CN1526358A - Electric impedance tomographic imaging method and apparatus for imaging monitoring beside sickbed - Google Patents
Electric impedance tomographic imaging method and apparatus for imaging monitoring beside sickbed Download PDFInfo
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Abstract
The present invention discloses electric impedance tomographic imaging method and apparatus for imaging nursing beside sickbed. The integral computerized data collecting system and the re-construction algorithm provides the interface and controls the imaging nursing process. The apparatus includes one computer and one connected data collecting system, the computer is equipped with program for controlling the data collecting system and algorithm for re-constructing image, and the data collecting system has also control module to apply excitation current to body signal collecting electrodes. The present invention features the several pairs of electrodes for applying excitation current and collecting body signals, the data collecting system providing constant AC excitation, high precision signal detection and programmed driving and measuring mode, and the calculation of body resistivity distribution and image display.
Description
Technical field
The invention belongs to medical apparatus and instruments or instrument, relate to an a kind of impedance tomograph imaging method and device thereof of other image monitoring that can be used for.
Background technology
The disease that some sickness rate is very high in clinical diagnosis now and the treatment needs to be used for the imaging technique of bedside monitoring: apoplexy, the subacute pathological changes of craniocerebral injury, chronic intracranial hemorrhage, operation back brain complication, intracranial hemorrhage of newborn, abdominal organs retardance internal hemorrhage or ischemia, organ transplantation etc. all need an other image monitoring technology.
And existing imaging technique all can not be used for a bed other image monitoring: not only need huge equipment and high expense as existing C T, MRI, PET, ultrasonic etc., complicated operation, human body there is certain infringement, and can not accomplishes that all bed is other dynamically, the real time imaging monitoring.In the clinical practice field, the other image monitoring of bed is still a blank, causes many patients best rescue opportunity of forfeiture in clinical diagnosis and treatment.
Electrical impedance imaging by apply safe electric excitation, in-vitro measurements response signal to human body, is rebuild the image of resistivity or its change profile of inside of human body exactly.
The advantage of this technology aspect the other function image monitoring of bed: at first to the sensitivity of changes of function, what it extracted is to change relevant electrical characteristics with function of organization, and those are influenced the factor of electrical characteristics, as flowing and distribution of blood, body fluid variation etc. are very responsive, and the image of formation is a function image, secondly, do not use nucleic or ray, nontoxic, not damaged, can repeatedly measure, reuse the 3rd, equipment is small-sized, and cost is lower.
The different tissues that the electrical impedance imaging technology is based on human body has this physical principle of different electrical impedance, applies safe electric current (voltage) to human body, from body surface measurement voltage (electric current), utilizes the body surface measurement signal reconstruction to go out to reflect the image that the human body internal impedance distributes.Be aspect the quiescent imaging of imageable target at the absolute value that distributes with human body impedance, owing to, only be in the laboratory research stage at present to the system requirements harshness; Be that nowadays the imaging system of being reported comes from tens seminar of states such as Britain, the U.S., Finland, France and Turkey aspect the dynamic imaging of imageable target at the relative variation that distributes with human body impedance.They carry out many-sided exploration aspect the clinical application research of impedance imaging, functional imagings such as digestive system, respiratory system, brain, heart, mammary gland have this to property do a lot of work, but because the resolution of impedance image is high not enough, can not reach the level of the resolution of present CT, MRI, can not be used as clinical disease as CT, MRI and become and accurately detect, achieve no breakthrough so far.
Domestic present impedance imaging technical research also has University Of Tianjin, University Of Chongqing, Hebei University of Technology etc., at present also all in the basic research stage in addition to apply for artificial main carrying out.
Summary of the invention
The objective of the invention is to, give full play to the applicant at impedance imaging in the advantage aspect the function image monitoring research, the impedance imaging Clinical application is positioned the function image monitoring that is sought after again that other imaging techniques are difficult to realize, clinical.According to the years of researches result, provide an a kind of impedance tomograph imaging method and a device thereof that is used for a bed other image monitoring for clinical, and proposed to be used for data collecting system and the image reconstruction algorithm and the design of software corresponding of the impedance imaging of bedside monitoring.
The technical solution that realizes the foregoing invention purpose is: be used for an impedance tomograph imaging method of other image monitoring, by the computer control data collecting system of integral body and the algorithm of reconstructed image, provide the interface, the process of control figure picture monitoring; Be characterized in, may further comprise the steps at least:
1) adopts many counter electrode, exciting current is added to human body, and the signal of human body is passed to data collecting system;
2) provide interchange constant current drive, high-precision signal to detect, drive the program control function that is provided with of measurement pattern by data collecting system;
3) according to the voltage signal that collects, the distribution that changes by the algorithm computation body internal resistance rate of the reconstructed image that is provided with in the computer, and display image.
Above-mentioned interchange constant current drive, high-precision signal detect, drive the program control function that is provided with of measurement pattern and be respectively:
Exchange the constant current drive function:
Adopt simulation vibration, phaselocked loop and Direct Digital synthetic technology, comprise produce frequency about 50KHz sinusoidal signal and realize constant current output and start-up control signal that demodulating control signals that generation and pumping signal are synchronous and A/D change;
The high-precision signal measuring ability comprises:
High-precision signal amplification, dynamic range adjustment, high accuracy demodulation and data acquisition;
Driving and the program control function that is provided with of measurement pattern comprise:
1. drive pattern on demand is loaded into pumping signal many on the pair of electrodes in the drive electrode;
2. measurement pattern on demand is with many inputs that signal loading on the pair of electrodes in the individual measurement electrode arrived signal amplification circuit.
The algorithm of described reconstructed image is: adopt dynamic equipotential line back projection method, this equipotential line back projection method is based on the following hypothesis that the imaging target is done:
1. be two dimension by the imageable target distribution of impedance;
2. the zone boundary is circle;
3. electrode on the border for being spacedly distributed;
4. the anti-disturbance that distributes of target area internal resistance compare with the absolute value of distribution of impedance very little, thereby make the disturbance of boundary voltage become linear approximate relationship with the distribution of impedance disturbance;
The equipotential line impedance imaging is actually the turbulent imaging of target area distribution of impedance:
If in distribution of impedance is that (x loads one group of drive current around target area y) to σ, and obtaining one group of response voltage is V
0, after a less variation (disturbance) takes place in distribution of impedance, and σ (x, y) → σ (x, y)+(x, y), record response voltage is V to Δ σ
1,, can obtain the disturbance of distribution of impedance with carrying out back projection after two groups of voltage difference regularization.
A kind ofly realize an above-mentioned device that is used for the impedance tomograph imaging method of bed other image monitoring, comprise a computer, computer is connected with a data collecting system, it is characterized in that, be provided with the program of control data acquisition system and the algorithm of reconstructed image in the computer, data collecting system also is provided with manyly gathers the electrode system (adopting electrocardio or electrode for encephalograms at present) of the signal of human body to exciting current being added to human body;
Above-mentioned data collecting system comprises:
One driving source module, be used to produce frequency about 50KHz sinusoidal signal and realize constant current output and start-up control signal that demodulating control signals that generation and pumping signal are synchronous and A/D change;
One signal detection module is used for signal amplification, dynamic range adjustment, high accuracy demodulation and data acquisition;
One D/A modular converter is used for the selection of D/A and the realization of wave generator circuit;
One motivation model is provided with module, and the drive pattern that is used on demand is loaded into many pair of electrodes to drive electrode with pumping signal;
One measurement pattern is provided with module, be used on demand measurement pattern with many to the signal loading on the pair of electrodes of individual measurement electrode to the inputs of signal amplification circuit.
Above-mentioned said electrode is 32.
Description of drawings
Fig. 1 is the The general frame of electrical impedance tomography device of the present invention, a) is block diagram wherein, b) is the device sketch map;
Fig. 2 is 32 electrode data acquisition system block diagrams;
Fig. 3 is the driving source block diagram;
Fig. 4 is the voltage-controlled current source circuit diagram of three amplifier structures;
Fig. 5 is with being in parallel differential amplifier circuit figure;
The big logotype of contiguous measuring-signal when Fig. 6-1 is 32 electrode drive;
Fig. 6-2 is the big logotypes of 16 stage gains;
Fig. 6-the 3rd, the big logotype of output signal behind PGA, (Max/Min=2.40) unit: mV;
Output was to (μ s) sketch map time delay of input, signal frequency 47KHz when Fig. 6-4 was 16 stage gains;
Fig. 7 is the signal detection module block diagram with phasing and dynamic range adjustment;
Fig. 8 is the signal detection module circuit diagram with phase compensation and direct current PGA;
Fig. 9 is signal waveform and a sequential sketch map in the 32 electrode hardware systems;
Figure 10 is a MAX306 variable connector structural representation;
Figure 11 is that measurement pattern is provided with schematic diagram;
Figure 12 is a Real Time Image System distribution of electrodes sketch map;
Figure 13 is back projection's district's sketch map, and wherein D1 is the equivalent electric dipole, and dash area is the back projection district, and P is a pixel in the projected area;
Figure 14 is the diagram of asking for of back projection's weights;
Figure 15 is back projection's process sketch map;
Figure 16 is the imaging system workflow diagram;
Figure 17 is software system basic function figure;
Figure 18 is the initialization flowchart of software;
Figure 19 is the reference data frame collecting flowchart figure of software;
Figure 20 is the imaging data frame collecting flowchart figure of software.
The specific embodiment
The present invention is described in further detail according to embodiment that the technical program is finished below in conjunction with accompanying drawing and inventor.
1, population structure
Population structure of the present invention a) is a block diagram among the figure as shown in Figure 1, b) is the device sketch map.
Whole computer control: the algorithm of control data acquisition system and reconstructed image, provide the interface to user, make the process that the staff can the monitoring of control figure picture.
Electrode: adopt electrocardioelectrode or electrode for encephalograms, exciting current is added to human body, and the signal of human body is passed to data collecting system.
Data collecting system: provide to exchange constant current drive, high-precision signal and detect, drive the program control function such as be provided with of measurement pattern.
The algorithm of image reconstruction: according to the voltage signal that collects, calculate the distribution that body internal resistance rate changes, and display image.
2, data collecting system structure
2.1 data collecting system and whole computer control
2.1.1 driving source module (among Fig. 2 1)
The driving source modular structure block diagram of a complete employing DDS technology as shown in Figure 3.
1) function finished of this module
A) produce the sinusoidal signal of frequency about 50KHz;
B) realize constant current output;
C) produce and the synchronous demodulating control signals of pumping signal and the start-up control signal of A/D conversion;
2) circuit structure is chosen
A) sinusoidal wave form generation circuit: produce the known sinusoidal signal of frequency, on circuit, can adopt the synthetic technology such as (DDS) of simulation vibration, phaselocked loop and Direct Digital.First-selected DDS technology.For reducing the harmonic component of DDS circuit output waveform, among the EPROM weekly the phase waveform count and be designed to 128 points, Theoretical Calculation shows weekly phase 128 sinusoidal datas in the ladder sine wave shape that D/A is converted to, and 2 order harmonic components are that 0.52%, 3 order harmonic components is 0.29%.For further reducing the output signal harmonic component, after D/A output, design the one-level band filter, with the input signal of its output as constant-current circuit.
B) constant-current circuit: its input signal is an ac voltage signal, and output signal is to exchange constant current signal, therefore selects the voltage controlled current source circuit (VCCS) of three amplifier structures for use, as shown in Figure 4.
C) control signal produces circuit: select the high-speed coding circuit for use, the specific time sequence of sinusoidal signal among the DDS is deciphered, to produce and accurate synchronous demodulating control signals and the A/D conversion starting signal of pumping signal.
3) selection of main devices and functional circuit are realized
A) realization of the selection of D/A and wave generator circuit
Select 12 D/A for use.By designing requirement, driving frequency has 128 point data to change through D/A because of interim weekly near 50KHz, so its switching rate should be greater than 50KHz * 128=6.4MHz, promptly the conversion time of D/A should be less than 160ns.Consider that driving frequency may be higher in the future, 12 AD9713 of high accuracy that selected AD Analog Devices Inc are the D/A among the DDS, and satisfy the needs of present driving frequency less than 30ns its conversion time.
In circuit is realized, select for use the 12MHz crystal oscillator as clock, frequency is 6MHz behind 2 frequency divisions, read 128 sinusoidal datas among the EPROM by its control circulation, after the AD9713D/A conversion, the actual frequency of output signal are 6000/128 ≈ 47KHz, and the cycle is 21.33 μ s.
A, B, C are respectively clock, D/A output waveform, the output waveform behind the band filter of mid frequency 47KHz among Fig. 9.
To the control of exciting current size, adopt the method for section location decoding to read the data that deposit in advance at place, different sections location among the EPROM, make D/A export the sine voltage signal of different amplitudes, behind voltage-controlled current source, produce the different constant current drive signal of amplitude.
B) realization of voltage current transformating circuit: preferred low-noise, high open-loop gain operational amplifier A D829 are as the constant current out amplifier, and the peripheral resistance of precision-matched, make matching error less than 0.01%;
2.1.2 the design of signal detection module and realization (among Fig. 2 4)
1) this module functions
Therefore for satisfying the needs of high-acruracy survey, this module major function has following three:
A) high-precision signal amplifies;
B) dynamic range adjustment;
C) high accuracy demodulation and data acquisition;
2) amplifying circuit
The voltage amplifier that can satisfy high accuracy, high cmrr requirement mainly contains two classes: and same differential amplifier of forming by three amplifiers that is in parallel (as shown in Figure 5) and monolithic instrument amplifier (Instrumentation Amplifier, IA).
Therefore, selecting the preamplifier of instrument amplifier as measurement module, is the main foundation of considering with high-precision, and the AD624 that selects low noise, low imbalance and low offset drift is as preamplifier.
3) dynamic range is adjusted the design and the realization of circuit
In order to adjust dynamic range of signals, do not give the signal additional phase shift again, further analyzing on the basis of this module by signal characteristics, designed structured flowchart signal detection module as shown in Figure 7.
Design principle and implementation method are as follows:
A) preposition fixed gain is amplified: to the signal on the measurement electrode, carry out the fixed gain high accuracy earlier and amplify, amplifier is selected AD624 for use, and its internal fixation gain is made as 100, and it produces the delay of 1.76 μ s to the measured signal of f=47KHz.
B) bandpass filtering and phase shift compensation: be the fixed delay that the fixed gain of compensation preamplifier produces signal, and further improve signal to noise ratio, the second order that is provided with mid frequency in the preamplifier back and is 47KHz, the Q=4 band filter that infinitely gains.Utilize the Phase-Shifting Characteristics of this wave filter, the compensation preamplifier is to the delay of input signal.
C) synchronous demodulation: filter output signal is behind synchronous demodulation circuit, and it is output as direct current signal.
D) the direct current programme-controlled gain amplifies: to the direct current signal of demodulator circuit output, adopt the direct current gain-programmed amplifier to adjust the dynamic range of signal.Requirement to gain-programmed amplifier is single-ended input, low noise, low output drift, low linearity error and higher DC precision.Select AD526 PGA for use, according to the different control word of signal magnitude output, it is 1,2,4,8 or 16 that its gain is set, thereby the dynamic range of input signal can be reduced to 16dB from 40dB by program.
Sort circuit version had both reduced dynamic range of signals, had eliminated the influence of amplifier to signal phase shift again.Experimental results show that this is that performance comprehensively in the impedance imaging hardware system, the precision higher signal amplifies and processing module.Its circuit theory diagrams as shown in Figure 8.
4) realization of demodulator circuit and data acquisition
A) realization of demodulator circuit:
Table 1 phase shift and demodulation pulsewidth not simultaneously, sampling instant changes (mV) s (the 2Vp-p cycle is the sinusoidal signal of 21.3 μ s) with keeping signal constantly
From Fig. 9 E, F and table 1 all can find out, the transition peak value in the demodulation output and the phase shift of demodulation pulsewidth and signal all have relation, and phase shift is on [0, pi/2] interval the time, and the transition peak value increases with phase shift; Phase shift one timing, the transition peak value increases with the demodulation pulsewidth.Therefore, except adopting top phase shift compensation circuit, also should select narrow pulsewidth demodulator circuit.The high accuracy of AD Analog Devices Inc, high-speed sampling holder AD783 have been selected.Its characteristic is as follows: pull-in time was 250ns when precision reached full scale 0.01%, the low rate of releasing of 0.02 μ V/ μ S, aperture shake time 50ps, nonlinearity erron be full scale ± 0.005%, inside is provided with maintenance electric capacity.It also adopts self calibration patent technology in addition, adopts with accurate maintenance and protects control impuls trailing edge input signal values constantly, and reduce the influence of temperature to retention value.The demodulation control impuls is obtained after simultaneous decoding, shaping, pulsewidth fine setting and the light-coupled isolation constantly by the peak value to output signal in the driving source DDS circuit, at present pulsewidth is got 600ns, is carved into the transition peak value of sampling instant less than 50mV during maintenance in the demodulated output signal.
B) collecting method: the direct current signal that demodulates carries out the A/D conversion by 12 data acquisition cards after the direct current gain-programmed amplifier is adjusted dynamic range.For preventing that A/D is accidental transition spike in the signal is collected, adopt DMA external trigger mode, signal is carried out the accurate timing synchronized sampling.Fig. 9: G is for starting the control impuls of A/D sampling, fixed delay is 5 μ s between it and demodulation control impuls, the A/D conversion is carried out in the maintenance stable phase of demodulator circuit all the time, effectively avoided sampling in the demodulation output, kept the influence of transition spike constantly, improved certainty of measurement transformation result.
2.1.3 excitation and measurement pattern are provided with module
Referring among Fig. 22 (1), 2 (2).Module mainly is achieved as follows two functions:
1) drive pattern on demand is loaded into pumping signal on 32 pair of electrodes in the drive electrode, sees among Fig. 22 (1);
2) measurement pattern on demand to the input of signal amplification circuit, sees among Fig. 22 (2) with the signal loading on the pair of electrodes in 32 measurement electrode.
No matter be excitation or measurement pattern, the signal of this module loading is and exchanges low current (less than 10mA) signal, therefore considers to adopt the multipath high-speed electronic switching device.Selected the MAX306 16 of MAXIM company to select 1 CMOS variable connector, its structure as shown in figure 10.It selects the upgrading products of 1 variable connector as DG406, DG407, DG506A and DG507A etc. 16, its conducting resistance is less than 100 Ω, and the interchannel matching error is less than 5 Ω, and channels crosstalk is less than-92dB, COM end leakage current is less than 20nA, and switch time is less than 400nS.The designing requirement that its performance satisfies.
Figure 11 selects 2 any measurement patterns that module principle figure is set for 32 of design, utilizes the EN control end of MAX306, with two MAX306 cascades, forms one 32 to select 1 variable connector, shown in SW1 among Figure 11 (1-16) and SW1 (17-32).Select for two group 32 1 switch in parallel to realize that just 32 select 2 arbitrary patterns that function is set.It is similar to Figure 11 that drive pattern is provided with the schematic diagram of module, and the difference between them is that signal flow is opposite.
3, the Real Time Image System data acquisition interface requires and realizes
3.1 general introduction
The applicant has proposed that a kind of (VirtualDevice Driver VxD) finishes method to hardware operation, thereby has solved the problem of Real Time Image System real-time data acquisition by writing the Windows95 virtual device driver.
3.1.1 based on the real-time data acquisition interface of 32-bit Windows platform (among Fig. 2 5)
ADC in imaging system adopts 12 AC1220 data collecting cards, sample frequency 200kHz.For satisfying the requirement of realtime imaging acquisition speed, AD can be operated in interrupt mode or dma mode, but for system's parallelization and extensibility are considered, adopts dma mode to carry out data acquisition.
Although dma controller is one of standard device of PC, 32 Windows also provides virtual device driver for it, but because most AD plates are not PnP (plug and play) devices of 32-bit Windows in the market, thereby the DMA virtual device driver that provides of operating system can not use at existing AD plate, and must write the ADDMA virtual device driver of oneself.
For AC1220 writes the memory-mapped (Mapping) that another technology barrier of 32-bit Windows virtual device driver is DMA, that is to say in order to finish direct memory access, need in main memory, keep successive memory field on one section physical address, and its address write address register on the AD plate, so that the sampled result order is deposited in this section main memory, and then finish subsequent treatment.Because the address that can visit of application program is a linear address, can only be physical address and hardware device can be discerned, thereby must after applying for internal memory, respectively physical address and linear address be passed to AD plate and application program.Here adopt that DDK provides _ PageAllocate funcall (compilation or C form) application main memory in one section successive memory field of physical address, and to call (compilation form) with _ MapPhysToLinear be linear address with physical address translations, is kept in the data structure of call back function.Because the AC1220 address register is only supported 24 bit addressings---be that maximum physical address is 16M, thereby when application DMA map section, it must be limited in below the 16M.
3.1.2 ADDMA.VxD describes
Virtual device driver ADDMA.VxD provides 4 funcalls: 1. DMA data sampling; 2. AD status poll; 3. dma state inquiry; 4. the DMA relief area discharges.1. function is mainly finished and is applied for functions such as DMA relief area, dma controller setting, AD port are provided with.The DMA relief area is a contiguous memory piece, when obtaining this relief area, be necessary for the physical address that VxD returns relief area, for application program returns its linear address, wherein physical address is used to write the dma controller address register, and linear address is used to read institute's image data.2. function reaches the 3. end of major control DMA and AD; 4. function discharges the DMA relief area.
Virtual device driver can load by static, also CreateFile () the function dynamic load that can provide by Win95 SDK.In the realtime imaging data collecting system, adopt dynamic load, each funcall of VxD is realized by DeviceIoControl () function, sees also the relevant API document of Win32SDK that Microsoft provides about CreateFile () introduces in detail with DeviceIoControl () two function calls.
Sampling parameter is given virtual device driver by following structure by application passes:
typedef?struct?DmaParameters
{ USHORT uAdTime; // the sampling interval
USHORT uAdLength; // sampling length
DWORD lpDmaAdr; //DMA relief area physical address
USHORT uAdChEnd; //AD finishes channel number
USHORT uDmaCh; //DMA channel number
USHORT uTriger; // sampling starts the triggering sign } AdDmaIoP;
The realization of concrete invoked procedure is finished by DeviceIoControl () function.
Source program compiles, links generation VxD jointly by Masm6.11, Visual C++ (5.0), Win95 DDK.
4, Real Time Image System impedance reconstruct imaging algorithm
Because calculating anti-distribution of target resistance from boundary voltage, current relationship is a typical partial differential equation inverse problem, adopt analytic method to find the solution very difficulty of this problem, iteration and approximately linear method are mainly adopted in impedance reconstruct in actual applications, because static iterative algorithm (as the N-R restructing algorithm) holding time is longer, be not suitable for Real Time Image System at present, thereby Real Time Image System in, adopted dynamic equipotential line back projection method.
Equipotential line back projection method is based on the following hypothesis that the imaging target is done:
1. be two dimension by the imageable target distribution of impedance;
2. the zone boundary is circle;
3. electrode on the border for being spacedly distributed;
4. the anti-disturbance that distributes of target area internal resistance compare with the absolute value of distribution of impedance very little, thereby make the disturbance of boundary voltage become linear approximate relationship with the distribution of impedance disturbance;
The equipotential line impedance imaging is actually the turbulent imaging of target area distribution of impedance: if be that (x loads one group of drive current around target area y) to σ, and obtaining one group of response voltage is v in distribution of impedance
0, after a less variation (disturbance) takes place in distribution of impedance, and σ (x, y) → σ (x, y)+(x, y), record response voltage is V to Δ σ
1,, can obtain the disturbance of distribution of impedance with carrying out back projection after two groups of voltage difference regularization.
4.1 back projection
The isoelectric level collimation method is a kind of impedance reconstructing method of approximately linearization, and its main thought source is in early stage X line CT imaging technique.Each forms a specific Electric Field Distribution after to drive electrode load driver electric current in the target area, such electric field equivalence that two drive electrodes are formed is the electric field that an electric dipole produces, electric dipole is positioned at two electrode centers, there are a series of equipotential lines by electric dipole to each measurement electrode like this, zone between the adjacent equipotential line is the back projection district, the voltage difference that records before and after the impedance disturbance is superimposed to this zone to get final product, after the voltage difference back projection of all projections returned corresponding projected area, just obtained the disturbance (variation) of regional electrical impedance distribution.Figure 13 has described back projection's process.
The calculating in back projection district is the forward problem of an electric Field Calculation, and (FiniteElement Method FEM) calculates Potential distribution, obtains the back projection district to adopt FInite Element.
4.2 weighting
Because to measure and drive all be to carry out on the border, target area, thereby it is responsive to have caused the information that obtains that the borderline region electrical impedance is changed in the electrical impedance imaging, and insensitive to the variation of central area, this difference can be brought the error in the imaging.The pixel that for this reason is positioned at central area and marginal area when back projection should have the weight that varies in size.Adopt following method to ask for the weights of back projection.
P is a pixel as shown in figure 14, with distance of center circle from being d, driving the electric dipole distance with equivalence is r, then the P weights of ordering are:
In actual imaging, calculate earlier each pixel or the unitary weights of FEM in good each back projection district, this pixel or unit go back in the back projection of earlier voltage disturbance that records and this pixel or unitary weights being multiplied each other again when back projection.
4.3 the program of algorithm realizes
Design has realized imaging system software, and this software is based on 32 Windows (Windows95/Windows 98/Windows NT) platform, and Visual C++ is adopted in programming, and code has portability and extensibility preferably.This system is easy to use flexibly, thereby provides a good software environment for EIT system experimentation research.
5. work process
5.1 imaging system workflow
Referring to Figure 16, after the start, the computer image monitoring software system that brings into operation, lay electrode system this moment, treat system initialization, calibration after, just can the calling graph picture guard user interface, continuous imaging or single frames imaging be can also select, document function or management carried out; No matter be to select single frames imaging or selection continuous imaging, computer program carries out the witness mark Frame automatically, measures imaging data frame, image reconstruction, pictorial display, processing, finishes until imaging.
5.2 software system basic function
Referring to Figure 17, the software system basic function that the page shows comprises: program circuit, system initialization, hardware system detection, software environment detection, user interface, selection imaging pattern, input relevant information, collection reference data frame, collection imaging data frame, reconstructed image, post processing of image, pictorial display, printing, storage, monitoring condition prompting, report etc.
5.3 hardware system workflow
5.3.1 initialization
Referring to Figure 18, initialized main purpose is to carry out electric current setting, frequency configuration, gain setting, DAQ setting, system calibration and electrode state detects, finish above-mentioned every after, can begin to measure.
5.3.2 the reference data frame is gathered
Referring to Figure 19, when the reference data frame is gathered, at first carry out DATA REASONING, carry out the drive electrode setting, after time-delay, carry out the measurement electrode setting, time-delay again, carry out data acquisition and date processing subsequently,, then return if the measurement under the current excitation finishes, if continue to measure, be back to the measurement electrode setting; Get back to the drive electrode setting.
5.3.3 the imaging data frame is gathered
Referring to Figure 20, imaging data frame collecting flowchart and reference data frame are gathered similar.
Claims (5)
1. one kind is used for an impedance tomograph imaging method of other image monitoring, by the computer control data collecting system of integral body and the algorithm of reconstructed image, provides the interface, the process of control figure picture monitoring; It is characterized in that, may further comprise the steps at least:
1) adopts many counter electrode to be placed on the periphery at the position that human body need guard, exciting current is added to human body, and the signal of human body is passed to data collecting system;
2) provide interchange constant current drive, high-precision signal to detect, drive the program control function that is provided with of measurement pattern by data collecting system;
3) according to the voltage signal that collects, the distribution that changes by the algorithm computation body internal resistance rate of the reconstructed image that is provided with in the computer, and display image.
2. an impedance tomograph imaging method that is used for a bed other image monitoring as claimed in claim is characterized in that, described interchange constant current drive, high-precision signal detect, drive the program control function that is provided with of measurement pattern and be respectively:
Exchange the constant current drive function:
Adopt simulation vibration, phaselocked loop and Direct Digital synthetic technology, comprise produce frequency about 50KHz sinusoidal signal and realize constant current output and start-up control signal that demodulating control signals that generation and pumping signal are synchronous and A/D change;
The high-precision signal measuring ability comprises:
High-precision signal amplification, dynamic range adjustment, high accuracy demodulation and data acquisition;
Driving and the program control function that is provided with of measurement pattern comprise:
1. drive pattern on demand is loaded into pumping signal on a pair of drive electrode in many counter electrode;
2. measurement pattern on demand is with many inputs that signal loading on the pair of electrodes in the measurement electrode arrived signal amplification circuit.
3. an impedance tomograph imaging method that is used for a bed other image monitoring as claimed in claim, it is characterized in that, the algorithm of described reconstructed image is: adopt dynamic equipotential line back projection method, this equipotential line back projection method is based on the following hypothesis that the imaging target is done:
1. be two dimension by the imageable target distribution of impedance;
2. the zone boundary is circle;
3. electrode on the border for being spacedly distributed;
4. the anti-disturbance that distributes of target area internal resistance compare with the absolute value of distribution of impedance very little, thereby make the disturbance of boundary voltage become linear approximate relationship with the distribution of impedance disturbance;
The equipotential line impedance imaging is actually the turbulent imaging of target area distribution of impedance:
If in distribution of impedance is that (x loads one group of drive current around target area y) to σ, and obtaining one group of response voltage is V
0, after a less variation (disturbance) takes place in distribution of impedance, and σ (x, y) → σ (x, y)+(x, y), record response voltage is V to Δ σ
1,, can obtain the disturbance of distribution of impedance with carrying out back projection after two groups of voltage difference regularization.
4. one kind is used for an electrical impedance tomography device of other image monitoring, comprise a computer, computer is connected with a data collecting system, it is characterized in that, be provided with the program of control data acquisition system and the algorithm of reconstructed image in the computer, data collecting system also is provided with exciting current is added to the control module of electrode that human body is gathered the signal of human body;
Above-mentioned data collecting system comprises:
One driving source module [1], be used to produce frequency about 50KHz sinusoidal signal and realize constant current output and start-up control signal that demodulating control signals that generation and pumping signal are synchronous and A/D change;
One signal detection module [4] is used for signal amplification, dynamic range adjustment, high accuracy demodulation and data acquisition;
One D/A modular converter [5] is used for the selection of D/A and the realization of wave generator circuit;
One motivation model is provided with module [2 (1)], and the drive pattern that is used on demand is loaded into many pair of electrodes to drive electrode with pumping signal;
One measurement pattern is provided with module [2 (2)], be used on demand measurement pattern with many to the signal loading on the pair of electrodes of individual measurement electrode to the inputs of signal amplification circuit.
5. an electrical impedance tomography device of other image monitoring that is used for as claimed in claim 4 is characterized in that described many counter electrode are 16 pairs, totally 32.
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