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ITM is a real-time, noninvasive imaging device
for breast examination, based on mapping the local electrical impedance properties of breast tissue. Detection of cancer is
based on the large inherent differences in capacitance and resistance between neoplastic tissue and surrounding normal tissue.
Differences by factors of 10 to 50 between normal adipose tissue and malignant tissue have been reported by in vitro measurements
on freshly excised breast tissue. ITM maps the local distribution of tissue electrical impedance in a range
of frequencies from 50 - 50,000 Hz, by applying a minuscule electrical signal (approximately 0,5 mA ± 20%,) via a reference
electrode on the body, and detecting the resulting impedance values at each of 256 sensors pressed against the breast. . For each frequency, the electrical
capacitance and conductance (the inverse of the resistance) at each sensor are computed and converted to gray scale -- high
values are displayed as light shades of gray, and low values as dark shades or colors from blue to red. This image is processed
using standard mathematical methods of reconstruction. . The impedance
images are displayed as pairs of scale maps : when viewing the standard display, one image represents capacitance, and the
other conductivity. The exact scale mapping function is typically preset by the system software (using factory pre¬set
values or alternatives set by the operator), but is also operator adjustable on screen, so as to enhance the differences among
the measured values. . In the normal breast, moderate variations in impedance values reflect the
differences in the inherent impedance of various types of breast tissue in the vicinity of the sensor electrodes. A malignant
tumor typically has very substantially increased capacitance and conductance compared to variations in the surroundings, and
its presence results in a bright region on the displayed image. . . The display parameters are adjusted so as to enhance small local impedance deviations from their surroundings. When replaying previous recordings, the image typically shows the impedance map at any one of the frequencies recorded. The operator can select which frequency is to be displayed. Alternatively, the operator can choose to display an image representing parameters derived from data acquired at several different frequencies ITM clinical investigation TCI
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