Components of evaluation:

• Test Overview
• Evaluation procedure
• Performance parameters

Test Overview:

To evaluate and compare the performance of a complete EIT system, we proposed a test methodology and phantom system design based on reproducible procedures with completely characterized and traceable test objects. Components of system performance evaluation are shown in figure 1:

Figure: Schematic diagram of proposed test setup and procedure to evaluate EIT system performance

An EIT system consists of an electrode interface, EIT stimulation and measurement hardware and an image reconstruction algorithm. Measurements are performed using a specified measurement protocol and characterized traceable test objects.The data and images are systematically analysed by performance analysis algorithm.

Evaluation procedure:

Three important components for this test are test phantoms, a test protocol, and evaluation methodology/software. The EIT system is connected to the phantom, and three sets of measurements are performed:

1. Homogeneous tank measurements, designed to evaluate system noise, accuracy, drift and symmetric measurement electrodes.
2. Measurements with one conductivity contrast which is moved horizontally at several vertical offsets from the electrode plane, designed to measure amplitude response, position accuracy, resolution, and detectability limits;
3. Measurements with two conductivity contrasts, designed to measure limits of distinguishability of contrasts.The position of two objects highly affected the image reconstruction where two closely positioned objects look like a bigger single object.

   (a)	(b)	(c)

   Figure : Photo of the phantom and position controller; (b) Schematic drawing of movement protocols - a horizontal movement of a single object in two planes separately (3D view); (c) horizontal movement of two cubes of 50 ml (top) away from the center to the edge and a cube of 100 ml (bottom) fixed in the center of the tank (2D view).

   Performance parameters:

   A set of parameters is proposed:

   A.	data and image noise, and data accuracy,
   B.	detectability and distinguishability of single and multiple contrasts, and
   C.	Accuracy of reconstructed images.

   which correspond to the block diagram:
   
   Figure: Concept diagram of evaluation of EIT system performance, where A block is for noise and accuracy: B block is for detectability of a single target and distinguishability of two targets: C block is image reconstruction accuracy.

   The calculation of these figures of merit is illustrated in figure below:
   

   
   Figure:Procedures for analyzing image data: first row- phantom system, EIT measurement system and reconstruction algorithm, and N frames of the reconstructed images; second row: calculation of ROI over one-fourth amplitude set; third row: calculation of z and GREIT parameters (Adler etal 2009).

   For better performance, it is desirable for AR, PE and RES to be constant, while PE, RES and RNG should be as small as possible for any target position.

   Last Modified: $Date: 2017-02-28 13:12:08 -0500 (Tue, 28 Feb 2017) $ by $Author: aadler $