1,027 research outputs found

    New Technology and Techniques for Needle-Based Magnetic Resonance Image-Guided Prostate Focal Therapy

    Get PDF
    The most common diagnosis of prostate cancer is that of localized disease, and unfortunately the optimal type of treatment for these men is not yet certain. Magnetic resonance image (MRI)-guided focal laser ablation (FLA) therapy is a promising potential treatment option for select men with localized prostate cancer, and may result in fewer side effects than whole-gland therapies, while still achieving oncologic control. The objective of this thesis was to develop methods of accurately guiding needles to the prostate within the bore of a clinical MRI scanner for MRI-guided FLA therapy. To achieve this goal, a mechatronic needle guidance system was developed. The system enables precise targeting of prostate tumours through angulated trajectories and insertion of needles with the patient in the bore of a clinical MRI scanner. After confirming sufficient accuracy in phantoms, and good MRI-compatibility, the system was used to guide needles for MRI-guided FLA therapy in eight patients. Results from this case series demonstrated an improvement in needle guidance time and ease of needle delivery compared to conventional approaches. Methods of more reliable treatment planning were sought, leading to the development of a systematic treatment planning method, and Monte Carlo simulations of needle placement uncertainty. The result was an estimate of the maximum size of focal target that can be confidently ablated using the mechatronic needle guidance system, leading to better guidelines for patient eligibility. These results also quantified the benefit that could be gained with improved techniques for needle guidance

    The current state-of-the-art of spinal cord imaging: methods.

    Get PDF
    A first-ever spinal cord imaging meeting was sponsored by the International Spinal Research Trust and the Wings for Life Foundation with the aim of identifying the current state-of-the-art of spinal cord imaging, the current greatest challenges, and greatest needs for future development. This meeting was attended by a small group of invited experts spanning all aspects of spinal cord imaging from basic research to clinical practice. The greatest current challenges for spinal cord imaging were identified as arising from the imaging environment itself; difficult imaging environment created by the bone surrounding the spinal canal, physiological motion of the cord and adjacent tissues, and small cross-sectional dimensions of the spinal cord, exacerbated by metallic implants often present in injured patients. Challenges were also identified as a result of a lack of "critical mass" of researchers taking on the development of spinal cord imaging, affecting both the rate of progress in the field, and the demand for equipment and software to manufacturers to produce the necessary tools. Here we define the current state-of-the-art of spinal cord imaging, discuss the underlying theory and challenges, and present the evidence for the current and potential power of these methods. In two review papers (part I and part II), we propose that the challenges can be overcome with advances in methods, improving availability and effectiveness of methods, and linking existing researchers to create the necessary scientific and clinical network to advance the rate of progress and impact of the research

    A Feasibility Study of Ultra-Short Echo Time MRI for Positive Contrast Visualization of Prostate Brachytherapy Permanent Seed Implants for Post-Implant Dosimetry

    Get PDF
    Purpose: Ultra-short echo time (UTE) imaging is a magnetic resonance imaging (MRI) technique that uses very short echo times (on the order of microseconds) to measure rapid T2 relaxation. An application of UTE is the visualization of magnetic susceptibility-induced shortening of T2 in tissues adjacent to metal, such as prostate tissue with implanted brachytherapy seeds. This study assessed UTE imaging of prostate brachytherapy seeds on a clinical 3T MRI scanner to provide images for post-implant dosimetry. Methods: A prostate tissue phantom was made of gelatin mixed with Gd and other materials to mimic the prostate peripheral zone’s T1 and T2 relaxation times; this phantom was used to investigate the effect of UTE acquisition parameters on brachytherapy seed visibility. A second phantom was made to model prostate tissue surrounded by muscle tissue; this pelvic phantom was implanted with 85 titanium brachytherapy seeds (STM1251, Bard Medical). Both phantoms were scanned on a 3T GE scanner with a 3D UTE pulse sequence and a fast spin echo (FSE) pulse sequence. The average seed SNR, the CNR between seed and prostate material, and visual characteristics of the seeds were assessed. A seed counting procedure was developed based on the visual seed characteristics, and subsequently used by two physicists to locate seeds in UTE images of the pelvic phantom. Results: On 3D UTE images, the metal seeds caused a bright ring-link artifact in adjacent prostate tissue due to susceptibility-induced T2 shortening. The average seed SNR was 15.99±1.52 for UTE compared to 32.32±22.43 for FSE; CNR between seed and prostate was 6.73±1.85 for UTE vs. 23.76±12.87 for FSE. The ring was larger in diameter than a seed itself; apparent seed diameters were 4.65±0.363 mm for UTE compared to 1.46±0.38 mm for FSE. The 3D spatial ring pattern facilitated differentiation of seeds from needle tracks and seed spacers. The two physicists counted 83 and 86 seeds respectively in the UTE images. Prostate boundaries were less well visualized with UTE compared to FSE. Conclusion: With its ability to visualize brachytherapy seeds, UTE imaging appears to provide an alternative approach to CT for seed identification. Compared to fusion of separately-acquired CT images and T2-weighted MR images (for delineation of prostate boundaries), UTE and T2-weighted MR can be acquired in a single imaging session – a convenience to patients while potentially minimizing inter-modality image registration issues. A study in prostate brachytherapy patients of the quality of post-implant dosimetry with UTE imaging compared to CT imaging is recommended

    Dual echo positive contrast bSSFP for real-time visualization of passive devices during magnetic resonance guided cardiovascular catheterization

    Get PDF
    Abstract Background: Cardiovascular magnetic resonance (CMR) guided cardiovascular catheterizations can potentially reduce ionizing radiation exposure and enable new interventions. Commercially available paramagnetic X-Ray devices create a small signal void in CMR images, which is ambiguous and insufficient to guide catheterization procedures. This work aims to improve real-time CMR of off-the-shelf X-Ray devices by developing a real-time positive contrast sequence with color overlay of the device onto anatomy

    Head Motion Correction in Magnetic Resonance Imaging Using NMR Field Probes

    Get PDF
    Magnetic Resonance Imaging (MRI) is a widely used imaging technology in medicine. Its advantages include good soft tissue contrast and the use of non-ionizing radiation in contrast to for example computed tomography (CT). One drawback are the long acquisition times that are needed. They depend on the diagnostic use case but are usually within the range of minutes. These long scan times make the images prone to patient motion during image acquisition which can lead to blurring or ghosting artifacts. Those artifacts might render the diagnostic value of the images useless which requires the image to be reacquired or the patient to be sedated before the scan to prevent motion artifacts. This is where motion correction comes into play. One can distinguish between retrospective and prospective motion correction (PMC) methods. Retrospective motion correction tries to improve image quality after the image acquisition by post-processing and possibly using additional motion tracking information, if available. Prospective motion correction relies on a motion tracking modality that is used to provide motion information to update imaging parameters during image acquisition. Both motion correction methods can also be used in combination with each other. This thesis, however, will focus on the implementation and validation of a system for prospective head motion correction. The system consisted of four nuclear magnetic resonance (NMR) field probes using. Those feld probes were attached to the head and used to measure the spatiotemporal evolution of magnetic felds. By switching spatially varying magnetic fields, this information can be used to track the field probes' positions and calculate the corresponding head motion in order to perform prospective motion correction.Die Magnetresonanztomographie (MRT) ist ein in der Medizin weitverbreitetes bildgebendes Verfahren. Ihre Vorteile sind unter anderem der gute Gewebekontrast und die Verwendung von nichtionisierender Strahlung im Gegensatz zur Computertomographie (CT). Ein Nachteil ist die Länge der Zeit, die notwendig ist um ein Bild aufzunehmen. Sie hängt natürlich vom jeweiligen diagnostischen Anwendungsfall ab, bewegt sich aber normalerweise im Bereich von Minuten. Diese langen Aufnahmezeiten machen die Bilder anfällig für Patientenbewegungen, welche zu unscharfen Bildern oder sogenannten Ghostingartefakten, bei denen sich Bildteile wiederholen, führen. Diese Artefakte können dazu führen, dass eine Diagnose nicht mehr möglich ist, was entweder eine erneute Aufnahme des Bildes notwendig macht oder eine Sedierung des Patienten, um Bewegung zu vermeiden. Hier kommen Bewegungskorrekturverfahren ins Spiel. Die sogenannte prospektive Bewegungskorrektur benötigt zusätzliche Bewegungsinformationen, die noch während der Bildaufnahme dazu verwendet werden, die Bildgebungsparameter so zu verändern, dass der Bildausschnitt der Bewegung folgt. Diese Arbeit beschäftigt sich mit der Entwicklung und Validierung eines Systems zur prospektiven Bewegungskorrektur. Das entwickelte System bestand aus vier Kernspinresonanz-Magnetfeldsensoren (NMR field probes). Diese Sensoren wurden am Kopf der Probanden befestigt und konnten die räumliche und zeitliche Veränderung des Magnetfeldes messen. Das Ziel war es, dadurch die Sensorpositionen zu bestimmen und die zugehörigen Kopfbewegungen zu berechnen, um mit diesen Informationen die prospektive Bewegungskorrektur zu implementieren. Dabei war der erste Schritt die Entwicklung eines eigenständigen Sende- und Empfangssystems zur Signalgeneration und -akquise der Sensoren. Dieses System bestand aus mikroelektronischen Komponenten und war nötig, um die Messungen der Sensoren unabhängig von der Hardware des Kernspintomographen durchführen zu können. Im zweiten Schritt sollte die Genauigkeit der Positionsbestimmung der Sensoren verbessert werden. Die Position der Sensoren wurde durch lineare Magnetfeldgradienten bestimmt, die nacheinander auf allen räumlichen Achsen geschaltet wurden. Echte Gradienten besitzen allerdings ein charakteristisches nichtlineares Verhalten, das ausgemessen werden musste, um das lineare Modell der Positionsbestimmung zu verbessern. Dazu wurden Messungen mit einem Sensor in verschiedenen bekannten Positionen durchgeführt sowie zusätzlich Messungen mit einer sogenannten Feldkamera, welche aus 16 dieser Sensoren besteht. Im letzten Schritt wurde dann das fertige System zur Bewegungskorrektur für verschiedene Bildgebungssequenzen getestet und schließlich mit einem anderen Bewegungskorrektursystem verglichen, welches auf einer optischen Kamera basiert

    High-resolution diffusion-weighted brain MRI under motion

    Get PDF
    Magnetic resonance imaging is one of the fastest developing medical imaging techniques. It provides excellent soft tissue contrast and has been a leading tool for neuroradiology and neuroscience research over the last decades. One of the possible MR imaging contrasts is the ability to visualize diffusion processes. The method, referred to as diffusion-weighted imaging, is one of the most common clinical contrasts but is prone to artifacts and is challenging to acquire at high resolutions. This thesis aimed to improve the resolution of diffusion weighted imaging, both in a clinical and in a research context. While diffusion-weighted imaging traditionally has been considered a 2D technique the manuscripts and methods presented here explore 3D diffusion acquisitions with isotropic resolution. Acquiring multiple small 3D volumes, or slabs, which are combined into one full volume has been the method of choice in this work. The first paper presented explores a parallel imaging driven multi-echo EPI readout to enable high resolution with reduced geometric distortions. The work performed on diffusion phase correction lead to an understanding that was used for the subsequent multi-slab papers. The second and third papers introduce the diffusion-weighted 3D multi-slab echo-planar imaging technique and explore its advantages and performance. As the method requires a slightly increased acquisition time the need for prospective motion correction became apparent. The forth paper suggests a new motion navigator using the subcutaneous fat surrounding the skull for rigid body head motion estimation, dubbed FatNav. The spatially sparse representation of the fat signal allowed for high parallel imaging acceleration factors, short acquisition times, and reduced geometric distortions of the navigator. The fifth manuscript presents a combination of the high-resolution 3D multi-slab technique and a modified FatNav module. Unlike our first FatNav implementation, using a single sagittal slab, this modified navigator acquired orthogonal projections of the head using the fat signal alone. The combined use of both presented methods provides a promising start for a fully motion corrected high-resolution diffusion acquisition in a clinical setting

    Motion robust acquisition and reconstruction of quantitative T2* maps in the developing brain

    Get PDF
    The goal of the research presented in this thesis was to develop methods for quantitative T2* mapping of the developing brain. Brain maturation in the early period of life involves complex structural and physiological changes caused by synaptogenesis, myelination and growth of cells. Molecular structures and biological processes give rise to varying levels of T2* relaxation time, which is an inherent contrast mechanism in magnetic resonance imaging. The knowledge of T2* relaxation times in the brain can thus help with evaluation of pathology by establishing its normative values in the key areas of the brain. T2* relaxation values are a valuable biomarker for myelin microstructure and iron concentration, as well as an important guide towards achievement of optimal fMRI contrast. However, fetal MR imaging is a significant step up from neonatal or adult MR imaging due to the complexity of the acquisition and reconstruction techniques that are required to provide high quality artifact-free images in the presence of maternal respiration and unpredictable fetal motion. The first contribution of this thesis, described in Chapter 4, presents a novel acquisition method for measurement of fetal brain T2* values. At the time of publication, this was the first study of fetal brain T2* values. Single shot multi-echo gradient echo EPI was proposed as a rapid method for measuring fetal T2* values by effectively freezing intra-slice motion. The study concluded that fetal T2* values are higher than those previously reported for pre-term neonates and decline with a consistent trend across gestational age. The data also suggested that longer than usual echo times or direct T2* measurement should be considered when performing fetal fMRI in order to reach optimal BOLD sensitivity. For the second contribution, described in Chapter 5, measurements were extended to a higher field strength of 3T and reported, for the first time, both for fetal and neonatal subjects at this field strength. The technical contribution of this work is a fully automatic segmentation framework that propagates brain tissue labels onto the acquired T2* maps without the need for manual intervention. The third contribution, described in Chapter 6, proposed a new method for performing 3D fetal brain reconstruction where the available data is sparse and is therefore limited in the use of current state of the art techniques for 3D brain reconstruction in the presence of motion. To enable a high resolution reconstruction, a generative adversarial network was trained to perform image to image translation between T2 weighted and T2* weighted data. Translated images could then be served as a prior for slice alignment and super resolution reconstruction of 3D brain image.Open Acces
    • …
    corecore