20 Hits in 0.82 sec

RF shimming for spectroscopic localization in the human brain at 7 T

Hoby P. Hetherington, Nikolai I. Avdievich, Andrey M. Kuznetsov, Jullie W. Pan
2009 Magnetic Resonance in Medicine  
Spectroscopic imaging of the human head at short TEs (≤15ms) typically requires suppression of signals from extracerebral tissues. However, at 7, decreasing efficiency in generation (Hz/Watt) and increasing spectral bandwidth result in dramatic increases in power deposition and increased chemical shift registration artifacts for conventional gradient based in-plane localization. In this work, we describe a novel method using RF shimming and an 8 element transceiver array to generate a field
more » ... ribution that excites a ring about the periphery of the head and leaves central brain regions largely unaffected. We have used this novel distribution to provide in-plane outer volume suppression (>98% suppression of extracerebral lipids) without the use of gradients. This novel distribution is used in conjunction with a double inversion recovery method to provide suppression of extracerebral resonances with T1s greater than 400ms, while having negligible effect on metabolite ratios of cerebral resonances with T1s >1000ms. Despite the use of two adiabatic pulses, the high efficiency of the ring distribution allows RF power deposition to be limited to 3-4W for a TR of 1.5s. The short TE enabled the acquisition of images of the human brain displaying glutamate, glutamine, macromolecules and other major cerebral metabolites.
doi:10.1002/mrm.22182 pmid:19918903 pmcid:PMC2811270 fatcat:h3pq7hh7breg7berk4vobpdg2m

Folded‐end dipole transceiver array for human whole‐brain imaging at 7 T

Nikolai I. Avdievich, Georgiy Solomakha, Loreen Ruhm, Anton V. Nikulin, Arthur W. Magill, Klaus Scheffler
2021 NMR in Biomedicine  
ORCID Nikolai I. Avdievich Arthur W. Magill  ...  Also, an addition of the local RF shield to this design, as suggested by Avdievich et al., 23 did not lead to any significant changes in the B 1 + field distribution (not shown).  ...  combining the developed TxRx dipole array with multiple Rx-only surface loops, as suggested previously. 37, 38 Simultaneous reception using loops and dipoles in a human head array was also demonstrated by Avdievich  ... 
doi:10.1002/nbm.4541 pmid:33978270 fatcat:ycspb4scxfekzocectz5a7n5a4

Unshielded bent folded-end dipole 9.4 T human head transceiver array decoupled using modified passive dipoles

Nikolai I Avdievich, Georgiy Solomakha, Loreen Ruhm, Anke Henning, Klaus Scheffler
2021 Magnetic Resonance in Medicine  
| 593 AVDIEVICH Et Al.  ...  . | 585 AVDIEVICH Et Al. the cylindrical phantom. Both the short and folded-end dipoles measured 170 mm in z direction (along the axis of the cylinder).  ...  (B), and transversal (C) in-vivo 1-mm isotropic whole-brain MP2RAGE images obtained using the 1 × 8 30-mm bent folded-end dipole array for the same subject as in Figure 9 How to cite this article: Avdievich  ... 
doi:10.1002/mrm.28711 pmid:33629436 fatcat:pac57ieprbcltfwzgt5gng4ajq

Improved homogeneity of the transmit field by simultaneous transmission with phased array and volume coil

Nikolai I. Avdievich, Sukhoon Oh, Hoby P. Hetherington, Christopher M. Collins
2010 Journal of Magnetic Resonance Imaging  
Purpose-To improve the homogeneity of transmit volume coils at high magnetic fields (≥ 4 T). Due to RF field/ tissue interactions at high fields, 4-8 T, the transmit profile from head-sized volume coils shows a distinctive pattern with relatively strong RF magnetic field B 1 in the center of the brain. Materials and Methods-In contrast to conventional volume coils at high field strengths, surface coil phased arrays can provide increased RF field strength peripherally. In theory, simultaneous
more » ... nsmission from these two devices could produce a more homogeneous transmission field. To minimize interactions between the phased array and the volume coil, counter rotating current (CRC) surface coils consisting of two parallel rings carrying opposite currents were used for the phased array. Results-Numerical simulations and experimental data demonstrate that substantial improvements in transmit field homogeneity can be obtained. Conclusion- We have demonstrated the feasibility of using simultaneous transmission with human head-sized volume coils and CRC phased arrays to improve homogeneity of the transmit RF B 1 field for high-field MRI systems.
doi:10.1002/jmri.22257 pmid:20677280 pmcid:PMC2925674 fatcat:phbyyvxtxrfflc6z3a56c6ikae

System Identification and Signal Processing for PID Control of B0 Shim Systems in Ultra-High Field Magnetic Resonance Applications

Yu-Chun Chang, Nikolai Avdievich, Anke Henning
2014 IFAC Proceedings Volumes  
Magnetic resonance (MR) scanners are important tools in medical diagnostics and in many areas of neuroscience. MR technology is moving towards ultra-high field (UHF) 7T and 9.4T scanners which provide more signal intensity. However they also suffer from inhomogeneity of the static (B0) magnetic field which can lead to artifacts and uninterpretable data. B0 shimming is a technique used to reduce inhomogeneities but most MR scanners use static shim settings for the duration of the experiment.
more » ... mic shim updating (DSU) updates the shim in real-time while the scan is in process and can hence reduce any fluctuations in B0 field which may arise due to patient breathing, mechanical vibrations and soforth. However DSU is currently very slow and if we intend to increase the update rate then control theory needs to be applied. This paper presents an application of basic system identification and signal processing in the context of MR systems for DSU. Although system identification of these systems has been done before, they are non-parametric frequency domain approaches. These systems can be modelled as linear multivariable systems.
doi:10.3182/20140824-6-za-1003.01828 fatcat:s66dfs45mnc33l3f2ib4uonnpu

Dynamic observation of 2H labeled compounds in the human brain with 1H versus 2H magnetic resonance spectroscopy at 9.4T [article]

Loreen Ruhm, Theresia Ziegs, Andrew Martin Wright, Claudius Sebastian Mathy, Saipavitra Murali-Manohar, Johanna Dorst, Nikolai Avdievich, Anke Henning
2022 bioRxiv   pre-print
AbstractThe metabolic pathway of [6,6'-2H2]-labeled glucose was investigated with two different techniques. The first technique used direct detection of deuterium applying Deuterium Metabolic Imaging (DMI). The second technique used the indirect detection of deuterium with proton MR spectroscopy (MRS) called Quantitative Exchanged-label Turnover (QELT) MRS. For the first time, time-resolved data was acquired for both techniques in the same healthy human subjects and directly compared. The
more » ... urves were used in a kinetic model to estimate rates of the metabolic pathway of glucose. Two different kinetic models were compared. One included only DMI data, the second one combined DMI and QELT. For the first model, a tricarboxylic acid (TCA) cycle rate of 0.69 ± 0.10 μmol·min-1·g-1 was determined. For the second model, the estimated TCA cycle rate was 0.68 ± 0.12 μmol·min-1·g-1. In addition, the rate of glutamine synthesis from glutamate could be estimated with model 2 (0.51 ± 0.15 μmol·min-1·g-1). The sensitivity of both methods was evaluated and compared to alternative techniques.
doi:10.1101/2022.01.24.477582 fatcat:carv3rfz5fht5dgg3bl6njlf4e

9.4 T double-tuned 13 C/1 H human head array using a combination of surface loops and dipole antennas

Nikolai I Avdievich, Georgiy Solomakha, Loreen Ruhm, Anke Henning, Klaus Scheffler
2021 NMR in Biomedicine  
ORCID Nikolai I. Avdievich  ... 
doi:10.1002/nbm.4577 pmid:34169590 fatcat:zjo274p6ojd5dj32wf74ngcue4

4T split TEM volume head and knee coils for improved sensitivity and patient accessibility

Nikolai I. Avdievich, Ken Bradshaw, Jing-Huei Lee, Andrey M. Kuznetsov, Hoby P. Hetherington
2007 Journal of magnetic resonance (San Diego, Calif. 1997 : Print)  
Split RF coils offer improved patient access by eliminating the need for the coil to be slid over the region of interest. For unshielded birdcage coils, the presence of end ring currents necessitates a direct electrical connection between two halves of the coil. For high-field (>3T) shielded birdcage coils, both the shield and the coil must be split and reliably connected electrically. This problem can be circumvented by the use of split TEM volume coils. Since the elements of a TEM coil are
more » ... pled inductively, no direct electrical connection between the halves is necessary. In this work we demonstrate that the effects of splitting the shield for head and knee TEMs can be compensated for, and performance retained. For the knee, the improved access allowed the coil diameter to be reduced, enhancing the sensitivity by 15-20 %.
doi:10.1016/j.jmr.2007.05.006 pmid:17533142 pmcid:PMC2749647 fatcat:q6cti6tb5zen5eaeisne6wm3xu

Double‐tuned 31 P/ 1 H human head array with high performance at both frequencies for spectroscopic imaging at 9.4T

Nikolai I. Avdievich, Loreen Ruhm, Johanna Dorst, Klaus Scheffler, Andreas Korzowski, Anke Henning
2020 Magnetic Resonance in Medicine  
Cover is removed for better visualization. 1 H and 31 P loops are marked by red and yellow dashed lines, respectively 4 | AVDIEVICH Et Al.  ...  | 3 AVDIEVICH Et Al. | METHODS | Phased array design As mentioned above, increasing the number of smaller surface loops in a human head Rx array can be harmful for X-nuclei MRI and MRSI.  ...  | AVDIEVICH Et Al. FIGURE S1 A, Central sagittal, coronal, and transversal SNR maps obtained using the 31  ... 
doi:10.1002/mrm.28176 pmid:32003031 fatcat:fn2va2n37rf35ltcw4sj7srbbm

Relaxation‐corrected macromolecular model enables determination of 1 H longitudinal T 1 ‐relaxation times and concentrations of human brain metabolites at 9.4T

Andrew Martin Wright, Saipavitra Murali‐Manohar, Tamas Borbath, Nikolai I. Avdievich, Anke Henning
2021 Magnetic Resonance in Medicine  
Ultrahigh field MRS has improved characterization of the neurochemical profile. To compare results obtained at 9.4T to those from lower field strengths, it is of interest to quantify the concentrations of metabolites measured. Thus, measuring T1 -relaxation times is necessary to correct for T1 -weighting that occurs in acquisitions for single-voxel spectroscopy and spectroscopic imaging. A macromolecule (MM) simulation model was developed to fit MM contributions to the short TE inversion series used to measure T1 -relaxation times.
doi:10.1002/mrm.28958 pmid:34374449 fatcat:mnip4ybr5rajxpnj3qtyvpcq7i

Molecular Features of the Copper Binding Sites in the Octarepeat Domain of the Prion Protein†

Colin S. Burns, Eliah Aronoff-Spencer, Christine M. Dunham, Paula Lario, Nikolai I. Avdievich, William E. Antholine, Marilyn M. Olmstead, Alice Vrielink, Gary J. Gerfen, Jack Peisach, William G. Scott, Glenn L. Millhauser
2002 Biochemistry  
Recent evidence suggests that the prion protein (PrP) is a copper binding protein. The N-terminal region of human PrP contains four sequential copies of the highly conserved octarepeat sequence PHGGGWGQ spanning residues 60-91. This region selectively binds Cu 2+ in vivo. In a previous study using peptide design, EPR, and CD spectroscopy, we showed that the HGGGW segment within each octarepeat comprises the fundamental Cu 2+ binding unit [Aronoff-Spencer et al. (2000) Biochemistry 40,
more » ... 1]. Here we present the first atomic resolution view of the copper binding site within an octarepeat. The crystal structure of HGGGW in a complex with Cu 2+ reveals equatorial coordination by the histidine imidazole, two deprotonated glycine amides, and a glycine carbonyl, along with an axial water bridging to the Trp indole. Companion S-band EPR, X-band ESEEM, and HYSCORE experiments performed on a library of 15 N-labeled peptides indicate that the structure of the copper binding site in HGGGW and PHGGGWGQ in solution is consistent with that of the crystal structure. Moreover, EPR performed on PrP(23-28, 57-91) and an 15 N-labeled analogue demonstrates that the identified structure is maintained in the full PrP octarepeat domain. It has been shown that copper stimulates PrP endocytosis. The identified Gly-Cu linkage is unstable below pH ≈6.5 and thus suggests a pH-dependent molecular mechanism by which PrP detects Cu 2+ in the extracellular matrix or releases PrP-bound Cu 2+ within the endosome. The structure also reveals an unusual complementary interaction between copper-structured HGGGW units that may facilitate molecular recognition between prion proteins, thereby suggesting a mechanism for transmembrane signaling and perhaps conversion to the pathogenic form. 1 Abbreviations: PrP, prion protein; PrP C , cellular isoform of PrP; PrP Sc , scrapie isoform of PrP; PrP(57-91), residues 57 through 91 of PrP; EPR, electron paramagnetic resonance; ESEEM, electron spinecho envelope modulation; HYSCORE, hyperfine sublevel correlation spectroscopy; e 2 qQ/h, maximum quadrupole coupling; η, quadrupole asymmetry parameter; NQI, nuclear quadrupole interaction; DQ, double quantum; Aiso, isotropic component of the hyperfine coupling constant; T, anisotropic component of the hyperfine coupling
doi:10.1021/bi011922x pmid:11900542 pmcid:PMC2905306 fatcat:j4ko6rtyyncepf2k7t4dwtitgi

Identification of the Cu2+Binding Sites in the N-Terminal Domain of the Prion Protein by EPR and CD Spectroscopy†

Eliah Aronoff-Spencer, Colin S. Burns, Nikolai I. Avdievich, Gary J. Gerfen, Jack Peisach, William E. Antholine, Haydn L. Ball, Fred E. Cohen, Stanley B. Prusiner, Glenn L. Millhauser
2000 Biochemistry  
Recent evidence indicates that the prion protein (PrP) plays a role in copper metabolism in the central nervous system. The N-terminal region of human PrP contains four sequential copies of the highly conserved octarepeat sequence PHGGGWGQ spanning residues 60-91. This region selectively binds divalent copper ions (Cu 2+ ) in vivo. To elucidate the specific mode and site of binding, we have studied a series of Cu 2+ -peptide complexes composed of 1-, 2-, and 4-octarepeats and several
more » ... at peptides, by electron paramagnetic resonance (EPR, conventional X-band and lowfrequency S-band) and circular dichroism (CD) spectroscopy. At pH 7.45, two EPR active binding modes are observed where the dominant mode appears to involve coordination of three nitrogens and one oxygen to the copper ion, while in the minor mode two nitrogens and two oxygens coordinate. ESEEM spectra demonstrate that the histidine imidazole contributes one of these nitrogens. The truncated sequence HGGGW gives EPR and CD that are indistinguishable from the dominant binding mode observed for the multi-octarepeat sequences and may therefore comprise the fundamental Cu 2+ binding unit. Both EPR and CD titration experiments demonstrate rigorously a 1:1 Cu 2+ / octarepeat binding stoichiometry regardless of the number of octarepeats in a given peptide sequence. Detailed spin integration of the EPR signals demonstrates that all of the bound Cu 2+ is detected thereby ruling out strong exchange coupling that is often found when there is imidazolate bridging between paramagnetic metal centers. A model consistent with these data is proposed in which Cu 2+ is bound to the nitrogen of the histidine imidazole side chain and to two nitrogens from sequential glycine backbone amides.
doi:10.1021/bi001472t pmid:11076515 pmcid:PMC2903970 fatcat:bogsylait5ddnjvb6gj6lmvifi

In vivo characterization of the downfield part of 1 H MR spectra of human brain at 9.4 T: Magnetization exchange with water and relation to conventionally determined metabolite content

Nicole D. Fichtner, Ioannis-Angelos Giapitzakis, Nikolai Avdievich, Ralf Mekle, Daniel Zaldivar, Anke Henning, Roland Kreis
2017 Magnetic Resonance in Medicine  
Purpose: To perform exchange-rate measurements on the in vivo human brain downfield spectrum (5-10ppm) at 9.4T and to compare the variation in concentrations of the downfield resonances and of known upfield metabolites to determine potential peak labels. Methods: Non-water suppressed metabolite cycling was used in combination with an inversion transfer technique in two brain locations in healthy volunteers to measure the exchange rates and T 1 values of exchanging peaks. Spectra were fitted
more » ... a heuristic model of a series of 13 or 14 Voigt lines, and a Bloch-McConnell model was used to fit exchange rate curves. Concentrations from non-water inverted spectra upfield and downfield were compared. Results: Mean T 1 values ranged from 0.40 to 0.77 s and exchange rates from 0.74 to 13.8 s -1 . There were no significant correlations between downfield and upfield concentrations, except for NAA, with a correlation coefficient of 0.63 and p<0.01. Conclusions: Using ultra-high field allowed improved separation of peaks in the 8.2-8.5ppm amide proton region, and the exchange rates of multiple downfield resonances including the 5.8ppm peak, previously tentatively assigned to urea, were measured in vivo in human brain. Downfield peaks are comprised of overlapping components, and largely missing correlations between upfield and downfield resonances -though not conclusive -indicate limited contributions from metabolites present upfield to the downfield spectrum. Figure S2 : Scatter plots for the range of correlations tested between upfield and downfield peak areas. Occipital ROI data points shown in blue, WM ROI data points shown in red. The downfield peaks are along the x-axes, and the upfield peaks along the y-axes, as labeled in the figure. Supporting
doi:10.1002/mrm.26968 pmid:29034505 fatcat:lunxi4kobrhb5fxvp5jw3dhoiu

ISMRM Best Practices for Safety Testing of Experimental RF Hardware

Nicola De Zanche, Cornelis van den Berg, David Brunner, Joseph Murphy-Boesch, Joseph Rispoli, Gregor Adriany, Nikolai Avdievich, Nicolas Boulant, Wyger Brink, Ryan Brown, Thomas Fiedler, Kyle Gilbert (+14 others)
This document was written by a working group of twenty-six experts who are members of the Safety and Engineering Study Groups of the International Society for Magnetic Resonance in Medicine (ISMRM). While the authors are based in several countries and continents, no assurance is given that these recommendations comply with the law in any particular jurisdiction. The reader is responsible for assuring, before implementing any of the recommendations below, that the reader is complying with the
more » ... s and regulations of the jurisdiction in which the reader is located.
doi:10.7939/r3-7vpe-x737 fatcat:d4bo2mvjpbg4lbmfsdwjvqrniu

RF probe recovery time reduction with a novel active ringing suppression circuit

A.S. Peshkovsky, J. Forguez, L. Cerioni, D.J. Pusiol
2005 Journal of magnetic resonance (San Diego, Calif. 1997 : Print)  
Acknowledgments The authors thank Nikolai I. Avdievich for helpful discussions. This work was supported by NIH NRSA #1 F32 HL078187-01 and by the Argentine National Research Council (CONICET).  ... 
doi:10.1016/j.jmr.2005.07.004 pmid:16111906 pmcid:PMC1479304 fatcat:zz2ek553snb2nezrjpz7tppa24
« Previous Showing results 1 — 15 out of 20 results