Electrical Impedance Tomography of Breast Cancer

摘要

In screening for breast cancer, once abnormalities or lesions are discovered by the X-ray mammogram, other imaging techniques are usually needed as an adjunct to diagnose the lesion as benign or malignant. It has been shown that cancer cells exhibit altered local electrical impedance. However, existing technology to measure the electrical impedance of the breast relies on a device that has poor spatial resolution. The authors proposed to map the impedance distribution in breast tissue with high spatial resolution by using the existing technology in conjunction with Magnetic Resonance Imaging (MRI) to improve the diagnostic accuracy of the screening. During the first phase of this project, they developed the necessary MRI pulse sequences, the software needed to analyze acquired images to extract impedance information, and the hardware components to inject electric current in synchrony with the MRI scanner. Several different pulse sequences were tested to determine their sensitivity and specificity. A spin-echo based sequence with alternating current injection at 200 Hz was found to be the most efficient sequence tested. Various gel phantoms were prepared to mimic the electrical impedance variations in tissues. Using these phantoms, spatial resolution and sensitivity of the method to various current amplitudes and impedance perturbations were measured. The method also was tested on a single animal with a malignant tumor. Results demonstrate that the proposed method clearly distinguishes objects separated by 1 to 2 millimeters, thus providing good resolution, and it can be used with safe current amplitudes (down to 0.5). Moreover, the method was able to distinguish 50% impedance variations. These results support the hypothesis that MRI-impedance imaging can be used to distinguish benign and malignant tissues. In the second phase of the project, the authors will perform experiments on tumor-induced rats.