EIS Breast Imaging Research at Dartmouth College

(Last updated by Preston Manwaring: August 2, 2006)

1. Introduction

· EIS = Electrical Impedance Spectroscopy

· Noninvasive, inexpensive medical imaging device that does not use radiation, injected dyes, etc.

· Works by passing low-level electrical currents through the body via array of surface electrodes

· Measures the magnitude and phase of the resulting voltages at all electrodes

· Displays electrical properties in imaging plane corresponding to anatomy and pathology

· Multi-frequency measurements should enable us to identify specific tissue types and pathology

Example EIT Apparatus for Arm

2. Technical Details

Patient Apparatus for Breast Imaging

A. Hardware:

· Completely computer controlled

· Portable and self-contained

· 64 channels expandable to 128;

· Simultaneously apply signal and measure at ALL electrodes - Isaacson excitation pattern

· Measure magnitude & phase of signal in HARDWARE using BlackFin DSP Chips

· Voltage (+/- 15V) or Current Mode (+/- 50 mA)

· Variable Frequency: DC to 10 MHz

· 16 A/D with 1MHz Effective Sampling (oversampling for higher rates is used)

· 0.01% to 1% Measurement Precision Spanning Freq's

· Exam time/breast ~ 10 minutes for 20 frequencies

Simplied Electronic Schematic of Single Channel

Basic System Overview

B. Software:

· 2 GHz Pentium Host PC Running WindowsXP

Controls all hardware
Automates Experiments
Acquires/saves all raw data
Uses Matlab to display final 3D reconstructed SIGMA & EPSILON images

MATLAB Scripts

Produce ABSOLUTE Electrical CONDUCTIVITY and PERMITTIVITY values for data files
FORWARD PROBLEM

Finite Triangular Element - Galerkin Method
Solve Complex Laplace Equation Given Material Property Guesses to Calculate B.C.'s

REVERSE PROBLEM

Minimize difference between measured and calculated B.C.'s (collapsed into error function F)
Simultaneously set dF with respect to each material property to zero
Using Newton Method Iteratively Solve for Material Properties
Dual Mesh Scheme to reduce computational load

Coarse Mesh: 353 nodes, 640 elements --> material properties
Fine Mesh: 1345 nodes, 2560 elements --> voltages calculated

Flow Diagram of Overall Reconstruction Algorithm

C. Benchmarking:

· Calibrated each channel with known parallel resistor-capacitor loads (simple electrical model of tissue)

· Control experiments completed with tank, physiological saline solution, brass, and nylon cylinders

· Minimum detectable object width is 0.32 cm 1cm from edge and 3.4 cm 8 cm from the edge

3. In Vitro Experiments

Typical Saline Tank Setup and 64-Ch Electrode Geometry

ABSOLUTE Conductivity Image of 3mm Brass Conductor

4. In Vivo Experiments

Viewing Plane of Anatomical Breast and Breast Electrode Setup

ABSOLUTE PERMITTIVITY IMAGE: Coronal View Normal Breast at 125 kHz

ABSOLUTE PERMITTIVITY IMAGE: Coronal View Breast with CYST at 125 kHz

ABSOLUTE PERMITTIVITY IMAGE: Coronal View Breast with MALIGNANT TUMOR at 750 kHz

ABSOLUTE PERMITTIVITY IMAGE: Axial View Upper Arm at 125 kHz

5. Conclusions

· Successfully recovered meaningful images both in vitro and in vivo

· 100+ total individual breasts imaged; exams were quick and comfortable

· 12 normal, 2 malignant tumors, 2 benign tumors, 6 cysts, 3 with radiation therapy or lumpectomy

· Images corresponded well with given clinical information

· System is quite sensitive but not very specific - good for RULING OUT tumors

· Difficult to distinguish pathology (cysts, scars, benign tumors) from malignancies

· Need to eliminate electrode artifacts to improve veracity of absolute measurements

· Will try new current patterns (i.e. 4-point measurements) in future

6. Video Examples

7. Publications Pertaining to Our EIS Work

A multichannel continuously selectable multifrequency electrical impedance spectroscopy measurement system,
Biomedical Engineering, IEEE Transactions on, vol 47(1), pp 49-58, Jan-00
A novel data calibration scheme for electrical impedance tomography,
Physiol. Meas., vol 24, pp 421-435, 2003
An Enhanced Electrical Impedance Imaging Algorithm for Hyperthermia Applications,
Int. Journal Hyperthermia, vol 14(5), pp 459-480, 1997
An improved data acquisition method for electrical impedance tomography,
Physiol. Meas., vol 22, pp 31-38, 2001
Application of Linear Circuit Models to Impedance Spectra in Irradiated Muscle,
Annals of the New York Academy of Sciences, vol 873, pp 21-29, 20-Apr-99
Dartmouth's next generation EIS system: preliminary hardware considerations,
Physiol. Meas., vol 22, pp 25-30, 2001
Design and implementation of a high frequency electrical impedance tomography system,
Physiol. Meas., vol 25, pp 379-390, Jun-05
EIS for non-Invasive Thermometry and Treatment Evaluation,
North American Hyperthermia Society & Radiation Research Society Annual Meeting, Providence RI, May 3-7, 1997
Electrical impedance imaging at multiple frequencies in phantoms,
Physiol. Meas., vol 21, pp 67-77, Jun-05
Electrical Impedance Imaging for Tissue Monitoring and Assessment During Thermal Therapy,
SPIE internal Symposium: Surgical Applications of Thermal Energy, San Jose, CA, vol 3249, 1998
Electrical impedance imaging with electrode models: initial in vivo experience in the breast,
Biomedical Imaging, 2002. Proceedings. 2002 IEEE International Symposium on, pp 1043-1046, July 7-10, 2002
Electrical impedance spectroscopy of the breast: clinical imaging results in 26 subjects,
Medical Imaging, IEEE Transactions on, vol 21(6), pp 638-645, Jun-02
Excitation patterns in three-dimensional electrical impedance tomography,
Physiol. Meas., vol 26, pp S195-S197, 2005
Feasibility Studies of Electrical Impedance Spectroscopy for Monitoring Tissue Response to Photodynamic Therapy,
International SPIE Proceedings: Laser-Tissue Interactions, vol 3247, pp 69-80, 1998
Finite element implementation of Maxwell's equations for image reconstruction in electrical impedance tomography,
Medical Imaging, IEEE Transactions on, vol 25(1), pp 55-61, Jan-06
Imaging the breast with EIW: and initial study of exam consistency,
Physiol. Meas., vol 23, pp 221-236, Jun-05
In vivo electrical impedance spectroscopic monitoring of the progression of radiation-induced tissue injury.,
Radiation Research, vol 152(1), pp 41-50, Jul-99
In Vivo Electrical Impedance Spectroscopy of Irradiated Muscle Tissue,
Proceedings of the 19th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Chicago, IL, pp 2512-2515, 1997
Interpretation of Impedance Spectra of Irradiated Tissue Using Multiple Analysis Planes,
Proceedings of the 1st Joint BMES/EMBS Conference, Chicago Atlanta, GA, pg.1128, Oct. 13-16, 1999
Monitoring tissue response to photodynamic therapy: The potential of minimally invasive electrical impedance spectroscopy and high-frequency ultrasound,
International SPIE Proceedings, pg. 3247, 1998
Multi-frequency electrical impedance tomography of the breast: new clinical results,
Physiol. Meas., vol 25, pp 301-314, 2004
Multi-frequency electrical impedance tomography of the breast: preliminary in vivo experience in breast,
Physiol. Meas., vol 21, pp 99-109, 2000
On optimal current patterns for electrical impedance tomography,
Biomedical Engineering, IEEE Transactions on, vol 52(2), pp 238-248, Feb-05
Simulation of error propagation in finite element image reconstruction for electrical impedance tomography,
Measu. Sci. Technolo., vol 12, pp 1040-1049, 2001
Statistical estimation of resistance/conductance by electrical impedance tomography measurements,
Medical Imaging, IEEE Transactions on, vol 23(7), pp 829-838, Jul-04
Temperature Field Estimation using Electrical Impedance Profiling Methods. I. Reconstruction Algorithm and Simulated Results,
Int. Journal Hyperthermia, vol 10(2), pp 209-228, 1994
The Dartmouth Electical Impedance Tomography System for Thermal Imaging,
Annual International Conference of the IEEE Engineering in Medicine and Biology Society, vol 13(1), pp 321-322, 1991
Thermal Images Obtained by a Combined Invasive-Noninvasive Approach Using Electrical Impedance Tomography,
Engineering in Medicine and Biology Society, 1993. Proceedings of the 15th Annual International Conference of the IEEE, pp 88-89, Oct 28-31, 1993
Using multiple-electrode impedance measurements to monitor cryosurgery,
Med. Phys., vol 29(12), pp 2806-2814, Dec-02
Using voltage sources as current drivers for electrical impedance tomography,
Measu. Sci. Technolo., vol 13, pp 1425-1430, Jun-05
Development of a Multi-High Frequency Electrical Impedance Tomography System for Breast Imaging,
Thesis, Ryan J. Halter, 2006

7. Links to Other EIS & Numerical Methods Research On the Web

· 1. Biomedical Projects at Thayer

· 2. NML at Dartmouth College

· 3. Major EIT Groups Worldwide

· 4. Marko Vauhkonen's Web Page (UK)