Microwave Imaging for Detecting Breast Cancer

1
Microwave Imaging for Detecting Breast Cancer

• Amir Golnabi
• ENGS 166
• Spring 2008

2
Outline

• Electrical Properties
• Tissue Dielectric Properties
• Dielectric Property Measurement
• Measured Tissue Dielectric Properties
• Normal Tissue vs. Malignant Tissue
• Microwave Tomography
• Breast Microwave Imaging at Dartmouth College
• Acknowledgements and References

3
Basic Concepts of Electrical Properties

• The interaction of an electromagnetic (EM) field
  with a biological system
• Electrical properties
• Conductivity s the conductance of a unit volume
  of matter
• Permittivity e the capacitance of a unit volume
  of matter
• Complex Permittivity
• Loss Factor
• permittivity of free space (8.85 x 10(-12)
  F/m)
• angular frequency and f represents
  the frequency of the EM field in hertz

4
Tissue Dielectric Properties Range 1Hz 30GHz

• 3 Dispersion regions a, ß, and ?
• Alpha Dispersion (0.1-100kHz)
• Frequency dependence of the outer
• cell membrane
• Beta Dispersion (1-20MHz)
• Insulating structure
• Cellular membrane enclose bound water
• EM frequency ? ? Cellular membranes are
  short-circuited ? Bound water insulating effects
  ? ? Conduction through cell membrane ? ? s ?
• Gamma Dispersion (about 20GHz)
• Dipolar relaxation of water in the tissue

5
Dielectric Properties of Different
tissuesBlood, Muscle, and Fatty tissue in
Microwave Frequencies Range Water and
electrolyte content

• Tissues
• High water content Muscle, Blood, Brain, and
  Internal organs
• Low water content Fat, Bone, Lung, and Outer
  layer of skin
• Low water content
• Low Permittivity

6
Dielectric Property Measurement

• Measuring the effects of the intervention of
  tissue with an electromagnetic field at specific
  frequency
• Open-ended coaxial cable
• Network Analyzer Measures the relative amplitude
  and phase difference between the reference and
  reflected signal channels.
• Computer Algorithm Computes the dielectric
  properties.

7
Measured Dielectric Properties (results)

• Joines et.al. 1994, In-vitro Normal vs.
  Malignant Tissues
• Colon, kidney, liver, lung, and breast
• Frequency range 50-900 MHz
• ratio of the power absorbed in the malignant
  tissue (Pm) to that absorbed in the normal tissue
  (Pn)
• n Normal
• m Malignant

8
Measured Dielectric Properties (results)

• Higher water content in malignant tissue
• Higher dielectric properties

9
Measured Dielectric Properties (results)

• Meaney et.al. 2000, In-vivo clinical prototype
  of a microwave tomographic system for breast
  imaging
• contrast between normal and malignant breast
  tissue close to 21
• Sha et.al. 2002 Diagnostic value of dielectric
  properties of normal and malignant breast tissue
  at a wide range of frequencies
• The low conductivity values of the normal breast
  tissue enable penetration of microwave
  frequencies up to the low GHz range.
• At 100 MHz 1 GHz, dielectric properties can
  significantly help classify normal and malignant
  breast tissues.

10
Microwave Tomography

• Basic idea
• Microwave Imaging at Dartmouth College

(A) Microwave illumination tank (B) Antenna
motion actuator (C) the coupling medium
reservoir (D) Patient examination table (E)
Electronics cart.
11
Microwave Imaging at Dartmouth College

• 16 monopole antennas
• Frequency range 500-2500 MHz
• 7 vertical positions
• 1 antenna transmits and
• other 15 antennas receive
• the signal
• 2D Image reconstruction

12
Microwave Imaging at Dartmouth College (cont.)

• Reconstructed Images patient 1914 left Breast

?r
?
?r
?
13
Microwave Imaging at Dartmouth College (cont.)

• Reconstructed Images patient 1914 left Breast

?r
?
?r
?
14
References
Acknowledgements
Prof. Paul Meaney, Prof. Keith Paulsen, MIS group
at Thayer School of Engineering

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