear implants

IntroductionThe maximum comfort level (MCL), threshold level (THR) and electrical impedance change in the postoperative period of the cochlear implant for months until they stabilize. The objective of this article is to establish the variation during 5 post-surgical years of impedance, and its relationship with MCL in unilaterally implanted adults. MethodsRetrospective study over 5 years, with 78 adult patients implanted with MED-EL in a tertiary hospital from the year 2000 to 2015. The variation in impedance, MCL and the relationship between them were analyzed in basal (9–12), medial (5–8) and apical electrodes (1–4), performing an inferential ANOVA analysis of repeated measures with comparisons between consecutive times, corrected with Bonferroni criteria. Results33 men (42.3%) and 45 women (57.7%), with a mean age of 52.7±14.6 years. “Stability” was considered the time of follow-up without statistically significant differences between one visit and the next. Changes in impedance in medial electrodes ceased to be statistically significant at 3 months, and in apicals at 6 months, with mean values of 5.84 and 6.43kΩ. MCL stabilized at 2 years in basal and apical electrodes, and at 3 years in medial, with mean values of 24.9, 22.7, and 25.6qu. There was a correlation between MCL and impedance in medium electrodes up to 3 months and in apical ones up to one year. ConclusionsElectrical impedance drops significantly in medial and apical electrodes up to 3 and 6 months. MCL increases significantly up to two years. Impedance is related to MCL up to 6 months.

Development of robust ultra-high-performance carbon nanofiber aggregates (UHPCNFAs) for structural health monitoring

Ultra-high-performance concrete (UHPC) is rapidly implemented to build robust, durable, and sustainable structures. This study presents the development of a robust self-sensing sensor with the motivation to monitor structures with high-performance construction material, such as UHPC. The ultra-high-performance carbon nanofiber aggregates (UHPCNFAs) are carbon nanofibers (CNFs) and UHPC-based smart aggregates. The newly developed UHPCNFAs are experimentally investigated in uniaxial compression. Sweep-frequency and fixed-frequency tests are adopted in alternating current measurements for determining the electrical behavior of the UHPCNFAs. UHPCNFAs are compressed in parallel and perpendicular loading orientations to understand the difference in the sensor's electrical sensitivity and mechanical behavior in each case. In addition, the robustness of the UHPCFNA is examined to the point of failure in both orientations. The relationship between stress, strain, and electrical impedance variation is established for eight different frequencies. Furthermore, the UHPCNFAs are compressed at a fixed frequency to verify the repeatable behavior. This paper examines the effect of loading orientations on electrical and mechanical response, robustness, and sensitivity of UHPCNFA in a wide range of frequency spectrum to check its suitability in real-time structural health monitoring.

Effects of fiber dosage, loading orientation and stress on frequency response of enhanced Carbon Nano-Fiber Aggregates

Nanomaterial additives have been broadly used in cement and concrete-based sensors to measure the stress and strain in the structure. Most of the studies focused on measuring the resistivity of sensors with Direct Current (DC) or relatively low-frequency. In this work, the impedance responses of enhanced Carbon Nano-Fiber Aggregates (CNFAs) at different frequencies are rigorously studied and utilized as a tool for real-time structural health monitoring (SHM). The CNFA impedance measurements at different measurement frequencies provide an extra dimension (frequency dimension) to allow the characterization of different phenomena and multimodal measurements simultaneously. First, a comprehensive physical model is established to understand the frequency responses of the CNFA impedance. Second, COMSOL Multiphysics is used to simulate the frequency responses of the CNFA impedance, which provides more insights into the electric field and current density distribution. The impedance of CNFAs decreased with the increased dosage of carbon nanofibers (CNFs). Third, experimental studies are reported in detail. The electrical impedance variation (EZV) of the CNFA in parallel orientation is 151% higher than that of perpendicular orientation at the frequency of 2612 Hz and uniaxial compression stress of 4.65 MPa. The strain-EZV curve obtained from the response spectrum is linear for frequencies ranging from 98 Hz to 463.9 kHz. The strain-EZV curve for 5625 Hz has a linear fit with the gauge factor of 147.78. At 1000 Hz, the CNFA exhibited a repeatable behavior up to 9.35 MPa and detection limit up to the stress of 18.62 MPa.

Evaluation of a Novel Contactless Electrical Impedance Device for Measuring Respiratory and Heart Rates: A Pilot Study.

Although the respiratory rate is an important vital sign, it is rarely recorded in hospitals given the lack of convenient measurement devices. Posh Wellness Laboratory Inc. (Tokyo, Japan) developed a novel contactless card-type respiratory/heart rate monitoring device that measures electrical impedance variations on the human chest. This study was aimed to test and validate the accuracy of the proposed device compared with conventional medical monitors. To evaluate the card-type monitoring device, we compared the measurements from the device with those from the mechanical ventilators and electrocardiogram monitors. Patients who were hospitalized in the Emergency Department of Shimane University Hospital from April 5 to 30, 2021 were included in this study. A card-type sensor was attached to five patients who agreed to participate in this study. Four of the five patients were receiving mechanical ventilation. The respiratory rate error provided by the card-type sensor remained within 15% compared with the measurements of the conventional medical monitor. In contrast, the heart rate counts were largely different from the measurements. Thus, the proposed device can successfully measure the respiratory rate, whereas heart rate measurements require further improvement. Our small, lightweight, radiation-free, and contactless monitoring device can conveniently measure the respiratory rate of patients. With the improvement of measuring the heart rate, we would like to assess a larger number and a wider range of patients.

Monitoring Influenza Virus Survival Outside the Host Using Real-Time Cell Analysis.

Methods for virus particle quantification represent a critical aspect of many virology studies. Although several reliable techniques exist, they are either time-consuming or unable to detect small variations. Presented here is a protocol for the precise quantification of viral titer by analyzing electrical impedance variations of infected cells in real-time. Cellular impedance is measured through gold microelectrode biosensors located under the cells in microplates, in which magnitude depends on the number of cells as well as their size and shape. This protocol allows real-time analysis of cell proliferation, viability, morphology and migration with enhanced sensitivity. Also provided is an example of a practical application by quantifying the decay of influenza A virus (IAV) submitted to various physicochemical parameters affecting viral infectivity over time (i.e., temperature, salinity, and pH). For such applications, the protocol reduces the workload needed while also generating precise quantification data of infectious virus particles. It allows the comparison of inactivation slopes among different IAV, which reflects their capacity to persist in given environment. This protocol is easy to perform, is highly reproducible, and can be applied to any virus producing cytopathic effects in cell culture.

High-resolution impedance mapping using electrically activated quantitative phase imaging

Retrieving electrical impedance maps at the nanoscale rapidly via nondestructive inspection with a high signal-to-noise ratio is an unmet need, likely to impact various applications from biomedicine to energy conversion. In this study, we develop a multimodal functional imaging instrument that is characterized by the dual capability of impedance mapping and phase quantitation, high spatial resolution, and low temporal noise. To achieve this, we advance a quantitative phase imaging system, referred to as epi-magnified image spatial spectrum microscopy combined with electrical actuation, to provide complementary maps of the optical path and electrical impedance. We demonstrate our system with high-resolution maps of optical path differences and electrical impedance variations that can distinguish nanosized, semi-transparent, structured coatings involving two materials with relatively similar electrical properties. We map heterogeneous interfaces corresponding to an indium tin oxide layer exposed by holes with diameters as small as ~550 nm in a titanium (dioxide) over-layer deposited on a glass support. We show that electrical modulation during the phase imaging of a macro-electrode is decisive for retrieving electrical impedance distributions with submicron spatial resolution and beyond the limitations of electrode-based technologies (surface or scanning technologies). The findings, which are substantiated by a theoretical model that fits the experimental data very well enable achieving electro-optical maps with high spatial and temporal resolutions. The virtues and limitations of the novel optoelectrochemical method that provides grounds for a wider range of electrically modulated optical methods for measuring the electric field locally are critically discussed.

Fundamental Experiment on Invisible Crack Detection of Concrete Covered with Fiber Reinforced Polymer (FRP) through Electrical Impedance Variations and Phase Transition

Fundamental Experiment on Invisible Crack Detection of Concrete Covered with Fiber Reinforced Polymer (FRP) through Electrical Impedance Variations and Phase Transition

Experimental investigation of innovative active packaging biofilms using electrical impedance spectroscopy

This work explores a novel simple technique to investigate the shelf life of fruit using Electrical Impedance Spectroscopy (EIS). EIS is a non-destructive analysis that focuses on studying the electrical impedance variations during ripening of fruit. The purpose of this study is the use of a biodegradable natural plastic packaging for extending fruit and vegetable shelf life. Polyethylene Terephthalate is currently used for food packaging such vegetables, fruit and meat. It is a tough and flexible plastic material with high impact strength, but it has the disadvantages of synthetic plastics, which includes non-biodegradability. EIS method analyzes the differences in weight loss of the tomato fruit wrapped with innovative biopolymer composite films and anticipates the effect of these bioplastic films on the ripening state. EIS studies were conducted by applying an alternating current through a range of silver (Ag/AgCl) electrodes attached to the fruit wrapped with the films. The impedance of the wrapped tomato fruit was measured at frequency sweeps ranging from 10Hzto200KHz for 100 frequency points. The results revealed that the rate of change of the impedance decreased due to the effectiveness of the new biofilm packaging in prolonging the shelf life of fruit. The wrapped novel film prolonged the ripening and aging stages of tomatoes compared to the non-wrapped tomato. Chitosan proven to extend the shelf life as an edible coating on fruits and vegetables by reducing water-loss and as a defensive barrier of contamination.

A diagrammatic approach of impedimetric phase angle-modulus sensing for identification and quantification of various polar and non-polar/ionic adulterants in milk

The current article demonstrates a novel diagrammatic approach for the detection and quantification of polar and non-polar/ionic adulterants in milk by employing electrical impedance spectroscopy (EIS). For such study, some commonly used milk adulterants including melamine, starch, urea, allantoin, cyanuric acid, benzoic acid, ammonium sulphate and sodium bicarbonate are incorporated in a controlled manner in the pure milk sample. The presence of such adulterants in milk is confirmed by Fourier transform mid-infrared (FT-MIR) spectroscopy prior to impedimetric measurements. A Pt/Teflon/SiO2/Si biosensor device is fabricated for EIS measurement where the combination of SiO2 and Teflon layer thicknesses are optimized to obtain an appropriate hydrophobicity/dielectricity for the liquid milk samples. The EIS study shows an opposite trend in the variation of electrical impedance, capacitance and conductance for the polar samples in comparison to non-polar/ionic adulterants, upon their controlled addition from 0.5 to 9 (mg/g). Such results are utilized for detection and quantification of the milk-adulterants by developing a diagrammatic approach based on impedimetric phase angle-modulus mapping. Such diagrammatic impedance spectroscopy provides a generic scheme for a rapid, cost-effective and point-of-care detection and quantification of adulterants in milk which can be further extended to other bio-consumables.

Optimization of the electrode configuration of electrical impedance myography for wearable application

Electrical Impedance Myography (EIM) based on the four-electrode method is a novel method for assessing muscle state in the fields of sports, fitness, and medical rehabilitation. However, commonly used configuration of electrodes is not suitable for the wearable field, because of its large total area and low sensitivity. An optimized electrode configuration for wearable application is proposed as Mode B. Equivalent circuit model B of the four-electrode method is established by using the equivalent circuit of biological tissues, and in-vivo measurements of the electrical impedance of the biceps muscle are carried out on six volunteers using bioimpedance spectroscopy device ImpTM SFB7. The experimental results show that equivalent circuit model B of the four-electrode method is reliable. Moreover, the variation in muscle electrical impedance measured using the optimal configuration of model B is twice that measured using the optimal configuration of model A. The optimized electrode configuration of EIM based on this approach is model B (i.e. square electrodes in parallel array; size, 20 mm × 20 mm; spacing, 5–24 mm).

Electrical Impedance Myography Applied to Monitoring of Muscle Fatigue During Dynamic Contractions

Muscle fatigue, as a common physiological phenomenon, has attracted much attention in the fields of rehabilitation and athletic training. A wearable technology for monitoring the muscle fatigue anytime and anywhere is urgently needed. In this paper we apply Electrical impedance myography (EIM) technique, usually used for non-invasive detection of neuromuscular diseases with the four-electrode array, for evaluation of the local muscle fatigue status via the variation of electrical impedance. An equivalent multilayer inhomogeneous 3D finite element model of human arm was built in order to optimize the four-electrode configuration to improve EIM detection sensitivity. Current density in muscle layer and differential potential of induction electrodes were selected as the evaluation indexes for optimization. Then the in vivo experiments of dynamic contraction with different maximal voluntary contractions (MVC) were performed on the biceps brachii muscle of eight healthy volunteers. The results showed that muscle resistance ( $R$ ) decreased almost $8~\Omega $ from the completely relaxed muscle to exhaustion, which is the same trend as for the median frequency (MF) of measured surface electromyography (sEMG) signals. The model and experiments in this paper indicate the feasibility and efficiency of EIM for detection of muscle fatigue using wearable devices.

Effect of molecular weight on humidity-sensitive characteristics of electrospun polyethylene oxide

Polymeric humidity sensors have been widely studied because of their advantages in terms of low cost, simple preparation, and easy process. Most of those researches focused on the improvement in the humidity sensing performance by adding other materials. However, it is also important to understand the correlation between the polymer property and sensing characteristics. In this study, polyethylene oxide (PEO) of various molecular weights was used for the humidity sensing material and prepared by electrospinning. The morphological change and electrochemical properties of the humidity active layer were investigated to demonstrate the effect of the molecular weight on the sensing performance, including the sensitivity and linearity of electrical impedance variation, response and recovery time, and moisture stability. The humidity sensor having the highest molecular weight presented the best sensitivity and linearity of the impedance change in the specific humidity range over 67% because it was composed of complete nanofibers and showed good electrochemical property. In addition, the fastest response and recovery time, least hysteresis, and excellent moisture stability were achieved by the high surface area and connectivity of the nanofibers.

Performance improvement of magneto-acousto-electrical tomography for biological tissues with sinusoid-Barker coded excitation**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474166 and 11604156), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20161013), the Postdoctoral Science Foundation of China (Grant No. 2016M591874), the Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (Grant No. KYCX17

By combining magnetics, acoustics and electrics, the magneto-acoustic-electrical tomography (MAET) proves to possess the capability of differentiating electrical impedance variation and thus improving the spatial resolution. However, the signal-to-noise ratio (SNR) of the collected MAET signal is still unsatisfactory for biological tissues with low-level electrical conductivity. In this study, the formula of MAET measurement with sinusoid-Barker coded excitation is derived and simplified for a planar piston transducer. Numerical simulations are conducted for a four-layered gel phantom with the 13-bit sinusoid-Barker coded excitation, and the performances of wave packet recovery with side-lobe suppression are improved by using the mismatched compression filter, which is also demonstrated by experimentally measuring a three-layered gel phantom. It is demonstrated that comparing with the single-cycle sinusoidal excitation, the amplitude of the driving signal can be reduced greatly with an SNR enhancement of 10 dB using the 13-bit sinusoid-Barker coded excitation. The amplitude and polarity of the wave packet filtered from the collected MAET signal can be used to achieve the conductivity derivative at the tissue boundary. In this study, we apply the sinusoid-Barker coded modulation method and the mismatched suppression scheme to MAET measurement to ensure the safety for biological tissues with improved SNR and spatial resolution, and suggest the potential applications in biomedical imaging.

Mapping the electrical activity of the heart in vivo using ultrafast acoustoelectric imaging

The heart is driven by an electrical activation that propagates in cells and triggers their concerted contraction. When this electrical activation pattern is altered, it can lead to debilitating diseases such as arrhythmia or heart failure. Yet, directly imaging the electrical activity of the heart remains difficult to achieve. We have recently introduced Ultrafast Acoustoelectric Imaging (UAI) that combines ultrasound plane wave emissions and the acoustoelectric effect, i.e., the modulation of electrical impedance by ultrasound waves, to map electrical current densities in real-time with 1-mm and 5-ms spatial and temporal resolutions, respectively. Herein, we present its application to direct mapping of the cardiac activation in isolated live rat hearts and in pig hearts in vivo. UAI was performed in isolated rat hearts (n = 4) and in open-chest pigs (n = 1) using a 5-MHz linear array ultrasound probe fitted to a 256 channel- Vantage ultrasound system (Verasonics, Inc., WA). Two electrodes positioned on the heart and fed to the Vantage system were used to detect electrical impedance variations caused by ultrasound plane waves, which were then backprojected to reconstruct images of electrical current densities. UAI images depicted the propagation of the electrical activation of the cardiac tissue as validated by the electrocardiogram. These first in-vivo results suggest that UAI may allow the emergence of new biomarkers for the diagnosis and pre-clinical study of cardiac activation diseases such as arrhythmias.

UV‐Printable and Flexible Humidity Sensors Based on Conducting/Insulating Semi‐Interpenetrated Polymer Networks

Humidity sensors are of great interest in many fields because humidity plays a crucial role in several processes. Nevertheless, their application is often limited by the expensive fabrication and the stiffness of the substrates usually employed. In this work, novel UV‐curable and flexible humidity sensors based on semi‐interpenetrated polymer networks are fabricated. They can be prepared either as self‐standing sensors or applied on different bendable substrates. The fabrication consists of a simultaneous UV‐curing of an insulating network (acrylic or epoxy) and photopolymerization of conducting polypyrrole (PPy). The detection mechanism involves proton transfer on the PPy chains that can be macroscopically observed by electrical impedance variations. These devices show promising humidity‐sensing properties from 20 to 97% of relative humidity with a maximum response of about 180%. The dynamic sensing investigation proves that the recovery process can be tailored playing on the glass transition temperature and wettability of the films. The remarkable sensing capabilities of these sensors make them a valid alternative in many applications where printability and flexibility are required along with simple fabrication method consisting of one‐step synthesis.

Power amplifier circuits for functional electrical stimulation systems

Abstract Introduction: Functional electrical stimulation (FES) is a technique that has been successfully employed in rehabilitation treatment to mitigate problems after spinal cord injury (SCI). One of the most relevant modules in a typical FES system is the power or output amplifier stage, which is responsible for the application of voltage or current pulses of proper intensity to the biological tissue, applied noninvasively via electrodes, placed on the skin surface or inside the muscular tissue, closer to the nervous fibers. The goals of this paper are to describe and discuss about the main power output designs usually employed in transcutaneous functional electrical stimulators as well as safety precautions taken to protect patients. Methods A systematic review investigated the circuits of papers published in IEEE Xplore and ScienceDirect databases from 2000 to 2016. The query terms were “((FES or Functional electric stimulator) and (circuit or design))” with 274 papers retrieved from IEEE Xplore and 29 from ScienceDirect. After the application of exclusion criteria the amount of papers decreased to 9 and 2 from IEEE Xplore and ScienceDirect, respectively. One paper was inserted in the results as a technological contribution to the field. Therefore, 12 papers presented power stage circuits suitable to stimulate great muscles. Discussion The retrieved results presented relevant circuits with different electronic strategies and circuit components. Some of them considered patient safety strategies or aimed to preserve muscle homeostasis such as biphasic current application, which prevents charge accumulation in stimulated tissues as well as circuits that dealt with electrical impedance variation to keep the electrode-tissue interface within an electrochemical safe regime. The investigation revealed a predominance of design strategies using operational amplifiers in power circuits, current outputs, and safety methods to reduce risks of electrical hazards and discomfort to the individual submitted to FES application.

Regional ventilation redistribution measured by electrical impedance tomography during spontaneous breathing trial with automatic tube compensation**This study was endorsed by the Far Eastern Memorial Hospital Research Ethics Review Committee, approval number: FEMH-IRB-103133-E.

Objective. Automatic tube compensation (ATC) was developed to overcome the flow resistance of endotracheal tube and decrease the imposed work of breathing. Although ATC is used as an evidence-based strategy to predict successful weaning from assisted ventilation, the changes in regional ventilation distribution induced by this technique are not known. We hypothesized that continuous positive airway pressure plus ATC (CPAP + 100%ATC) could reactivate the respiratory muscles in patients with prolonged mechanical ventilation (PMV) more effectively than volume assist-control mandatory ventilation (ACMV). Approach. A total of 16 PMV patients were included. Patients were ventilated under volume ACMV mode and subsequently under CPAP + 100%ATC for 50 min. Two periods of 5 min electrical impedance tomography (EIT) data at the end of each mode were analyzed. Main results. Tidal variations of electrical impedance determined by EIT during CPAP + 100%ATC were significantly smaller than during ACMV (p < 0.001), while no significant differences in end-expiratory lung impedance were found. Regional ventilation was distributed significantly more towards dorsal regions during CPAP + 100%ATC as indicated by the EIT-based index center of ventilation (46.2 ± 5.8 during ACMV versus 51.7 ± 6.5 during CPAP + 100%ATC, values in %, p < 0.001). However, the overall degree of ventilation inhomogeneity was not improved as indicated by the global inhomogeneity index (0.42 ± 0.09 during ACMV versus 0.42 ± 0.06 during CPAP + 100%ATC). The onset of ventilation was significantly less delayed during CPAP + 100%ATC in both ventral and dorsal regions as indicated by the ventilation delay index (ACMV versus CPAP + 100%ATC, 53.0 versus 42.6 in ventral; 50.2 versus 39.3 in dorsal regions; values in %, p < 0.001). Significance. Dorsal redistribution of ventilation and reduction of ventilation delay as identified by EIT indicate that CPAP + 100%ATC was effective in reactivating the respiratory muscles in the PMV patients of the present study.

Electrical impedance spectroscopic study of mandarin orange during ripening

Electrical impedance spectroscopy (EIS) as non-destructive investigation has been conducted to study the electrical impedance variations during ripening of mandarin orange. The objective of the work is to study the electrical impedance variations and variations in weight of the orange fruit with different ripening state. Electrical equivalent circuit has been modeled relative to the Nyquist plot obtained during the ripening of orange by non-linear curve fitting technique. EIS studies on orange fruit have been conducted by applying a small amount of alternating current through an array of Ag/AgCl electrodes attached to the orange fruit. The impedance and phase angles of orange fruit are measured at frequency sweep from 50 Hz to 1 MHz for 100 frequency points. The results revealed that the impedance, real part and imaginary part of the impedance all are increased and the weight of orange are decreased with the increase in ripening state. It is observed that the electrical equivalent circuit of orange fruit contains a constant phase element.

Noninvasive treatment efficacy monitoring and dose control for high-intensity focused ultrasound therapy using relative electrical impedance variation**Project supported by the National Natural Science Foundation of China (Grant Nos. 11604156 and 11474166), the Science and Technology Cooperation Projects of China and Romania (Grant No. 42-23), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20161013), the Postdoctoral Science Foundation of

As an effective therapeutic modality, high-intensity focused ultrasound (HIFU) can destroy tumour tissues by thermocoagulation with less metastasis, but it is still limited by inaccurate non-invasive temperature monitoring and efficacy evaluation. A model of electrical impedance measurement during HIFU therapy was established using the temperature-impedance relationship. Based on the simulations of acoustic pressure, temperature, and electrical conductivity, the impedance of the phantom was calculated and experimentally demonstrated for different values of acoustic power values and treatment time. We proved that the relative impedance variation (RIV) increases linearly with the increasing treatment time at a fixed acoustic power, and the relative impedance variation rate shows a linear relationship with the acoustic power. The RIV and treatment time required for HIFU treatment efficacy are inversely proportional to the acoustic power and the square of acoustic power, respectively. The favourable results suggest that RIV can be used as an efficient indicator for noninvasive temperature monitoring and efficacy evaluation and may provide new strategy for accurate dose control of HIFU therapy.