Invasive cardiac catheterisation is a precursor to ablation therapy for ventricular tachycardia. Invasive cardiac diagnostics are fraught with risks. Decades of research has been conducted on the inverse problem of electrocardiography, which can be used to reconstruct Heart Surface Potentials (HSPs) from Body Surface Potentials (BSPs), for non-invasive cardiac diagnostics. State of the art solutions to the inverse problem are unsatisfactory, since the inverse problem is known to be ill-posed. In this paper we propose a novel approach to reconstructing HSPs from BSPs using a Time-Delay Artificial Neural Network (TDANN). We first design the TDANN architecture, and then develop an iterative search space algorithm to find the parameters of the TDANN, which results in the best overall HSP prediction. We use recorded BSPs and HSPs from individuals suffering from serious cardiac conditions to validate our TDANN. The results are encouraging, in that the predicted and recorded HSPs have an average correlation coefficient of 0.7 under diseased conditions.
The number of neurons in the hidden layer, the weight vector associated with each neuron, and the activation function together decide the efficacy of the ANN. Neural network weights are chosen to minimize the mean square error using Levenberg @cite_2 algorithm. Furthermore, the activation function is the sigmoid function. The number of neurons in the hidden layer are chosen using cross-validation techniques described later in .
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A hammer is provided with a housing accommodating a barrel which is axially movable relative to the housing. The barrel has two portions of different diameter. One portion adjacent to the handle is of a smaller diameter, and the other portion is of a greater diameter. These portions form therebetween a shoulder having the end wall facing the handle. An annular space is provided between the outer surface of the barrel and the inner surface of the housing, and mounted in this annular space on both the first and second portions of the barrel are sealing bushings which are in sealing engagement with the housing so that annular spaces are provided between the outer periphery of the bushings and the inner surface of the housing, and a spring member is mounted between the bushings. The invention is aimed at lowering the vibration level at the hammer handle and at reducing the compressed air leakage.