ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA

1. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA TUT Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling–––––––––––––––––––––––––––––––––––––––––––––––––––– by Ants Ronk, Mart Min, and Toomas Parve Department of Electronics Tallinn University of Technology, Tallinn, Estonia

2. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 2 TUT *** In this paper the possibilities to perform multi-frequency bio-impedance measurement simultaneously for several tissue channels are discussed, and a method of synchronous signal sampling by applying uniform or non-uniform sampling, together with digital signal processing is presented.

3. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 3 TUT I. INTRODUCTION Measurement of electrical bio-impedance enables to characterise a state of tissues/organs, to get diagnostic images, to find hemodynamical parameters, etc. Simultaneous multichannel and multifrequency measurements are needed. Why multichannel ? Why multifrequency ? Why simultaneous ? Some examples of electrical bioimpedance measurement from cardiography a noninvasive b multielectrode invasive estimation c intracardiac impedance measured plethysmography of the ventricular volume for pacing control

4. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 4 I. INTRODUCTION . Complex bioimpedance Ż=R+jX is found as Ż=V/I from the measured voltage response Vto the sine wave excitation current Ipassed through the bio-object, commonly. Explanation of the EBI. Simple 3-element equivalent. Phasor diagram for a frequency f. What is so specific in the bioimpedance (EBI) The phasor diagramme of the static EBI (▬), and of its 3-element equivalent (▬), and the phasors of the static EBI for 2 frequencies, low ωl and high ωh.

5. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 5 TUT II. MEASUREMENT SYSTEM:SIGNALS AND ALGORITHMS Simultaneous multifrequency EBI measurement system . . . . VZ = Iexcit Z = If1Z(f1) + If2 Z(f2) Sampling pulses Fig.1 A system for simultaneous two-frequency bio-impedance measurement applying synchronised sampling

6. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 6 TUT II. MEASUREMENT SYSTEM: SIGNALS AND ALGORITHMS Multi-site EBI measurement using synchronous sampling Re+ Im– Im+ Re– fsampling =4·fsignal The real Re and imaginary Im parts of the phasor Ż are determined as Re=(Re+ – Re–) ∕ 2 and Im=(Im+ – Im–) ∕ 2 Synchronous sampling of a single sine wave response. Real part samples Re+ are designated as filled red dots●and Re– as unfilled red ones ○, imaginary part samples Im+ as filled green squares ■, and Im– as unfilled green squares □

7. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 7 TUT II. MEASUREMENT SYSTEM: SIGNALS AND ALGORITHMS Two typical cases of multifrequency measurement Multi-site Multi-frequency a)  Two different impedances are measured  b)  The same impedance is measured       at a slightly differing frequency at (two) essentially different frequencies non-uniform synchronous sampling Fig. 3. Simultaneous measurement of responses to two excitations Note: Only the Re+ samples are shown for the response signal.

8. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 8 f1 f2 fSP,1 =f1 f2 f1 fSP,2 =f2 fSP 6 A1= ΣAi ⁄6 i=1 6 ΣAi = 0 i=1 5 A2= ΣAi ⁄5 i=1 5 ΣAi = 0 i=1 non-uniform sampling II. MEASUREMENT SYSTEM: SIGNALS AND ALGORITHMS Using the non-uniform sampling at simultaneous measurement An example: f1  ⁄f2 = 6 ⁄ 5 tmeas = 6 ⁄f1  = 5 ⁄f2 Convergence of results in the case of simultaneous measurement of the responses to two excitations with near (slightly differing) frequencies f1 and f2

9. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 9 TUT II. MEASUREMENT SYSTEM: SIGNALS AND ALGORITHMS Simultaneous multifrequency measurement using uniform sampling Timing and weighting of the samples usable for determining the real and the imaginary part of the components of the VZ signal in the case of two-frequency operation f2 = 2f1

10. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 10 TUT II. MEASUREMENT SYSTEM: SIGNALS AND ALGORITHMS Timing and weighting of the samples usable for determining the real part of the VZ signal in the case of two-frequency operation f2 = 3f1

11. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 11 TUT II. MEASUREMENT SYSTEM: SIGNALS AND ALGORITHMS Timing and weighting of the samples usable for determining the real part of the VZ signal in the case of two-frequency operation f2 = 6f1

12. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 12 TUT II. MEASUREMENT SYSTEM: SIGNALS AND ALGORITHMS Choice of frequencies(Examples for some more general cases) Example 1 –Decade distances Example 2 –Half decade distances k = 2i + 1 i = 0, 1, 2, ….

13. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 13 4 2 0 -2 -4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 0.5 0 =>real part -0.5 =>imag. part =>modulus -1 0 5 10 15 20 25 30 II. MEASUREMENT SYSTEM: SIGNALS AND ALGORITHMS Processing of one component of a 4-component multi-sine response with 2 pairs of close frequencies. ν(t) The signal ν(t) , its four components and 32 samples taken per its period (measurement interval) wRe1 wIm1 Weighting patterns forνc1(t) 1.0 0.5 0 –0.5 –1.0 Z1 ReŻ1=R1 νc1(t) ImŻ1=X1 Convergence of results to real and imaginary parts and module forνc1(t) Main text

14. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Simultaneous multi-frequency bio-impedance measurement applying synchronised uniform or non-uniform sampling A. Ronk, M. Min and T. Parve 14 TUT CONCLUSIONS The presented measurement signal system(s) and digital signalprocessingmethodenable to measure bioimpedance and to demodulatebio-modulationsof components of a multi-sine measurementsignal,which coversa widefrequency range (from kHz up to several MHz)simultaneously. The same can be done applying Fourier transformation but the proposed approach is significantly simpler andsuits well for microelectronic implementation (e.g. in FPGA). Thus it looks promising for applications in portable/wearable bioimpedance measurement systems of low power consumption. Thank you for your attention ! ACKNOWLEDGMENT Estonian Science Foundation supported this work under the grants 7243 and 7212. Address of the corresponding author: Ants Ronk,Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia Email:ronk@ttu.ee