15 Fakultätsübergreifend / Sonstige Einrichtung
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/16
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Item Open Access Fast multi-modality image matching(1989) Apicella, Anthony; Kippenhan, Jonathan Shane; Nagel, Joachim H.Automated image matching has important applications, not only in the fields of machine vision and general pattern recognition, but also in modern diagnostic and therapeutic medical imaging. Image matching, including the recognition of objects within images as well as the combination of images that represent the same object or process using different descriptive parameters, is particularly important when complementary physiological and anatomical images, obtained with different imaging modalities, are to be combined. Correlation analysis offers a powerful technique for the computation of translational, rotational and scaling differences between the image data sets, and for the detection of objects or patterns within an image. Current correlation-based approaches do not efficiently deal with the coupling of the registration variables, and thus yield iterative and computationally-expensive algorithms. A new approach is presented which improves on previous solutions. In this new approach, the registration variables are de-coupled, resulting in a much less computationally expensive algorithm. The performance of the new technique is demonstrated in the matching of MRI and PET scans, and in an application of pattern recognition in linear accelerator images.Item Open Access The correlation of maternal and fetal heart rates : an important aspect of CTG interpretation(1986) Nagel, Joachim H.The heart rate is a rather poor indicator of the physiological condition both in the fetus and in the mother. Even such simple measurements as maternal blood pressure recording can provide additional information. However, for an accurate analysis of the feto-maternal coupling at least cardiac output and maternal oxygen saturation should be monitored. Nevertheless, our investigations have shown that for routine use even the MHR provides sufficient information to improve the interpretation of the CTG quite considerably. The correlation analysis of fetal and maternal heart rates facilitates diagnosis, particularly in borderline cases, and may help to prevent misinterpretation of the CTG. Since the provision of an additional MHR channel in perinatal monitors is very simple and inexpensive, future systems should not be without one.Item Open Access Coherent ensemble averaging techniques for impedance cardiography(1990) Hurwitz, Barry E.; Shyu, Liang-Yu; Reddy, Sridhar P.; Schneiderman, Neil; Nagel, Joachim H.EKG synchronized ensemble averaging of the impedance cardiogram tends to blur or suppress signal events due to signal jitter or event latency variability. Although ensemble averaging provides some improvement in the stability of the signal and signal to noise ratio under conditions of nonperiodic influences of respiration and motion, coherent averaging techniques were developed to determine whether further enhancement of the impedance cardiogram could be obtained. Physiological signals were obtained from sixteen male and female subjects during resting conditions, while delivering a speech and while undergoing submaximal bicycle exercise. Results indicated that improved resolution of dZ/dt signal events could be obtained using coherent ensemble averaging. Although some improvement in precision of event location was obtained, most enhancement of the impedance cardiogram occurred in measurement of the amplitude of the dZ/dt maximum (ejection velocity) during speaking and exercise conditions. Validated increases in dZ/dt maximum exceeding 20% were obtained in some subjects with coherent averaging, suggesting that the diagnostic utility of impedance cardiography can be improved by using this technique.Item Open Access The spectrum of the fetal phonocardiogram as an indicator of fetal maturity(1986) Nagel, Joachim H.On the basis of these experimental results we believe that analysis of the spectrum - a passive measuring technique - may be a real alternative to such well-known active measurements as ultrasonic imaging in the determination of fetal maturity. Besides the information on physical dimensions, it also contains data on the function and the strength of the heart muscle. We must, of course, also consider possible disturbing influences such as changing cardiovascular conditions (e.g. the heart rate). So far we have found no such effects. It should be mentioned that the PCGs have always been picked up at the basal heart rate with no labour activity and not during acclerations nor decelerations. At the present time we are investigating the reliability of this method, and its applicability to routine examinations.Item Open Access Registration of high resolution images of the retina(1992) Cideciyan, Artur V.; Jacobson, Samuel G.; Kemp, Colin M.; Knigthon, Robert W.; Nagel, Joachim H.A method of image registration is presented for the case when the deformation between two images can be well approximated with a combination of translation, rotation and global scaling. The method achieves very high accuracy by combining a global optimization in the 4-dimensional discrete parameter space with a local optimization in the 4-dimensional continuous parameter space. The 4-dimensional global optimization is accomplished with two 2-dimensional optimizations. The Fourier magnitude is used to decouple translation from rotation and scaling, and a log-polar mapping of the Fourier magnitude is used to convert rotation and scaling into shifts. Optimal rotation and scaling parameters are determined with a cross-correlation in the log-polar domain. After compensation for rotation and scaling differences, cross-correlation in the spatial domain yields the translation parameters. The four registration parameters are further refined with a local optimization using the correlation coefficient as a similarity measure in the 4-dimensional continuous parameter space. Results are shown from simulations and from registration of retinal images. For simulated images with a signal-to-noise ratio of -5 dB, the accuracy of the registration method is estimated to be better than 0.07 degrees, 0.1 %, and 0.3 pixels for rotation, scaling, and translation, respectively. In the case of 512x512 pixel images the computation resource requirements are compatible with high end PCs, i.e., approximately 25 minutes on an Intel 80486/33MHz based IBM/PC compatible.