The wandering spleen: an unusual case of thrombocytopenia

Thrombocytopenia is a common laboratory finding in current medical practices. The workup of thrombocytopenia can be challenging with numerous causes that can be included in the differential diagnosis. Thrombocytopenia can be due to bone marrow hypoproliferation, peripheral destruction, or sequestration. This paper presents a case of isolated thrombocytopenia in a young female and discusses the causes of thrombocytopenia

Sodium Magnetic Resonance Imaging at 9.4 Tesla

The motivation to perform magnetic resonance imaging (MRI) at ultra-high field strength (UHF) (B0 ≥ 7 Tesla) is primarily driven by the increased sensitivity compared to low field MRI. This is especially true for nuclei which exhibit intrinsically a low signal-to-noise ratio (SNR) either due to their physical properties or their small in vivo concentrations. The aim of this thesis was to establish the measurement techniques required for sodium magnetic resonance imaging at 9.4 Tesla and to overcome some of the limitations faced at lower field strengths. For this purpose, the hardware as well as the software used for the acquisition of the MR signal were designed and adapted to each other with great care in order to harness the full potential offered by UHF MRI. In the first part of this thesis, a novel coil setup consisting of a single-tuned sodium birdcage coil and a proton patch antenna was used to acquire high-resolution quantitative sodium images of several healthy volunteers. This setup provided a satisfactory sensitivity at the sodium frequency and offered at the same time the possibility to acquire the proton signal for anatomical localization and B0 shimming. Correction methods for inhomogeneities of the B0 and radio-frequency (RF) transmit field (B1) were implemented and partial volume effects were mitigated by the reduced voxel size, which enabled a more accurate quantification of the sodium concentration in the human brain. However, the spatial resolution was insufficient to completely avoid quantifications errors at tissue boundaries, although the achieved sensitivity was considerably higher compared to previous studies. The second part of the thesis focused on further increasing the sensitivity of the coil setup at the sodium frequency without sacrificing the proton imaging capability. The final coil design was made up of an assembly of three coils arranged in layers. The innermost layer consisted of a multi-channel receiver array to boost the sensitivity for sodium imaging. The middle layer comprised the sodium transmit array and the outer layer was formed by a dipole array to enable proton imaging. It could be shown that the proposed coil setup possessed all the required features needed for efficient multi-nuclear MRI at UHF and enabled the acquisition of sodium images having a quality not previously achieved. In the last part of the thesis, the high sensitivity provided by the multi-channel coil array and the strong static magnetic field was used to perform sodium triple quantum filtered (TQF) imaging, which is known to be an SNR-critical application. The latter allows differentiating between intra- and extracellular sodium, which might be valuable information for disease diagnosis and monitoring. Apart from the low SNR, the high power deposition rates associated with this type of imaging technique are challenging, especially at UHF. To overcome this problem, at least partially, a modulation of the flip angles of the TQ preparation module was proposed and shown to improve the sensitivity by about 20%.Das Bestreben Magnetresonanztomographie (MRT) bei ultra-hohen Feldstärken (UHF) (B0 ≥ 7 Tesla) durchzuführen kann in erster Linie mit der deutlich erhöhten MR-Empfindlichkeit im Gegensatz zu niedrigeren Feldstärken erklärt werden. Dies gilt insbesondere für die Bildgebung mit Kernen, die an sich schon ein niedriges Signal-Rausch-Verhältnis (SNR) ausweisen; dies entweder aufgrund ihrer physikalischen Eigenschaften oder ihrer geringen In-vivo-Konzentrationen. Das Ziel dieser Arbeit war es die erforderlichen Messverfahren für die Natriumbildgebung bei 9,4 Tesla zu erarbeiten und einige Einschränkungen, die bei niedrigeren Feldstärken auftreten, zu überwinden. Zu diesem Zweck wurde maßgeschneiderte Hard- und Software für die Erfassung des MR-Signals entwickelt und aufeinander abgestimmt um das volle Potential, das UHF-MRT bietet, zu nutzen. Im ersten Teil der Arbeit wurde ein neuartiger Spulenaufbau, bestehend aus einer mono-resonanten Natrium-Birdcage-Spule und einer Protonen-Patch-Antenne, verwendet um hochauflösende quantitative Natriumbilder von mehreren gesunden Probanden aufzunehmen. Dieser Aufbau stellte eine zufriedenstellende Empfindlichkeit bei der Natriumfrequenz sicher und bot gleichzeitig die Möglichkeit das Protonensignal für anatomische Lokalisation und B0-Shimming zu nutzen. Korrekturverfahren wurden implementiert und angewendet um Inhomogenitäten des B0 und Radiofrequenz- (RF) Feldes (B1) entgegenzuwirken. Durch die Reduzierung der Voxelgröße konnten Partialvolumeneffekte gemindert und eine genauere Quantifizierung der Natriumkonzentration im menschlichen Gehirn erreicht werden. Jedoch war die erreichte räumliche Auflösung unzureichend um Quantifizierungsfehler an Gewebegrenzen gänzlich zu vermeiden, obwohl die erzielte Empfindlichkeit deutlich höher war als bei vorhergehenden Studien. Der zweite Teil der Arbeit konzentrierte sich auf eine weitere Erhöhung der Empfindlichkeit des Spulenaufbaus für die Natriumbildgebung ohne dabei die Möglichkeit der Protonenbildgebung zu verlieren. Der endgültige Messaufbau bestand aus drei in Schichten angeordneten Spulen. Die innerste Schicht bildete eine Mehrkanalempfangsanordnung, welche eine möglichst hohe Empfindlichkeit für das Natriumsignal gewährleisten sollte. Die Natriumsendespule stellte die mittlere Schicht dar. Eine Dipolantennenanordnung bildete die äußerste Schicht und wurde für die Protonenbildgebung benutzt. Es konnte gezeigt werden, dass der vorgeschlagene Spulenaufbau alle erforderlichen Funktionen besitzt, die für eine effiziente Mehrkern-MRT-Messung bei ultra-hohem Feld benötig werden, und es erlaubt Natriumbilder mit einer vorher unerreichten Qualität aufzunehmen. Im letzten Teil der Arbeit wurde die hohe MR-Empfindlichkeit, resultierend aus der Verwendung einer Mehrkanalspule und eines starken statischen Magnetfeldes, genutzt um Tripelquanten (TQ)-Kohärenzen zu messen, welche nur ein sehr geringes SNR aufweisen. Tripelquanten-gefilterte (TQF) Bilder ermöglichen die Unterscheidung zwischen intra- und extrazellulären Natrium und können möglicherweise wertvolle Informationen für die Diagnose und Überwachung von Krankheiten liefern. Abgesehen von dem niedrigen SNR, bereiten die hohen RF-Sendeleistungen, die für diese Bildgebungstechnik benötigt werden, Probleme insbesondere bei UHF. Um dieses Problem zumindest teilweise zu mindern wurde eine Modulation der Flipwinkel, welche die TQ-Kohärenzen erzeugen, vorgeschlagen und gezeigt, dass sich so die Sensitivität der TQ Sequenz um etwa 20% steigern lässt

Paramagnetic lanthanide chelates for multicontrast MRI

[Abstract] The preparation of a paramagnetic chelator that serves as a platform for multicontrast MRI, and can be utilized either as a T1-weighted, paraCEST or 19F MRI contrast agent is reported. Its europium(III) complex exhibits an extremely slow water exchange rate which is optimal for the use in CEST MRI. The potential of this platform was demonstrated through a series of MRI studies on tube phantoms and animals.Ministerio de Economía y Competitividad; CTQ2013-43243-PMinisterio de Economía y Competitividad; CTQ2015-71211-RED

Volumetric imaging with homogenised excitation and static field at 9.4 T

Objectives: To overcome the challenges of B and RF excitation inhomogeneity at ultra-high field MRI, a workflow for volumetric B and flip-angle homogenisation was implemented on a human 9.4 T scanner. Materials and methods: Imaging was performed with a 9.4 T human MR scanner (Siemens Medical Solutions, Erlangen, Germany) using a 16-channel parallel transmission system. B- and B-mapping were done using a dual-echo GRE and transmit phase-encoded DREAM, respectively. B shims and a small-tip-angle-approximation kT-points pulse were calculated with an off-line routine and applied to acquire T- and T -weighted images with MPRAGE and 3D EPI, respectively. Results: Over six in vivo acquisitions, the B-distribution in a region-of-interest defined by a brain mask was reduced down to a full-width-half-maximum of 0.10\ua0±\ua00.01\ua0ppm (39\ua0±\ua02\ua0Hz). Utilising the kT-points pulses, the normalised RMSE of the excitation was decreased from CP-mode’s 30.5\ua0±\ua00.9 to 9.2\ua0±\ua00.7\ua0% with all B \ua0voids eliminated. The SNR inhomogeneities and contrast variations in the T- and T -weighted volumetric images were greatly reduced which led to successful tissue segmentation of the T-weighted image. Conclusion: A 15-minute B- and flip-angle homogenisation workflow, including the B- and B-map acquisitions, was successfully implemented and enabled us to reduce intensity and contrast variations as well as echo-planar image distortions in 9.4 T images

Quantitative and functional pulsed arterial spin labeling in the human brain at 9.4 t

Purpose: The feasibility of multislice pulsed arterial spin labeling (PASL) of the human brain at 9.4 T was investigated. To demonstrate the potential of arterial spin labeling (ASL) at this field strength, quantitative, functional, and high-resolution (1.05 × 1.05 × 2 mm3) ASL experiments were performed. Methods: PASL was implemented using a numerically optimized adiabatic inversion pulse and presaturation scheme. Quantitative measurements were performed at 3 T and 9.4 T and evaluated on a voxel-by-voxel basis. In a functional experiment, activation maps obtained with a conventional blood-oxygen-level-dependent (BOLD)-weighted sequence were compared with a functional ASL (fASL) measurement. Results: Quantitative measurements revealed a 23% lower perfusion in gray matter and 17% lower perfusion in white matter at 9.4 T compared with 3 T. Furthermore almost identical transit delays and bolus durations were found at both field strengths whereas the calculated voxel volume corrected signal-to-noise ratio was 1.9 times higher at 9.4 T. This result was confirmed by the high-resolution experiment. The functional experiment yielded comparable activation maps for the fASL and BOLD measurements. Conclusion: Although PASL at ultrahigh field strengths is limited by high specific absorption rate, functional and quantitative perfusion-weighted images showing a high degree of detail can be obtained