@phdthesis{Brackertz2008,
  author    = {Brackertz, Anita},
  title     = {Absolutquantifizierung der myokardialen Perfusion in Ruhe und unter Adenosin-induziertem Stress mittels First-Pass MR-Bildgebung},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-34921},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {In der Diagnostik und Therapie der KHK sind das fr{\"u}hzeitige Erkennen und die Beurteilung funktioneller Folgen atherosklerotischer Ver{\"a}nderungen von großer Bedeutung. Die First-Pass MR-Bildgebung erm{\"o}glicht Aussagen {\"u}ber die myokardiale Perfusion und damit die h{\"a}modynamische Relevanz einer Koronarstenose. In der vorliegenden Arbeit wurden quantitative Werte f{\"u}r die myokardiale Durchblutung gesunder Probanden unter Adenosin-induziertem Stress und in Ruhe unter Einsatz der Pr{\"a}bolustechnik bestimmt. Eine exakte Darstellung der arteriellen Inputfunktion wurde durch einen Kontrastmittelbolus in niedriger Dosierung erreicht, die Verwendung h{\"o}herer Kontrastmitteldosen f{\"u}hrte dagegen zu einem verbesserten Signal-zu-Rausch-Verh{\"a}ltnis im Myokard. Die Absolutwerte der myokardialen Perfusion unter Stressbedingungen und in Ruhe wie auch die myokardiale Perfusionsreserve zeigten vergleichbare Mittelwerte, wiesen aber eine geringere Streubreite im Vergleich zu fr{\"u}heren MR Studien auf und waren vergleichbar mit in PET-Studien erzielten Ergebnissen. Weiterhin wurden unter Verwendung dieser Methode Werte f{\"u}r das myokardiale Verteilungsvolumen des Kontrastmittels als wichtiger Parameter in der Differenzierung von gesundem und infarziertem Herzmuskelgewebe ermittelt und die Laufzeit der Boluspassage nach Injektion in Ruhe und unter Stress bestimmt, die zur Unterscheidung von antegrad perfundiertem und von {\"u}ber Kollateralen versorgtem Myokard dienen kann. Mit Hilfe der MRT war es auch m{\"o}glich, Unterschiede zwischen subendo- und subepimyokardialer Perfusion zu quantifizieren. Die erzielten Ergebnisse entsprechen bisher publizierten Werten, die mit anderen Modalit{\"a}ten gewonnen wurden. Der Vergleich der absoluten Perfusion bei verminderter zeitlicher Aufl{\"o}sung mit den bei hoher zeitlicher Aufl{\"o}sung gemessenen Werten ergab nur geringf{\"u}gige Abweichungen der Ergebnisse voneinander. Dadurch er{\"o}ffnet sich die M{\"o}glichkeit, durch die Zeitersparnis mehrere Schichten abwechselnd bei verschiedenen Herzschl{\"a}gen zu messen und damit eine erweiterte Abdeckung des linksventrikul{\"a}ren Myokards zu erreichen. Durch die quantitative Auswertung der First-Pass MR-Perfusionsmessung stellt die beschriebene Methode eine vielversprechende Option im Bereich der nichtinvasiven Diagnostik verschiedener myokardialer Erkrankungen dar.},
  subject      = {NMR-Tomographie},
  language  = {de}
}
@phdthesis{Eirich2022,
  author    = {Eirich, Philipp},
  title     = {Accelerated non-Cartesian cardiovascular MR Imaging at 3T and 7T},
  doi       = {10.25972/OPUS-25397},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-253974},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {In this work, accelerated non-Cartesian Magnetic Resonance Imaging (MRI) methods were established and applied to cardiovascular imaging (CMR) at different magnetic field strengths (3T and 7T). To enable rapid data acquisition, highly efficient spiral k-space trajectories were created. In addition, hybrid sampling patterns such as the twisting radial lines (TWIRL) k-space trajectory were studied. Imperfections of the dynamic gradient system of a MR scanner result in k-space sampling errors. Ultimately, these errors can lead to image artifacts in non-Cartesian acquisitions. Among other reasons such as an increased reconstruction complexity, they cause the lack of spiral sequences in clinical routine compared to standard Cartesian imaging. Therefore, the Gradient System Transfer Functions (GSTFs) of both scanners were determined and used for k-space trajectory correction in post-correction as well as in terms of a pre-emphasis. The GSTF pre-emphasis was implemented as a fully automatic procedure, which enabled a precise correction of arbitrary gradient waveforms for double-oblique slice orientations. Consequently, artifacts due to trajectory errors could be mitigated, which resulted in high image quality in non-Cartesian MRI. Additionally, the GSTF correction was validated by measuring pre-emphasized spiral gradient outputs, which showed high agreement with the theoretical gradient waveforms. Furthermore, it could be demonstrated that the performance of the GSTF correction is superior to a simple delay compensation approach. The developed pulse sequences were applied to gated as well as real-time CMR. Special focus lied on the implementation of a spiral imaging protocol to resolve the beating heart of animals and humans in real time and free breathing. In order to achieve real-time CMR with high spatiotemporal resolution, k-space undersampling was performed. For this reason, efficient sampling strategies were developed with the aim to facilitate compressed sensing (CS) during image reconstruction. The applied CS approach successfully removed aliasing artifacts and yielded high-resolution cardiac image series. Image reconstruction was performed offline in all cases such that the images were not available immediately after acquisition at the scanner. Spiral real-time CMR could be performed in free breathing, which led to an acquisition time of less than 1 minute for a whole short-axis stack. At 3T, the results were compared to the gold standard of electrocardiogram-gated Cartesian CMR in breath hold, which revealed similar values for important cardiovascular functional and volumetric parameters. This paves the way to an application of the developed framework in clinical routine of CMR. In addition, the spiral real-time protocol was transferred to swallowing and speech imaging at 3T, and first images were presented. The results were of high quality and confirm the straightforward utilization of the spiral sequence in other fields of MRI. In general, the GSTF correction yielded high-quality images at both field strengths, 3T and 7T. Off-resonance related blurring was mitigated by applying non-Cartesian readout gradients of short duration. At 7T, however, B1-inhomogeneity led to image artifacts in some cases. All in all, this work demonstrated great advances in accelerating the MRI process by combining efficient, undersampled non-Cartesian k-space coverage with CS reconstruction. Trajectory correction using the GSTF can be implemented at any scanner model and enables non-Cartesian imaging with high image quality. Especially MRI of dynamic processes greatly benefits from the presented rapid imaging approaches.},
  subject      = {Kernspintomografie},
  language  = {en}
}
@phdthesis{Neumann2014,
  author    = {Neumann, Daniel},
  title     = {Advances in Fast MRI Experiments},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-108165},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technique, that is rou- tinely used in clinical practice for detection and diagnosis of a wide range of different diseases. In MRI, no ionizing radiation is used, making even repeated application unproblematic. This is an important advantage over other common imaging methods such as X-rays and Computer To- mography. One major drawback of MRI, however, are long acquisition times and associated high costs of experiments. Since the introduction of MRI, several important technical developments have been made to successfully reduce acquisition times. In this work, novel approaches were developed to increase the efficiency of MRI acquisitions. In Chapter 4, an improved radial turbo spin-echo (TSE) combined acquisition and reconstruction strategy was introduced. Cartesian turbo spin-echo sequences [3] are widely used especially for the detection and diagnosis of neurological pathologies, as they provide high SNR images with both clinically important proton density and T2 contrasts. TSE acquisitions combined with radial sampling are very efficient, since it is possible to obtain a number of ETL images with different contrasts from a single radial TSE measurement [56-58]. Conventionally, images with a particular contrast are obtained from both radial and Cartesian TSE acquisitions by combining data from different echo times into a single image. In the radial case, this can be achieved by employing k-space weighted image contrast (KWIC) reconstruction. In KWIC, the center region of k-space is filled exclusively with data belonging to the desired contrast while outer regions also are assembled with data acquired at other echo times. However, this data sharing leads to mixed contrast contributions to both Cartesian and radial TSE images. This is true especially for proton density weighted images and therefore may reduce their diagnostic value. In the proposed method, an adapted golden angle reordering scheme is introduced for radial TSE acquisitions, that allows a free choice of the echo train length and provides high flexibility in image reconstruction. Unwanted contrast contaminations are greatly reduced by employing a narrow-band KWIC filter, that restricts data sharing to a small temporal window around the de- sired echo time. This corresponds to using fewer data than required for fully sampled images and consequently leads to images exhibiting aliasing artifacts. In a second step, aliasing-free images are obtained using parallel imaging. In the neurological examples presented, the CG-SENSE algorithm [42] was chosen due to its stable convergence properties and its ability to reconstruct arbitrarily sampled data. In simulations as well as in different in vivo neurological applications, no unwanted contrast contributions could be observed in radial TSE images reconstructed with the proposed method. Since this novel approach is easy to implement on today's scanners and requires low computational power, it might be valuable for the clinical breakthrough of radial TSE acquisitions. In Chapter 5, an auto-calibrating method was introduced to correct for stimulated echo contribu- tions to T2 estimates from a mono-exponential fit of multi spin-echo (MSE) data. Quantification of T2 is a useful tool in clinical routine for the detection and diagnosis of diseases as well as for tis- sue characterization. Due to technical imperfections, refocusing flip angles in a MSE acquisition deviate from the ideal value of 180○. This gives rise to significant stimulated echo contributions to the overall signal evolution. Therefore, T2 estimates obtained from MSE acquisitions typically are notably higher than the reference. To obtain accurate T2 estimates from MSE acquisitions, MSE signal amplitudes can be predicted using the extended phase graph (EPG, [23, 24]) algo- rithm. Subsequently, a correction factor can be obtained from the simulated EPG T2 value and applied to the MSE T2 estimates. However, EPG calculations require knowledge about refocus- ing pulse amplitudes, T2 and T1 values and the temporal spacing of subsequent echoes. While the echo spacing is known and, as shown in simulations, an approximate T1 value can be assumed for high ratios of T1/T2 without compromising accuracy of the results, the remaining two parameters are estimated from the data themselves. An estimate for the refocusing flip angle can be obtained from the signal intensity ratio of the second to the first echo using EPG. A conventional mono- exponential fit of the MSE data yields a first estimate for T2. The T2 correction is then obtained iteratively by updating the T2 value used for EPG calculations in each step. For all examples pre- sented, two iterations proved to be sufficient for convergence. In the proposed method, a mean flip angle is extracted across the slice. As shown in simulations, this assumption leads to greatly reduced deviations even for more inhomogeneous slice profiles. The accuracy of corrected T2 values was shown in experiments using a phantom consisting of bottles filled with liquids with a wide range of different T2 values. While T2 MSE estimates were shown to deviate significantly from the spin-echo reference values, this is not the case for corrected T2 values. Furthermore, applicability was demonstrated for in vivo neurological experiments. In Chapter 6, a new auto-calibrating parallel imaging method called iterative GROG was pre- sented for the reconstruction of non-Cartesian data. A wide range of different non-Cartesian schemes have been proposed for data acquisition in MRI, that present various advantages over conventional Cartesian sampling such as faster acquisitions, improved dynamic imaging and in- trinsic motion correction. However, one drawback of non-Cartesian data is the more complicated reconstruction, which is ever more problematic for non-Cartesian parallel imaging techniques. Iterative GROG uses Calibrationless Parallel Imaging by Structured Low-Rank Matrix Completion (CPI) for data reconstruction. Since CPI requires points on a Cartesian grid, it cannot be used to directly reconstruct non-Cartesian data. Instead, Grappa Operator Gridding (GROG) is employed in a first step to move the non-Cartesian points to the nearest Cartesian grid locations. However, GROG requires a fully sampled center region of k-space for calibration. Combining both methods in an iterative scheme, accurate GROG weights can be obtained even from highly undersampled non-Cartesian data. Subsequently, CPI can be used to reconstruct either full k- space or a calibration area of arbitrary size, which can then be employed for data reconstruction with conventional parallel imaging methods. In Chapter 7, a new 2D sampling scheme was introduced consisting of multiple oscillating effi- cient trajectories (MOET), that is optimized for Compressed Sensing (CS) reconstructions. For successful CS reconstruction of a particular data set, some requirements have to be met. First, ev- ery data sample has to carry information about the whole object, which is automatically fulfilled for the Fourier sampling employed in MRI. Additionally, the image to be reconstructed has to be sparse in an arbitrary domain, which is true for a number of different applications. Last, data sam- pling has to be performed in an incoherent fashion. For 2D imaging, this important requirement of CS is difficult to achieve with conventional Cartesian and non-Cartesian sampling schemes. Ra- dial sampling is often used for CS reconstructions of dynamic data despite the streaking present in undersampled images. To obtain incoherent aliasing artifacts in undersampled images while at the same time preserving the advantages of radial sampling for dynamic imaging, MOET com- bines radial spokes with oscillating gradients of varying amplitude and alternating orientation orthogonal to the readout direction. The advantage of MOET over radial sampling in CS re- constructions was demonstrated in simulations and in in vivo cardiac imaging. MOET provides superior results especially when used in CS reconstructions with a sparsity constraint directly in image space. Here, accurate results could be obtained even from few MOET projections, while the coherent streaking artifacts present in the case of radial sampling prevent image recovery even for smaller acceleration factors. For CS reconstructions of dynamic data with sparsity constraint in xf-space, the advantage of MOET is smaller since the temporal reordering is responsible for an important part of incoherency. However, as was shown in simulations of a moving phantom and in the reconstruction of ungated cardiac data, the additional spatial incoherency provided by MOET still leads to improved results with higher accuracy and may allow reconstructions with higher acceleration factors.},
  subject      = {Kernspintomografie},
  language  = {en}
}
@phdthesis{Zuechner2003,
  author    = {Z{\"u}chner, Mark},
  title     = {Auswirkungen einer moderaten Hypothermie auf das neurologische Outcome, das histologische und kernspintomographische Sch{\"a}digungsausmaß nach Induktion einer epiduralen fokalen Raumforderung im Tiermodell},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-9034},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2003},
  abstract  = {In dieser experimentellen Studie wurde der Einfluss einer moderaten Hypothermie nach Induktion einer epiduralen, extraaxialen Raumforderung auf das neurologische Outcome, auf histopathologische Ver{\"a}nderungen und mittels bildgebender Methoden untersucht. Der Hauptaugenmerk wurde dabei eindeutig auf die neurologischen Verlaufsuntersuchungen mit Hilfe einer neuropsychologischen Testbatterie gelegt.Damit konnte in etwa die Hauptphase der klinischen Rekonvaleszens nach Trauma abgedeckt werden.Zudem hatten die meisten experimentellen Arbeiten bereits nach wesentlich k{\"u}rzeren Zeitr{\"a}umen ihre Nachuntersuchungen abgeschlossen.Die Gesamtmortalit{\"a}t betrug bei den normotherm behandelten Tieren 55\% und bei den hypotherm behandelten Tieren 45\%. Der Unterschied betrug damit nur 10\% und war nicht signifikant. Betrachtet man aber die Mortalit{\"a}tsraten differenzierter, so zeigt sich bez{\"u}glich der rein sch{\"a}digungsbedingten Mortalit{\"a}t als Folge von schweren neurologischen Defiziten wie Hemiparese, Inaktivit{\"a}t und damit verbundenen dramatischen Gewichtsverlust eine Mortalit{\"a}t von 5\% f{\"u}r die Hypothermiegruppe und 30\% in der Normothermiegruppe. Dies findet seine Best{\"a}tigung auch in anderen experimentellen Untersuchungen. F{\"u}r die Anwendung von Hypothermie bei Sch{\"a}del - Hirn -Traumen und zerebralen Isch{\"a}mien in klinischen Studien ist die Datenlage bisher noch widerspr{\"u}chlich. Die bisher gr{\"o}ßte Multicenterstudie in den USA von 1994 -1998 musste bei 392 Patienten mit SHT abgebrochen werden, nachdem kein therapeutischer Effekt unter Hypothermie festzustellen war (Clifton et al., 2001¹). N{\"a}here Analysen zeigten jedoch eine Verbesserung des Outcomes bei Patienten unter 45 Jahren welche bei Aufnahme bereits hypothermen Bedingungen ausgesetzt waren. Damit stellt sich nat{\"u}rlich die Frage nach dem optimalen Zeitfenster f{\"u}r den Beginn einer hypothermen Behandlung. Als therapeutische Konsequenz erscheint damit unter Umst{\"a}nden ein sofortiger Beginn der Hypothermiebehandlung mit Eintreffen des Notarztes als wirkungsvoller. Zus{\"a}tzlich konnten wiederum neueste Untersuchungen bei Patienten mit zerebraler Isch{\"a}mie nach Herz- und Kreislaufstillstand einen protektiven Effekt einer moderater Hypothermie auf das neurologische Outcome aufzeigen (Bernard et al., 2002; Holzer et al., 2002).In unserer Studie sollte aber auf keinen Fall der nur geringe Unterschied in der Gesamtmortalit{\"a}t mit 55 \% in der normothermen und 45 \% in der hypothermen Gruppe vernachl{\"a}ssigt werden. Die Ann{\"a}herung der Gesamtmortalit{\"a}t war hierbei auf eine deutlich erh{\"o}hte Rate systemischer oder lokaler Infektionen unter den hypothermen Tieren zur{\"u}ckzuf{\"u}hren.In klinischen Studien mehren sich allerdings die Hinweise auf eine durch Hypothermie bedingte Immunsuppression und damit verbundenen erh{\"o}hten Infektionsneigung. So konnten erh{\"o}hte Pneumonieraten (Schwab et al., 1998; 2001 ; Shiozaki et al., 2001) aber auch ein vermehrtes Auftreten von Meningitiden (Shiozaki et al.,2001) beobachtet werden. Shiozaki konnte zudem signifikant erh{\"o}hte Raten von Leuko- und Thrombozytopenien sowie Elektrolytentgleisungen im hypothermen Kollektiv finden (Shiozaki et al., 2001). Schwab fand in einer eigens zur {\"U}berpr{\"u}fung der Nebenwirkungen von Hypothermie bei Patienten mit zerebraler Isch{\"a}mie aufgelegten Studie erh{\"o}hte Raten an Pneumonien (48\%), Thrombozytopenien (70\%) und Bradykardien (62\%) (Schwab et al.,2001). Prospektive Studien von Patienten mit kolorektalen Eingriffen wiesen ebenso unter milder Hypothermie signifikant vermehrt Wundheilungsst{\"o}rungen (Kurz et al., 1996) und eine geringere Lymphozytenaktivit{\"a}t auf (Beilin et al., 1998). Angewandt auf unsere Studie zeigte sich ebenfalls eine erh{\"o}hte Rate von Wundheilungsst{\"o}rungen unter Hypothermie, ohne dabeijedoch zu einer Beeinflussung der Ergebnisse in den neuropsychologischen Testreihen zu f{\"u}hren.Abschließend kann festgehalten werden, dass in dieser Studie die Induktion einer moderaten Hypothermie nach epiduraler, extraaxialer Raumforderung, zu einer Verbesserung neurologischer Defizite und damit zu einer Besserung der Lebensqualit{\"a}t jener Versuchstiere f{\"u}hrte, die den Beobachtungszeitraum {\"u}berlebten. Eine Verringerung der Gesamtmortalit{\"a}t konnte nicht erreicht werden.},
  language  = {de}
}
@phdthesis{Kortuem2011,
  author    = {Kort{\"u}m, Karsten Ulrich},
  title     = {Beurteilung der regionalen Herzwandbewegung bei Probanden und Kardiomyopathiepatienten mit Friedreich Ataxie mittels hochaufgelöster MR-Phasenkonstrastbildgebung},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-65769},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2011},
  abstract  = {In der vorliegenden prospektiven experimentellen Studie wurden jeweils 18 Probanden sowie Patienten, die unter einer genetisch gesicherten Friedrich-­Ataxie leiden, mit der Tissue-­Phase-Mapping (TPM) Sequenz im MRT untersucht. Mit der erwähnten Sequenz ist es möglich, die Geschwindigkeit der Herzwandbewegung {\"u}ber einen Herzzyklus zeitlich hoch aufgelöst (13,8 ms) darzustellen. Es wurde in der Vergangenheit gezeigt, dass die Daten der TPM-Messung reproduzierbar sowie mit denen aus einer Ultraschalluntersuchung gewonnenen Daten vergleichbar sind. Die Aufnahme erfolgt unter freier Atmung in Navigatortechnik. Dadurch ist diese Untersuchung auch bei Patienten möglich, die aufgrund Ihrer Erkrankung sonst nicht ausreichend lange die Luft anhalten könnten. Die Friedreich-Ataxie ist die häufigste aller Ataxien in der Adoleszenzphase und wird autosomal-­rezessiv vererbt. Neben neurologischen Ausfällen kann es auch zu einer kardialen Beteiligung kommen. Dabei zeigt sich bei einem großen Teil der Patienten eine Kardiomyopathie mit asymmetrischer septaler Hypertrophie sowie einer dynamischen linksventrikulären Ausflussobstruktion. Die American Heart Association klassifiziert dieses Krankeitsbild als sekundäre Kardiomyopathie neuromuskulären Ursprungs. Es wurde in der Vergangenheit bereits gezeigt, dass es unter einer Therapie mit dem Medikament Idebenone zu einer Verbesserung der kardialen Funktion kommen kann. Im Zusammenhang mit einer groß angelegten, multizentrischen Phase III Studie (MICONOS-­Studie) kamen diese Patienten nach W{\"u}rzburg f{\"u}r eine MRT-­Untersuchung. Im Rahmen dessen erfolgte dann auf freiwilliger Basis eine Untersuchung mit der TPM-­Sequenz. Diese Substudie wurde von der lokalen Ethikkommission genehmigt und die Patienten wie auch Probanden haben selbst oder durch Erziehungsberechtigte der Untersuchung zugestimmt. Es konnte durch diese Arbeit gezeigt werden, dass zum einen die Methode des Tissue-­Phase-Mappings erfolgreich am Institut f{\"u}r Röntgendiagnostik des Universitätsklinikums W{\"u}rzburg eingef{\"u}hrt werden konnte. Zum anderen, dass die Ergebnisse der herzgesunden Probanden mit anderen, in der Vergangenheit durchgef{\"u}hrten Studien, ähnlich und vergleichbar sind. Zudem konnten teilweise signifikante Unterschiede der systolischen wie auch der diastolischen Geschwindigkeiten zwischen Probanden und Patienten der MICONOS Studie in einigen ROIs bzw. global nachgewiesen werden. Dies bedeutet, dass das hier vorgestellte Verfahren in der Lage ist, Unterschiede in den Geschwindigkeiten der regionalen wie auch globalen Herzwandbewegung in allen drei Bewegungsachsen zwischen verschiedenen Kollektiven zu detektieren. Diese Differenzen können ein Fr{\"u}hzeichen f{\"u}r eine pathologische Herzmuskelerkrankung sein und somit helfen, dass fr{\"u}hzeitig eine entsprechende Therapie begonnen wird. Aufgrund der Ergebnisse dieser Dissertation werden weitere Studien folgen, die helfen werden, dass das Tissue-­Phase-Mapping Verfahren Einzug in die klinische Routine erhalten wird.},
  subject      = {Friedreich-Ataxie},
  language  = {de}
}
@phdthesis{Gossger2005,
  author    = {Gossger, Nicoletta Philippine},
  title     = {Bildgebende Verfahren in der Diagnostik von Myopathien},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-14712},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2005},
  abstract  = {Ziel dieser Arbeit war es, die Aussagef{\"a}higkeit der Kernspintomographie mit der der Histologie und der Sonographie im Hinblick auf Umbauvorg{\"a}nge im Muskel in einem Patientenkollektiv mit Myopathien verschiedener {\"A}tiologie zu vergleichen. Weiterhin sollte {\"u}berpr{\"u}ft werden, ob die MRT-Untersuchung mittels fettsupprimierter TIRM-Sequenz und T1-gewichteter Sequenz nach Kontrastmittelgabe eine zus{\"a}tzliche Hilfe bei der Diagnosefindung darstellt. Hierzu wurden {\"u}ber den Zeitraum von zwei Jahren 26 Patienten, die in der Neurologischen Universit{\"a}tsklinik W{\"u}rzburg mit einer Myopathie aufgenommen wurden, nach einem standardisierten Protokoll klinisch, laborchemisch, sonographisch (n=16) sowie kernspintomographisch untersucht. Außerdem erfolgte zur histologischen Diagnostik nach Aufkl{\"a}rung des Patienten eine Muskelbiopsie. Die kernspintomographische Untersuchung umfasste eine konventionelle T1-gewichtete Sequenz, eine fettunterdr{\"u}ckte TIRM-Sequenz und eine T1-gewichtete Sequenz nach der Gabe von Gadolinium-DTPA. Das Patientenkollektiv wurde f{\"u}r die statistische Auswertung in drei klinische Diagnosegruppen aufgeteilt: nicht-entz{\"u}ndliche, degenerative Myopathien (Gruppe A1), nicht-entz{\"u}ndliche, nicht-degenerative Myopathien (Gruppe A2) und entz{\"u}ndliche Myopathien (Gruppe B). Die T1-gewichtete Spinechosequenz zeigte sich in diesen Untersuchungen wie in vorangegangenen Arbeiten im Bezug auf fett- und bindegewebigen Umbauvorg{\"a}nge des Muskelparenchyms am sensitivsten. Muskul{\"a}re Ver{\"a}nderungen in der T1-gewichteten Sequenz korrelieren mit der Schwere des Muskelumbaus in der Histologie und dem MRC-Kraftgrad als funktionellen Parameter. Pathologische Befunde in der {\"o}demsensitiven TIRM-Sequenz fanden sich bei entz{\"u}ndlichen und nicht-entz{\"u}ndlichen Myopathien etwa gleich h{\"a}ufig. Unsere Ergebnisse legen also nahe, dass eine {\"O}dementstehung nicht zwangsl{\"a}ufig an eine entz{\"u}ndliche Genese gebunden ist. Eine Korrelation des histologischen Entz{\"u}ndungsscores mit der TIRM-Sequenz konnte in keiner der Diagnosegruppen nachgewiesen werden. Hieraus ist abzuleiten, dass zur genauen Lokalisation der Muskelbiopsie eine MRT-Diagnostik vor allem bei entz{\"u}ndlichen Myopathien sehr zu empfehlen ist. In dieser Arbeit fanden sich in der Patientengruppe mit einer degenerativen Myopathie h{\"a}ufiger als bisher beschrieben pathologische Auff{\"a}lligkeiten (46 \% der Patienten) in der T1-Sequenz nach Kontrastmittelgabe. Die Kontrastmittelanreicherung entspricht nicht in jedem Fall einer in der TIRM-Sequenz festgestellten {\"O}demausbreitung. Bei den entz{\"u}ndlichen Myopathien zeigte sich eine Korrelation der CK-Aktivit{\"a}t mit der T1-gewichteten Sequenz nach Kontrastmittelgabe, jedoch nicht mit den beiden anderen MRT-Sequenzen. An Hand der vorliegenden Befunde l{\"a}sst sich vermuten, dass Kontrastmittelanreicherung ein Ausdruck aktiver muskul{\"a}rer Umbauprozesse im Rahmen entz{\"u}ndlicher und degenerativer Myopathien ist. Damit scheint unter dem Aspekt der Erfassung der Aktivit{\"a}t einer Myopathie eine Kontrastmittelgabe bei der MRT-Diagnostik auch bei degenerativen neuromuskul{\"a}ren Erkrankungen sinnvoll. Die Befunde der Sonographie korrelieren mit den Befunden aus der T1-gewichteten MRT- Sequenz, mit der Schwere des Muskelumbaus in der Histologie und dem MRC-Kraftgrad. Diese Ergebnisse zeigen die gute Nachweisrate von muskul{\"a}ren Ver{\"a}nderungen durch die Sonographie. Alle drei zu vergleichenden Untersuchungsmethoden eignen sich f{\"u}r die Diagnostik von Myopathien. Eine spezifische Diagnose der Muskelerkrankungen auf Grund der MRT allein, ist, auch bei der hier untersuchten Anwendung von zus{\"a}tzlicher Kontrastmittelgabe, noch nicht m{\"o}glich. Die Diagnosestellung erfolgt letztendlich aus der Anamnese und der Gesamtheit aller Befunde. Welche apparativen und bildgebenden Verfahren hierbei zum Einsatz kommen, muss individuell entschieden werden, da die Untersuchungsverfahren unterschiedliche Aspekte der Erkrankung beleuchten. Die vorliegenden Ergebnisse k{\"o}nnten hierbei eine Entscheidungshilfe sein.},
  language  = {de}
}
@article{HeinzMellerLuetkensetal.2022,
  author    = {Heinz, Tizian and Meller, Felix and Luetkens, Karsten Sebastian and Horas, Konstantin and Sch{\"a}fer, Thomas and Rudert, Maximilian and Reppenhagen, Stephan and Weißenberger, Manuel},
  title     = {Can the MRI based AMADEUS score accurately assess pre-surgery chondral defect severity according to the ICRS arthroscopic classification system?},
  series = {Journal of Experimental Orthopaedics},
  volume    = {9},
  journal   = {Journal of Experimental Orthopaedics},
  number    = {1},
  issn      = {2197-1153},
  doi       = {10.1186/s40634-022-00511-w},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300781},
  year      = {2022},
  abstract  = {Purpose The AMADEUS (Area Measurement And DEpth and Underlying Structures) scoring and grading system has been proposed for the MRI based evaluation of untreated focal chondral defects around the knee. The clinical practicability, its correlation with arthroscopically assessed grading systems (ICRS - International Cartilage Repair Society) and thereby its clinical value in terms of decision making and guiding prognosis was yet to determine. Methods From 2008 to 2019 a total of 89 individuals were indicated for high tibial valgus osteotomy (HTO) due to tibial varus deformity and concomitant chondral defects of the medial compartment of the knee. All patients received a preoperative MRI (1.5 Tesla or 3.0 Tesla) and pre-osteotomy diagnostic arthroscopy. Chondral defects of the medial compartment were scored and graded with the MRI based AMADEUS by three independent raters and compared to arthroscopic defect grading by the ICRS system. Interrater and intrarater reliability as well as correlation analysis with the ICRS classification system were assessed. Results Intraclass correlation coefficients for the various subscores of the AMADEUS showed an overall good to excellent interrater agreement (min: 0.26, max: 0.80). Intrarater agreement turned out to be substantially inferior (min: 0.08, max: 0.53). Spearman correlation revealed an overall moderate correlative association of the AMADEUS subscores with the ICRS classification system, apart from the defect area subscore. Sensitivity of the AMADEUS to accurately identify defect severity according to the ICRS was 0.7 (0.69 for 3.0 Tesla MRI, 0.67 for 1.5 Tesla MRI). The mean AMADEUS grade was 2.60 ± 0.81 and the mean ICRS score 2.90 ± 0.63. Conclusions Overall, the AMADEUS with all its subscores shows moderate correlation with the arthroscopic chondral grading system according to ICRS. This suggests that chondral defect grading by means of the MRI based AMADEUS is well capable of influencing and guiding treatment decisions. Interrater reliability shows overall good agreement.},
  language  = {en}
}
@phdthesis{Andelovic2024,
  author    = {Andelovic, Kristina},
  title     = {Characterization of arterial hemodynamics using mouse models of atherosclerosis and tissue-engineered artery models},
  doi       = {10.25972/OPUS-30360},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-303601},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {Within this thesis, three main approaches for the assessment and investigation of altered hemodynamics like wall shear stress, oscillatory shear index and the arterial pulse wave velocity in atherosclerosis development and progression were conducted: 1. The establishment of a fast method for the simultaneous assessment of 3D WSS and PWV in the complete murine aortic arch via high-resolution 4D-flow MRI 2. The utilization of serial in vivo measurements in atherosclerotic mouse models using high-resolution 4D-flow MRI, which were divided into studies describing altered hemodynamics in late and early atherosclerosis 3. The development of tissue-engineered artery models for the controllable application and variation of hemodynamic and biologic parameters, divided in native artery models and biofabricated artery models, aiming for the investigation of the relationship between atherogenesis and hemodynamics Chapter 2 describes the establishment of a method for the simultaneous measurement of 3D WSS and PWV in the murine aortic arch at, using ultra high-field MRI at 17.6T [16], based on the previously published method for fast, self-navigated wall shear stress measurements in the murine aortic arch using radial 4D-phase contrast MRI at 17.6 T [4]. This work is based on the collective work of Dr. Patrick Winter, who developed the method and the author of this thesis, Kristina Andelovic, who performed the experiments and statistical analyses. As the method described in this chapter is basis for the following in vivo studies and undividable into the sub-parts of the contributors without losing important information, this chapter was not split into the single parts to provide fundamental information about the measurement and analysis methods and therefore better understandability for the following studies. The main challenge in this chapter was to overcome the issue of the need for a high spatial resolution to determine the velocity gradients at the vascular wall for the WSS quantification and a high temporal resolution for the assessment of the PWV without prolonging the acquisition time due to the need for two separate measurements. Moreover, for a full coverage of the hemodynamics in the murine aortic arch, a 3D measurement is needed, which was achieved by utilization of retrospective navigation and radial trajectories, enabling a highly flexible reconstruction framework to either reconstruct images at lower spatial resolution and higher frame rates for the acquisition of the PWV or higher spatial resolution and lower frame rates for the acquisition of the 3D WSS in a reasonable measurement time of only 35 minutes. This enabled the in vivo assessment of all relevant hemodynamic parameters related to atherosclerosis development and progression in one experimental session. This method was validated in healthy wild type and atherosclerotic Apoe-/- mice, indicating no differences in robustness between pathological and healthy mice. The heterogeneous distribution of plaque development and arterial stiffening in atherosclerosis [10, 12], however, points out the importance of local PWV measurements. Therefore, future studies should focus on the 3D acquisition of the local PWV in the murine aortic arch based on the presented method, in order to enable spatially resolved correlations of local arterial stiffness with other hemodynamic parameters and plaque composition. In Chapter 3, the previously established methods were used for the investigation of changing aortic hemodynamics during ageing and atherosclerosis in healthy wild type and atherosclerotic Apoe-/- mice using the previously established methods [4, 16] based on high-resolution 4D-flow MRI. In this work, serial measurements of healthy and atherosclerotic mice were conducted to track all changes in hemodynamics in the complete aortic arch over time. Moreover, spatially resolved 2D projection maps of WSS and OSI of the complete aortic arch were generated. This important feature allowed for the pixel-wise statistical analysis of inter- and intragroup hemodynamic changes over time and most importantly - at a glance. The study revealed converse differences of local hemodynamic profiles in healthy WT and atherosclerotic Apoe-/- mice, with decreasing longWSS and increasing OSI, while showing constant PWV in healthy mice and increasing longWSS and decreasing OSI, while showing increased PWV in diseased mice. Moreover, spatially resolved correlations between WSS, PWV, plaque and vessel wall characteristics were enabled, giving detailed insights into coherences between hemodynamics and plaque composition. Here, the circWSS was identified as a potential marker of plaque size and composition in advanced atherosclerosis. Moreover, correlations with PWV values identified the maximum radStrain could serve as a potential marker for vascular elasticity. This study demonstrated the feasibility and utility of high-resolution 4D flow MRI to spatially resolve, visualize and analyze statistical differences in all relevant hemodynamic parameters over time and between healthy and diseased mice, which could significantly improve our understanding of plaque progression towards vulnerability. In future studies the relation of vascular elasticity and radial strain should be further investigated and validated with local PWV measurements and CFD. Moreover, the 2D histological datasets were not reflecting the 3D properties and regional characteristics of the atherosclerotic plaques. Therefore, future studies will include 3D plaque volume and composition analysis like morphological measurements with MRI or light-sheet microscopy to further improve the analysis of the relationship between hemodynamics and atherosclerosis. Chapter 4 aimed at the description and investigation of hemodynamics in early stages of atherosclerosis. Moreover, this study included measurements of hemodynamics at baseline levels in healthy WT and atherosclerotic mouse models. Due to the lack of hemodynamic-related studies in Ldlr-/- mice, which are the most used mouse models in atherosclerosis research together with the Apoe-/- mouse model, this model was included in this study to describe changing hemodynamics in the aortic arch at baseline levels and during early atherosclerosis development and progression for the first time. In this study, distinct differences in aortic geometries of these mouse models at baseline levels were described for the first time, which result in significantly different flow- and WSS profiles in the Ldlr-/- mouse model. Further basal characterization of different parameters revealed only characteristic differences in lipid profiles, proving that the geometry is highly influencing the local WSS in these models. Most interestingly, calculation of the atherogenic index of plasma revealed a significantly higher risk in Ldlr-/- mice with ongoing atherosclerosis development, but significantly greater plaque areas in the aortic arch of Apoe-/- mice. Due to the given basal WSS and OSI profile in these two mouse models - two parameters highly influencing plaque development and progression - there is evidence that the regional plaque development differs between these mouse models during very early atherogenesis. Therefore, future studies should focus on the spatiotemporal evaluation of plaque development and composition in the three defined aortic regions using morphological measurements with MRI or 3D histological analyses like LSFM. Moreover, this study offers an excellent basis for future studies incorporating CFD simulations, analyzing the different measured parameter combinations (e.g., aortic geometry of the Ldlr-/- mouse with the lipid profile of the Apoe-/- mouse), simulating the resulting plaque development and composition. This could help to understand the complex interplay between altered hemodynamics, serum lipids and atherosclerosis and significantly improve our basic understanding of key factors initiating atherosclerosis development. Chapter 5 describes the establishment of a tissue-engineered artery model, which is based on native, decellularized porcine carotid artery scaffolds, cultured in a MRI-suitable bioreactor-system [23] for the investigation of hemodynamic-related atherosclerosis development in a controllable manner, using the previously established methods for WSS and PWV assessment [4, 16]. This in vitro artery model aimed for the reduction of animal experiments, while simultaneously offering a simplified, but completely controllable physical and biological environment. For this, a very fast and gentle decellularization protocol was established in a first step, which resulted in porcine carotid artery scaffolds showing complete acellularity while maintaining the extracellular matrix composition, overall ultrastructure and mechanical strength of native arteries. Moreover, a good cellular adhesion and proliferation was achieved, which was evaluated with isolated human blood outgrowth endothelial cells. Most importantly, an MRI-suitable artery chamber was designed for the simultaneous cultivation and assessment of high-resolution 4D hemodynamics in the described artery models. Using high-resolution 4D-flow MRI, the bioreactor system was proven to be suitable to quantify the volume flow, the two components of the WSS and the radStrain as well as the PWV in artery models, with obtained values being comparable to values found in literature for in vivo measurements. Moreover, the identification of first atherosclerotic processes like intimal thickening is achievable by three-dimensional assessment of the vessel wall morphology in the in vitro models. However, one limitation is the lack of a medial smooth muscle cell layer due to the dense ECM. Here, the utilization of the laser-cutting technology for the generation of holes and / or pits on a microscale, eventually enabling seeding of the media with SMCs showed promising results in a first try and should be further investigated in future studies. Therefore, the proposed artery model possesses all relevant components for the extension to an atherosclerosis model which may pave the way towards a significant improvement of our understanding of the key mechanisms in atherogenesis. Chapter 6 describes the development of an easy-to-prepare, low cost and fully customizable artery model based on biomaterials. Here, thermoresponsive sacrificial scaffolds, processed with the technique of MEW were used for the creation of variable, biomimetic shapes to mimic the geometric properties of the aortic arch, consisting of both, bifurcations and curvatures. After embedding the sacrificial scaffold into a gelatin-hydrogel containing SMCs, it was crosslinked with bacterial transglutaminase before dissolution and flushing of the sacrificial scaffold. The hereby generated channel was subsequently seeded with ECs, resulting in an easy-to-prepare, fast and low-cost artery model. In contrast to the native artery model, this model is therefore more variable in size and shape and offers the possibility to include smooth muscle cells from the beginning. Moreover, a custom-built and highly adaptable perfusion chamber was designed specifically for the scaffold structure, which enabled a one-step creation and simultaneously offering the possibility for dynamic cultivation of the artery models, making it an excellent basis for the development of in vitro disease test systems for e.g., flow-related atherosclerosis research. Due to time constraints, the extension to an atherosclerosis model could not be achieved within the scope of this thesis. Therefore, future studies will focus on the development and validation of an in vitro atherosclerosis model based on the proposed bi- and three-layered artery models. In conclusion, this thesis paved the way for a fast acquisition and detailed analyses of changing hemodynamics during atherosclerosis development and progression, including spatially resolved analyses of all relevant hemodynamic parameters over time and in between different groups. Moreover, to reduce animal experiments, while gaining control over various parameters influencing atherosclerosis development, promising artery models were established, which have the potential to serve as a new platform for basic atherosclerosis research.},
  subject      = {H{\"a}modynamik},
  language  = {en}
}
@article{TaegerMuellerGraffLukasetal.2021,
  author    = {Taeger, Johannes and M{\"u}ller-Graff, Franz-Tassilo and Lukas, Ilgen and Schendzielorz, Philipp and Hagen, Rudolf and Neun, Tilman and Rak, Kristen},
  title     = {Cochlear duct length measurements in computed tomography and magnetic resonance imaging using newly developed techniques},
  series = {OTO Open},
  volume    = {5},
  journal   = {OTO Open},
  number    = {3},
  doi       = {10.1177/2473974X211045312},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-263922},
  pages     = {1-8},
  year      = {2021},
  abstract  = {Objective Growing interest in measuring the cochlear duct length (CDL) has emerged, since it can influence the selection of cochlear implant electrodes. Currently the measurements are performed with ionized radiation imaging. Only a few studies have explored CDL measurements in magnetic resonance imaging (MRI). Therefore, the presented study aims to fill this gap by estimating CDL in MRI and comparing it with multislice computed tomography (CT). Study Design Retrospective data analyses of 42 cochleae. Setting Tertiary care medical center. Methods Diameter (A value) and width (B value) of the cochlea were measured in HOROS software. The CDL and the 2-turn length were determined by the elliptic circular approximation (ECA). In addition, the CDL, the 2-turn length, and the angular length were determined via HOROS software by the multiplanar reconstruction (MPR) method. Results CDL values were significantly shorter in MRI by MPR (d = 1.38 mm, P < .001) but not by ECA. Similar 2-turn length measurements were significantly lower in MRI by MPR (d = 1.67 mm) and ECA (d = 1.19 mm, both P < .001). In contrast, angular length was significantly higher in MRI (d = 26.79°, P < .001). When the values were set in relation to the frequencies of the cochlea, no clinically relevant differences were estimated (58 Hz at 28-mm CDL). Conclusion In the presented study, CDL was investigated in CT and MRI by using different approaches. Since no clinically relevant differences were found, diagnostics with radiation may be omitted prior to cochlear implantation; thus, a concept of radiation-free cochlear implantation could be established.},
  language  = {en}
}
@article{GilbertBoehmEdenetal.2016,
  author    = {Gilbert, Fabian and B{\"o}hm, Dirk and Eden, Lars and Schmalzl, Jonas and Meffert, Rainer H. and K{\"o}stler, Herbert and Weng, Andreas M. and Ziegler, Dirk},
  title     = {Comparing the MRI-based Goutallier Classification to an experimental quantitative MR spectroscopic fat measurement of the supraspinatus muscle},
  series = {BMC Musculoskeletal Disorders},
  volume    = {17},
  journal   = {BMC Musculoskeletal Disorders},
  number    = {355},
  doi       = {10.1186/s12891-016-1216-3},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-147788},
  year      = {2016},
  abstract  = {Background The Goutallier Classification is a semi quantitative classification system to determine the amount of fatty degeneration in rotator cuff muscles. Although initially proposed for axial computer tomography scans it is currently applied to magnet-resonance-imaging-scans. The role for its clinical use is controversial, as the reliability of the classification has been shown to be inconsistent. The purpose of this study was to compare the semi quantitative MRI-based Goutallier Classification applied by 5 different raters to experimental MR spectroscopic quantitative fat measurement in order to determine the correlation between this classification system and the true extent of fatty degeneration shown by spectroscopy. Methods MRI-scans of 42 patients with rotator cuff tears were examined by 5 shoulder surgeons and were graduated according to the MRI-based Goutallier Classification proposed by Fuchs et al. Additionally the fat/water ratio was measured with MR spectroscopy using the experimental SPLASH technique. The semi quantitative grading according to the Goutallier Classification was statistically correlated with the quantitative measured fat/water ratio using Spearman's rank correlation. Results Statistical analysis of the data revealed only fair correlation of the Goutallier Classification system and the quantitative fat/water ratio with R = 0.35 (p < 0.05). By dichotomizing the scale the correlation was 0.72. The interobserver and intraobserver reliabilities were substantial with R = 0.62 and R = 0.74 (p < 0.01). Conclusion The correlation between the semi quantitative MRI based Goutallier Classification system and MR spectroscopic fat measurement is weak. As an adequate estimation of fatty degeneration based on standard MRI may not be possible, quantitative methods need to be considered in order to increase diagnostic safety and thus provide patients with ideal care in regard to the amount of fatty degeneration. Spectroscopic MR measurement may increase the accuracy of the Goutallier classification and thus improve the prediction of clinical results after rotator cuff repair. However, these techniques are currently only available in an experimental setting.},
  language  = {en}
}