Final Ppt Mwt

8/13/2019 Final Ppt Mwt

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Contents Current Medical Imaging Methods Introduction Why Microwaves Applications Examples of Diagnostic Applications Consclusion


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In computerised tomography (CT) the X-ray source rotates around a plane of the body, taking serial pictures with a detector

(instead of a film) which are synthesized by a computer. The resulting picture created by the computer is like a section of

the body and can be recorded on a film. CT pictures are therefore like X-ray images.

Magnetic resonance imaging (MRI) uses the property of protons aligning themselves in a magnetic field and their reaction

to radio frequency waves. The protons resonate to the radio frequency and revert to normal (decay) when the radiation is

stopped. Effectively it is the imaging of protons. The most commonly imaged proton is a hydrogen nucleus. So far it is

believed that this method does not damage body t issues as X-rays do. MRI images are even more realistic than CT images.

Ultrasound on the other hand uses mechanical waves of frequencies beyond the audible range. These waves are reflected

to various degrees from junctions of tissues of different nature. Ultrasound pictures require considerable skill to interpret.

Ultrasound has a great advantage it does not cause cellular damage when used in quantities required for imaging.

CT, MRI and Ultrasound

Key Points :CT : Synthesis of multiple X-ray images of a slice .MRI : Imaging protons excited by radio waves.Ultrasound : High - frequency sound waves reflected from tissue junctions.All these methods illustrate structure of the body in some form of sectional view.


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3

CT Scan system

X-rays have a wavelength of between 10 and 0.01 nanometers


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UltraSound MRI

ultrasound is usually between 2 and 18 MHz. Higher frequencies provide better qualityimages, but are more readily absorbed by the skin and other tissue, so they cannot

penetrate as deeply as lower frequencies. Lower frequencies can penetrate deeper,but the image quality is inferior.

They provide high spatial resolution images, they lack functionalinformation about molecular changes in tissue.


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APPLICATION OF MICROWAVE IN MEDICAL


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Prominent clinical technique: X-raymammography

Low sensitivity,

High false-positive rate ( 1% to 29% mean10% )

Unnecessary and costly surgicalinterventions

Uncomfortable compression Ionizing radiation

1. Introduction


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Microwave Vs Ultrasound

With ultrasounds ( 5 MHz /\t= 0.007 cm) :microwaves cross media containing airwithout being attenuated and are absorbed byhigh water content media. When theultrasounds are strongly attenuated, themicrowaves are almost transparent - for

example, in bone tissues- attenuation ofultrasounds is equal 10.6 db/cm - and for 3GHz microwave : 1. 18 db/cm


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Microwave vs X- Ray

With X-rays on the one hand, the nature ofinteractions with matter is different - theyoccur at molecular level with microwaves andat atomic level, with X-rays. Mammary tissuescontaining a tumor, a better contrast isobtained with microwaves due to the

dielectric variations of tissues (ratios 6 to 40for the microwaves)


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Active microwaves (ranging from high MHz to low GHz) to detectabnormalities in the mammary tissues

Mammary glands : largest difference in dielectric properties of variousnormal and malignant tissues

Advantages:

Substantial information about the malignancy or healthiness of breasttissue

Fat Easy penetration Easy accessibility Non-ionizing and non-compressive

Dielectric Properties of tissues: Permittivity

Conductivity

Microwave Imaging


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Principles in Microwave Imaging Dielectric Properties

Permittivity, a measurement of energy storage in a material from an

external electric field Conductivity, (siemens/m)

how dissipative or lossy a material is to an external electricfield*

*Agilent tech notes

11The interrogating frequency ranges are between 1 and 4 GHz in which the tissues are the least attenuated.


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APPLICATION OF RADAR CONCEPTS

Radars in their principles show that thedistance resolution is determined either bythe emitted impulse duration or by theemitted wave bandwidth.

By transposition of these methods to medicalmedium and to biological media assimilatedto high water content media gives a distanceresolution of about 8 mm.


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The two techniques

The interrogating frequency ranges are between 1 and 4 GHz inwhich the tissues are the least attenuated.

a monofrequency CW continuous radar from which can be obtained

bidimensional imaging of a dielectric target.With this type of radar,we measure the phase and amplitude of the diffracted wave by thedielectric target. We measure the complex Sij diffracted parametersassociated to the target with a network analyzer.Biological mediahaving properties depending on their water content degree showdifferent properties. small dielectric targets (diameter being 15 mmabout) immersed in water and spaced by 10 mm can be detected aswell as imaging on an isolated kidney. This gives a distanceresolution between 5 to 10 mm.


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The two techniques contd.. with a linear frequency modulation CW radar (chirp radar), we

can obtain tri-dimensional imaging Using this technique, wecan measure the propagation delay and the wave attenuationat the crossing of various dielectric media. It provides afrequency spaced distribution induced by the multipledielectric interfaces.

Continuous radar with frequency modulation requires anantenna sensor, the band of which being infinite, the aperturedimensions being small and the phase center remaininginvariable in frequency. This large bandwidth antenna must be

radioelectrically matched to tissues properties and it coulddiscern and discriminate two beam targets, the delay of whichbeing 100 ps, corresponding to various targets of 6 m in thebrain and 4.5 mm in muscles.


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microwave Imaging

Microwave Imaging at Dartmouth:

frequency range from 500 MHz to 3 GHz Sub centimeter resolution


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Applications of Microwave

Extremities soft-tissue imagingThe successful management of a fractured boneinvolves an understanding of the two majorcomponents of any segments of injuredextremity. These two components are the bonyelement and the soft-tissue elements (skin,muscle, nerve and vessels)


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Reconstructed images of an excised segment of a pig hind leg.Scales are in cm. Frequency0.9 GHz. Reconstruction using a three-dimensional gradient approach. (Reproduced from the

Biophysical Laboratory, Carolinas Medical Center, Charlotte, NC, USA.)

the frequency used was 0.9 GHz, applicable for imaging larger objects,

for example whole-body imaging. Higher frequencies (up to 3 4 GHz)


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Diagnostics of tissue malignancies.

Malignancies and dielectric properties oftissueThe dielectric properties of normal and malignant

tissues have been studied. Almost a century ago, at20 kHz, the permittivity of malignant mammarytumour is higher than that of normal mammarytissue

The dielectric properties of malignant tumours andnormal tissues are different in the mammary gland,liver and lungs.


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Diagnostics of tissue malignancies

Liver tissues The most up-to-date study of ex vivo and in

vivo normal and malignant liver tissuesconcluded that the dielectric properties of exvivo malignant liver tissue are 19 30% higherthan normal, while the same differences in invivo tissues are not statistically significantwith the exception of conductivity at 915 MHz.


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Diagnostics of tissue malignancies

Blood perfusion, malignancies and dielectricproperties

Microwave Imaging Tomography (MWT) issuch an imaging modality, which can indeeddetect both malignancies and local bloodperfusion. It can detect malignant tissuetogether with an assessment of local tissueblood supply, tissue hypoxia and infarction


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Mammary cancer detection

Microwave tomographic mammography. Computer-simulatedimaging of tumour with radius 3 mm. Frequency 3.5 GHz.


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Lung cancer detection The challenging problem of lung imaging is in the

detection of small malignant tumours within thehighly dielectrically inhomogeneous and

structurally complex human chest. At a frequency of 0.9 GHz the average by volumedielectric properties are measured, including lungtissue, blood and air. This is also supported by the

dependence of the dielectric properties of lungon the inhalation/exhalation phase of therespiratory cycle


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Brain imaging

Reconstructed MWT images of a simulated brain model with a stroke injury with radius 2 cm

using multi-frequency reconstruction: (a) 0.5 and 1.0 GHz; and (b) 2.0 and 1.0 GHz. 1% noise.Area with suspected stroke injury is circled in white. Reconstruction using a three-dimensional

gradient method. computer simulation using the head model with tabulated dielectric properties of tissues andthose of embalmed brain tissues for the same experimental setting: antenna antenna distance

of 24 cm and frequency 0.81 GHz. The overall measured and simulated attenuations in solutionalone are in good agreement: 97.8 and 99 dB


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Cardiac imaging

Both MRI and CT have good spatial resolution butsuffer from poor temporal resolution. Since MWThas the competitive advantage of very short frame

rates/time resolution (within ms), it is expected thatthis technology might be used for more sophisticatedanalyses of cardiac function and viability ofmyocardial tissue.


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Cardiac imaging

Reconstructed images (at 2.4 GHz) of explanted canine .Two different vertical cross sections((a) X=1.5 cm and (b) Y=1.5 cm) are shown. Reconstruction using a three -dimensional gradient method


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Thank You

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