Electrical Capacitance Tomography

How do you accomadate the change in capacitence caused by different body mass ?

Perhaps:

Total Capacitance is a direct function of area, the dielectric constant of the material, and inversely as plate separation (dielectric depth).

Perhaps the "mass" is simply defined by the compound or molecular density of the dielectric material, the dielectric area, and dielectric depth. I wish I knew what chemical properties define the dielectric constant. Does the type of molecular bonding or electro-negativity affect the dielectric constant? If so how?

Gavilan

I produced the control and data processing software for a radioisotope emission tomographic scanner (many, many years ago).

The technique used was convolution of each of the linear profiles, followed by back projection to produce the image. My recollection of the maths is rather shaky, but I presented a couple of papers to conferences at the time (I didn't publish, as it was based on an algorithm given to our company in a commercial arrangement with a University). I'll see if I still have any related documents (it's over 30 years since I worked on it).

If you check out this Google search, it comes up with some good-looking hits, but you'll need to trawl though them to find the juicy bits, and you may need to pay for some of the published papers.

Good luck.

Hi,

how do you separate electrical conductivity (ionic) and capacitance?

Our skin contributes the major part of the capacitance and the body interior is mostly conductive.

Regarding tomografy there is a major literature that you have to dig and digest if you intend to do a self-made approach. Or you may hire an expert. Or you may try a licensing approach. Depending on time and money you are able to spend and the needs of time to market this may be a difficult situation.

RHABE

First, see if your microcontroller is best suited to transfer data to a PC, a USB enabled controller such as 18F4550 may be best.

The UBW platform and firmware are real fun and easy to start with: http://www.schmalzhaus.com/UBW/ a 32bit version is also available at low cost.

Then again, the unknown signal parameters you are seeking may be best acquisitionned with a scientific grade data acquisition card, using LabView and Math-lab to build method and algorithms.

There are numerous papers on electrical capacitance tomography and on electrical resistance tomography, your problem is interfacing the electrodes to the micro?

Do you have an electrical circuit generating a signal proportional to capacitance? Or is this the main subject of your question?

If you understand the RC circuit equivalent to your sample, you may be able to adapt a basic resistance/reactance measurement circuit.

I guess you look for electrical response from DC to several KHz.

I think you are asking for a way to show the Capacitive field super-imposed on the body. If that is the case, you could use a software package called STAR to do this. It was developed for Structural and Acoustic applications, but the transducer inputs could be anything (capacitance in your case).

The process is to "build" a stick model of the body first, then acquire the data at every point of interest. STAR will then process the data and graphically plot the body and the amplitudes of the C values (it will animate this, too, but that may not help for your application).

STAR is available from Spectral Dynamics Corporation, San Diego.