SUMMARYActigraphy can assist in the detection of periodic limb movements in sleep. Although several actigraphs have been previously reported to accurately detect periodic limb movements, many are no longer available; of the existing actigraphs, most sample too infrequently to accurately detect periodic limb movements. The purpose of this study was to use advanced signal analysis to validate a readily available actigraph that has the capability of sampling at relatively high frequencies. We simultaneously recorded polysomnography and bilateral ankle actigraphy in 96 consecutive patients presenting to our sleep laboratory. After pre-processing and conditioning, the bilateral ankle actigraphy signals were then analysed for 14 simple time, frequency and morphology-based features. These features reduced the signal dimensionality and aided in better representation of the periodic limb movement activity in the actigraph signals. These features were then processed by a Na€ ıve-Bayes binary classifier for distinguishing between normal and abnormal periodic limb movement indices. We trained the Na€ ıve-Bayes classifier using a training set, and subsequently tested its classification accuracy using a testing set. From our experiments, using a periodic limb movement index cut-off of 5, we found that the Na€ ıve-Bayes classifier had a correct classification rate of 78.9%, with a sensitivity of 80.3% and a specificity of 73.7%. The algorithm developed in this study has the potential of facilitating identification of periodic limb movements across a wide spectrum of patient populations via the use of bilateral ankle actigraphy.
Clutter noise is an important challenge in photocoustic (PA) and ultrasound (US) imaging as they degrade the image quality. In this paper, the short-lag spatial coherence (SLSC) imaging technique is used to reduce clutter and side lobes in PA images. In this technique, images are obtained through the spatial coherence of PA signals at small spatial distances across the transducer aperture. The performance of this technique in improving image quality and detecting point targets is compared with a conventional delay-and-sum (DAS) beamforming technique. A superior contrast, contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) are observed when SLSC imaging is employed. Point spread function of point targets shows an improved spatial resolution and reduced side lobes when compared with DAS beamforming. Also shown is the impact of increasing the number of frames on which SLSC is applied. The results show that contrast, CNR, and SNR are improved with increasing number of frames.
Stroke is a leading cause of death and disability in adults, and incurs a significant economic burden to society. Periodic limb movements (PLMs) in sleep are repetitive movements involving the great toe, ankle, and hip. Evolving evidence suggests that PLMs may be associated with high blood pressure and stroke, but this relationship remains underexplored. Several issues limit the study of PLMs including the need to manually score them, which is time-consuming and costly. For this reason, we developed a novel automated method for nocturnal PLM detection, which was shown to be correlated with (a) the manually scored PLM index on polysomnography, and (b) white matter hyperintensities on brain imaging, which have been demonstrated to be associated with PLMs. Our proposed algorithm consists of three main stages: (1) representing the signal in the time-frequency plane using time-frequency matrices (TFM), (2) applying K-nonnegative matrix factorization technique to decompose the TFM matrix into its significant components, and (3) applying kernel sparse representation for classification (KSRC) to the decomposed signal. Our approach was applied to a dataset that consisted of 65 subjects who underwent polysomnography. An overall classification of 97 % was achieved for discrimination of the aforementioned signals, demonstrating the potential of the presented method.
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