RU96123647A

RU96123647A - METHOD FOR PRODUCING TOMOGRAPHIC BODY IMAGE AND ELECTRIC IMPEDANCE TOMOGRAPH

Info

Publication number: RU96123647A
Application number: RU96123647/14A
Authority: RU
Inventors: А.В. Корженевский; Ю.С. Культиасов; В.А. Черепенин
Original assignee: А.В. Корженевский; В.А. Черепенин
Filing date: 1996-12-11
Publication date: 1999-02-10

Claims

1. A method of obtaining a tomographic image of the body, including placing a series of contact electrodes on the surface of the body, sequentially connecting a current source to the pairs of electrodes, measuring the potential difference between each pair of the remaining electrodes, determining the reference values of the potential differences, and reconstructing the image of the spatial distribution of the conductivity of the body by reverse projection along equipotentials, characterized in that the reference values of the potential differences u

\binom{i}{r}

(j) is determined by approximating the measured distribution of potential differences u

\binom{i}{m}

(j) in accordance with the expression:
u

\binom{i}{r}

(j) = c

\binom{i}{l}

f

\binom{i}{l}

(j) + c

\binom{i}{2}

f

\binom{i}{2}

(j) + c

\binom{i}{3}

,
where i is the number of the exciting pair of electrodes;
j is the number of the measuring pair of electrodes;
f ₁ (j) is the predetermined voltage distribution between adjacent electrodes along the boundary of the reference object;
f

\binom{i}{2}

(j) - signals due to spurious connections;
c

\binom{i}{a}

(a = 1,2,3) - approximation coefficients of the measured distribution of potential differences u

\binom{i}{m}

(j)
2. The method according to claim 1, characterized in that the approximation coefficients are determined by the least squares method with weighting by minimizing the sum of the squared residuals of the approximated u

\binom{i}{r}

(j) and approximated u

\binom{i}{m}

(j) a function multiplied by weights k ⁱ (j):

3. The method according to claims 1 and 2, characterized in that the weight coefficients are determined from the expression
k ⁱ (j) = 1 / u

\binom{i}{m}

(j) ² .
4. The method according to claim 1, characterized in that the signals f

\binom{i}{2}

(j) due to spurious bonds is determined by measurement.

5. The method according to claim 1, characterized in that for the diagnosis of organs with time-varying conductivity, a series of measurements of potential differences is automatically performed sequentially in time, Fourier spectral transformation of the time dependences of the results is performed, and images of the spatial distribution of the conductivity of organs for each frequency component are reconstructed .

6. The method according to claim 1, characterized in that the image is reconstructed of the spatial distribution of the absolute conductivity of the body by normalizing the obtained conductivity values, based on the fact that the lowest conductivity value corresponds to bone tissue conductivity, and the highest conductivity value corresponds to blood conductivity.

7. An electric impedance tomograph comprising a contact electrode system, a voltage excitation device, a potential difference measuring device, a microprocessor control circuit, a differential amplifier, analog switches, the inputs of which are connected to the contact electrodes, and the outputs to the input of a differential amplifier, characterized in that the tomograph contains a compensation circuit for the common-mode voltage component on each pair of electrodes, a compensation circuit for the contact potential difference on each electrode.

8. The tomograph according to claim 7, characterized in that it contains a program-controlled compensator for parasitic capacitive coupling.

9. The tomograph according to claim 7, characterized in that the common-mode voltage compensation circuit is designed as a feedback circuit containing an operational amplifier, the common-mode signal output of the differential amplifier is connected to the inverting input of the operational amplifier, the output of which is connected to an excitation device.

10. The tomograph according to claim 7, characterized in that the compensation circuit of the contact potential difference is made in the form of a feedback circuit including an analog key and an integrator connected in series, while the input of the analog key is connected to the measuring device, and the integrator output is connected to the zero setting input differential amplifier.