Test data *

To analyse the performance of the image reconstruction algorithm used in the EIT investigation, a sequence of reconstructions using various phantoms is performed on a simulated vessel of 10 cm diameter.

In order to quantify the areas represented by pixels of different resistivities and relate them to the object areas, the number of pixels for each resistivity are summed and their percentage area of the total image area determined from

y '1 pixels of specified resistivity

^ ₈₂₄ x 100%

The results provide quantifiable information relating to measurement accuracy and resolution (Section 5.3).

The results of the simulations are as follows: a) Phantom study 1

In this case a 10 cm diameter vessel full of air is used and the reconstructed image is shown in Figure 5.1(b).

b) Phantom study 2

In this case a 2.5 cm diameter air bubble, represented by a resistivity in excess of 1000 Cl cm, is placed at the centre of the 10 cm diameter 500 £2 cm representing the vessel background resistivity, as shown in Figure 5.2(a). The reconstructed image is shown in Figure 5.2(b).

c) Phantom study 3

In this case a 2.5 cm diameter perspex rod, represented by a resistivity of 960

Cl cm, is placed at the centre of a 10 cm diameter 500 Cl cm, representing the vessel background resistivity as shown in Figure 5.3(a). The reconstructed image is shown in Figure 5.3(b).

d) Phantom study 4

In this example the resolution of the reconstruction is illustrated. This phantom consists of two 2.5 cm diameter perspex rods with the same resistivity. The position of the phantom is shown in Figures 5.4(a) and 5.5(a). The aim of the investigation is

to see if it is possible to distinguish the two rods. The results are shown in Figures 5.4(b) and 5.5(b).

e) Phantom study 5

In this example the result of using different resistivity objects is illustrated. The phantom consists of a 2.5 cm diameter aluminium rod, represented by a resistivity of 360 Cl cm, and a 2.5 cm diameter air bubble, represented by a resistivity of 1000 Cl

cm. The position of the phantom is shown in Figures 5.6(a) and 5.7(a). The aim of the investigation is to see if it is possible to distinguish the two rods with different resistivities. The reconstructed image is shown in Figures 5.6(b) and 5.7(b).

f) Phantom study 6

In this example the effects on the reconstruction when the water level of a horizontal pipe varies from nearly full to nearly empty are investigated. The reconstructed images are shown in Figures 5.8(b), 5.9(b) and 5.10(b).

g) Phantom study 7

The final example illustrates the results obtained when the aluminium rods, represented by a resistivity o f360 Cl cm, are placed inside a horizontal pipe for varying depths of water level. The aim of the investigation is to see if it is possible to distinguish the air, water and aluminium rod (solid) in a horizontal pipe. The results are shown in Figures 5.11(b), 5.12(b) and 5.13(b).

Percentage area of air = 100% Area R esistivity <0hm cm) 1000 and above (b)

Figure 5.1 Reconstruction for the EIT system for a 10 cm diameter vessel full of air. a) actual position b) reconstructed

Percentage area of water = 93.75% Percentage area of air = 6.25%

R esistivity <Ohm cm) 1000 and above 71 (b)

Figure 5.2 Reconstruction for the EIT system for a 2.5 cm diameter of air bubble (1000 D cm) placed at the centre of a 10 cm diameter 500 Q cm saline filled vessel.

Percentage area of water = 93.75% Percentage area of perspex = 6.25%

(a)

R esistivity <0hm cm)

(b)

Figure 5.3 Reconstruction for the EIT system for a 2.5 cm diameter of perspex rod (960 Q cm) placed at the centre of a 10 cm diameter 500 Q cm saline filled vessel.

Percentage area of water = 87.5% Percentage area of perspex = 12.5%

perspex perspex

(a)

(b)

Figure 5.4 Reconstruction for the EIT system for two 2.5 cm diameter of perspex rods (960 Q cm) placed in a 10 cm diameter 500 Q cm saline filled vessel, a) actual position b) reconstructed

Percentage area of water = 87.5% Percentage area of perspex = 12.5%

(a)

Area R esistivity

<*> (Ohm cm)

(b)

Figure 5.5 Reconstruction for the EIT system for two 2.5 cm diameter of perspex rods (960 Q cm) placed in a 10 cm diameter 500 Q cm saline filled vessel,

Percentage area of water =87.5% Percentage area of air = 6.25%

Percentage area of aluminium = 6.25%

(a)

fVea R esistivity

C-O <Qhm cm>

(b)

Figure 5.6 Reconstruction for the EIT system for a 2.5 cm diameter of aluminium rod (360 fl cm) and a 2.5 cm diameter air bubble (1000 Q cm) placed in a 10 cm diameter 500 Q cm saline filled vessel,

Percentage area of water = 87.5% Percentage area of air = 6.25%

Percentage area of aluminium = 6.25%

(a)

Area R esistivity

(Ohm cm)

(b)

Figure 5 .7 Reconstruction for the EIT system for a 2.5 cm diameter of aluminium rod (360 Q cm) and a 2.5 cm diameter air bubble (1000 Q cm) placed in a 10 cm diameter 500 Q cm saline filled vessel,

air Percentage area of water = 85 .93%

Percentage area of air = 14.07%

2 cm water 8 cm Area R esistivity <>;> <Qh» c»> (b)

Figure 5.8 Reconstruction for the EIT system for a 10 cm diameter horizontal pipe when the depth of the water is 8 cm.

Percentage area of water = 50% Percentage area of air = 50%

(a) water R e sistiv ity <0h» cm) 5.34 1030 end above (b)

Figure 5.9 Reconstruction for the EIT system for a 10 cm diameter horizontal pipe when the depth of the water is 5 cm.

Percentage area of water = 14.07% Percentage area of air = 85 .93%

8 cm

water

Area R esistivity

<V.) <0h» cm)

(b)

Figure 5.10 Reconstruction for the EIT system for a 10 cm diameter horizontal pipe when the depth of the water is 2 cm.

Percentage area Percentage area Percentage area

(b)

Figure 5.11 Reconstruction for the EIT system for a 10 cm diameter horizontal pipe when the depth of water is 8 cm and two 2.5 cm diameter of aluminium rods (360 Q cm) are placed inside the pipe,

aluminium aluminium of water = 73 .43% of aluminium = 12 .5% of air = 14.07% water

Percentage area of water = 37 .5% Percentage area of aluminium =12 .5% Percentage area of air = 50%

water aluminium

(a) aluminium

0.971

(b)

Figure 5.12 Reconstruction for the EIT system for a 10 cm diameter horizontal pipe when the depth of water is 5 cm and two 2.5 cm diameter of aluminium rods (360 Q cm) are placed inside the pipe,

air Percentage area of water = 12 .51%

Percentage area of air = 85 .93% Percentage area of aluminium = 1.56%

i 8 cm aluminium water Area R esistivity <‘4> <0hm cm) (b)

Fig 5.13 Reconstruction for the EIT system for a 10 cm diameter horizontal pipe when the depth of water is only 2 cm and 1.25 cm diameter of aluminium rod (360 Q cm) is placed inside the pipe,