Table of contents

Retinal imaging with a confocal scanning laser ophthalmoscope (cSLO) involves scanning a small laser beam over the retina and constructing an image from the reflected light. By applying the confocal principle, tomographic images can be produced. However, the thickness of such slices, when compared with the retinal thickness, is too large to give useful 3D retinal images.

In this study an algorithm has been developed which fits a double Gaussian curve to the axial intensity profiles generated from a stack of image slices. The underlying assumption is that the laser light has mainly been reflected by two structures in the retina, the internal limiting membrane and the retinal pigment epithelium. From the fitted curve, topographic images and novel thickness images of the retina can be generated.

The technique has been applied to three normal volunteers and seven patients with macular pathology (cystoid macular oedema and macular hole) demonstrating the clinical value of the technique. The improvement in accuracy achieved by using a double rather than a single Gaussian is also demonstrated.

Keywords: confocal, scanning laser ophthalmoscope, reconstruction, tomographic imaging

The airflow perturbation device (APD) is an instrument for the measurement of respiratory resistance. The APD is small, lightweight, fast and requires no special breathing manoeuvres. Airflow perturbation determines resistance by superimposing a periodic signal onto spontaneous breathing with a variable resistance device. Respiratory impedance is the ratio of magnitude of pressure perturbation to magnitude of flow perturbation, and respiratory resistance is the in-phase portion of respiratory impedance. The APD was tested to determine its responses to repeated resistance measurements and to changes in resistance. A mechanical model test showed that the APD could detect increased resistance levels, but overestimated resistance when resistance increased with flow. Tests with human subjects showed that the APD gave results consistent from day to day, was able to detect added resistances, and gave resistance values correlated with airway resistance values obtained by body plethysmography. Accelerometers placed on the chests of the subjects showed that perturbations extend to the chest surface. Thus, the APD must measure total respiratory resistance.

Keywords: respiration, resistance

A system for noninvasive assessment of an all-inclusive function of respiratory muscles at different lung volumes is presented. The apparatus was based on the interrupter technique and facilitated simultaneous measurements of mouth pressure and airflow rate during dynamic or quasi-static manoeuvres. In this study, mouth pressure values were continuously acquired during and after interruption of a forced inspiratory or expiratory manoeuvre for as long as the subject could sustain an elevated mouth pressure against the obstructed opening. These measurements provided information on both muscle strength and power. A total of 420 forced maximal inspiratory and expiratory manoeuvres performed by six healthy subjects were monitored at different lung volumes. The pattern of maximal pressure-time curves was consistent for the same subject regardless of lung volume. Similar values of maximal mouth pressure can be generated by healthy subjects by using either a flange-style mouthpiece or facial mask. For both methods mouth pressure shows a significant ( p < 0.05) second order dependency on lung volume for both inspiration and expiration. The standard deviation of measurements from a single subject about a second order curve is of the order of 5-15%. The findings of interchangeability between methods of measurement may be useful in allegedly non-compliant patients.

Keywords: mouth pressure, respiratory muscle strength, respiratory muscle endurance, interrupter technique

In a previous paper we introduced a non-invasive respiratory monitoring system (NIRMS) for monitoring respiratory movements during sleep. Unlike standard sleep laboratory methods, the NIRMS can be used in frail older adults to describe breathing patterns during sleep that will mark individuals with declining neurological function. The present study evaluates the use of the NIRMS as a respiratory monitor and identifies variables that can reliably detect changes in breathing patterns and the presence of other body movements.

Data were obtained from eleven healthy adults (six women, five men) whose body mass indices ranged from 20 to , and whose baseline respiratory rates ranged from 4 to 19 breaths per minute. We evaluated three variables derived from frequency and amplitude measurements of the NIRMS: (1) the interval between breathing cycles (the interbreath interval or IBI); (2) the period between breathing cycles (the interbreath frequency or IBF); and (3) the amplitude of breath cycles (AMP).

The frequency of NIRMS waveform deflections correlated highly with the frequency of visually observed chest movements ( r = 0.99). Compared with a subject's baseline, a standard deviation of IBI > 3.0 s consistently identified time segments with three or more apnoeic events. The IBF and AMP differentiated respiratory from other body movements. An IBF > 20 cycles/s or an AMP > 0.4 V identified experimentally introduced body movements much more accurately than wrist accelerometry (NIRMS detected 99% of events, ; WA detected 50%, ). These findings support the use of the NIRMS in monitoring changes in breathing patterns during sleep, especially in frail and cognitively impaired subjects.

Keywords: breathing, movements, non-invasive monitoring device, sleep, older adults

Microlightguide measurements of the spectral composition of backscattered light may be used to determine local tissue oxygen saturation and monitor tissue perfusion using intravenous injection of fluorescein dye as a contrast agent. We have used a combination of microlightguide spectrophotometry and microendoscopy to measure intravascular oxygen saturation (%) and monitor blood flow in the sciatic nerve of 12 healthy male Sprague-Dawley rats. The microlightguide and endoscope combination is a relatively new measurement technique. The aims of this study were to determine whether microlightguide spectrophotometry and microendoscopy could be used to measure and blood flow in peripheral nerves and to compare the measurements made using the flexible lightguide with the endoscope-lightguide combination. We found no significant difference between the two types of measurement over similar regions of the nerve, mean % values 77.1% (95% CI = 75.4-78.8) and 78.8% (95% CI = 77.5-80.1) respectively. During a period of hypoxia there was a similar fall in both arterial and nerve oxygen saturation. Following injection of fluorescein, the rate of increase in nerve fluorescence was used as a measure of perfusion. The combination of microlightguide spectrophotometry and microendoscopy allows the exact site of measurement to be directly visualized. The minimally invasive nature of this technique may allow its application to the study of peripheral nerves in human subjects in conditions such as diabetic neuropathy where vascular factors are thought to have an important role in aetiology.

Keywords: lightguide, oxygen saturation, spectrophotometry, peripheral nerve

A convenient and simple method of measuring cerebral blood volume (CBV) will aid in the clinical management of patients with cerebrovascular diseases and head trauma. Using a two-compartment model to characterize the distribution of x-ray contrast agent in the brain, we have developed a non-equilibrium (dynamic) x-ray CT method to measure CBV and have applied this method to study the effects of isoflurane.

CBV and cerebral blood flow (CBF, ex vivo) measurements were made in two groups of New Zealand White rabbits at varying (study group) and constant (control group) arterial concentration. ANOVA for repeated measures was used on the control data to determine the precision of our two-compartment CT-CBV method. The results showed that the precision of our CT-CBV measurement was 9.8%. In addition a paired t-test analysis of the control data revealed that the duration of isoflurane anaesthesia had no effect on the repeated measurements of CBV or CBF. The rate of change in CBV (0.049 ml/100 g/mmHg) and CBF (6.2 ml/min/100 g/mmHg) with respect to changes in arterial concentration under the influence of isoflurane anaesthesia was similar to those reported in previous studies, thus validating our experimental CT-CBV and CBF measurements. Our CT-CBV method will lead to more information on the relationship between CBV and CBF under different pharmacological interventions in both normal and disease conditions.

Keywords: cerebral blood volume, CT, isoflurane, contrast

Image reconstruction in electrical impedance tomography using the sensitivity theorem is generally based on the assumption that the initial conductivity distribution of the body being imaged is uniform. The technique of image reconstruction using this method is described and reconstructed images are presented. Improvements in image quality and accuracy are demonstrated when accurate a priori `anatomical' information, in the form of a model of the distribution of conductivity within the region to be imaged, is used to construct the sensitivity matrix. In practice correct a priori information is not available, for example the conductivity values within the various anatomical regions will not be known. An iterative algorithm is presented which allows the conductivity parameters of the a priori model to be determined during reconstruction.

Keywords: electrical impedance tomography, image reconstruction, a priori information

Temporal changes in the impedance spectra of bioelectrodes in contact with skin provide useful data for comparisons between differing electrode materials and skin preparation methods. Traditional impedance measuring systems employ swept frequency methods which will distort results in the impedance spectra of a sample which has nonstationary electrical characteristics. The system reported here obtains impedance spectra by applying a digitally constructed waveform consisting of many frequency components. This allows impedance values to be measured at a number of frequencies simultaneously. Sample data are provided and compared with data obtained using similar square wave techniques.

Keywords: skin, electrode, bioimpedance, spectroscopy

Bioelectrical impedance spectroscopy has become a widely used method with various applications in physiological and clinical investigations. Its measurement results are often analysed using the Cole-Cole model in an attempt to relate its parameters to structural or physiological characteristics of the studied object.

The model parameter values are usually assessed by nonlinear curve fitting based on the least mean square method. A new approach is proposed, leading to better accuracy. It is based on the notion that the difference between measured and model parameter values is randomly distributed with zero mean. The values of the unknown parameters are then deduced by minimizing the covariance matrix determinant. This method can be considered as a minimization of the volume of an ellipsoid, or a joint minimization of two regressions having the same argument and common parameters.

Keywords: bioelectrical impedance analysis, Cole-Cole model, nonlinear curve fitting

The book seems to be useful as an answer to how and where to begin with applications of Monte Carlo calculations in nuclear medicine imaging.

It includes basic principles of gamma cameras (SPECT and PET), but basic principles of Monte Carlo calculations are presented just for physicist; physicians interested in the field must find adequate references. From the other side, the basics of nuclear medicine instrumentation are given with plenty of physical insight.

The majority of the chapters are written with a clear, uniform level; they are well linked, and the editors' work is evident.

Authors demonstrate how efficient Monte Carlo simulation packages have allowed the study of scatter for more realistic activity distributions and attenuation maps, and according to a variety of physical parameters. Some of the packages commented on are:

(1) SIMSET. For SPECT and PET. PET collimators simulation based on the PETSIM code. This program is under continuous development to include improvements in several physical effects and simulation of SPECT collimators and detectors.

(2) MCMATV3D. A vectorized Monte Carlo code for phantom transport in heterogeneous media. Useful, for example, to study nonuniform attenuation compensation for simulated SPECT studies and to evaluate scatter subtraction methods in nonuniform media.

(3) SIMSPECT. This validated code models tomographic imaging from nonuniform, asymmetric radionuclide source geometries. Can be used to investigate collimator geometric response including cone beam; positron emitters in SPECT can also be modelled with SIMSPECT. The code is suited to examining different collimator designs (materials and dimensions) and considering `contamination' of images by higher energy photons.

(4) SIMIND. This program simulates clinical SPECT cameras including different types of detector parameters and has the capability to simulate transmission sources. Research works performed with SIMIND are commented on: comparison of different scatter corrections techniques, multiple windows scatter correction methods, high-count-rate detector response, transmission SPECT, downscatter and properties of collimators.

Even if some important applications, such as the evaluation of iterative reconstruction scatter compensation, deserve more space, the authors show that Monte Carlo simulation is valuable for development, testing and comparison of scatter correction models in nuclear medicine tomographic imaging.

The problem of image quality degradation when imaging a radionuclide with multiple emissions (111-In, 123-I, 67-Ga), or when acquiring simultaneous dual isotope images, is considered in relation to the design of specific collimators. A Monte Carlo simulation of photon transport that accounts for penetration of and scatter in the collimator is discussed. One of the codes presented to face this problem has been adapted for use with the SIMIND Monte Carlo code. Another one combines a theoretical, Bayesian observer model with the Monte Carlo numerical tool.

It would be useful to know how and which of the analysed Monte Carlo methods and results are (or could be) applied in multiple head detector commercial systems. One always tries to recognize reconstructed artefacts in relation to attenuation and scatter corrections methods applied by different brands and models.

The Monte Carlo tool could be an economical way to initiate technological developments of, for example, collimators or crystal design and materials or detectors geometries.

Monte Carlo is presented as a useful method both for evaluating existing PET scanners and in designing new ones. The Monte Carlo technique is also applied to scatter correction for quantitative 3D-PET. Simulations of a wide variety of count rates and source distributions are essential to manufacturers, and it is shown how Monte Carlo could be a way to evaluate the performance of PET systems under such conditions. The presented program PETSIM includes independent programs for activity distribution, collimator and detector array. The results obtained are useful in designing block detectors and PET geometries for new systems.

The Oxygen Transport to Tissue series (that, with the present publication, has reached the XIXth volume) has become a `classic' for those interested in the field of transport to and utilization by tissues and organs. The present volume summarizes the proceedings of the 24th Annual Meeting of the International Society on Oxygen Transport to Tissue (August 19-23, 1996, Dundee, Scotland) and compares favourably with previous ones of the same series. The volume covers aspects ranging from molecular/cellular biology to tissue/organ oxygenation, in different conditions. Emphasis is given to `cutting edge' technological advances in the field (related to near-infrared spectroscopy, nuclear magnetic resonance spectroscopy and imaging, electron paramagnetic resonance, and others), as well as to their application to the evaluation of various physiological and pathological conditions, such as muscular exercise, peripheral vascular diseases, neoplastic disorders, hypoxia and hyperoxia. Recent advancements in research on the systemic and local mechanisms of regulation of transport and utilization are reported. Sections of the book deal with specific organs, such as heart, lung, skeletal muscle and brain. A section on the effects of fluorocarbons on transport and utilization is also included. The book appears to be of value to scientists interested in the study of basic physiological and pathophysiological mechanisms, as well as for research-oriented clinicians.

This book complements the many texts on nuclear medicine imaging, and offers a unified approach to the use of radionuclides for quantifying physiological processes. The first few chapters are concerned with general principles, first presenting a review of the underlying mathematical concepts, then dealing in turn with transit time and clearance measurements, blood flow, pharmacokinetics, the technology of scintillation detectors and problems of data processing. Following chapters are concerned with accounts of how these principles can be applied to the various organ systems of the body, dealing in turn with the peripheral circulation, the heart, the lung, the gastro-intestinal system, blood and the spleen, the genito-urinary system and the brain. The concluding chapter deals with body fluids, electrolytes and bone. The authors, radiologist and clinical scientist respectively, and both from Hammersmith Hospital, London, have endeavoured to maintain consistency of terminology and approach throughout, particularly where symbols and format of equations are concerned. Certain symbols will be encountered which are not those conventionally associated with the variable in question, but this been done to aid understanding and to create a unified framework for the measurements discussed. While the book will be of interest to clinical practitioners, it will be of greater interest to scientist and researchers who have not previously had access to as thorough and complete an account of quantitative methods as is contained in this book.

Send notice of meetings to: Dr S J Meldrum, Norfolk and Norwich Hospital, Norwich NR1 3SR

1999 Physics and Technology of Medical Ultrasound 30-31 March, York, UK Contact: Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK

Technical and User Training for Medical Equipment 6 May, York, UK Contact: Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK

NASPE (North American Society of Pacing and Electrophysiology) 20th Annual Scientific Sessions 12-15 May, Toronto, Canada Contact: NASPE, Natick Executive Park, 2 Vision Drive, Natick, MA 01760-2059, USA (http://www.naspe.org)

7th World Congress on Heart Failure: Mechanisms and Management 23-26 May, Montreal, Canada Contact: World Congress on Heart Failure, PO Box 17659, Beverly Hill, CA 90209, USA

AAMI 99, Annual Meeting of the Association for the Advancement of Medical Instrumentation 5-9 June, Boston, USA Contact: AAMI, 3330 Washington Blvd, Suite 400, Arlington, VA 22201-4598, USA (http://www.aami.org)

11th Nordic Baltic Conference on Biomedical Engineering 6-10 June, Tallinn, Estonia Contact: 11th NBCBME, Biomedical Engineering Center, Tallinn Technical University, 5 Ehitajate Road, EE0026 Tallinn, Estonia (e-mail: nbc99@bmt.cb.ttu.ee; http://www.cb.ttu.ee/nbc99)

Measurements and Simulation in Musculo-Skeletal Biomechanics 11 June, London, UK Contact: Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK

Third International Workshop on Biosignal Interpretation 12-14 June, Chicago, USA Contact: BSI99, EECS Department, MC-154 University of Illinois at Chicago, 851 South Morgan Street, Chicago, IL 60607, USA (http://www.eecs.uic.edu/ bsi99/)

XI World Symposium on Cardiac Pacing and Electrophysiology 27-30 June, Berlin, Germany Contact: Eurokongress, Rosental 3, D-80331, Munich, Germany

21st Congress of the European Society of Cardiology 28 August-1 September, Barcelona, Spain Contact: ECOR, European Heart House, 2035 Route des Colles, Les Templiers BP 179, 06903 Sophia Antipolis Cedex, France (http://www.escardio.org)

5th Annual Conference of the Institute of Physics and Engineering in Medicine 7-9 September, Nottingham, UK Contact: Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK

9th International Conference on Artificial Neural Networks 7-10 September, Edinburgh, UK Contact: ICANN 99, IEE Conference and Exhibition Services, Savoy Place, London WC2R 0BL (E-mail: icann99@iee.org.uk)

Ultrasound '99 26-29 September, Berlin, Germany Contact: CPO Hanser Service GmbH, Schaumburgallee 12, D-14052, Berlin, Germany (http://www.cpo-hanser.de)

Computers in Cardiology 26-29 September, Hannover, Germany Contact: Prof Christoph Zywietz, Medizinische Hochschule, Biosignalverarbeitung-8440, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany (e-mail: Zywietz.Christoph@MH-Hannover.de)