TY - JOUR A1 - Salinger, Tim A1 - Hu, Kai A1 - Liu, Dan A1 - Taleh, Scharoch A1 - Herrmann, Sebastian A1 - Oder, Daniel A1 - Gensler, Daniel A1 - Müntze, Jonas A1 - Ertl, Georg A1 - Lorenz, Kristina A1 - Frantz, Stefan A1 - Weidemann, Frank A1 - Nordbeck, Peter T1 - Association between Comorbidities and Progression of Transvalvular Pressure Gradients in Patients with Moderate and Severe Aortic Valve Stenosis JF - Cardiology Research and Practice N2 - Background. Fast progression of the transaortic mean gradient (P-mean) is relevant for clinical decision making of valve replacement in patients with moderate and severe aortic stenosis (AS) patients. However, there is currently little knowledge regarding the determinants affecting progression of transvalvular gradient in AS patients. Methods. This monocentric retrospective study included consecutive patients presenting with at least two transthoracic echocardiography examinations covering a time interval of one year or more between April 2006 and February 2016 and diagnosed as moderate or severe aortic stenosis at the final echocardiographic examination. Laboratory parameters, medication, and prevalence of eight known cardiac comorbidities and risk factors (hypertension, diabetes, coronary heart disease, peripheral artery occlusive disease, cerebrovascular disease, renal dysfunction, body mass index >= 30 Kg/m(2), and history of smoking) were analyzed. Patients were divided into slow (P-mean < 5 mmHg/year) or fast (P-mean >= 5 mmHg/year) progression groups. Results. A total of 402 patients (mean age 78 +/- 9.4 years, 58% males) were included in the study. Mean follow-up duration was 3.4 +/- 1.9 years. The average number of cardiac comorbidities and risk factors was 3.1 +/- 1.6. Average number of cardiac comorbidities and risk factors was higher in patients in slow progression group than in fast progression group (3.3 +/- 1.5 vs 2.9 +/- 1.7; P = 0.036). Patients in slow progression group had more often coronary heart disease (49.2% vs 33.6%; P = 0.003) compared to patients in fast progression group. LDL-cholesterol values were lower in the slow progression group (100 +/- 32.6 mg/dl vs 110.8 +/- 36.6 mg/dl; P = 0.005). Conclusion. These findings suggest that disease progression of aortic valve stenosis is faster in patients with fewer cardiac comorbidities and risk factors, especially if they do not have coronary heart disease. Further prospective studies are warranted to investigate the outcome of patients with slow versus fast progression of transvalvular gradient with regards to comorbidities and risk factors. KW - Valvular heart-desease KW - Prognostic impact KW - Risk-factors KW - Chronic heart-failure KW - Prevalence KW - mild KW - statins KW - therapy KW - mortality Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-227291 ER - TY - JOUR A1 - Reiter, Theresa A1 - Gensler, Daniel A1 - Ritter, Oliver A1 - Weiss, Ingo A1 - Geistert, Wolfgang A1 - Kaufmann, Ralf A1 - Hoffmeister, Sabine A1 - Friedrich, Michael T. A1 - Wintzheimer, Stefan A1 - Düring, Markus A1 - Nordbeck, Peter A1 - Jakob, Peter M. A1 - Ladd, Mark E. A1 - Quick, Harald H. A1 - Bauer, Wolfgang R. T1 - Direct cooling of the catheter tip increases safety for CMR-guided electrophysiological procedures JF - Journal of Cardiovascular Magnetic Resonance N2 - Background: One of the safety concerns when performing electrophysiological (EP) procedures under magnetic resonance (MR) guidance is the risk of passive tissue heating due to the EP catheter being exposed to the radiofrequency (RF) field of the RF transmitting body coil. Ablation procedures that use catheters with irrigated tips are well established therapeutic options for the treatment of cardiac arrhythmias and when used in a modified mode might offer an additional system for suppressing passive catheter heating. Methods: A two-step approach was chosen. Firstly, tests on passive catheter heating were performed in a 1.5 T Avanto system (Siemens Healthcare Sector, Erlangen, Germany) using a ASTM Phantom in order to determine a possible maximum temperature rise. Secondly, a phantom was designed for simulation of the interface between blood and the vascular wall. The MR-RF induced temperature rise was simulated by catheter tip heating via a standard ablation generator. Power levels from 1 to 6 W were selected. Ablation duration was 120 s with no tip irrigation during the first 60 s and irrigation at rates from 2 ml/min to 35 ml/min for the remaining 60 s (Biotronik Qiona Pump, Berlin, Germany). The temperature was measured with fluoroscopic sensors (Luxtron, Santa Barbara, CA, USA) at a distance of 0 mm, 2 mm, 4 mm, and 6 mm from the catheter tip. Results: A maximum temperature rise of 22.4 degrees C at the catheter tip was documented in the MR scanner. This temperature rise is equivalent to the heating effect of an ablator's power output of 6 W at a contact force of the weight of 90 g (0.883 N). The catheter tip irrigation was able to limit the temperature rise to less than 2 degrees C for the majority of examined power levels, and for all examined power levels the residual temperature rise was less than 8 degrees C. Conclusion: Up to a maximum of 22.4 degrees C, the temperature rise at the tissue surface can be entirely suppressed by using the catheter's own irrigation system. The irrigated tip system can be used to increase MR safety of EP catheters by suppressing the effects of unwanted passive catheter heating due to RF exposure from the MR scanner. KW - EP Procedures KW - radiofrequency ablation KW - contact force KW - lesion size KW - MRI KW - temperature KW - tissue KW - wires KW - model KW - ablation KW - safety KW - catheter tip KW - MR guidance Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-134927 VL - 14 IS - 12 ER - TY - JOUR A1 - Nordbeck, Peter A1 - Bönhof, Leoni A1 - Hiller, Karl-Heinz A1 - Voll, Sabine A1 - Arias-Loza, Paula A1 - Seidlmaier, Lea A1 - Williams, Tatjana A1 - Ye, Yu-Xiang A1 - Gensler, Daniel A1 - Pelzer, Theo A1 - Ertl, Georg A1 - Jakob, Peter M. A1 - Bauer, Wolfgang R. A1 - Ritter, Oliver T1 - Impact of Thoracic Surgery on Cardiac Morphology and Function in Small Animal Models of Heart Disease: A Cardiac MRI Study in Rats JF - PLoS ONE N2 - Background Surgical procedures in small animal models of heart disease might evoke alterations in cardiac morphology and function. The aim of this study was to reveal and quantify such potential artificial early or long term effects in vivo, which might account for a significant bias in basic cardiovascular research, and, therefore, could potentially question the meaning of respective studies. Methods Female Wistar rats (n = 6 per group) were matched for weight and assorted for sham left coronary artery ligation or control. Cardiac morphology and function was then investigated in vivo by cine magnetic resonance imaging at 7 Tesla 1 and 8 weeks after the surgical procedure. The time course of metabolic and inflammatory blood parameters was determined in addition. Results Compared to healthy controls, rats after sham surgery showed a lower body weight both 1 week (267.5±10.6 vs. 317.0±11.3 g, n<0.05) and 8 weeks (317.0±21.1 vs. 358.7±22.4 g, n<0.05) after the intervention. Left and right ventricular morphology and function were not different in absolute measures in both groups 1 week after surgery. However, there was a confined difference in several cardiac parameters normalized to the body weight (bw), such as myocardial mass (2.19±0.30/0.83±0.13 vs. 1.85±0.22/0.70±0.07 mg left/right per g bw, p<0.05), or enddiastolic ventricular volume (1.31±0.36/1.21±0.31 vs. 1.14±0.20/1.07±0.17 µl left/right per g bw, p<0.05). Vice versa, after 8 weeks, cardiac masses, volumes, and output showed a trend for lower values in sham operated rats compared to controls in absolute measures (782.2±57.2/260.2±33.2 vs. 805.9±84.8/310.4±48.5 mg, p<0.05 for left/right ventricular mass), but not normalized to body weight. Matching these findings, blood testing revealed only minor inflammatory but prolonged metabolic changes after surgery not related to cardiac disease. Conclusion Cardio-thoracic surgical procedures in experimental myocardial infarction cause distinct alterations upon the global integrity of the organism, which in the long term also induce circumscribed repercussions on cardiac morphology and function. This impact has to be considered when analyzing data from respective animal studies and transferring these findings to conditions in patients. KW - heart rate KW - body weight KW - surgical and invasive medical procedures KW - magnetic resonance imaging KW - blood KW - vascular surgery KW - myocardial infarction KW - cardiac ventricles Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-130064 VL - 8 IS - 8 ER - TY - JOUR A1 - Gram, Maximilian A1 - Gensler, Daniel A1 - Winter, Patrick A1 - Seethaler, Michael A1 - Arias-Loza, Paula Anahi A1 - Oberberger, Johannes A1 - Jakob, Peter Michael A1 - Nordbeck, Peter T1 - Fast myocardial T\(_{1P}\) mapping in mice using k-space weighted image contrast and a Bloch simulation-optimized radial sampling pattern JF - Magnetic Resonance Materials in Physics, Biology and Medicine N2 - Purpose T\(_{1P}\) dispersion quantification can potentially be used as a cardiac magnetic resonance index for sensitive detection of myocardial fibrosis without the need of contrast agents. However, dispersion quantification is still a major challenge, because T\(_{1P}\) mapping for different spin lock amplitudes is a very time consuming process. This study aims to develop a fast and accurate T\(_{1P}\) mapping sequence, which paves the way to cardiac T1ρ dispersion quantification within the limited measurement time of an in vivo study in small animals. Methods A radial spin lock sequence was developed using a Bloch simulation-optimized sampling pattern and a view-sharing method for image reconstruction. For validation, phantom measurements with a conventional sampling pattern and a gold standard sequence were compared to examine T\(_{1P}\) quantification accuracy. The in vivo validation of T\(_{1P}\) mapping was performed in N = 10 mice and in a reproduction study in a single animal, in which ten maps were acquired in direct succession. Finally, the feasibility of myocardial dispersion quantification was tested in one animal. Results The Bloch simulation-based sampling shows considerably higher image quality as well as improved T\(_{1P}\) quantification accuracy (+ 56%) and precision (+ 49%) compared to conventional sampling. Compared to the gold standard sequence, a mean deviation of - 0.46 ± 1.84% was observed. The in vivo measurements proved high reproducibility of myocardial T\(_{1P}\) mapping. The mean T\(_{1P}\) in the left ventricle was 39.5 ± 1.2 ms for different animals and the maximum deviation was 2.1% in the successive measurements. The myocardial T\(_{1P}\) dispersion slope, which was measured for the first time in one animal, could be determined to be 4.76 ± 0.23 ms/kHz. Conclusion This new and fast T\(_{1P}\) quantification technique enables high-resolution myocardial T\(_{1P}\) mapping and even dispersion quantification within the limited time of an in vivo study and could, therefore, be a reliable tool for improved tissue characterization. KW - TT\(_{1rho}\) mapping KW - small animal KW - KWIC KW - radial KW - cardiac KW - mice KW - spin lock KW - T\(_{1P}\) dispersion KW - T\(_{1P}\) mapping Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-268903 SN - 1352-8661 VL - 35 IS - 2 ER - TY - JOUR A1 - Gram, Maximilian A1 - Gensler, Daniel A1 - Albertova, Petra A1 - Gutjahr, Fabian Tobias A1 - Lau, Kolja A1 - Arias-Loza, Paula-Anahi A1 - Jakob, Peter Michael A1 - Nordbeck, Peter T1 - Quantification correction for free-breathing myocardial T1ρ mapping in mice using a recursively derived description of a T\(_{1p}\)\(^{*}\) relaxation pathway JF - Journal of Cardiovascular Magnetic Resonance N2 - Background Fast and accurate T1ρ mapping in myocardium is still a major challenge, particularly in small animal models. The complex sequence design owing to electrocardiogram and respiratory gating leads to quantification errors in in vivo experiments, due to variations of the T\(_{1p}\) relaxation pathway. In this study, we present an improved quantification method for T\(_{1p}\) using a newly derived formalism of a T\(_{1p}\)\(^{*}\) relaxation pathway. Methods The new signal equation was derived by solving a recursion problem for spin-lock prepared fast gradient echo readouts. Based on Bloch simulations, we compared quantification errors using the common monoexponential model and our corrected model. The method was validated in phantom experiments and tested in vivo for myocardial T\(_{1p}\) mapping in mice. Here, the impact of the breath dependent spin recovery time T\(_{rec}\) on the quantification results was examined in detail. Results Simulations indicate that a correction is necessary, since systematically underestimated values are measured under in vivo conditions. In the phantom study, the mean quantification error could be reduced from − 7.4% to − 0.97%. In vivo, a correlation of uncorrected T\(_{1p}\) with the respiratory cycle was observed. Using the newly derived correction method, this correlation was significantly reduced from r = 0.708 (p < 0.001) to r = 0.204 and the standard deviation of left ventricular T\(_{1p}\) values in different animals was reduced by at least 39%. Conclusion The suggested quantification formalism enables fast and precise myocardial T\(_{1p}\) quantification for small animals during free breathing and can improve the comparability of study results. Our new technique offers a reasonable tool for assessing myocardial diseases, since pathologies that cause a change in heart or breathing rates do not lead to systematic misinterpretations. Besides, the derived signal equation can be used for sequence optimization or for subsequent correction of prior study results. KW - T1rho KW - radial KW - cardiac KW - correction KW - quantitative MRI KW - mapping KW - spin-lock KW - T1ρ Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-300491 VL - 24 IS - 1 ER - TY - THES A1 - Gensler, Daniel T1 - Entwicklung klinischer Methoden zur Quantifizierung der longitudinalen Relaxationszeit T1 in der MRT T1 - Development of clinical methods for quantifying the longitudinal relaxation time T1 in MRI N2 - Die Aufgabenstellung in der vorliegenden Arbeit bestand in der Entwicklung und Umsetzung neuer T1-Quantifizierungsverfahren, die zuverlässig in der klinischen Routine angewendet werden können. Die ausgearbeiteten Techniken umfassten dabei zwei Hauptarbeitsschwerpunkte. Zum einen die Implementierung einer neuartigen dynamischen T1- Thermometriemethode für MR-Sicherheitsuntersuchungen medizinischer Geräte und Implantate, wie beispielsweise Kathetern oder Herzschrittmachern, und zum anderen die Entwicklung eines robusten kardialen T1-Mapping-Verfahrens, welches auch bei stärker erkrankten Patienten mit eingeschränkter Atemanhaltefähigkeit stabil anwendbar ist. Mit der entwickelten kombinierten Heiz- und T1-Thermometriesequenz konnte ein neues Verfahren präsentiert werden, mit dem ein zu untersuchendes medizinisches Gerät oder Implantat kontrolliert erwärmt und die Temperaturänderung zeitgleich präzise erfasst werden kann. Dabei war es möglich, die HF-induzierte Erwärmung der metallischen Beispielimplantate sowohl in homogenem Gel als auch in inhomogenem Muskelgewebe exakt und ortsaufgelöst zu quantifizieren. Die MR-technisch errechneten Temperaturwerte zeigten dabei eine sehr gute Übereinstimmung zu den ermittelten Referenzwerten mit einer Temperaturabweichung von meist weniger als 1K. Die Ergebnisse zeigen, dass es mit der präsentierten Methode möglich ist, die räumliche Temperaturverteilung in einem großen Bereich mit einer einzigen Messung quantitativ zu erfassen. Dies ist neben der Nichtinvasivität der Methode der größte Vorteil im Vergleich zu der Einzelpunktmessung mittels eines bei solchen Messungen sonst zumeist verwendeten fluoroptischen Temperatursensors. Bei gestreckten Implantaten kann demnach idealerweise das gesamte Objekt während einer einzigen Messung auf potentielle Temperaturänderungen oder sogenannte Hotspots untersucht werden, was bei der Verwendung von Temperatursensoren lediglich mit großem Zeitaufwand möglich ist, da hier die Temperatur jeweils nur punktuell erfasst werden kann. Im Vergleich zu anderen publizierten MR-Thermometrieverfahren, welche auf der PRF-Technik basieren, bietet die hier präsentierte Methode vor allem den Vorteil, dass hiermit auch eine präzise Temperaturquantifizierung in inhomogenem biologischem Gewebe mit starken Suszeptibilitätsunterschieden wie beispielsweise zwischen Herz und Lunge möglich ist. Somit stellt die Methode ein leistungsstarkes Hilfsmittel für nicht-invasive MR-Sicherheitsuntersuchungen nicht nur an medizinischen Implantaten sondern beispielsweise auch für MR-geführte Interventionen dar. Mit der entwickelten kardialen T1-Mapping-Sequenz TRASSI wurde eine leistungsstarke Methode zur exakten und hoch aufgelösten Generierung kardialer T1-Karten in äußerst kurzer Messzeit (< 6 s) vorgestellt. Durch ihre außerordentliche Robustheit sowohl gegenüber Bildartefakten als auch Herzrhythmusstörungen während der Datenakquisition bietet die Sequenz deutlich verbesserte Möglichkeiten für die Diagnostik verschiedener Herzerkrankungen. Aufgrund der sehr kurzen Akquisitionszeit wird insbesondere auch die Generierung von T1-Karten bei schwer erkrankten Patienten mit kurzer Atemanhaltefähigkeit ermöglicht. Im Vergleich zu derzeit üblicherweise verwendeten alternativen Verfahren wie etwa MOLLI, konnten die T1-Karten mit vergleichbarer Bildauflösung in bis zu 70% kürzerer Messzeit akquiriert werden. Die Ergebnisse der durchgeführten Phantommessungen belegen außerdem, dass die Methode exaktere T1-Werte liefert als dies beispielsweise mit MOLLI möglich ist. Des Weiteren weist TRASSI im Gegensatz zu MOLLI keine T1-Abhängigkeit von der Herzrate auf, wodurch die vorgestellte Technik besonders für diagnostische Studien geeignet ist, welche eine sehr hohe Genauigkeit und Reproduzierbarkeit im Zeitverlauf oder zwischen verschiedenen Patienten erfordern. Mit TRASSI konnten die Strukturen des Herzens bei den durchgeführten in vivo Untersuchungen durchweg mit scharfen Kanten und ohne Bewegungsartefakte dargestellt werden. Dabei wurde unabhängig von der Herzrate und der Bildebene stets eine sehr gute Bildqualität erreicht. Der Hauptgrund hierfür ist vermutlich in der sehr kurzen Akquisitionszeit und der radialen Datenaufnahme zu sehen. Beide Verfahren reduzieren Artefakte aufgrund von Bewegungen wie beispielsweise Herzschlag und Atmung erheblich. Die aufgenommenen T1-Karten zeigen bei allen Probanden und Patienten eine gute diagnostische Bildqualität. So konnten auch die infarzierten Bereiche bei Patienten mit Myokardinfarkt deutlich visualisiert und quantitativ erfasst werden. Nochmals hervorzuheben ist die beobachtete besondere Robustheit der TRASSI Methode gegenüber Artefakten beziehungsweise T1-Quantifizierungsfehlern bei Patienten mit Herzrhythmusstörungen. Auch bei untersuchten Patienten mit starken Arrhythmien während der Bildgebung konnte eine sehr gute Bildqualität und Genauigkeit der errechneten T1-Karten erreicht werden. Die Ergebnisse der Extrazellularvolumen-Quantifizierung zeigen zudem, dass mittels TRASSI auch weiterführende diagnostische Methoden entwickelt und angewandt werden können. Dabei konnten durch Rückrechnung hochaufgelöster und präziser Extrazellularvolumen-Karten beispielsweise Infarktbereiche deutlich visualisiert und signifikante Unterschiede zwischen akut und chronisch infarziertem Herzmuskelgewebe nicht nur identifiziert sondern auch quantitativ charakterisiert werden. Somit ist diese Methode insbesondere für eine potentielle Differenzierung zwischen reversibel und irreversibel geschädigten Herzarealen interessant. Für die Zukunft ist es wünschenswert, weitergehende Untersuchungen an verschiedenen spezifischen Herzerkrankungen vorzunehmen. Zu solchen Erkrankungen gehören beispielsweise die Herzmuskelentzündung (Myokarditis) oder Herzklappenerkrankungen. Diese Krankheitsbilder sind hinsichtlich einer möglichen transienten oder permanenten Schädigung des Herzmuskels mit den bisher verfügbaren Verfahren nur sehr schwer oder lediglich im weit fortgeschrittenen Stadium exakt diagnostizierbar. Die vorgestellte TRASSI-Sequenz bietet hier eine gute Möglichkeit für eine frühzeitige Erkennung der Auswirkungen solcher Erkrankungen auf den Herzmuskel. Weiterführende Untersuchungen der TRASSI-Methode zu deren Robustheit gegenüber spezifischen Herzrhythmusstörungen und ein umfassender Vergleich zum bereits etablierten MOLLI-Verfahren könnten darüber hinaus die Alltagstauglichkeit von TRASSI weiter spezifizieren und den Weg in die klinische Routine ebnen. Die bereits dargelegten positiven Ergebnisse des Verfahrens lassen vermuten, dass TRASSI potentiell ein sehr gutes nicht-invasives Diagnoseverfahren für verschiedenste Herzerkrankungen darstellt. Im Vergleich zu bereits bestehenden Techniken liegen die Vorteile der TRASSI-Methode nach den bisher vorliegenden Ergebnissen zusammenfassend vor allem in der Generierung diagnostisch verlässlicherer T1-Werte bei gleichzeitig verringerter Messzeit, wodurch das Verfahren insbesondere auch für schwer erkrankte Patienten mit starken Arrhythmien und eingeschränkter Atemanhaltefähigkeit geeignet ist. TRASSI ist darüber hinaus aber auch für MR-Untersuchungen im Hochfeld besser geeignet als entsprechende bSSFP-basierende Verfahren wie beispielsweise MOLLI. Dies liegt vor allem daran, dass TRASSI eine Gradientenecho-basierte Bildgebungsmethode ist und somit eine niedrige spezifische Absorptionsrate aufweist. Zudem sind Gradientenecho-Sequenzen allgemein weniger empfindlich gegenüber Suszeptibilitätsartefakten, so dass beispielsweise metallische Implantate bei Patienten sich weniger störend auf die erreichbare Bildqualität auswirken. In der vorliegenden Arbeit wurde sowohl eine exakte T1-Thermometriesequenz als auch eine sehr schnelle und präzise kardiale T1-Mapping-Methode vorgestellt. Für zukünftige Arbeiten ist es wünschenswert, beide Sequenzen bzw. deren Mechanismen zu vereinen und eine Temperaturquantifizierung am Herzen praktisch durchzuführen. Dies wäre zum einen für MR-Sicherheitsuntersuchungen von Schrittmacherelektroden in vivo vorteilhaft, und zum anderen wäre hiermit eine direkte Erfolgskontrolle während einer Katheterablation realisierbar. Eine solche Ablationsbehandlung könnte durch eine genaue Lokalisierung des behandelten - also erhitzten - Herzareals sehr viel präziser durchgeführt werden, wodurch auch bei komplexeren Ablationen die Behandlungserfolge erhöht werden könnten. In einer ersten Veröffentlichung hierzu konnte bereits gezeigt werden, dass eine MR-gestützte Katheterablation die Heilungs- und Erfolgsaussichten des Eingriffes steigern kann. Dieses Verfahren könnte potentiell mit Hilfe einer Echtzeittemperaturüberwachung basierend auf dem TRASSI-Verfahren noch weiter verbessert werden. In Zusammenfassung wurden in dieser Arbeit zwei neue T1-Quantifizierungsverfahren entwickelt und vorgestellt, die voraussichtlich zuverlässig im klinischen Alltag angewendet werden können und neue nicht-invasive diagnostische Möglichkeiten eröffnen. Die implementierten Sequenzen ermöglichen dabei zum einen eine exakte Temperaturquantifizierung und zum anderen ein präzises kardiales T1-Mapping. Beide Verfahren versprechen dabei robuste und reproduzierbare Ergebnisse und könnten in Zukunft den Weg in die klinische Routine finden und so bei einer fundierten Diagnostik verschiedenster Herzerkrankungen behilflich sein. N2 - The goal of the present study was to develop and implement new T1-quantification methods that can be reliably applied in clinical practice. The elaborated techniques focused on two main objectives: first, the implementation of a novel dynamic T1-thermometry technique for MR-safety investigations of medical devices and implants, such as catheters or pacemakers; and second, the development of a robust cardiac T1-mapping method, which is applicable even in severely ill patients with limited breath-hold capabilities. With the newly developed combined heating and T1-thermometry sequence, a new MR method was presented, which allowed a controlled heating of a medical device or implant under investigation, while simultaneously detecting temperature changes near these devices with high accuracy. With this MR sequence it was possible to quantify and spatially accurately resolve the radio frequency-induced heating of exemplary metallic implants both in a homogeneous gel phantom and in inhomogeneous porcine muscle. The MR-calculated temperature values showed good agreement with the determined reference values, with a temperature deviation of usually less than 1K. The results show that with the presented method it is possible to quantify the spatial temperature distribution in a large area. This is - in addition to the non-invasiveness of the method - the main advantage compared to the single-point measurement of commonly used fluoroptic temperature sensors: Ideally, elongated implants can be characterized regarding potential temperature changes or hot spots along the whole device during a single MR measurement. Compared to other published MR-thermometry methods based on the PRF technique the presented T1-based technique particularly provides the advantage of a precise temperature quantification even in inhomogeneous biological tissue with strong susceptibility differences such as between the heart and the lungs. Thus, the method represents a powerful tool for non-invasive MR-safety investigations not only for implanted medical devices, but also for MR-guided interventions. With the developed cardiac T1-mapping sequence TRASSI, a powerful technique for the generation of exact, high-resolution cardiac T1-maps acquired in very short measurement time (< 6 s) was presented. Through the extraordinary robustness both to image artifacts and heart rhythm disturbances during data acquisition, this sequence provides significantly improved possibilities for various diagnostic purposes in clinical cardiology. Due to the very short acquisition time, TRASSI particularly offers the possibility for the generation of T1-maps in severely ill patients with short breath-hold capabilities. Compared to currently commonly used alternative MR techniques, such as MOLLI, T1-maps with similar resolution could be acquired in up to 70 % shorter measurement time. Furthermore, the results of the phantom measurements show that TRASSI provides more accurate T1 values than MOLLI. In addition, TRASSI shows - in contrast to MOLLI - no heart rate T1-dependency. Thus, the presented technique is particularly suited for diagnostic studies, which require a very high accuracy and reproducibility over time or between different patients. With TRASSI, the heart morphology could consistently be identified with sharp edges and without any motion artifacts in the performed in vivo studies. The good image quality could be achieved in all measurements regardless of the heart rate and the image plane. The main reason for these findings can be anticipated in the very short acquisition time and the radial data acquisition. Both significantly reduce artifacts due to motion such as heartbeat and breathing. Diagnostic image quality of the T1 maps in patients with myocardial infarction allowed for visualization and spatial T1-quantification in all subjects. Of note is the observed extraordinary robustness of the TRASSI method against artifacts and T1-errors in patients with cardiac arrhythmias. Even in patients with severe arrhythmias during the imaging procedure a very good image quality and accuracy of the calculated T1-maps could be achieved. Moreover, the results of the extracellular volume quantification show that with TRASSI additional diagnostic methods can be developed and applied. The calculation of accurate high-resolution extracellular volume maps was suitable for visualization of infarcted areas in the myocardium. Furthermore, significant differences between acute and chronically infarcted myocardial tissue could not only be visually identified, but also quantitatively characterized. Thus, this method is particularly interesting for a differentiation between reversible and irreversible myocardial injury. For the future, it is desirable to carry out further clinical studies on various specific heart diseases. Such diseases include, for example, inflammation of the heart muscle (myocarditis) or valvular heart diseases. The diagnosis of these diseases regarding a possible damage of the myocardium is currently problematic and only possible in advanced stages using the methods available today. Here, the presented TRASSI sequence provides a favorable opportunity for the early detection of transient or permanent myocardial damage. Further studies of TRASSI for its robustness against specific cardiac arrhythmias and a comprehensive comparison with the already established MOLLI method could further confirm the everyday practicality of TRASSI and pave the way into clinical routine. The already available positive results of TRASSI suggest this method to be well suited as a non-invasive diagnostic technique for various heart diseases. From the experiments available, it can be concluded that, compared to existing techniques like MOLLI, TRASSI provides more accurate T1-values in a simultaneously reduced measurement time. This positions TRASSI particularly suitable for severely ill patients with distinctive arrhythmias and/or reduced breath-hold capabilities. In addition, TRASSI is better suited for high field MR examinations than corresponding bSSFPbased methods such as MOLLI. This is because TRASSI is a gradient echo-based imaging method and thus it has a lower specific absorption rate. Gradient echo-based sequences are also generally less sensitive to susceptibility artifacts and thus interferences caused by metallic implants of correspondent patients show less negative effects on image quality. In the current work an exact T1-thermometry sequence as well as a very fast and accurate cardiac T1-mapping method was presented. For future work, it is desirable to combine these two sequences and their mechanisms to be able to perform accurate temperature quantification in the beating heart. This would be on the one hand beneficial for MR-safety examinations of pacemaker electrodes in vivo, and on the other hand allow for a direct control of success during catheter ablation. Hence, a catheter ablation procedure could be performed with greatly increased spatial accuracy due to precise localization of heat development in the myocardium. Consequently, the safety and outcomes especially in complex ablations could be increased. In a first publication it could be already shown that MR-guided catheter ablation has the potential to increase procedural success in the future. This interventional technique could potentially be further improved by implementation of a real-time temperature visualization using TRASSI. In summary, two new T1-quantification methods have been developed and presented in this work, which can be reliably applied in clinical practice and which are expected to allow for new non-invasive diagnostic possibilities. The implemented sequences allow on the one hand exact temperature quantification in the myocardium and on the other hand accurate cardiac T1-mapping. Both methods promise robust and reproducible results, so that they are expected to find the way into clinical routine, helping in diagnosis and treatment of various heart diseases in the near future. KW - Kernspintomographie KW - Thermometrie KW - kardiale MRT KW - Gewebecharakterisierung KW - T1-Quantifizierung KW - cardiac MRI KW - tissue characterization KW - T1 quantification KW - Relaxationszeit Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-126582 ER -