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Motion Compensation (motion + compensation)
Selected AbstractsMotion compensation by phase correction for synthetic-aperture side-scan sonar imagingINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 6 2004Hua Lee This article presents a robust motion estimation and correction technique for the realization of synthetic-aperture side-scan sonar imaging. It utilizes the redundancy provided by the multiple-element receiver array configuration. Physical-array subimages are used for the estimation of the motion errors between adjacent receiver positions. Subsequently, the motion errors are formulated in the form of phase perturbations and are corrected accordingly by making adjustments to the wave-field data samples prior to the formation of synthetic-aperture images. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 14, 259,261, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20029 [source] A new fast block matching algorithm based on complexity-distortion optimizationINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2 2002Pol Lin Tai Most fast block matching algorithms ignore the efficiency in motion compensation within each checking step. In order to achieve better-compensated performance, the limited computational complexity should be allocated more carefully into each block. It means that the fast block matching algorithm can be viewed as a kind of rate-distortion optimization problem. The complexity-distortion optimal fast block matching algorithm should find the maximized quality of the compensated image under a target computational complexity. In order to approach the optimal complexity-distortion solution, some strategies are developed. For example, a domination-based motion vector prediction technique is developed to set the initial motion vector for each block. A predictive complexity-distortion benefit list is established to predict the compensated benefit for each block. Also, a three-level pattern searching is employed to check the candidate motion vector. Experimental results show that our proposed algorithm outperforms significantly the three-step search. For example, in "Salesman," the average checkpoints for one block is 33 by using the three-step search. The average checkpoint is 1.75 by using our proposal algorithm under the same average PSNR condition. © 2002 Wiley Periodicals, Inc. Int J Imaging Syst Technol 12, 63,67, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10012 [source] Artifact-reduced two-dimensional cine steady state free precession for myocardial blood- oxygen-level-dependent imagingJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2010Xiangzhi Zhou PhD Abstract Purpose: To minimize image artifacts in long TR cardiac phase-resolved steady state free precession (SSFP) based blood-oxygen-level-dependent (BOLD) imaging. Materials and Methods: Nine healthy dogs (four male, five female, 20,25 kg) were studied in a clinical 1.5 Tesla MRI scanner to investigate the effect of temporal resolution, readout bandwidth, and motion compensation on long repetition time (TR) SSFP images. Breath-held 2D SSFP cine sequences with various temporal resolutions (10,204 ms), bandwidths (239,930 Hz/pixel), with and without first-order motion compensation were prescribed in the basal, mid-ventricular, and apical along the short axis. Preliminary myocardial BOLD studies in dogs with controllable coronary stenosis were performed to assess the benefits of artifact-reduction strategies. Results: Shortening the readout time by means of increasing readout bandwidth had no observable reduction in image artifacts. However, increasing the temporal resolution in the presence of first-order motion compensation led to significant reduction in image artifacts. Preliminary studies demonstrated that BOLD signal changes can be reliably detected throughout the cardiac cycle. Conclusion: Artifact-reduction methods used in this study provide significant improvement in image quality compared with conventional long TR SSFP BOLD MRI. It is envisioned that the methods proposed here may enable reliable detection of myocardial oxygenation changes throughout the cardiac cycle with long TR SSFP-based myocardial BOLD MRI. J. Magn. Reson. Imaging 2010;31:863,871. ©2010 Wiley-Liss, Inc. [source] Image-based coronary tracking and beat-to-beat motion compensation: Feasibility for improving coronary MR angiographyMAGNETIC RESONANCE IN MEDICINE, Issue 3 2008Maneesh Dewan Abstract A method to reduce the effect of motion variability in MRI of the coronary arteries is proposed. It involves acquiring real-time low-resolution images in specific orthogonal orientations, extracting coronary motion from these images, and then using this motion information to guide high-resolution MR image acquisition on a beat-to-beat basis. The present study establishes the feasibility and efficacy of the proposed approach using human motion data in an offline implementation, prior to future online implementation on an MRI scanner. To track the coronary arteries in low-resolution real-time MR images in an accurate manner, a tracking approach is presented and validated. The tracking algorithm was run on real-time images acquired at 15,20 frames per second in four-chamber, short-axis, and coronal views in five volunteers. The systolic and diastolic periods in the cardiac cycles, computed from the extracted motion information, had significant variability during the short time periods typical of cardiac MRI. It is also demonstrated through simulation analysis using human tracked coronary motion data that accounting for this cardiac variability by adaptively changing the trigger delay for acquisition on a beat-to-beat basis improves overall motion compensation and hence MR image quality evaluated in terms of SNR and CNR values. Magn Reson Med 60:604,615, 2008. © 2008 Wiley-Liss, Inc. [source] Navigator gating and volume tracking for double-triggered cardiac proton spectroscopy at 3 TeslaMAGNETIC RESONANCE IN MEDICINE, Issue 6 2004Michael Schär Abstract Respiratory motion compensation based on navigator echoes for double-triggered cardiac proton spectroscopy at 3.0T is presented. The navigators measure the displacement of the liver,lung interface during free breathing. This information allows for double triggering on a defined window within the respiratory cycle and on a defined trigger delay after the R-wave based on the ECG. Furthermore, it allows the excitation volume to be shifted by the determined respiratory displacement within the defined window in real-time (volume tracking). Static and motion phantom experiments were performed in this study, and it was demonstrated that volume tracking permits the suppression of signal from tissue next to the localized volume. However, triggering on a defined respiratory position is still necessary to achieve high spectral quality, because shimming and water suppression calibration are only optimal for a small window of the respiratory cycle. Single-volume spectra obtained in the myocardial septum of healthy subjects are presented. Magn Reson Med 51:1091,1095, 2004. © 2004 Wiley-Liss, Inc. [source] Novel interleaved spiral imaging motion correction technique using orbital navigatorsMAGNETIC RESONANCE IN MEDICINE, Issue 2 2003Hisamoto Moriguchi Abstract Although spiral imaging seldom produces apparent artifacts related to flow, it remains sensitive to rapid object motion. In this article, a new correction method is presented for rapid rigid body motion in interleaved spiral imaging. With this technique, an identical circular navigator k -space trajectory is linked to each spiral trajectory. Data inconsistency due to both rotation and translation among spiral interleaves can be corrected by evaluating the magnitudes and phases of the data contained in the navigator "ring." Further, it is difficult to create a frequency field map for off-resonance correction when an object moves during a scan, because there is motion-dependent misregistration between the two images acquired with different TEs. However, this difficulty can be overcome by combining the motion-correction method with a recently proposed technique (off-resonance correction using variable-density spirals (ORC-VDS)), thereby enabling both motion compensation and off-resonance correction with no additional scanning. Magn Reson Med 50:423,428, 2003. © 2003 Wiley-Liss, Inc. [source] Volume tracking cardiac 31P spectroscopyMAGNETIC RESONANCE IN MEDICINE, Issue 2 2002Sebastian Kozerke Abstract The limited reliability and accuracy of cardiac spectroscopy have been partly attributed to effects from respiratory motion. In this work, we developed a prospective volume tracking method for respiratory motion compensation based on multiple navigator echoes and demonstrated its application in cardiac 31P spectroscopy. The sequence consists of two 2D selective excitation pulses preceding the spectroscopic experiment to sample respiratory motion components. The navigator information is evaluated in real-time to calculate the shift of the heart from respiration. Based on the displacement information, the spectroscopic volume and/or grid position is prospectively corrected to track the volume of interest. The method was validated with a moving compartment phantom simulating in vivo respiratory motion. With volume tracking, no signal contamination was apparent. Spectra obtained in 14 healthy volunteers were evaluated using time-domain fitting procedures. The fitting accuracy improved consistently with volume tracking compared to data from non-navigated reference acquisitions. Compared to other gating approaches available for spectroscopy, the current technique does not degrade the scan efficiency, thus allowing effective use of scan time. Magn Reson Med 48:380,384, 2002. © 2002 Wiley-Liss, Inc. [source] | ||||||||||