Kim Blomqvist

A feasibility study of altered spatial distribution of losses induced by eddy currents in body composition analysis

BackgroundTomographic imaging has revealed that the body mass index does not give a reliable state of overall fitness. However, high measurement costs make the tomographic imaging unsuitable for large scale studies or repeated individual use. This paper reports an experimental investigation of a new electromagnetic method and its feasibility for assessing body composition. The method is called body electrical loss analysis (BELA).MethodsThe BELA method uses a high-Q parallel resonant circuit to produce a time-varying magnetic field. The Q of the resonator changes when the sample is placed in its coil. This is caused by induced eddy currents in the sample. The new idea in the BELA method is the altered spatial distribution of the electrical losses generated by these currents. The distribution of losses is varied using different excitation frequencies. The feasibility of the method was tested using simplified phantoms. Two of these phantoms were rough estimations of human torso. One had fat in the middle of its volume and saline solution in the outer shell volume. The other had reversed conductivity distributions. The phantoms were placed in the resonator and the change in the losses was measured. Five different excitation frequencies from 100 kHz to 200 kHz were used.ResultsThe rate of loss as a function of frequency was observed to be approximately three times larger for a phantom with fat in the middle of its volume than for one with fat in its outer shell volume.ConclusionsAt higher frequencies the major signal contribution can be shifted toward outer shell volume. This enables probing the conductivity distribution of the subject by weighting outer structural components. The authors expect that the loss changing rate over frequency can be a potential index for body composition analysis.

Performance of commercial over-head camera sensors in recognizing patterns of two and three persons: A case study

Accurate visitor counting is needed in the research of people flows and people distributions. A case study about the performance of four commercial direction-sensitive over-head camera sensors (Axis and Biodata video camera counters, Sick time-of-flight camera, and Irisys thermographic people counter) in detecting patterns of two and three persons was carried out. Although all the tested sensors except Axis generally performed well with the patterns of two people, error rates of even over 20% were observed with the three-person patterns. Simultaneous false positive and false negative detections also occasionally speciously improved the counting results of Axis and Sick. Due to these flaws the accuracies of the sensors do not allow reliable people flow modeling or estimation of room occupancy levels, but is sufficient e.g. for measuring the order of magnitude of customer flows. However, as there are differences between separate counting sites, the results are only indicative in general.

An open-source hardware for electrical bioimpedance measurement

This paper describes open-source hardware to measure both the magnitude and phase of the electrical bioimpedance in a frequency range from few kilohertz up to 100 kHz by using a four-electrode technique. The amount of current injected and the sensitivity of the system can be set to the desired range by changing the front-end resistor values. The system can be easily built and adapted with the help of the design details made available at GitHub. The practical performance was evaluated in abdominal impedance measurement, which was the primary motivation to build the system. Other experiments were performed with a 2R-1C circuit, a 10-Ω resistor, and a 100-nF capacitor, with observed relative errors in the impedances of -0.73 ± 0.34 %, -2.47 ± 1.43 % and -8.81 ± 0.64 % (mean ± SD), respectively, from 10 kHz to 100 kHz.

Instrumentation amplifier implements second-order active low-pass filter with high gain factor

A single-ended second-order active low-pass filter can simultaneously provide high gain factor and dc voltage subtraction. This makes it possible to reduce the number of components and signal processing stages needed in an application where small voltage changes are measured on the top of large dc voltage masked by a large amplitude oscillating carrier. The filter described in this paper is constructed from a conventional 3-op-amp instrumentation amplifier and five passive circuit elements.

Body electrical loss analysis (BELA) in the assessment of visceral fat: a demonstration

BackgroundBody electrical loss analysis (BELA) is a new non-invasive way to assess visceral fat depot size through the use of electromagnetism. BELA has worked well in phantom measurements, but the technology is not yet fully validated.MethodsTen volunteers (5 men and 5 women, age: 22-60 y, BMI: 21-30 kg/m2, waist circumference: 73-108 cm) were measured with the BELA instrument and with cross-sectional magnetic resonance imaging (MRI) at the navel level, navel +5 cm and navel -5 cm. The BELA signal was compared with visceral and subcutaneous fat areas calculated from the MR images.ResultsThe BELA signal did not correlate with subcutaneous fat area at any level, but correlated significantly with visceral fat area at the navel level and navel +5 cm. The correlation was best at level of navel +5 cm (R2 = 0.74, P < 0.005, SEE = 29.7 cm2, LOOCV = 40.1 cm2), where SEE is the standard error of the estimate and LOOCV is the root mean squared error of leave-one-out style cross-validation. The average estimate of repeatability of the BELA signal observed through the study was ±9.6 %. One of the volunteers had an exceptionally large amount of visceral fat, which was underestimated by BELA.ConclusionsThe correlation of the BELA signal with the visceral but not with the subcutaneous fat area as measured by MRI is promising. The lack of correlation with the subcutaneous fat suggests that subcutaneous fat has a minor influence to the BELA signal. Further research will show if it is possible to develop a reliable low-cost method for the assessment of visceral fat either using BELA only or combining it, for example, with bioelectrical impedance measurement. The combination of these measurements may help assessing visceral fat in a large scale of body composition. Before large-scale clinical testing and ROC analysis, the initial BELA instrumentation requires improvements. The accuracy of the present equipment is not sufficient for such new technology.

Integrating performance and production oriented design of satellite oscillators

This paper is based on background research [1] in which a manufacturability analysis was carried out for of an oscillator made for 5 GHz satellite and radar bands. The electronic circuit uses two cascaded bipolar microwave transistors in an emitter feedback amplifier configuration which is combined with a cylindrical dielectric resonator. Three miniature coupling loops are included in it, one for amplifier input, one for amplifier output via a Wilkinson power divider and another for the optional tuning varactor diode. We have formulated two research questions: Firstly, how much is it possible to increase the Q-value of the resonator by improving the manufacturing quality of its milled geometries? Secondly, is it possible to describe the required manufacturing accuracy with the Q-value added to the Product Data Management (PDM) data set? This paper focuses on the multidisciplinary aspects of the integrated performance and production oriented design of satellite oscillators. For the first time, the quality characteristic (Q-value) could be utilized directly in the mechanical PDM data of an oscillator to guide production.

Body Electrical Loss Analysis (BELA) – An Electromagnetic Method for the Assessment of Abdominal Visceral Fat Accumulation

A new electromagnetic measurement method for the direct assessment of abdominal visceral adiposity is presented. The method relies on the measurement of the electrical losses arising from the subject standing in a tuned radio frequency coil excited into resonance. The coil is positioned so that it surrounds an individual at the abdomen. The conductive tissue (muscle) loads the coil more being lossier than the low conductive fatty tissue. The idea here is that, measuring the losses at multiple frequencies, the fat distribution of the subject could be assessed by weighting outer structural components as the frequency increases. The coil voltage was used as an indication of the loss changes. The method was tested by phantom measurements and, for a demonstration, in a one-volunteer measurement. Phantom A had saline in the middle of its volume and fat in the outer shell volume while phantom B had the reversed conductivity distribution. The measured coil-loading rates as a function of frequency were 0.14 mV/kHz and 0.41 mV/kHz for phantoms A and B, respectively. This result suggests that the loading rate can be a potential index for body composition analysis, which should be applicable in the assessment of visceral fat accumulation, so that the higher rates are an indication of a larger amount of visceral fat. In the one-volunteer measurement, the loading rate of 0.64±0.04 mV/kHz was observed. The 1.5-T magnetic resonance imaging showed that visceral and subcutaneous fat areas in this volunteer were 112.1 cm2 and 269.4 cm2, respectively, at the umbilicus level.