Searching \ for '[EE]: Electrical Impedance Tomography - any experi' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=electrical+impedance
Search entire site for: 'Electrical Impedance Tomography - any experi'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: Electrical Impedance Tomography - any experi'
2000\06\12@175339 by Russell McMahon

picon face
Anyone here had any involvement or knowledge of EIT (Electrical Impedance
Tomography).
This is a simple and cheap means of obtaining internal images of the body -
some similarity to eg CAT scans but with lower resolution but also some
advantages (safer, much cheaper, ...). A number of electrodes are placed on
the subject and impedances measured between all combinations. Standard
tomographic algorithms (plus some extras) allow an image to be generated.

This is something that could be handled very easily by a low level processor
and I can think of several possible applications.




     Russell McMahon
_____________________________

What can one man* do?   Help the hungry at no cost to yourself!
at  http://www.thehungersite.com/
(* - or woman, child or internet enabled intelligent entity :-))
From other worlds:
http://www.changingourworld.com    http://www.easttimor.com   http://www.sudan.com

2000\06\12@204320 by Dan Michaels

flavicon
face
Russell McMahon wrote:
>Anyone here had any involvement or knowledge of EIT (Electrical Impedance
>Tomography).
>This is a simple and cheap means of obtaining internal images of the body -
>some similarity to eg CAT scans but with lower resolution but also some
>advantages (safer, much cheaper, ...). A number of electrodes are placed on
>the subject and impedances measured between all combinations. Standard
>tomographic algorithms (plus some extras) allow an image to be generated.
>
>This is something that could be handled very easily by a low level processor
>and I can think of several possible applications.
>

My gut feeling is the resolution here wouldn't be usable for
much other than curiosity. But PaulB certainly would know.

cheers,
- Dan Michaels

2000\06\13@110353 by Tim Hayward

flavicon
face
If you moved the electrode array across the body, or even vibrated the
pickups, couldn't you use synthetic aperture algorithms to increase
resolution dramatically.

{Original Message removed}

2000\06\13@120015 by Dr. Chris Kirtley

flavicon
face
Dear all,

I mentioned this to a friend of mine in Sheffield, England, where they
did the pioneering work on impedance imaging (and continue to work on
it). Here's what he says:

1)  What you get out isn't really an 'image' as there is no knowledge of
the body surface shape - the assumption is made that the cross-section
is circular, but you get some very bad artefacts if it is significantly
non-
circular (e.g. if there is any concavity)

2)  Current is passed through adjacent pairs of electrodes (at least in
the
Sheffield system) rather than between all combinations.  Voltage
measurements
are made between all other adjacent pairs.

3)  There is a lot of complex analog circuitry involved in measuring the
impedances.  Signal to noise ratio is critical to be able to reconstruct
an
image.

4)  Although the data collection is fairly trivial, the image
reconstruction
is far
from trivial.  Unless you want to reconstruct off-line, a low-level
processor will
not be able to do it.  We used transputers in our first real-time system
(about 10 years ago).  We are now using one DSP per channel.

Some refs
http://www.shef.ac.uk/uni/academic/I-M/mpce/rsch/paps/sercfr.html

http://www.shef.ac.uk/uni/academic/I-M/mpce/rsch/research.html

and especially

http://www.shef.ac.uk/uni/academic/I-M/mpce/rsch/pmeth/index.html


Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: spam_OUTkirtleyTakeThisOuTspamcua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
Send subscribe/unsubscribe to .....listprocKILLspamspam@spam@info.curtin.edu.au

2000\06\13@135844 by Don B. Roadman

flavicon
face
On 13 Jun 2000, at 9:50, Tim Hayward wrote:

> My gut feeling is the resolution here wouldn't be usable for
> much other than curiosity. But PaulB certainly would know.
>

You are correct. The resolution would be quite worthless. This
would only be suitable to sell with snake oils, etc. No usefull
information could be obtained. The standard xray of  circa 1930
would be superior.

2000\06\14@073111 by Russell McMahon

picon face
> My gut feeling is the resolution here wouldn't be usable for
> much other than curiosity. But PaulB certainly would know.
>

>>You are correct. The resolution would be quite worthless. This
>>would only be suitable to sell with snake oils, etc. No usefull
>>information could be obtained. The standard xray of  circa 1930
>>would be superior.


Not totally true  (surprisingly) I'm pleased to say.
Certainly the industry could easily produce snake-oil products but, AFAI can
see  it is also capable of much more than that.

- A web search reveals much EIT work being by reputable organisations and
with resolutions which depend on the number of electrodes.
- The results are different than for XRays rather than worse - horses for
courses.
- One advantage is the lack of ionising radiation (unlike X-Ray) and the
ability to produce quite high speed real time images.
- While resolutions are not ever going to be as high as MRI the cost is in
the order of two orders of magnitude less. The response times are also
faster than functional MRI can achieve. When used for brain imaging it is
likely that some useful real-time results can be achieved.
- Applications can include ongoing heart or lung action imaging - not
something one would like to have done with XRay.
- While X-Ray is not a suitable technology for indiscriminate or unregulated
use there may be applications for EIT which are - due to its essential
safety.
eg Psychologists would dearly LOVE their own internal non-invasive brain
activity monitoring system - albeit every so coarse in resolution. Would you
like to have this done to your brain with XRay :-) ?
- EIT results vary with "excitation" frequency and may allow some very
interesting differential
- Current research efforts are being directed to better resolution by data
processing based on known attributes of the scanned medium.
Vastly increased numbers of electrodes could produce substantial
improvements - this may be achievable by "clever" rather than brute force
techniques (cf resistive graphics tablets).
- I am aware of a similar technique used with success to detect cracks in
alumina smelting electrodes.

I'd be interested in Paul's comments.



RM

2000\06\14@143957 by Dan Michaels

flavicon
face
Russell McMahon wrote:
>> My gut feeling is the resolution here wouldn't be usable for
>> much other than curiosity. But PaulB certainly would know.
>>
>>>You are correct. The resolution would be quite worthless. This
>>>would only be suitable to sell with snake oils, etc. No usefull
>>>information could be obtained. The standard xray of  circa 1930
>>>would be superior.
>
>
>Not totally true  (surprisingly) I'm pleased to say.
>Certainly the industry could easily produce snake-oil products but, AFAI can
>see  it is also capable of much more than that.
>
>- A web search reveals much EIT work being by reputable organisations and
>with resolutions which depend on the number of electrodes.
>- The results are different than for XRays rather than worse - horses for
>courses.


I still think you have a problem here. You presented this as
some kind of replacement for x-ray imaging, and no matter how many
electrodes you use, and what your stimulation frequency is, resolution
is not gonna approach anything near x-rays.

Electric fields don't penetrate far into tissue. Low frequencies, ie
poorer resolution, penetrate farther. Hi freq penetrate less. And
now you have a potential "safety" problem too, as you are driving
currents into the body/brain.

You also have a "volume effect". The body/brain is a volume conductor
and currents divide according to resistance, so the currents spread out
in 3 dimensions, and then all superimpose on the other side. This is
the basic problem with EEGs - resolution is not good, since all the
signals within the brain superimpose.

You can probably get something, but let's face it, x-rays work
becuase they have tiny wavelengths, penetrate the body easily,
and don't spread like currents. Surely, the EIT workers you cited
realize this.
===============

.......
>- While X-Ray is not a suitable technology for indiscriminate or unregulated
>use there may be applications for EIT which are - due to its essential
>safety.

Injection of current into the body has own set of safety problems. In
the US, the FDA closely regulates anything "connected" to the body - such
as EEG amplifiers. And if you want to "inject" something into the body,
like currents, it's scrutinized much more.
==================

>eg Psychologists would dearly LOVE their own internal non-invasive brain
>activity monitoring system - albeit every so coarse in resolution. Would you
>like to have this done to your brain with XRay :-) ?
.........

This statement is rather confusing. Psychologists normally want to study
function, not form [anatomy], whereas it would appear that EIT, like
x-ray imaging, does the latter and not the former. Are you sure you don;t
want to look at EEG imaging here? If so, look up something called "BEAM"
technology, starting in early 80s. Forget the guy's name who started
this, but it means brain electrical activity mapping.

I did some of this stuff a while back - actually developed the first
BEAM system to run on a PC-compatible. The psychologists loved this stuff,
and the neurologists feared it - after the neurosurgeons said in a
meeting "hey, we don;t need the neurologists any longer" - right in
front of their faces. Good thing guns weren't so popular back then.

- DanM

2000\06\15@164214 by l.allen

picon face
Dan Wrote...
>
> I did some of this stuff a while back - actually developed the first
> BEAM system to run on a PC-compatible. The psychologists loved this stuff,
> and the neurologists feared it - after the neurosurgeons said in a
> meeting "hey, we don;t need the neurologists any longer" - right in
> front of their faces. Good thing guns weren't so popular back then.
>
We have lovely colour 3D EEG images of Brain Activity super-imposed on
a human head image running in our High Density EEG Lab.
Calibrating the phase delay from electrode to electrode was a bitch..
took me 4 months designing an in house system ( I really hate
gleaning microvolt signals).
The next BIG challenge is turning an RF shielded room into a 50Hz
silent room. Yes there has to be a computer, lights, intercom,
camera, VDU, Net Amp front end etc etc inside the room linked to
a battery of computers outside the room.
A combination of fibre optics, super regulated D.C. supplies and a
mains frequency changer should do the trick.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

2000\06\15@200441 by Dan Michaels

flavicon
face
Lance Allen wrote:
.......
>We have lovely colour 3D EEG images of Brain Activity super-imposed on
>a human head image running in our High Density EEG Lab.
>Calibrating the phase delay from electrode to electrode was a bitch..
>took me 4 months designing an in house system ( I really hate
>gleaning microvolt signals).


Lance,

Sounds like you are the guy Russell McMahon wants to talk to.
Plus, you are both in NZ, AFAICT. Same city? Same university?
Wouldn't that be a stitch.

BTW, regarding phase, don't most commercial EEG machines have
pretty equivalent phase shifts between the many channels? BAck when
I did this, I don;t recall us having any particular problems along
those lines. ??????

cheers,
- Dan Michaels
==============

More... (looser matching)
- Last day of these posts
- In 2000 , 2001 only
- Today
- New search...