Components of evaluation:
- Test Overview
- Evaluation procedure
- Performance parameters
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.
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:
- Homogeneous tank measurements, designed to evaluate system noise,
accuracy, drift and symmetric measurement electrodes.
- 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;
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.
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
A set of parameters is proposed:
which correspond to the block diagram:
|| data and image noise, and data accuracy,
detectability and distinguishability of single and multiple contrasts,
Accuracy of reconstructed images.
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 $