Medical App 2 Microwaves. Bhaskar Naik s

Introduction

Some of the dielectric characteristics of Human cells.

Antonios Drossos, Member, IEEE, Veli Santomaa, Senior Member, IEEE, and Niels Kuster, Member, IEEE“ The Dependence of Electromagnetic Energy Absorption Upon Human Head Tissue Composition in the Frequency Range of 300–3000 MHz ‘’

Out Line..

Analyzing biological effects of electromagnetic radiation at the cellular level from two different viewpointsMacroscopically Microscopically

Continued…Applications revieved

Diagnostic Applications

1. MRI

Therapeutic Applications1. Microwave-assisted balloon

angioplasty(MABA)

Continued…

Examples of diagnostic applications.1. Microwave Tomography.2. MRI3. Breast Tumour Detection

Examples of Therapeutic applications.1. RF/Microwave Ablation for the Treatment of Cardiac Arrhythmias.2. Angioplasty.3. Treatment of Benign Prostatic Hypertrophy (BPH)4. RF in the Treatment of Obstructive Sleep Apnea (OSA).

Conclusions.References

What happens macroscopically?

Problem of electromagnetic wave incidence on a lossy medium (tissue)

Incident EM energy is reflected and refracted at the interface of air and tissue

Fundamental constants defining how much is reflected and refracted are parameters of the medium

Biological TissueAir

Ei

SiHi

Et

StHt

Er

SrHr

Inte

rfac

e

Electromagnetic incidence

Relative amplitudes of the reflected and transmitted components of the incident electric field wave are defined below:

Reflection coefficient,, and transmission coefficient are determined by the parameters of the two media of conduction:

r iE E

t iE E

1 2

1 2

1

1 2

2

Parameters of media

Permeability, , is analogous to the permittivity ,in that it describes the relationship between the magnetic dipole vector and the magnetic field Most of the cells and tissues that are studied are non-magnetic For these types of materials, is considered to be equivalent to 0,

the permeability of free space

Parameters(Permeability, permittivity, and conductivity ) fundamentally characterize any medium macroscopically Parameters can be used to determine depth of penetration and

absorbed power of an incident electromagnetic wave on the medium

B H

Dielectric constant of living material (muscle) as a function of frequency

This Variations due to, different electrical charges are not able to follow the changes in the applied electric field

α -Dispersion ---Counter ion polarization effects. --- “active membrane conductance”, “charging of

intracellular structures” connected to the outer cell

membrane.---Conductivity is very low as 0.005sm-1 due to cells

are poorly conductive as compared to surrounding electrolyte.

• β dispersion(0.1 t0 1000MHz.) --- Due to “Capacitive charging of cellular

membranes” in tissues, and dipolar orientation of tissue proteins.

Gamma dispersion(0.1 t0 100GHz)It is primarily due to dipolar relaxation of water(fc

around=25G).

Depth of penetration

Any wave that enters a lossy medium will be attenuated after some distance

Depth of penetration (D.O.P.) characterizes the distance after which the field intensity is 1 / e of its incident value

For a low-loss dielectric medium, the D.O.P. is described by the following equation, in which tan(c) is the loss tangent of the material

2 1/2

2. . .

'[ 1 tan 1]r r c

cDO P

Loss Tangent =σ/ ωε

Relative power absorbed in human muscles as a function of skin depth at frequencies 10, 27.12, 40.68, 100, 433, 915, and 2450 MHz

Resonance and mirror effect

Transmitted component of the incident wave adds energy to the tissue, resulting in heating

The change in tissue temperature for a given wave intensity is strongly dependent on frequency of the wave: Human body absorbs waves at

frequencies that are close to its resonant frequency much more strongly than others

Resonance is approximately 35 MHz ( = 8.56m) for a human that is grounded and 70 MHz ( = 4.28m) for one who is insulated (figure describes why)

RF waves, for example, are much closer to this resonant frequency of the body than 60 Hz power lines or other forms of LF energy thus they are absorbed much more efficiently

Yao

Yao

Yao

Conductor (Mirror effect)

2.24m

= 8.56m

= 4.48m

Human body as a “dipole antenna”

Microwave thermotherapyMicrowave thermotherapy (0.4 - 2.5 GHz)1

Tissue is heated with microwaves because of the efficiency of energy absorption unique to this frequency band shown previously

Additionally, higher frequencies (than human body resonance) are used to reduce depth of penetration and effectively focus the energy of the wave to a shallow region (tumor)

Cancerous cells are killed by the heating since healthy cells can survive at higher temperatures due to greater blood flow (45 degrees Celsius for healthy cells, 41 for cancerous)

Vrba et al. state that they have treated over 500 patients with tumors ranging up to 4 cm in depth using these methods

Their results show, in the long run: Complete response of tumor: 53% Partial response of tumor: 31% No response of tumor: 16%

Vrba, J. et al., Microwave Thermotherapy in the Czech Republic: Technical and Clinical Aspects. www2.elec.qmul.ac.uk/iop/

Microscopically…Plasma

MembraneCellular

Membrane

Enzymes,Genes,Proteins

BiochemicalMessenger

Nucleus

EM Radiation(CW or Non

CW)

1.Non-ionizing 2.Ionizing

Ratio of conduction to displacement current

Skin depth in biological Media

1. Ionizi

ng

(Frequency range: > 1013 Hz)

Radiation Therapy.

(LNA)

LNA(Courtasy -

Sameer MUMBA

I)4MeV

2.Non Ionizing

Radiation

I. Non-Thermal

II. Thermal Efect

I. Non Thermal Effect

Due to Direct interactions of E-fields or H-fields with the body cells or tissues

This Effect used in MRI(Magnetic resonance imaging)

Real-time MRI of a human heart at a resolution of 50 ms” Wikipedia”

MRI(Magnetic Resonance Imaging)

Properties of nuclear spinsRadio frequency (RF) excitation propertiesTissue relaxation properties(i.e Time taken

by flipped proton to align with magnetic fields)

Magnetic field strengthTiming of, RF pulses and signal detection

Factors Contributing to MRI

1Hspin 5.87

177.0460

9.3947

11.7434

14.092

250 300 400 500 600

NMR Frequency (MHz) at field (T)

Source….http://www.google.co.in/search?q=electromagnetic+waves+on+skin&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

Type of Nuclei that MRI can Respond

Nucleus needs to have 2 properties

-Spin -ChargeNuclei are made of protons and neutrons

- Both have spin ½-Protons have charge

Pairs of spins tend to cancel, so odd number of protons or neutrons have

spin

-Good MR nuclei are 1H, 13C, 19F, 23Na, 31P

•Hydrogen atom is the only major species that is MR sensitive(1H)•Hydrogen is the most abundant atom in the body•The majority of hydrogen is in water (H2O).•Essentially all MRI is hydrogen (proton) imaging

MRI uses a combination of Magnetic and Electromagnetic Fields

NMR measures the net magnetization of atomic nuclei in the presence of magnetic fields

Magnetization can be manipulated by changing the magnetic field environment (static, gradient, and RF fields)

Static magnetic fields --- The main field is static and (nearly)

homogeneousRF (radio frequency) fields are electromagnetic

fields that oscillate at radio frequencies (tens of millions of times per second)

• RF electromagnetic fields are used to manipulate the magnetization of specific types of atoms • This is because some atomic nuclei are sensitive to magnetic fields and their magnetic properties are tuned to particular RF frequencies• Externally applied RF waves can be transmitted into a subject to perturb those nuclei• Perturbed nuclei will generate RF signals at the same frequency – these can be detected coming out of the subject-This is The NMR(Nuclear Magnetic Resonance) signal. This signal is proportional to the proton density.

Thermal effect

•Induced heating from EM power absorbed within the tissue .•Temperature rise is caused by absorption of EM energy within a given mass of Biological material.•Temperature keeps rising until the heat input is balanced by heat conduction and convention from blood flow and surrounded tissues.•Power absorbed by a mass-Expressed as SAR(Specific absorption Rate).•Specific Absorption Rate (SAR) is defined as the time derivative of the incremental energy (dW) absorbed by an incremental mass contained in a volume of a given mass density (ρdV).

where σ is the conductivity, |E| is the r.m.s. amplitude of electric field and ρ is the mass density of the object

•Relation between SAR and temperature is very complex.•Heat sink model developed by Pennes has given remarkable result.

•where ρ is the tissue density (kg/m3) c is the tissue heat capacity (J/kg·K).

T is the tissue temperature (K).k is the tissue thermal conductivity (W/m·K).ρb is the blood density (kg/m3).ωb is the blood perfusion.qm is the metabolic volume heat.

• “SAR of 1 W/kg produces an increase of 1◦ C in human body temperature”.•A biological cell can with stand up to (46-47) ◦ C .•Cancerous cells are heated up to (43 ◦ C–45 ◦ C) since these cells will die in this range of temperature. •Heating of cells is mainly due to its water content.

Tissues

High Water content(HWC)

Tissues

Low Water content(LWC)

Tissues

Muscle, skin, and connective tissues

Bone and fat tissues

The heating in tissues possibly results from both ionic conduction and vibration of the dipole molecules of the water and the protein in tissue cell. So power absorption in HWC tissues are high as compared to LWC tissues

•The electrical characteristics (Conductivity and permittivity) of these two tissue groups are different•Figure below shows the conductivity σ and real relative•permittivity ε‘ with respect to water content of tissues

Volume fraction of water

Perm

itti

vity

Con

du

ctiv

ity

Volume fraction of water This large dielectric constant difference between HWC and LWC tissue is used for preferential therapeutic heating.

Different Therapeutic applications

1.Diathermia

2.Hperthermia

3.MW abalation

4.MW balloon angioplasty

For mild orthopedic heating.

Cell killing for cancer therapy

Uses heat from MW energy to destroy cancerous cells.(Can be used to treat the cancer that spread from liver to other parts of the body.)

For Major cardiac operations

Microwave-assisted balloon angioplasty(MABA)

•It is the most commonly performed major cardiac operations.•Its is relatively simple.•A special catheter (Medical tube) tipped with a collapsed narrow inflatable balloon is inserted into a vein through an incision in the neck or leg.fed through blood vessels until it reaches the diseased arteries of the heart.•Fluid is then pumped into the balloon. The enlarged tip quickly compresses the layer of plaque which is clogging the artery and also stretches the walls of the artery, leaving a much wider opening for blood flow.

•X-ray

•Microwave breast tumour detection.--- Microwave tomography -Not suitable for pregnant woman. -Hazardous especially with respect to younger women. -Scanning process is discomfort to the patients. -MRI may be a best alternative, but highly costlier and lacks the ability to image the calcifications.

--- Ultra-wideband microwave radar techniques.

Experimental setup Photo of UWB Tapered Slot Antenna. (3.1GHz to 10.6 GHz )

Experimental results

Even though research on effect of EM waves on biological cells in cellular level is still in progress, we can conclude that RF & microwave field can play a effective role in Diagnostic and therapeutic applications.

References.Applications of RF/Microwaves in Medicine ”Arye

Rosen, Fellow, IEEE, Maria A. Stuchly, Fellow, IEEE, and André Vander Vorst, Life Fellow, IEEE”.

Structural Changes in Cell Membranes After Ionizing

Electromagnetic Field Exposure” Jurgen Hannig and Raphael C. Lee, Senior Member, IEEE”

Dual-Mode Antenna Design for Microwave Heating and Noninvasive Thermometry of Superficial Tissue Disease.

Svein Jacobsen, Paul R. Stauffer*, Member, IEEE, and Daniel G. Neuman.

ContinuedMEDICAL MICROWAVE RADIOMETRY AND

ITS CLINICAL APP1,ICATIONS . “D.V. Land”.RF-Field and Microwave Interaction with

Biological Systems- Fall 2009: Term paper, Amir H. Golnabi

http://www.adradcentre.com.au/physics_of_rt.html

http://en.wikipedia.org/wiki/Bloch_equationshttp://en.wikipedia.org/wiki/

Nuclear_magnetic_momenthttp://en.wikipedia.org/wiki/

Magnetic_dipole_moment

•http://www.adradcentre.com.au/physics_of_rt.html.• http://en.wikipedia.org/wiki/Relaxation_%28NMR%29.

•“Biological Applications of Large Electric Fields: ome History and Fundamentals”. Charles Polk, Life Fellow, IEEEIEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 28, NO. 1, FEBRUARY 2000.