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  • Knee Cartilage MRI with In Situ Mechanical Loading Using Prospective Motion Correction MAGNETIC RESONANCE IN MEDICINE Lange, T., Maclaren, J., Herbst, M., Lovell-Smith, C., Izadpanah, K., Zaitsev, M. 2014; 71 (2): 516-523

    View details for DOI 10.1002/mrm.24679

    View details for Web of Science ID 000330769700007

  • Reproduction of Motion Artifacts for Performance Analysis of Prospective Motion Correction in MRI MAGNETIC RESONANCE IN MEDICINE Herbst, M., Maclaren, J., Lovell-Smith, C., Sostheim, R., Egger, K., Harloff, A., Korvink, J., Hennig, J., Zaitsev, M. 2014; 71 (1): 182-190

    Abstract

    Despite numerous publications describing the ability of prospective motion correction to improve image quality in magnetic resonance imaging of the brain, a reliable approach to assess this improvement is still missing. A method that accurately reproduces motion artifacts correctable with prospective motion correction is developed, and enables the quantification of the improvements achieved.A software interface was developed to simulate rigid body motion by changing the scanning coordinate system relative to the object. Thus, tracking data recorded during a patient scan can be used to reproduce the prevented motion artifacts on a volunteer or a phantom. The influence of physiological motion on image quality was investigated by filtering these data. Finally, the method was used to reproduce and quantify the motion artifacts prevented in a patient scan.The accuracy of the method was tested in phantom experiments and in vivo. The calculated quality factor, as well as a visual inspection of the reproduced artifacts shows a good correspondence to the original.Precise reproduction of motion artifacts assists qualification of prospective motion correction strategies. The presented method provides an important tool to investigate the effects of rigid body motion on a wide range of sequences, and to quantify the improvement in image quality through prospective motion correction.

    View details for DOI 10.1002/mrm.24645

    View details for Web of Science ID 000328580300020

    View details for PubMedID 23440737

  • Prospective slice-by-slice motion correction reduces false positive activations in fMRI with task-correlated motion NEUROIMAGE Schulz, J., Siegert, T., Bazin, P., MacLaren, J., Herbst, M., Zaitsev, M., Turner, R. 2014; 84: 124-132

    Abstract

    We aimed to test the hypothesis that slice-by-slice prospective motion correction at 7T using an optical tracking system reduces the rate of false positive activations in an fMRI group study with a paradigm that involves task-correlated motion.Brain activation during right leg movement was measured using a block design on 15 volunteers, with and without prospective motion correction. Clearly erroneous activations were compared between both cases, at the individual level. Additionally, conventional group analysis was performed.The number of falsely activated voxels with T-values higher than 5 was reduced by 48% using prospective motion correction alone, without additional retrospective realignment. In the group analysis, the statistical power was increased - the peak T-value was 26% greater, and the number of voxels in the cluster representing the right leg was increased by a factor of 9.3.Slice-by-slice prospective motion correction in fMRI studies with task-correlated motion can substantially reduce false positive activations and increase statistical power.

    View details for DOI 10.1016/j.neuroimage.2013.08.006

    View details for Web of Science ID 000328868600012

    View details for PubMedID 23954484

  • Prospective motion correction using inductively coupled wireless RF coils MAGNETIC RESONANCE IN MEDICINE Ooi, M. B., Aksoy, M., Maclaren, J., Watkins, R. D., Bammer, R. 2013; 70 (3): 639-647

    View details for DOI 10.1002/mrm.24845

    View details for Web of Science ID 000323543600005

  • Ballistocardiographic artifact removal from simultaneous EEG-fMRI using an optical motion-tracking system NEUROIMAGE LeVan, P., Maclaren, J., Herbst, M., Sostheim, R., Zaitsev, M., Hennig, J. 2013; 75: 1-11

    Abstract

    The combination of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) allows the investigation of neuronal activity with high temporal and spatial resolution. While much progress has been made to overcome the multiple technical challenges associated with the recording of EEG inside the MR scanner, the ballistocardiographic (BCG) artifact, which is caused by cardiac-related motion inside the magnetic field, remains a major issue affecting EEG quality. The BCG is difficult to remove by standard average artifact subtraction (AAS) methods due to its variability across cardiac cycles. We thus investigate the possibility of directly recording the BCG motion using an optical motion-tracking system. In 5 subjects, the system is shown to accurately measure BCG motion. Regressing out linear and quadratic functions of the measured motion parameters resulted in a significant reduction (p<0.05) in root-mean-square (RMS) amplitudes across cardiac cycles compared to AAS. A further significant RMS reduction was obtained when applying the regression and AAS methods sequentially, resulting in RMS amplitudes that were not significantly different from those of EEG recorded outside the scanner, although with higher residual variability. The large contributions of pure translational parameters and of non-linear terms to the BCG waveforms indicate that non-rigid motion of the EEG wires (originating from rigid head motion) is likely an important cause of the artifact.

    View details for DOI 10.1016/j.neuroimage.2013.02.039

    View details for Web of Science ID 000318208000001

    View details for PubMedID 23466939

  • Prospective motion correction in brain imaging: A review MAGNETIC RESONANCE IN MEDICINE Maclaren, J., Herbst, M., Speck, O., Zaitsev, M. 2013; 69 (3): 621-636

    Abstract

    Motion correction in magnetic resonance imaging by real-time adjustment of the imaging pulse sequence was first proposed more than 20 years ago. Recent advances have resulted from combining real-time correction with new navigator and external tracking mechanisms capable of quantifying rigid-body motion in all 6 degrees of freedom. The technique is now often referred to as "prospective motion correction." This article describes the fundamentals of prospective motion correction and reviews the latest developments in its application to brain imaging and spectroscopy. Although emphasis is placed on the brain as the organ of interest, the same principles apply whenever the imaged object can be approximated as a rigid body. Prospective motion correction can be used with most MR sequences, so it has potential to make a large impact in clinical routine. To maximize the benefits obtained from the technique, there are, however, several challenges still to be met. These include practical implementation issues, such as obtaining tracking data with minimal delay, and more fundamental problems, such as the magnetic field distortions caused by a moving object. This review discusses these challenges and summarizes the state of the art. We hope that this work will motivate further developments in prospective motion correction and help the technique to reach its full potential.

    View details for DOI 10.1002/mrm.24314

    View details for Web of Science ID 000315331300003

    View details for PubMedID 22570274

  • An embedded optical tracking system for motion-corrected magnetic resonance imaging at 7T MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Schulz, J., Siegert, T., Reimer, E., Labadie, C., Maclaren, J., Herbst, M., Zaitsev, M., Turner, R. 2012; 25 (6): 443-453

    Abstract

    Prospective motion correction using data from optical tracking systems has been previously shown to reduce motion artifacts in MR imaging of the head. We evaluate a novel optical embedded tracking system.The home-built optical embedded tracking system performs image processing within a 7 T scanner bore, enabling high speed tracking. Corrected and uncorrected in vivo MR volumes are acquired interleaved using a modified 3D FLASH sequence, and their image quality is assessed and compared.The latency between motion and correction of the slice position was measured to be (19 ± 5) ms, and the tracking noise has a standard deviation no greater than 10 ?m/0.005° during conventional MR scanning. Prospective motion correction improved the edge strength by 16 % on average, even though the volunteers were asked to remain motionless during the acquisitions.Using a novel method for validating the effectiveness of in vivo prospective motion correction, we have demonstrated that prospective motion correction using motion data from the embedded tracking system considerably improved image quality.

    View details for DOI 10.1007/s10334-012-0320-0

    View details for Web of Science ID 000311675100004

    View details for PubMedID 22695771

  • Measurement and Correction of Microscopic Head Motion during Magnetic Resonance Imaging of the Brain PLOS ONE Maclaren, J., Armstrong, B. S., Barrows, R. T., Danishad, K. A., Ernst, T., Foster, C. L., Gumus, K., Herbst, M., Kadashevich, I. Y., Kusik, T. P., Li, Q., Lovell-Smith, C., Prieto, T., Schulze, P., Speck, O., Stucht, D., Zaitsev, M. 2012; 7 (11)

    Abstract

    Magnetic resonance imaging (MRI) is a widely used method for non-invasive study of the structure and function of the human brain. Increasing magnetic field strengths enable higher resolution imaging; however, long scan times and high motion sensitivity mean that image quality is often limited by the involuntary motion of the subject. Prospective motion correction is a technique that addresses this problem by tracking head motion and continuously updating the imaging pulse sequence, locking the imaging volume position and orientation relative to the moving brain. The accuracy and precision of current MR-compatible tracking systems and navigator methods allows the quantification and correction of large-scale motion, but not the correction of very small involuntary movements in six degrees of freedom. In this work, we present an MR-compatible tracking system comprising a single camera and a single 15 mm marker that provides tracking precision in the order of 10 m and 0.01 degrees. We show preliminary results, which indicate that when used for prospective motion correction, the system enables improvement in image quality at both 3 T and 7 T, even in experienced and cooperative subjects trained to remain motionless during imaging. We also report direct observation and quantification of the mechanical ballistocardiogram (BCG) during simultaneous MR imaging. This is particularly apparent in the head-feet direction, with a peak-to-peak displacement of 140 m.

    View details for DOI 10.1371/journal.pone.0048088

    View details for Web of Science ID 000311935800034

    View details for PubMedID 23144848

  • Spectroscopic imaging with prospective motion correction and retrospective phase correction MAGNETIC RESONANCE IN MEDICINE Lange, T., Maclaren, J., Buechert, M., Zaitsev, M. 2012; 67 (6): 1506-1514

    Abstract

    Motion-induced artifacts are much harder to recognize in magnetic resonance spectroscopic imaging than in imaging experiments and can therefore lead to erroneous interpretation. A method for prospective motion correction based on an optical tracking system has recently been proposed and has already been successfully applied to single voxel spectroscopy. In this work, the utility of prospective motion correction in combination with retrospective phase correction is evaluated for spectroscopic imaging in the human brain. Retrospective phase correction, based on the interleaved reference scan method, is used to correct for motion-induced frequency shifts and ensure correct phasing of the spectra across the whole spectroscopic imaging slice. It is demonstrated that the presented correction methodology can reduce motion-induced degradation of spectroscopic imaging data.

    View details for DOI 10.1002/mrm.23136

    View details for Web of Science ID 000304086000002

    View details for PubMedID 22135041

  • Prospective motion correction with continuous gradient updates in diffusion weighted imaging MAGNETIC RESONANCE IN MEDICINE Herbst, M., Maclaren, J., Weigel, M., Korvink, J., Hennig, J., Zaitsev, M. 2012; 67 (2): 326-338

    Abstract

    Despite the existence of numerous motion correction methods, head motion during MRI continues to be a major source of artifacts and can greatly reduce image quality. This applies particularly to diffusion weighted imaging, where strong gradients are applied during long encoding periods. These are necessary to encode microscopic movements. However, they also make the technique highly sensitive to bulk motion. In this work, we present a prospective motion correction method where all applied gradients are adjusted continuously to compensate for changes of the object position and ensure the desired phase evolution in the image coordinate frame. Additionally, in phantom experiments this new technique is used to reproduce motion artifacts with high accuracy by changing the position of the imaging frame relative to the measured object. In vivo measurements demonstrate the validity of the new correction method.

    View details for DOI 10.1002/mrm.23230

    View details for Web of Science ID 000299376500007

    View details for PubMedID 22161984

  • Optical motion tracking to improve image quality in MRI of the brain IMAGE RECONSTRUCTION FROM INCOMPLETE DATA VII Maclaren, J., Aksoy, M., Ooi, M., Bammer, R. 2012; 8500

    View details for DOI 10.1117/12.953612

    View details for Web of Science ID 000312165100002

  • An Adaptive MR-Compatible Lens and Objective CONCEPTS IN MAGNETIC RESONANCE PART B-MAGNETIC RESONANCE ENGINEERING Maclaren, J., Schneider, F., Herbst, M., Hennig, J., Bammer, R., Zaitsev, M., Wallrabe, U. 2011; 39B (3): 141-148
  • Microcoil-based MRI: feasibility study and cell culture applications using a conventional animal system MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Weber, H., Baxan, N., Paul, D., Maclaren, J., Schmidig, D., Mohammadzadeh, M., Hennig, J., von Elverfeldt, D. 2011; 24 (3): 137-145

    Abstract

    The aim of this study was to demonstrate the feasibility of MR microimaging on a conventional 9.4 T horizontal animal MRI system using commercial available microcoils in combination with only minor modifications to the system, thereby opening this field to a larger community.Commercially available RF microcoils designed for high-resolution NMR spectrometers were used in combination with a custom-made probehead. For this purpose, changes within the transmit chain and modifications to the adjustment routines and image acquisition sequences were made, all without requiring expensive hardware. To investigate the extent to which routine operation and high-resolution imaging is possible, the quality of phantom images was analysed. Surface and solenoidal microcoils were characterized with regard to their sensitive volume and signal-to-noise ratio. In addition, the feasibility of using planar microcoils to achieve high-resolution images of living glioma cells labelled with MnCl(2) was investigated.The setup presented in this work allows routine acquisition of high-quality images with high SNR and isotropic resolutions up to 10 μm within an acceptable measurement time.This study demonstrates that MR microscopy can be applied at low cost on animal MR imaging systems, which are in widespread use. The successful imaging of living glioma cells indicates that the technique promises to be a useful tool in biomedical research.

    View details for DOI 10.1007/s10334-011-0244-0

    View details for Web of Science ID 000291041900003

    View details for PubMedID 21331647

  • Combined Prospective and Retrospective Motion Correction to Relax Navigator Requirements MAGNETIC RESONANCE IN MEDICINE Maclaren, J., Lee, K. J., Luengviriya, C., Speck, O., Zaitsev, M. 2011; 65 (6): 1724-1732

    Abstract

    Prospective motion correction can prevent motion artifacts in magnetic resonance imaging of the brain. However, for high-resolution imaging, the technique relies on precise tracking of head motion. This precision is often limited by tracking noise, which leads to residual errors in the prospectively-corrected k-space data and artifacts in the image. This work shows that it is possible to estimate these tracking errors, and hence the true k-space sample locations, by applying a two-sided filter to the tracking data after imaging. A conjugate gradient reconstruction is compared to gridding as a means of using this information to retrospectively correct for the effects of the residual errors.

    View details for DOI 10.1002/mrm.22754

    View details for Web of Science ID 000291115500023

    View details for PubMedID 21590805

  • Combining prospective motion correction and distortion correction for EPI: towards a comprehensive correction of motion and susceptibility-induced artifacts MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Boegle, R., Maclaren, J., Zaitsev, M. 2010; 23 (4): 263-273

    Abstract

    State-of-the-art MR techniques that rely on echo planar imaging (EPI), such as real-time fMRI, are limited in their applicability by both subject motion and B(0) field inhomogeneities. The goal of this work is to demonstrate that in principle it is possible to accurately predict the B(0) field inhomogeneities that occur during echo planar imaging in the presence of large scale head motion and apply this knowledge for distortion correction.In this work, prospective motion correction is combined with a field-prediction method and a method for correcting geometric distortions in EPI. To validate the methods, echo planar images were acquired of a custom-made phantom rotated to different angles relative to the B(0) field. For each orientation, field maps were acquired for comparison with the field predictions.The calculated field maps are very similar to the measured field maps for all orientations used in the experiments. The root mean squared error (RMSE) of the difference maps was between 15 to 20 Hz. The quality of distortion correction using calculated field maps is comparable to distortion correction done with measured field maps.The results suggest that distortion-free echo planar imaging of moving objects may be feasible if prospective motion correction is combined with a field inhomogeneity estimation approach.

    View details for DOI 10.1007/s10334-010-0225-8

    View details for Web of Science ID 000281250700007

    View details for PubMedID 20694501

  • Navigator Accuracy Requirements for Prospective Motion Correction MAGNETIC RESONANCE IN MEDICINE Maclaren, J., Speck, O., Stucht, D., Schulze, P., Hennig, J., Zaitsev, M. 2010; 63 (1): 162-170

    Abstract

    Prospective motion correction in MRI is becoming increasingly popular to prevent the image artifacts that result from subject motion. Navigator information is used to update the position of the imaging volume before every spin excitation so that lines of acquired k-space data are consistent. Errors in the navigator information, however, result in residual errors in each k-space line. This paper presents an analysis linking noise in the tracking system to the power of the resulting image artifacts. An expression is formulated for the required navigator accuracy based on the properties of the imaged object and the desired resolution. Analytical results are compared with computer simulations and experimental data.

    View details for DOI 10.1002/mrm.22191

    View details for Web of Science ID 000273578600017

    View details for PubMedID 19918892

  • Determination of Myosin Filament Orientations in Electron Micrographs of Muscle Cross Sections IEEE TRANSACTIONS ON IMAGE PROCESSING Yoon, C. H., Bodvarsson, B., Klim, S., Morkebjerg, M., Mortensen, S., Chen, J., Maclaren, J. R., Luther, P. K., Squire, J. M., Bones, P. J., Millane, R. P. 2009; 18 (4): 831-839

    Abstract

    An automated image analysis system for determining myosin filament azimuthal rotations, or orientations, in electron micrographs of muscle cross sections is described. The micrographs of thin sections intersect the myosin filaments which lie on a triangular lattice. The myosin filament profiles are variable and noisy, and the images exhibit a variable contrast and background. Filament positions are determined by filtering with a point spread function that incorporates the local symmetry of the lattice. Filament orientations are determined by correlation with a template that incorporates the salient filament characteristics, and the orientations are classified using a Gaussian mixture model. The precision of the technique is assessed by application to a variety of micrographs and comparison with manual classification of the orientations. The system provides a convenient, robust, and rapid means of analysing micrographs containing many filaments to study the distribution of filament orientations.

    View details for DOI 10.1109/TIP.2008.2011379

    View details for Web of Science ID 000264397100012

    View details for PubMedID 19278921

  • A morphological image processing method for locating myosin filaments in muscle electron micrographs IMAGE AND VISION COMPUTING Bodvarsson, B., Klim, S., Morkebjerg, M., Mortensen, S., Yoon, C. H., Chen, J., Maclaren, J. R., Luther, P. K., Squire, J. M., Bones, P. J., Millane, R. P. 2008; 26 (8): 1073-1080
  • MRI with TRELLIS: a novel approach to motion correction MAGNETIC RESONANCE IMAGING Maclaren, J. R., Bones, P. J., Millane, R. P., Watts, R. 2008; 26 (4): 474-483

    Abstract

    A motion-correcting pulse sequence and reconstruction algorithm, termed TRELLIS, is presented. k-Space is filled using orthogonal overlapping strips and the directions for phase- and frequency-encoding are alternated such that the frequency-encode direction always runs lengthwise along each strip. The overlap between strips is used both for signal averaging and to produce a system of equations that, when solved, quantifies the rotational and translational motion of the object. Results obtained from simulations with computer-generated phantoms, a purpose-built moving phantom, and in human subjects show the method is effective. TRELLIS offers some advantages over existing techniques in that k-space is sampled uniformly and all acquired data are used for both motion detection and image reconstruction.

    View details for DOI 10.1016/j.mri.2007.08.013

    View details for Web of Science ID 000255299100005

    View details for PubMedID 18068932

  • Ordered k-space acquisition in contrast enhanced magnetic resonance angiography (CE-MRA) MEDICAL IMAGING 2008: PHYSICS OF MEDICAL IMAGING, PTS 1-3 Wu, B., Maclaren, J. R., Millane, R. P., Watts, R., Bones, P. J. 2008; 6913

    View details for DOI 10.1117/12.769429

    View details for Web of Science ID 000256660300139

  • Robust statistical extension to TRELLIS motion correction in MRI IMAGE RECONSTRUCTION FROM INCOMPLETE DATA V Bones, P. J., Maclaren, J. R. 2008; 7076

    View details for DOI 10.1117/12.796814

    View details for Web of Science ID 000263955500016

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