Proceedings of the 19th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. 'Magnificent Milestones and Emerging Opportunities in Medical Engineering' (Cat. No.97CH36136)

Magnetic resonance tagging is usually achieved by means of a train of non-selective radio-frequency pulses separated by gradient pulses. Thus, the modulation of the M/sub 2/ magnetization component expands all over the imaging plane. It has been proposed that the use of selective excitation pulses may limit the modulation only to regions of interest, thus preserving anatomical data in the rest of the image. In this paper, we intend to expand the tagging k-space concept in order to account for pulse selectivity, and offer a prediction and design tool for localized MR tagging sequences.

Epileptic seizures correspond to episodes of increased rhythmicity of the normally chaotic activity in biological neural networks. We propose to use hybrid neural networks where artificial neural networks are used to control the biological neural networks by learning their different states. The learning is dramatically accelerated when using a conjugate gradient method in conjunction with the Fletcher-Reeves method of optimization.

The effect of segmented polyurethane coating on thrombus formation was quantitatively studied under a shear field in vitro. Segmented polyurethane, has been applied to coat the inner surface in blood pumps in artificial hearts. Here, the Couette-type of shear rate was applied to canine blood between concave and the convex cones. The material of the cones was varied: polymethyl-methacrylate, polyvinyl chloride, and polyvinyl chloride coated with segmented polyurethane. The study shows that the clotting time extends on the segmented polyurethane especially at the higher shear rates, although the clot ratio is at the same level as that without coating. This clotting time extension should regulate thrombus formation under pulsatile shear flow.

MRI tagging created new opportunities for motion analysis within the body. With tagged cardiac MRI, detailed motion analysis has been previously shown; e.g. measurements of local strain of the heart could be obtained easily for normal and pathological hearts. In this study, we calculate the activation times using the local time-strain relationship and compute the propagation velocity of the activation for both chambers of the heart. Here, in this initial analysis, we obtained propagation velocities for four canine hearts paced either at the atrium or right ventricle. The first case provides a condition similar to the normal physiological activation. We show here for the first time an activation propagation speed over the right ventricle in vivo. The overall method provides a unique noninvasive method to examine the underlying electrical activation of the heart, but further studies are needed to establish its true clinical value.

A new technique based on freezing curve monitoring to quickly evaluate the viability of the biological materials subject to freezing or rewarming was established. A practical integrated device was fabricated which is simple in structure and cheap in price. Preliminary freezing experiments on the fresh fish blood demonstrated that minor changes in a biological material due to freezing or warming injury may result in significant deviation in its freezing curve compared with that of the intact biomaterials. Three thermal indexes to quantify the damage degree of the biomaterials were pointed out. This method also opens many opportunities for the evaluation of biological material defect in diverse life science fields.

Many cardiac diseases cause transmural differences in myofiber function. With the Magnetic Resonance Imaging Tagging technique a grid of magnetic tags was attached to the heart. Using a model of cardiac mechanics the motion of these tags was analyzed to deduct the transmural gradient or myofiber shortening. In normal, young healthy subjects (n=9), the transmural difference in myofiber shortening varies little, about /spl plusmn/4% (sd) of mean shortening. In patients with aortic stenosis subendocardial function is at risk. In a group of such patients (n=5) fiber shortening in the subendocardial layers was found to be decreased by 23/spl plusmn/20% relative to the subepicardial layers. This finding indicates that a model of cardiac mechanics can be used as a tool to convert MRI-tagging motion data to clinically useful information on a transmural gradient in contractile function. Presently, no other methods are available to detect such transmural gradient noninvasively.

At present, the most widespread method of monitoring uterine contractions activity during pregnancy and labour is the external tocography method. This mechanical method, however, has limited value resulting from its low accuracy and sensibility. Recent progress in new techniques of perinatal monitoring requires a more precise method of monitoring uterine activity. The most promising seems to be electrohysterography, which consists in the recording of electrical uterine activity by means of electrodes attached to abdominal wall. We made an attempt to evaluate the possibility to replace the traditional mechanical method by this electrical one. We developed methods of extraction of the slow wave from an electrohysterogram. This slow wave corresponds to mechanical signal and can be regarded as a contractions wave. Then, using this wave, the contractions detection can be performed in a similar way as in a conventional tocogram. The results obtained allow one to conclude that there is a close relation between the electrical and mechanical signals of uterine activity. It is manifested by a similar number of contractions detected and a large number of contractions being consistent.

A programmable multi-channel neuroprosthesis for functional electrical therapy was developed. This research follows the neurorehabilitation studies indicating that the provision of life-like reaching and grasping in stroke subjects is essential for their faster and more effective recovery. The designed 16-channel neuroprosthesis delivers charge-balanced impulses, and controls the pulse width, frequency and stimulus intensity on each channel independently. The main novelty is a controller that supports sensory driven, rule-based control. The rules use sensory information and mappings that can be determined by machine learning. The controller supports up to eight analog sensors, six digital sensors, five timers, and comprises a flash memory for handling time series. An interface for downloading programs from a PC computer was realized via a serial communication channel by means of an infrared link.

The Poincare plot is an emerging Heart Rate Variability (HRV) analysis technique, the geometry of which has been shown to distinguish between healthy and unhealthy subjects in clinical settings. The Poincare plot is able to display nonlinear aspects of the interval sequence and is therefore of interest in characterizing the nonlinear aspects of HRV. The problem is, how do we quantitatively characterize the geometry of the plot to capture useful descriptors that are independent of existing HRV measures? In this paper, we investigate a popular existing category of techniques and show that they measure linear aspects of the intervals which existing HRV indices already specify. The fact that these methods appear insensitive to the nonlinear characteristics of the intervals is an important finding because the Poincare plot is primarily a nonlinear technique.

Utilization of advanced information, telecommunication and implant technology for cardiac risk stratification and management is one of the greatest challenges for modern health care provision. Sudden cardiac death is the major contributor to overall cardiovascular mortality with approximately 60% of all coronary heart disease fatalities occurring annually. Although some high-risk patient groups have been identified with reasonable sensitivity and specificity based on statistical evaluation, it is still not possible to assess the acute risk of individuals. Implants like cardiac pacemakers with telemetric capability offer the possibility for continuous, permanent surveillance. Hence, advanced technology renders possible a new systematic approach with the aim to identify high-risk individuals, to support the initiation of appropriate therapy management and to prevent the occurrence of sudden death. First results obtained from heart transplant patients, patients after myocardial infarction, and patients with coronary risks render possible the assessment of presently available technology and reveal the potential of cardiac telemonitoring as an emerging field.