Table of contents

Most of the papers in this issue are devoted to biomedical electrical impedance tomography (EIT). Still a young and exciting field for research, there are perhaps thirty or so groups in the world which are engaged actively in its research and development. We are fortunate to have excellent relationships, with good communication and co-operation between us. This is due in large part to the leadership of Professor Brian Brown and David Barber at Sheffield, UK, who have organized regular meetings since 1987 under the auspices of European Community Concerted Actions. The last meeting under this scheme was in Heidelberg in 1995.

Over the course of these concerted actions, EIT has been transformed from a fledgling idea into an established field for research. There was clinical validation in imaging pulmonary and gastric function, and several groups had constructed robust systems capable of imaging in saline filled tanks and a number of experimental clinical areas. New interest was developing in the technical improvements of multifrequency recording and imaging in 3D.

Although there were several good clinical pilot studies, the majority of the research effort lay in making technical advances. There was a great deal of interest internationally in EIT from a bioengineering point of view, but the sad truth was that it had not been accepted for routine medical diagnosis in any of the areas in which it had been shown to be effective in pilot studies. (As a method, it has the advantages that it is inexpensive, rapid, safe and portable. Its principal drawback is a relatively poor spatial resolution. Nevertheless, there appear to be several clinical areas where its advantages make it appear likely that it could offer significant advantages as a diagnostic method.)

The next step in its development appeared logically to be to arrange a multicentre collaboration to perform clinical trials on the efficacy of the best available EIT systems. The purpose would be to collect solid evidence of its ability to contribute to management in defined clinical settings, and so convince physicians to take it up as a clinical tool. An application was therefore made to the UK Engineering and Physical Sciences Research Council, with the aim of forming a collaboration to pursue a multicentre clinical trial of EIT. Funding was duly granted, in the form of an `Engineering Network'. This provided support for meetings over a period of three years, a Web site (www.eit.org.uk ) and an administrator. The plan was to have three annual general meetings in April of each year, and smaller workshops or committee meetings each Autumn.

The first meetings were in the Autumn of 1998. Bill Lionheart (Oxford Brookes University) organized a software workshop, which successfully agreed a common strategy for developing EIT reconstruction software. A steering committee also met, and agreed on a plan for a multicentre clinical trial. The concept was that ten participating groups would each use the same hardware - the latest design from the group at Sheffield - and common software, but each work on a clinical area of their own interest. In practice, several groups agreed to work on common areas, so the principal topics were EIT imaging of cardiac, pulmonary, gastric and brain function. Funding was sought for equipment and a research physician for two years for each group, as well as a co-ordinating engineer to be based in London. Unfortunately, the application was rejected by the UK Medical Research Council, on the grounds that it was a technology assessment rather than a therapeutic trial, but we will still vigorously pursue funding elsewhere for this.

The papers presented in this issue derive from presentations made at the first general conference on Biomedical Applications of Electrical Impedance Tomographyunder the auspices of the EPSRC Engineering Network in EIT, held at Middlesex Hospital (part of University College London), central London, in April 1999. It was a pleasure to welcome new groups from the UK, Holland, USA and Russia, as well as meet old friends. There were presentations of advances in hardware and reconstruction algorithms, a novel magnetic induction system, and first examples of human images in breast cancer and brain function. A second conference is to be held at the same venue in London in April 2000, and I am grateful to the editor of this journal and the Institute of Physics Publishing for kindly agreeing to another special issue for papers relating to that meeting.

Physiological Measurementhas a proud tradition of supporting research in EIT by publishing special issues related to the various conferences held since 1987. This is the latest, and I hope it will be of interest to the general reader as well as a valuable source, like its predecessors, of the latest developments in EIT for those working in the field.

David Holder Special Issue Editor

Multi-frequency electrical impedance tomography (EIT) systems require stable voltage controlled current generators that will work over a wide frequency range and with a large variation in load impedance. In this paper we compare the performance of two commonly used designs: the first is a modified Howland circuit whilst the second is based on a current mirror. The output current and the output impedance of both circuits were determined through PSPICE simulation and through measurement. Both circuits were stable over the frequency ranges 1 kHz to 1 MHz. The maximum variation of output current with frequency for the modified Howland circuit was 2.0% and for the circuit based on a current mirror 1.6%. The output impedance for both circuits was greater than 100 k for frequencies up to 100 kHz. However, neither circuit achieved this output impedance at 1 MHz. Comparing the results from the two circuits suggests that there is little to choose between them in terms of a practical implementation.

We show that nonlinear EIT provides images with well defined characteristics when smoothness of the image is used as a constraint in the reconstruction process. We use the gradient of the logarithm of resistivity as an effective measure of image smoothness, which has the advantage that resistivity and conductivity are treated with equal weight. We suggest that a measure of the fidelity of the image to the object requires the explicit definition and application of such a constraint. The algorithm is applied to the simulation of intra-ventricular haemorrhaging (IVH) in a simple head model. The results indicate that a 5% increase in the blood content of the ventricles would be easily detectable with the noise performance of contemporary instrumentation. The possible implementation of the algorithm in real time via high performance computing is discussed.

Electrical impedance tomography is a technology for producing images of internal body structures based upon electrical measurements made from electrodes on the body surface. Typically a single plane of electrodes is used, seeking to reconstruct a cross-section of the body. Yet the majority of image reconstruction algorithms ignore the three-dimensional (3D) characteristics of the current flow in the body. Actually, a substantial amount of current flows out of the electrode plane, creating distortions in the resulting images. This paper describes a reconstruction algorithm, ToDLeR, for solving a linearized 3D inverse problem in impedance imaging. The algorithm models the body as a homogeneous cylinder and accounts for the 3D current flow in the body by analytically solving for the current flow from one or more layers of electrodes on the surface of the cylinder. The algorithm was implemented on the ACT3 real-time imaging system and data were collected from a 3D test phantom using one, two and four layers of electrodes. By using multiple planes of electrodes, improved accuracy in any particular electrode plane was obtained, with decreased sensitivity to out-of-plane objects. A cylindrical target located vertically more than 8 cm below a single layer of 16 electrodes, and positioned radially midway between the centre and the boundary, produced an image that had 35% of the value obtained when the target was in the electrode plane. By adding an additional layer of 16 electrodes below the first electrode plane, and using 3D current patterns, this artefact was reduced to less than 10% of the peak value. We conclude that the 3D algorithm, used with multiple planes of electrodes, reduces the distortions from out-of-plane structures in the body.

Three dimensional (3D) electrical impedance tomography (EIT) presents many additional challenges over and above those associated with two dimensional EIT systems. With present two dimensional (2D) systems, tomographs can be reconstructed and displayed on a PC with a standard computer monitor. In addition, using appropriate data acquisition hardware and simple image reconstruction algorithms, it is possible to collect, reconstruct and display volumetric EIT images in real time using parallel processing architectures. The advantages of this `real-time' capability are many and include the ability to immediately assess the correct functioning of the system and the ability to track patient events and the effect of procedures in real time.

Whilst 3D EIT boundary datasets can be collected in real time, their real-time image reconstruction and display presents some computational challenges. This explains why, to date, no real-time solutions have been presented. In addition the use of a standard computer monitor to display 3D volumes is unsatisfactory since not all depth cues are preserved when using this type of 2D display device.

We present a system which is capable of displaying 3D EIT datasets in real time and allows interactive modification of the user's viewpoint. This allows the user to fly around (and through) the EIT volumetric dataset.

In this work we show the algorithms developed to extract the Cole parameters from multi-frequency EIT. With these parameters it is possible to obtain information about various different tissues and their pathologies. The algorithms developed obtain the Cole-model parameters from the real and imaginary parts of impedance, or using only the real part, without problems of convergence. A study of the influence of noise is performed with simulations. We find a correct solution in all cases with signal to noise ratio in the data higher than 40 dB. Finally, we show parametric images of the human abdomen obtained with these algorithms.

Electrical impedance tomography (EIT) could allow the early diagnosis of infant brain injury following birth asphyxia. The purpose of this work was to determine the effect of variations in skull, scalp or cerebrospinal fluid (CSF) resistivity, as these vary in clinical conditions and could degrade image quality. These factors were investigated using finite element models of the adult and neonatal head. The results suggest that there is a wide range over which the resistivity of the neonatal skull has little effect on the sensitivity to a central impedance change. The scalp and CSF appear to shunt current away from the brain; when their resistivity was decreased from normal values, this shunting effect increased and caused a decrease in sensitivity to a central resistance change. The resistivity of neonatal skull has not, to our knowledge, been directly measured and will anyway vary within and between individuals; this work suggests that EIT will be relatively insensitive to variations in neonatal skull impedance.

The test concept as well as the design of a simple resistor phantom suitable for the evaluation of the properties of electrical impedance tomographic (EIT) systems is presented. Input and transfer impedance of the phantom are matched with those of the human thorax. Amplitude of the local impedance variations similar to in vivoconditions (ventilation) can be intentionally set to perform measurements on different states. The theoretical potential differences between the electrodes are calculated. The evaluation procedure is performed in terms of the local amplitude of the relative impedance change as well as the local distribution of noise. The whole procedure can be applied either to compare quantitatively the performance of different EIT data acquisition systems or to determine the amount of measurement disturbance caused by the external electrical environment in clinical settings.

In electrical impedance tomography (EIT) two-dimensional models continue to be applied despite their known inability to provide correct reconstruction. In this paper, a reconstruction algorithm that assumes a translationally invariant conductivity distribution is described. A more precise forward solver is obtained by taking off-slice currents into consideration. An appropriate sensitivity matrix is derived. Numerical evidence for the improvement in precision compared to two-dimensional reconstruction is given.

We have recently built and tested a 32 channel, multi-frequency (1 kHz to 1 MHz) voltage mode system to investigate electrical impedance spectroscopy (EIS) imaging. We completed a series of phantom experiments to define the baseline imaging performance of our system. Our phantom consisted of a plastic circular tank (20 cm diameter) filled with 0.9% aqueous NaCl solution. Conductors and nonconductors of decreasing width (W5: 3.4 cm, W4: 2.54 cm, W3: 0.95 cm, W2: 0.64 cm and W1: 0.32 cm) were positioned at various distances from the tank edge (1 cm, 2 cm, 4 cm and 8 cm). The results suggest that the detection of objects less than 1 cm in width is limited to the first 1 to 2 cm from the tank edge for absolute images, but this depth can extend to 8 cm in difference images. Larger 3.4 cm wide objects can be detected in absolute images at depths up to 8 cm from the tank edge. Generally, conductor images were clearer than their nonconductor counterparts. Not only did electrode artefacts lessen as the frequency increased, but the system's maximum resolution was attained at the highest operating frequencies. Although the system recovered the value of the electrical conductivity at the correct order of magnitude, it tended to smooth out large property discontinuities. The calculated electrical permittivity in these phantom studies was inconclusive due to the presence of electrode artefacts.

In this paper, we have proposed a technique for reducing movement artefacts in impedance pneumography by placing six electrodes at appropriate locations and suitably combining the measurements obtained. The strategy for electrode placement was based on the observation that the electrodes appeared to slide over the rib cage along with the skin, during movement. A volume conductor model of the thoracic cavity was developed and movement artefacts were simulated by shifting the electrodes to a different location on the surface. The impedance changes due to movement in one of the measurements of a `symmetrical pair' were 180° out of phase with respect to those observed in the other measurement of that pair. However, the impedance changes due to breathing were in phase in both these measurements. Thus, it was possible to reduce movement artefacts by taking a mean of these measurements without affecting the breathing related changes. The six electrodes could be configured into two such symmetrical pairs. The same observation was made in experimental data recorded from human subjects. This indicated that movement artefacts were caused by sliding of electrodes along with the skin and could be reduced by using the six-electrode configuration.

Magnetic induction tomography (MIT) is a new non-contacting technique for visualization of the electrical impedance distribution inside inhomogeneous media. A measuring system for MIT has been developed. An oscillating magnetic field is applied in the system as a sounding agent. The system is designed mainly for biomedical applications. Experiments demonstrate that with proper selection of measurement conditions it is possible to use the phase shifts between inductor and detector signals for image reconstruction by filtered backprojection along magnetic lines. Measurements with saline filled phantoms having various spatial distributions of conductivity were carried out and images were reconstructed. The experiments have demonstrated the applicability of MIT for medical imaging and diagnostics.

The move from two to three dimensions in the study of electrical impedance tomography (EIT) has generated a great increase in computational demands. It is therefore interesting to investigate ways in which this demand can be reduced, and in this paper we have presented some results of one such approach. The NOSER algorithm was introduced some years ago and we have extended it to include more realistic electrode models. The main feature of the method is that by starting from a uniform conductivity distribution many quantities can be pre-calculated.

We have deployed a recently completed spectroscopic electrical impedance tomography (EITS) imaging system in a small series of women (13 participants accrued to date) in order to investigate the feasibility of delivering EITS breast examinations on a routine basis. Hardware is driven with sinusoidally varying spatial patterns of applied voltage delivered to 16 electrodes over the 10 kHz to 1 MHz spectral range using a radially translating interface which couples the electrodes to the breast through direct contact. Imaging examinations have consisted of the acquisition of multi-channel measurements at ten frequencies on both breasts. Participants lie prone on an examination table with the breast to be imaged pendant in the electrode array that is located below the table. Examinations were comfortable and easy to deliver (about 10 minutes per breast including electrode-positioning time). Although localized near-surface electrode artefacts are evident in the acquired images, several findings have emerged. Permittivity images have generally been more informative than their conductivity counterparts, except in the case of fluid-filled cysts. Specifically, the mammographically normal breast appears to have characteristic absolute EITS permittivity and conductivity images that emerge across subjects. Structural features in the EITS images have correlated with limited clinical information available on participants with benign and malignant abnormality, cysts and scarring from previous lumpectomy and follow-up radiation therapy. Several cases from this preliminary experience are described.

Systematic errors have been measured with a multi-frequency data-collection system operating between 10.24 and 81.92 kHz. The errors were present even though a conventional background measurement on a uniform saline phantom had already been subtracted. Errors due to changes in transimpedance between the calibration and the tissue measurements, cable movement and electrode-skin contact impedance were simulated giving a total systematic error estimate equivalent to a 9% change in tissue conductivity. It was shown that more than 89% of the image was above the total error magnitude, indicating that most of the image revealed true changes in tissue conductivity. In three human subjects, the largest conductivity changes were in two regions, located posteriorly on either side of the midline, and were interpreted as due to the erector spinaemuscles. These regions showed increases in conductivity of 73-104%. Identification of other anatomical features was difficult because of the poor spatial resolution of the images.

A preliminary analysis is presented concerning the use of EIT for detecting impedance inhomogeneities within the human brain. The work to date is centred around the monitoring of two distinct impedance variations: those associated with the application of a carotid clamp during surgery and changes caused by the redistribution of blood flow during auditory stimuli. Using the commercially available Ansoft Maxwell package, a 3D finite element model of the human head has been developed to solve the forward problem. The model is hemispherical in shape and comprises regions of brain, cerebrospinal fluid, skull and skin and includes 16 scalp electrodes each of area 1 cm² . Results from simulations using the model suggest that an EIT system, incorporating diametric current excitation, would require a voltage measurement sensitivity of 100-120 dB in order to detect the impedance variations in the above cases.

In electrical impedance tomography (EIT), an approximation for the internal resistivity distribution is computed based on the knowledge of the injected currents and measured voltages on the surface of the body. The currents spread out in three dimensions and therefore off-plane structures have a significant effect on the reconstructed images. A question arises: how far from the current carrying electrodes should the discretized model of the object be extended? If the model is truncated too near the electrodes, errors are produced in the reconstructed images. On the other hand if the model is extended very far from the electrodes the computational time may become too long in practice. In this paper the model truncation problem is studied with the extended finite element method. Forward solutions obtained using so-called infinite elements, long finite elements and separable long finite elements are compared to the correct solution. The effects of the truncation of the computational domain on the reconstructed images are also discussed and results from the three-dimensional (3D) sensitivity analysis are given. We show that if the finite element method with ordinary elements is used in static 3D EIT, the dimension of the problem can become fairly large if the errors associated with the domain truncation are to be avoided.

Electrical impedance measurements are used to obtain information about a subject, tissue sample or tissue model under test. There are several ways of obtaining these impedance data and thereafter analysing the data to obtain relevant parameters. This paper shows how a completely isolated drive and receive system using current pulses, as opposed to sine waves, achieves good fitted results with resistor-capacitor Cole phantoms.

The transthoracic electrical impedance is an important defibrillation parameter, affecting the defibrillating current amplitude and energy, and therefore the defibrillation efficiency. A close relationship between transthoracic impedance and defibrillation success rate was observed. Pre-shock measurements (using low amplitude high frequency current) of the impedance were considered a solution for selection of adequate shock voltages or for current-based defibrillation dosage. A recent approach, called `impedance-compensating defibrillation' was implemented, where the pulse duration was controlled with respect to the impedance measured during the initial phase of the shock.

These considerations raised our interest in reassessment of the transthoracic impedance characteristics and the corresponding measurement methods. The purpose of this work is to study the variations of the transthoracic impedance by a continuous measurement technique during the defibrillation shock and comparing the data with results obtained by modelling.

Voltage and current impulse waveforms were acquired during cardioversion of patients with atrial fibrillation or flutter. The same type of defibrillation pulse was taken from dogs after induction of fibrillation. The electrodes were located in the anterior position, for both the patients and animals.

Monitoring patients with left ventricular failure can be difficult. Electrical impedance tomography (EIT) produces cross-sectional images of changes in the impedance of the thorax. We measured changes in the electrical impedance of the lung in nine volunteers following a diuretic challenge. The hypothesis was that lung impedance would increase with diuretic induced fluid loss. Heart rate, blood pressure and urine output were also recorded. After diuretic the mean urine output was 1220 ml compared with 187 ml after placebo. Following diuretic administration, mean thoracic impedance increased by 13.6% ( p< 0.01) and lung impedance increased by 7.8% ( p< 0.05). Taken as a group there was a correlation between overall impedance change and total urine output. However, for each individual, the time course of change in impedance and urine output did not correlate significantly. Our findings show that EIT may offer a better guide to the response of the lung to diuretic treatment than simply measuring urine output. The urine output is neither specific nor sensitive in the assessment of lung water. Mean lung impedance, however, is largely determined by lung water. The study showed that lung impedance can be recorded at supra-normal values. EIT may help in the management of patients with excess lung water.

A quality assurance system is essential for the credibility and structured growth of anaesthesiology-based transoesophageal echocardiography (TEE) programmes. We have developed software (Q/A Kappa), involving a 400-line source code, capable of directly reporting kappa correlation coefficient values, using external reviewer interpretations as the `gold standard', and thereby allowing systematic assessment of the validity of intraoperative echocardiographic interpretation. This paper presents assessment of the validity of 240 intraoperative anaesthesiologists' echocardiographic interpretations, and, in addition, the results of field testing of this prototypical software.

Data, derived from consecutive cardiac surgery patients, consisted of standardized two-dimensional transoesophageal echocardiographic, colour flow and Doppler imaging sequences. Intraoperative and off-line `gold standard' TEE interpretations were compared for 19 fields or variables using the Q/A Kappa program.

The kappa correlation coefficients were highly variable and dependent on the examination field, ranging from 0.08 for apical regional wall motion scores to 1.00 for tricuspid regurgitation grade, left atrial measurement, aortic valve anatomy and left ventricular long axis and short axis global function. The correlation coefficients were also operator dependent. These data (480 interpretations) were also manually integrated into the equation required for calculation of values of the variable kappa correlation coefficient. The relationship between Q/A Kappa-derived values and manually calculated values was highly significant (p< 0.001; r= 1.0).

The implications and possible explanations of the results for particular examination fields are discussed. This study also demonstrates successful seamless functioning of this software program from data entry, segmentation into tables and valid statistical analysis. These findings suggest that it is practical to provide sophisticated continuous quality improvement TEE data on a routine basis.

This study was designed to assess, using the echocardiographic acoustic quantification technique, the influence of respiration on left ventricular (LV) function and its modifications connected with the ageing process, quantifying in a non-invasive way the respiratory contribution to the LV volume variability. An automated algorithm is applied to extract the beat-to-beat measurements of LV function parameters from the LV volume signal, obtained from recordings lasting a few minutes. Mean values, amount of variability and spectral content were studied in a population of 17 normal young (mean age 25±1 years) and 12 normal old (mean age 64±2 years) subjects. Mean values of the beat-to-beat measurements of LV function parameters were able to point out alterations connected with the ageing process in peak filling rate, peak atrial filling rate and peak ejection rate. Spectral analysis, applied to the extracted variability series, displayed a predominance of the high-frequency (HF) component corresponding to respiration in all LV function parameters; moreover, age related changes of HF variability were observed in peak ejection rate. The HF power spectrum component of beat-to-beat series extracted from the LV signal can provide a non-invasive assessment of the fluctuations in ventricular parameters associated with respiration.

A simple but highly integrated digital signal processing system is described for real time filtering of biomedical signals. It includes the necessary processing and communications hardware, the processing code itself and a high-level software interface that enables the user to design and download arbitrary finite impulse response filters to the run-time system. The filter coefficients are calculated using the frequency sampling method. Since the filters are realized using a finite impulse response, no phase distortion is introduced into the processed signals. A unique feature of the design is the manner in which the software and hardware components have been organized as an intelligent system, obviating on the part of the user a detailed knowledge of filter design theory or any abilities in processor architecture and assembly code programming.

We have developed a spectroscopy system dedicated to eye banks in order to standardize the evaluation of the donated corneas, with respect to their transparency.

The system for measuring the corneal transmission spectrum basically consists of a conventional spectroscopy single beam optical apparatus, with particularities in order to attend to the needs of the eye banks, having a linear CCD (2048 sensors) as a detector. The range of evaluation of the system is from 400 to 700 nm, which is the range of interest for these kinds of sample (corneas).

Dedicated software has been developed in order to acquire the data from the system and to provide the graphical interface for the user. The software is quite easy to manipulate and provides the diagnostic with respect to the transparency of the cornea, which is based on research done in association with the clinicians of the Eye Bank of Hospital das Clínicas de Ribeirão Preto (Brazil).

The system presents a resolution of 9 nm (which is good enough for this kind of measurement, that presents large bandwidths) and it is in agreement with the spectra obtained from commercial spectrophotometers (the correlation factor between our system and a Beckman DU-70 is 0.995 43 for samples of well defined bandwidths, and 0.989 73 for corneas - large bandwidth).

Electrogastrography (EGG) is a method for recording and analysis of the bioelectrical activity of the stomach, acquired by cutaneous electrodes. The problem of obtaining an EGG signal as free of artefact as possible has recently found some solutions. Good quality recordings of several hours duration can be acquired, often needed, especially if clinical applications are envisaged. Therefore, a next problem to be considered would be time-compressed presentation of the EGG signal without loss of relevant signal characteristics. Relative amplitude changes can be of clinical value, while frequency variations are traditionally regarded as more important.

A method for simple compressed presentation of long term EGG recordings, without losing information about the real amplitude and/or frequency changes or transients, is presented. It makes use of detection of successive wave extrema in an EGG. Successive wave amplitudes and durations are measured and momentaneous frequencies are derived. Then a compressed two-trace plot is generated, representing amplitude and frequency variations with respect to time. The method is virtually insensitive to baseline drift, as only the peak amplitudes are detected and followed. A compression factor with respect to the traditional signal recording (1 cm min^-1or 2 cm min^-1paper speed) of 5 up to 15 per trace can be obtained.

2000

25th Int. Acoustical Imaging Symposium 19 - 22 March, Bristol, UK Contact: The Organiser, 25th IAIS, Medical Physics, Bristol General Hospital, Bristol BS1 6SY

MRI in the 21st Century: Advances in Cardiac MRI, MR Perfusion Imaging and Multimodal Imaging 22 March, London, UK Contact: Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK (www.ipem.org.uk )

Annual Congress of the American Institute of Ultrasound In Medicine (AIUM) 2 - 5 April, San Francisco, USA Contact: AIUM, 14750 Sweitzer Lane, Suite 10, Laurel, MD 20707-5906, USA

Prototype, Design, Modification and Testing of Medical Devices 5 April, York, UK Contact: Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK (www.ipem.org.uk )

6th IPEM Meeting on Clinical Functional Electrical Stimulation 12 - 13 April, Guildford, UK Contact: Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK (www.ipem.org.uk )

9th Congress of World Federation for Ultrasound in Medicine and Biology (WFUMB 2000) 6 - 10 May, Florence, Italy Contact: WFUMB 2000 Secretariat, OSC Bologna, Via S Stefano 30, 40125 Bologna, Italy

NASPE (North American Society of Pacing and Electrophysiology) 21st Annual Scientific Sessions 17 - 20 May, Washington, DC, USA Contact: NASPE, Natick Executive Park, 2 Vision Drive, Natick, MA 01760-2059, USA (www.naspe.org )

AAMI 2000, Annual Meeting of the Association for the Advancement of Medical Instrumentation 3 - 7 June, San Jose, USA Contact: AAMI, 3330 Washington Blvd, Suite 400, Arlington, VA 22201-4598, USA (www.aami.org )

World Congress on Medical Physics and Bioengineering 23 - 28 July, Chicago, USA Contact: AAPM Headquarters, One Physics Ellipse, College Park, MD 20740-3846, USA (www.wc2000.org )

22nd Congress of the European Society of Cardiology 26 - 30 August, Amsterdam, The Netherlands Contact: ECOR, European Heart House, 2035 Route des Colles, Les Templiers BP 179, 06903 Sophia Antipolis Cedex, France (www.escardio.org )

12th Conference of the European Society of Biomechanics 27 - 30 August, Dublin, Ireland Contact: ESB2000-Dublin, Incentive Conference Ireland, 1 Pembroke Place, Ballsbridge, Dublin 4, Ireland (www.mme.tcd.ie/esb2000 )

MEDSIP 2000, International Conference on Advances in Medical Signal and Information Processing 4 - 6 September, Bristol, UK Contact: IEE Conference and Exhibition Services, Savoy Place, London WC2R OBL, UK (www.iee.org.uk/Conf )

6th Annual Conference of the Institute of Physics and Engineering in Medicine 12 - 14 September, Southampton, UK Contact: Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK

9th Congress of the International Society for Holter and Non-invasive Electrocardiology 23 - 27 September, Istanbul, Turkey Contact: Prof Ali Oto, 9th ISHNE, Department of Cardiology, Hacettepe University School of Medicine, 06100 Ankara, Turkey