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Congres International du Traitement du Signal en Electrophysiologie Experimentale et Clinique du Systeme Nerveux Central
CONGRES INTERNATIONAL DU TRAITEMENT ELECTROPHYSIOLOGIE EXPERIMENTALE ET CLINIQUE DU SYSTEME NERVEUX CENTRAL Paris, December 1984,
Dr Court and his staff, of the Centre de Recherches du Service de Sante des Armees, with no little courage assembled a relatively small band of 50 scientists to debate the merits or otherwise of applying numerical methods to the extraction of information from electrophysiological signals, principally from the EEG. It was in every sense a multinational, multidisciplinary and multilingual occasion, on which engineering, mathematics, medicine, physiology, psychology and statistics were all represented. There was general agreement that most clinical interpretations are likely to remain for some time a matter of non-numerate experienced opinion, although emulation of the clinical decision process by means of computers is still a common aim. Apart from its obvious clinical convenience and a lack of clinical/statistical communication problems, there is no clear indication that with so many potentially useful numerate procedures available, this emulation is the most profitable course to choose; new approaches from different disciplines might deserve more support The Hadamard-Haar Transform has been used to follow the time course of EEG activity; it does not demand stationary data and can represent either the activity in one band of one channel, or when linearly combined, the overall activity in all bands of one channel. Principal Components may be used to classify signal shapes, the number of components which need to be calculated being dependent upon the degree of information extraction required; in the case of the ECG 98% of the signal variance can be explained by 6 Principal Components. Linear Splines have shown that alpha rhythm in the EEG is not, as is commonly assumed, ‘almost sinusoidal’ but is composed of a relatively small number of straight line segments, which if written on an ordinary pen recorder, with all its inherent distortions, does become disturbingly like a series of sine waves. Problems related to the size and cost of storage for digital data may be solved in part by the use of ‘source coding’, which was shown to reduce the volume of data by some 75%. Its essential element is a non-linear ADC which instead of having uniform voltage increments per bit, provides a higher resolution for small amplitudes than for the less frequent large amplitudes. Traces were shown of the ‘before’ and ‘after’ effects; the loss due to small variations superimposed on large peaks, and
260
J. Biomed.
Eng.
1985. Vol. 7, July
DU SIGNAL EN
the effect of the process on statistical analyses were not explained. Some EEG laboratories make us of a special head helmet, equipped with moveable electrodes; it is automatically applied to the patient under computer control. Colour ‘brain maps’, but no colour boundary statistics, are produced every 10 s, together with an on-line alpha band spectrum. The extensive use of large remote computers is now relatively common but there seems not yet to be, as is almost inevitable, a move towards the increasingly powerful microcomputers. Suggestions that 16 bit, and even 32 bit, ADCs might have some contribution to make to electrophysiological analysis, were not accompanied by convincing evidence that such a resolution would increase the extractable information content of the EEG, there were those who maintained that for particular occasions a 1 bit ADC would be adequate. A general plea for increased use of digital magnetic recording for primary data stores fails to take account of the trend in modern magnetic tape technology, in which 12 bit analogue data are written ‘digitally’ across the tape on 12tracks, with a very high packing density; from these “analogue” recorders a digital output is simultaneously available - the best of all worlds. In spite of the many advanced topics discussed, common sense was not absent Statistical procedures demand assumptions, which must be matched to conditions associated with the data; if such procedures can be justifiably criticized then either the assumptions or the conditions are wrong. Reliance on statistics to the exclusion of common sense is to be deprecated, although it was difficult to agree with one cynic who maintained that statistics was ‘80% good fortune and 20% hopeful anticipation’. Avoid replacing one picture (the EEG) with another but more attractive one (e.g. coloured brain maps) from which only another opinion can be obtained; the numbers from which v.d.u. pictures are produced are readily accessible and can be used to derive a numerical ‘opinion’ and its associated probability. The production of high resolution spectra is a technical triviality, but its justification is difficult and the poor statistical confidence with which they are associated render false witness to the facts. Naturally many controversial issues were not resolved, in particular the suggestion that a dynamic spatial analysis should take precedence over the more conventional analyses as a function of time. A detailed examination of amplitude, frequency and phase in
the EEG is unjustified since almost invariably little is known of the complex phase response of the tortuous electronic pathway through which the signal passes. The large variance of high definition spectral estimates permits only a low confidence. Most of those who work in the EEG world have grown accustomed to differences amongst clinicians over the interpretation of clinical records; it came as something of a surprise to find argument and similar differences of opinion among statisticians discussing the validity and interpretation of their results. Discussion was brisk and uninhibited, one of the advantages of a small group, but above all considerable credit must go to the omnipresent but rarely seen simultaneous interpreters. To translate medicine, physiology and psychology is no doubt difficult, as is the translation of mathematics and
engineering, but to combine all in a simultaneous three language translation, when on occasions the speaker is not using his native language, merits the highest appreciation; without that competent service the conference would not have been the success it certainly was. Dr. Court deserves the thanks of all for the conference organisation. Much more was discussed than is reported here, enquiries concerning the abstracts should be addressed to Monsieur le Medecin en Chef L Court, Division de Radiobiologie e Radioprotection, Centre de Recherches du Service de Sante Armees, 1 bis rue due Lieutenant Raoul Batany, 92 14 1 Clamart, France. The complete papers will be published in book form in English. GH. Bvford
ACOUSTICAL IMAGING Eds M. Kaveh, E.K. Mueller
and J.F. Greenleaf
Plenum Publishing Co?-, New York, 1984, $89.50 This volume of papers is the proceedings of the 13 th International Symposium on Acoustical Imaging held in Minneapolis in October 1983. Some 48 papers are included covering such topics as the theory of acoustic propagation and scattering, the theory of image reconstruction, tissue and material characterization, acoustic microscopy, transducers, imaging systems and signal processing. Apart from six papers which, regrettably, are in abstract form only, the length of the contributions are quite reasonable, typically 15 pages. The quality of the copy is variable since this volume was assembled from submitted manuscripts using photocopy techniques but on the whole is good. These proceedings along with the proceedings from the twelve preceding symposia clearly form an important source of information for anyone working in this area This volume identifies the principal problem areas currently of interest. However, there are no review papers and none of the contributions can be considered to be introductory in nature so this volume would not be easy reading for a novice in this field. The general scientific standard of the contributions to these proceedings appears high. The content of such a volume is determined partly by the selection committee but largely by the nature of the papers submitted to the symposium. Such a volume should therefore reflect reasonably accurately the current state of the subject. What is interesting about this volume is that for a book on imaging it contains relatively few images and most of those that are included are either from simulated data or from data taken from laboratory
phantoms. In fact the whole volume is heavy with theory and light on practice. The reason for this situation is not really tackled by any of the authors but is I suspect due to the coupling problem. The problem of coupling the transducer to the medium being investigated is a fundamental problem with acoustical imaging, especially in the medical field and especially if large area transducers (or scanning transducers) are being used as in the case of coherent imaging techniques or tomographic techniques. Using a water bath is rarely satisfactory, especially for routine medical applications. The most successful acoustical imaging technique to date, that of pulsed echo imaging has achieved its success largely because the coupling roblem has been solved for this method. The de Pects of this technique are well known, especially the fact that it does not achieve the resolution theoretically possible for the wavelengths being used and it is not possible to quantitatively extract information such as attenuation from the detected signals, but poor images are better than none. The only paper in this volume which arrives close to appreciating this point is that of Leeman and Jones. It is clear that more attention needs to be given to imaging techniques which only require a limited amount of coupling if acoustical imaging is to realise its full potential. Nevertheless, having made this point, this volume shows that the field of acoustical imaging is clearly a very active one and this book is essential reading for workers in this area They can reasonably look forward to the proceedings of the 14th Symposium with pleasurable anticipation. D. C. Barber Royal Hallamshire Hospital Shzfield
J. Biomed.
Eng. 1985, Vol. 7, July
261
Dr Court and his staff, of the Centre de Recherches du Service de Sante des Armees, with no little courage assembled a relatively small band of 50 scientists to debate the merits or otherwise of applying numerical methods to the extraction of information from electrophysiological signals, principally from the EEG. It was in every sense a multinational, multidisciplinary and multilingual occasion, on which engineering, mathematics, medicine, physiology, psychology and statistics were all represented. There was general agreement that most clinical interpretations are likely to remain for some time a matter of non-numerate experienced opinion, although emulation of the clinical decision process by means of computers is still a common aim. Apart from its obvious clinical convenience and a lack of clinical/statistical communication problems, there is no clear indication that with so many potentially useful numerate procedures available, this emulation is the most profitable course to choose; new approaches from different disciplines might deserve more support The Hadamard-Haar Transform has been used to follow the time course of EEG activity; it does not demand stationary data and can represent either the activity in one band of one channel, or when linearly combined, the overall activity in all bands of one channel. Principal Components may be used to classify signal shapes, the number of components which need to be calculated being dependent upon the degree of information extraction required; in the case of the ECG 98% of the signal variance can be explained by 6 Principal Components. Linear Splines have shown that alpha rhythm in the EEG is not, as is commonly assumed, ‘almost sinusoidal’ but is composed of a relatively small number of straight line segments, which if written on an ordinary pen recorder, with all its inherent distortions, does become disturbingly like a series of sine waves. Problems related to the size and cost of storage for digital data may be solved in part by the use of ‘source coding’, which was shown to reduce the volume of data by some 75%. Its essential element is a non-linear ADC which instead of having uniform voltage increments per bit, provides a higher resolution for small amplitudes than for the less frequent large amplitudes. Traces were shown of the ‘before’ and ‘after’ effects; the loss due to small variations superimposed on large peaks, and
260
J. Biomed.
Eng.
1985. Vol. 7, July
DU SIGNAL EN
the effect of the process on statistical analyses were not explained. Some EEG laboratories make us of a special head helmet, equipped with moveable electrodes; it is automatically applied to the patient under computer control. Colour ‘brain maps’, but no colour boundary statistics, are produced every 10 s, together with an on-line alpha band spectrum. The extensive use of large remote computers is now relatively common but there seems not yet to be, as is almost inevitable, a move towards the increasingly powerful microcomputers. Suggestions that 16 bit, and even 32 bit, ADCs might have some contribution to make to electrophysiological analysis, were not accompanied by convincing evidence that such a resolution would increase the extractable information content of the EEG, there were those who maintained that for particular occasions a 1 bit ADC would be adequate. A general plea for increased use of digital magnetic recording for primary data stores fails to take account of the trend in modern magnetic tape technology, in which 12 bit analogue data are written ‘digitally’ across the tape on 12tracks, with a very high packing density; from these “analogue” recorders a digital output is simultaneously available - the best of all worlds. In spite of the many advanced topics discussed, common sense was not absent Statistical procedures demand assumptions, which must be matched to conditions associated with the data; if such procedures can be justifiably criticized then either the assumptions or the conditions are wrong. Reliance on statistics to the exclusion of common sense is to be deprecated, although it was difficult to agree with one cynic who maintained that statistics was ‘80% good fortune and 20% hopeful anticipation’. Avoid replacing one picture (the EEG) with another but more attractive one (e.g. coloured brain maps) from which only another opinion can be obtained; the numbers from which v.d.u. pictures are produced are readily accessible and can be used to derive a numerical ‘opinion’ and its associated probability. The production of high resolution spectra is a technical triviality, but its justification is difficult and the poor statistical confidence with which they are associated render false witness to the facts. Naturally many controversial issues were not resolved, in particular the suggestion that a dynamic spatial analysis should take precedence over the more conventional analyses as a function of time. A detailed examination of amplitude, frequency and phase in
the EEG is unjustified since almost invariably little is known of the complex phase response of the tortuous electronic pathway through which the signal passes. The large variance of high definition spectral estimates permits only a low confidence. Most of those who work in the EEG world have grown accustomed to differences amongst clinicians over the interpretation of clinical records; it came as something of a surprise to find argument and similar differences of opinion among statisticians discussing the validity and interpretation of their results. Discussion was brisk and uninhibited, one of the advantages of a small group, but above all considerable credit must go to the omnipresent but rarely seen simultaneous interpreters. To translate medicine, physiology and psychology is no doubt difficult, as is the translation of mathematics and
engineering, but to combine all in a simultaneous three language translation, when on occasions the speaker is not using his native language, merits the highest appreciation; without that competent service the conference would not have been the success it certainly was. Dr. Court deserves the thanks of all for the conference organisation. Much more was discussed than is reported here, enquiries concerning the abstracts should be addressed to Monsieur le Medecin en Chef L Court, Division de Radiobiologie e Radioprotection, Centre de Recherches du Service de Sante Armees, 1 bis rue due Lieutenant Raoul Batany, 92 14 1 Clamart, France. The complete papers will be published in book form in English. GH. Bvford
ACOUSTICAL IMAGING Eds M. Kaveh, E.K. Mueller
and J.F. Greenleaf
Plenum Publishing Co?-, New York, 1984, $89.50 This volume of papers is the proceedings of the 13 th International Symposium on Acoustical Imaging held in Minneapolis in October 1983. Some 48 papers are included covering such topics as the theory of acoustic propagation and scattering, the theory of image reconstruction, tissue and material characterization, acoustic microscopy, transducers, imaging systems and signal processing. Apart from six papers which, regrettably, are in abstract form only, the length of the contributions are quite reasonable, typically 15 pages. The quality of the copy is variable since this volume was assembled from submitted manuscripts using photocopy techniques but on the whole is good. These proceedings along with the proceedings from the twelve preceding symposia clearly form an important source of information for anyone working in this area This volume identifies the principal problem areas currently of interest. However, there are no review papers and none of the contributions can be considered to be introductory in nature so this volume would not be easy reading for a novice in this field. The general scientific standard of the contributions to these proceedings appears high. The content of such a volume is determined partly by the selection committee but largely by the nature of the papers submitted to the symposium. Such a volume should therefore reflect reasonably accurately the current state of the subject. What is interesting about this volume is that for a book on imaging it contains relatively few images and most of those that are included are either from simulated data or from data taken from laboratory
phantoms. In fact the whole volume is heavy with theory and light on practice. The reason for this situation is not really tackled by any of the authors but is I suspect due to the coupling problem. The problem of coupling the transducer to the medium being investigated is a fundamental problem with acoustical imaging, especially in the medical field and especially if large area transducers (or scanning transducers) are being used as in the case of coherent imaging techniques or tomographic techniques. Using a water bath is rarely satisfactory, especially for routine medical applications. The most successful acoustical imaging technique to date, that of pulsed echo imaging has achieved its success largely because the coupling roblem has been solved for this method. The de Pects of this technique are well known, especially the fact that it does not achieve the resolution theoretically possible for the wavelengths being used and it is not possible to quantitatively extract information such as attenuation from the detected signals, but poor images are better than none. The only paper in this volume which arrives close to appreciating this point is that of Leeman and Jones. It is clear that more attention needs to be given to imaging techniques which only require a limited amount of coupling if acoustical imaging is to realise its full potential. Nevertheless, having made this point, this volume shows that the field of acoustical imaging is clearly a very active one and this book is essential reading for workers in this area They can reasonably look forward to the proceedings of the 14th Symposium with pleasurable anticipation. D. C. Barber Royal Hallamshire Hospital Shzfield
J. Biomed.
Eng. 1985, Vol. 7, July
261