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

Blomqvist KH, Sepponen RE - Biomed Eng Online (2010)

Bottom Line: The 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.At higher frequencies the major signal contribution can be shifted toward outer shell volume.The authors expect that the loss changing rate over frequency can be a potential index for body composition analysis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electronics, Aalto University, PO BOX 13340, 00076 Aalto, Finland. kim.h.blomqvist@tkk.fi

ABSTRACT

Background: Tomographic 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).

Methods: The 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.

Results: The 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.

Conclusions: At 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.

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Example sensor response. Equation 5 plotted for two different excitation frequencies over the region of ΔRloss observed in practice. V0 = 1 V, Q1 = 95, Q2 = 145, f1 = 103 kHz and f2 = 186 kHz (refer to Figure 12).
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Figure 4: Example sensor response. Equation 5 plotted for two different excitation frequencies over the region of ΔRloss observed in practice. V0 = 1 V, Q1 = 95, Q2 = 145, f1 = 103 kHz and f2 = 186 kHz (refer to Figure 12).

Mentions: where V0 is the amplitude of the time-varying voltage applied across the voltage divider. The approximation Z ≈ X2/R was used. As can be seen from this equation, the sensitivity of the sensor is not flat over the frequency bandwidth. Although a reasonably flat Q could be achieved over the bandwidth, there is still the frequency dependency which affects the impedance level of the voltage divider. However, in the region of ΔRloss observed in practice, the response is very linear, as shown in Figure 4. A compensation factor k ≈ Q1f2/Q2f1 between two resonance frequencies can be found and the measured voltages at different resonance frequencies can be made comparable.


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

Blomqvist KH, Sepponen RE - Biomed Eng Online (2010)

Example sensor response. Equation 5 plotted for two different excitation frequencies over the region of ΔRloss observed in practice. V0 = 1 V, Q1 = 95, Q2 = 145, f1 = 103 kHz and f2 = 186 kHz (refer to Figure 12).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2992533&req=5

Figure 4: Example sensor response. Equation 5 plotted for two different excitation frequencies over the region of ΔRloss observed in practice. V0 = 1 V, Q1 = 95, Q2 = 145, f1 = 103 kHz and f2 = 186 kHz (refer to Figure 12).
Mentions: where V0 is the amplitude of the time-varying voltage applied across the voltage divider. The approximation Z ≈ X2/R was used. As can be seen from this equation, the sensitivity of the sensor is not flat over the frequency bandwidth. Although a reasonably flat Q could be achieved over the bandwidth, there is still the frequency dependency which affects the impedance level of the voltage divider. However, in the region of ΔRloss observed in practice, the response is very linear, as shown in Figure 4. A compensation factor k ≈ Q1f2/Q2f1 between two resonance frequencies can be found and the measured voltages at different resonance frequencies can be made comparable.

Bottom Line: The 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.At higher frequencies the major signal contribution can be shifted toward outer shell volume.The authors expect that the loss changing rate over frequency can be a potential index for body composition analysis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electronics, Aalto University, PO BOX 13340, 00076 Aalto, Finland. kim.h.blomqvist@tkk.fi

ABSTRACT

Background: Tomographic 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).

Methods: The 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.

Results: The 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.

Conclusions: At 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.

Show MeSH