**3.6.2 Array of 3 microwave stripline applicators**

The other possible configuration is array of 3 applicators coupled to homogeneous cylindrical agar phantom (Fig. 9a.). Consequently, we studied simulations of 3 applicators coupled to the 3D anatomical model (Fig. 9b.).

Another interesting case is shown on Fig. 10. –in this picture there are displayed interesting shapes of SAR distribution by change of phases of applicators and change of amplitude of one type of applicator located in the middle of all applicators.

Prospective Applications of Microwaves in Medicine 515

a) b)

By using 4 applicators we can see in following picture (Fig. 11.), that in both cases there is a

By alternation of phases of several applicators we achieved better focusing in the middle of both homogeneous agar phantom and 3D anatomical model (Fig. 12.). Such array of 4

a) b)

a) b)

Fig. 11. Array of 4 applicators a) on cylindrical agar phantom, b) on anatomical model

applicators could be used for treatment tumors located in the middle of human limb.

Fig. 10. Normalized SAR a) in agar phantom, b) in normalized SAR in anatomical model

very good focusing effect of SAR distribution near to the cylindrical axis.

Fig. 12. Normalized SAR a) in agar phantom, b) in anatomical model

**3.6.3 Array of 4 microwave stripline applicators** 

Fig. 7. Array of 2 applicators a) on cylindrical agar phantom, b) on anatomical model

Fig. 8. Normalized SAR a) in agar phantom, b) in anatomical model

Fig. 9. Composition of 3 applicators a) on cylindrical agar phantom, b) on anatomical model

In homogeneous phantom were created 3 maxima, instead in anatomical model we can observe only one maximum of SAR distribution – that demonstrates very nice example of focussing possibilities. By setting of phases and/or amplitude of applicators we can accomplish required shape of SAR.

Fig. 7. Array of 2 applicators a) on cylindrical agar phantom, b) on anatomical model

 a) b)

a) b) Fig. 9. Composition of 3 applicators a) on cylindrical agar phantom, b) on anatomical model In homogeneous phantom were created 3 maxima, instead in anatomical model we can observe only one maximum of SAR distribution – that demonstrates very nice example of focussing possibilities. By setting of phases and/or amplitude of applicators we can

Fig. 8. Normalized SAR a) in agar phantom, b) in anatomical model

accomplish required shape of SAR.

a) b)

Fig. 10. Normalized SAR a) in agar phantom, b) in normalized SAR in anatomical model

#### **3.6.3 Array of 4 microwave stripline applicators**

By using 4 applicators we can see in following picture (Fig. 11.), that in both cases there is a very good focusing effect of SAR distribution near to the cylindrical axis.

By alternation of phases of several applicators we achieved better focusing in the middle of both homogeneous agar phantom and 3D anatomical model (Fig. 12.). Such array of 4 applicators could be used for treatment tumors located in the middle of human limb.

Fig. 12. Normalized SAR a) in agar phantom, b) in anatomical model

Fig. 11. Array of 4 applicators a) on cylindrical agar phantom, b) on anatomical model

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applicator is more complicated, than has been the first idea. SAR can be measured either in

One of our tools for experimental evaluation of microwave applicators is the apparatus, which enable us to do 3D measurements of SAR distribution. It can be used for both local

The basic part of this apparatus is big salt water phantom (water with 0.3% to 0.6% NaCl) and the measurement probe with the possibility of 3D scan around the applicators. As probes we use a Light Emitting Diodes (LED) with a fibber optic link connection to interface of the computer. The purpose of this link is to reduce influence of the metallic (i.e. conductive) components from the measured electromagnetic field. The schematics of the

fiber optic link

intracavitary applicator

coaxial cable

computer

power generator

interfeace

water phantom

During measurements of SAR along the applicator we have found, that typically there is not only a one main SAR maximum (first from the right side), but also a second and/or higher order maxima can be created, being produced by outside back wave propagating along the coaxial cable, see Fig. 15a. In Fig. 15b. SAR distribution improvement (i.e. reduction of second maximum) can be noticed for the case of dipole like applicator. To eliminate this second maximum and optimise the focusing of SAR in predetermined area of biological

After coil radius and length optimisation we have obtained very good results of SAR distribution, see Fig. 16a,b. Some problems can be with the antenna self-heating, but it can

apparatus for 3D measurements of SAR distribution is shown in Fig. 14.

water phantom or by infrared camera.

**4.2 Evaluation of BPH applicators** 

external and intracavitary applicators.

Fig. 14. Apparatus for 3D SAR measurements

3D scaning system measurement probe

tissue needs to use the helical coil antenna structure.

be reduced by cooler at the end of applicator tip.
