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Journal Cover Magnetic Resonance Materials in Physics, Biology and Medicine
  [SJR: 0.928]   [H-I: 40]   [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  [2334 journals]
  • Endoluminal high-resolution MR imaging protocol for colon walls analysis
           in a mouse model of colitis
    • Authors: Hugo Dorez; Raphaël Sablong; Laurence Canaple; Hervé Saint-Jalmes; Sophie Gaillard; Driffa Moussata; Olivier Beuf
      Pages: 657 - 669
      Abstract: Objective An endoluminal magnetic resonance (MR) imaging protocol including the design of an endoluminal coil (EC) was defined for high-spatial-resolution MR imaging of mice gastrointestinal walls at 4.7 T. Materials and methods A receive-only radiofrequency single-loop coil was developed for mice colon wall imaging. Combined with a specific protocol, the prototype was first characterized in vitro on phantoms and on vegetables. Signal-to-noise ratio (SNR) profiles were compared with a quadrature volume birdcage coil (QVBC). Endoluminal MR imaging protocol combined with the EC was assessed in vivo on mice. Results The SNR measured close to the coil is significantly higher (10 times and up to 3 mm of the EC center) than the SNR measured with the QVBC. The gain in SNR can be used to reduce the in-plane pixel size up to 39 × 39 µm2 (234 µm slice thickness) without time penalty. The different colon wall layers can only be distinguished on images acquired with the EC. Conclusion Dedicated EC provides suitable images for the assessment of mice colon wall layers. This proof of concept provides gains in spatial resolution and leads to adequate protocols for the assessment of human colorectal cancer, and can now be used as a new imaging tool for a better understanding of the pathology.
      PubDate: 2016-08-01
      DOI: 10.1007/s10334-016-0539-2
      Issue No: Vol. 29, No. 4 (2016)
       
  • Amide proton transfer (APT) magnetic resonance imaging of prostate cancer:
           comparison with Gleason scores
    • Authors: Yukihisa Takayama; Akihiro Nishie; Masaaki Sugimoto; Osamu Togao; Yoshiki Asayama; Kousei Ishigami; Yasuhiro Ushijima; Daisuke Okamoto; Nobuhiro Fujita; Akira Yokomizo; Jochen Keupp; Hiroshi Honda
      Pages: 671 - 679
      Abstract: Objective To evaluate the utility of amide proton transfer (APT) imaging in estimating the Gleason score (GS) of prostate cancer (Pca). Materials and methods Sixty-six biopsy-proven cancers were categorized into four groups according to the GS: GS-6 (3 + 3); GS-7 (3 + 4/4 + 3); GS-8 (4 + 4) and GS-9 (4 + 5/5 + 4). APT signal intensities (APT SIs) and apparent diffusion coefficient (ADC) values of each GS group were compared by one-way analysis of variance with Tukey’s HSD post hoc test. Results The mean and standard deviation of the APT SIs (%) and ADC values (×10−3 mm2/s) were as follows: GS-6, 2.48 ± 0.59 and 1.16 ± 0.26; GS-7, 5.17 ± 0.66 and 0.92 ± 0.18; GS-8, 2.56 ± 0.85 and 0.86 ± 0.17; GS-9, 1.96 ± 0.75 and 0.85 ± 0.18, respectively. The APT SI of the GS-7 group was highest, and there were significant differences between the GS-6 and GS-7 groups and the GS-7 and GS-9 groups (p < 0.05). The ADC value of the GS-6 group was significantly higher than each value of the GS-7, GS-8, and GS-9 groups (p < 0.05), but no significant differences were obtained among the GS-7, GS-8, and GS-9 groups. Conclusion The mean APT SI in Pca with a GS of 7 was higher than that for the other GS groups.
      PubDate: 2016-08-01
      DOI: 10.1007/s10334-016-0537-4
      Issue No: Vol. 29, No. 4 (2016)
       
  • Topographical variations in zonal properties of canine tibial articular
           cartilage due to early osteoarthritis: a study using 7-T magnetic
           resonance imaging at microscopic resolution
    • Authors: Ji Hyun Lee; Farid Badar; John Matyas; Xianggui Qu; Yang Xia
      Pages: 681 - 690
      Abstract: Objective Our aim was to determine topographical variations in zonal properties of articular cartilage over the medial tibia in an experimental osteoarthritis (OA) model using 7-T magnetic resonance imaging (MRI). Materials and methods An anterior cruciate ligament (ACL)-transection canine model was subjected to study at 8 (six) and 12 (seven) weeks after the surgery. Each medial tibia was divided into five topographical locations. For each specimen, T2 relaxation (at 0° and 55°) was quantified at microscopic resolution. The imaging data grouped the five locations into two topographical areas (meniscus-covered and -uncovered). Results The T2 (55°) bulk values from the meniscus-covered area were significantly lower than those from the uncovered area. The total cartilage thicknesses on the meniscus-covered area were significantly thinner than those on the meniscus-uncovered area. Significant differences in the T2 (0°) values were observed in most thicknesses of the four subtissue zones and whole-tissue from the uncovered area, while the same significant changes were detected in the superficial zone from the meniscus-covered area. Conclusion By quantifying high-resolution imaging data both topographically and depth-dependently (zonal-wise), this study demonstrates that the rate of disease progression varies topographically over the medial tibia. Future correlation with OA pathology could lead to better detection of early OA.
      PubDate: 2016-08-01
      DOI: 10.1007/s10334-016-0528-5
      Issue No: Vol. 29, No. 4 (2016)
       
  • Design of a mobile, homogeneous, and efficient electromagnet with a large
           field of view for neonatal low-field MRI
    • Authors: Steffen Lother; Steven J. Schiff; Thomas Neuberger; Peter M. Jakob; Florian Fidler
      Pages: 691 - 698
      Abstract: Objective In this work, a prototype of an effective electromagnet with a field-of-view (FoV) of 140 mm for neonatal head imaging is presented. The efficient implementation succeeded by exploiting the use of steel plates as a housing system. We achieved a compromise between large sample volumes, high homogeneity, high B0 field, low power consumption, light weight, simple fabrication, and conserved mobility without the necessity of a dedicated water cooling system. Materials and methods The entire magnetic resonance imaging (MRI) system (electromagnet, gradient system, transmit/receive coil, control system) is introduced and its unique features discussed. Furthermore, simulations using a numerical optimization algorithm for magnet and gradient system are presented. Results Functionality and quality of this low-field scanner operating at 23 mT (generated with 500 W) is illustrated using spin-echo imaging (in-plane resolution 1.6 mm × 1.6 mm, slice thickness 5 mm, and signal-to-noise ratio (SNR) of 23 with a acquisition time of 29 min). B0 field-mapping measurements are presented to characterize the homogeneity of the magnet, and the B0 field limitations of 80 mT of the system are fully discussed. Conclusion The cryogen-free system presented here demonstrates that this electromagnet with a ferromagnetic housing can be optimized for MRI with an enhanced and homogeneous magnetic field. It offers an alternative to prepolarized MRI designs in both readout field strength and power use. There are multiple indications for the clinical medical application of such low-field devices.
      PubDate: 2016-08-01
      DOI: 10.1007/s10334-016-0525-8
      Issue No: Vol. 29, No. 4 (2016)
       
  • Minimizing the effects of magnetization transfer asymmetry on
           inhomogeneous magnetization transfer (ihMT) at ultra-high magnetic field
           (11.75 T)
    • Authors: Valentin H. Prevost; Olivier M. Girard; Gopal Varma; David C. Alsop; Guillaume Duhamel
      Pages: 699 - 709
      Abstract: Objectives The recently reported inhomogeneous magnetization transfer technique (ihMT) has been proposed for specific imaging of inhomogeneously broadened lines, and has shown great promise for characterizing myelinated tissues. The ihMT contrast is obtained by subtracting magnetization transfer images obtained with simultaneous saturation at positive and negative frequency offsets (dual frequency saturation experiment, MT +/−) from those obtained with single frequency saturation (MT +) at the same total power. Hence, ihMT may be biased by MT-asymmetry, especially at ultra-high magnetic field. Use of the average of single positive and negative frequency offset saturation MT images, i.e., (MT ++MT −) has been proposed to correct the ihMT signal from MT-asymmetry signal. Materials and methods The efficiency of this correction method was experimentally assessed in this study, performed at 11.75 T on mice. Quantitative corrected ihMT and MT-asymmetry ratios (ihMTR and MTRasym) were measured in mouse brain structures for several MT-asymmetry magnitudes and different saturation parameter sets. Results Our results indicated a “safe” range of magnitudes (/MTRasym/<4 %) for which MT-asymmetry signal did not bias the corrected ihMT signal. Moreover, experimental evidence of the different natures of both MT-asymmetry and inhomogeneous MT contrasts were provided. In particular, non-zero ihMT ratios were obtained at zero MTRasym values. Conclusion MTRasym is not a confounding factor for ihMT quantification, even at ultra-high field, as long as MTRasym is restricted to ±4 %.
      PubDate: 2016-08-01
      DOI: 10.1007/s10334-015-0523-2
      Issue No: Vol. 29, No. 4 (2016)
       
  • Theory of MRI contrast in the annulus fibrosus of the intervertebral disc
    • Authors: Alexander C. Wright; Jonathon H. Yoder; Edward J. Vresilovic; Dawn M. Elliott
      Pages: 711 - 722
      Abstract: Objective Here we develop a three-dimensional analytic model for MR image contrast of collagen lamellae in the annulus fibrosus of the intervertebral disc of the spine, based on the dependence of the MRI signal on collagen fiber orientation. Materials and methods High-resolution MRI scans were performed at 1.5 and 7 T on intact whole disc specimens from ovine, bovine, and human spines. An analytic model that approximates the three-dimensional curvature of the disc lamellae was developed to explain inter-lamellar contrast and intensity variations in the annulus. The model is based on the known anisotropic dipolar relaxation of water in tissues with ordered collagen. Results Simulated MRI data were generated that reproduced many features of the actual MRI data. The calculated inter-lamellar image contrast demonstrated a strong dependence on the collagen fiber angle and on the circumferential location within the annulus. Conclusion This analytic model may be useful for interpreting MR images of the disc and for predicting experimental conditions that will optimize MR image contrast in the annulus fibrosus.
      PubDate: 2016-08-01
      DOI: 10.1007/s10334-015-0522-3
      Issue No: Vol. 29, No. 4 (2016)
       
  • Comparison of two quantitative proton density mapping methods in multiple
           sclerosis
    • Authors: René-Maxime Gracien; Sarah C. Reitz; Marlies Wagner; Christoph Mayer; Steffen Volz; Stephanie-Michelle Hof; Vinzenz Fleischer; Amgad Droby; Helmuth Steinmetz; Sergiu Groppa; Elke Hattingen; Johannes C. Klein; Ralf Deichmann
      Abstract: Objective Proton density (PD) mapping requires correction for the receive profile (RP), which is frequently performed via bias-field correction. An alternative RP-mapping method utilizes a comparison of uncorrected PD-maps and a value ρ(T1) directly derived from T1-maps via the Fatouros equation. This may be problematic in multiple sclerosis (MS), if respective parameters are only valid for healthy brain tissue. We aimed to investigate whether the alternative method yields correct PD values in MS patients. Materials/methods PD mapping was performed on 27 patients with relapsing-remitting MS and 27 healthy controls, utilizing both methods, yielding reference PD values (PDref, bias-field method) and PDalt (alternative method). Results PDalt-values closely matched PDref, both for patients and controls. In contrast, ρ(T1) differed by up to 3 % from PDref, and the voxel-wise correlation between PDref and ρ(T1) was reduced in a patient subgroup with a higher degree of disability. Still, discrepancies between ρ(T1) and PDref were almost identical across different tissue types, thus translating into a scaling factor, which cancelled out during normalization to 100 % in CSF, yielding a good agreement between PDalt and PDref. Conclusion RP correction utilizing the auxiliary parameter ρ(T1) derived via the Fatouros equation provides accurate PD results in MS patients, in spite of discrepancies between ρ(T1) and actual PD values.
      PubDate: 2016-08-20
      DOI: 10.1007/s10334-016-0585-9
       
  • Influence of spatial resolution and contrast agent dosage on myocardial T1
           relaxation times
    • Authors: Edyta Blaszczyk; Agnieszka Töpper; Luisa Schmacht; Felix Wanke; Andreas Greiser; Jeanette Schulz-Menger; Florian von Knobelsdorff-Brenkenhoff
      Abstract: Objective Our aim was to study the influence of small variations in spatial resolution and contrast agent dosage on myocardial T1 relaxation time. Materials and methods Twenty-nine healthy volunteers underwent cardiovascular magnetic resonance at 3T twice, including a modified look-locker inversion recovery (MOLLI) technique—3(3)3(3)5—for T1 mapping. Native T1 was assessed in three spatial resolutions (voxel size 1.4 × 1.4 × 6, 1.6 × 1.6 × 6, 1.7 × 1.7 × 6 mm3), and postcontrast T1 after 0.1 and 0.2 mmol/kg gadobutrol. Partition coefficient was calculated based on myocardial and blood T1. T1 analysis was done per segment, per slice, and for the whole heart. Results Native T1 values did not differ with varying spatial resolution per segment (p = 0.116–0.980), per slice (basal: p = 0.772; middle: p = 0.639; apex: p = 0.276), and globally (p = 0.191). Postcontrast T1 values were significantly lower with higher contrast agent dosage (p < 0.001). The global partition coefficient was 0.43 ± 0.3 for 0.2 and 0.1 mmol gadobutrol (p = 0.079). Conclusion Related to the tested MOLLI technique at 3T, very small variations in spatial resolution (voxel sizes between 1.4 × 1.4 × 6 and 1.7 × 1.7 × 6 mm3) remained without effect on the native T1 relaxation times. Postcontrast T1 values were naturally shorter with higher contrast agent dosage while the partition coefficient remained constant. Further studies are necessary to test whether these conclusions hold true for larger matrix sizes and in larger cohorts.
      PubDate: 2016-08-20
      DOI: 10.1007/s10334-016-0581-0
       
  • The aging effect on prostate metabolite concentrations measured by 1 H MR
           spectroscopy
    • Authors: Monika Dezortova; Filip Jiru; Antonin Skoch; Vaclav Capek; Zuzana Ryznarova; Viktor Vik; Milan Hajek
      Abstract: Objective The effects of aging, magnetic field and the voxel localization on measured concentrations of citrate (Cit), creatine (Cr), cholines (Cho) and polyamines (PA) in a healthy prostate were evaluated. Materials and methods 36 examinations at both 1.5T and 3T imagers of 52 healthy subjects aged 19–71 years were performed with PRESS 3D-CSI sequences (TE = 120 and 145 ms). Concentrations in laboratory units and their ratios to citrate were calculated using the LCModel technique. Absolute concentrations were also obtained after the application of correction coefficients. Statistical analysis was performed using a robust linear mixed effects model. Results Significant effects of aging, the magnetic field strength and the voxel position in central (CZ) or peripheral (PZ) zones on all measured metabolites were found. The concentrations (mmol/kg wet tissue) including prediction intervals in a range of 20–70 years were found: Cit: 7.9–17.2; Cho: 1.4–1.7; Cr: 2.8-2.5; PA (as spermine): 0.6–2.1 at 3T in CZ. In PZ, the concentrations were higher by about 10 % as compared to CZ. Conclusion Increasing citrate and spermine concentrations with age are significant and correlate well with a recently described increase of zinc in the prostate. These findings should be considered in decision-making if the values obtained from a subject are in the range of control values.
      PubDate: 2016-08-13
      DOI: 10.1007/s10334-016-0584-x
       
  • 3D single point imaging with compressed sensing provides high temporal
           resolution R 2 * mapping for in vivo preclinical applications
    • Authors: James A. Rioux; Steven D. Beyea; Chris V. Bowen
      Abstract: Objective Purely phase-encoded techniques such as single point imaging (SPI) are generally unsuitable for in vivo imaging due to lengthy acquisition times. Reconstruction of highly undersampled data using compressed sensing allows SPI data to be quickly obtained from animal models, enabling applications in preclinical cellular and molecular imaging. Materials and methods TurboSPI is a multi-echo single point technique that acquires hundreds of images with microsecond spacing, enabling high temporal resolution relaxometry of large-R 2* systems such as iron-loaded cells. TurboSPI acquisitions can be pseudo-randomly undersampled in all three dimensions to increase artifact incoherence, and can provide prior information to improve reconstruction. We evaluated the performance of CS-TurboSPI in phantoms, a rat ex vivo, and a mouse in vivo. Results An algorithm for iterative reconstruction of TurboSPI relaxometry time courses does not affect image quality or R 2* mapping in vitro at acceleration factors up to 10. Imaging ex vivo is possible at similar acceleration factors, and in vivo imaging is demonstrated at an acceleration factor of 8, such that acquisition time is under 1 h. Conclusions Accelerated TurboSPI enables preclinical R 2* mapping without loss of data quality, and may show increased specificity to iron oxide compared to other sequences.
      PubDate: 2016-08-08
      DOI: 10.1007/s10334-016-0583-y
       
  • Diffusion-weighted echo planar MR imaging of the neck at 3 T using
           integrated shimming: comparison of MR sequence techniques for reducing
           artifacts caused by magnetic-field inhomogeneities
    • Authors: Sergios Gatidis; Hansjörg Graf; Jakob Weiß; Alto Stemmer; Berthold Kiefer; Konstantin Nikolaou; Mike Notohamiprodjo; Petros Martirosian
      Abstract: Objective Our objective was to compare available techniques reducing artifacts in echo planar imaging (EPI)-based diffusion-weighed magnetic resonance imaging MRI (DWI) of the neck at 3 Tesla caused by B0-field inhomogeneities. Materials and methods A cylindrical fat–water phantom was equipped with a Maxwell coil allowing for additional linear B0-field variations in z-direction. The effect of increasing strength of this superimposed gradient on image quality was observed using a standard single-shot EPI-based DWI sequence (sEPI), a zoomed single-shot EPI sequence (zEPI), a readout-segmented EPI sequence (rsEPI), and an sEPI sequence with integrated dynamic shimming (intEPI) on a 3-Tesla system. Additionally, ten volunteers were examined over the neck region using these techniques. Image quality was assessed by two radiologists. Scan durations were recorded. Results With increasing strength of the external gradient, marked distortions, signal loss, and failure of fat suppression were observed using sEPI, zEPI, and rsEPI. These artifacts were markedly reduced using intEPI. Significantly better in vivo image quality was also observed using intEPI compared with the other techniques. Scan time of intEPI was similar to sEPI and zEPI and shorter than rsEPI. Conclusion The use of integrated 2D shim and frequency adjustment for EPI-based DWI results in a significant improvement in image quality of the head/neck region at 3 Tesla. Combining integrated shimming with rsEPI or zEPI can be expected to provide additional improvements.
      PubDate: 2016-08-08
      DOI: 10.1007/s10334-016-0582-z
       
  • Application of the limited-memory quasi-Newton algorithm for
           multi-dimensional, large flip-angle RF pulses at 7T
    • Authors: Mads S. Vinding; Daniel Brenner; Desmond H. Y. Tse; Sebastian Vellmer; Thomas Vosegaard; Dieter Suter; Tony Stöcker; Ivan I. Maximov
      Abstract: Objective Ultrahigh field MRI provides great opportunities for medical diagnostics and research. However, ultrahigh field MRI also brings challenges, such as larger magnetic susceptibility induced field changes. Parallel-transmit radio-frequency pulses can ameliorate these complications while performing advanced tasks in routine applications. To address one class of such pulses, we propose an optimal-control algorithm as a tool for designing advanced multi-dimensional, large flip-angle, radio-frequency pulses. We contrast initial conditions, constraints, and field correction abilities against increasing pulse trajectory acceleration factors. Materials and methods On an 8-channel 7T system, we demonstrate the quasi-Newton algorithm with pulse designs for reduced field-of-view imaging with an oil phantom and in vivo with scans of the human brain stem. We used echo-planar imaging with 2D spatial-selective pulses. Pulses are computed sufficiently rapid for routine applications. Results Our dataset was quantitatively analyzed with the conventional mean-square-error metric and the structural-similarity index from image processing. Analysis of both full and reduced field-of-view scans benefit from utilizing both complementary measures. Conclusion We obtained excellent outer-volume suppression with our proposed method, thus enabling reduced field-of-view imaging using pulse trajectory acceleration factors up to 4.
      PubDate: 2016-08-02
      DOI: 10.1007/s10334-016-0580-1
       
  • A USPIO doped gel phantom for R 2* relaxometry
    • Authors: Gregory C. Brown; Gary J. Cowin; Graham J. Galloway
      Abstract: Objective This work describes a phantom containing regions of controlled R2* (1/T2*) values to provide a stable reference object for testing implementations of R2* relaxometry commonly used for liver and heart iron assessments. Materials and methods A carrageenan-strengthened gadolinium DTPA doped agarose gel was used to enclose nine gels additionally doped with ultra-small superparamagnetic iron oxide. R2* values were determined at 1.5 T using multi-echo GRE sequences and exponential regression of pixel values from a region of interest against echo time using non-linear regression algorithms. We measured R2*, R2 and R1 values and the inter-scan and inter-operator reproducibility. Results The phantom reliably demonstrated R2* values in seven steps between 22.4 s−1 (SE 1.98) and 441.9 s−1 (SE 6.76), with an R2* relaxivity (r2*) of 792 (SE 5.6) mM−1 s−1. The doped gels displayed a concentration-dependent R2ʹ component of R2* phantom, indicating superparamagnetic enhancement effects. We observed no significant change in relaxivity (r2*) over 12 months, and estimate a useful life of 3 years. Detailed descriptions of the production process and calculators are been provided as Online Resources. Conclusion The phantom provides a durable test object with controlled R2* relaxation behaviour, useful for a range of R2* relaxometry reference work.
      PubDate: 2016-07-19
      DOI: 10.1007/s10334-016-0576-x
       
  • Assessing the accuracy of using oscillating gradient spin echo sequences
           with AxCaliber to infer micron-sized axon diameters
    • Authors: Morgan Mercredi; Trevor J. Vincent; Christopher P. Bidinosti; Melanie Martin
      Abstract: Objective Current magnetic resonance imaging (MRI) axon diameter measurements rely on the pulsed gradient spin-echo sequence, which is unable to provide diffusion times short enough to measure small axon diameters. This study combines the AxCaliber axon diameter fitting method with data generated from Monte Carlo simulations of oscillating gradient spin-echo sequences (OGSE) to infer micron-sized axon diameters, in order to determine the feasibility of using MRI to infer smaller axon diameters in brain tissue. Materials and methods Monte Carlo computer simulation data were synthesized from tissue geometries of cylinders of different diameters using a range of gradient frequencies in the cosine OGSE sequence . Data were fitted to the AxCaliber method modified to allow the new pulse sequence. Intra- and extra-axonal water were studied separately and together. Results The simulations revealed the extra-axonal model to be problematic. Rather than change the model, we found that restricting the range of gradient frequencies such that the measured apparent diffusion coefficient was constant over that range resulted in more accurate fitted diameters. Thus a careful selection of frequency ranges is needed for the AxCaliber method to correctly model extra-axonal water, or adaptations to the method are needed. This restriction helped reduce the necessary gradient strengths for measurements that could be performed with parameters feasible for a Bruker BG6 gradient set. For these experiments, the simulations inferred diameters as small as 0.5 μm on square-packed and randomly packed cylinders. The accuracy of the inferred diameters was found to be dependent on the signal-to-noise ratio (SNR), with smaller diameters more affected by noise, although all diameter distributions were distinguishable from one another for all SNRs tested. Conclusion The results of this study indicate the feasibility of using MRI with OGSE on preclinical scanners to infer small axon diameters.
      PubDate: 2016-07-13
      DOI: 10.1007/s10334-016-0575-y
       
  • Assessment of the myelin water fraction in rodent spinal cord using
           T2-prepared ultrashort echo time MRI
    • Authors: Tim Klasen; Cornelius Faber
      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: 2016-07-09
      DOI: 10.1007/s10334-016-0579-7
       
  • 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
      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: 2016-07-08
      DOI: 10.1007/s10334-016-0578-8
       
  • 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
      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: 2016-07-06
      DOI: 10.1007/s10334-016-0577-9
       
  • Accelerated visualization of selected intracranial arteries by cycled
           super-selective arterial spin labeling
    • Authors: Thomas Lindner; Naomi Larsen; Olav Jansen; Michael Helle
      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: 2016-06-29
      DOI: 10.1007/s10334-016-0574-z
       
  • 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
      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: 2016-06-22
      DOI: 10.1007/s10334-016-0573-0
       
  • 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
      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: 2016-06-13
      DOI: 10.1007/s10334-016-0567-y
       
 
 
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