Abstract
1. Introduction
This special (part) issue of Physiological Measurement is the third annual edition produced in relation to conferences held each year in London under the auspices of the EPSRC Engineering Network in Biomedical EIT. In this issue (from page 95) there are sixteen papers which reflect the healthy state of interest and activity in biomedical EIT; these represent a selection of the presentations at the last annual network conference held in London in April 2001. There has again been good progress in all fields covered - algorithms, hardware, theory and clinical applications. Promising new areas include magnetic induction tomography (MIT), the now commercial use of impedance mapping for breast cancer diagnosis, the potential use of bioimpedance to diagnose cervical cancer, and EIT of brain function. All are reflected in papers in this issue.
However, EIT has not yet made the transition from an exciting medical physics discipline into widespread routine clinical use. The engineering network was primarily created in 1998 to try and further this by co-ordinating a multi-centre clinical trial. As the official funding for the network finished in September 2001, I have included in the next paragraphs a summary of the achievements as I see them.
2. EPSRC Engineering Network in Biomedical EIT (1998-2001)
2.1 Application for a multi-centre clinical trial of electrical impedance tomography
Shortly after the establishment of the engineering network in 1998, a workshop was held for interested parties. The leaders of approximately eight groups all met to establish a steering committee for a large-scale clinical application. No international agreement had previously been achieved on this issue, and there was concern lest each group might wish to use its own EIT system, so that a common platform could not be agreed.
In the event, matters proceeded very smoothly. The following plan was commonly agreed: a common hardware and software platform would be used by each of the participating groups. This was agreed to be the latest EIT system from Professor Brian Brown's group at Sheffield, termed the `Sheffield Mark 3'. This system was based on systems which were by far the most widely used in published clinical studies and included the new development of multi-frequency recording. In contrast, each group was free to pursue clinical applications in their own sphere of interest. This included recordings in medical conditions in heart and chest medicine, gastric emptying, breast imaging, and imaging of brain function. A working plan was put forward, and this was put to all attendees at the next international conference which was held in London in April 2000.
The plan was commonly agreed at this conference and ten groups agreed to participate. Enquiries were made to suitable grant-giving bodies in order to see which of them would be suitable for this application. Of the UK national bodies, the only one which would permit an application of this type was the Medical Research Council. Unfortunately, the application was rejected on strategic, not scientific, grounds; the referees' scientific reports were attached and were strongly supportive. The difficulty with this sort of application is that it is not strictly a clinical trial, in the sense that it is not a trial of therapy. It was for a relatively large sum - about £1 million - and so would have been too large for a project grant application to one of the research councils. At least in the UK, there does not appear to be suitable funding source for this sort of project; it does not qualify as a clinical trial, and is too early to be funded as a trial by a commercial concern.
Agreement had thus been obtained between participating groups, and the matter was raised at subsequent conferences. In 2001, a further application was made to the basic technology call from the combined research councils, but an outline application for this was unfortunately also rejected.
Further discussion at subsequent conferences led to the proposition that the chance of success may be greater if the application was for a single clinical field, rather than across several different ones, as in the original proposal. An application for four collaborating groups in EIT of chest function, organized by Anca Boonstra (Amsterdam), is currently being considered by the European Community.
The Engineering Network has therefore been successful in providing a forum for hitherto disparate groups to agree on a common approach and platform, and a collaboration in the field of assessing EIT for imaging in chest and heart function is currently still being considered. It is unfortunate that the full applications to the MRC or research councils were not successful, but the field is still active and healthy, as individual groups are pursuing EIT clinical trials in the fields of chest, heart, breast, and brain imaging. As the network is now self-sustaining (see below), international effort into clinical trials can still continue in a co-ordinated way.
2.2 Development of a common software platform for the IT community
A direct result of the collaborations developed at the international conferences has been the development of a common software suite for reconstruction of EIT images. There are numerous different possible approaches for mathematical reconstruction of EIT images. Until now, individual groups have produced their own algorithms and, as a result, there has been considerable duplication of resources. With the help of a network funded workshop in 2000, Bill Lionheart from UMIST, in collaboration with several different members of the network, has produced a common software platform for reconstruction of the EIT images (EIDORS). This is written in Matlab so that it can be implemented on different platforms and is a generally available resource for any researcher in EIT.
2.3. Website and EIT discussion list
At present, there is no specific society for electrical impedance tomography. However, funded by the network, we have set up a website which serves the national and international EIT community. It has been used as the repository of information about the network, publications, and other relevant information. We have also set up a discussion mailing list which provides a common informal forum for discussion and exchange of information.
3. Future perspectives for biomedical EIT
The biomedical EIT research community has been fortunate in that there have been annual conferences and special issues in most years since 1987, so there is a forum for exchanging ideas and making a common effort. The EPSRC Engineering Network has been particularly valuable over the past three years in allowing us to continue this tradition and concentrate on establishing clinical trials. There is currently no formal mechanism to continue this, but Richard Bayford and I, here at University College London, are happy to continue to maintain our virtual community whether further explicit funding becomes available or not. The website and discussion list will continue (www.eit.org.uk), and we shall continue to organize annual conferences, probably in London. In this year (2002), David Isaacson and Jennifer Mueller have organized a conference to be held in Colorado, USA, which will take its place (www.eitworkshop.org). We hope, therefore, that the tradition will continue.
The state of EIT research is still healthy. There are about 20 or 30 groups worldwide who are actively performing research, and I think it is still seen as an exciting area of medical physics. In the past year or two, there has been a breakthrough into clinical practice, with the granting of FDA approval for the use of impedance scanning hardware on a commercial basis for the adjuvant diagnosis of breast cancer. However, a major drawback is that it is not yet accepted for routine clinical use in any other area, in spite of the existence of a score or so of good pilot studies. As mentioned above, I think a major element of this is that the clinical community needs to be convinced if its utility by convincing large scale clinical trials; at present, the great majority of researchers in the field are physicists or engineers, and doctors need to be involved to see the benefits of the technology.
In terms of technical developments, there appear to be two main streams. One stream is to concentrate on tissue characterization by multifrequency recording, and to use the imaging ability of EIT to delineate a small number of regions of interest. This has been the approach of the Sheffield group, whose Mark 3.5 system usually has only eight channels. My personal view is to press on with the development of the imaging capability of EIT; our new system for brain imaging has 64 electrodes and records several hundred different electrode combinations. This approach certainly works reasonably well in tanks, but there are practical limitations in human recordings. Other groups producing new systems appear to lie between these two viewpoints.
It is not entirely clear where the bottleneck in EIT image and data quality lies; my guess is that it is principally in the errors produced by the interaction of skin impedance with instrumentation. These errors are then magnified by the ill-conditioned inverse solution in the reconstruction algorithms. Although there have been several pilot publications on the use of active electrodes to reduce errors, a practical system which employs these may well be the next major advance in our field. At the same time, there is considerable interest in magnetic induction tomography, which avoids the skin interface problem, and I look forward to seeing the first clinical trials with this novel technology.
In conclusion, the past three years have seen a healthy, steady advance in the field. We still need to break into widespread clinical acceptance, and effort is continuing actively into the clinical trials and pilot studies which will achieve this. Continuation of a virtual research community over the web and with annual conferences will allow research groups to co-ordinate and collaborate in achieving this. Technical advances may allow us to obtain more accurate tissue characterization and image quality, and this will undoubtedly help to advance clinical acceptance.