Non-invasive imaging method
Electrical impedance mammograph measures electromagnetic phenomena and their changes by way of external scanning.
3-D tomography system
Since distribution of electric current cannot be limited by a two-dimensional plane, the measured data show changes of electrical conductivity in three-dimensional space ensuring layer-by-layer image of the object.
Soft-field tomography
Unlike computerized X-ray tomography, magnet resonance imaging, positron emission tomography, which are characterized as hard-field tomography.
Uses non-local EIT imaging
The specific feature of tomographic imaging with non-local properties is that all points at the scanned object affect the measurement results creating the so-called cross measurement. Value of pixel will depend both on the structure of the object and on the structure of surrounding tissues.
Alternating current (50 kHz, 0,5 mA)
Direct, or unidirectional, current going through electrolytes, biological tissues in particular, creates irrevocable chemical reactions on electrodes via which the object is connected to the external part of the electric chain. That’s why in medical diagnostics only alternating current of rather high frequency is used (as a rule, higher than 1 kHz). The acceptable current value is limited by its biological impact, and rises alongside with the increasing frequency.
Parameters of electric current used in the mammograph are allowed for medical use and are safe for the doctor and patient and are much lower than the limits, i.e. they don’t cause any pain or other sensations in the patient.
256 electrode panel with planar location of electrodes
Planar set of electrodes is used. Electrodes in planar configuration are located in one plane. In such configuration the electrodes are mounted on the mammograph platform, which can be held in one hand.
Planar configuration of electrodes gives the following advantages for its use:
a. Electrodes are fixed on the plate and the position of electrodes is known, which helps to avoid the positioning error.
b. Scanning panel is maneuverable and can be easily moved along the patient’s body so the device can be used in real time.
c. Resolution of electrodes located in the same plane is higher than in the case with circular configuration of electrodes since the minimum distance to internal structures is created.
Cross method of data collection
During electrical impedance examination the set of electrodes is located on the surface of the object, part of these electrodes are used as inductors and part as measuring electrodes. Usually, the current source is used as the inductor, and the difference of potentials between measuring electrodes is measured. All measurements are done on the surface of the object under examination. It is the so-called complementary method in which two electrodes located on the surface of the object are used as the source of low alternating current generating electrical field, and two other electrodes, which are also located on the surface of the object are used for registration of changes in electrical potential. All electrodes are involved in measurements in pairs.
Method of back projection as algorithm of image reconstruction
Algorithm of back projection along equipotential surfaces of the electric field with horizontal and vertical weighing function is used for reconstruction of three-dimensional static frequency-based image. The image is reconstructed layer by layer, layers are located in parallel to the panel of electrodes. Originally, the method of back projection was developed as an empirical method based on the rectilinear propagation of scanning radiation in the tissue (i.e. on the presence of ‘rays’). It was widely used in X-ray tomography and then it was transferred onto EIT where lines of force of the electric field are used instead of ‘rays’. Electrical impedance mammography has no rays, thus the definition of ‘pseudoray’ is applied. It became possible to introduce such a term due to the following: change of superficial difference of potentials (compared to homogenous cases) caused by the presence of a local non-uniformity is concentrated for the most part in the area, which is the projection of the non-uniformity on the surface of the object located along the equipotential lines (or surfaces) of the field. Therefore, the method of back projection is transferred onto the case where force lines of electric field calculated for homogenous distribution of conductivity are used instead of rays.
Static image
The advantage of mammograph is the possibility of reconstruction of absolute or static conductivity in the absence of the basic data. Static image implies creation of the image of absolute distribution of impedance in a body part, i.e., as the result, anatomical image of the scanned area is created. Electrical impedance mammography aims to receive the image of the object, which would be closely related to its internal structure.
Quantitative diagnostic information
The fundamental difference of electrical impedance image from other tomographic methods is that besides visual evaluation of the image electrical impedance mammography provides quantitative information. Quantitative information allows to understand breast structure, detect areas with anomalous electrical conductivity, to form breast cancer risk groups, etc.Basic parameters and dimensions
- Total dimensions of mammograph: 220х190х100 mm
- Weight of assembled mammograph not more than 2.9 kg
- Components:
- Measuring unit consisting of embedded microprocessor and matrix (diameter 12 cm) with contact measuring electrodes. Number of gilt electrodes – 256 units
- Signal cable for patient with double contacts for gel self-adhesive electrodes
- Device stand ensuring no contact of electrodes with other objects in idle mode
- Software and database on a CD
- User’s manual on a CD
- Atlas of electrical impedance images on a CD
- Disinfecting tissues
Electrical specifications
- The device is powered via a standard USB port of a PC with 5V DC
- Current received via USB port not more than 0.4A
- Current injected for scanning: 0.5+ 10% mA
- Frequency of scanning current: 50±5% kHz
- Mammograph is operable at the range of electrode-skin resistance change from 100 Ohm to 2 kOhm
- Mammograph emits a ‘bad contact’ alarm if electrode-skin contact resistance is 20 kOhm or more
Operational characteristics
- Mammograph is operable continuously for 8 hours with constant load
- Time required for one scanning cycle is below 35 seconds
- Time of image reconstruction is below 1 minute (depending on PC characteristics)
- Time of examination in screening mode 3/5 min. per patient
- Time of examination in a regular in-hospital mode 15-20 minutes/patient
- Warranty period for MEIK®, computerized electrical impedance mammograph version 5.0 – 2 years from the date of purchase
- Failure-free performance of electronic components (manufacturer’s warranty) not less than 5 years