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
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.
To widen the
narrowed or the obstructed arteries using a process called as “microwave
assisted balloon angioplasty (MABA)”.
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”.
Microwave assisted balloon angioplasty :
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
delivery system :
Ø 2450MHz signal generator : A microwave signal of
2450MHz frequency is generated using a signal generator.
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
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
Ø Thermocouple : This thermocouple is used to measure
the heating temperature.
v Catheter system :
: 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
procedure begins by giving local anesthesia to the groin area of the leg.
the catheter wire is guided through the femoral artery to the site of lesion.
balloon is then guided along then guided along the wire.
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.
balloon is then inflated and is ready to deliver the microwave energy.
microwave power between 10-15 watts is delivered it takes approximately 45s for
the LWC tissue (plaque) to heat up.
the end of the microwave power delivery the balloon is deflated.
the balloon as well as the fluid (deionized water) inside the balloon are
relatively transparent to microwave energy.
the deflated balloon is withdrawn along with the catheter.
Fig 4 : MABA applicator
consisting of an antenna inside a catheter balloon 1
: 5 (a)
: 5 (b)
Fig : 5(c)
(a, b, c) : Procedure of MABA 3
of restenosis are less.
can return to normal activities shortly after the procedure.
procedure is performed using local anesthesia, which involves fewer risks than
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 begins by giving local anesthesia to the point where the catheter is
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
lessen or eliminate the heart rhythm problems.
to decrease or stop long term medications for heart rhythm problems.