Conservation and characterisation of spatial features in a new method of data compression for body surface potential maps

Body surface potential maps consist of a huge amount of data represented as a series of three-dimensional maps, which are time consuming to process and expensive to store. In spite of the continuous interest in body surface potential maps, their use has not become common and they are of no practical use in the clinics. This is due to the overwhelming amount of measured data required to generate the maps and the lack of quantitative methods to analyse them. Data compression or reduction may solve these deficiencies. Such a procedure must conserve the fine spatial details of the maps, which are usually extracted from low level surface potentials, as these are reported to be significant in diagnostic electrocardiography. A technique is presented for data reduction, that implements two-level thresholding and conserves the fine significant spatial features of each map. A sequence of annuli thus produced is shown to describe the dynamic nature of the underlying process. This sequence is further processed and characterised by features which quantify its dynamic behaviour: time of annuli sequence appearance, its duration, three-dimensional loci of centres of mass of the annuli, distances between successive centres of mass and cross-correlation coefficients between successive annuli. To test the data reduction procedure and the usefulness of the features, maps from 20 subjects are studied (both normal patients and those with various pathologies). It is found that the use of annuli instead of the whole measured information allows simple storage, display and calculations; the features, which vary in time, represent closely the changes in location of the annuli and their dynamic variations of shape. The features are also found to be grouped together for the maps of the normal patients and for each pathology Thus, body surface potential maps may become more commonly used in clinics by being represented by a set of features, which conserve their dynamic and spatial nature, and which may serve for classification of cardiac pathologies.     

Body surface mapping of cardiac activity after partial left ventriculectomy

MECG measurements were performed using 35 electrodes in 10 patients operated with partial left ventriculectomy (PLV). Body surface ECG signals were recorded and five measurements were done: prior to PLV, second, third, fourth and fifth postoperative day. This work was concentrated on the following mapping methods: average isopotential ST segment maps (STM), QRS interval isointegral maps (QRM) and isochronal activation maps (IAM). STMs of the patients show a great positive area (elevation) over the anterior aspect of the heart and a great negative area (depression) over the lateral and posterior aspect of the heart before the operation. After the operation, the ST elevation over the anterior, lateral and posterior aspect of the heart was reduced. A substantial positive value over the excised area of the heart was present also on the end of the postoperative monitoring interval. Minimal and maximal values of the QRMs were smaller and also show some kind of normalisation. The area of the left ventricle, where PLV was performed, was carefully analysed for any changes of activation time for different heart regions. IAMs indicate that the start of the first activation was quite stable and in accordance with the position of the QRMs minimum.     

Computer analysis of multichannel ECG

Multichannel electrocardiography (MECG) is an extension of the conventional electrocardiography that is aimed at refining the non-invasive characterisation of cardiac activity. Body surface mapping is a graphical presentation of cardiac activity as measured from the body surface. Body surface maps can show the distribution of the potential at a selected moment in time or over a specified time interval. A new family of maps, based on the characteristics derived from the complete analysed beat, is described. Some new computer supported methods, which are able to calculate automatically different temporal maps, are proposed. MECG measurements can be seen in this context as a powerful research and clinical tool for improving the resolution of cardiac measurements.     

Low-power electrocardiographic data-acquisition module for microprocessor systems

The advantages of a portable microcomputer system for e.c.g. studies is stressed. A data-acquisition system was interfaced with two different microcomputers (the Motorola 6800 and the Intersil 6100 based systems), and both systems were successfully applied to the acceptance and processing of e.c.g. signals from subjects. The data-acquisition module interfaced with the Intersil 6100 central processor was found to draw very low power and was completely battery operated. This system could be used as a portable device for recording e.c.g.s from ambulatory patients. The system was designed to conform to present AHA standards and provides real-time e.c.g. signal processing. Several e.c.g. signals are exhibited to show the performance of the system. The e.c.g.s. that were processed and stored in the microcomputer memory are displayed alongside the original e.c.g.s to show that complete e.c.g. information is available subsequent to the data processing.     

Effect of cardiac motion on body surface electrocardiographic potentials: an MRI-based simulation study

This paper describes an electrical model of cardiac ventricles incorporating real geometry and motion. The heart anatomy and its motion through the cardiac cycle are obtained from segmentations of multiple-slice MRI time sequences; the special conduction system is constructed using an automated mapping procedure from an existing static heart model. The heart model is mounted in an anatomically realistic voxel model of the human body. The cardiac electrical source and surface potentials are determined numerically using both a finite-difference scheme and a boundary-element method with the incorporation of the motion of the heart. The electrocardiograms (ECG) and body surface potential maps are calculated and compared to the static simulation in the resting heart. The simulations demonstrate that introducing motion into the cardiac model modifies the ECG signals, with the most obvious change occurring during the T-wave at peak contraction of the ventricles. Body surface potential maps differ in some local positions during the T-wave, which may be of importance to a number of cardiac models, including those incorporating inverse methods.     

Human body surface area: measurement and prediction using three dimensional body scans

The development of three dimensional laser scanning technology and sophisticated graphics editing software have allowed an alternative and potentially more accurate determination of body surface area (BSA). Raw whole-body scans of 641 adults (395 men and 246 women) were obtained from the anthropometric data base of the Civilian American and European Surface Anthropometry Resource project. Following surface restoration of the scans (i.e. patching and smoothing), BSA was calculated. A representative subset of the entire sample population involving 12 men and 12 women (G24) was selected for detailed measurements of hand surface area (SA_hand) and ratios of surface area to volume (SA/VOL) of various body segments. Regression equations involving wrist circumference and arm length were used to predict SA_hand of the remaining population. The overall [mean (SD)] of BSA were 2.03 (0.19) and 1.73 (0.19) m² for men and women, respectively. Various prediction equations were tested and although most predicted the measured BSA reasonably closely, residual analysis revealed an overprediction with increasing body size in most cases. Separate non-linear regressions for each sex yielded the following best-fit equations (with root mean square errors of about 1.3%): BSA (cm<SUP>2</SUP>)=128.1·<I>m</I><SUP>0.44</SUP>·<I>h</I><SUP>0.60</SUP>for men and BSA=147.4·<I>m</I><SUP>0.47</SUP>·<I>h</I><SUP>0.55</SUP>for women, where m, body mass, is in kilograms and h, height, is in centimetres. The SA/VOL ratios of the various body segments were higher for the women compared to the men of G24, significantly for the head plus neck (by 7%), torso (19%), upper arms (15%), forearms (20%), hands (18%), and feet (11%). The SA/VOL for both sexes ranged from approximately 12·m^–1 for the pelvic region to 104–123·m^–1 for the hands, and shape differences were a factor for the torso and lower leg. Electronic Publication     

Assessment of spatial resolution of pace mapping when using body surface potentials

Using computer simulations and statistical methods, the resolution of pace mapping when used in combination with body surface potentials was systematically investigated. In an anatomical model of the human ventricular myocardium, pre-excitation sequences were initiated at 69 sites positioned along the atrioventricular (AV) ring and corresponding body surface potential maps (BSPMs) were calculated at 32 leads placed on the anterior torso. For each time after the onset of pre-excitation (every 4 ms to 40 ms) and each root-mean-square (RMS) noise level (5, 10, 20 and 50 microV), BSPMs were cros-correlated and the spatial resolution defined as the largest pacing site separation at which the differences in correlation coefficients were not statistically significant (level p > or = 0.05). The findings indicate that when random RMS noise of 5 microV was added to the simulated BSPMs, average spatial resolution over all 60 sites was at 20 ms after the onset of pre-excitation within 3.5 +/- 0.9 mm. The results provide theoretical evidence that statistical analysis of BSPMs obtained during pace mapping can offer improved means for subcentimetre identification of accessory pathways located along the AV ring.     

Assessment of spatial resolution of pace mapping when using body surface potentials

Using computer simulations and statistical methods, the resolution of pace mapping when used in combination with body surface potentials was systematically investigated. In an anatomical model of the human ventricular myocardium, pre-excitation sequences were initiated at 69 sites positioned along the atrioventricular (AV) ring and corresponding body surface potential maps (BSPMs) were calculated at 32 leads placed on the anterior torso. For each time after the onset of pre-excitation (every 4ms to 40ms) and each root-mean-square (RMS) noise level (5, 10, 20 and 50μV), BSPMs were cross-correlated and the spatial resolution defined as the largest pacing site separation at which the differences in correlation coefficients were not statistically significant (level p≥0.05). The findings indicate that when random RMS noise of 5μV was added to the simulated BSPMs, average spatial resolution over all 69 sites was at 20ms after the onset of pre-excitation within 3.5±0.9mm. The results provide theoretical evidence that statistical analysis of BSPMs obtained during pace mapping can offer improved means for subcentimetre identification of accessory pathways located along the AV ring.     

Spectrum analysis of gastrointestinal potentials from the body surface

Spectral analysis was employed to assess the electric activity of the stomach and intestine from the body surface. Equipment including a microcomputer and a specially designed program were used. Examinations of 134 normal subjects and patients with various gastrointestinal conditions have demonstrated a sufficient accuracy of the method in the detection of gastrointestinal dyskinesia and in assessment of gastrointestinal function, as well as in presentation of individual elements of regular gastrointestinal activity.     

Spatial resolution of body surface potential maps and magnetic field maps: A simulation study applied to the identification of ventricular pre-excitation sites

The spatial resolution of body surface potential maps (BSPMs) and magnetic field maps (MFMs) is investigated by means of an anatomically accurate computer model of the human ventricular myocardium. BSPMs and MFMs are calculated for the simulated activation sequences initiated at 35 pre-excitation sites located along the atrioventricular (AV) ring of the epicardium. Changes in the BSPMs and MFMs corresponding to different pre-excitation sites are quantified in terms of the correlation coefficient r. The spatial resolution (selectivity) for a given pre-excitation site is defined as the half-distance between those neighbouring locations at which morphological features of maps, in terms of r, become distinct (r<0.95). It is found that, at 28 ms after the onset of pre-excitation and with no noise added, this distance ±SD, for all sites along the AV ring for the 117-lead BSPMs, is 0.83±0.32 cm, and for the 64-lead and 128-lead MFMs it is 1.54±0.84 cm and 1.15±0.43 cm, respectively. The findings suggest that, when features of non-invasively recorded electrocardiographic and magnetocardiographic map patterns are used for identifying accessory pathways in patients suffering from WPW syndrome, BSPMs are likely to provide more detailed information for guiding the ablative treatment than MFMs. For some sites MFMs provide more information. Both modalities may provide additional assistance to the cardiologist in locating the site of the accessory pathway.     

Computing the activation sequence at the ventricular heart surface from body surface potentials

A previously published inverse procedure to calculate the activation sequence at the ventricular heart surface from body surface potentials has been newly implemented and tested. An inability of this procedure to recover endocardial activation times has been detected. This has led to the development of a new inverse method. The new method has been tested in a simulation study and is shown to result in much better estimates of the activation sequence at the heart surface.     

Apparatus for the measurement of total body nitrogen using prompt neutron activation analysis with californium-252

Details of clinical apparatus designed for the measurement of total body nitrogen (as an indicator of body protein), suitable for the critically ill, intensive-care patient are presented. Californium-252 radio-isotopic neutron sources are used, enabling a nitrogen measurement by prompt neutron activation analysis to be made in 40 min with a precision of +/- 3.2% for a whole body dose equivalent of 0.145 mSv. The advantages of Californium-252 over alternative neutron sources are discussed. A comparison between two irradiation/detection geometries is made, leading to an explanation of the geometry adopted for the apparatus. The choice of construction and shielding materials to reduce the count rate at the detectors and consequently to reduce the pile-up contribution to the nitrogen background is discussed. Salient features of the gamma ray spectroscopy system to reduce spectral distortion from pulse pile-up are presented.     

3D surface roughness measurement for scaliness scoring of psoriasis lesions

Psoriasis is an incurable skin disorder affecting 2–3% of the world population. The scaliness of psoriasis is a key assessment parameter of the Psoriasis Area and Severity Index (PASI). Dermatologists typically use visual and tactile senses in PASI scaliness assessment. However, the assessment can be subjective resulting in inter- and intra-rater variability in the scores. This paper proposes an assessment method that incorporates 3D surface roughness with standard clustering techniques to objectively determine the PASI scaliness score for psoriasis lesions. A surface roughness algorithm using structured light projection has been applied to 1999 3D psoriasis lesion surfaces. The algorithm has been validated with an accuracy of 94.12%. Clustering algorithms were used to classify the surface roughness measured using the proposed assessment method for PASI scaliness scoring. The reliability of the developed PASI scaliness algorithm was high with kappa coefficients>0.84 (almost perfect agreement).     

Electrophysiological basis of mono-phasic action potential recordings

Monophasic action potentials (MAPs) have been recorded for over a century, however, the exact mechanism responsible for their genesis has yet to be elucidated fully. The goal of the paper is to examine the physical basis of MAP recordings. MAP recordings are simulated by modelling a three-dimensional block of cardiac tissue. The effect of the MAP electrode is modelled by introducing a large, non-specific leakage conductance to the small region under the electrode. From the spread of the electrical activity, the equivalent extracellular current flow can be efficiently determined. These computed current sources are then input into a boundary element model of the tissue to determine the surface potentials. Finally, differences in surface potentials are used to compute waveforms that closely resemble MAP recordings. By varying model parameters, the mechanisms responsible for the MAP are determined, and a theory is put forward that can account for all observations. It is hypothesised that the leakage current causes the formation of a double-layer potential with a strength equal to the difference in transmembrane voltage between the regions under the electrode and those outside the electrode, leading to a recorded potential that mimics the transmembrane voltage outside the electrode region, although offset. Based on experimental MAP recordings, an equivalent leakage channel with a conductance of 0.1 mS cm-2 and a reversal potential of -43 mV is introduced by the electrode.     

A revision of body surface area estimations

Summary The results from the present study inidicate that the equation of Dubois and Dubois (1916), now in common use for estimating body surface area, is not the most accurate of those available. Our new equation is based on the measurement of body weight and upper calf circumference only. It accounts for a large percentage of the toal variance (88.9%), and has a low standard error of estimate (0.05 m²), which suggests that this equation may be more useful in the estimation of human body surface area than many of the equations previously produced. Direct comparisons of the accuracy of other workers' equations is difficult to assess due to the different methods by which the equations have been produced and expressed. We do not advocate the use of different equations for males and females because the data indicate that the present equation probably applies equally well to both sexes.     

Real-time optical measurement of the dynamic body surface for use in guided radiotherapy

Optical measurements are increasingly used in radiotherapy. In this paper we present, in detail, the design and implementation of a multi-channel optical system optimized for fast, high spatial resolution, dynamic body surface measurement in guided therapy. We include all algorithmic modifications and calibration procedures required to create a robust, practical system for clinical use. Comprehensive static and dynamic phantom validation measurements in the radiotherapy treatment room show: conformance with simultaneously measured cone beam CT data to within 1 mm over 62% ± 8% of the surface and 2 mm over 90% ± 3%; agreement with the measured radius of a precision geometrical phantom to within 1 mm; and true real-time performance with image capture through to surface display at 23 Hz. An example patient dataset is additionally included, indicating similar performance in the clinic.     

传统方法与快速曲面方法进行复杂曲面重建的比较

背景：逆向工程技术在外科手术中的应用越来越广泛,如何快速、高效地制作出满足快速原型加工所需的模型越来越受到医务人员的关注。 目的：在对常用曲面重构方法建模技术进行总结的基础上,针对传统方法和快速曲面方法对面部复杂曲面进行了重建比较分析。 方法：采用日本Konica公司生产的VIVID9i非接触式三维数字化仪对30名在校大学生面部进行三维坐标测量。采用传统方法和快速曲面方法对扫描得到的面部点云数据进行曲面重建,并对结果进行误差分析和光顺性评价。 结果与结论：传统方法和快速曲面方法重建曲面与原始点云的最大误差分别为2.99 mm和0.69 mm,传统方法重建曲面的光顺性优于快速曲面方法。综合比较得出了快速曲面方法是更适合复杂曲面重建的高效的方法,为复杂曲面的三维重建提供了参考依据。