microwave imaging technique for biomedical application
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Microwave Imaging Technique for Biomedical
ApplicationGunjan Gupta
Nirma University
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Introduction
• The penetration through opaque media makes microwaves a convenient agent for non invasive testing, evaluating cold measurements
• Microwaves have been considered for medical applications involving the detection of organ movements and changes in tissue water content
• Cardiopulmonary interrogation via microwaves has resulted in various sensors for monitoring various movements and changes inside human body
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Introduction
• In all these applications, microwave sensors perform local measurements and need to be displaced for obtaining an image reproducing the spatial variations of a given quantity
• Recently advances in the area of inverse scattering theory and microwave technology have made possible the development of microwave imaging and tomographic instruments
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What Paper Covers ?
• Equipments developed at Supelec and UPC Barcelona, within the frame of successive French-Spanish PICASSO cooperation programs
• Brief historical survey for both technological and numerical aspects
• Capabilities of the existing equipment, as well as difficulty in dealing with clinical situations
• Expected development of microwave imaging techniques for biomedical applications
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Reconstruction Algorithm
• Main difficulty in producing microwave images of quality was to compensate for complex diffraction mechanisms
• Two Approaches:• First , Efficient reconstruction algorithms used with X-ray CT
• Second, Scattering Mechanism with more rigorous nature in Reconstruction Process
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Reconstruction Algorithm
X-Ray CT Reconstruction• Compensate the effect of
Scattering Phenomenon
• Neglect Multiple Scattering
• Approach, imported from Ultrasound Imaging technique , is known as Diffraction Topography
Scattering Reconstruction
• Scattering mechanism are formally taken into account with more rigorous nature
• Linearize the inverse scattering problem, scattered field are linearly related to equivalent current induced by interrogating beam
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Reconstruction Algorithm
X-Ray CT Reconstruction• Fast Fourier Transform
Algorithm
• Efficient under computational aspect & suited for real time op
• Does not allow quantitative imaging
• Reproduce shape of structure
Scattering Reconstruction
• Fourier Transform Algorithm
• Allow quantitative imaging, even for high contrast targets
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Iterative Reconstruction Algorithm
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Iterative Reconstruction Algorithm
• At each step , the measured scattered field is compared to the scattered field calculated from a numerical model
• Such an approach, equivalently known as Distorted Born Method or Newton Kantorovitch Technique (NKT) , has been developed at the end of the 80’s and has been shown to be able to deal with high contrasted structures
• Spatial resolution is not so strictly related to the wavelength
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Equipments
• Equipment differ from the geometry of the transmitter receiver arrangement
• Designed for operation according to a transmission mode in water, at a frequency of the order of 2 GHz
• Provides a satisfactory optimization between a desired investigation depth of about 20 cm, and a spatial resolution comprised between 5 and 10 mm
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Equipments
Planer Microwave Camera @2.45 GHz
Circular Microwave Scanner @2.33 GHz
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Result
• Microwave camera has been initially designed for non-invasive thermometry (NIT) purposes during hyperthermia sessions
• Hyperthermia is demanding for an accurate control of the temperature distribution in the heated tissues
• Such a control is impossible to obtain in case of deep seated tumors, except with invasive thermometric probes
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Result
• In all trials, the time required for reconstructing images was too long for obtaining interactivity between operator and equipment
• However, very recently, the microwave camera has been made compatible with real time constraints
• Images can now be produced at the rate of more than 10 images per second, which is enough for most biological processes
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Result
Fig : Microwave image of a human hand. Mono-view reconstruction with a diffraction tomography algorithm
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Human for-arm reconstructed from Microwave scanner data
Linear Diffraction Tomography
Non-linear Iterative Technique
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Conclusion
• From the beginning of the 80’s , microwave imaging techniques for biomedical applications have been drastically improved
• Various assessments conducted with preliminary Equipments have confirmed the sensitivity of microwave images to factors of medical relevance
• Even if operational and clinical efficacy is not yet achieved, different steps for succeeding are now well identified
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Indeed, without a significant development effort, microwave imaging techniques will still
have to wait a long time before being recognized and accepted by their potential
users
Thank You !
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Reference IEEE Paper