Patrick Gaydecki

The use of the Hilbert transform in ECG signal analysis

This paper presents a new robust algorithm for QRS detection using the first differential of the ECG signal and its Hilbert transformed data to locate the R wave peaks in the ECG waveform. Using this method, the differentiation of R waves from large, peaked T and P waves is achieved with a high degree of accuracy. In addition, problems with baseline drift, motion artifacts and muscular noise are minimised. The performance of the algorithm was tested using standard ECG waveform records from the MIT-BITH Arrhythmia database. An average detection rate of 99.87%, a sensitivity (Se) of 99.94% and a positive prediction (+P) of 99.93% have been achieved against study records from the MIT-BITH Arrhythmia database. A detection error rate of less than 0.8% was achieved in every study case. The reliability of the proposed detector compares very favorably with published results for other QRS detectors.

A new QRS detection algorithm based on the Hilbert transform

A robust new algorithm for QRS defection using the properties of the Hilbert transform is proposed. The method allows R waves to be differentiated from large, peaked T and P waves with a high degree of accuracy and minimizes the problems associated with baseline drift, motion artifacts and muscular noise. The performance of the algorithm was tested using the records of the MIT-BIH Arrhythmia Database. Beat by beat comparison was performed according to the recommendation of the American National Standard for ambulatory ECG analyzers (ANSI/AAMI EC38-1998). A QRS detection rate of 99.64%, a sensitivity of 99.81% and a positive prediction of 99.83% was achieved against the MIT-BIH Arrhythmia database. The noise tolerance of the new proposed QRS detector was also tested using standard records from the MIT-BIH Noise Stress Test Database. The sensitivity of the detector remains about 94% even for signal-to-noise ratios (SNR) as low as 6 dB.

The propagation and attenuation of medium-frequency ultrasonic waves in concrete: a signal analytical approach

The manner in which medium-frequency ultrasonic pulses travelling through concrete are generated, received, digitized and analysed is described. Due to the highly attenuating nature of this medium and its differential effects on the frequency composition of broad-band signals, signal analysis was performed by partitioning the signal into discrete windows in the time domain, corresponding to the emergence of individual wave phenomena within the medium. These windows were then transformed to the frequency domain for subsequent filtering and interpretation. Experimentation combined with theoretical modelling has shown that the appearance and decay of discrete frequency bands depends on both the composition of the concrete, termed the resonance phase, and its external importance with respect to the ultrasonic inspection of concrete and other such inhomogeneous materials.

Within-day and between-days reliability of quadriceps isometric muscle fatigue using mechanomyography on healthy subjects.

This study aimed to examine within-day and between-days intratester reliability of mechanomyography (MMG) in assessing muscle fatigue. An accelerometer was used to detect the MMG signal from rectus femoris. Thirty one healthy subjects (15 males) with no prior knee problems initially performed three maximum voluntary contractions (MVCs) using an ISOCOM dynamometer. After 10 min rest, subjects performed a fatiguing protocol in which they performed three isometric knee extensions at 75% MVC for 40 s. The fatiguing protocol was repeated on two other days, two to four days apart for between-days reliability. MMG activity was determined by overall root mean squared amplitude (RMS), mean power frequency (MPF) and median frequency (MF) during a 40s contraction. RMS, MPF and MF linear regression slopes were also analysed. Intraclass Correlation Coefficients (ICC); ICC1,1 and ICC1,2 were used to assess within-day reliability and between-days reliability respectively. Standard error of measurement (SEM) and smallest detectable difference (SDD) described the within-subjects variability. MMG fatigue measures using linear regression slopes showed low reliability and large between-days error (ICC1,2=0.43-0.46; SDD=306.0-324.8% for MPF and MF slopes respectively). Overall MPF and MF, on the other hand, were reliable with high ICCs and lower SDDs compared to linear slopes (ICC1,2=0.79-0.83; SDD=21.9-22.8% for MPF and MF respectively). ICC1,2 for overall MMG RMS and linear RMS slopes were 0.81 and 0.66 respectively; however, the SDDs were high (56.4% and 268.8% respectively). The poor between-days reliability found in this study suggests caution in using MMG RMS, MPF and MF and their corresponding slopes in assessing muscle fatigue.

A portable inductive scanning system for imaging steel-reinforcing bars embedded within concrete

Abstract A novel portable scanning system and inductive sensor that produces images of steel-reinforcing bars embedded within concrete by an inductive principle is described. The sensing element, which comprises a field-compensated receiving coil, detects the magnetic field generated by the steel bars due to eddy currents induced on their surfaces by an excitation coil. The sensor is mounted within a purpose-designed computer-controlled x – y scanner used to collect data within a 400×400 mm 2 area in 18 min, using a scan step of 1 mm along the x -axis and 2 mm along the y -axis. This scanner assembly is fabricated from a unique combination of plastic components to avoid disruption of the magnetic field as signals are acquired. The sensor is translated within the frame using remotely placed stepper motors, and images are generated with a grey-scale resolution of 16 bits/pixel. These images are then enhanced using application-specific image processing techniques developed by the authors. The complete system incorporates fully integrated control, acquisition and processing software, which makes it convenient for on-site use.

An inductive scanning system for two-dimensional imaging of reinforcing components in concrete structures

A novel form of imaging steel reinforcing components in concrete is described which employs a scanning inductive sensor. A host computer, linked to the scanning and data acquisition system, generates grey-scale images whose intensities are proportional to the signal strengths produced by the sensor. Simple signal subtraction algorithms have been employed to achieve considerable improvements in image contrast, spatial resolution and the extraction of dimensional information. Models of the sensor response suggest that with further signal manipulation, detailed quantitative measurements on image features will also be possible.

A portable system for acquiring and removing motion artefact from ECG signals

A novel electrocardiograph (ECG) signal acquisition and display system is under development. It is designed for patients ranging from the elderly to athletes. The signals are obtained from electrodes integrated into a vest, amplified, digitally processed and transmitted via Bluetooth to a PC with a Labview ® interface. Digital signal processing is performed to remove movement artefact and electromyographic (EMG) noise, which severely distorts signal morphology and complicates clinical diagnosis. Independent component analysis (ICA) is also used to improve the signal quality. The complete system will integrate the electronics into a single module which will be embedded in the vest.

Radiographic image analysis in the study of bone morphology.

Early changes in bone morphology, arising from such conditions as rheumatoid arthritis and osteoarthritis, are difficult to detect and even more difficult to quantify when estimates are based upon visual examination of conventional radiographs. In this paper, we describe in detail the software operations of a computer-based image analysis system that will readily detect small changes in periarticular bone contours. Detailed studies have shown that the system compares favourably with clinical evaluations, and that the results so obtained are both reliable and reproducible.

Data reduction for cough studies using distribution of audio frequency content

BackgroundRecent studies suggest that objectively quantifying coughing in audio recordings offers a novel means to understand coughing and assess treatments. Currently, manual cough counting is the most accurate method for quantifying coughing. However, the demand of manually counting cough records is substantial, demonstrating a need to reduce record lengths prior to counting whilst preserving the coughs within them. This study tested the performance of an algorithm developed for this purpose.Methods20 subjects were recruited (5 healthy smokers and non-smokers, 5 chronic cough, 5 chronic obstructive pulmonary disease and 5 asthma), fitted with an ambulatory recording system and recorded for 24 hours. The recordings produced were divided into 15 min segments and counted. Periods of inactive audio in each segment were removed using the median frequency and power of the audio signal and the resulting files re-counted.ResultsThe median resultant segment length was 13.9 s (IQR 56.4 s) and median 24 hr recording length 62.4 min (IQR 100.4). A median of 0.0 coughs/h (IQR 0.0-0.2) were erroneously removed and the variability in the resultant cough counts was comparable to that between manual cough counts. The largest error was seen in asthmatic patients, but still only 1.0% coughs/h were missed.ConclusionsThese data show that a system which measures signal activity using the median audio frequency can substantially reduce record lengths without significantly compromising the coughs contained within them.

Measurement of radiographic changes occurring in rheumatoid arthritis by image analysis techniques.

We have applied image analysis techniques to serial measurements of bone contour in standard radiographs of single small joints of the hands in subjects with rheumatoid arthritis (RA) and controls. Adequate reproducibility was shown in 20 controls radiographed twice over a six month period. The technique showed significant changes in a proximal interphalangeal joint of 13 of 15 patients with RA studied over periods of three to 10 months. In further serial studies in selected small joints of RA hands significant changes could be shown as early as four months. These results justify further development of these techniques to allow their full scale evaluation in multiple joints in patients with RA receiving long term drug therapy.