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 Magnetic Resonance Materials in Physics, Biology and Medicine   [SJR: 0.787]   [H-I: 46]   [2 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 0968-5243 - ISSN (Online) 1352-8661    Published by Springer-Verlag  [2336 journals]
• 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)

• Automated assessment of thigh composition using machine learning for Dixon
magnetic resonance images
• Authors: Yu Xin Yang; Mei Sian Chong; Laura Tay; Suzanne Yew; Audrey Yeo; Cher Heng Tan
Pages: 723 - 731
Abstract: Objectives To develop and validate a machine learning based automated segmentation method that jointly analyzes the four contrasts provided by Dixon MRI technique for improved thigh composition segmentation accuracy. Materials and methods The automatic detection of body composition is formulized as a three-class classification issue. Each image voxel in the training dataset is assigned with a correct label. A voxel classifier is trained and subsequently used to predict unseen data. Morphological operations are finally applied to generate volumetric segmented images for different structures. We applied this algorithm on datasets of (1) four contrast images, (2) water and fat images, and (3) unsuppressed images acquired from 190 subjects. Results The proposed method using four contrasts achieved most accurate and robust segmentation compared to the use of combined fat and water images and the use of unsuppressed image, average Dice coefficients of 0.94 ± 0.03, 0.96 ± 0.03, 0.80 ± 0.03, and 0.97 ± 0.01 has been achieved to bone region, subcutaneous adipose tissue (SAT), inter-muscular adipose tissue (IMAT), and muscle respectively. Conclusion Our proposed method based on machine learning produces accurate tissue quantification and showed an effective use of large information provided by the four contrast images from Dixon MRI.
PubDate: 2016-10-01
DOI: 10.1007/s10334-016-0547-2
Issue No: Vol. 29, No. 5 (2016)

• Coronary MR angiography at 3T: fat suppression versus water-fat separation
• Authors: Maryam Nezafat; Markus Henningsson; David P. Ripley; Nathalie Dedieu; Gerald Greil; John P. Greenwood; Peter Börnert; Sven Plein; René M. Botnar
Pages: 733 - 738
Abstract: Objectives To compare Dixon water-fat suppression with spectral pre-saturation with inversion recovery (SPIR) at 3T for coronary magnetic resonance angiography (MRA) and to demonstrate the feasibility of fat suppressed coronary MRA at 3T without administration of a contrast agent. Materials and methods Coronary MRA with Dixon water-fat separation or with SPIR fat suppression was compared on a 3T scanner equipped with a 32-channel cardiac receiver coil. Eight healthy volunteers were examined. Contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), right coronary artery (RCA), and left anterior descending (LAD) coronary artery sharpness and length were measured and statistically compared. Two experienced cardiologists graded the visual image quality of reformatted Dixon and SPIR images (1: poor quality to 5: excellent quality). Results Coronary MRA images in healthy volunteers showed improved contrast with the Dixon technique compared to SPIR (CNR blood-fat: Dixon = 14.9 ± 2.9 and SPIR = 13.9 ± 2.1; p = 0.08, CNR blood-myocardium: Dixon = 10.2 ± 2.7 and SPIR = 9.11 ± 2.6; p = 0.1). The Dixon method led to similar fat suppression (fat SNR with Dixon: 2.1 ± 0.5 vs. SPIR: 2.4 ± 1.2, p = 0.3), but resulted in significantly increased SNR of blood (blood SNR with Dixon: 19.9 ± 4.5 vs. SPIR: 15.5 ± 3.1, p < 0.05). This means the residual fat signal is slightly lower with the Dixon compared to the SIPR technique (although not significant), while the SNR of blood is significantly higher with the Dixon technique. Vessel sharpness of the RCA was similar for Dixon and SPIR (57 ± 7 % vs. 56 ± 9 %, p = 0.2), while the RCA visualized vessel length was increased compared to SPIR fat suppression (107 ± 21 vs. 101 ± 21 mm, p < 0.001). For the LAD, vessel sharpness (50 ± 13 % vs. 50 ± 7 %, p = 0.4) and vessel length (92 ± 46 vs. 90 ± 47 mm, p = 0.4) were similar with both techniques. Consequently, the Dixon technique resulted in an improved visual score of the coronary arteries in the water fat separated images of healthy subjects (RCA: 4.6 ± 0.5 vs. 4.1 ± 0.7, p = 0.01, LAD: 4.1 ± 0.7 vs. 3.5 ± 0.8, p = 0.007). Conclusions Dixon water-fat separation can significantly improve coronary artery image quality without the use of a contrast agent at 3T.
PubDate: 2016-10-01
DOI: 10.1007/s10334-016-0550-7
Issue No: Vol. 29, No. 5 (2016)

• Scan time minimization in hepatic diffusion-weighted imaging: evaluation
of the simultaneous multislice acceleration technique with different
acceleration factors and gradient preparation schemes
• Authors: Jana Taron; Petros Martirosian; Nina F. Schwenzer; Michael Erb; Thomas Kuestner; Jakob Weiß; Ahmed Othman; Mike Notohamiprodjo; Konstantin Nikolaou; Christina Schraml
Pages: 739 - 749
Abstract: Objective To evaluate simultaneous multislice (sms) accelerated diffusion-weighted imaging (DWI) of the liver in comparison to conventional sequences. Materials and methods Ten volunteers underwent DWI of the liver at 1.5 T. Four different sms-accelerated sequences with monopolar and bipolar gradient preparation (MP, BP) and acceleration factors 2 and 3 (sms2-DWI, sms3-DWI) were compared to conventional DWI (c-DWI). Image quality criteria rated on a 5-point Likert scale (5 = excellent), image quality sum scores (maximum 120), and ADC were compared using Friedman test and Dunn-Bonferroni post hoc test. Bland–Altman plots were calculated for ADC comparison. p values <0.05 were considered significant. Results Sms2-DWI offered scan time minimization of 67 % without significant difference in image quality (sum score: sms2-DWI MP/BP: 97 ± 8/92 ± 9; c-DWI MP/BP: 99 ± 8/97 ± 8). Sms3-DWI offered slight additional scan time minimization with significantly inferior image quality (sum score: sms3-DWI MP/BP: 75 ± 14/69 ± 14; p < 0.001). MP preparation provided slightly higher image quality in sms-DWI without statistical significance. ADC in sms-DWI were significantly lower (sms2-DWI MP 1.01 × 10−3 mm2/s; c-DWI MP 1.20 × 10−3 mm2/s; p < 0.001). Conclusion Sms2-DWI provides considerable scan time minimization without significant shortcomings in image quality. Sms3-DWI provides significantly inferior image quality without further scan time minimization. Potentially lower ADC in sms-DWI should be considered in clinical routine.
PubDate: 2016-10-01
DOI: 10.1007/s10334-016-0553-4
Issue No: Vol. 29, No. 5 (2016)

• A novel alternative to classify tissues from T 1 and T 2 relaxation times
for prostate MRI
• Authors: Jorge Zavala Bojorquez; Stéphanie Bricq; François Brunotte; Paul M. Walker; Alain Lalande
Pages: 777 - 788
Abstract: Objective To segment and classify the different attenuation regions from MRI at the pelvis level using the T 1 and T 2 relaxation times and anatomical knowledge as a first step towards the creation of PET/MR attenuation maps. Materials and methods Relaxation times were calculated by fitting the pixel-wise intensities of acquired T 1- and T 2-weighted images from eight men with inversion-recovery and multi-echo multi-slice spin-echo sequences. A decision binary tree based on relaxation times was implemented to segment and classify fat, muscle, prostate, and air (within the body). Connected component analysis and an anatomical knowledge-based procedure were implemented to localize the background and bone. Results Relaxation times at 3 T are reported for fat (T 1 = 385 ms, T 2 = 121 ms), muscle (T 1 = 1295 ms, T 2 = 40 ms), and prostate (T 1 = 1700 ms, T 2 = 80 ms). The relaxation times allowed the segmentation–classification of fat, prostate, muscle, and air, and combined with anatomical knowledge, they allowed classification of bone. The good segmentation–classification of prostate [mean Dice similarity score (mDSC) = 0.70] suggests a viable implementation in oncology and that of fat (mDSC = 0.99), muscle (mDSC = 0.99), and bone (mDSCs = 0.78) advocates for its implementation in PET/MR attenuation correction. Conclusion Our method allows the segmentation and classification of the attenuation-relevant structures required for the generation of the attenuation map of PET/MR systems in prostate imaging: air, background, bone, fat, muscle, and prostate.
PubDate: 2016-10-01
DOI: 10.1007/s10334-016-0562-3
Issue No: Vol. 29, No. 5 (2016)

• 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
ischemia
• 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

• Insight into the labeling mechanism of acceleration selective arterial
spin labeling
• Authors: Sophie Schmid; Esben T. Petersen; Matthias J. P. Van Osch
Abstract: Objectives Acceleration selective arterial spin labeling (AccASL) is a spatially non-selective labeling technique, used in traditional ASL methods, which labels spins based on their flow acceleration rather than spatial localization. The exact origin of the AccASL signal within the vasculature is not completely understood. To obtain more insight into this, the acceleration selective module was performed followed by a velocity selective module, which is used in velocity selective arterial spin labeling (VS-ASL). Materials and methods Nine healthy volunteers were scanned with various combinations of the control and label conditions in both the acceleration and velocity selective module. The cut-off acceleration (0.59 m/s2) or velocity (2 cm/s) was kept constant in one module, while it was varied over a large range in the other module. With the right subtractions this resulted in AccASL, VS-ASL, combined AccASL and VS-ASL signal, and signal from one module with crushing from the other. Results The label created with AccASL has an overlap of approximately 50% in the vascular region with VS-ASL, but also originates from smaller vessels closer to the capillaries. Conclusion AccASL is able to label spins both in the macro- and meso-vasculature, as well as in the microvasculature.
PubDate: 2016-10-27
DOI: 10.1007/s10334-016-0596-6

• Can MRI T 1 be used to detect early changes in 5xFAD Alzheimer’s
mouse brain?
• Authors: Nicholas G. Spencer; David P. Lovell; Kay Elderfield; Brian Austen; Franklyn A. Howe
Abstract: Objectives In the present study, we have tested whether MRI T1 relaxation time is a sensitive marker to detect early stages of amyloidosis and gliosis in the young 5xFAD transgenic mouse, a well-established animal model for Alzheimer’s disease. Materials and methods 5xFAD and wild-type mice were imaged in a 4.7 T Varian horizontal bore MRI system to generate T1 quantitative maps using the spin-echo multi-slice sequence. Following immunostaining for glial fibrillary acidic protein, Iba-1, and amyloid-β, T1 and area fraction of staining were quantified in the posterior parietal and primary somatosensory cortex and corpus callosum. Results In comparison with age-matched wild-type mice, we observed first signs of amyloidosis in 2.5-month-old 5xFAD mice, and development of gliosis in 5-month-old 5xFAD mice. In contrast, MRI T1 relaxation times of young, i.e., 2.5- and 5-month-old, 5xFAD mice were not significantly different to those of age-matched wild-type controls. Furthermore, although disease progression was detectable by increased amyloid-β load in the brain of 5-month-old 5xFAD mice compared with 2.5-month-old 5xFAD mice, MRI T1 relaxation time did not change. Conclusions In summary, our data suggest that MRI T1 relaxation time is neither a sensitive measure of disease onset nor progression at early stages in the 5xFAD mouse transgenic mouse model.
PubDate: 2016-10-26
DOI: 10.1007/s10334-016-0593-9

• Erratum to: Thin film based semi-active resonant marker design for low
profile interventional cardiovascular MRI devices
• Authors: Engin Baysoy; Dursun Korel Yildirim; Cagla Ozsoy; Senol Mutlu; Ozgur Kocaturk
PubDate: 2016-10-12
DOI: 10.1007/s10334-016-0592-x

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