Impedance Imaging for Breast Cancer Diagnosis

1
Impedance Imaging for Breast Cancer
Diagnosis Tzu-Jen Kao1, Ning Liu3, Hongjun Xia1,
Bong Seok Kim1, David Isaacson2, Gary J.
Saulnier3, Jonathan C. Newell1 1Departments of
Biomedical Engineering, 2Mathematical
Sciences 3Department of Electrical, Computer and
Systems Engineering Rensselaer Polytechnic
Institute
Model of the mammogram geometry
Importance of this work The reconstruction of
conductivity images in a mammogram geometry will
provide a foundation for the comparison of EIT as
a breast cancer detection tool with the X-ray
mammography.
Introduction The long-term goal of this project
is to develop Electrical Impedance Tomography
(EIT) technology to improve the diagnosis of
breast cancer. Breast Cancer is responsible for
over 40,000 deaths annually among women in the
United Stated. Early detection of breast cancer
improves the chances that it can be treated
successfully. Also, improved detection techniques
may be able to reduce the number of biopsies that
are performed. Even using combined diagnostic
techniques, such as mammography, MRI, clinical
breast examination, only 20-40 of the biopsies
that are performed actually reveal cancer 4.
Electrical Impedance Tomography, also called
Electrical Impedance Imaging, is a non-invasive
technique used to image the electrical
conductivity and permittivity within a body from
measurements taken on the body surface 5.
Small electric currents are passed through the
body using electrodes attached to the skin the
resulting voltages are then measured and used by
mathematical algorithms to reconstruct the values
of the electrical conductivity and permittivity
within the body. It has been known for some time
that breast tumors have a significantly higher
conductivity and permittivity than surrounding
normal tissue. Hence, by forming images of the
electrical conductivity of the breast, tumors may
be detected and differentiated from normal
tissue. EIT does not use ionizing radiation and
employs relatively low-cost instrumentation,
making it less expensive and/or safer than x-ray
mammography, MRI and CT.
Experimental Design 3
Size of Electrode Array 5 x 5 cm Dim. of the
box 5 cm x 5 cm x 5 cm Size of Electrode 1.0 x
1.0 cm Gap between Electrodes 2
mm Conductivity s0 0.364 S/m Agar Target size
5 mm cube Conductivity s 0.901 S/m
This work is supported in part by CenSSIS, the
Center for Subsurface Sensing and Imaging
Systems, under the Engineering Research Centers
Program of the National Science Foundation (Award
Number EEC-9986821). This work is supported in
part by NIBIB, the National Institute of
Biomedical Imaging and Bioengineering under Grant
Number R01-EB000456-01.
Hardware and Software 1, 2 The ACT 4 hardware
and software supports 64 electrodes that will
produce 3-D images of conductivity and
permittivity in real time using applied
excitations with frequencies between 1 KHz and 1
MHz. It will be able to apply arbitrary patterns
of voltage or currents while measuring the
resulting currents and voltages, respectively.
The operator will be able to select various
combinations of image rate and measurement
precision, including real-time operation to
visualization cardiac-frequency events.
Future Plans We are presently testing the ACT 4
hardware and implementing the initial version of
the system software and firmware. Over the next
few weeks we expect to begin collecting complete
data sets and testing the instrument performance.
Initial testing will use laboratory test
phantoms with conductivity similar to that of the
human body. Once the instrument is fully tested
and its performance characterized, it will be
used to study breast cancer patients at
Massachusetts General Hospital. The study,
involving a small number of patients who will be
undergoing biopsies, will establish the ability
of EIT to detect cancer by directly comparing EIT
results with biopsy results.

• References
• Publications Acknowledging NSF Support
• Ning Liu, Gary J. Saulnier, J.C. Newell, D.
  Isaacson and T-J Kao. ACT4 A
• High-Precision, Multi-frequency Electrical
  Impedance Tomography Conference
• on Biomedical Applications of Electrical
  Impedance Tomography, University
• College London, June 22-24th, 2005.
• 2. Hongjun Xia, A. S. Ross E. Brevdo, T-J Kao,
  Ning Liu, B. S. Kim, J.C. Newell,
• G. J. Saulnier and D. Isaacson. The
  Application software of ACT4. Conference
• on Biomedical Applications of Electrical
  Impedance Tomography, University
• College London, June 22-24th, 2005.
• 3. Choi, M.H., T-J Kao, D. Isaacson, G.J.
  Saulnier and J.C. Newell. A Simplified
• Model of a Mammography Geometry for Breast
  Cancer Imaging with Electrical
• Impedance Tomography Proc. IEEE-EMBS Conf.
  26, In Press 2005.
• Others
• 4. American Cancer Society, http//www.cancer.org
  /docroot/home
• 5. M. Cheney, D. Isaacson, Newell, S. Simske, and
  J. Goble, NOSER An
• Algorithm for Solving the Inverse
  Conductivity Problem Int.. J. Imag. Syst.
• Tech., vol. 2, pp. 66-75,1990.

Reconstructed Images
To support a high-speed, high-precision,
multi-channel instrument, we designed a
distributed digital system, including a computer,
digital signal processors (DSPs) and
field-programmable gate arrays (FPGAs). The
computer provides a user interface to control the
instrument and to display the results for
analysis. Four DSPs are working in parallel to
implement the real-time reconstruction algorithm.
We use FPGAs mainly to implement the signal
generation, voltmeter and control for the ACT 4
analog circuits. FPGAs are also used to
implement the interface between multiple channels
through a VME-64x backplane, and between the
computer and the instrument.
Contact Info Jonathan Newell, Ph. D.
Professor of Biomedical Engineering E-mail
newelj_at_rpi.edu Rensselaer Polytechnic Institute
Web site http//www.rpi.edu/newelj/eit.html 11
0 Eighth St. Troy, NY 12180-3590 Phone
518-276-6433 FAX [phone]
The ACT 4 system is hosted by a Pentium-based
personal computer. Through the computer, the
operator is able to control the hardware, display
and manipulate images and manage the information
database. The user interface software is designed
to be used in both clinical and laboratory
environments and is implemented as a window-style
program coded in Visual C. The interface to
allow access to low-level hardware functions will
be available for laboratory/experimental use. A
simplified interface offering only the functions
needed for collecting patient data will be
available for clinical use.
Solid line reconstructed voxel conductivity
Dotted line ideal computed conductivity of voxel