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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]
  • 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
      Pages: 1 - 14
      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: 2017-02-01
      DOI: 10.1007/s10334-016-0575-y
      Issue No: Vol. 30, No. 1 (2017)
       
  • A USPIO doped gel phantom for R 2* relaxometry
    • Authors: Gregory C. Brown; Gary J. Cowin; Graham J. Galloway
      Pages: 15 - 27
      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: 2017-02-01
      DOI: 10.1007/s10334-016-0576-x
      Issue No: Vol. 30, No. 1 (2017)
       
  • 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
      Pages: 29 - 39
      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: 2017-02-01
      DOI: 10.1007/s10334-016-0580-1
      Issue No: Vol. 30, No. 1 (2017)
       
  • 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
      Pages: 41 - 55
      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: 2017-02-01
      DOI: 10.1007/s10334-016-0583-y
      Issue No: Vol. 30, No. 1 (2017)
       
  • 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
      Pages: 57 - 63
      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: 2017-02-01
      DOI: 10.1007/s10334-016-0582-z
      Issue No: Vol. 30, No. 1 (2017)
       
  • 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
      Pages: 65 - 74
      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: 2017-02-01
      DOI: 10.1007/s10334-016-0584-x
      Issue No: Vol. 30, No. 1 (2017)
       
  • 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
      Pages: 75 - 83
      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: 2017-02-01
      DOI: 10.1007/s10334-016-0585-9
      Issue No: Vol. 30, No. 1 (2017)
       
  • 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
      Pages: 85 - 91
      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: 2017-02-01
      DOI: 10.1007/s10334-016-0581-0
      Issue No: Vol. 30, No. 1 (2017)
       
  • 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
      Pages: 93 - 101
      Abstract: Objectives A new microfabrication method to produce low profile radio frequency (RF) resonant markers on catheter shafts was developed. A semi-active RF resonant marker incorporating a solenoid and a plate capacitor was constructed on the distal shaft of a 5 Fr guiding catheter. The resulting device can be used for interventional cardiovascular MRI procedures. Materials and methods Unlike current semi-active device visualization techniques that require rigid and bulky analog circuit components (capacitor and solenoid), we fabricated a low profile RF resonant marker directly on guiding the catheter surface by thin film metal deposition and electroplating processes using a modified physical vapor deposition system. Results The increase of the overall device profile thickness caused by the semi-active RF resonant marker (130 µm thick) was lowered by a factor of 4.6 compared with using the thinnest commercial non-magnetic and rigid circuit components (600 µm thick). Moreover, adequate visibility performance of the RF resonant marker in different orientations and overall RF safety were confirmed through in vitro experiments under MRI successfully. Conclusion The developed RF resonant marker on a clinical grade 5 Fr guiding catheter will enable several interventional congenital heart disease treatment procedures under MRI.
      PubDate: 2017-02-01
      DOI: 10.1007/s10334-016-0586-8
      Issue No: Vol. 30, No. 1 (2017)
       
  • 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
      Pages: 103 - 105
      PubDate: 2017-02-01
      DOI: 10.1007/s10334-016-0592-x
      Issue No: Vol. 30, No. 1 (2017)
       
  • Interpretation of cardiac wall motion from cine-MRI combined with
           parametric imaging based on the Hilbert transform
    • Authors: Narjes Benameur; Enrico Gianluca Caiani; Younes Arous; Nejmeddine ben Abdallah; Tarek Kraiem
      Abstract: Object The aim of this study was to test and validate the clinical impact of parametric amplitude images obtained using the Hilbert transform on the regional interpretation of cardiac wall motion abnormalities from cine-MR images by non-expert radiologists compared with expert consensus. Materials and methods Cine-MRI short-axis images obtained in 20 patients (10 with myocardial infarction, 5 with myocarditis and 5 with normal function) were processed to compute a parametric amplitude image for each using the Hilbert transform. Two expert radiologists blindly reviewed the cine-MR images to define a gold standard for wall motion interpretation for each left ventricular sector. Two non-expert radiologists reviewed and graded the same images without and in combination with parametric images. Grades assigned to each segment in the two separate sessions were compared with the gold standard. Results According to expert interpretation, 264/320 (82.5%) segments were classified as normal and 56/320 (17.5%) were considered abnormal. The accuracy of the non-expert radiologists’ grades compared to the gold standard was significantly improved by adding parametric images (from 87.2 to 94.6%) together with sensitivity (from 64.29 to 84.4%) and specificity (from 92 to 96.9%), also resulting in reduced interobserver variability (from 12.8 to 5.6%). Conclusion The use of parametric amplitude images based on the Hilbert transform in conjunction with cine-MRI was shown to be a promising technique for improvement of the detection of left ventricular wall motion abnormalities in less expert radiologists.
      PubDate: 2017-02-20
      DOI: 10.1007/s10334-017-0609-0
       
  • Track-weighted imaging methods: extracting information from a streamlines
           tractogram
    • Authors: Fernando Calamante
      Abstract: A whole-brain streamlines data-set (so-called tractogram) generated from diffusion MRI provides a wealth of information regarding structural connectivity in the brain. Besides visualisation strategies, a number of post-processing approaches have been proposed to extract more detailed information from the tractogram. One such approach is based on exploiting the information contained in the tractogram to generate track-weighted (TW) images. In the track-weighted imaging (TWI) approach, a very large number of streamlines are often generated throughout the brain, and an image is then computed based on properties of the streamlines themselves (e.g. based on the number of streamlines in each voxel, or their average length), or based on the values of an associated image (e.g. a diffusion anisotropy map, a T2 map) measured at the coordinates of the streamlines. This review article describes various approaches used to generate TW images and discusses the flexible formalism that TWI provides to generate a range of images with very different contrast, as well as the super-resolution properties of the resulting images. It also explains how this approach provides a powerful means to study structural and functional connectivity simultaneously. Finally, a number of key issues for its practical implementation are discussed.
      PubDate: 2017-02-08
      DOI: 10.1007/s10334-017-0608-1
       
  • Highly-accelerated self-gated free-breathing 3D cardiac cine MRI:
           validation in assessment of left ventricular function
    • Authors: Jing Liu; Li Feng; Hsin-Wei Shen; Chengcheng Zhu; Yan Wang; Kanae Mukai; Gabriel C. Brooks; Karen Ordovas; David Saloner
      Abstract: Objective This work presents a highly-accelerated, self-gated, free-breathing 3D cardiac cine MRI method for cardiac function assessment. Materials and methods A golden-ratio profile based variable-density, pseudo-random, Cartesian undersampling scheme was implemented for continuous 3D data acquisition. Respiratory self-gating was achieved by deriving motion signal from the acquired MRI data. A multi-coil compressed sensing technique was employed to reconstruct 4D images (3D+time). 3D cardiac cine imaging with self-gating was compared to bellows gating and the clinical standard breath-held 2D cine imaging for evaluation of self-gating accuracy, image quality, and cardiac function in eight volunteers. Reproducibility of 3D imaging was assessed. Results Self-gated 3D imaging provided an image quality score of 3.4 ± 0.7 vs 4.0 ± 0 with the 2D method (p = 0.06). It determined left ventricular end-systolic volume as 42.4 ± 11.5 mL, end-diastolic volume as 111.1 ± 24.7 mL, and ejection fraction as 62.0 ± 3.1%, which were comparable to the 2D method, with bias ± 1.96 × SD of −0.8 ± 7.5 mL (p = 0.90), 2.6 ± 3.3 mL (p = 0.84) and 1.4 ± 6.4% (p = 0.45), respectively. Conclusion The proposed 3D cardiac cine imaging method enables reliable respiratory self-gating performance with good reproducibility, and provides comparable image quality and functional measurements to 2D imaging, suggesting that self-gated, free-breathing 3D cardiac cine MRI framework is promising for improved patient comfort and cardiac MRI scan efficiency.
      PubDate: 2017-01-24
      DOI: 10.1007/s10334-017-0607-2
       
  • Assessment of edema using STIR+ via 3D cardiovascular magnetic resonance
           imaging in patients with suspected myocarditis
    • Authors: Michael Jeserich; Bela Merkely; Pascal Schlosser; Simone Kimmel; Gabor Pavlik; Stephan Achenbach
      Abstract: Objective To evaluate three-dimensional T2-weighted fast spin echo triple inversion recovery sequences (STIR+) for the diagnosis of myocardial edema in patients with suspected early myocarditis after respiratory or gastrointestinal tract viral infection and at follow-up. Materials and methods We prospectively examined 28 patients with suspected myocarditis and 37 controls matched for gender and age. An ECG-triggered STIR+ was used to cover the entire left ventricle in short-axis images with 10-mm slice thickness and no interslice gap. The global signal intensity ratio (heart muscle in relation to skeletal muscle) was calculated (global STIR+ ratio) to evaluate edema. All patients had repeat examinations at follow-up (mean interval 4.9 months, 1–12 months). Results The mean global STIR+ ratio was 2.15 ± 0.4 in the initial examination of patients as compared to 1.78 ± 0.3 in controls (p < 0.0001) and 1.89 ± 0.3 in patients at follow-up (p = 0.0001 vs. first visit). Left ventricular ejection fraction did not differ between patients and controls at baseline and at follow-up. Conclusion We could identify a significantly higher global STIR+ ratio in patients with suspected myocarditis compared to controls, and a dynamic change during follow-up. The global STIR+ ratio may, therefore, be useful for the diagnosis of myocarditis and should be further explored.
      PubDate: 2017-01-16
      DOI: 10.1007/s10334-016-0603-y
       
  • 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
       
  • 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
       
  • 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
       
  • Semi-automated myocardial segmentation of bright blood multi-gradient
           echo images improves reproducibility of myocardial contours and T2*
           determination
    • 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
       
 
 
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