Focused Impedance Method Research Articles

Sensitivity study of a locally developed six electrode focused impedance method.

The Focused Impedance Method (FIM) is a new technique of electrical bioimpedance measurements in the human body. The idea originated in Bangladesh and provides an opportunity for localized measurement of bioimpedance down to reasonable depths from the body surface using skin surface electrodes. This has potential applications for physiological studies of targeted organs in the body and in detecting or diagnosing diseases and disorders. FIM is based on the age-old Tetra-Polar Impedance Measurement (TPIM) but provides a few significant improvements. Technology must be developed indigenously to obtain long-term benefits, particularly in Low and Medium Income countries (LMIC). This paper presents an experimental sensitivity study of the six-electrode version of the Focused Impedance method (FIM-6) with the circuit and phantom indigenously designed in Nepal. The work involved sensitivity studies of both FIM-6 and TPIM with the necessary circuit blocks developed through experimental validation. The sensitivity studies were performed on a simple 2D phantom with different electrode arrangements for FIM-6 and linear TPIM. A cylindrical object was placed at different positions for this study. The FIM-6 gave a high sensitivity in the central part, which remained almost constant within a small region that may be termed as the focused region. On the other hand, TPIM results fell off sharply away from the central point, making it unsuitable for practical measurements on target organs. Besides, there were areas with large negative sensitivities in TPIM, which were much smaller in FIM. The results obtained through this work clearly show the improvement offered by FIM over TPIM.

Improving sensitivity in the deep regions of a volume conductor using electrical focused impedance methods.

Bioimpedance measurements are becoming important in probing the human body for diagnosis and monitoring. An age old 4-electrode technique called tetrapolar impedance measurement (TPIM), giving transfer impedance, cannot localize a specific zone besides having large zones of negative sensitivity. A new technique named the focused impedance method (FIM) from Dhaka University (DU), Bangladesh used the algebraic average of two concentric and orthogonal TPIMs, localizing a zone of interest and having reduced magnitudes of negative sensitivity. Earlier, this was implemented with electrodes applied from one side of the human body giving information to shallow depths only. To get information from deeper regions, specifically, of the thorax, the same DU group placed two electrodes of a 4-electrode version of FIM at the front and two at the back in a horizontal plane of the thorax, using physics-based visualization. This was followed by a few quantitative studies using point sensitivity, which supported the concept. However, more quantitative studies still need to be performed, particularly using objects of finite sizes, in order to establish the technique on a stronger footing. The present study was taken up with this objective. A simplified approach was used in which the volume conductor was a rectangular non-conducting container filled with saline of uniform conductivity with an embedded spherical object - first an insulator and then a conductor. Electrodes were placed at specific chosen positions following the above visualization. Percentage change in transfer impedance with the object placed at different internal positions, compared to that without the object was obtained first using COMSOL simulation and then through experimental measurements. These were performed for both TPIM and FIM. The new configuration of 4-electrode FIM gave good depth sensitivity supporting the effectiveness of the new placement of electrodes.

Improving Deep Sensitivity of Four-Electrode Focused Impedance Method In Lungs by Varying Electrode Geometries

Bio-Electrical impedance is of special interest in the detection and diagnosis of lung problems, particularly in the low and medium income countries. An age old simple technique employing four electrodes is known as ‘Tetra Polar Impedance Measurement (TPIM)’ but it cannot localize a particular zone of interest region. A new technique named as ‘Focused Impedance Method (FIM)’ was innovated by a Dhaka University group which gives high sensitivity in a localized zone of interest. Previously FIM was used from one side of the thorax which gave a rather limited information from the lungs, from shallow depths only. In order to get information from deeper regions of the lungs a new configuration of electrodes for FIM was proposed by the same group at Dhaka University which placed two electrodes at the front and two electrodes at the back of the thorax in a horizontal plane. It is expected that the degree of depth sensitivity would depend on electrode separation on both the sides. The electrode width may also have an effect. In order to study these quantitatively, COMSOL Multiphysics software was used to simulate the measurements in a rounded rectangular volume to represent a typical thorax, which was filled with isotonic saline. Electrode separations of 5cm, 10cm, 15cm and 20cm were studied while electrode widths studied were 0.15cm, 1cm and 3cm. The work supported the proposed new configuration of electrodes for FIM in that this method gives enhanced sensitivity throughout the depths of a lung and that for a thorax with a cross section of 33cm26cm, an electrode separation between 10cm and 15cm would give optimum results. For electrode width, the ones studied did not give any significant difference, however, the smallest (0.15cm) one appeared to give slightly better results.
 Bangladesh Journal of Medical Physics Vol.15 No.1 2022 P 43-54

Instrumentation for Six Electrode Focused Impedance Method (FIM-6) for the study of localized regions in a volume conductor

Focused Impedance Method (FIM) is a new and simple technique of electrical bio-impedance that provides an opportunity for localized measurement down to reasonable depths of the body surface using skin surface electrodes. Conceived by one of the authors (KSR) and developed in Bangladesh by a group led by him, FIM has potential applications in physiological study and in the detection or diagnosis of diseases and disorders. Being a simple technique, it is particularly suitable for low and medium income countries (LMIC). To obtain long term benefit from any technology it is necessary that the technology is understood and developed indigenously, particularly under the limitation of a resource limited country. Indigenous development also allows for further improvisation, innovation, and application in future. This paper presents the indigenous design and development of the electronic instrumentation necessary for the implementation of six electrode version of Focused Impedance Method (FIM-6) in Nepal. The work involved basic characterization of the necessary circuit blocks developed through experimental validation. In particular, the design of isolating ferrite transformers required for the instrumentation posed a challenge which was solved limiting the range of the instrumentation to range variations encountered in practice on the human body, for which initial experiments were carried out on a live human subject. This led to a simplified design. The values obtained using the developed circuitry appears to give reasonable accuracy and would be useful for further implementation of the instrumentation using PCBs. However, further work can also be taken to improve the design of the current source used and of the transformers. Thus this work satisfies the initial requirement of attempting indigenous development of the FIM technique in an LMIC like Nepal.
 Bangladesh Journal of Medical Physics Vol.14 No.1 2021 P 1-15

A Multi-Frequency Focused Impedance Measurement System Based on Analogue Synchronous Peak Detection

Monitoring of anatomical structures and physiological processes by electrical impedance has attracted scientists as it is noninvasive, nonionizing and the instrumentation is relatively simple. Focused Impedance Method (FIM) is attractive in this context, as it has enhanced sensitivity at the central region directly beneath the electrode configuration minimizing contribution from neighboring regions. FIM essentially adds or averages two concentric and orthogonal combinations of conventional Tetrapolar Impedance Measurements (TPIM) and has three versions with 4, 6, and 8 electrodes. This paper describes the design and testing of a multi-frequency FIM (MFFIM) system capable of measuring all three versions of FIM at 8 frequencies in the range 10 kHz—1 MHz. A microcontroller based multi-frequency signal generator and a balanced Howland current source with high output impedance (476 kΩ at 10 kHz and 58.3 kΩ at 1 MHz) were implemented for driving currents into biological tissues with an error <1%. The measurements were carried out at each frequency sequentially. The peak values of the amplified voltage signals were measured using a novel analogue synchronous peak detection technique from which the transfer impedances were obtained. The developed system was tested using TPIM measurements on a passive RC Cole network placed between two RC networks, the latter representing skin-electrode contact impedances. Overall accuracy of the measurement was very good (error <4% at all frequencies except 1 MHz, with error 6%) and the resolution was 0.1 Ω. The designed MFFIM system had a sampling rate of >45 frames per second which was deemed adequate for noninvasive real-time impedance measurements on biological tissues.

Combined FIM-PHI-Based Wearable Biosensor

Focused impedance method (FIM) is a simple non-invasive way of diagnosing epidermal tissue health by subsequent measurements of localized impedance using a set of tetra-polar orthogonal electrodes. The concept is further advanced to an increased number of electrodes with repeated FIM cells that combinedly form a pigeon hole image (PHI) and used to diagnose a range of physiological conditions and disorders. In this work, a wearable imaging device has been demonstrated by combining the attributes of FIM-based pigeon hole imaging and utilised them for detecting unusual body mass within a biological system. The device uses a total of twenty-five Cu electrodes uniformly distributed over a spatial area <inline-formula> <tex-math notation="LaTeX">${A} = 16$ </tex-math></inline-formula> cm² which combinedly form the 16 elements of a <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> PHI matrix. The PHI device is capable to produce a 2D crude image of bio-impedance with a pixel resolution of 1 cm and visualise an unusual body mass underneath the testing surface at depth, <inline-formula> <tex-math notation="LaTeX">${d}_{p} \sim 0.3$ </tex-math></inline-formula> to 2.0 cm. The ubiquitous functionality of the device has been demonstrated by integrating into a custom made flexible fabric as wearable wrist band that measures the PHI image and recognizes three common gesture positions using a well-known artificial neural network classifier. The wearable device can be an emerging telemedicine solution for rapid screening of a range of abnormal physiological phenomenon at patient&#x2019;s home or in a regional hospital with resource limited settings.

Electrode Placement Strategies for the Measurement of Radial Artery Bioimpedance: Simulations and Experiments

Continuous cardiac output is a significant matter that must be considered in monitoring the functioning of cardiovascular system. A noninvasive sensing system that is based on measuring electrical bioimpedance variations of radial artery is proposed to evaluate the physical condition of a patient. To optimize the signal acquisition, different electrode placement strategies are compared with the goal of finding the most suitable ones. The finite-element method (FEM) simulation of sensitivity distribution and experimental measurements on radial artery are performed for experimenting circular and distal electrode placements. Importantly, also the modified electrode placement strategies, guided by the idea of focused impedance method (FIM), are investigated. To reduce the number of electrodes in measurement setup, its novel version is proposed: a five-electrode FIM strategy. The efficiency of the proposed strategy can be seen in the reduced amount of required number of electrodes: the smaller area of electrode-skin contact interface results in smaller influence of uncertainties. Moreover, the reduced number of electrodes contributes to benefit through developing simpler instrumentation having lower energy consumption and cheaper manufacturing costs. The results show the advances of the proposed novel five-electrode FIM strategy for measuring the pulsating volume of blood in radial artery with the goal of determining the central aortic pressure (CAP) of blood.

Probing for Stomach using the Focused Impedance Method (FIM).

For probing deep organs of the body using electrical impedance, the conventional method is to use Electrical Impedance Tomography (EIT). However, this would be a sophisticated machine and will be very expensive when a full 3D EIT is developed in the future. Furthermore, for most low income countries such expensive devices may not deliver the benefits to a large number of people. Therefore, this paper suggests the use of simpler techniques like Tetrapolar Impedance Measurement (TPIM) or Focused Impedance Method (FIM) in probing deeper organs. Following a method suggested earlier by one of the authors, this paper studies the possibility of using TPIM and FIM for the stomach. Using a simplified model of the human trunk with an embedded stomach, a finite element simulation package, COMSOL, was used to obtain transfer impedance values and percentage contribution of the stomach region in the total impedance. For this work, judicious placement of electrodes through qualitative visualizations based on point sensitivity equations and equipotential concepts were made, which showed that reasonable contribution of the stomach region is possible through the use of TPIM and FIM. The contributions were a little over 20% which is of similar order of the cross-sectional area percentage of the stomach with respect to that of the trunk. For the case where the conductivity of the stomach region was assumed about 4 times higher, the contributions increased to about 38%. Through further studies this proposed methods may contribute greatly in the study of deeper organs of the body.

Simple electrode configurations for probing deep organs using Electrical Bio-Impedance techniques

Tetrapolar Impedance Method (TPIM) and Focused Impedance Method (FIM) are two simple modalities of electrical bio-impedance measurement that could be employed to give useful physiological and diagnostic information of the human body. FIM is based on TPIM but uses a combination of two sets of TPIM, producing a focusing effect, which is useful to localize specific target organs. Most non-invasive electrical bio-impedance measurements based on TPIM and FIM use electrodes on one side of the body, outside the skin surface, which gives a shallow depth sensitivity. The sensitivity decreases with depth so that deep organs like lungs, heart, liver, stomach and bladder are not fully assessed through such measurements. Based on a long experience of studying electrical impedance methods, several qualitative ideas are presented in this article for probing deep organs using a few modified TPIM and FIM configurations. The suggestions are based on visualisations of both equipotentials and a popular sensitivity equation for transfer impedance, but not based on any quantitative analysis. Simulation and phantom studies based on these ideas may produce some practically useful electrode configurations for real life bio-impedance measurements.&#x0D; Bangladesh Journal of Medical Physics Vol.11 No.1 2018 P 1-15

Improved Understanding of the Sensitivity of Linear Tetrapolar Impedance Measurement (TPIM) and 8-Electrode Focused Impedance Method (FIM) in a Volume Conductor

Tetrapolar Impedance Measurement (TPIM) is a 4-electrode impedance measurement system appropriate for a volume conductor in which current is driven through a pair of electrodes while potential developed across another pair of electrodes is measured to provide a value of transfer impedance. The 8-electrode Focused Impedance Method (FIM-8) consists of two concentric and orthogonal linear TPIM systems with their transfer impedances added for the purpose of localizing the central zone. Detailed 3D sensitivity studies are necessary for proper application of the techniques in specific biomedical applications and most reported work present point sensitivity distributions. The present work mainly focuses on planar average sensitivity in planes parallel to the electrode plane and its variation with depth due to different combinations of electrode separations – both for current drive pair and the potential measuring pair. This was obtained through finite element simulation using COMSOL Multiphysics software for a 40x40x40cm3 volume. The results give useful information that can be used to design electrode configurations and measurement modalities for various applications.Bangladesh Journal of Medical Physics Vol.8 No.1 2015 22-31

Determination of the Thickness of a Resistive Material Layer in a Finite Volume Conductor using Focused Impedance Method (FIM) – a simulation study

Focused Impedance Method (FIM) is an innovative and relatively new electrical impedance measurement technique that allows localized measurement of the properties of electrically conducting materials in a volume conductor such as the human body using simple measurement setups. In a previous work, FIM, with dual electrode separation, was used to determine thicknesses of subcutaneous fat layers through experimental study on phantoms and human subjects. The present work, carried out using COMSOL Multiphysics software package, is a finite element simulation study for a similar target object that verifies and extends the results of the previous experimental work. A rectangular box of different heights containing a material of uniform conductivity such as saline together with internally embedded layers of resistive materials of different thicknesses were used for this study. The measured transfer impedance in the FIM method showed marked change with the variation of the thickness of the resistive layer and with electrode separation, showing a point of maximum curvature in the latter. We obtained a calibration curve for the thickness from the electrode separation of this point. This allowed a unique method for the determination of thickness of embedded resistive layers which is more general than what had been done in the previous experimental work. This work will help standardize the application of 4-electrode FIM for determination of the thickness of less-conducting material layer in any finite volume, including determination of fat layer thickness, etc.Bangladesh Journal of Medical Physics Vol.7 No.1 2014 8-23

Determination of organ volume using Focused Impedance Method (FIM): a simulation approach

A noninvasive and radiation free technique for in-vivo measurement of the volume of organs or fluids in the human body is necessary for many clinical applications. Focused Impedance Method (FIM) is a novel technique of electrical impedance measurements which has enhanced sensitivity in a localized region. FIM can sense the change in transfer impedance of an organ within a reasonable depth of the human body using surface electrodes, minimizing contributions from its neighbouring regions. This of course assumes that the impedance properties of the embedded object are different from that of its surrounding tissues. This paper presents a new method for the determination of the volume of an organ within body using dual electrode separations of a concentric 4-electrode FIM configuration. In order to develop this formalism simulated FIM measurements using surface electrodes on a cubic volume conductor with embedded spherical objects were performed using a Finite Element (FE) based simulation software, COMSOL Multiphysics®. For the present methodology, the conductivity of the object with respect to its surroundings and its depth need to be known. The former is obtainable through some primary invasive or in vivo measurements while the latter may be approximated using anatomy. Experimental results on a phantom made up of a cubic tank filled with saline showed that the proposed method can be used to determine the volume of embedded objects to an accuracy of about 5% which is adequate for most physiological measurements. The technique may also find use in geology, oceanography and industry.Bangladesh Journal of Medical Physics Vol.7 No.1 2014 24-33

Sensitivity study for a 4-electrode Focused Impedance Method (FIM) using Finite Element Method analysis

Focused Impedance Method (FIM) is a recent technique, innovated by one of the authors at Dhaka, and shows a promise in providing practical results with a minimum of instrumentation complexity. Out of three version using 8, 6 and 4 electrodes, this paper concentrates on the 4-electrode FIM. Earlier work mainly used phantom experiments to verify the concept and analytical methods for a semi-infinite medium. The present work uses Finite Element Method (FEM), implemented by a software package named COMSOL to obtain various sensitivity graphs for 4-FIM. Firstly, it has verified the focusing effect for a homogenous medium using point sensitivity calculations. Secondly, it obtained simulated impedances for finite sized objects embedded in a medium of uniform conductivity considering five important variables namely, electrode spacing, object size, object resistivity, background resistivity and depth. In this paper the effect of each of these variables has been studied by keeping the other four constant. The obtained graphs give an insight which is expected to lead to quantitative assessment of target objects, needed in physiological study and diagnosis.Bangladesh Journal of Medical Physics Vol.7 No.1 2014 1-7

FOCUSED IMPEDANCE METHOD TO DETECT LOCALIZED LUNG VENTILATION DISORDERS IN COMBINATION WITH CONVENTIONAL SPIROMETRY

Conventional spirometry gives information on the overall ventilation of a person's lung; it cannot detect localized disorders in ventilation as occurring in pulmonary edema, pneumonia, tumor, TB, etc. Here we propose a new technique involving the recently developed focused impedance method (FIM) in combination with conventional spirometry to detect localized lung ventilation disorders. Electrical impedance of lung tissue changes as a function of air content and FIM provides a measurement of localized electrical impedance with sensitivity down to reasonable depths inside the body using a few surface electrodes; here we used a six-electrode version. At least four quadrants of the lungs in the frontal plane can be separately measured using a hand-held probe with spring backed skin surface electrodes. Firstly, spatial sensitivity distribution of the six-electrode FIM was obtained using finite element simulation which verified the focusing effect and its depth sensitivity. Percent change in impedance between maximum inspiration and expiration were measured at four quadrants of the chest of a healthy male subject giving four different values; that at the lower right quadrant was found to be the maximum, as also expected based on anatomy. Changes in impedance at this quadrant of the same subject were found to vary proportionately with exhaled air volumes, measured using a bellows-type spirometer. Similar FIM measurements at lower right lung of seven healthy subjects were found to be almost proportional (R2= 0.7) to the total exhaled air volumes (vital capacity). This was the basis of the new technique. For a healthy individual, the ratio of the local impedance change to vital capacity (VC) will fall within a certain range for each of the four lung quadrants. A lower value at any quadrant would indicate disorder within that quadrant, while a larger value would indicate disorder in a region outside the particular quadrant. The FIM electrode probe can then be moved to take measurements at the other quadrants to locate the region of disorder. This preliminary study indicates that FIM in combination with conventional spirometry could be used to detect localized ventilation defects.

3D Sensitivity of 8-Electrode FIM through Experimental Study in a Phantom

Focused Impedance Method (FIM) is a relatively new technique developed in the Biomedical Physics Laboratory of Dhaka University which allows improved localization of a zone without much increase in the complexity of measurement. Three versions using 8, 6 and 4 electrodes respectively have been conceived and developed. FIM has potential for characterization of biological tissues at depths non-invasively placing electrodes on the skin surface at appropriate locations, leading to detection or diagnosis of diseases or disorders. The present work is an experimental study of the sensitivity of the 8-electrode FIM system at different depths and lateral positions inside a volume conductor with respect to the electrode-positions using a cubical phantom with saline. An object of different conductivity and of size smaller than the electrode separation was placed inside the phantom at different positions to measure the change of FIM value, called sensitivity in this work. The study verified the focusing effect at the central zone where the sensitivity remained high and almost constant laterally for a certain depth, falling sharply outside. At shallow depths, the sensitivity showed enhanced peaks under the electrodes which however, decreased fast with depth. The sensitivity falls off sharply with depth becoming almost constant at greater depths but with greatly reduced value. The sensitivity at off axis positions from the centre also reduced outside the focused zone. Slightly negative zones of sensitivity were observed at lateral positions far from the center of the electrodes, but the values were negligible. This work will help standardize the application of 8-electrode FIM for determination of impedance of organs inside the human body. DOI: http://dx.doi.org/10.3329/bjmp.v6i1.19759 Bangladesh Journal of Medical Physics Vol.6 No.1 2013 55-65

Possible Applications of Focussed Impedance Method (FIM) in Biomedical and Other Areas of Study

Focused Impedance Method (FIM) based on 8, 6 and 4 electrode configurations have been innovated and developed for measuring the electrical impedance of a localised zone in a volume conductor, all based on tetrapolar impedance technique. The zone localization in FIM has been visualized through equipotential distributions, current density at the target point and perturbation produced at the potential measuring electrodes. The predicted behaviour has been verified though phantom measurements and analytical techniques by different groups. FIM is particularly sensitive and useful if the electrical impedance of a target object in the sensitive zone changes between two sets of measurements. This can be either due to a physical change in the target object, or, if its impedance has frequency dependence, through a change in the measurement frequency. In medical applications FIM is being developed for studying stomach and bladder emptying, localized lung function, detection of cervical and oral cancer, etc. FIM may have applications in industry to study physical mixtures of liquids and gases in pipelines and tanks, in geology to detect groundwater and other minerals, in oceanography, and in many other applications. Thus FIM appears to have a huge potential for application in different areas. DOI: http://dx.doi.org/10.3329/bjmp.v4i1.14689 Bangladesh Journal of Medical Physics Vol.4 No.1 2011 67-74

Design of a Microcontroller Based System to Implement 4-Electode Focused Impedance Method (FIM)

Designing of electronic circuitry and development of necessary software has been performed in the present work for a microcontroller based 4-electrode Focused Impedance measurement system. This needs a complex sequential analog switching of constant current ac signal generator and a potential measuring unit to 4 electrodes on the object under study. The performances of the designed system and the developed microcontroller software have been studied using a commercially available simulation software, ‘Proteus-7’, and the results are very satisfactory. DOI: http://dx.doi.org/10.3329/bjmp.v4i1.14690 Bangladesh Journal of Medical Physics Vol.4 No.1 2011 75-79

An Image Smearing Technique to Improve Pigeon Hole Imaging (PHI)

This new imaging modality arises as an extension of the 6-electrode Focused Impedance Method (FIM) developed in our laboratory earlier. Current is driven through two concentric pairs of orthogonally placed electrodes while several potential electrodes are located along a diagonal centrally. Through a combination of current drives and potential measurements across adjacent diagonal electrodes, it is possible to obtain admittance sums along the rows and columns of a square matrix formed by these diagonally placed potential electrodes. Through simple backprojection along the rows and columns it is possible to reconstruct a crude image in a square matrix form. Due to its resemblance, the name Pigeon Hole Imaging (PHI) has been coined. The concept has been experimentally tested to identify the location of a single target object in a background of uniform conductivity in 2D and 3D phantoms, in 2x2 and 6x6 matrix formations respectively. Taking the highest pixel to represent the object position the images were correct in all the pixels of the 2x2 image but in only 16 of the 36 pixels adjacent to the diagonal electrodes in the 6x6 image. However, a systematic pattern of image shift was observed in most of the other pixels in the latter, based on which a set of rules were made to correct the image in another 14 pixels. Thus excepting the furthest 6 pixels, correct image could be obtained in all 30 pixels. Thus PHI will be useful in locating exact positions of single target objects simply. DOI: http://dx.doi.org/10.3329/bjmp.v4i1.14673 Bangladesh Journal of Medical Physics Vol.4 No.1 2011 11-20

Effect of a spherical object in 4 electrode Focused Impedance Method (FIM): measurement and simulation

Focused Impedance Method (FIM) gives enhanced localized sensitivity at the centre of a zone defined by a simple system of electrodes, of which a 4-electrode version with electrodes at the corners of a square region has been studied in detail in the present work. The present work studies the effect of a large sphere whose diameter almost equals the dimensions of the central focused zone, or, the Focused Impedance. The sphere is placed at different positions with respect to the centre of the system at the electrode plane. The study has been made using a phantom in which the electrodes are fixed on a side wall while an insulating ball is hung at various positions inside the saline and moved with respect to the electrodes in their vicinity. The same was then simulated by providing appropriate parameters in COMSOL multiphysics, a software package utilizing Finite Element Method, by providing appropriately matching parameters. The measured impedance decreases as the ball is moved away from the centre in the electrode plane or along the depth. The sensitivity also decreases with an increase in electrode spacing. Although the behaviours were similar in both the studies, simulated values by COMSOL deviated from the measured values significantly. It suggests that COMSOL may not give accurate simulations for large objects.

Determination of abdominal fat thickness using dual electrode separation in the focused impedance method (FIM)

Subcutaneous fat layer thickness in the abdomen is a risk indicator of several diseases and disorders like diabetes and heart problems and could be used as a measure of fitness. Skinfold measurement using mechanical calipers is simple but prone to error. Ultrasound scanning techniques are yet to be established as accurate methods for this purpose. magnetic resonance imaging (MRI) and computed tomography (CT) scans can provide the answer but are expensive and not available widely. Some initiatives were made earlier to use electrical impedance to this end, but had inadequacies. In the first part of this paper, a 4-electrode focused impedance method (FIM) with different electrode separations has been studied for its possible use in the determination of abdominal fat thickness in a localized region. For this, a saline phantom was designed to provide different electrode separations and different layers of resistive materials adjacent to the electrodes. The background saline simulated the internal organs having low impedance while the resistive layers simulated the subcutaneous fat. The plot of the measured impedance with electrode separation had different ‘slopes’ for different thicknesses of resistive layers, which offered a method to obtain an unknown thickness of subcutaneous fat layer. In the second part, measurements were performed on seven human subjects using two electrode separations. Fat layer thickness was measured using mechanical calipers. A plot of the above ‘slope’ against fat thickness could be fitted using a straight line with an R2 of 0.93. Then this could be used as a calibration curve for the determination of unknown fat thickness. Further work using more accurate CT and MRI measurements would give a better calibration curve for practical use of this non-invasive and low-cost technique in abdominal fat thickness measurement.