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Patient Motion (patient + motion)
Selected AbstractsProspective real-time correction for arbitrary head motion using active markersMAGNETIC RESONANCE IN MEDICINE, Issue 4 2009Melvyn B. Ooi Abstract Patient motion during an MRI exam can result in major degradation of image quality, and is of increasing concern due to the aging population and its associated diseases. This work presents a general strategy for real-time, intraimage compensation of rigid-body motion that is compatible with multiple imaging sequences. Image quality improvements are established for structural brain MRI acquired during volunteer motion. A headband integrated with three active markers is secured to the forehead. Prospective correction is achieved by interleaving a rapid track-and-update module into the imaging sequence. For every repetition of this module, a short tracking pulse-sequence remeasures the marker positions; during head motion, the rigid-body transformation that realigns the markers to their initial positions is fed back to adaptively update the image-plane,maintaining it at a fixed orientation relative to the head,before the next imaging segment of k -space is acquired. In cases of extreme motion, corrupted lines of k -space are rejected and reacquired with the updated geometry. High-precision tracking measurements (0.01 mm) and corrections are accomplished in a temporal resolution (37 ms) suitable for real-time application. The correction package requires minimal additional hardware and is fully integrated into the standard user interface, promoting transferability to clinical practice. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Single-step nonlinear diffusion tensor estimation in the presence of microscopic and macroscopic motion,MAGNETIC RESONANCE IN MEDICINE, Issue 5 2008Murat Aksoy Abstract Patient motion can cause serious artifacts in diffusion tensor imaging (DTI), diminishing the reliability of the estimated diffusion tensor information. Studies in this field have so far been limited mainly to the correction of miniscule physiological motion. In order to correct for gross patient motion it is not sufficient to correct for misregistration between successive shots; the change in the diffusion-encoding direction must also be accounted for. This becomes particularly important for multishot sequences, whereby,in the presence of motion,each shot is encoded with a different diffusion weighting. In this study a general mathematical framework to correct for gross patient motion present in a multishot and multicoil DTI scan is presented. A signal model is presented that includes the effect of rotational and translational motion in the patient frame of reference. This model was used to create a nonlinear least-squares formulation, from which the diffusion tensors were obtained using a nonlinear conjugate gradient algorithm. Applications to both phantom simulations and in vivo studies showed that in the case of gross motion the proposed algorithm performs superiorly compared to conventional methods used for tensor estimation. Magn Reson Med 59:1138,1150, 2008. © 2008 Wiley-Liss, Inc. [source] Improved dynamic susceptibility contrast (DSC)-MR perfusion estimates by motion correctionJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2007Robert K. Kosior BSc Abstract Purpose To investigate the effect of patient motion on quantitative cerebral blood flow (CBF) maps in ischemic stroke patients and to evaluate the efficacy of a motion-correction scheme. Materials and Methods Perfusion data from 25 ischemic stroke patients were selected for analysis. Two motion profiles were applied to a digital anthropomorphic brain phantom to estimate accuracy. CBF images were generated for motion-corrupted and motion-corrected data. To correct for motion, rigid-body registration was performed. The realignment parameters and mean CBF in regions of interest were recorded. Results All patient data with motion exhibited visibly reduced intervolume misalignment after motion correction. Improved flow delineation between different tissues and a more clearly defined ischemic lesion (IL) were achieved in the motion-corrected CBF. A significant difference occurred in the IL (P < 0.05) for patients with severe motion with an average difference between corrupted and corrected data of 4.8 mL/minute/100 g. The phantom data supported the patient results with better CBF accuracy after motion correction and high registration accuracy (<1 mm translational and <1° rotational error). Conclusion Motion degrades flow differentiation between adjacent tissues in CBF maps and can cause ischemic severity to be underestimated. A registration motion correction scheme improves dynamic susceptibility contrast (DSC)-MR perfusion estimates. J. Magn. Reson. Imaging 2007;26:1167,1172. © 2007 Wiley-Liss, Inc. [source] Patient motion correction for multiplanar, multi-breath-hold cardiac cine MR imagingJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2007Piotr J. Slomka PhD Abstract Purpose To correct for spatial misregistration of multi-breath-hold short-axis (SA), two-chamber (2CH), and four-chamber (4CH) cine cardiac MR (CMR) images caused by respiratory and patient motion. Materials and Methods Twenty CMR studies from consecutive patients with separate breath-hold 2CH, 4CH, and SA 20-phase cine images were considered. We automatically registered the 2CH, 4CH, and SA images in three dimensions by minimizing the cost function derived from plane intersections for all cine phases. The automatic alignment was compared with manual alignment by two observers. Results The processing time for the proposed method was <20 seconds, compared to 14,24 minutes for the manual correction. The initial plane displacement identified by the observers was 2.8 ± 1.8 mm (maximum = 14 mm). A displacement of ,5 mm was identified in 15 of 20 studies. The registration accuracy (defined as the difference between the automatic parameters and those obtained by visual registration) was 1.0 ± 0.9 mm, 1.1 ± 1.0 mm, 1.1 ± 1.2 mm, and 2.0 ± 1.8 mm for 2CH-4CH alignment and SA alignment in the mid, basal, and apical regions, respectively. The algorithm variability was higher in the apex (2.0 ± 1.9 mm) than in the mid (1.4 ± 1.4 mm) or basal (1.2 ± 1.2 mm) regions (ANOVA, P < 0.05). Conclusion An automated preprocessing algorithm can reduce spatial misregistration between multiple CMR images acquired at different breath-holds and plane orientations. J. Magn. Reson. Imaging 2007;25:965,973. © 2007 Wiley-Liss, Inc. [source] An automated method for nonparametric kinetic analysis of clinical DCE-MRI data: Application to glioblastoma treated with bevacizumabMAGNETIC RESONANCE IN MEDICINE, Issue 5 2010Gregory Z. Ferl Abstract Here, we describe an automated nonparametric method for evaluating gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) kinetics, based on dynamic contrast-enhanced,MRI scans of glioblastoma patients taken before and after treatment with bevacizumab; no specific model or equation structure is assumed or used. Tumor and venous blood concentration-time profiles are smoothed, using a robust algorithm that removes artifacts due to patient motion, and then deconvolved, yielding an impulse response function. In addition to smoothing, robustness of the deconvolution operation is assured by excluding data that occur prior to the plasma peak; an exhaustive analysis was performed to demonstrate that exclusion of the prepeak plasma data does not significantly affect results. All analysis steps are executed by a single R script that requires blood and tumor curves as the sole input. Statistical moment analysis of the Impulse response function yields the area under the curve (AUC) and mean residence time (MRT). Comparison of deconvolution results to fitted Tofts model parameters suggests that and AUC of the Impulse response function closely approximate fractional clearance from plasma to tissue (Ktrans) and fractional interstitial volume (ve) . Intervisit variability is shown to be comparable when using the deconvolution method (11% [] and 13%[AUC]) compared to the Tofts model (14%[Ktrans] and 24%[ve]). AUC and both exhibit a statistically significant decrease (P < 0.005) 1 day after administration of bevacizumab. Magn Reson Med 63:1366,1375, 2010. © 2010 Wiley-Liss, Inc. [source] Generalized MRI reconstruction including elastic physiological motion and coil sensitivity encodingMAGNETIC RESONANCE IN MEDICINE, Issue 6 2008Freddy Odille Abstract This article describes a general framework for multiple coil MRI reconstruction in the presence of elastic physiological motion. On the assumption that motion is known or can be predicted, it is shown that the reconstruction problem is equivalent to solving an integral equation,known in the literature as a Fredholm equation of the first kind,with a generalized kernel comprising Fourier and coil sensitivity encoding, modified by physiological motion information. Numerical solutions are found using an iterative linear system solver. The different steps in the numerical resolution are discussed, in particular it is shown how over-determination can be used to improve the conditioning of the generalized encoding operator. Practical implementation requires prior knowledge of displacement fields, so a model of patient motion is described which allows elastic displacements to be predicted from various input signals (e.g., respiratory belts, ECG, navigator echoes), after a free-breathing calibration scan. Practical implementation was demonstrated with a moving phantom setup and in two free-breathing healthy subjects, with images from the thoracic-abdominal region. Results show that the method effectively suppresses the motion blurring/ghosting artifacts, and that scan repetitions can be used as a source of over-determination to improve the reconstruction. Magn Reson Med, 2008. © 2008 Wiley-Liss, Inc. [source] Single-step nonlinear diffusion tensor estimation in the presence of microscopic and macroscopic motion,MAGNETIC RESONANCE IN MEDICINE, Issue 5 2008Murat Aksoy Abstract Patient motion can cause serious artifacts in diffusion tensor imaging (DTI), diminishing the reliability of the estimated diffusion tensor information. Studies in this field have so far been limited mainly to the correction of miniscule physiological motion. In order to correct for gross patient motion it is not sufficient to correct for misregistration between successive shots; the change in the diffusion-encoding direction must also be accounted for. This becomes particularly important for multishot sequences, whereby,in the presence of motion,each shot is encoded with a different diffusion weighting. In this study a general mathematical framework to correct for gross patient motion present in a multishot and multicoil DTI scan is presented. A signal model is presented that includes the effect of rotational and translational motion in the patient frame of reference. This model was used to create a nonlinear least-squares formulation, from which the diffusion tensors were obtained using a nonlinear conjugate gradient algorithm. Applications to both phantom simulations and in vivo studies showed that in the case of gross motion the proposed algorithm performs superiorly compared to conventional methods used for tensor estimation. Magn Reson Med 59:1138,1150, 2008. © 2008 Wiley-Liss, Inc. [source] The acoustic hood: a patient-independent device improving acoustic noise protection during neonatal magnetic resonance imagingACTA PAEDIATRICA, Issue 8 2009Anders Nordell Abstract Background:, Magnetic resonance imaging (MRI) is today the imaging modality of choice to investigate the neonatal brain. However, the acoustic noise during scanning is very loud, often exceeding 100 dBA. Aim:, To reduce the acoustic noise during MRI for neonatal patients. If effective, this would create a safer environment and also result in fewer aborted examinations due to poor image quality from patient motion. Methods:, A passive acoustic noise protector, the acoustic hood, was built out of dampening material. Sound pressure measurements with and without the acoustic hood were performed using our clinical neonatal scan protocol, consisting of eight imaging sequences. The acoustic hood is placed over the newborn inside the MR scanner tunnel during the examination to absorb acoustic noise. Results:, The acoustic noise level was substantially reduced using the acoustic hood. Peak sound pressure was reduced 16.18,22.21 dBA depending on the pulse sequence. For the entire frequency spectra, reduction were between 4,13.59 dBA again varying with the pulse sequence. Conclusion:, Acoustic noise can be reduced further than before by using the patient-independent acoustic hood in addition to other noise protection. We recommend the use of three passive hearing protections during neonatal MRI: (1) dental putty, (2) paediatric ear muffs, and (3) the acoustic hood. [source] Turboprop IDEAL: A motion-resistant fat,water separation techniqueMAGNETIC RESONANCE IN MEDICINE, Issue 1 2009Donglai Huo Abstract Suppression of the fat signal in MRI is very important for many clinical applications. Multi-point water,fat separation methods, such as IDEAL (Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation), can robustly separate water and fat signal, but inevitably increase scan time, making separated images more easily affected by patient motions. PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) and Turboprop techniques offer an effective approach to correct for motion artifacts. By combining these techniques together, we demonstrate that the new TP-IDEAL method can provide reliable water,fat separation with robust motion correction. The Turboprop sequence was modified to acquire source images, and motion correction algorithms were adjusted to assure the registration between different echo images. Theoretical calculations were performed to predict the optimal shift and spacing of the gradient echoes. Phantom images were acquired, and results were compared with regular FSE-IDEAL. Both T1- and T2-weighted images of the human brain were used to demonstrate the effectiveness of motion correction. TP-IDEAL images were also acquired for pelvis, knee, and foot, showing great potential of this technique for general clinical applications. Magn Reson Med 61:188,195, 2009. © 2008 Wiley-Liss, Inc. [source] | ||||||||||