Download or read book Detection and Correction of Patient Motion in Magnetic Resonance Imaging written by Murat Aksoy and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the sequential nature of magnetic resonance imaging (MRI) data acquisition, correction of image artifacts originating from involuntary patient motion is essential for reliable diagnostic quality. Especially during MRI scans of certain patient populations such as children, elderly or patients with certain medical conditions (e.g. stroke, Parkinson's), motion correction methods must be incorporated into the MR imaging protocol for adequate image quality. With increased demands for higher resolution or time-resolved examinations (e.g. functional MRI), examination times also increase and even willing patients might have trouble staying still during the course of the examination. The first part of this thesis provides a method for retrospective correction of head motion artifacts using a multi-shot spiral-in \ & out readout and parallel-imaging based iterative image reconstruction. The spiral-in part provided a low resolution image that was used for measurement of head motion. Due to rotational motion, locally undersampled areas appear in MR acquisition space (i.e., k-space), which violate the Nyquist theorem and cause artifacts even after motion correction. These artifacts were addressed through the data redundancy provided by multiple receiver channels that is present in modern receiver coils and an iterative conjugate-gradient based reconstruction. This method was then applied to diffusion tensor imaging (DTI) with multi-shot readout. Since DTI uses directional gradients to encode diffusion, rotational motion causes the image contrast to change, and it becomes incorrect to combine data with varying diffusion encodings on them. To address this issue, a non-linear conjugate gradient based reconstruction is presented and it is shown that this method provided more accurate description of white matter pathways compared to traditional methods. In the second part of this thesis, a prospective motion correction system using an optical tracking device is presented. Such systems are preferable compared to retrospective navigator-based methods due to various reasons, such as ability to perform motion correction independent of the MR data acquisition and immunity to spin history effects. The system proposed used a single camera mounted on the head coil and a self-encoded checkerboard marker mounted on the patient's forehead. Results on structural and diffusion imaging revealed that prospective motion correction outperforms retrospective navigator-based schemes. In the last part of the thesis, entropy-based retrospective autofocusing was used in combination with motion data obtained from prospective tracking to remove residual motion artifacts in the images. This method was especially useful for removing errors caused by inaccurate cross-calibration between the scanner and camera frame-of-references. It was also shown that prospective tracking can be the enabling technology for autofocusing in 3D acquisitions.
Download or read book Motion Correction in MR written by Andre van der Kouwe and published by Academic Press. This book was released on 2022-10-28 with total page 622 pages. Available in PDF, EPUB and Kindle. Book excerpt: Motion Correction in MR: Correction of Position, Motion, and Dynamic Changes, Volume Eight provides a comprehensive survey of the state-of-the-art in motion detection and correction in magnetic resonance imaging and magnetic resonance spectroscopy. The book describes the problem of correctly and consistently identifying and positioning the organ of interest and tracking it throughout the scan. The basic principles of how image artefacts arise because of position changes during scanning are described, along with retrospective and prospective techniques for eliminating these artefacts, including classical approaches and methods using machine learning. Internal navigator-based approaches as well as external systems for estimating motion are also presented, along with practical applications in each organ system and each MR modality covered. This book provides a technical basis for physicists and engineers to develop motion correction methods, giving guidance to technologists and radiologists for incorporating these methods in patient examinations. Provides approaches for correcting scans prospectively and retrospectively Shows how motion and secondary effects such as field changes manifest in MR scans as artifacts and subtle biases in quantitative research Gives methods for measuring motion and associated field changes, quantifying motion and judging the accuracy of the motion and field estimates
Download or read book Motion Correction and Reduction Techniques in Magnetic Resonance Imaging written by Hope Waggener Korin and published by . This book was released on 1991 with total page 334 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Motion Correction in Magnetic Resonance Imaging Using the Signal of Free Induction Decay written by Maryna Volodimirivna Waszak and published by . This book was released on 2016 with total page 89 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mots-clés de l'autrice: structural MRI ; FID navigator ; motion detection ; motion correction.
Download or read book Motion Detection and Correction in Magnetic Resonance Imaging written by Julian Roscoe Maclaren and published by . This book was released on 2007 with total page 171 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Motion Correction Techniques for Magnetic Resonance Imaging written by Edward Brian Welch and published by . This book was released on 2003 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nonrigid Registration of Dynamic Contrast Enhanced MRI Data Using Motion Informed Intensity Corrections written by Anthony Lausch and published by . This book was released on 2011 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: Effective early detection and monitoring of patient response to cancer therapy is important for improved patient outcomes, avoiding unnecessary procedures and their associated toxicities, as well as the development of new therapies. Dynamic contrast-enhanced magnetic resonance imaging shows promise as a way to evaluate tumour vasculature and assess the efficacy of new anti-angiogenic drugs. However, unavoidable patient motion can decrease the accuracy of subsequent analyses rendering the data unusable. Motion correction algorithms are challenging to develop for contrast-enhanced data since intensity changes due to contrast-enhancement and patient motion must somehow be differentiated from one another. A novel method is presented that employs a motion-informed intensity correction in order to facilitate the registration of contrast-enhanced data. The intensity correction simulates the presence or absence of contrast agent in the image volumes to be registered in an attempt to emulate the level of contrast-enhancement present in a single reference image volume.
Download or read book Motion Correction Method in Magnetic Resonance Image Reconstruction written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Motion Correction in Orbital Imaging Using MRI Compatible Eye Tracker written by Anita Dushyanth and published by . This book was released on 2014 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt: The body motion of patients during magnetic resonance imaging (MRI) causes significant artifacts in the reconstructed image. Artifacts are manifested as a motion induced blur and ghost repetitions of the moving structures, which obscure vital anatomical and pathological detail. The techniques that have been proposed for suppressing motion artifacts fall into two major categories. Realtime techniques that attempt to prevent the motion from corrupting the data by restricting the data acquisition times or motion of the patients, and post-processing techniques that use information embedded in the corrupted data to restore the image. The post-processing techniques usually demand an appropriate model of the motion that requires the parameters be determined in order to invert the data degradation process. However, motion is manifested differently depending on the time and duration it occurred during Magnetic Resonance (MR) data acquisition. Estimating motion parameters from such cases are heavily based on assumptions and the reconstructed image is compromised on either contrast or resolution. A major challenge in high resolution MR imaging of the orbit (eyeball and associated tissues in the eye socket) is image degradation by artifacts resulting from eye movements and eyelid blinks. In this thesis a novel method for motion correction has been developed by incorporating an optical sensor that detects these eye movements during MR scan acquisition without generating signal artifacts, and which is not affected by either the strong static magnetic field or the pulsed field gradients. Detection of the subjects eye movements and blinks is essential for determining the exact times during the MR scan when each such movement occurred. This thesis presents a method for refining orbital MRI techniques to compensate for the effects of blinking and fixation instability. It employs an eye tracker system to track eye/eyelid movements in the MRI studies of strabismus in humans that is based on infrared (IR) light reflection. It incorporates custom-fabricated optical fiber probes that illuminate the eye with low intensity infrared light, while eye/eyelid movements are detected by changes in ocular surface reflectance transmitted by another optical fiber cable coupled to a photodiode. Additionally, there is another light source that serves as a visible point target for ocular fixation during MRI scanning. The volunteer's eye movements are recorded simultaneously while the orbit is scanned using MRI. The output signal from the detector is amplified and synchronized in time with the MR acquired data. Image data corrupted by motion is flagged so that the affected data can be removed during image reconstruction. The purpose of this experiment is to outline experimental protocols for acquiring and correcting the above mentioned images in high quality, discuss these protocols from a wide range of perspectives, and finally present some observations on pilot data from volunteer subjects as well as patient with pathology. The MRI methodology developed was able to suppress motion artifacts considerably to provide interpretable MRI images.
Download or read book A Navigator based Rigid Body Motion Correction for Magnetic Resonance Imaging written by Marcus Görge Ullisch and published by . This book was released on 2012 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Improvement of Vibration and End to end Latency for Optical Motion Detection System in Magnetic Resonance Imaging written by Yifan Wu and published by . This book was released on 2017 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents improvements to both software and hardware for a marker-less optical motion detection system used in magnetic resonance imaging. Multiple devices have been developed to eliminate artifacts in MRI caused by patient movement, as motion is a common cause of artifact. Most developed devices require attaching pieces to a subject's body; however, our optical motion detection system is attachment-free. Previously, we successfully reduced imaging artifacts retrospectively using carotid artery MR data. We used gathered motion data to determine beginning and ending times of the movement, then discarded the corresponding k-space lines within the movement duration to eliminate artifacts. Now we would like to push this process from retrospective correction to real time. However, the camera and laser mounting vibration, as well as the system time delay variation, generate inaccuracies which make it difficult to find the exact k-space lines to be removed. To make the artifact-eliminating process more efficient, we reduced the overall end-to-end latency from 110ms ± 21ms to 100ms ± 12ms by coding the motion processing program in Python with OpenCV library. We also designed a new laser and camera holder using 3D printing with PLA for better stability. The noise and drift in both x and y directions are decreased with the new holder compared to the previous setup. The same result for decrease in vibration was seen during phantom scanning with T1-weighted (TR = 100ms) gradient echo (GRE) and with T1-weighted turbo spin-echo (TSE) quadruple inversion-recovery (QIR) (TR = 800ms) sequence. Furthermore, the 3D printed holder decreases the overall assembly time required to set up the system. Overall, the new design of the system reduces the event-to-display latency, the latency variation, the hardware vibration, and the assembly time. The new design improves the old design and provides a path to pursue prospective optical motion correction.
Download or read book Head Motion Correction in Magnetic Resonance Imaging Using NMR Field Probes written by and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Adaptive Motion Correction in 2DFT Magnetic Resonance Imaging written by Joel Patrick Felmlee and published by . This book was released on 1992 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Motion Artifact Reduction in Steady state Magnetic Resonance Imaging written by Richard Reeve Ingle and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic resonance imaging (MRI) is a powerful medical imaging modality that offers excellent soft-tissue contrast and numerous contrast-generation mechanisms. However, due to the relatively low signal-to-noise ratio (SNR) of MRI, many volumetric and high-resolution imaging techniques require long acquisition times yielding an increased sensitivity to motion. In many cardiac MRI applications, one of the most significant challenges is the reduction of motion artifacts caused by cardiac and respiratory motion. In these applications, a combination of SNR-efficient balanced steady-state free precession (bSSFP) pulse sequences, high-temporal-resolution motion tracking acquisitions, and retrospective motion correction algorithms are commonly employed to mitigate motion artifacts. Despite recent advances in steady-state pulse sequence development, navigator motion tracking acquisitions, and motion correction algorithms, motion artifact reduction continues to be a significant challenge for many cardiac MRI applications. A novel class of perturbed steady-state free precession (SSFP) pulse sequences is developed and analyzed, yielding new forms of steady-state image contrast. These sequences utilize alternating perturbations of sequence parameters such as the repetition time (TR) and flip angle to produce oscillating steady-state frequency responses. Large oscillations of the signal magnitude and phase occur at specific off-resonant frequencies, and the combination of these signals can yield spectrally selective image contrast. Applications are demonstrated for retrospective motion correction using cardiac fat navigator acquisitions in free-breathing whole-heart cardiac MRI and for positive-contrast imaging of superparamagnetic iron-oxide nanoparticles. The bSSFP pulse sequence is widely used in cardiac imaging due to its high signal per unit time and excellent blood-myocardial contrast. A drawback of this pulse sequence is the generation of bright signal from fat, which can lead to unwanted image artifacts. Alternating repetition time (ATR) SSFP is a recently developed sequence that generates fat-suppressed steady-state contrast, but it requires the addition of an unused time interval every repetition, making it less time efficient than bSSFP. A small modification to the ATR pulse sequence is proposed to enable the acquisition of a one-dimensional self-gating signal during this unused time interval. The self-gating signals are used for retrospective cardiac triggering in breath-held cardiac cine imaging, and the proposed sequence is evaluated in volunteer and patient populations. The resulting ECG-free self-gated images have no statistically significant differences compared with conventional ECG-gated images. The proposed sequence also yields robust suppression of epicardial fat compared with standard bSSFP cardiac cine imaging. In coronary MR angiography (CMRA), high-resolution, whole-heart acquisitions are typically required for visualization of the relatively small coronary vasculature. These acquisitions require long scan times that are carried out during free breathing, which can lead to severe ghosting and blurring artifacts without motion compensation. A nonrigid retrospective motion correction technique is proposed for motion artifact reduction in image-navigated CMRA. The technique reconstructs a bank of motion-compensated CMRA images using many candidate motion estimates derived from navigator images acquired throughout the scan. A metric-based autofocusing approach is used to automatically generate a final nonrigid-motion-corrected image from this bank of images. The proposed technique is evaluated in volunteer and patient studies, leading to improvements in vessel sharpness and image quality compared with rigid-body translational motion correction. These new steady-state pulse sequences, motion tracking acquisitions, and nonrigid reconstruction techniques address several of the challenges to cardiac MRI, enabling the reduction of motion artifacts and improvement of image quality.
Download or read book Acquisition and Processing Techniques for Image Based Prospective Motion Correction in Magnetic Resonance Imaging written by Daniel Christopher Hoinkiss and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Motion Correction Techniques for Three dimensional Magnetic Resonance Imaging Acquired with the Elliptical Centric View Order Or the Shells Trajectory written by Yunhong Shu and published by . This book was released on 2006 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Prospective Multiaxial Motion Correction for Functional Magnetic Resonance Imaging written by Heidi Alissa Ward and published by . This book was released on 2001 with total page 418 pages. Available in PDF, EPUB and Kindle. Book excerpt:
