INTRODUCTION

The
tissue of the human body is enormously varied and complex, with innumerable
types of structures, components, and cells. From the point of view of RF and
microwaves, however biological tissue can be viewed macroscopically in terms of
its bulk shape and electromagnetic characteristics. All biological tissue is
somewhat electrically conductive, absorbing microwave power and converting it
to heat as it penetrates the tissue. Delivering heat at depth is not only
valuable for cooking dinner, but it can be quite useful for many therapeutic
medical applications as well. These include: diathermy for mild orthopedic
heating, hyperthermia cell killing for cancer therapy, microwave ablation and
microwave assisted balloon angioplasty. It should also be mentioned that based
on the long history of high power microwave exposure in humans, it is
reasonably certain that, barring overheating effects, microwave radiation is
medically safe.

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Preliminary
experiments on the induction of localized myocardial tissue modification by
microwave energy without causing any cardiac arrhythmias, were the first step
in the development of an innovative procedure called microwave balloon
angioplasty (MBA). MBA combines the traditional angioplasty technique with
microwave energy to open narrowed arteries and reduce the occurrence of
restenosis. Microwave cardiac ablation (MCA) works by scarring and destroying
tissue in heart that triggers or sustains abnormal heart rhythm.

 

1.1           
 OBJECTIVES

1.     
To widen the
narrowed or the obstructed arteries using a process called as “microwave
assisted balloon angioplasty (MABA)”.

2.     
To create scars
and destroy the diseased tissues of the heart that triggers or sustains
abnormal heart rhythms using a process called as “microwave cardiac ablation”.

 

 

 

 

Chapter
2

                                       LITERATURE SURVEY

2.1
Balloon angioplasty :

Balloon angioplasty is also known as percutaneous
transluminal angioplasty (PTA), is a minimally invasive endovascular procedure
to widen the narrowed or obstructed arteries or veins.
The procedure avoids cardiac bypass surgery, or other more traumatic
operations, and has been very successful at both extending and improving the
quality of life 3.

 

 Procedure :

Ø  A
special catheter tipped with a collapsed narrow inflatable balloon is inserted
into the artery through an incision in the neck or leg and fed through blood
vessels until it reaches the diseased arteries of the heart.

Ø  Fluid
(de-ionized water) is then pumped into the balloon, inflating it to several
times its nominal diameter.

Ø  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.

Ø  The
balloon is then deflated and it is withdrawn along with the catheter.

Ø  Finally
the vessel puncture site is treated with vascular closure device.

         

 

 

      

               

 

                                               
     Fig
1 : Balloon inserted into an artery 3

 

 

                                                          
Fig 2 : Balloon angioplasty 3

 

 Disadvantages 
:

Ø  Embolization or the launching of debris into the
bloodstream.

Ø  Arterial rupture from over-inflation of a balloon
catheter or the use of an inappropriately large or stiff balloon.

Ø  Restenosis.

 

2.2
RF cardiac ablation :

Catheter-fed ablation or excessive heating of
tissue, destroys the region of the heart responsible for the anomalous
electrical activity. Radio frequency (RF) ablation, operates at frequencies
between 100 kHz – 10 MHz 3.

 

Procedure
:

Ø  More than 1 Catheter wire is guided through the
arteries, to the site of lesion.

Ø  Mapping catheter is used to map the electrical
activities of the diseased cardiac tissue.

Ø  Later the co-axial RF system is inserted to create
scars on the diseased cardiac tissues.

 

                              

                                                   
  Fig 3 : RF cardiac ablation 3

 

Disadvantages  :

Ø  Larger lesions cannot be created by increasing the
power to the RF electrode, as this leads to tissue charring.

Ø  RF ablation (100kHz – 10MHz) is generally limited to
a depth of 0.5 cm, which is insufficient for eliminating deep diseased tissue.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 3

                                          METHODOLOGY

1.
Microwave assisted balloon angioplasty :

MABA
with a helix and mode filter balloon uses the large differences in the
dielectric characteristics (relative permittivity, electrical conductivity) of
high water content (HWC) and low water content (LWC) tissue to preferentially
heat and weld plaque while sparing healthy artery walls. MABA is an minimally
invasive procedure that uses microwave (300 MHz – 300 GHz) to heat the plaque
which makes the plaque thermally fixed in place by compressing it against the
artery wall. The plaque deposition is detected by using fluoroscopy technique.
MABA consists of 2 main systems, they are microwave delivery system and the
catheter system.

 

v  Microwave
delivery system :

Ø  2450MHz signal generator : A microwave signal of
2450MHz frequency is generated using a signal generator.

Ø   Directional
coupler : This is used to divide and distribute the power.

Ø  Two power meters : Here two power meters are used,
one for measuring the forward power and the other one for measuring the
reflected power.

Ø  Co-axial cable : A thin flexible co-axial cable
of  0.034 diameter is used which fits
within a conventional balloon angioplasty catheter and this co-axial cable is
terminated by a radiating antenna which radiates the desired range of
microwaves.

Ø  Thermocouple : This thermocouple is used to measure
the heating temperature.

 

v   Catheter system :

Ø  Balloon
: The catheter is tipped with an inflatable balloon which is made up of nylon
or polyethylene terephthalate (PET). Deionized water is used to inflate the
balloon.

           

            Procedure :

Ø  The
procedure begins by giving local anesthesia to the groin area of the leg.

Ø  Then
the catheter wire is guided through the femoral artery to the site of lesion.

Ø  A
balloon is then guided along then guided along the wire.

Ø  Once
the position of the balloon catheter is established the guide wire is removed
and the same lumen is used to insert the co-axial microwave system.

Ø  The
balloon is then inflated and is ready to deliver the microwave energy.

Ø  When
microwave power between 10-15 watts is delivered it takes approximately 45s for
the LWC tissue (plaque) to heat up.

Ø  After
the end of the microwave power delivery the balloon is deflated.

Ø  Both
the balloon as well as the fluid (deionized water) inside the balloon are
relatively transparent to microwave energy.

Ø  Then
the deflated balloon is withdrawn along with the catheter.

 

 

              Fig 4 : MABA applicator
consisting of an antenna inside a  catheter balloon 1        

                                                                          Fig
:  5 (a)                                                  

                                                                        Fig
: 5 (b)

                                                                         Fig : 5(c)

                                              Fig  5
(a, b, c) : Procedure of MABA  3  

Advantages :

Ø  Chances
of restenosis are less.

Ø  Patient
can return to normal activities shortly after the procedure.

Ø  The
procedure is performed using local anesthesia, which involves fewer risks than
general anesthesia.

2.
Microwave cardiac ablation :

Microwave cardiac ablation (MCA) is an minimally
invasive procedure that works by scarring or destroying tissues of the heart
that triggers or sustains abnormal heart rhythms. MCA is used to treat heart
tissues that allow abnormal electrical conduction by heating it to the point of
inactivation. Microwave antenna that fits within the catheter system can be
positioned close to the diseased tissue. MCA is an important procedure used to
correct heart rhythm problems (arrthymia).

 

 

Procedure
:

Ø  The
procedure begins by giving local anesthesia to the point where the catheter is
being inserted.

Ø  In microwave cardiac ablation catheter are inserted
through the arteries in order to reach the heart. Catheters may be inserted
through groin, shoulder or through neck. 

Ø  More than 1 Catheter wire is guided through the
arteries, to the site of lesion.

Ø  Mapping catheter is used to map the electrical
activities of the diseased cardiac tissue.

Ø  Later the co-axial microwave system is inserted to
create scars on the diseased cardiac tissues.

Ø  Once the procedure is completed the mapping as well
as the ablation catheters are removed.

Ø  The punctured site is ten treated with either direct
pressure or vascular closure device.

                              Fig 6  : Points from where catheter can be inserted 3

 

                                      Fig 7 3 : Ablation Catheter

 

 

 

 

                                           Fig 7 (A, B)  : 
Microwave cardiac ablation 3

 

Advantages :

Ø  Can
lessen or eliminate the heart rhythm problems.

Ø  Allows
to decrease or stop long term medications for heart rhythm problems.

 

 

 

 

 

 

 

 

Chapter
– 4

                       Conclusion

Ø  In
microwave balloon angioplasty (MABA) the plaque was heated and compressed
against the arterial walls using microwave delivery system and catheter. And
also microwaves were more advantageous than RF waves.

Ø  In
microwave cardiac ablation (MCA), microwave catheters were used to create scars
on the diseased tissue that were responsible for abnormal heart rhythms.

 

                                     

 

 

 

 

 

 

                         

 

 

 

 

 

 

                                    REFERENCES

 

1.     
Carey Rappaport , “Treating cardiac
disease with catheter – based tissue heating”, USA, IEEE.

2.     
Rosen, Thomas Jefferson, “Microwave
balloon angioplasty”, Baxter Healthcare Corporation, Edwards LIS Division,
Irvine California, USA.

3.     
Wikipedia.