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NMR in Biomedicine

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https://www.readbyqxmd.com/read/28211968/verse-guided-parallel-rf-excitations-using-dynamic-field-correction
#1
Mustafa Çavuşoğlu, Ronald Mooiweer, Klaas P Pruessmann, Shaihan J Malik
In parallel RF pulse design, peak RF magnitudes and specific absorption rate levels are critical concerns in the hardware and safety limits. The variable rate selective excitation (VERSE) method is an efficient technique to limit the peak RF power by applying a local-only RF and gradient waveform reshaping while retaining the on-resonance profile. The accuracy of the excitation performed by the VERSEd RF and gradient waveforms strictly depends on the performance of the employed hardware. Any deviation from the nominal gradient fields as a result of frequency dependent system imperfections violates the VERSE condition similarly to off-resonance effects, leading to significant excitation errors and the RF pulse not converging to the targeted peak RF power...
February 17, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28211963/a-parametric-model-of-the-brain-vascular-system-for-estimation-of-the-arterial-input-function-aif-at-the-tissue-level
#2
Siamak P Nejad-Davarani, Hassan Bagher-Ebadian, James R Ewing, Douglas C Noll, Tom Mikkelsen, Michael Chopp, Quan Jiang
In this paper, we introduce a novel model of the brain vascular system, which is developed based on laws of fluid dynamics and vascular morphology. This model is used to address dispersion and delay of the arterial input function (AIF) at different levels of the vascular structure and to estimate the local AIF in DCE images. We developed a method based on the simplex algorithm and Akaike information criterion to estimate the likelihood of the contrast agent concentration signal sampled in DCE images belonging to different layers of the vascular tree or being a combination of different signal levels from different nodes of this structure...
February 17, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28211961/an-extended-vascular-model-for-less-biased-estimation-of-permeability-parameters-in-dce-t1-images
#3
Siamak P Nejad-Davarani, Hassan Bagher-Ebadian, James R Ewing, Douglas C Noll, Tom Mikkelsen, Michael Chopp, Quan Jiang
One of the key elements in dynamic contrast enhanced (DCE) image analysis is the arterial input function (AIF). Traditionally, in DCE studies a global AIF sampled from a major artery or vein is used to estimate the vascular permeability parameters; however, not addressing dispersion and delay of the AIF at the tissue level can lead to biased estimates of these parameters. To find less biased estimates of vascular permeability parameters, a vascular model of the cerebral vascular system is proposed that considers effects of dispersion of the AIF in the vessel branches, as well as extravasation of the contrast agent (CA) to the extravascular-extracellular space...
February 17, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28205341/spatiotemporal-microstructural-white-matter-changes-in-diffusion-tensor-imaging-after-transient-focal-ischemic-stroke-in-rats
#4
Won-Beom Jung, Yong Hee Han, Julius Juhyun Chung, Sun Young Chae, Sung Hoon Lee, Geun Ho Im, JiHoon Cha, Jung Hee Lee
Structural reorganization in white matter (WM) after stroke is a potential contributor to substitute or to newly establish the functional field on the injured brain in nature. Diffusion tensor imaging (DTI) is an imaging modality that can be used to evaluate damage and recovery within the brain. This method of imaging allows for in vivo assessment of the restricted movements of water molecules in WM and provides a detailed look at structural connectivity in the brain. For longitudinal DTI studies after a stroke, the conventional region of interest method and voxel-based analysis are highly dependent on the user-hypothesis and parameter settings for implementation...
February 16, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28195684/extended-rf-shimming-sequence-level-parallel-transmission-optimization-applied-to-steady-state-free-precession-mri-of-the-heart
#5
Arian Beqiri, Anthony N Price, Francesco Padormo, Joseph V Hajnal, Shaihan J Malik
Cardiac magnetic resonance imaging (MRI) at high field presents challenges because of the high specific absorption rate and significant transmit field (B1(+) ) inhomogeneities. Parallel transmission MRI offers the ability to correct for both issues at the level of individual radiofrequency (RF) pulses, but must operate within strict hardware and safety constraints. The constraints are themselves affected by sequence parameters, such as the RF pulse duration and TR, meaning that an overall optimal operating point exists for a given sequence...
February 14, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28195664/an-adaptive-model-for-rapid-and-direct-estimation-of-extravascular-extracellular-space-in-dynamic-contrast-enhanced-mri-studies
#6
Azimeh N V Dehkordi, Alireza Kamali-Asl, James R Ewing, Ning Wen, Indrin J Chetty, Hassan Bagher-Ebadian
Extravascular extracellular space (ve ) is a key parameter to characterize the tissue of cerebral tumors. This study introduces an artificial neural network (ANN) as a fast, direct, and accurate estimator of ve from a time trace of the longitudinal relaxation rate, ΔR1 (R1  = 1/T1 ), in DCE-MRI studies. Using the extended Tofts equation, a set of ΔR1 profiles was simulated in the presence of eight different signal to noise ratios. A set of gain- and noise-insensitive features was generated from the simulated ΔR1 profiles and used as the ANN training set...
February 14, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28195663/optimization-of-inhomogeneous-magnetization-transfer-ihmt-mri-contrast-for-preclinical-studies-using-dipolar-relaxation-time-t1d-filtering
#7
V H Prevost, O M Girard, S Mchinda, G Varma, D C Alsop, G Duhamel
A pulsed inhomogeneous magnetization transfer (ihMT)-prepared fast imaging sequence was implemented at 11.75 T for preclinical studies on mouse central nervous system. A strategy based on filtering the ihMT signal originating from short dipolar relaxation time (T1D ) components is proposed. It involves increasing the repetition time of consecutive radiofrequency (RF) pulses of the dual saturation and allows improved signal specificity for long T1D myelinated structures. Furthermore, frequency offset, power and timing saturation parameters were adjusted to optimize the ihMT sensitivity...
February 14, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28187250/phase-imaging-with-multiple-phase-cycled-balanced-steady-state-free-precession-at-9-4%C3%A2-t
#8
Jae-Woong Kim, Seong-Gi Kim, Sung-Hong Park
While phase imaging with a gradient echo (GRE) sequence is popular, phase imaging with balanced steady-state free precession (bSSFP) has been underexplored. The purpose of this study was to investigate anatomical and functional phase imaging with multiple phase-cycled bSSFP, in expectation of increasing spatial coverage of steep phase-change regions of bSSFP. Eight different dynamic 2D pass-band bSSFP studies at four phase-cycling (PC) angles and two TE /TR values were performed on rat brains at 9.4 T with electrical forepaw stimulation, in comparison with dynamic 2D GRE...
February 10, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28187249/parallel-transmission-rf-pulse-design-with-strict-temperature-constraints
#9
Cem M Deniz, Giuseppe Carluccio, Christopher Collins
RF safety in parallel transmission (pTx) is generally ensured by imposing specific absorption rate (SAR) limits during pTx RF pulse design. There is increasing interest in using temperature to ensure safety in MRI. In this work, we present a local temperature correlation matrix formalism and apply it to impose strict constraints on maximum absolute temperature in pTx RF pulse design for head and hip regions. Electromagnetic field simulations were performed on the head and hip of virtual body models. Temperature correlation matrices were calculated for four different exposure durations ranging between 6 and 24 min using simulated fields and body-specific constants...
February 10, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28186677/imaging-porcine-cardiac-substrate-selection-modulations-by-glucose-insulin-and-potassium-intervention-a-hyperpolarized-1-13-c-pyruvate-study
#10
Esben Søvsø Szocska Hansen, Rasmus Stilling Tougaard, Thomas Stokholm Nørlinger, Emmeli Mikkelsen, Per Mose Nielsen, Lotte Bonde Bertelsen, Hans Erik Bøtker, Hans Stødkilde Jørgensen, Christoffer Laustsen
Cardiac metabolism has received considerable attention in terms of both diagnostics and prognostics, as well as a novel target for treatment. As human trials involving hyperpolarized magnetic resonance in the heart are imminent, we sought to evaluate the general feasibility of detection of an imposed shift in metabolic substrate utilization during metabolic modulation with glucose-insulin-potassium (GIK) infusion, and thus the limitations associated with this strategy, in a large animal model resembling human physiology...
February 10, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28186661/brain-neurochemical-and-hemodynamic-findings-in-the-ny1dd-mouse-model-of-mild-sickle-cell-disease
#11
Min-Hui Cui, Sandra M Suzuka, Nicholas A Branch, Kamalakar Ambadipudi, Sangeetha Thangaswamy, Seetharama A Acharya, Henny H Billett, Craig A Branch
To characterize the cerebral profile associated with sickle cell disease (SCD), we used in vivo proton MRI and MRS to quantify hemodynamics and neurochemicals in the thalamus of NY1DD mice, a mild model of SCD, and compared them with wild-type (WT) control mice. Compared with WT mice, NY1DD mice at steady state had elevated cerebral blood flow (CBF) and concentrations of N-acetylaspartate (NAA), glutamate (Glu), alanine, total creatine and N-acetylaspartylglutamate. Concentrations of glutathione (GSH) at steady state showed a negative correlation with BOLD signal change in response to 100% oxygen, a marker for oxidative stress, and mean diffusivity assessed using diffusion-tensor imaging, a marker for edematous inflammation...
February 10, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28186652/on-the-contribution-of-curl-free-current-patterns-to-the-ultimate-intrinsic-signal-to-noise-ratio-at-ultra-high-field-strength
#12
Andreas Pfrommer, Anke Henning
The ultimate intrinsic signal-to-noise ratio (SNR) is a coil independent performance measure to compare different receive coil designs. To evaluate this benchmark in a sample, a complete electromagnetic basis set is required. The basis set can be obtained by curl-free and divergence-free surface current distributions, which excite linearly independent solutions to Maxwell's equations. In this work, we quantitatively investigate the contribution of curl-free current patterns to the ultimate intrinsic SNR in a spherical head-sized model at 9...
February 10, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28164396/improved-multiparametric-mri-discrimination-between-low-risk-prostate-cancer-and-benign-tissues-in-a-small-cohort-of-5%C3%AE-reductase-inhibitor-treated-individuals-as-compared-with-an-untreated-cohort
#13
Olga Starobinets, John Kurhanewicz, Susan M Noworolski
The purpose of this study was to determine whether 5α-reductase inhibitors (5-ARIs) affect the discrimination between low-grade prostate cancer and benign tissues on multiparametric MRI (mpMRI). Twenty men with biopsy-proven Gleason 3 + 3 prostate cancer and 3 T mpMRI were studied. Ten patients (Tx) had been receiving 5-ARIs for at least a year at scan time. Ten untreated patients (Un) were matched to the treated cohort. For each subject two regions of interest representing cancerous and benign tissues were drawn within the peripheral zone of each prostate, MR measures evaluated, and cancer contrast versus benign (contrast = (MRTumor  - MRHealthy )/MRHealthy ) calculated...
February 6, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28164391/multiparametric-cmr-imaging-of-infarct-remodeling-in-a-percutaneous-reperfused-yucatan-mini-pig-model
#14
David Lopez, Jonathan A Pan, Peter M Pollak, Samantha Clarke, Christopher M Kramer, Mark Yeager, Michael Salerno
To further understanding of the temporal evolution and pathophysiology of adverse ventricular remodeling over the first 60 days following a myocardial infarction (MI) in both the infarcted and remote myocardium, we performed multi-parametric cardiac magnetic resonance (CMR) imaging in a closed-chest chronic Yucatan mini-pig model of reperfused MI. Ten animals underwent 90 min left anterior descending artery occlusion and reperfusion. Three animals served as controls. Multiparametric CMR (1.5T) was performed at baseline, Day 2, Day 30 and in four animals on Day 60 after MI...
February 6, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28128481/spatial-hadamard-encoding-of-j-edited-spectroscopy-using-slice-selective-editing-pulses
#15
Kimberly L Chan, Georg Oeltzschner, Michael Schär, Peter B Barker, Richard A E Edden
A new approach for simultaneous dual-voxel J-difference spectral editing is described, which uses spatially selective spectral-editing pulses and Hadamard encoding. A theoretical framework for spatial Hadamard editing and reconstruction for parallel acquisition (SHERPA) was developed, applying gradient pulses during the frequency-selective editing pulses. Spectral simulations were performed for either one (gamma-aminobutyric acid, GABA) or two molecules (glutathione and lactate) simultaneously detected in two voxels...
January 27, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28111824/on-the-transmit-field-inhomogeneity-correction-of-relaxation-compensated-amide-and-noe-cest-effects-at-7%C3%A2-t
#16
Vitaliy Khlebnikov, Johannes Windschuh, Jeroen C W Siero, Moritz Zaiss, Peter R Luijten, Dennis W J Klomp, Hans Hoogduin
High field MRI is beneficial for chemical exchange saturation transfer (CEST) in terms of high SNR, CNR, and chemical shift dispersion. These advantages may, however, be counter-balanced by the increased transmit field inhomogeneity normally associated with high field MRI. The relatively high sensitivity of the CEST contrast to B1 inhomogeneity necessitates the development of correction methods, which is essential for the clinical translation of CEST. In this work, two B1 correction algorithms for the most studied CEST effects, amide-CEST and nuclear Overhauser enhancement (NOE), were analyzed...
January 23, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28111820/an-indirect-method-for-in-vivo-t2-mapping-of-1-13-c-pyruvate-using-hyperpolarized-13-c-csi
#17
Eunhae Joe, Hansol Lee, Joonsung Lee, Seungwook Yang, Young-Suk Choi, Eunkyung Wang, Ho-Taek Song, Dong-Hyun Kim
An indirect method for in vivo T2 mapping of (13) C-labeled metabolites using T2 and T2 * information of water protons obtained a priori is proposed. The T2 values of (13) C metabolites are inferred using the relationship to T2 ' of coexisting (1) H and the T2 * of (13) C metabolites, which is measured using routine hyperpolarized (13) C CSI data. The concept is verified with phantom studies. Simulations were performed to evaluate the extent of T2 estimation accuracy due to errors in the other measurements...
January 23, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28085211/evaluating-kurtosis-based-diffusion-mri-tissue-models-for-white-matter-with-fiber-ball-imaging
#18
Jens H Jensen, Emilie T McKinnon, G Russell Glenn, Joseph A Helpern
In order to quantify well-defined microstructural properties of brain tissue from diffusion MRI (dMRI) data, tissue models are typically employed that relate biological features, such as cell morphology and cell membrane permeability, to the diffusion dynamics. A variety of such models have been proposed for white matter, and their validation is a topic of active interest. In this paper, three different tissue models are tested by comparing their predictions for a specific microstructural parameter to a value measured independently with a recently proposed dMRI method known as fiber ball imaging (FBI)...
January 13, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28058747/towards-a-neurochemical-profile-of-the-amygdala-using-short-te-1-h-magnetic-resonance-spectroscopy-at-3%C3%A2-t
#19
Florian Schubert, Simone Kühn, Jürgen Gallinat, Ralf Mekle, Bernd Ittermann
The amygdala plays a key role in emotional learning and in the processing of emotions. As disturbed amygdala function has been linked to several psychiatric conditions, a knowledge of its biochemistry, especially neurotransmitter levels, is highly desirable. The spin echo full intensity acquired localized (SPECIAL) sequence, together with a transmit/receive coil, was used to perform very short-TE magnetic resonance spectroscopy at 3 T to determine the neurochemical profile in a spectroscopic voxel containing the amygdala in 21 healthy adult subjects...
January 6, 2017: NMR in Biomedicine
https://www.readbyqxmd.com/read/28052436/quantification-of-1-h-mrs-signals-based-on-sparse-metabolite-profiles-in-the-time-frequency-domain
#20
Mohammad Ali Parto Dezfouli, Mohsen Parto Dezfouli, Alireza Ahmadian, Alejandro F Frangi, Melika Esmaeili Rad, Hamidreza Saligheh Rad
MRS is an analytical approach used for both quantitative and qualitative analysis of human body metabolites. The accurate and robust quantification capability of proton MRS ((1) H-MRS) enables the accurate estimation of living tissue metabolite concentrations. However, such methods can be efficiently employed for quantification of metabolite concentrations only if the overlapping nature of metabolites, existing static field inhomogeneity and low signal-to-noise ratio (SNR) are taken into consideration. Representation of (1) H-MRS signals in the time-frequency domain enables us to handle the baseline and noise better...
January 4, 2017: NMR in Biomedicine
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