Technology and Health Care - Volume 12, issue 6

Authors: Liepsch, D. | Schmid, T. | McLean, J. | Weigand, C.

Article Type: Research Article

Abstract: The use of iodine contrast agents during angiography can put patients at risk. The replacement of angiography through duplex ultrasound methods would, therefore, be of great interest. Even when duplex sonography is used however, an x-ray angiography is often performed afterwards to verify the diagnosis. This causes complications in an unacceptable number of patients. The safety of duplex ultrasound sonography diagnosis can be improved by using low-risk Doppler contrast agents. Slow blood flow through vessels with a high degree stenosis and intracerebral flow can be more easily and accurately detected using these agents. However, amplification of the Doppler echo alters …the measurements during both high and low flow, so that the flow rate cannot be recorded very precisely. Our goal was to study the effect of a contrast agent on velocity measurements with color-coded Doppler ultrasonography and on pulsed, one-goal measurements. We used a laser-Doppler-anemometer (LDA) with high temporal and spatial resolution as a reference method to compare the measurements. Show more

DOI: 10.3233/THC-2004-12601

Citation: Technology and Health Care, vol. 12, no. 6, pp. 411-423, 2004

Authors: Golkhou, V. | Parnianpour, M. | Lucas, C.

Article Type: Research Article

Abstract: In this study, we consider the role of multisensor data fusion in neuromuscular control using an actor-critic reinforcement learning method. The model we use is a single link system actuated by a pair of muscles that are excited with alpha and gamma signals. Various physiological sensor information such as proprioception, spindle sensors, and Golgi tendon organs have been integrated to achieve an oscillatory movement with variable amplitude and frequency, while achieving a stable movement with minimum metabolic cost and coactivation. The system is highly nonlinear in all its physical and physiological attributes. Transmission delays are included in the afferent and …efferent neural paths to account for a more accurate representation of the reflex loops. This paper proposes a reinforcement learning method with an Actor-Critic architecture instead of middle and low level of central nervous system (CNS). The Actor in this structure is a two layer feedforward neural network and the Critic is a model of the cerebellum. The Critic is trained by the State-Action-Reward-State-Action (SARSA) method. The Critic will train the Actor by supervisory learning based on previous experiences. The reinforcement signal in SARSA is evaluated based on available alternatives concerning the concept of multisensor data fusion. The effectiveness and the biological plausibility of the present model are demonstrated by several simulations. The system showed excellent tracking capability when we integrated the available sensor information. Addition of a penalty for activation of muscles resulted in much lower muscle coactivation while keeping the movement stable. Show more

Keywords: motor control, reinforcement learning, multisensor data fusion, Actor-Critic, CMAC, simulink

DOI: 10.3233/THC-2004-12602

Citation: Technology and Health Care, vol. 12, no. 6, pp. 425-438, 2004

Authors: van Tuil, Cornelia | Saxena, Amulya K. | Willital, Günter H.

Article Type: Research Article

Abstract: An unusual case of a needle head injury, with deep embodiment of the needle head in the neck of the left talus bone is presented. The needle head was removed at our centre after two previous unsuccessful surgical attempts at other hospitals. The mechanism of trauma and the surgical procedure has been described.

Keywords: foreign body, penetrating injury, talus neck, hydroxyapatite

DOI: 10.3233/THC-2004-12603

Citation: Technology and Health Care, vol. 12, no. 6, pp. 439-441, 2004

Authors: Fankhauser, Franz | Niederer, Peter F. | Kwasniewska, Sylwia | van der Zypen, Eugen

Article Type: Research Article

Abstract: Wavelength-corrected, adaptive optics and their relevance for diagnostic procedures of the human retina are considered. First, it is shown that the compensation of errors of the dioptric apparatus of the eye allows sharp and high-contrast images of retinal elements, such as the photoreceptors, to be generated. This technology is expected to enable on the one hand an improved laser therapy by the application of laser spots of the size of single receptors as well as on the other a further understanding of the mechanisms of vision, in particular of colour vision by using colour stimuli not larger than the cones. …Second, femtosecond laser pulses, emitted from lasers working in the near infrared, based on multiphoton effects allow both imaging and laser effects to be generated which are in the submicron range and which do not cause collateral damage (nanoimaging and nanosurgery). These procedures, related to experimental ophthalmology may be considered a milestone for the research of cell physiology, in particular in the subcellular range. Show more

Keywords: superresolution, supervision, nanoresolution, wave-front correction, aberrometry, adaptive optics, femtosecond laser, picosecond laser

DOI: 10.3233/THC-2004-12604

Citation: Technology and Health Care, vol. 12, no. 6, pp. 443-453, 2004

Authors: Kortright, Eduardo | Xia, Rui | Anayiotos, Andreas S. | Doyle, Mark

Article Type: Research Article

Abstract: Control-volume (CV) methods applied to magnetic resonance velocity-encoded cine images of the convergent proximal flow field of a regurgitant valve have been shown to measure reverse blood flow volume accurately. Spatial and temporal averaging are known to affect accuracy, but the effects of slice thickness and orientation relative to the flow field have not been systematically studied, nor have CV configurations requiring fewer scans been explored. Further, surface area calculations at the intersection of CV walls are a previously unrecognized source of error. Using a computational fluid dynamics model of steady flow through an orifice, we evaluated five different CV …configurations in terms of accuracy, time costs, and clinical potential. CVs incorporating a basal wall were affected by blurring of axial velocity gradients near the orifice, and voxel grid alignment relative to the orifice was the most significant source of inaccuracy. Errors in surface area calculations at plane intersections produced deviations of 7–20%, depending on configuration. A CV formed by slices parallel to the orifice plane was deemed clinically unusable, while a cylindrical CV yielded good accuracy in simulated tests and showed potential for practical implementation based on scan time, ease of view selection, and visualization of the flow field. Show more

DOI: 10.3233/THC-2004-12605

Citation: Technology and Health Care, vol. 12, no. 6, pp. 455-468, 2004