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Journal Cover Magnetic Resonance Materials in Physics, Biology and Medicine
  [SJR: 0.787]   [H-I: 46]   [2 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0968-5243 - ISSN (Online) 1352-8661
   Published by Springer-Verlag Homepage  [2335 journals]
  • Fast T1 and T2 mapping methods: the zoomed U-FLARE sequence compared with
           EPI and snapshot-FLASH for abdominal imaging at 11.7 Tesla
    • Authors: Géraldine Pastor; María Jiménez-González; Sandra Plaza-García; Marta Beraza; Torsten Reese
      Abstract: Objective A newly adapted zoomed ultrafast low-angle RARE (U-FLARE) sequence is described for abdominal imaging applications at 11.7 Tesla and compared with the standard echo-plannar imaging (EPI) and snapshot fast low angle shot (FLASH) methods. Materials and methods Ultrafast EPI and snapshot-FLASH protocols were evaluated to determine relaxation times in phantoms and in the mouse kidney in vivo. Owing to their apparent shortcomings, imaging artefacts, signal-to-noise ratio (SNR), and variability in the determination of relaxation times, these methods are compared with the newly implemented zoomed U-FLARE sequence. Results Snapshot-FLASH has a lower SNR when compared with the zoomed U-FLARE sequence and EPI. The variability in the measurement of relaxation times is higher in the Look–Locker sequences than in inversion recovery experiments. Respectively, the average T1 and T2 values at 11.7 Tesla are as follows: kidney cortex, 1810 and 29 ms; kidney medulla, 2100 and 25 ms; subcutaneous tumour, 2365 and 28 ms. Conclusion This study demonstrates that the zoomed U-FLARE sequence yields single-shot single-slice images with good anatomical resolution and high SNR at 11.7 Tesla. Thus, it offers a viable alternative to standard protocols for mapping very fast parameters, such as T1 and T2, or dynamic processes in vivo at high field.
      PubDate: 2017-01-09
      DOI: 10.1007/s10334-016-0604-x
  • Feasibility of in vivo three-dimensional T 2 * mapping using
           dicarboxy-PROXYL and CW-EPR-based single-point imaging
    • Authors: Harue Kubota; Denis A. Komarov; Hironobu Yasui; Shingo Matsumoto; Osamu Inanami; Igor A. Kirilyuk; Valery V. Khramtsov; Hiroshi Hirata
      Abstract: Objectives The aim of this study was to demonstrate the feasibility of in vivo three-dimensional (3D) relaxation time T 2 * mapping of a dicarboxy-PROXYL radical using continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Materials and methods Isotopically substituted dicarboxy-PROXYL radicals, 3,4-dicarboxy-2,2,5,5-tetra(2H3)methylpyrrolidin-(3,4-2H2)-(1-15N)-1-oxyl (2H,15N-DCP) and 3,4-dicarboxy-2,2,5,5-tetra(2H3)methylpyrrolidin-(3,4-2H2)-1-oxyl (2H-DCP), were used in the study. A clonogenic cell survival assay was performed with the 2H-DCP radical using squamous cell carcinoma (SCC VII) cells. The time course of EPR signal intensities of intravenously injected 2H,15N-DCP and 2H-DCP radicals were determined in tumor-bearing hind legs of mice (C3H/HeJ, male, n = 5). CW-EPR-based single-point imaging (SPI) was performed for 3D T 2 * mapping. Results 2H-DCP radical did not exhibit cytotoxicity at concentrations below 10 mM. The in vivo half-life of 2H,15N-DCP in tumor tissues was 24.7 ± 2.9 min (mean ± standard deviation [SD], n = 5). The in vivo time course of the EPR signal intensity of the 2H,15N-DCP radical showed a plateau of 10.2 ± 1.2 min (mean ± SD) where the EPR signal intensity remained at more than 90% of the maximum intensity. During the plateau, in vivo 3D T 2 * maps with 2H,15N-DCP were obtained from tumor-bearing hind legs, with a total acquisition time of 7.5 min. Conclusion EPR signals of 2H,15N-DCP persisted long enough after bolus intravenous injection to conduct in vivo 3D T 2 * mapping with CW-EPR-based SPI.
      PubDate: 2017-01-06
      DOI: 10.1007/s10334-016-0606-8
  • A low-cost Mr compatible ergometer to assess post-exercise phosphocreatine
           recovery kinetics
    • Authors: Niels D. Naimon; Jerzy Walczyk; James S. Babb; Oleksandr Khegai; Xuejiao Che; Leeor Alon; Ravinder R. Regatte; Ryan Brown; Prodromos Parasoglou
      Abstract: Objective To develop a low-cost pedal ergometer compatible with ultrahigh (7 T) field MR systems to reliably quantify metabolic parameters in human lower leg muscle using phosphorus magnetic resonance spectroscopy. Materials and methods We constructed an MR compatible ergometer using commercially available materials and elastic bands that provide resistance to movement. We recruited ten healthy subjects (eight men and two women, mean age ± standard deviation: 32.8 ± 6.0 years, BMI: 24.1 ± 3.9 kg/m2). All subjects were scanned on a 7 T whole-body magnet. Each subject was scanned on two visits and performed a 90 s plantar flexion exercise at 40% maximum voluntary contraction during each scan. During the first visit, each subject performed the exercise twice in order for us to estimate the intra-exam repeatability, and once during the second visit in order to estimate the inter-exam repeatability of the time constant of phosphocreatine recovery kinetics. We assessed the intra and inter-exam reliability in terms of the within-subject coefficient of variation (CV). Results We acquired reliable measurements of PCr recovery kinetics with an intra- and inter-exam CV of 7.9% and 5.7%, respectively. Conclusion We constructed a low-cost pedal ergometer compatible with ultrahigh (7 T) field MR systems, which allowed us to quantify reliably PCr recovery kinetics in lower leg muscle using 31P-MRS.
      PubDate: 2017-01-04
      DOI: 10.1007/s10334-016-0605-9
  • MRI-based assessment of liver perfusion and hepatocyte injury in the
           murine model of acute hepatitis
    • Authors: Katarzyna Byk; Krzysztof Jasinski; Zaneta Bartel; Agnieszka Jasztal; Barbara Sitek; Boguslaw Tomanek; Stefan Chlopicki; Tomasz Skorka
      Pages: 789 - 798
      Abstract: Objective To assess alterations in perfusion and liver function in the concanavalin A (ConA)-induced mouse model of acute liver failure (ALF) using two magnetic resonance imaging (MRI)-based methods: dynamic contrast-enhanced MRI (DCE-MRI) with Gd-EOB-DTPA contrast agent and arterial spin labelling (ASL). Materials and methods BALB/c mice were studied using a 9.4 T MRI system. The IntraGateFLASHTM and FAIR-EPI pulse sequences were used for optimum mouse abdomen imaging. Results The average perfusion values for the liver of the control and ConA group were equal to 245 ± 20 and 200 ± 32 ml/min/100 g (p = 0.008, respectively). DCE-MRI showed that the time to the peak of the image enhancement was 6.14 ± 1.07 min and 9.72 ± 1.69 min in the control and ConA group (p < 0.001, respectively), while the rate of the contrast wash-out in the control and ConA group was 0.037 ± 0.008 and 0.021 ± 0.008 min−1 (p = 0.004, respectively). These results were consistent with hepatocyte injury in the ConA-treated mice as confirmed by histopathological staining. Conclusions Both the ASL and DCE-MRI techniques represent a reliable methodology to assess alterations in liver perfusion and hepatocyte integrity in murine hepatitis.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0563-2
      Issue No: Vol. 29, No. 6 (2016)
  • Three-dimensional echo-planar cine imaging of cerebral blood supply using
           arterial spin labeling
    • Authors: Manoj Shrestha; Toralf Mildner; Torsten Schlumm; Scott Haile Robertson; Harald Möller
      Pages: 799 - 810
      Abstract: Objective Echo-planar imaging (EPI) with CYlindrical Center-out spatiaL Encoding (EPICYCLE) is introduced as a novel hybrid three-dimensional (3D) EPI technique. Its suitability for the tracking of a short bolus created by pseudo-continuous arterial spin labeling (pCASL) through the cerebral vasculature is demonstrated. Materials and methods EPICYCLE acquires two-dimensional planes of k-space along center-out trajectories. These “spokes” are rotated from shot to shot about a common axis to encode a k-space cylinder. To track a bolus of labeled blood, the same subset of evenly distributed spokes is acquired in a cine fashion after a short period of pCASL. This process is repeated for all subsets to fill the whole 3D k-space of each time frame. Results The passage of short pCASL boluses through the vasculature of a 3D imaging slab was successfully imaged using EPICYCLE. By choosing suitable sequence parameters, the impact of slab excitation on the bolus shape could be minimized. Parametric maps of signal amplitude, transit time, and bolus width reflected typical features of blood transport in large vessels. Conclusion The EPICYCLE technique was successfully applied to track a short bolus of labeled arterial blood during its passage through the cerebral vasculature.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0565-0
      Issue No: Vol. 29, No. 6 (2016)
  • Denoising of MR spectroscopic imaging data using statistical selection of
           principal components
    • Authors: Abas Abdoli; Radka Stoyanova; Andrew A. Maudsley
      Pages: 811 - 822
      Abstract: Objectives To evaluate a new denoising method for MR spectroscopic imaging (MRSI) data based on selection of signal-related principal components (SSPCs) from principal components analysis (PCA). Materials and methods A PCA-based method was implemented for selection of signal-related PCs and denoising achieved by reconstructing the original data set utilizing only these PCs. Performance was evaluated using simulated MRSI data and two volumetric in vivo MRSIs of human brain, from a normal subject and a patient with a brain tumor, using variable signal-to-noise ratios (SNRs), metabolite peak areas, Cramer-Rao bounds (CRBs) of fitted metabolite peak areas and metabolite linewidth. Results In simulated data, SSPC determined the correct number of signal-related PCs. For in vivo studies, the SSPC denoising resulted in improved SNRs and reduced metabolite quantification uncertainty compared to the original data and two other methods for denoising. The method also performed very well in preserving the spectral linewidth and peak areas. However, this method performs better for regions that have larger numbers of similar spectra. Conclusion The proposed SSPC denoising improved the SNR and metabolite quantification uncertainty in MRSI, with minimal compromise of the spectral information, and can result in increased accuracy.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0566-z
      Issue No: Vol. 29, No. 6 (2016)
  • Dynamic susceptibility contrast perfusion MRI using phase-based venous
           output functions: comparison with pseudo-continuous arterial spin
           labelling and assessment of contrast agent concentration in large veins
    • Authors: Ronnie Wirestam; Emelie Lind; André Ahlgren; Freddy Ståhlberg; Linda Knutsson
      Pages: 823 - 831
      Abstract: Objectives Contrast agent (CA) relaxivities are generally not well established in vivo, and the relationship between frequency/phase shift and magnetic susceptibility might be a useful alternative for CA quantification. Materials and methods Twenty volunteers (25–84 years old) were investigated using test–retest pre-bolus dynamic susceptibility-contrast (DSC) magnetic resonance imaging (MRI). The pre-bolus phase-based venous output function (VOF) time integral was used for arterial input function (AIF) rescaling. Resulting cerebral blood flow (CBF) data for grey matter (GM) were compared with pseudo-continuous arterial spin labelling (ASL). During the main bolus CA passage, the apparent spatial shift (pixel shift) of the superior sagittal sinus (seen in single-shot echo-planar imaging (EPI)) was converted to CA concentration and compared with conventional ΔR2*-based data and with a predicted phase-based VOF from the pre-bolus experiment. Results The phase-based pre-bolus VOF resulted in a reasonable inter-individual GM CBF variability (coefficient of variation 28 %). Comparison with ASL CBF values implied a tissue R2*-relaxivity of 32 mM−1 s−1. Pixel-shift data at low concentrations (data not available at peak concentrations) were in reasonable agreement with the predicted phase-based VOF. Conclusion Susceptibility-induced phase shifts and pixel shifts are potentially useful for large-vein CA quantification. Previous predictions of a higher R2*-relaxivity in tissue than in blood were supported.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0567-y
      Issue No: Vol. 29, No. 6 (2016)
  • Quantitative T 1 and T 2 MRI signal characteristics in the human brain:
           different patterns of MR contrasts in normal ageing
    • Authors: Michael J. Knight; Bryony McCann; Demitra Tsivos; Elizabeth Couthard; Risto A. Kauppinen
      Pages: 833 - 842
      Abstract: Objective The objective of this study was to examine age-dependent changes in both T1-weighted and T2-weighted image contrasts and spin-echo T2 relaxation time in the human brain during healthy ageing. Methods A total of 37 participants between the ages of 49 and 87 years old were scanned with a 3 Tesla system, using T1-weighted, T2 weighted and quantitative spin-echo T2 imaging. Contrast between image intensities and T2 values was calculated for various regions, including between individual hippocampal subfields. Results The T1 contrast-to-noise (CNR) and gray:white signal intensity ratio (GWR) did not change in the hippocampus, but it declined in the cingulate cortex with age. In contrast, T2 CNR and GWR declined in both brain regions. T2 relaxation time was almost constant in gray matter and most (but not all) hippocampal subfields, but increased substantially in white matter, pointing to an age effect on water relaxation in white matter. Conclusions Changes in T1 and T2 MR characteristics influence the appearance of brain images in later life and should be considered in image analyses of aged subjects. It is speculated that alterations at the cell biology level, with concomitant alterations to the local magnetic environment, reduce dephasing and subsequently prolong spin-echo T2 through reduced diffusion effects in later life.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0573-0
      Issue No: Vol. 29, No. 6 (2016)
  • Accelerated visualization of selected intracranial arteries by cycled
           super-selective arterial spin labeling
    • Authors: Thomas Lindner; Naomi Larsen; Olav Jansen; Michael Helle
      Pages: 843 - 852
      Abstract: Objective To accelerate super-selective arterial spin labeling (ASL) angiography by using a single control condition denoted as cycled super-selective arterial spin labeling. Materials and methods A single non-selective control image is acquired that is shared by selective label images. Artery-selective imaging is possible by geometrically changing the position of the labeling focus to more than one artery of interest during measurement. The presented approach is compared to conventional super-selective imaging in terms of its labeling efficiency inside and outside the labeling focus using numerical simulations and in vivo measurements. Additionally, the signal-to-noise ratios of the images are compared to non-selective ASL angiography and analyzed using a two-way ANOVA test and calculating the Pearson’s correlation coefficients. Results The results indicate that the labeling efficiency is not reduced within the labeled artery, but can increase as a function of distance to the artery of interest when compared to conventional super-selective ASL. In the final images, no statistically significant difference of image quality can be observed while the acquisition duration could be reduced when the major brain feeding arteries are being tagged. Conclusion Using super-selective arterial spin labeling, a single non-selective control acquisition suffices for reconstructing selective angiograms of the cerebral vasculature, thereby accelerating image acquisition of the major intracranial arteries without notable loss of information.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0574-z
      Issue No: Vol. 29, No. 6 (2016)
  • Magnetization transfer imaging of cortical bone in vivo using a zero echo
           time sequence in mice at 4.7 T: a feasibility study
    • Authors: Magda Marcon; Markus Weiger; Daniel Keller; Moritz C. Wurnig; Christian Eberhardt; Daniel Eberli; Andreas Boss
      Pages: 853 - 862
      Abstract: Objective To investigate the feasibility of magnetization transfer (MT) imaging in mice in vivo for the assessment of cortical bone. Materials and methods MT-zero echo time data were acquired at 4.7 T in six mice using MT preparation pulses with two different flip angles (FAs) and a series of ten different off-resonance frequencies (500–15000 Hz). Regions of interest were drawn at multiple levels of the femoral cortical bone. The MT ratio (MTR) was computed for each combination of FAs and off-resonance frequencies. T1 measurements were used to estimate the direct saturation (DS) using a Bloch equation simulation. Estimation of the absorption line width of cortical bone from T2* measurements was also performed. Results MTR values were higher using 3000° FA than 1000° FA. MTR values decreased toward higher off-resonance frequencies. Maximum mean MTR ± standard deviation (SD) of 58.57 ± 5.22 (range 50.44–70.61) was measured with a preparation pulse of 3000° and off-resonance frequency of 500 Hz. Maximum “true” MT effect was estimated at around 2–3 and 5 kHz, respectively, for 1000° and 3000° FA. Mean full width at half maximum ± SD of 577 ± 91 Hz was calculated for the absorption spectral line of the cortical bone. Conclusion MT imaging can be used for the assessment of cortical bone in mice in vivo. DS effects are negligible using preparation pulses with off-resonance frequencies greater than 3 kHz.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0577-9
      Issue No: Vol. 29, No. 6 (2016)
  • Reproducibility of macromolecule suppressed GABA measurement using motion
           and shim navigated MEGA-SPECIAL with LCModel, jMRUI and GANNET
    • Authors: Muhammad G. Saleh; Jamie Near; Alqadafi Alhamud; Frances Robertson; André J. W. van der Kouwe; Ernesta M. Meintjes
      Pages: 863 - 874
      Abstract: Objective Measuring the pure form of GABA has become increasingly important because of its association with behaviour and certain pathologies. The aim of this study was to assess the reproducibility of GABA measurements using a shim and motion navigated MEGA-SPECIAL sequence with LCModel, jMRUI and GANNET software. Materials and methods Motion and shim navigated MEGA-SPECIAL scans were acquired in 20 healthy subjects. Two acquisitions were performed for each of two regions: the anterior cingulate (ACC) and medial-parietal (PAR) cortices. Absolute GABA concentration ( \({\text{GABA}}_{{{\text{H}}_{2} {\text{O}}}}\) ) and GABA-to-Creatine ratio (GABA/Cr) were quantified using the three software packages. Results Using the within-subject coefficient of variation (CVws) as an index, reproducibility for both GABAH20 and GABA/Cr ranged from 13 to 22 % in the ACC and 13 to 18 % in PAR using the three software packages. Conclusion Based on CVws, GABA concentrations in both the ACC and PAR are reproducible using a shim and motion navigated MEGA-SPECIAL sequence with any of the three software packages, thus demonstrating the ability to quantify the pure form of GABA using these software in studies relating GABA to pathology and healthy behaviour.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0578-8
      Issue No: Vol. 29, No. 6 (2016)
  • Assessment of the myelin water fraction in rodent spinal cord using
           T2-prepared ultrashort echo time MRI
    • Authors: Tim Klasen; Cornelius Faber
      Pages: 875 - 884
      Abstract: Objective Multi-component T2 relaxation allows for assessing the myelin water fraction in nervous tissue, providing a surrogate marker for demyelination. The assessment of the number and distribution of different T2 components for devising exact models of tissue relaxation has been limited by T2 sampling with conventional MR methods. Materials and methods A T2-prepared UTE sequence was used to assess multicomponent T2 relaxation at 9.4 T of fixed mouse and rat spinal cord samples and of mouse spinal cord in vivo. For in vivo scans, a cryogenically cooled probe allowed for 78-µm resolution in 1-mm slices. Voxel-wise non-negative least square analysis was used to assess the number of myelin water-associated T2 components. Results More than one myelin water-associated T2 component was detected in only 12 % of analyzed voxels in rat spinal cords and 6 % in mouse spinal cords, both in vivo and in vitro. However, myelin water-associated T2 values of individual voxels varied between 0.1 and 20 ms. While in fixed samples almost no components below 1 ms were identified, in vivo, these contributed 14 % of the T2 spectrum. No significant differences in MWF were observed in mouse spinal cord in vivo versus ex vivo measurements. Conclusion Voxel-wise analysis methods using relaxation models with one myelin water-associated T2 component are appropriate for assessing myelin content of nervous tissue.
      PubDate: 2016-12-01
      DOI: 10.1007/s10334-016-0579-7
      Issue No: Vol. 29, No. 6 (2016)
  • The effect of diffusion gradient direction number on corticospinal
           tractography in the human brain: an along-tract analysis
    • Authors: Claudia Testa; Stefania Evangelisti; Mariagrazia Popeo; Stefano Zanigni; Laura Ludovica Gramegna; Paola Fantazzini; Caterina Tonon; David Neil Manners; Raffaele Lodi
      Abstract: Objectives We evaluated diffusion imaging measures of the corticospinal tract obtained with a probabilistic tractography algorithm applied to data of two acquisition protocols based on different numbers of diffusion gradient directions (NDGDs). Materials and methods The corticospinal tracts (CST) of 18 healthy subjects were delineated using 22 and 66-NDGD data. An along-tract analysis of diffusion metrics was performed to detect possible local differences due to NDGD. Results FA values at 22-NDGD showed an increase along the central portion of the CST. The mean of partial volume fraction of the orientation of the second fiber (f2) was higher at 66-NDGD bilaterally, because for 66-NDGD data the algorithm more readily detects dominant fiber directions beyond the first, thus the increase in FA at 22-NDGD is due to a substantially reduced detection of crossing fiber volume. However, the good spatial correlation between the tracts drawn at 22 and 66 NDGD shows that the extent of the tract can be successfully defined even at lower NDGD. Conclusions Given the spatial tract localization obtained even at 22-NDGD, local analysis of CST can be performed using a NDGD compatible with clinical protocols. The probabilistic approach was particularly powerful in evaluating crossing fibers when present.
      PubDate: 2016-12-20
      DOI: 10.1007/s10334-016-0600-1
  • Semi-automated myocardial segmentation of bright blood multi-gradient
           echo images improves reproducibility of myocardial contours and T2*
    • Authors: Pandji Triadyaksa; Niek H. J. Prakken; Jelle Overbosch; Robin B. Peters; J. Martijn van Swieten; Matthijs Oudkerk; Paul E. Sijens
      Abstract: Objectives Early detection of iron loading is affected by the reproducibility of myocardial contour assessment. A novel semi-automatic myocardial segmentation method is presented on contrast-optimized composite images and compared to the results of manual drawing. Materials and methods Fifty-one short-axis slices at basal, mid-ventricular and apical locations from 17 patients were acquired by bright blood multi-gradient echo MRI. Four observers produced semi-automatic and manual myocardial contours on contrast-optimized composite images. The semi-automatic segmentation method relies on vector field convolution active contours to generate the endocardial contour. After creating radial pixel clusters on the myocardial wall, a combination of pixel-wise coefficient of variance (CoV) assessment and k-means clustering establishes the epicardial contour for each segment. Results Compared to manual drawing, semi-automatic myocardial segmentation lowers the variability of T2* quantification within and between observers (CoV of 12.05 vs. 13.86% and 14.43 vs. 16.01%) by improving contour reproducibility (P < 0.001). In the presence of iron loading, semi-automatic segmentation also lowers the T2* variability within and between observers (CoV of 13.14 vs. 15.19% and 15.91 vs. 17.28%). Conclusion Application of semi-automatic myocardial segmentation on contrast-optimized composite images improves the reproducibility of T2* quantification.
      PubDate: 2016-12-16
      DOI: 10.1007/s10334-016-0601-0
  • Evaluation of exposure to (ultra) high static magnetic fields during
           activities around human MRI scanners
    • Authors: Mahsa Fatahi; Jolanta Karpowicz; Krzysztof Gryz; Amirmohammad Fattahi; Georg Rose; Oliver Speck
      Abstract: Objective To assess the individual exposure to the static magnetic field (SMF) and the motion-induced time-varying magnetic field (TVMF) generated by activities in an inhomogeneous SMF near high and ultra-high field magnetic resonance imaging (MRI) scanners. The study provides information on the level of exposure to high and ultra-high field MRI scanners during research activities. Materials and methods A three-axis Hall magnetometer was used to determine the SMF and TVMF around human 3- and 7-Tesla (T) MRI systems. The 7-T MRI scanner used in this study was passively shielded and the 3-T scanner was actively shielded and both were from the same manufacturer. The results were compared with the exposure restrictions given by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Results The recorded exposure was highly variable between individuals, although they followed the same instructions for moving near the scanners. Maximum exposure values of B = 2057 mT and dB/dt = 4347 mT/s for the 3-T scanner and B = 2890 mT, dB/dt = 3900 mT/s for 7 T were recorded. No correlation was found between reporting the MRI-related sensory effects and exceeding the reference values. Conclusions According to the results of our single-center study with five subjects, violation of the ICNIRP restrictions for max B in MRI research environments was quite unlikely at 3 and 7 T. Occasions of exceeding the dB/dt limit at 3 and 7 T were almost similar (30% of 60 exposure scenarios) and highly variable among the individuals.
      PubDate: 2016-12-16
      DOI: 10.1007/s10334-016-0602-z
  • Reproducible segmentation of white matter hyperintensities using a new
           statistical definition
    • Authors: Soheil Damangir; Eric Westman; Andrew Simmons; Hugo Vrenken; Lars-Olof Wahlund; Gabriela Spulber
      Abstract: Objectives We present a method based on a proposed statistical definition of white matter hyperintensities (WMH), which can work with any combination of conventional magnetic resonance (MR) sequences without depending on manually delineated samples. Materials and methods T1-weighted, T2-weighted, FLAIR, and PD sequences acquired at 1.5 Tesla from 119 subjects from the Kings Health Partners-Dementia Case Register (healthy controls, mild cognitive impairment, Alzheimer’s disease) were used. The segmentation was performed using a proposed definition for WMH based on the one-tailed Kolmogorov–Smirnov test. Results The presented method was verified, given all possible combinations of input sequences, against manual segmentations and a high similarity (Dice 0.85–0.91) was observed. Comparing segmentations with different input sequences to one another also yielded a high similarity (Dice 0.83–0.94) that exceeded intra-rater similarity (Dice 0.75–0.91). We compared the results with those of other available methods and showed that the segmentation based on the proposed definition has better accuracy and reproducibility in the test dataset used. Conclusion Overall, the presented definition is shown to produce accurate results with higher reproducibility than manual delineation. This approach can be an alternative to other manual or automatic methods not only because of its accuracy, but also due to its good reproducibility.
      PubDate: 2016-12-09
      DOI: 10.1007/s10334-016-0599-3
  • Respiratory optimized data selection for more resilient self-navigated
           whole-heart coronary MR angiography
    • Authors: Jerome Chaptinel; Davide Piccini; Gabriele Bonanno; Simone Coppo; Pierre Monney; Matthias Stuber; Juerg Schwitter
      Abstract: Objectives Our objective was to test a data-exclusion strategy for respiratory motion suppression by retrospectively eliminating data acquired at extreme respiratory positions for improved coronary vessel sharpness (VS) of 1-D self-navigated 3-D radial whole-heart coronary angiography acquisitions. Materials and methods 3-D radial self-navigated acquisitions were performed on a 1.5T scanner in volunteers during free-breathing (n = 8), in coached volunteers (n = 13) who were asked to breathe in a controlled manner to mimic cardiovascular patients presenting with Cheyne-Stokes breathing, and in free-breathing patients (n = 20). Data collected during large respiratory excursions were gradually excluded retrospectively from the reconstruction yielding 14 data sets per subject on average. The impact on VS, blood and myocardium signal-to-noise and contrast-to-noise was measured. From these results, two retrospective gating strategies were defined for the k-line elimination procedure and tested in all groups. Results Maximum right coronary artery VS improvement was +7.4 and +2.7% in coached volunteers and patients (P < 0.0001 for both), respectively, and 1.6% for the free-breathing volunteers (P = 0.13). The first gating strategy was defined as a fixed undersampling factor of 5 compared to a fully sampled 3-D radial acquisition, yielding significant VS improvement in coached volunteers and patients while myocardial signal-to-noise decreased in these. The second strategy was defined as a fixed gating window of 5.7 mm, leading to similar improvements. Conclusion The presented strategies improve image quality of self-navigated acquisitions by retrospectively excluding data collected during end-inspiration.
      PubDate: 2016-11-14
      DOI: 10.1007/s10334-016-0598-4
  • Accelerating multi-echo water-fat MRI with a joint locally low-rank and
           spatial sparsity-promoting reconstruction
    • Authors: Felix Lugauer; Dominik Nickel; Jens Wetzl; Berthold Kiefer; Joachim Hornegger; Andreas Maier
      Abstract: Objectives Our aim was to demonstrate the benefits of using locally low-rank (LLR) regularization for the compressed sensing reconstruction of highly-accelerated quantitative water-fat MRI, and to validate fat fraction (FF) and \({R_2^*}\) relaxation against reference parallel imaging in the abdomen. Materials and methods Reconstructions using spatial sparsity regularization (SSR) were compared to reconstructions with LLR and the combination of both (LLR+SSR) for up to seven fold accelerated 3-D bipolar multi-echo GRE imaging. For ten volunteers, the agreement with the reference was assessed in FF and \({R_2^*}\) maps. Results LLR regularization showed superior noise and artifact suppression compared to reconstructions using SSR. Remaining residual artifacts were further reduced in combination with SSR. Correlation with the reference was excellent for FF with \(R^2\) = 0.99 (all methods) and good for \({R_2^*}\) with \(R^2\) = [0.93, 0.96, 0.95] for SSR, LLR and LLR+SSR. The linear regression gave slope and bias (%) of (0.99, 0.50), (1.01, 0.19) and (1.01, 0.10), and the hepatic FF/ \({R_2^*}\) standard deviation was 3.5%/12.1 s \(^{-1}\) , 1.9%/6.4 s \(^{-1}\) and 1.8%/6.3 s \(^{-1}\) for SSR, LLR and LLR+SSR, indicating the least bias and highest SNR for LLR+SSR. Conclusion A novel reconstruction using both spatial and spectral regularization allows obtaining accurate FF and \({R_2^*}\) maps for prospectively highly accelerated acquisitions.
      PubDate: 2016-11-07
      DOI: 10.1007/s10334-016-0595-7
  • K -space data processing for magnetic resonance elastography (MRE)
    • Authors: Nadège Corbin; Elodie Breton; Michel de Mathelin; Jonathan Vappou
      Abstract: Objective Magnetic resonance elastography (MRE) requires substantial data processing based on phase image reconstruction, wave enhancement, and inverse problem solving. The objective of this study is to propose a new, fast MRE method based on MR raw data processing, particularly adapted to applications requiring fast MRE measurement or high elastogram update rate. Materials and methods The proposed method allows measuring tissue elasticity directly from raw data without prior phase image reconstruction and without phase unwrapping. Experimental feasibility is assessed both in a gelatin phantom and in the liver of a porcine model in vivo. Elastograms are reconstructed with the raw MRE method and compared to those obtained using conventional MRE. In a third experiment, changes in elasticity are monitored in real-time in a gelatin phantom during its solidification by using both conventional MRE and raw MRE. Results The raw MRE method shows promising results by providing similar elasticity values to the ones obtained with conventional MRE methods while decreasing the number of processing steps and circumventing the delicate step of phase unwrapping. Limitations of the proposed method are the influence of the magnitude on the elastogram and the requirement for a minimum number of phase offsets. Conclusion This study demonstrates the feasibility of directly reconstructing elastograms from raw data.
      PubDate: 2016-11-07
      DOI: 10.1007/s10334-016-0594-8
  • Magnetic resonance imaging detection of multiple ischemic injury produced
           in an adult rat model of minor stroke followed by mild transient cerebral
    • Authors: Ursula I. Tuor; Min Qiao
      Abstract: Objectives To determine whether cumulative brain damage produced adjacent to a minor stroke that is followed by a mild transient ischemia is detectable with MRI and histology, and whether acute or chronic recovery between insults influences this damage. Materials and methods A minor photothrombotic (PT) stroke was followed acutely (1–2 days) or chronically (7 days) by a mild transient middle cerebral artery occlusion (tMCAO). MRI was performed after each insult, followed by final histology. Results The initial PT produced small hyperintense T2 and DW infarct lesions and peri-lesion regions of scattered necrosis and modestly increased T2. Following tMCAO, in a slice and a region adjacent to the PT, a region of T2 augmentation was observed when recovery between insults was acute but not chronic. Within the PT slice, a modest region of exacerbated T2 change proximate to the PT was also observed in the chronic group. Corresponding histological changes within regions of augmented T2 included increased vacuolation and cell death. Conclusion Within regions adjacent to an experimental minor stroke, a recurrence of a mild transient cerebral ischemia augmented T2 above increases produced by tMCAO alone, reflecting increased damage in this region. Exacerbation appeared broader with acute versus chronic recovery between insults.
      PubDate: 2016-11-04
      DOI: 10.1007/s10334-016-0597-5
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