Dissertations / Theses: 'Parallell imaging'

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Herterich, Rebecka, and Anna Sumarokova. "Coil Sensitivity Estimation and Intensity Normalisation for Magnetic Resonance Imaging." Thesis, KTH, Medicinteknik och hälsosystem, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-263149.

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The quest for improved efficiency in magnetic resonance imaging has motivated the development of strategies like parallel imaging where arrays of multiple receiver coils are operated simultaneously in parallel. The objective of this project was to find an estimation of phased-array coil sensitivity profiles of magnetic resonance images of the human body. These sensitivity maps can then be used to perform an intensity inhomogeneity correction of the images. Through investigative work in Matlab, a script was developed that uses data embedded in raw data from a magnetic resonance scan, to generate coil sensitivities for each voxel of the volume of interest and recalculate them to two-dimensional sensitivity maps of the corresponding diagnostic images. The resulting mapped sensitivity profiles can be used in Sensitivity Encoding where a more exact solution can be obtained using the carefully estimated sensitivity maps of the images.
Inom magnetresonanstomografi eftersträvas förbättrad effektivitet, villket bidragit till utvecklingen av strategier som parallell imaging, där arrayer av flera mottagarspolar andvänds samtidigt. Syftet med detta projekt var att uppskattamottagarspolarnas känslighetskarta för att utnyttja dem till i metoder inom magnetresonansavbildning. Dessa känslighetskartor kan användas för att utföra intensitetsinhomogenitetskorrigering av bilderna. Genom utforskande arbete i Matlab utvecklades ett skript som tillämpar inbyggd rådata, från en magnetiskresonansavbildning för att generera spolens känslighet för varje voxel av volymen och omberäkna dem till tvådimensionella känslighetskartor av motsvarande diagnostiska bilder. De resulterande kartlagda känslighetsprofilerna kan användas i känslighetskodning, där en mer exakt lösning kan erhållas med hjälp av de noggrant uppskattade känslighetskartorna.

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Spence, Dan Kenrick. "Array combination for parallel imaging in Magnetic Resonance Imaging." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5944.

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In Magnetic Resonance Imaging, the time required to generate an image is proportional to the number of steps used to encode the spatial information. In rapid imaging, an array of coil elements and receivers are used to reduce the number of encoding steps required to generate an image. This is done using knowledge of the spatial sensitivity of the array and receiver channels. Recently, these arrays have begun to include a large number of coil elements. Ideally, each coil element would have its own receiver channel to acquire the image data. In practice, this is not always possible due to economic or other constraints. In this dissertation, methods are explored to combine a large array to a limited number of receivers so as to optimize the performance for parallel imaging; this dissertation focuses on SENSE in particular. Simple combinations that represent larger coils that might be constructed are discussed. More complex solutions form current sheets. One solution uses Roemer'ÃÂÃÂs method to optimize image SNR at a set of points. In this dissertation, Roemer's solution is generalized to give the weighting coefficients that optimize SNR over regions. Also, solutions fitted to ideal profiles that minimize noise amplification are shown. These fitted profiles can allow the SENSE algorithm to function at optimal reduction factors. Finally, a description of how to build the combiner in hardware is discussed.

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Brown, David Gerald. "Instrumentation for parallel magnetic resonance imaging." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4784.

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Parallel magnetic resonance (MR) imaging may be used to increase either the throughput or the speed of the MR imaging experiment. As such, parallel imaging may be accomplished either through a "parallelization" of the MR experiment, or by the use of arrays of sensors. In parallelization, multiple MR scanners (or multiple sensors) are used to collect images from different samples simultaneously. This allows for an increase in the throughput, not the inherent speed, of the MR experiment. Parallel imaging with arrays of sensor coils, on the other hand, makes use of the spatial localization properties of the sensors in an imaging array to allow a reduction in the number of phase encodes required in acquiring an image. This reduced phase-encoding requirement permits an increase in the overall imaging speed by a factor up to the number of sensors in the imaging array. The focus of this dissertation has been the development of cost-effective instrumentation that would enable advances in the state of the art of parallel MR imaging. First, a low-cost desktop MR scanner was developed (< $13,000) for imaging small samples (2.54 cm fields-of view) at low magnetic field strengths (< 0.25 T). The performance of the prototype was verified through bench-top measurements and phantom imaging. The prototype transceiver has demonstrated an SNR (signal-to-noise ratio) comparable to that of a commercial MR system. This scanner could make parallelization of the MR experiment a practical reality, at least in the areas of small animal research and education. A 64-channel receiver for parallel MR imaging with arrays of sensors was also developed. The receiver prototype was characterized through both bench-top tests and phantom imaging. The parallel receiver is capable of simultaneous reception of up to sixty-four, 1 MHz bandwidth MR signals, at imaging frequencies from 63 to 200 MHz, with an SNR performance (on each channel) comparable to that of a single-channel commercial MR receiver. The prototype should enable investigation into the speed increases obtainable from imaging with large arrays of sensors and has already been used to develop a new parallel imaging technique known as single echo acquisition (SEA) imaging.

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Qu, Peng. "Advances in parallel imaging reconstruction techniques." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36898582.

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Qu, Peng, and 瞿蓬. "Advances in parallel imaging reconstruction techniques." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36898582.

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Kim, Wan. "Study of parallel MR imaging techniques." Thesis, State University of New York at Buffalo, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1594739.

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In MRI, it is more desirable to scan less data as possible because it reduces MRI scanning time. We want to get a clear image by reconstructing the signals we acquire from the MRI machine. Special scanning or sampling techniques are needed to overcome this issue based on various mathematical methods.

We present an improved random sampling pattern for SAKE (simultaneous autocalibrating and k-space estimation) reconstruction and an iterative GRAPPA reconstruction using Wiener filter.

In our iterative method using Wiener filter, in contrast to the conventional GRAPPA where only the auto calibration signals (ACS) are used to find the convolution weights, our proposed method iteratively updates the convolution weights using both the acquired and reconstructed data from previous iterations in the entire k-space. To avoid error propagation, the method applies adaptive Wiener filter on the reconstructed data. Experimental results demonstrate that even with a smaller number of ACS lines the proposed method improves the SNR when compared to GRAPPA.

In compressed sensing MRI, it is very important to design sampling pattern for random sampling. For example, SAKE (simultaneous auto-calibrating and k-space estimation) is a parallel MRI reconstruction method using random undersampling. It formulates image reconstruction as a structured low-rank matrix completion problem. Variable density (VD) Poisson discs are typically adopted for 2D random sampling. The basic concept of Poisson disc generation is to guarantee samples are neither too close to nor too far away from each other. However, it is difficult to meet such a condition especially in the high density region. Therefore the sampling becomes inefficient. In this paper, we present an improved random sampling pattern for SAKE reconstruction. The pattern is generated based on a conflict cost with a probability model. The conflict cost measures how many dense samples already assigned are around a target location, while the probability model adopts the generalized Gaussian distribution which includes uniform and Gaussian-like distributions as special cases. Our method preferentially assigns a sample to a k-space location with the least conflict cost on the circle of the highest probability. To evaluate the effectiveness of the proposed random pattern, we compare the performance of SAKEs using both VD Poisson discs and the proposed pattern. Experimental results for brain data show that the proposed pattern yields lower normalized mean square error (NMSE) than VD Poisson discs.

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Rane, Swati Dnyandeo. "Parallel magnetic resonance imaging: characterization and comparison." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2578.

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Magnetic Resonance Imaging (MRI) is now increasingly being used for fast imaging applications such as real-time cardiac imaging, functional brain imaging, contrast enhanced MRI, etc. Imaging speed in MRI is mainly limited by different imaging parameters selected by the pulse sequences, the subject being imaged and the RF hardware system in operation. New pulse sequences have been developed in order to decrease the imaging time by a faster k-space scan. However, they may not be fast enough to facilitate imaging in real time. Parallel MRI (pMRI), a technique initially used for improving image SNR, has emerged as an effective complementary approach to reduce image scan-time. Five methods, viz., SENSE [Pruesmann, 1999], PILS [Griswold, 2000], SMASH [Sodickson, 1997], GRAPPA [Griswold, 2002] and SPACE RIP [Kyriakos, 2000]; developed in the past decade have been studied, simulated and compared in this research. Because of the dependence of the parallel imaging methods on numerous factors such as receiver coil configuration, k-space subsampling factor, k-space coverage in the imaging environment, there is a critical need to find the method giving the best results under certain imaging conditions. The tools developed in this research help the selection of the optimal method for parallel imaging depending on a particular imaging environment and scanning parameters. Simulations on real MR phased-array data show that SENSE and GRAPPA provide better image reconstructions when compared to the remaining techniques.

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Gol, Gungor Derya. "Subspace Techniques for Parallel Magnetic Resonance Imaging." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406301655.

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Steeden, Jennifer Anne. "Rapid phase-contrast magnetic resonance imaging using spiral trajectories and parallel imaging." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1306873/.

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Phase contrast (PC) MRI is a proven method of measuring blood flow in the clinical environment. Traditionally, PCMR data is acquired using cardiac gated Cartesian sequences. However, these sequences are time consuming and difficult to perform in patients with irregular heart rates. The work of my thesis covers three alternative PC sequences, all using undersampled spiral sequences with SENSE reconstruction algorithms. The first piece of work investigates real-time spiral PCMR. The spiral flow sequence was validated at rest by comparing stroke volumes in the aorta of healthy volunteers, against a retrospectively gated Cartesian sequence. By combining flow data with simultaneous blood pressure measurements during exercise, this sequence was used to quantify the hemodynamic response to physical stress. The second piece of work investigates improvements in spatial or temporal resolution for real-time PCMR, by splitting the acquisition of flow-compensated and flow-encoded data into separate short blocks. The data is then retrospectively matched in cardio-respiratory space, to remove background phase offsets. This sequence was validated (at rest) in an adult population. The improved spatial resolution was shown to provide more accurate flow measurements than standard real-time flow measurements, in a paediatric population. The third piece of work investigates prospectively triggered spiral PCMR to achieve high spatio-temporal resolution, within a short breath-hold. Flow volumes, regurgitation fraction and shunt ratios were compared from a high spatial-resolution, free breathing retrospectively gated Cartesian sequence with 3 averages (~2.5 minute scan time), a low spatial-resolution breath-hold retrospectively gated Cartesian sequence (~20 second scan time), and the (high spatial-resolution) prospectively triggered spiral sequence (~6 second scan time). It was shown that accurate flow measurements can be made in the aorta, pulmonary artery and pulmonary branches, within manageable breath-hold times for children and sick adults. This sequence may improve patient compliance and increase patient throughput.

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Bjåstad, Tore Grüner. "High frame rate ultrasound imaging using parallel beamforming." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for sirkulasjon og bildediagnostikk, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-5298.

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The human heart contracts and relaxes approximately once each second. This is a complex process where different parts of the cardiac tissue contract and relax at different times and at different rates. The accurate evaluation of this deformation with ultrasound requires the use of a high frame rate. The frame rate of a conventional ultrasound image is limited by the round trip propagation time of the sound pulse along each of the scan lines covering the imaged object. A common technique to increase the frame rate is multiple line acquisition, MLA. Using this technique, several scan lines are acquired in parallel for each transmitted pulse. This technique is therefore also called parallel beamforming. Although it increases the frame rate in proportion to the number of parallel beams, this technique also introduces block-like artifacts in the B-mode image. These artifacts severely degrade the image quality, and are especially visible in image sequences (movies). An aim of this thesis is to investigate methods to increase the frame rate using parallel beamforming without introducing such image artifacts. Investigations of the mechanisms of MLA image artifacts have shown that the misalignment of the transmit and receive beams causes distortions to the pulse-echo responses. These distortions result in a shift variant imaging system and image artifacts. This thesis is comprised of four papers that document several metrics that have been developed to evaluate the pulse-echo distortions, image artifacts and shift invariance property. Different methods for artifact reduction have been compared and evaluated. The two methods that have been most thoroughly investigated are steering compensation and the synthetic transmit beam method, STB. In the first method, the receive beams are additionally steered to partially avoid the pulse-echo distortion. Applying this method reduced image artifacts under ideal conditions. However, the performance was heavily reduced in realistic scenarios with aberrations. In the STB method, synthetic transmit beams are created in each receive direction through interpolation. This method performed well both with and without aberrations. Additionally, it has been shown that from the same STB acquisition pattern it is also possible to estimate velocities with an accuracy comparable to that of conventional TDI. This enables higher TDI frame rates or a larger field of view compared to conventional TDI, which requires separate acquisitions for B-mode and tissue Doppler.

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Wu, Bing. "Exploiting data sparsity in parallel magnetic resonance imaging." Thesis, University of Canterbury. Electrical and Computer Engineering, 2010. http://hdl.handle.net/10092/3914.

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Magnetic resonance imaging (MRI) is a widely employed imaging modality that allows observation of the interior of human body. Compared to other imaging modalities such as the computed tomography (CT), MRI features a relatively long scan time that gives rise to many potential issues. The advent of parallel MRI, which employs multiple receiver coils, has started a new era in speeding up the scan of MRI by reducing the number of data acquisitions. However, the finally recovered images from under-sampled data sets often suffer degraded image quality. This thesis explores methods that incorporate prior knowledge of the image to be reconstructed to achieve improved image recovery in parallel MRI, following the philosophy that ‘if some prior knowledge of the image to be recovered is known, the image could be recovered better than without’. Specifically, the prior knowledge of image sparsity is utilized. Image sparsity exists in different domains. Image sparsity in the image domain refers to the fact that the imaged object only occupies a portion of the imaging field of view; image sparsity may also exist in a transform domain for which there is a high level of energy concentration in the image transform. The use of both types of sparsity is considered in this thesis. There are three major contributions in this thesis. The first contribution is the development of ‘GUISE’. GUISE employs an adaptive sampling design method that achieves better exploitation of image domain sparsity in parallel MRI. Secondly, the development of ‘PBCS’ and ‘SENSECS’. PBCS achieves better exploitation of transform domain sparsity by incorporating a prior estimate of the image to be recovered. SENSECS is an application of PBCS that achieves better exploitation of transform domain sparsity in parallel MRI. The third contribution is the implementation of GUISE and PBCS in contrast enhanced MR angiography (CE MRA). In their applications in CE MRA, GUISE and PBCS share the common ground of exploiting the high sparsity of the contrast enhanced angiogram. The above developments are assessed in various ways using both simulated and experimental data. The potential extensions of these methods are also suggested.

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Nana, Roger. "On optimality and efficiency of parallel magnetic resonance imaging reconstruction challenges and solutions /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26477.

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Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Hu, Xiaoping; Committee Member: Keilholz, Shella; Committee Member: Mao, Hui; Committee Member: Martin, Diego; Committee Member: Oshinski, John. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Chaari, Lotfi. "Parallel magnetic resonance imaging reconstruction problems using wavelet representations." Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00587410.

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Pour réduire le temps d'acquisition ou bien améliorer la résolution spatio-temporelle dans certaines application en IRM, de puissantes techniques parallèles utilisant plusieurs antennes réceptrices sont apparues depuis les années 90. Dans ce contexte, les images d'IRM doivent être reconstruites à partir des données sous-échantillonnées acquises dans le " k-space ". Plusieurs approches de reconstruction ont donc été proposées dont la méthode SENSitivity Encoding (SENSE). Cependant, les images reconstruites sont souvent entâchées par des artéfacts dus au bruit affectant les données observées, ou bien à des erreurs d'estimation des profils de sensibilité des antennes. Dans ce travail, nous présentons de nouvelles méthodes de reconstruction basées sur l'algorithme SENSE, qui introduisent une régularisation dans le domaine transformé en ondelettes afin de promouvoir la parcimonie de la solution. Sous des conditions expérimentales dégradées, ces méthodes donnent une bonne qualité de reconstruction contrairement à la méthode SENSE et aux autres techniques de régularisation classique (e.g. Tikhonov). Les méthodes proposées reposent sur des algorithmes parallèles d'optimisation permettant de traiter des critères convexes, mais non nécessairement différentiables contenant des a priori parcimonieux. Contrairement à la plupart des méthodes de reconstruction qui opèrent coupe par coupe, l'une des méthodes proposées permet une reconstruction 4D (3D + temps) en exploitant les corrélations spatiales et temporelles. Le problème d'estimation d'hyperparamètres sous-jacent au processus de régularisation a aussi été traité dans un cadre bayésien en utilisant des techniques MCMC. Une validation sur des données réelles anatomiques et fonctionnelles montre que les méthodes proposées réduisent les artéfacts de reconstruction et améliorent la sensibilité/spécificité statistique en IRM fonctionnelle

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Gagoski, Borjan Aleksandar. "Magnetic resonance spectroscopic imaging using parallel transmission at 7T." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/63069.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 123-130).
Conventional magnetic resonance spectroscopic imaging (MRSI), also known as phase-encoded (PE) chemical shift imaging (CSI), suffers from both low signal-to-noise ratio (SNR) of the brain metabolites, as well as inflexible tradeoffs between acquisition time and spatial resolution. In addition, although CSI at higher main field strengths, e.g. 7 Tesla (T), offers improved SNR over clinical 1.5T or 3.OT scanners, the realization of these benefits is limited by severe inhomogeneities of the radio frequency (RF) excitation magnetic field (B,+), which is responsible for significant signal variation within the volume of interest (VOI) resulting in spatially dependent SNR losses. The work presented in this dissertation aims to provide the necessary means for using spectroscopic imaging for reliable and robust whole brain metabolite detection and quantification at high main field strengths. It addresses the challenges mentioned above by improving both the excitation and the readout components of the CSI acquisition. The long acquisition times of the PE CSI are significantly shortened (at least 20 fold) by implementing the time-efficient spiral CSI algorithm, while the B1 non-uniformities are corrected for using RF pulses designed for new RF excitation hardware at 7T, so-called parallel transmission (pTx). The B1 homogeneity of the pTx excitations improved at least by a factor of 4 (measured by the normalized spatial standard deviations) compared to conventional single channel transmit systems. The first contribution of this thesis describes the implementation of spiral CSI algorithm for online gradient waveform design and spectroscopic image reconstruction with standard clinical excitation protocols and applied in studies of Late-Onset Tay- Sachs (LOTS), adrenoleukodystrophy (ALD) and brain tumors. A major contribution of this thesis is pTx excitation design for CSI to provide spectral-spatial mitigation of the B1+ inhomogeneities at 7T. Novel pTx RF designs are proposed and demonstrated to yield excellent flip angle mitigation of the brain metabolites, and also enable improved suppression of the undesired water and lipid signals. A major obstacle to the deployment of 7T pTx applications for clinical imaging is the monitoring and management of local specific absorption rate (SAR). This thesis also proposes a pTx SAR monitoring system with real-time RF monitoring and shut-off capabilities.
by Borjan Aleksandar Gagoski.
Ph.D.

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Setsompop, Kawin. "Design algorithms for parallel transmission in magnetic resonance imaging." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44902.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 153-158).
The focus of this dissertation is on the algorithm design, implementation, and validation of parallel transmission technology in Magnetic Resonance Imaging (MRI). Novel algorithms are proposed which yield excellent excitation control, low RF power requirements, methods that extend to non-linear large-flip-angle excitation, as well as a new algorithm for simultaneous spectral and spatial excitation critical to quantification of low-SNR brain metabolites in MR spectroscopic imaging. For testing and validation, these methods were implemented on a newly developed parallel transmission platform on both 3 T and 7 T MRI scanners to demonstrate the ability of these methods for highfidelity B1+ mitigation, first by excitation of phantoms and then by human imaging. Further, spatially tailored RF pulses were demonstrated beyond conventional slice- or slab-selective excitation.
by Kawin Setsompop.
Ph.D.

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Oliver-Taylor, A. "Parallel transit methods for arterial spin labelling magnetic resonance imaging." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1382488/.

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Vessel selective arterial spin labelling (ASL) is a magnetic resonance imaging technique which permits the visualisation and assessment of the perfusion territory of a specific set of feeding arteries. It is of clinical importance in both acute and chronic cerebrovascular disease, and the mapping of blood supplied to tumours. Continuous ASL is capable of providing the highest signal-to-noise (SNR) ratio of the various ASL methods. However on clinical systems it suffers from high hardware demands, and the control of systematic errors decreases perfusion sensitivity. A separate labelling coil avoids these problems, enabling high labelling efficiency and subsequent high SNR, and vessel specificity can be localised to one carotid artery. However this relies on the careful and accurate positioning of the labelling coil over the common carotid arteries in the neck. It is proposed to combine parallel transmission (multiple transmit coils, each transmitting with different amplitudes and phases) to spatially tailor the labelling field, removing the reliance on coil location for optimal labelling efficiency, and enabling robust vessel selective labelling with a high degree of specificity. Presented is the application of parallel transmission methods to continuous ASL, requiring the development of an ASL labelling coil array, and a two channel transmitter system. Coil safety testing was performed using a novel MRI temperature mapping technique to accurately measure small temperature changes on the order of 0.1 ⁰C. A perfusion phantom with distinct vascular territories was constructed for sequence testing and development. Phantom and in-vivo testing of parallel transmit CASL using a 3D-GRASE acquisition showed an improvement of up to 35% in vessel specificity when compared with using a single labelling coil, whilst retaining the high labelling efficiency and associated SNR of separate coil CASL methods.

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Duncan, Stephen Howard. "The application of parallel processing techniques in coded aperture imaging." Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239709.

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Beqiri, Arian. "Parallel transmission MRI for optimised cardiac imaging and improved safety." Thesis, King's College London (University of London), 2015. http://kclpure.kcl.ac.uk/portal/en/theses/parallel-transmission-mri-for-optimised-cardiac-imaging-and-improved-safety(217895a3-0a83-4212-b8c4-d4438a39bca3).html.

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The move towards higher static magnetic field strengths in MRI has allowed improved imaging quality from increased signal to noise ratio. However challenges have arisen from increased inhomogeneity in the radio frequency (RF) fields required to create MR signals and greater RF energy deposition – known as the specific absorption rate (SAR) – within imaging subjects. These factors have prompted the use of parallel transmission (PTx) MRI; in which multiple independent channels are used to control the RF electromagnetic fields. In this thesis the aim was to develop methods for controlling SAR using PTx and to assess the impact of RF safety in various scenarios. The electromagnetic behaviour of an 8-channel PTx RF coil was fully simulated which enabled the examination of differences between full simulations and a commonly modelled idealised situation. It was found that large discrepancies could result in the idealised model in certain situations. The full RF coil model was for producing SAR simulations of various adult male voxel models. These SAR models were used to perform RF shimming, in which a complex weighting is applied to each channel of a PTx system to yield improved RF conditions. This was done for two scenarios: to perform lower SAR cardiac MRI with greater RF field homogeneity in vivo for optimised imaging; and to explore methods for decoupling the transmit coil from a simulated prosthetic hip implant embedded within an adult male whilst still producing a uniform imaging field. In both scenarios, reduced SAR configurations could be found that enabled improved imaging with greater RF safety. A separate model of a 2-channel birdcage RF coil was developed to assess SAR deposition in neonates during MRI examinations. It was found that under normal operation at 3 T, local SAR constraints produced by the scanner are conservative by a factor of four.

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Gudino, Natalia. "NOVEL PARALLEL TRANSMIT SYSTEMS FOR MRI APPLICATIONS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1363178933.

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Brion, Véronique. "Towards real-time diffusion imaging : noise correction and inference of the human brain connectivity." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112058/document.

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La plupart des constructeurs de systèmes d'imagerie par résonance magnétique (IRM) proposent un large choix d'applications de post-traitement sur les données IRM reconstruites a posteriori, mais très peu de ces applications peuvent être exécutées en temps réel pendant l'examen. Mises à part certaines solutions dédiées à l'IRM fonctionnelle permettant des expériences relativement simples ainsi que d'autres solutions pour l'IRM interventionnelle produisant des scans anatomiques pendant un acte de chirurgie, aucun outil n'a été développé pour l'IRM pondérée en diffusion (IRMd). Cependant, comme les examens d'IRMd sont extrêmement sensibles à des perturbations du système hardware ou à des perturbations provoquées par le sujet et qui induisent des données corrompues, il peut être intéressant d'investiguer la possibilité de reconstruire les données d'IRMd directement lors de l'examen. Cette thèse est dédiée à ce projet innovant. La contribution majeure de cette thèse a consisté en des solutions de débruitage des données d'IRMd en temps réel. En effet, le signal pondéré en diffusion peut être corrompu par un niveau élevé de bruit qui n'est plus gaussien, mais ricien ou chi non centré. Après avoir réalisé un état de l'art détaillé de la littérature sur le bruit en IRM, nous avons étendu l'estimateur linéaire qui minimise l'erreur quadratique moyenne (LMMSE) et nous l'avons adapté à notre cadre de temps réel réalisé avec un filtre de Kalman. Nous avons comparé les performances de cette solution à celles d'un filtrage gaussien standard, difficile à implémenter car il nécessite une modification de la chaîne de reconstruction pour y être inséré immédiatement après la démodulation du signal acquis dans l'espace de Fourier. Nous avons aussi développé un filtre de Kalman parallèle qui permet d'appréhender toute distribution de bruit et nous avons montré que ses performances étaient comparables à celles de notre méthode précédente utilisant un filtre de Kalman non parallèle. Enfin, nous avons investigué la faisabilité de réaliser une tractographie en temps-réel pour déterminer la connectivité structurelle en direct, pendant l'examen. Nous espérons que ce panel de développements méthodologiques permettra d'améliorer et d'accélérer le diagnostic en cas d'urgence pour vérifier l'état des faisceaux de fibres de la substance blanche
Most magnetic resonance imaging (MRI) system manufacturers propose a huge set of software applications to post-process the reconstructed MRI data a posteriori, but few of them can run in real-time during the ongoing scan. To our knowledge, apart from solutions dedicated to functional MRI allowing relatively simple experiments or for interventional MRI to perform anatomical scans during surgery, no tool has been developed in the field of diffusion-weighted MRI (dMRI). However, because dMRI scans are extremely sensitive to lots of hardware or subject-based perturbations inducing corrupted data, it can be interesting to investigate the possibility of processing dMRI data directly during the ongoing scan and this thesis is dedicated to this challenging topic. The major contribution of this thesis aimed at providing solutions to denoise dMRI data in real-time. Indeed, the diffusion-weighted signal may be corrupted by a significant level of noise which is not Gaussian anymore, but Rician or noncentral chi. After making a detailed review of the literature, we extended the linear minimum mean square error (LMMSE) estimator and adapted it to our real-time framework with a Kalman filter. We compared its efficiency to the standard Gaussian filtering, difficult to implement, as it requires a modification of the reconstruction pipeline to insert the filter immediately after the demodulation of the acquired signal in the Fourier space. We also developed a parallel Kalman filter to deal with any noise distribution and we showed that its efficiency was quite comparable to the non parallel Kalman filter approach. Last, we addressed the feasibility of performing tractography in real-time in order to infer the structural connectivity online. We hope that this set of methodological developments will help improving and accelerating a diagnosis in case of emergency to check the integrity of white matter fiber bundles

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Breuer, Felix. "Development and application of efficient strategies for parallel magnetic resonance imaging." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=982469136.

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Ramb, Rebecca [Verfasser], and Jürgen [Akademischer Betreuer] Hennig. "K-t-sub-Nyquist sampled parallel echo planar imaging in MRI." Freiburg : Universität, 2016. http://d-nb.info/1122647654/34.

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Rao, Raman P. V. "Parallel implementation of the filtered back projection algorithm for tomographic imaging." Master's thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-02162010-020232/.

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Yeh, Ernest Nanjung 1975. "Advanced image reconstruction in parallel magnetic resonance imaging : constraints and solutions." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33078.

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Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2005.
Includes bibliographical references.
Imaging speed is a crucial consideration for magnetic resonance imaging (MRI). The speed of conventional MRI is limited by hardware performance and physiological safety measures. "Parallel" MRI is a new technique that circumvents these limitations by utilizing arrays of radiofrequency detector coils to acquire data in parallel, thereby enabling still higher imaging speeds. In parallel MRI, coil arrays are used to accomplish part of the spatial encoding that was traditionally performed by magnetic field gradients alone. MR signal data acquired with coil arrays are spatially encoded with the distinct reception patterns of the individual coil elements. T[he quality of parallel MR images is dictated by the accuracy and efficiency of an image reconstruction (decoding) strategy. This thesis formulates the spatial encoding and decoding of parallel MRI as a generalized linear inverse problem. Under this linear algebraic framework, theoretical and empirical limits on the performance of parallel MR image reconstructions are characterized, and solutions are proposed to facilitate routine clinical and research applications. Each research study presented in this thesis addresses one or more elements in the inverse problem, and the studies are collectively arranged to reflect three progressive stages in solving the inverse problem: 1) determining the encoding matrix, 2) computing a matrix inverse, 3) characterizing the error involved. First, a self-calibrating strategy is proposed which uses non-Cartesian trajectories to automatically determine coil sensitivities without the need of an external scan or modification of data acquisition, guaranteeing an accurate formulation of the encoding matrix.
(cont.) Second, two matrix inversion strategies are presented which, respectively, exploit physical properties of coil encoding and the phase information of the magnetization. While the former allows stable and distributable matrix inversion using the k-space locality principle, the latter integrates parallel image reconstruction with conjugate symmetry. Third, a numerical strategy is presented for computing noise statistics of parallel MRI techniques which involve magnitude image combination, enabling quantitative image comparison. In addition, fundamental limits on the performance of parallel image reconstruction are derived using the Cramer-Rao bounds. Lastly, the practical applications of techniques developed in this thesis are demonstrated by a case study in improved coronary angiography.
Ph.D.

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Balla, Apuroop. "IMPULSE RESPONSE CHARACTERIZATION OF BREAST TOMOSYNTHESIS RECONSTRUCTION WITH PARALLEL IMAGING CONFIGURATIONS." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/401.

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It's universally accepted that early detection, diagnosis, and suitable treatment are best hope to increase the survival chance for breast cancer (BC) patients. To date, the most cost effective method for breast screening and early detection is mammography. The mammography technique uses a low-dose X-ray system to acquire images of the breast. Limitations of mammography exist, including 20% false negative rate, many call backs for screening, low positive predictive value of about 15% to 34% from biopsy. Digital Breast tomosynthesis (DBT) is a new technique that acquires limited angle tomographic projection images to reconstruct three-dimensional information of the breast. The development of tomosynthesis is a substantial improvement over conventional tomography in that it allows retrospective reconstruction of an arbitrary number of planes with a acquisition dataset. In this project, we investigated three different tomosynthesis image reconstruction algorithms including shift-and-add (SAA), back projection (BP), filtered back projection (FBP) with parallel imaging geometry to improve breast cancer detection. In this project we also examined the effect of varying the number of projection images (N) and total view angle (VA) for each reconstruction algorithm characterized by impulse response (IR) analysis. IR data were generated by simulating the projection images of a very thin wire, using various combinations of VA and N. Based on this project, we hope to optimize the image configuration to contribute to the breast tomosynthesis field.

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Misal, Nilimb V. Mr. "A Fast Parallel Method of Interleaved Fft for Magnetic Resonance Imaging." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1164733382.

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Eriksson, Emil. "Simulation of Biological Tissue using Mass-Spring-Damper Models." Thesis, Örebro universitet, Institutionen för naturvetenskap och teknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-27663.

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The goal of this project was to evaluate the viability of a mass-spring-damper based model for modeling of biological tissue. A method for automatically generating such a model from data taken from 3D medical imaging equipment including both the generation of point masses and an algorithm for generating the spring-damper links between these points is presented. Furthermore, an implementation of a simulation of this model running in real-time by utilizing the parallel computational power of modern GPU hardware through OpenCL is described. This implementation uses the fourth order Runge-Kutta method to improve stability over similar implementations. The difficulty of maintaining stability while still providing rigidness to the simulated tissue is thoroughly discussed. Several observations on the influence of the structure of the model on the consistency of the simulated tissue are also presented. This implementation also includes two manipulation tools, a move tool and a cut tool for interaction with the simulation. From the results, it is clear that the mass-springdamper model is a viable model that is possible to simulate in real-time on modern but commoditized hardware. With further development, this can be of great benefit to areas such as medical visualization and surgical simulation.
Målet med detta projekt var att utvärdera huruvida en modell baserad på massa-fjäderdämpare är meningsfull för att modellera biologisk vävnad. En metod för att automatiskt generera en sådan modell utifrån data tagen från medicinsk 3D-skanningsutrustning presenteras. Denna metod inkluderar både generering av punktmassor samt en algoritm för generering av länkar mellan dessa. Vidare beskrivs en implementation av en simulering av denna modell som körs i realtid genom att utnyttja den parallella beräkningskraften hos modern GPU-hårdvara via OpenCL. Denna implementation använder sig av fjärde ordningens Runge-Kutta-metod för förbättrad stabilitet jämfört med liknande implementationer. Svårigheten att bibehålla stabiliteten samtidigt som den simulerade vävnaden ges tillräcklig styvhet diskuteras genomgående. Flera observationer om modellstrukturens inverkan på den simulerade vävnadens konsistens presenteras också. Denna implementation inkluderar två manipuleringsverktyg, ett flytta-verktyg och ett skärverktyg för att interagera med simuleringen. Resultaten visar tydligt att en modell baserad på massa-fjäder-dämpare är en rimlig modell som är möjlig att simulera i realtid på modern men lättillgänglig hårdvara. Med vidareutveckling kan detta bli betydelsefullt för områden så som medicinsk bildvetenskap och kirurgisk simulering.

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Seiberlich, Nicole. "Advances in Non-Cartesian Parallel Magnetic Resonance Imaging using the GRAPPA Operator." kostenfrei, 2008. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2008/2832/.

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29

Herikstad, Åsmund. "Parallel Techniques for Estimation and Correction of Aberration in Medical Ultrasound Imaging." Thesis, Norwegian University of Science and Technology, Department of Computer and Information Science, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9090.

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Medical ultrasound imaging is a great diagnostic tool for physicians because of its noninvasive nature. It is performed by directing ultrasonic sound into tissue and visualizing the echo signal. Aberration in the reflected signal is caused by inhomogeneous tissue varying the speed of sound, which results in a blurring of the image. Dr. Måsøy and Dr. Varslot at NTNU have developed and algorithm for estimating and correcting ultrasound aberration. This algorithm adaptively estimates the aberration and adjusts the next transmitted signal to account for the aberration, resulting in a clearer image. This master's thesis focuses on developing a parallelized version of this algorithm. Since NVIDIA CUDA (Compute Unified Device Architecture) is an architecture oriented towards general purpose computations on the GPU (Graphics Processing Unit), it also examines how suitable the parallelization is for modern GPUs. The goal is using the GPU to off-load the CPU with an aim of achieving real-time calculations of the correction filter. The ultrasound image creation is examined, including how the aberrations come into being. Next, how the algorithm can be implemented efficiently using the GPU is looked at using both NVIDIA's FFT (fast Fourier transform) library as well as developing several computational kernels to run on the GPU. Our findings show that the algorithm is highly parallelizable and achieves a speedup of over 5x when implemented on the GPU. This is, however, not fast enough for real-time correction, but taking into account suggestions for overcoming the limitations encountered, the study shows great promise for future work.

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Ohliger, Michael A. "Fundamental and practical limits to image acceleration in parallel magnetic resonance imaging." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33075.

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Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2005.
Includes bibliographical references (leaves 152-160).
Imaging speed in conventional magnetic resonance imaging (MRI) is limited by the performance of magnetic field gradients and the rate of power deposition in tissue. Parallel MRI techniques overcome these constraints by exploiting information stored within the spatial sensitivity patterns of radiofrequency detector arrays to substitute for some of the spatial information that would normally be obtained using magnetic field gradients. Parallel MRI strategies have been applied clinically to increase patient comfort, enhance spatial resolution, expand anatomical coverage, and reduce image artifacts. The effectiveness of parallel MRI techniques is largely determined by the amount of spatial information that is stored in the detector coil sensitivities. This dissertation investigates the spatial encoding properties of coil arrays from three practical and fundamental perspectives. First, a novel array design is presented that enables spatial encoding in multiple directions simultaneously. Second, the impact of inductive coupling between array elements in parallel MRI is investigated theoretically and experimentally. Finally, electromagnetic calculations are described that permit computation of the ultimate intrinsic signal-to-noise ratio available to any physically realizable coil array for parallel MR. These calculations help to establish fundamental limits to the image accelerations that may be achieved using parallel MRI techniques. These limits are intrinsically related to the wavelengths of the electromagnetic fields at MR imaging frequencies. The sensitivity patterns that correspond to the ultimate intrinsic SNR also represent potential starting points for new coil designs.
by Michael A. Ohliger.
Ph.D.

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Yetişir, Filiz. "Parallel radiofrequency transmission for 3 Tesla and 7 Tesla magnetic resonance imaging." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113982.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 141-146).
Magnetic resonance imaging (MRI) is a noninvasive imaging technique with high soft tissue contrast. MR scanners are characterized by their main magnetic field strength. Commercially available clinical MR scanners commonly have main field strengths of 1.5 and 3 Tesla. Researchers increasingly explore clinical benefits of higher field strength scanners as they provide higher signal to noise ratio and higher resolution images. On the other hand, higher field strength imaging comes with increased image shading leading to non-uniform image contrast. Moreover, the tissue heating rate due to radiofrequency (RF) energy deposition (also called specific absorption rate or SAR) increases, limiting the imaging speed. Parallel RF transmission (pTx) was proposed to address both of these challenges by optimization of RF pulses transmitted from multiple independent channels simultaneously. However, both the RF pulse design and RF safety management become more complicated with pTx. In this work, a framework to apply pTx to 3T fetal and 7T brain imaging is developed to address the image shading and high SAR issues. Fetal imaging where a large pregnant torso is imaged rapidly to avoid fetal motion artifacts, suffers from similar levels of image shading and imaging limitations by SAR to 7T brain MRI. Hence the same techniques benefit both application domains. First, a SAR constrained pTx RF pulse design technique is developed for slice selective high flip angle imaging which is clinically the most common imaging technique. Next, the performance of the developed technique in reducing SAR and the image contrast non-uniformity is demonstrated through simulations and in phantom experiments for 7T brain imaging. Then, a comprehensive RF safety workflow for an 8 channel pTx system at 7T is developed. Finally, the potential of pTx for fetal imaging at 3T is demonstrated with simulation studies and a protected fetus mode of pTx was created using additional constraints in the RF pulse design. By addressing the two main RF transmission challenges associated with high and ultrahigh field MRI, this work aims to help bring the benefits of 7T brain imaging into routine clinical use and significantly improve the clinical experience for 3T fetal imaging.
by Filiz Yetişir.
Ph. D.

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32

Ahlman, Gustav. "Improved Temporal Resolution Using Parallel Imaging in Radial-Cartesian 3D functional MRI." Thesis, Linköpings universitet, Datorseende, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-69123.

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MRI (Magnetic Resonance Imaging) is a medical imaging method that uses magnetic fields in order to retrieve images of the human body. This thesis revolves around a novel acquisition method of 3D fMRI (functional Magnetic Resonance Imaging) called PRESTO-CAN that uses a radial pattern in order to sample the (kx,kz)-plane of k-space (the frequency domain), and a Cartesian sample pattern in the ky-direction. The radial sample pattern allows for a denser sampling of the central parts of k-space, which contain the most basic frequency information about the structure of the recorded object. This allows for higher temporal resolution to be achieved compared with other sampling methods since a fewer amount of total samples are needed in order to retrieve enough information about how the object has changed over time. Since fMRI is mainly used for monitoring blood flow in the brain, increased temporal resolution means that we can be able to track fast changes in brain activity more efficiently.The temporal resolution can be further improved by reducing the time needed for scanning, which in turn can be achieved by applying parallel imaging. One such parallel imaging method is SENSE (SENSitivity Encoding). The scan time is reduced by decreasing the sampling density, which causes aliasing in the recorded images. The aliasing is removed by the SENSE method by utilizing the extra information provided by the fact that multiple receiver coils with differing sensitivities are used during the acquisition. By measuring the sensitivities of the respective receiver coils and solving an equation system with the aliased images, it is possible to calculate how they would have looked like without aliasing.In this master thesis, SENSE has been successfully implemented in PRESTO-CAN. By using normalized convolution in order to refine the sensitivity maps of the receiver coils, images with satisfying quality was able to be reconstructed when reducing the k-space sample rate by a factor of 2, and images of relatively good quality also when the sample rate was reduced by a factor of 4. In this way, this thesis has been able to contribute to the improvement of the temporal resolution of the PRESTO-CAN method.
MRI (Magnetic Resonance Imaging) är en medicinsk avbildningsmetod som använder magnetfält för att framställa bilder av människokroppen. Detta examensarbete kretsar kring en ny inläsningsmetod för 3D-fMRI (functional Magnetic Resonance Imaging) vid namn PRESTO-CAN som använder ett radiellt mönster för att sampla (kx,kz)-planet av k-rummet (frekvensdomänen), och ett kartesiskt samplingsmönster i ky-riktningen. Det radiella samplingsmönstret möjliggör tätare sampling av k-rummets centrala delar, som innehåller den mest grundläggande frekvensinformationen om det inlästa objektets struktur. Detta leder till att en högre temporal upplösning kan uppnås jämfört med andra metoder eftersom det krävs ett mindre antal totala sampel för att få tillräcklig information om hur objektet har ändrats över tid. Eftersom fMRI framförallt används för att övervaka blodflödet i hjärnan innebär ökad temporal upplösning att vi kan följa snabba ändringar i hjärnaktivitet mer effektivt.Den temporala upplösningen kan förbättras ytterligare genom att minska scanningstiden, vilket i sin tur kan uppnås genom att tillämpa parallell avbildning. En metod för parallell avbildning är SENSE (SENSitivity Encoding). Scanningstiden minskas genom att minska samplingstätheten, vilket orsakar vikning i de inlästa bilderna. Vikningen tas bort med SENSE-metoden genom att utnyttja den extra information som tillhandahålls av det faktum att ett flertal olika mottagarspolar med sinsemellan olika känsligheter används vid inläsningen. Genom att mäta upp känsligheterna för de respektive mottagarspolarna och lösa ett ekvationssystem med de vikta bilderna är det möjligt att beräkna hur de skulle ha sett ut utan vikning.I detta examensarbete har SENSE framgångsrikt implementerats i PRESTO-CAN. Genom att använda normaliserad faltning för att förfina mottagarspolarnas känslighetskartor har bilder med tillfredsställande kvalitet varit möjliga att rekonstruera när samplingstätheten av k-rummet minskats med en faktor 2, och bilder med relativt bra kvalitet också när samplingstätheten minskats med en faktor 4. På detta sätt har detta examensarbete kunnat bidra till förbättrandet av PRESTO-CAN-metodens temporala upplösning.

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García, Antonio. "Parallel time varying volume rendering on tile displays." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1135801433.

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34

Geng, Zhao. "Visual analysis of abstract multi-dimensional data with parallel coordinates." Thesis, Swansea University, 2013. https://cronfa.swan.ac.uk/Record/cronfa43002.

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35

Pierre, Eric Y. "Reliable Use of Acquired and Simulated Signal Databases to Reduce MRI Acquisition Time." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1404220001.

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36

Johansson, Adam. "Magnetic resonance imaging with ultrashort echo time as a substitute for X-ray computed tomography." Doctoral thesis, Umeå universitet, Radiofysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-93053.

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Radiotherapy dose calculations have evolved from simple factor based methods performed with pen and paper, into computationally intensive simulations based on Monte Carlo theory and energy deposition kernel convolution. Similarly, in the field of positron emission tomography (PET), attenuation correction, which was originally omitted entirely, is now a crucial component of any PET reconstruction algorithm. Today, both of these applications – radiotherapy and PET – derive their needed in-tissue radiation attenuation coefficients from images acquired with X-ray computed tomography (CT). Since X-ray images are themselves acquired using ionizing radiation, the intensity at a point in an image will reflect the radiation interaction properties of the tissue located at that point. Magnetic resonance imaging (MRI), on the other hand, does not use ionizing radiation. Instead MRI make use of the net transverse magnetization resulting from the spin polarization of hydrogen nuclei. MR image contrast can be varied to a greater extent than CT and the soft tissue contrast is, for most MR sequences, superior to that of CT. Therefore, for many cases, MR images provide a considerable advantage over CT when identifying or delineating tumors or other diseased tissues. For this reason, there is an interest to replace CT with MRI for a great number of diagnostic and therapeutic workflows. Also, replacing CT with MRI would reduce the exposure to ionizing radiation experienced by patients and, by extension, reduce the associated risk to induce cancer. In part MRI has already replaced CT, but for radiotherapy dose calculations and PET attenuation correction, CT examinations are still necessary in clinical practice. One of the reasons is that the net transverse magnetization imaged in MRI cannot be converted into attenuation coefficients for ionizing radiation in a straightforward way. More specifically, regions with similar appearance in magnetic resonance (MR) images, such as bone and air pockets, are found at different ends of the spectrum of attenuation coefficients present in the human body. In a CT image, bone will appear bright white and air as black corresponding to high and no attenuation, respectively. In an MR image, bone and air both appear dark due to the lack of net transverse magnetization. The weak net transverse magnetization of bone is a result of low hydrogen density and rapid transverse relaxation. A particular category of MRI sequences with so-called ultrashort echo time (UTE) can sample the MRI signal from bone before it is lost due to transverse relaxation. Thus, UTE sequences permit bone to be imaged with MRI albeit with weak intensity and poor resolution. Imaging with UTE in combination with careful image analysis can permit ionizing-radiation attenuation-maps to be derived from MR images. This dissertation and appended articles present a procedure for this very purpose. However, as attenuation coefficients are radiation-quality dependent the output of the method is a Hounsfield unit map, i.e. a substitute for a CT image. It can be converted into an attenuation map using conventional clinical procedure. Obviating the use of CT would reduce the number of examinations that patients have to endure during preparation for radiotherapy. It would also permit PET attenuation correction to be performed on images from the new imaging modality that combines PET and MRI in one scanner – PET/MR.

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De, Silva Weeraddana Manjula Kumara. "Correlation Imaging for Real-time Cardiac MRI." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1471346206.

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38

Lawlor, Michael Andrew. "A real-time parallel processing system for synthetic aperture sonar." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360273.

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Ramb, Rebecca [Verfasser]. "k-t-sub-Nyquist sampled Parallel Echo Planar Imaging in MRI / Rebecca Ramb." München : Verlag Dr. Hut, 2016. http://d-nb.info/1111160678/34.

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40

Chen, Kailiang. "A Column-Row-Parallel ASIC architecture for 3D wearable / portable medical ultrasonic imaging." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87916.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 163-174).
This work presents a scalable Column-Row-Parallel ASIC architecture for 3D wearable / portable medical ultrasound. It leverages programmable electronic addressing to achieve linear scaling for both hardware interconnection and software data acquisition. A 16x16 transceiver ASIC is fabricated and flip-chip bonded to a 16x16 capacitive micromachined ultrasonic transducer (CMUT) to demonstrate the compact, low-power front-end assembly. A 3D plane-wave coherent compounding algorithm is designed for fast volume rate (62.5 volume/s), high quality 3D ultrasonic imaging. An interleaved checker board pattern with I&Q excitations is also proposed for ultrasonic harmonic imaging, reducing transmitted second harmonic distortion by over 20dB, applicable to nonlinear transducers and circuits with arbitrary pulse shapes. Each transceiver circuit is element-matched to its CMUT element. The high voltage transmitter employs a 3-level pulse-shaping technique with charge recycling to enhance the power efficiency, requiring minimum off-chip components. Compared to traditional 2-level pulsers, 50% more acoustic power delivery is obtained with the same total power dissipation. The receiver is implemented with a transimpedance amplifier topology and achieves a lowest noise efficiency factor in the literature (2.1 compared to a previously reported lowest of 3.6, in unit of mPa - [square root sign]mW/Hz). A source follower stage is specially designed to combine the analog outputs of receivers in parallel, improving output SNR as parallelization increases and offering flexibility for imaging algorithm design. Lastly, fault-tolerance is incorporated into the transceiver to deal with faulty elements within the 2D MEMS transducer array, increasing yield for the system assembly.
by Kailiang Chen.
Ph. D.

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41

Jagtap, Vinod. "FAST FOURIER TRANSFORM USING PARALLEL PROCESSING FOR MEDICAL APPLICATIONS." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1270678206.

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Heilman, Jeremiah A. "Multi-Dimensional Excitation in Magnetic Resonance Imaging for Homogeneity Correction in the Presence of Dielectric Media." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1238442193.

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Ozturk, Isik Esin. "Implementation of parallel imaging techniques for lipid unaliasing and faster acquisition for improving spatial characterization of magnetic resonance spectroscopic imaging of gliomas." Diss., Search in ProQuest Dissertations & Theses. UC Only, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3251939.

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Liu, Xiaoqun. "Design of multi-channel radio-frequency front-end for 200mhz parallel magnetic resonance imaging." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3159.

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Chiu, Chi-tat, and 趙志達. "Design and development of a programmable micro-ultrasound research platform with parallel computing capacity." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B46290977.

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Huo, Donglai. "Quantitative Image Quality Evaluation of Fast Magnetic Resonance Imaging." Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1155913518.

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47

Ataseven, Yoldas. "Parallel Implementation Of The Boundary Element Method For Electromagnetic Source Imaging Of The Human Brain." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606548/index.pdf.

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Human brain functions are based on the electrochemical activity and interaction of the neurons constituting the brain. Some brain diseases are characterized by abnormalities of this activity. Detection of the location and orientation of this electrical activity is called electro-magnetic source imaging (EMSI) and is of signicant importance since it promises to serve as a powerful tool for neuroscience. Boundary Element Method (BEM) is a method applicable for EMSI on realistic head geometries that generates large systems of linear equations with dense matrices. Generation and solution of these matrix equations are time and memory consuming due to the size of the matrices and high computational complexity of direct methods. This study presents a relatively cheap and eective solution the this problem and reduces the processing times to clinically acceptable values using parallel cluster of personal computers on a local area network. For this purpose, a cluster of 8 workstations is used. A parallel BEM solver is implemented that distributes the model eciently to the processors. The parallel solver for BEM is developed using the PETSc library. The performance of the iv solver is evaluated in terms of CPU and memory usage for dierent number of processors. For a 15011 node mesh, a speed-up eciency of 97.5% is observed when computing transfer matrices. Individual solutions can be obtained in 520 ms on 8 processors with 94.2% parallellization eciency. It was observed that workstation clusters is a cost eective tool for solving complex BEM models in clinically acceptable time. Eect of parallelization on inverse problem is also demonstrated by a genetic algorithm and very similar speed-up is obtained.

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Rayford, II Cleveland Eugene. "Digital Breast Tomosynthesis (DBT) Computational Analysis With Parallel Imaging Configurations To Improve Breast Cancer Detection." OpenSIUC, 2011. https://opensiuc.lib.siu.edu/theses/574.

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The best way to conquer breast cancer is early detection of the disease. Research studies show that earlier detection results in the increase of life span of the affected person. Traditional two-dimensional mammography is the most prevalent method used in detecting breast cancer. Recently, a three-dimensional digital breast tomosynthesis (DBT) system has been created, which is hopeful to surpass the technology of traditional mammography systems. The DBT system can provide three-dimensional information, allowing physicians to reduce the amount of false negative screening in addition to better monitoring of breast cancer and to catch lesions that may be otherwise cancerous. In this research, the View Angle (VA) and number of projection images (N) were investigated and compared with parallel imaging configurations using two reconstruction algorithms, including Back Projection (BP) and Shift-And-Add (SAA). Modulation Transfer Function (MTF) analyses were conducted with both algorithms, in order to determine which method displayed better image qualities to ultimately improve the detection of breast cancer.

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Vogelgesang, Matthias [Verfasser], and A. [Akademischer Betreuer] Streit. "An Extensible Parallel Computing Framework for Ultra-Fast X-Ray Imaging / Matthias Vogelgesang. Betreuer: A. Streit." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1073204871/34.

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Vaksdal, Martin. "3D-EPI with parallel imaging acceleration along two Axis : Evaluated with Phantom Study and BOLD fMRI." Thesis, Norges Teknisk-Naturvitenskaplige Universitet, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-20679.

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The function of the human brain has for many years been an intriguing field of research, and has led to the discovery of functional MRI (fMRI). fMRI is dependent on high spatial and temporal resolution to acquire detailed activation maps of the brain. The required high temporal resolution is especially hard to achieve in MRI, as the data acquisition is time consuming. In this work, an accelerated three-dimensional echo planar imaging (3D-EPI) sequence is used to increase the temporal resolution in fMRI. The increased temporal resolution is achieved by accelerating the sequence in two phase encoding directions. As a result it is possible to acquire a full 3D-volume of the brain in only 0.5 seconds. A parallel imaging technique named GRAPPA has been used to accelerate the sequence. The present work include a comparison study between a 16 channel and a 32 channel head coil available at the scanner, and a fMRI study where the sensitivity of the accelerated 3D-EPI sequence to BOLD activation has been compared with a standard 2D-EPI sequence. The results from the coil comparison show a significant improvement in image quality for the 32 channel coil, especially when high acceleration factors is applied. Ghosting artifacts were reduced and the SNR in the images increased, compared to the results from the 16 channel coil. In the fMRI study the results show significantly higher z-values for the 3D-EPI sequence, which indicates an increased sensitivity to the BOLD signal compared to the 2D-EPI sequence. The observed increase in sensitivity provides a clear indication that 3D-EPI sequence has a promising future within fMRI.

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Dissertations / Theses on the topic 'Parallell imaging'

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