Method and equipment for monitoring the current drained by the grounding electrode in electric impedance tomography
There are disclosed a method and an equipment for monitoring current drained by a grounding electrode in an electric impedance tomography system. The grounding electrode and a set of electrodes may be simultaneously applied to a patient in an electric impedance tomography apparatus. The equipment may be configured to convert current into a voltage signal and amplify, demodulate, and filter the voltage signal in order to recover its almost continuous component. The equipment may further be configured to compare the value of the continuous component with limit/threshold values proportional to an intensity of an excitation current applied to the set of electrodes. In addition to detecting the disconnection of the grounding electrode, the comparison may also detect the disconnection of one or more tomography electrodes, as well as unbalance in the currents injected through the electrodes and the contact of the patient with voltage sources or conductive bodies.
1. A method of monitoring the current drained by a grounding electrode in electric impedance tomography, the method comprising:
receiving a ground drainage current from a grounding electrode that is applied along with a set of electrodes of a tomography apparatus to a patient;
generating a voltage signal from the ground drainage current; and
comparing a value of the voltage signal with at least one limit value that is dynamic and changes proportional to an intensity of an excitation current applied to the set of electrodes.
2. The method of claim 1 , wherein generating the voltage signal comprises amplifying, rectifying, and filtering the ground drainage current to generate a filtered signal.
3. The method of claim 2 , wherein generating the voltage signal further comprises digitizing the filtered signal to generate the value of the voltage signal prior to comparing the value with the at least one limit value.
4. The method of claim 1 , further comprising detecting that the grounding electrode is disconnected if the value of the voltage signal is substantially equal to zero.
5. The method of claim 1 , further comprising detecting an asymmetry in drained currents from the set of the electrodes of the tomography apparatus if the value of the voltage signal is substantially above the at least one limit value.
6. The method of claim 5 , wherein the asymmetry is produced by the disconnection of one or more electrodes among the set of electrodes.
7. The method of claim 1 , further comprising detecting contact of the patient with an external source of electrical energy if the value of the said voltage signal is substantially above the at least one limit value.
8. The method of claim 7 , wherein the external source of electrical energy comprises at least one of an electric scalpel, an electrically conductive body, and a defibrillator.
9. The method of claim 1 , further comprising:
storing a minimum value for a lower limit of a range for the at least one limit value;
storing a maximum value for an upper limit of the range for the at least one limit value;
correlating the minimum value with a first excitation current value for the set of electrodes; and
correlating the maximum value with a second excitation current value for the set of electrodes.
10. The method of claim 9 , further comprising adjusting the maximum value and the minimum value defining the range for the at least one limit value responsive to the excitation current being applied to the set of electrodes during operation.
11. The method of claim 1 , further comprising positioning the grounding electrode on the patient substantially symmetrically with relation to the set of electrodes applied to the patient.
12. A system for monitoring current drained by a grounding electrode in electric impedance tomography, the system comprising:
an electric impedance tomography including a set of electrodes and a grounding electrode; and
an equipment operably coupled with the ground electrode, the equipment configured to:
generate a voltage signal responsive to the receiving a ground drainage current from the grounding electrode;
compare a value of the voltage signal with at least one limit value; and
change the at least one limit value responsive to a change in an intensity of an excitation current applied to the set of electrodes.
13. The system of claim 12 , wherein the equipment includes a resistor operably coupled in a path of the ground drainage current drained by the grounding electrode in contact with a patient and a system ground for the electric impedance tomography apparatus.
14. The system of claim 12 , wherein the equipment comprises a surge protector operably coupled with the grounding electrode, the surge protector configured to protect the equipment against voltage surges on the grounding electrode.
15. The system of claim 14 , wherein the surge protector comprises a pair of diodes connected in counter-parallel fashion between input terminals of the equipment.
16. The system of claim 13 , wherein the equipment further comprises an amplifier operably coupled with resistor, the amplifier configured to amplify the voltage signal.
17. The system of claim 12 , wherein the equipment and the electric impedance tomography apparatus are incorporated into a common unit.
18. The system of claim 12 , wherein the at least one limit value includes a range defined by a minimum limit value and a maximum limit value.
19. The sys of claim 16 , wherein the equipment further comprises a demodulator provided with a filter configured to generate a filtered DC signal from the voltage signal derived from the ground drainage current.
20. The system of claim 19 , wherein the filter comprises a low-pass filter with a cut-off frequency of 0.5 Hz.
21. An equipment for detecting a condition of an electrical impedance tomography system, comprising:
an input configured to receive a ground drainage current from a grounding electrode of an electric impedance tomography apparatus; and
an analysis unit operably coupled with the input, and configured to:
compare a level of a voltage signal derived from the ground drainage current with at least one limit value; and
dynamically adjust the at least one limit value responsive to a change in an excitation current applied to a set of electrodes of the electric impedance tomography apparatus.