TY - JOUR A1 - Herold, Volker A1 - Herz, Stefan A1 - Winter, Patrick A1 - Gutjahr, Fabian Tobias A1 - Andelovic, Kristina A1 - Bauer, Wolfgang Rudolf A1 - Jakob, Peter Michael T1 - Assessment of local pulse wave velocity distribution in mice using k-t BLAST PC-CMR with semi-automatic area segmentation. JF - Journal of Cardiovascular Magnetic Resonance N2 - Background: Local aortic pulse wave velocity (PWV) is a measure for vascular stiffness and has a predictive value for cardiovascular events. Ultra high field CMR scanners allow the quantification of local PWV in mice, however these systems are yet unable to monitor the distribution of local elasticities. Methods: In the present study we provide a new accelerated method to quantify local aortic PWV in mice with phase-contrast cardiovascular magnetic resonance imaging (PC-CMR) at 17.6 T. Based on a k-t BLAST (Broad-use Linear Acquisition Speed-up Technique) undersampling scheme, total measurement time could be reduced by a factor of 6. The fast data acquisition enables to quantify the local PWV at several locations along the aortic blood vessel based on the evaluation of local temporal changes in blood flow and vessel cross sectional area. To speed up post processing and to eliminate operator bias, we introduce a new semi-automatic segmentation algorithm to quantify cross-sectional areas of the aortic vessel. The new methods were applied in 10 eight-month-old mice (4 C57BL/6J-mice and 6 ApoE\(^{(-/-)}\)-mice) at 12 adjacent locations along the abdominal aorta. Results: Accelerated data acquisition and semi-automatic post-processing delivered reliable measures for the local PWV, similiar to those obtained with full data sampling and manual segmentation. No statistically significant differences of the mean values could be detected for the different measurement approaches. Mean PWV values were elevated for the ApoE\(^{(-/-)}\)-group compared to the C57BL/6J-group (3.5 ± 0.7 m/s vs. 2.2 ± 0.4 m/s, p < 0.01). A more heterogeneous PWV-distribution in the ApoE \(^{(-/-)}\)-animals could be observed compared to the C57BL/6J-mice, representing the local character of lesion development in atherosclerosis. Conclusion: In the present work, we showed that k-t BLAST PC-MRI enables the measurement of the local PWV distribution in the mouse aorta. The semi-automatic segmentation method based on PC-CMR data allowed rapid determination of local PWV. The findings of this study demonstrate the ability of the proposed methods to non-invasively quantify the spatial variations in local PWV along the aorta of ApoE\(^{(-/-)}\)-mice as a relevant model of atherosclerosis. KW - pulse wave velocity KW - ApoE\(^{(-/-)}\) KW - magnetic resonance imaging KW - phase contrast Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-157696 VL - 19 IS - 77 ER - TY - THES A1 - Gutjahr, Fabian Tobias T1 - Neue Methoden der physiologischen Magnet-Resonanz-Tomographie: Modellbasierte T1-Messungen und Darstellung von chemischem Austausch mit positivem Kontrast T1 - Novell Methods for Physiological MRI: Model based T1-Quantification and Positive Contrast Chemical Exchange Measurements N2 - Ziel dieser Arbeit war es, neue quantitative Messmethoden am Kleintier, insbesondere die Perfusionsmessung am Mäuseherz, zu etablieren. Hierfür wurde eine retrospektiv getriggerte T1-Messmethode entwickelt. Da bei retrospektiven Methoden keine vollständige Abtastung garantiert werden kann, wurde ein Verfahren gefunden, das mit Hilfe von Vorwissen über das gemessene Modell sehr effizient die fehlenden Daten interpolieren kann. Mit Hilfe dieser Technik werden dynamische T1-Messungen mit hoher räumlicher und zeitlicher Auflösung möglich. Dank der hohen Genauigkeit der T1-Messmethode lässt sich diese für die nichtinvasive Perfusionsmessung am Mäuseherz mittels der FAIR-ASL-Technik nutzen. Da auf Grund der retrospektiven Triggerung Daten an allen Positionen im Herzzyklus akquiriert werden, konnten T1- und Perfusionskarten nach der Messung zu beliebigen Punkten im Herzzyklus rekonstruiert werden. Es bietet sich an, Techniken, die für die myokardiale Perfusion angewandt werden, auch für die Nierenperfusionsmessung zu verwenden, da die Niere in ihrer Rinde (Cortex) eine ähnlich hohe Perfusion aufweist wie das Myokard. Gleichzeitig führen Nierenerkrankungen oftmals zu schlechter Kontrastmittelverträglichkeit, da diese bei Niereninsuffizienz u.U. zu lange im Körper verweilen und die Niere weiter schädigen. Auch deshalb sind die kontrastmittelfreien Spin-Labeling-Methoden hier interessant. Die FAIR-ASL-Technik ist jedoch an Mäusen in koronaler Ansicht für die Niere schlecht geeignet auf Grund des geringen Unterschieds zwischen dem markierten und dem Vergleichsexperiment. Als Lösung für dieses Problem wurde vorgeschlagen, die Markierungsschicht senkrecht zur Messschicht zu orientieren. Hiermit konnte die Sensitivität gesteigert und gleichzeitig die Variabilität der Methode deutlich verringert werden. Mit Hilfe von kontrastmittelgestützten Messungen konnten auch das regionale Blutvolumen und das Extrazellularvolumen bestimmt werden. In den letzten Jahren hat das Interesse an Extrazellularvolumenmessungen zugenommen, da das Extrazellularvolumen stellvertretend für diffuse Fibrose gemessen werden kann, die bis dahin nichtinvasiven Methoden nicht zugänglich war. Die bisher in der Literatur verwendeten Quantifizierungsmethoden missachten den Einfluss, den das Hämatokrit auf den ECV-Wert hat. Es wurde eine neue Korrektur vorgeschlagen, die allerdings zusätzlich zur ECV-Messung auch eine RBV-Messung benötigt. Durch gleichzeitige Messung beider Volumenanteile konnte auch erstmals das Extrazellulare-Extravaskuläre-Volumen bestimmt werden. Eine gänzlich andere kontrastmittelbasierte Methode in der MRT ist die Messung des chemischen Austauschs. Hierbei wirkt das Kontrastmittel nicht direkt beschleunigend auf die Relaxation, sondern der Effekt des Kontrastmittels wird gezielt durch HF-Pulse an- und ausgeschaltet. Durch den chemischen Austausch kann die Auswirkung der HF-Pulse akkumuliert werden. Bislang wurde bei solchen Messungen ein negativer Kontrast erzeugt, der ohne zusätzliche Vergleichsmessungen schwer detektierbar war. Im letzten Teil dieser Arbeit konnte eine neue Methode zur Messung des chemischen Austauschs gezeigt werden, die entgegen der aus der Literatur bekannten Methoden nicht Sättigung, sondern Anregung überträgt. Diese Änderung erlaubt es, einen echten positiven chemischen Austausch-Kontrast zu erzeugen, der nicht zwingend ein Vergleichsbild benötigt. Gleichzeitig ermöglicht die Technik, dadurch dass Anregung übertragen wird, die Phase der Anregung zu kontrollieren und nutzen. Eine mögliche Anwendung ist die Unterscheidung verschiedener Substanzen in einer Messung. In der Summe wurden im Rahmen dieser Arbeit verschiedene robuste Methoden eta- bliert, die die Möglichkeiten der quantitativen physiologischen MRT erweitern. N2 - The objective of this dissertation was to develop new methods for physiological magnetic resonance imaging. A new retrospectively triggered T1-method was developed. Due to the retrospectivity, full sampling of k-space can not be warranted. Therefore a model- based interpolation method was developed to reconstruct missing data efficiently. Using this technique, dynamic T1-measurements with high temporal and spatial resolution could be acquired. Due to the high precision of the developed T1-method, perfusion could be quantified using Arterial Spin Labeling. In comparison to the method established previously in our laboratory, the resolution could be doubled. Retrospective triggering enables reconstruc- tion of parameter maps on arbitrary positions in the heart cycle, as data are acquired continuously over several heart cycles. The perfusion measurement benefits from recon- struction on the end systole, as partial volume effects are decreased, due to the increased myocardial wall thickness. This serves as an effective increase in resolution. Furthermore, the data distributed over the whole heart cycle could be used to accelerate and stabilize the measurement. Cardiac and renal diseases can be directly related, as deficiency in one of the organs affects the other one. Additionally several diseases like hypertension or diabetes affect both organs. Moreover, kidneys are highly perfused, similar to the myocardium. Renal insufficiency can also lead to contrast agent intolerance, as clearance rates can be redu- ced. Therefore the FAIR-ASL technique lends itself to kidney perfusion measurements. It can, however, be problematic in small animals in coronal view, as the control-experiment inadvertently labels much of the same tissue and blood, as the labeling experiment. A modified FAIR-ASL measurement could be shown to increase sensitivity and reduce in- ter-measurement-variability by repositioning the inversion slice of the control experiment orthogonally to the measurement slice. The T1-method was used in combination with contrast agent based measurements to quantify the regional blood volume and the extracellular volume fraction. There has been an increased interest in extracellular volume fraction measurements as the extracel- lular volume is used as a proxy for the detection of diffuse fibrosis, which has previously been inaccessible to non-invasive methods. Several correction factors are used in volume fraction quantification, but the influence of hematocrit in ECV measurements has been neglected so far. In mice and rats, the regional blood volume is a major constituent of the ECV, leading to a significant influence of hematocrit. A new correction is proposed to account for the volume fraction taken up by hematocrit. For this ECV hematocrit correction, the RBV has to be measured as well. Using both measurements, the ex- tracellular volume fraction can be corrected and the extracellular-extravascular-volume- fraction quantified. A fundamentally different contrast-mechanism can be utilized using the measurement of chemical exchange. Instead of shortening relaxation times, the contrast provided by chemical exchange agents can be turned on and off using frequency selective rf-pulses. Due to the chemical exchange the effect of these pulses can be accumulated. Measure- ments exploiting this accumulation effect in general produce a negative contrast requiring a control-experiment for further evaluation. In the last part of this dissertation, a new technique transferring excitation instead of saturation could be demonstrated. By ge- nerating a real positive contrast, no control experiment is required. Other properties unavailable to previously published chemical exchange transfer methods can be exploi- ted. One example demonstrated in this dissertation is the separation of simultaneously excited compounds by their respective phase information imprinted by the excitation pulses. In summary, several robust methods could be implemented to further the capabilities of quantitative physiological MRI. KW - Kernspintomografie KW - Physioloische MRT KW - Modellbasierte Rekonstruktion KW - FAIR-ASL KW - Chemischer Austausch KW - Regionales Blutvolumen KW - Extrazellularvolumen KW - T1-Quantifizierung KW - Kernspinresonanz KW - Myokardiale Perfusion KW - Niere KW - Perfusionsmessung Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-161061 ER - TY - JOUR A1 - Winter, Patrick A1 - Andelovic, Kristina A1 - Kampf, Thomas A1 - Gutjahr, Fabian Tobias A1 - Heidenreich, Julius A1 - Zernecke, Alma A1 - Bauer, Wolfgang Rudolf A1 - Jakob, Peter Michael A1 - Herold, Volker T1 - Fast self-navigated wall shear stress measurements in the murine aortic archusing radial 4D-phase contrast cardiovascular magnetic resonance at 17.6 T JF - Journal of Cardiovascular Magnetic Resonance N2 - Purpose 4D flow cardiovascular magnetic resonance (CMR) and the assessment of wall shear stress (WSS) are non-invasive tools to study cardiovascular risks in vivo. Major limitations of conventional triggered methods are the long measurement times needed for high-resolution data sets and the necessity of stable electrocardiographic (ECG) triggering. In this work an ECG-free retrospectively synchronized method is presented that enables accelerated high-resolution measurements of 4D flow and WSS in the aortic arch of mice. Methods 4D flow and WSS were measured in the aortic arch of 12-week-old wildtype C57BL/6 J mice (n = 7) with a radial 4D-phase-contrast (PC)-CMR sequence, which was validated in a flow phantom. Cardiac and respiratory motion signals were extracted from the radial CMR signal and were used for the reconstruction of 4D-flow data. Rigid motion correction and a first order B0 correction was used to improve the robustness of magnitude and velocity data. The aortic lumen was segmented semi-automatically. Temporally averaged and time-resolved WSS and oscillatory shear index (OSI) were calculated from the spatial velocity gradients at the lumen surface at 14 locations along the aortic arch. Reproducibility was tested in 3 animals and the influence of subsampling was investigated. Results Volume flow, cross-sectional areas, WSS and the OSI were determined in a measurement time of only 32 min. Longitudinal and circumferential WSS and radial stress were assessed at 14 analysis planes along the aortic arch. The average longitudinal, circumferential and radial stress values were 1.52 ± 0.29 N/m2, 0.28 ± 0.24 N/m2 and − 0.21 ± 0.19 N/m2, respectively. Good reproducibility of WSS values was observed. Conclusion This work presents a robust measurement of 4D flow and WSS in mice without the need of ECG trigger signals. The retrospective approach provides fast flow quantification within 35 min and a flexible reconstruction framework. KW - 4D flow KW - WSS KW - OSI KW - Self-navigation KW - Mouse KW - Aortic arch Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-201120 VL - 21 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 -