Die vorliegende Arbeit stellt die Powerdopplersonographie an Hand von Vergleichen und Gegenüberstellungen in deskriptiver Weise als nicht invasive Methode vor. Insgesamt wurden bei sechs klinisch-gynäkologisch gesunden Warmblutstuten 16 abgeschlossene, spontane und regelmäßige Zyklen mittels transrektalem Ultraschall aufgezeichnet. Es wurden 10590 dopplersonographische Messdaten ausgewertet, hinzu kamen 9601 powerdopplersonographische Bilddateien, die mittels Pixelanalysesoftware ANALYSIS PRO 1.1 analysiert wurden.

Neurologic injuries are major causes of mortality and morbidity after cardiac surgery. This thesis aimed to investigate cerebral metabolism and perfusion abnormalities in pigs during hypothermic circulatory arrest, selective antegrade cerebral perfusion (SACP) and extracorporeal circulation following progressive venous stasis. Hypothermic circulatory arrest induced a metabolic pattern consistent with overt ischaemia, which was absent following SACP. In contrast, metabolism during SACP was influenced by the perfusate temperature, where a colder perfusate (20 °C) preserved cellular metabolism and membrane integrity better than a warmer perfusate (28 °C). The minimum SACP flow required to maintain metabolism during hypothermia at 20 °C was investigated with magnetic resonance imaging, protein S100β, near infrared spectroscopy and microdialysis. The findings suggested an ischaemic threshold close to 6 ml/kg/min in the present models. Furthermore, regional differences in perfusion with a hemispheric distribution were apparent at all flow levels and differed from earlier studies where the differences were uniform and followed a neuranatomical pattern. Venus stasis following superior vena cava congestion produced measurable signs of impaired cerebral perfusion and patterns of cerebral ischaemia were evident in individual animals. As venous pressure increased, the mean arterial pressure stayed more or less unchanged, generating reduced cerebral perfusion pressure and consequently an increased risk of ischaemia, which may impair cerebral perfusion, especially in cases of compromised arterial flow during extracorporeal circulation. In conclusion, cerebral metabolism and perfusion are influenced by temperature, SACP flow levels and venous congestion. In clinical practice, the regional differences in perfusion during SACP may be of pathogenic importance in focal cerebral ischaemia. Furthermore, the reduced superior vena cava cannula flow may pass undetected during bicaval cardiopulmonary bypass if the superior vena cava flow is not specifically monitored.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2007. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [100]-118).

Zugl.: Berlin, Freie Universiẗat, Diss., 2008.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006. / Wick, Tim, Committee Member ; Neitzel, Paul, Committee Member ; Fyhrie, David, Committee Member ; Garcia, Andres, Committee Member ; Guldberg, Robert, Committee Chair. Vita.

Techn. Universiẗat, Diss., 2005--München.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on October 17, 2007) Vita. Includes bibliographical references.

The diagnosis and treatment of cerebrovascular disease, such as stroke and vascular lesions in the brain, requires knowledge of the status of brain tissue and cerebral arteries. Perfusion imaging and angiography offer information on blood flow to the tissue and through the brain-feeding arteries. A variety of imaging modalities exist to assess brain haemodynamics, including measures of cerebral blood flow and other parameters, however many of these are invasive and/or involve the use of contrast agents toxic to certain patient populations. One non-invasive magnetic resonance imaging alternative for perfusion imaging and angiography, which also provides vessel specific blood flow information, is vessel-encoded pseudocontinuous arterial spin labelling (VEPCASL). VEPCASL uses the blood as an endogenous tracer and can magnetically label the blood from different arteries of interest. The combination of VEPCASL with different imaging strategies can provide a map of the vascular perfusion territories in the brain, or dynamic information on blood flow through the cerebral arteries. The work in this thesis seeks to optimise and develop the encoding process of VEPCASL and accompanying angiographic readouts. Firstly, a rapid and automated method for calculating a minimal number of signal-to-noise ratio (SNR) efficient encodings, for any number and arrangement of vessels, was developed. Its use resulted in improved SNR in perfusion territories fed by more complicated vessel arrangements in the labelling plane. The labelling efficiency of VEPCASL, and its non-vessel-selective equivalent, PCASL, is affected by the presence of magnetic field inhomogeneities in the labelling plane. Consequently, a correction for phase offsets was introduced into the calculation of the optimised encodings. These encodings enabled the recovery of SNR in perfusion territories for PCASL and VEPCASL when phase offsets were present at the labelled arteries. As current VEPCASL angiography methods are relatively slow to acquire, an accelerated readout was developed to acquire two-dimensional vessel-selective dynamic angiograms in approximately one minute. A radial k-space trajectory was found to offer the best vessel definition and SNR. Three-dimensional (3D) angiograms provide the most detailed view of the cerebral vasculature for use in diagnosis and treatment of cerebrovascular disease. A 3D radial readout was optimised to acquire vessel-selective dynamic angiograms. These angiograms offer information on the structure of the vascular tree and how it is fed by the major arteries in the neck. The techniques developed here aim to increase the clinical viability and applicability of VEPCASL perfusion imaging and angiography. It is hoped that the techniques herein could be used in patient populations to add to and improve the diagnostic information available.

O mecanismo de contraste mais utilizado em imagens funcionais por ressonância magnética (functional Magnetic Resonance Imaging, fMRI), também conhecido por sinal BOLD (Blood Oxygenation Level Dependent) mede indiretamente a atividade neural, sendo sensível a mudanças no fluxo cerebral sangüíneo (Cerebral Blood Flow, CBF), na taxa cerebral metabólica do oxigênio (Cerebral Metabolic Rate of Oxygen, CMRO2) e no volume cerebral sanguíneo (Cerebral Blood Volume, CBV) e, em princípio, ele pode ser utilizado para mapear perfusão cerebral. Desse modo, o objetivo principal deste trabalho foi investigar, quantitativamente, alterações perfusionais no cérebro humano mapeadas pelas mudanças do sinal BOLD em resposta à indução transitória do estado de apnéia. Para isso, imagens por ressonância magnética foram obtidas através de um scanner de 1.5 T Siemens (Magneton Vision) com seqüências do tipo EPI-BOLD. Nesta pesquisa, foi analisada a influência da duração da apnéia no sinal BOLD. Observou-se, também, a diferença ocasionada no sinal em duas situações: apnéia iniciando-se após a inspiração ou após a expiração. Além disso, foi estudada a propagação deste sinal BOLD pelas diferentes regiões cerebrais. Por último, fazendo uso deste sinal BOLD, construiu-se mapas para obter informações a respeito do volume cerebral sangüíneo. Pelos dados obtidos, foi possível analisar o comportamento do sinal BOLD quando na presença de diferentes PaO2 e PaCO2. Observaram-se, também, diferenças regionais na sensibilidade do sinal BOLD ocasionada pelo estado de apnéia induzido. Essa diferença pode estar relacionada à reatividade das artérias que irrigam cada região ou ao volume sangüíneo basal dessas artérias. Além disso, foi possível obter informações a respeito das características temporais da mudança do CBF para diferentes regiões do cérebro em resposta a hipercapnia. Também, foi feita a identificação de áreas corticais responsáveis pelo controle voluntário da respiração. Por fim, os mapas de B-CBV obtidos utilizando o contraste BOLD em resposta à apnéia foram capazes de refletir o volume sangüíneo local, embora, estudos para análise dos outros parâmetros que influenciam o sinal devam ser realizados. / The BOLD (Blood Oxygenation Level Dependent) signal, is the most used contrast mechanism of the so called functional Magnetic Resonance Imaging (fMRI). Although it indirectly measures neuronal activity, its response is directly related to cerebral blood flow (CBF), Cerebral Metabolic Rate of Oxygen (CMRO2) and Cerebral Blood Volume (CBV) and can be, in principle, used to map cerebral perfusion. Thus, the main purpose of this study was to investigate, quantitatively, some aspects of perfusional alterations in the human brain. These changes were mapped by changes in the BOLD signal as a result of a global and uniform stimulation: hypercapnia induced by breath holding paradigms. Magnetic resonance images were acquired in a 1.5 T scanner (Siemens, Magneton Vision) with EPI-BOLD fMRI sequences. It was analyzed the BOLD dependency on breath holding duration and differences on the BOLD signal due the employed breath holding techniques: breath holding after expiration or after inspiration. The regional variability of the BOLD signal propagation was also studied. Moreover, the signal was used to construct maps based on CBV information. It was possible to gain information about the BOLD signal behavior that respond to PaO2 and PaCO2 alterations. Besides, it was demonstrated its regional variations sensibility, which can be correlated with arterial reactivity or the rest CBV of this arteries. It was also possible acquire information about the temporal characteristics of CBF changes induced by hypercapnia across brain regions as well as the identification of cortical areas that were responsible to the voluntary breathing. Finally, the B-CBV maps that used the BOLD con-trast were able to reflect CBV information, although, it is necessary the study of other parameters that can influence the signal.