CN108037156A - Multifrequency electrical impedance tomography system based on reference measure - Google Patents
Multifrequency electrical impedance tomography system based on reference measure Download PDFInfo
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- CN108037156A CN108037156A CN201711167096.0A CN201711167096A CN108037156A CN 108037156 A CN108037156 A CN 108037156A CN 201711167096 A CN201711167096 A CN 201711167096A CN 108037156 A CN108037156 A CN 108037156A
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
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- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/053—Measuring electrical impedance or conductance of a portion of the body
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Abstract
The present invention relates to a kind of multifrequency electrical impedance tomography system based on reference measure, including excitation current source, reference resistance and measurement selecting module, data acquisition and processing module, reference resistance and measurement selecting module include an accurate fixed value resistance and a multidiameter option switch, for measurement positive and negative terminal to be connected in reference resistance both ends or load both ends on request, fixed value resistance and load in series, the both ends of reference resistance and load are connected in the selection input terminal of multidiameter option switch, FPGA gives measurement end then signal, the both ends of reference resistance or the both ends of load are connected by instruction with the output terminal of multidiameter option switch, and then alternately realize reference measure and load measure.
Description
Technical field
The invention belongs to electricity chromatograph technical field of imaging, be related to it is a kind of based on reference measure multifrequency electrical impedance chromatography into
As system.
Background technology
Electricity chromatography imaging technique (Electrical Tomography, ET) is that occur from the later stage eighties in last century
A kind of new process tomographic imaging technology based on electrical characteristics sensitive mechanism, its physical basis are that different mediums have difference
Electrical characteristics (electrical conductivity/dielectric coefficient/complex admittance/magnetic conductivity), by judge object in sensitivity field electrical characteristics be distributed
Deduce the distribution situation of the middle medium of this.Electricity chromatography imaging technique mainly includes electrical resistance tomography (Electrical
Resistance Tomography, ERT), capacitance chromatography imaging (ElectricalCapacitance Tomography,
ECT), electrical impedance tomography (Electrical Impedance Tomography, EIT) and electromagnetic chromatographic
(Electrical MagneticTomography,EMT).Electricity chromatography, which is imaged on multiphase flow and biomedical sector, to be had extensively
Application prospect, it is possible to achieve it is long-term, continue to monitor.
Multifrequency electrical impedance tomography technology is a kind of new Non-invasive detection technique, which has the function of into
Picture, it is of low cost, it is harmless the advantages that, therefore be with a wide range of applications in clinical medicine field.The technology passes through
Array electrode is placed in human body surface, applies current excitation signal, test voltage signal, so as to extract Human Physiology, disease
The electrical characteristics of state tissue or organ.Since the amplitude of useful signal is smaller and is easily disturbed, high performance multifrequency electrical impedance chromatography
Imaging system requires current source to have higher output impedance, and output frequency can Bu Tong flexibly adjusting according to object with amplitude
It is whole.Signal acquisition terminal requires programmable gain amplifier, can carry out linear process to the signal measured and be at ADC cores
In the sensitivity interval of piece.
The electrology characteristic change that biological tissue changes and produces with driving frequency is mainly reflected on dielectric constant.Work as excitation
After electric current is by non-purely resistive load, the phase place change of voltage can be caused, this fractional phase information is load dielectric constant information
Important embodiment.Instantly processing of the multifrequency EIT system to phase information is broadly divided into two kinds：One kind be without considering phase information,
Only collection is easier to the amplitude information obtained, such as David Holder et al. were published in 2006《Physiological measurements》
(Physiological Measurement) volume 27, it is S199-S210 pages, entitled《For the portable more of Acute Stroke imaging
The design and calibration of frequency EIT system》(Design and calibration of a compact multi-frequency
EIT system for acute stroke imaging) article and David Holder et al. be published in 2007
《Physiological measurements》(Physiological Measurement) volume 28, it is S197-S215 pages, entitled《Multifrequency EIT instrument errors
Comment》The survey article of (A review of errors in multi-frequency EIT instrumentation)；Separately
One kind is to demarcate phase information by calculating according to driving frequency, such as Daniel Teichmann et al. were published in 2016
《Sensor》(Sensors) it is volume 16, the 8th phase, page 1158, entitled《Multifrequency electrical impedance tomography while based on FPGA
The design first of system》(System description and first application of an FPGA-based
Simultaneous multi-frequency electrical impedance tomography) article.The first side
Method abandons important phase information, is worthless in the collection of bio-impedance information.Second method is only applicable to mark
Determine the phase shift of the generations such as ADC, DAC, wave filter, for other such as phase shifts of stray capacitance introducing and do not apply to.
The content of the invention
It is an object of the invention to overcome the above-mentioned deficiency of the prior art, a kind of new multifrequency electrical impedance tomography is proposed
System.Present invention introduces reference measure circuit, and by reference resistance and load in series, the voltage on fixed value resistance is referred to by measurement
The current information of signal tracing reality.The phase information on reference resistance and load obtained by comparing demodulation, is loaded
The phase modulation actually produced is poor, and the dielectric constant information that can be further loaded, meets bio-impedance measurement system
It is required that.
Technical scheme is as follows：
A kind of multifrequency electrical impedance tomography system based on reference measure, including excitation current source, reference resistance and survey
Measure selecting module, data acquisition and processing module, it is characterised in that
Excitation current source includes DDS module, amplitude control and D/A modular converters, differential amplification module, low-pass filtering mould
Block, voltage controlled current source VCCS modules etc..Wherein, DDS module is based on the DDS IP kernels carried in ISE, the structure inside FPGA
Build, output meets the digital waveform of needs；Amplitude controls and D/A modular converters are converted by the adjustable D/A of output can be achieved, output
Satisfactory analog current；The analog current that prime exports is converted to analog voltage by differential amplification module, via low pass filtered
Wave circuit and the high-precision exciting current of VCCS circuit outputs；
Reference resistance and measurement selecting module include an accurate fixed value resistance and a multidiameter option switch, for that will survey
Amount positive and negative terminal is connected in reference resistance both ends or load both ends, fixed value resistance and load in series, reference resistance and load on request
Both ends are connected in the selection input terminal of multidiameter option switch, and FPGA gives measurement end then signal, indicates the both ends of reference resistance
Or the both ends of load are connected with the output terminal of multidiameter option switch, and then alternately realize reference measure and load measure.
The present invention by adding reference measure, by reference measurement values and load measurement directly compared with, avoid survey
Amount result is influenced be subject to stray circuit in circuit, obtains amplitude change and phase difference completely as caused by actual loading.With showing
Modern existing the methods of calculating calibration, is compared, and the present invention can undoubtedly obtain the capacitive information of the load closer to reality, to resistance
Application of the anti-tomography in biological bulk measurement is of great significance.
Brief description of the drawings
Fig. 1 is the structure diagram of the present invention；
Fig. 2 is the structure diagram of driving source of the present invention；
Fig. 3 is the hardware connection figure of VCCS of the present invention；
Fig. 4 is the reference resistance of the present invention and the schematic diagram for measuring selection circuit；
Fig. 5 is the hardware connection figure of the measurement selection circuit of the present invention.
Embodiment
A kind of multifrequency electrical impedance based on reference measure of the present invention is chromatographed with reference to the accompanying drawings and detailed description
Imaging system is described in detail.
Fig. 1 show the structure diagram of the present invention.As shown in the figure, the number using the DDS IP kernels structure output inside FPGA
Word sine wave, the identifiable true form data flow of DAC chip is converted into by interface routine, through D/A circuits, low-pass filter circuit,
The exciting current that amplitude is adjustable, frequency is controllable is converted into after VCCS circuits；Reference resistance and load are in circuit the shape of series connection
Formula, variable connector are used for the electrode of selected excitation and measurement；The chosen switch of voltage on reference resistance and load at the same time can only
There is one to enter digital sampling and processing；The voltage signal of receiving is through differential amplifier circuit, programmable gain amplifier, ADC
Digital signal is converted to after chip to enter inside FPGA；Digital signal carries out digital phase-sensitive demodulation inside FPGA, and demodulation obtains
Amplitude and phase information be stored in FIFO, after measurement period is full by one group of data by USB transmission to host computer into
Row image reconstruction and display.Whole process is by the in-built soft nuclear control of PICOBLAZE microprocessors of FPGA.
It is the structure diagram of driving source of the present invention shown in Fig. 2.Excitation current source include FPGA inside waveform generating module,
Amplitude control module, D/A modular converters, differential amplification module, low-pass filtering module, VCCS modules etc..DDS module is in FPGA
Cage structure, is programmed by hardware language and realized, by setting DDS IP kernel inner parameters, can change DDS output digits, and in fact
Existing single-frequency and multi-frequency excitation.14 sinusoidal digital signals that DDS module produces are input to 14 data input of D/A modular converters
End, is converted into analog differential electric current by D/A conversions and exports.Amplitude control module can receive 8 digits of FPGA outputs
Word amount, is converted into analog reference voltage output, and D/A modular converters can receive this reference voltage, realizes that electric current exports.This
Output current can be exchanged into analog voltage via differential amplifier circuit, and low-pass filtered circuit can filter the high-frequency noise in voltage
Remove, then through voltage-controlled current source (VCCS) circuit conversion be pumping signal of the current drive signal as multifrequency EIT system.
Fig. 3 show VCCS circuit hardware connection figures.This circuit is opened up for the combination of conventional current mirror circuit and differential configuration
Flutter circuit.DC component in the voltage output of AD844 chips is fed back to voltage input end, is removed by this negative feedback structure
Flip-flop in output, prevents from charging to capacitive load.Differential configuration is the combination of inverting amplifier and voltage follower, is made
The magnitude of voltage at both ends opposite number each other must be loaded, compared in more traditional EIT system by the mode of overload current earthing, this method
The output impedance of current source can be effectively improved, and reduces common mode interference.
Fig. 4 show the schematic diagram with reference to selection circuit.In a measurement period, to the drop measurement one of reference resistance
Secondary, as the calibration value of actual current value, this calibration value and the measured value loaded are corresponding by digital quadrature demodulation acquisition
Amplitude and phase information.The electrical conductivity and dielectric constant information of actual loading can be obtained by comparing both amplitude and phase information.
Fig. 5 show the hardware connection figure of this part.Multi-path digital switch chip DG413DY is selected to realize Measurement channel selection function.
Measurement termination reference resistance or load may be selected in the control word instruction (0 or 1) of FPGA outputs.Wherein, it is actual as caused by load
The amplitude change of voltage and phase difference can be expressed from the next：
In formula, UxAnd UrThe amplitude in load and reference resistance respectively demodulated, φxAnd φrRespectively demodulate
To load and reference resistance on phase value, A andVoltage linear conversion multiple and phase difference respectively caused by load.
Agent structure and some typical circuit of the above for the present invention, the present invention is not limited to interior disclosed in attached drawing
Hold.It is every not depart from the lower equivalent or modification completed of spirit disclosed in this invention, all in the scope of protection of the invention.
Claims (1)
1. a kind of multifrequency electrical impedance tomography system based on reference measure, including excitation current source, reference resistance and measurement
Selecting module, data acquisition and processing module, it is characterised in that
Excitation current source includes DDS module, amplitude control and D/A modular converters, differential amplification module, low-pass filtering module, electricity
Voltage-controlled current source VCCS modules etc..Wherein, DDS module is defeated in FPGA internal builds based on the DDS IP kernels carried in ISE
Go out to meet the digital waveform of needs；Amplitude controls and D/A modular converters are converted by the adjustable D/A of output can be achieved, and output meets
It is required that analog current；The analog current that prime exports is converted to analog voltage by differential amplification module, via low-pass filtering electricity
Road and the high-precision exciting current of VCCS circuit outputs；
Reference resistance and measurement selecting module include an accurate fixed value resistance and a multidiameter option switch, for that will measure just
Negative terminal is connected in the both ends of reference resistance both ends or load both ends, fixed value resistance and load in series, reference resistance and load on request
The selection input terminal of multidiameter option switch is connected in, FPGA gives measurement end then signal, indicates the both ends of reference resistance or negative
The both ends of load are connected with the output terminal of multidiameter option switch, and then alternately realize reference measure and load measure.
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| CN201711167096.0A CN108037156A (en) | 2017-11-21 | 2017-11-21 | Multifrequency electrical impedance tomography system based on reference measure |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109363674A (en) * | 2018-08-22 | 2019-02-22 | 西安电子科技大学 | A kind of bio-impedance testing system |
| CN110123320A (en) * | 2019-05-13 | 2019-08-16 | 南京航空航天大学 | A kind of portable frequency sweep impedance bioelectrical measurement system and its measurement method |
| CN110279416A (en) * | 2019-05-20 | 2019-09-27 | 南京航空航天大学 | A kind of portable impedance imaging system and its working method based on FPGA |
| CN113760025A (en) * | 2020-06-04 | 2021-12-07 | 中国科学院苏州生物医学工程技术研究所 | Adjustable constant current source, electrical impedance imaging system and image reconstruction method thereof |
| US20230082500A1 (en) * | 2021-08-26 | 2023-03-16 | Beihang University | Dynamic impedance imaging system |
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| CN1709203A (en) * | 2005-07-01 | 2005-12-21 | 天津大学 | Analogue demodulation mode mixing biological impedance measuring method |
| CN1723844A (en) * | 2005-07-01 | 2006-01-25 | 天津大学 | Analog demodulation mode type frequency-mixing bio-impedance testing system |
| CN105656489A (en) * | 2016-03-08 | 2016-06-08 | 天津大学 | Exciting current source for bioelectrical impedance imaging |
| CN107184211A (en) * | 2017-06-15 | 2017-09-22 | 南京邮电大学 | A kind of multifrequency electrical impedance imaging device based on FPGA |
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2017
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| CN1709203A (en) * | 2005-07-01 | 2005-12-21 | 天津大学 | Analogue demodulation mode mixing biological impedance measuring method |
| CN1723844A (en) * | 2005-07-01 | 2006-01-25 | 天津大学 | Analog demodulation mode type frequency-mixing bio-impedance testing system |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109363674A (en) * | 2018-08-22 | 2019-02-22 | 西安电子科技大学 | A kind of bio-impedance testing system |
| CN109363674B (en) * | 2018-08-22 | 2020-07-17 | 西安电子科技大学 | Biological impedance measuring system |
| CN110123320A (en) * | 2019-05-13 | 2019-08-16 | 南京航空航天大学 | A kind of portable frequency sweep impedance bioelectrical measurement system and its measurement method |
| CN110279416A (en) * | 2019-05-20 | 2019-09-27 | 南京航空航天大学 | A kind of portable impedance imaging system and its working method based on FPGA |
| CN113760025A (en) * | 2020-06-04 | 2021-12-07 | 中国科学院苏州生物医学工程技术研究所 | Adjustable constant current source, electrical impedance imaging system and image reconstruction method thereof |
| US20230082500A1 (en) * | 2021-08-26 | 2023-03-16 | Beihang University | Dynamic impedance imaging system |
| US11754520B2 (en) * | 2021-08-26 | 2023-09-12 | Beihang University | Dynamic impedance imaging system |
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