Sampling In Parallel-Beam Tomography

We pesent Shannon sampling theory for functions defined on T \Theta IR, where T denotes the circle group, prove a new estimate for the aliasing error, and apply the result to parallel-beam diffraction tomography. The class of admissible sampling lattices is characterized and general sampling conditions are derived which lead to the identification of new efficient sampling schemes. Corresponding results for x-ray tomography are obtained in the high-frequency limit. 1. INTRODUCTION Sampling theorems provide interpolation formulas for functions whose Fourier transform is compactly supported. If the Fourier transform does not have compact support, a so-called aliasing error occurs. In this paper we pesent a new estimate for the aliasing error for functions defined on T \Theta IR, where T denotes the circle group, and work out its application to computed tomography. In computed tomography (CT) an object is exposed to radiation which is measured after passing through the object. From the..

Fatiguing handgrip exercise alters maximal force-generating capacity of plantar-flexors

Exercise-induced fatigue causes changes within the central nervous system that decrease force production capacity in fatigued muscles. The impact on unrelated, non-exercised muscle performance is still unclear. The primary aim of this study was to examine the impact of a bilateral forearm muscle contraction on the motor function of the distal and unrelated ankle plantar-flexor muscles. The secondary aim was to compare the impact of maximal and submaximal forearm contractions on the non-fatigued ankle plantar-flexor muscles. Maximal voluntary contractions (MVC) of the forearm and ankle plantar-flexor muscles as well as voluntary activation (VA) and twitch torque of the ankle plantar-flexor muscles were assessed pre-fatigue and throughout a 10-min recovery period. Maximal (100 % MVC) and submaximal (30 % MVC) sustained isometric handgrip contractions caused a decreased handgrip MVC (to 49.3 ± 15.4 and 45.4 ± 11.4 % of the initial MVC for maximal and submaximal contraction, respectively) that remained throughout the 10-min recovery period. The fatigue protocols also caused a decreased ankle plantar-flexor MVC (to 77 ± 8.3 and 92.4 ± 6.2 % of pre-fatigue MVC for maximal and submaximal contraction, respectively) and VA (to 84.3 ± 15.7 and 97.7 ± 16.1 % of pre-fatigue VA for maximal and submaximal contraction, respectively). These results suggest central fatigue created by the fatiguing handgrip contraction translated to the performance of the non-exercised ankle muscles. Our results also show that the maximal fatigue protocol affected ankle plantar-flexor MVC and VA more severely than the submaximal protocol, highlighting the task-specificity of neuromuscular fatigue