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Journal Cover Magnetic Resonance Materials in Physics, Biology and Medicine
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 0968-5243 - ISSN (Online) 1352-8661
     Published by Springer-Verlag Homepage  [2209 journals]   [SJR: 0.821]   [H-I: 36]
  • Age-related differences in the response of leg muscle cross-sectional area
           and water diffusivity measures to a period of supine rest
    • Abstract: Object The object was to assess whether cross-sectional area (CSA) and water diffusion properties of leg muscles in young and older women change with increased time spent in supine rest. Materials and methods Healthy young (n = 9, aged 20–30 years) and older (n = 9, aged 65–75 years) women underwent MRI scanning of the right leg at baseline, 30 and 60 min of supine rest. Muscle CSA was derived from proton density images. Water diffusion properties [apparent diffusion coefficient (ADC) and fractional anisotropy (FA)] of the tibialis anterior and posterior, soleus, and medial and lateral heads of the gastrocnemius were derived from diffusion tensor imaging (DTI). Repeated measures ANOVAs and Bonferroni post hoc tests determined the effects of time and group on each muscle outcome. Results In both groups, muscle CSA and FA did not significantly change over time, whereas ADC significantly decreased. A greater decline at 30 min for young women was only observed for ADC in the medial gastrocnemius. Conclusion Regardless of age, ADC values decreased with fluid shift associated with time spent supine, whereas CSA and FA were not affected. For leg muscle assessment in young and older women, DTI scanning protocols should consider the amount of time spent in a recumbent position.
      PubDate: 2014-10-15
  • Proton spectroscopic imaging of brain metabolites in basal ganglia of
           healthy older adults
    • Abstract: Object We sought to measure brain metabolite levels in healthy older people. Materials and methods Spectroscopic imaging at the level of the basal ganglia was applied in 40 participants aged 73–74 years. Levels of the metabolites N-acetyl aspartate (NAA), choline, and creatine were determined in "institutional units" (IU) corrected for T1 and T2 relaxation effects. Structural imaging enabled determination of grey matter (GM), white matter (WM), and cerebrospinal fluid content. ANOVA analysis was carried out for voxels satisfying quality criteria. Results Creatine levels were greater in GM than WM (57 vs. 44 IU, p < 0.001), whereas choline and NAA levels were greater in WM than GM [13 vs. 10 IU (p < 0.001) and 76 versus 70 IU (p = 0.03), respectively]. The ratio of NAA/cre was greater in WM than GM (2.1 vs. 1.4, p = 0.001) as was that of cho/cre (0.32 vs. 0.16, p < 0.001). A low voxel yield was due to brain atrophy and the difficulties of shimming over an extended region of brain. Conclusion This study addresses the current lack of information on brain metabolite levels in older adults. The normal features of ageing result in a substantial loss of reliable voxels and should be taken into account when planning studies. Improvements in shimming are also required before the methods can be applied more widely.
      PubDate: 2014-10-14
  • An optically coupled sensor for the measurement of currents induced by MRI
           gradient fields into endocardial leads
    • Abstract: Object The gradient fields generated during magnetic resonance imaging (MRI) procedures have the potential to induce electrical current on implanted endocardial leads. Whether this current can result in undesired cardiac stimulation is unknown. Materials and methods This paper provides a detailed description of how to construct an optically coupled sensor for the measurement of gradient-field–induced currents into endocardial leads. The system is based on a microcontroller that works as analog-to-digital converter and sends the current signal acquired from the lead to an optical high-speed, light-emitting diode transmitter. A plastic fiber guides the light outside the MRI chamber to a photodiode receiver and then to an acquisition board connected to a PC laptop. Results The performance of the system has been characterized in terms of power consumption (8 mA on average), sampling frequency (20.5 kHz), measurement range (−12.8 to 10.3 mA) and resolution (22.6 µA). Results inside a 3 T MRI scanner are also presented. Conclusions The detailed description of the current sensor could permit more standardized study of MRI gradient current induction in pacemaker systems. Results show the potential of gradient currents to affect the pacemaker capability of triggering a heartbeat, by modifying the overall energy delivered by the stimulator.
      PubDate: 2014-10-11
  • Multiparametric oxygen-enhanced functional lung imaging in 3D
    • Abstract: Objective To develope a self-gated free-breathing 3D sequence allowing for simultaneous T 1-weighted imaging and quantitative \(T_{2}^{ *}\) mapping in different breathing phases in order to assess the feasibility of oxygen-enhanced 3D functional lung imaging. Materials and methods A 3D sequence with ultrashort echo times and interleaved double readouts was implemented for oxygen-enhanced lung imaging at 1.5 T. Six healthy volunteers were examined while breathing room air as well as 100 % oxygen. Images from expiratory and inspiratory breathing phases were reconstructed and compared for the two breathing gases. Results The average \(T_{2}^{*}\) value measured for room air was 2.10 ms, with a 95 % confidence interval (CI) of 1.95–2.25 ms, and the average for pure oxygen was 1.89 ms, with a 95 % CI of 1.76–2.01 ms, resulting in a difference of 10.1 % (95 % CI 8.9–11.3 %). An 11.2 % increase in signal intensity (95 % CI 10.4–12.1 %) in the T 1-weighted images was detected when subjects were breathing pure oxygen compared to room air. Furthermore, a significant change in signal intensity (26.5 %, 95 % CI 18.8–34.3 %) from expiration to inspiration was observed. Conclusions This study demonstrated the feasibility of simultaneous \(T_{2}^{*}\) mapping and T 1-weighted 3D imaging of the lung. This method has the potential to provide information about ventilation, oxygen transfer, and lung expansion within one experiment. Future studies are needed to investigate the clinical applicability and diagnostic value of this approach in various pulmonary diseases.
      PubDate: 2014-10-09
  • Numerical and experimental evaluation of RF shimming in the human brain at
           9.4 T using a dual-row transmit array
    • Abstract: Objective To provide a numerical and experimental investigation of the static RF shimming capabilities in the human brain at 9.4 T using a dual-row transmit array. Materials and methods A detailed numerical model of an existing 16-channel, inductively decoupled dual-row array was constructed using time-domain software together with circuit co-simulation. Experiments were conducted on a 9.4 T scanner. Investigation of RF shimming focused on B1 + homogeneity, efficiency and local specific absorption rate (SAR) when applied to large brain volumes and on a slice-by-slice basis. Results Numerical results were consistent with experiments regarding component values, S-parameters and B1 + pattern, though the B1 + field was about 25 % weaker in measurements than simulations. Global shim settings were able to prevent B1 + field voids across the entire brain but the capability to simultaneously reduce inhomogeneities was limited. On a slice-by-slice basis, B1 + standard deviations of below 10 % without field dropouts could be achieved in axial, sagittal and coronal orientations across the brain, even with phase-only shimming, but decreased B1 + efficiency and SAR limitations must be considered. Conclusion Dual-row transmit arrays facilitate flexible 3D RF management across the entire brain at 9.4 T in order to trade off B1 + homogeneity against power-efficiency and local SAR.
      PubDate: 2014-10-01
  • High-resolution 3D whole-heart coronary MRA: a study on the combination of
           data acquisition in multiple breath-holds and 1D residual respiratory
           motion compensation
    • Abstract: Object To study a scan protocol for coronary magnetic resonance angiography based on multiple breath-holds featuring 1D motion compensation and to compare the resulting image quality to a navigator-gated free-breathing acquisition. Image reconstruction was performed using L1 regularized iterative SENSE. Materials and methods The effects of respiratory motion on the Cartesian sampling scheme were minimized by performing data acquisition in multiple breath-holds. During the scan, repetitive readouts through a k-space center were used to detect and correct the respiratory displacement of the heart by exploiting the self-navigation principle in image reconstruction. In vivo experiments were performed in nine healthy volunteers and the resulting image quality was compared to a navigator-gated reference in terms of vessel length and sharpness. Results Acquisition in breath-hold is an effective method to reduce the scan time by more than 30 % compared to the navigator-gated reference. Although an equivalent mean image quality with respect to the reference was achieved with the proposed method, the 1D motion compensation did not work equally well in all cases. Conclusion In general, the image quality scaled with the robustness of the motion compensation. Nevertheless, the featured setup provides a positive basis for future extension with more advanced motion compensation methods.
      PubDate: 2014-10-01
  • Neurochemicals measured by        class="a-plus-plus">1H-MR spectroscopy: putative
           vulnerability biomarkers for obsessive compulsive disorder
    • Abstract: Object Obsessive compulsive disorder (OCD) is the fourth most common psychiatric disorder characterized by recurrent, intrusive thoughts and repetitive, ritualistic behaviors that are debilitating to the patient. Despite its high prevalence and the attendant morbidity, the pathophysiology of OCD remains unclear. Magnetic resonance spectroscopy (MRS) provides a noninvasive method to characterize the molecular biochemistry that may contribute to the pathophysiology of OCD. This study aimed to identify alterations in neurochemical measures that are specific to OCD using in vivo proton (1H) MRS of the caudate nucleus, anterior cingulate cortex, and medial thalamus in these patients, and to identify their role as vulnerability markers by comparing them with the healthy first degree relatives of these patients and healthy controls. Materials and methods Appropriate psychometric instruments were applied in the study population followed by 1H- MRS. The absolute neurochemical measures were quantified using a linear combination model. Results Significant differences in neurochemical measures were demonstrated in two of the three candidate regions (except the medial thalamus) between the three study groups. Conclusions Our results lend support to the neurodegenerative hypothesis of OCD, and also raise the possibility of exploring these neurochemical measures (as measured by MRS) as putative vulnerability biomarkers in OCD that may aid in early identification and devising early prevention or management strategies for the population vulnerable to OCD.
      PubDate: 2014-10-01
  • Erratum to: Fetal blood flow velocimetry by phase-contrast MRI using a new
           triggering method and comparison with Doppler ultrasound in a sheep model:
           a pilot study
    • PubDate: 2014-10-01
  • Automated segmentation and volumetric analysis of renal cortex, medulla,
           and pelvis based on non-contrast-enhanced T1- and T2-weighted MR images
    • Abstract: Object The aim of our study was to enable automatic volumetry of the entire kidneys as well as their internal structures (cortex, medulla, and pelvis) from native magnetic resonance imaging (MRI) data sets. Materials and methods Segmentation of the entire kidneys and differentiation of their internal structures were performed in 12 healthy volunteers based on non-contrast-enhanced T1- and T2-weighted MR images. Two data sets (each acquired in one breath-hold) were co-registered using a rigid registration algorithm compensating for possible breathing-related displacements. An automatic algorithm based on thresholding and shape detection segmented the kidneys into their compartments and was compared to a manual labeling procedure. Results The resulting kidney volumes of the automated segmentation correlated well with those created manually (R 2 = 0.96). Average volume errors were determined to be 4.97 ± 4.08 % (entire kidney parenchyma), 7.03 ± 5.56 % (cortex), 12.33 ± 7.35 % (medulla), and 17.57 ± 14.47 % (pelvis). The variation of the kidney volume resulting from the automatic algorithm was found to be 4.76 % based on the measuring of one volunteer with three independent examinations. Conclusion The results demonstrate the feasibility of an accurate and repeatable automatic segmentation of the kidneys and their internal structures from non-contrast-enhanced magnetic resonance images.
      PubDate: 2014-10-01
  • Assessment of diffusion tensor imaging indices in calf muscles following
           postural change from standing to supine position
    • Abstract: Object To investigate whether postural change from erect to recumbent position affects calf muscle water diffusivity. Materials and methods Ten healthy adults (27.2 ± 4.9 years, 3 females) were imaged at baseline (following assumption of recumbent position), and after 34 min (session 2) and 64 min (session 3) of laying supine within a 3T MRI scanner. Diffusion tensor imaging (DTI) eigenvalues, fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were evaluated in five calf muscles (anterior and posterior tibialis and triceps surae) during each of the three imaging sessions. Results Significant decreases were observed in all of the eigenvalues and ADC in each of the muscles with postural change. These reductions ranged from 3.2 to 6.7 % and 3.4 to 7.5 % for the various DTI metrics, following 34 and 64 min of supine rest, respectively (P < 0.05). No significant differences were noted in ADC or eigenvalues between the second and third imaging sessions for any muscle. FA did not change significantly with postural manipulation in any muscle compartment. Conclusion Diffusion tensor imaging indices were altered with postural change. As differences were not apparent between the latter two imaging sessions, we suggest that a short supine resting period (~34 min) is sufficient for muscle diffusivity to stabilize prior to quantitative MR imaging in healthy young adults.
      PubDate: 2014-10-01
  • Spatial phase encoding exploiting the Bloch–Siegert shift effect
    • Abstract: Objective The present work introduces an alternative to the conventional \(B_{0}\) -gradient spatial phase encoding technique. By applying far off-resonant radiofrequency (RF) pulses, a spatially dependent phase shift is introduced to the on-resonant transverse magnetization. This so-called Bloch–Siegert (BS) phase shift has been recently used for \(B_{1}^{ + }\) -mapping. The current work presents the theoretical background for the BS spatial encoding technique (BS-SET) using RF-gradients. Materials and methods Since the BS-gradient leads to nonlinear encoding, an adapted reconstruction method was developed to obtain undistorted images. To replace conventional phase encoding gradients, BS-SET was implemented in a two-dimensional (2D) spin echo sequence on a 0.5 T portable MR scanner. Results A 2D spin echo (SE) measurement imaged along a single dimension using the BS-SET was compared to a conventional SE 2D measurement. The proposed reconstruction method yielded undistorted images. Conclusions BS-gradients were demonstrated as a feasible option for spatial phase encoding. Furthermore, undistorted BS-SET images could be obtained using the proposed reconstruction method.
      PubDate: 2014-10-01
  • Initial clinical application of modified Dixon with flexible echo times:
           hepatic and pancreatic fat assessments in comparison with        class="a-plus-plus">1H MRS
    • Abstract: Objects Hepatic and pancreatic fat content become increasingly important for phenotyping of individuals with metabolic diseases. This study aimed to (1) evaluate hepatic fat fractions (HFF) and pancreatic fat fractions (PFF) using 1H magnetic resonance spectroscopy (MRS) and the recently introduced fast mDixon method, and to examine body fat effects on HFF and PFF, (2) investigate regional differences in HFF and PFF by mDixon. Materials and methods HFF and PFF were quantified by mDixon with two flexible echo times and by single voxel 1H MRS in 24 healthy subjects. The regional differences of PFF within the pancreas were assessed with mDixon. Abdominal visceral and subcutaneous fat was assessed by T1-weighted MRI at 3T. Results Both methods correlated well for quantification of HFF (r = 0.98, p < 0.0001) and PFF (r = 0.80, p < 0.0001). However, mDixon showed a higher low limit in HFF and PFF. PFF showed no regional differences using mDixon. In addition, both visceral and subcutaneous fat correlated with pancreatic fat, while only visceral fat correlated with liver fat, employing both 1H MRS and mDixon. Conclusion The novel and fast two-point mDixon exhibits a good correlation with the gold-standard 1H MRS for assessment of HFF and PFF, with limited sensitivity for assessing lower fat content.
      PubDate: 2014-10-01
  • Erratum to: Cylinders or walls' A new computational model to estimate
           the MR transverse relaxation rate dependence on trabecular bone
    • PubDate: 2014-10-01
  • Two-dimensional accelerated MP-RAGE imaging with flexible linear
    • Abstract: Object Implementation of an accelerated Magnetization Prepared RApid Gradient Echo (MP-RAGE) sequence for T1 weighted neuroimaging; exploiting modern MRI technologies to minimize scan time while preserving the image quality. Materials and methods A custom MP-RAGE sequence was implemented on a state-of-the-art 3T MR scanner equipped with a 32-channel receiver array head coil. The sequence utilized a shifted CAIPIRINHA k y –k z under-sampling pattern combined with elliptical scanning and a two-dimensional view ordering scheme to achieve high parallel imaging acceleration factors at maintained image contrast. Results It could be shown that MP-RAGE accelerated in two k-space directions outperforms single direction acceleration, which is the common practice with standard view ordering. Applying the CAIPIRINHA technique in conjunction with elliptical scanning further increased this benefit. Conclusion By combining MP-RAGE with CAIPIRINHA sampling and elliptical scanning, the scan time can be reduced from 4–5 min to 2–3 min with insignificant reduction in image quality.
      PubDate: 2014-10-01
  • Automated flow quantification for spin labeling MR imaging
    • Abstract: Objective The Time-Spatial Labeling Inversion Pulse (Time-SLIP) technique enables tracing of regional fluid flows without the use of contrast medium. The objective of this study is to quantify automatically slow and complex fluid flows using the Time-SLIP technique. Materials and methods Series images were acquired with a 1.5-T MRI scanner using the Time-SLIP technique with half-Fourier fast spin-echo (FSE) and balanced steady-state free precession (bSSFP) sequences. In this method, labeled fluid regions in images were automatically detected based on image processing techniques for a given point. The flow velocity of the labeled fluid region was calculated using regression fitting for the region’s position. To evaluate our method, constant and non-constant laminar flows in a water phantom were studied. In addition, volunteer experiments were conducted to quantify the flow of cerebrospinal fluid. Results In the constant flow experiments the correlation factor r 2 between the flow velocity calculated from our method and the laminar peak velocity calculated from the volumetric flow rate was 0.9992 for the FSE sequence and 0.9982 for the bSSFP sequence. In the non-constant flow study, the flow velocity was calculated accurately for any period inversion time even when the flow velocity was changed, and the quantification error was negligible. In the volunteer experiments, r 2 between the flow velocity calculated by the proposed method and that obtained by manual annotation was 0.9383. Conclusion The experimental results showed that our proposed method can quickly and accurately provide information on flow velocities especially for slower and complex flows. Our method is, therefore, expected to be useful in diagnostic support systems.
      PubDate: 2014-10-01
  • ViP MRI: virtual phantom magnetic resonance imaging
    • Abstract: Object The ability to generate reference signals is of great benefit for quantitation of the magnetic resonance (MR) signal. The aim of the present study was to implement a dedicated experimental set-up to generate MR images of virtual phantoms. Materials and methods Virtual phantoms of a given shape and signal intensity were designed and the k-space representation was generated. A waveform generator converted the k-space lines into a radiofrequency (RF) signal that was transmitted to the MR scanner bore by a dedicated RF coil. The k-space lines of the virtual phantom were played line-by-line in synchronization with the magnetic resonance imaging data acquisition. Results Virtual phantoms of complex patterns were reproduced well in MR images without the presence of artifacts. Time-series measurements showed a coefficient of variation below 1 % for the signal intensity of the virtual phantoms. An excellent linearity (coefficient of determination r 2 = 0.997 as assessed by linear regression) was observed in the signal intensity of virtual phantoms. Conclusion Virtual phantoms represent an attractive alternative to physical phantoms for providing a reference signal. MR images of virtual phantoms were here generated using a stand-alone, independent unit that can be employed with MR scanners from different vendors.
      PubDate: 2014-10-01
  • In vivo proton magnetic resonance spectroscopic imaging of the healthy
           human brain at 9.4 T: initial experience
    • Abstract: Object In this study, the feasibility of in vivo proton magnetic resonance spectroscopic imaging (1H MRSI) of the healthy human brain at a field strength of 9.4 T, using conventional acquisition techniques, is examined and the initial experience is summarized. Materials and methods MRSI measurements were performed on a 9.4 T MR scanner (Siemens, Erlangen, Germany) equipped with head-only gradient insert (AC84, Siemens) and custom-developed, 8-channel transmit/24-channel receive, and 16-channel transmit/31-channel receive coils. Spectra were acquired from the superior part of the human brain with a modified STEAM sequence. Spectral quantification was done with LCModel software. Results Reasonable quality and signal-to-noise ratio of the acquired spectra allowed reliable quantification of 12 metabolites (Cramer-Rao lower bounds < 20 %), some of which may be difficult to quantify at field strengths below 7 T due to overlapping resonances or low concentrations. Conclusion While further developments are necessary to minimize chemical shift displacement and homogeneity of the transmit field, it is demonstrated that in vivo 1H MRSI at a field strength of 9.4 T is possible. However, further studies applying up-to-date techniques to overcome high-field specific problems are needed in order to assess the potential gain in sensitivity that may be offered by MRSI at 9.4 T.
      PubDate: 2014-09-24
  • Characterizing blood oxygen level-dependent (BOLD) response following
           in-magnet quadriceps exercise
    • Abstract: Object There have been no studies to investigate the effects of cycling exercise protocols, as well as repeated bouts of exercise, on the blood oxygen level-dependent (BOLD) response in the quadriceps muscles. This study characterized BOLD signal recovery following non-ischemic bouts of exercise in the quadriceps muscles of healthy adults in order to provide a basis for application of a protocol for clinical populations. Materials and methods Healthy male subjects (23.7 ± 2.0 years of age, n = 10) completed three cycles of one-minute exercise (65 % of maximum workload), with two  minutes of rest between each bout, on an MRI-compatible ergometer. The BOLD responses during recovery were fitted to a sigmoid model, and response kinetics (post-exercise intensity [S0]), response time (α), change in baseline BOLD signal (κ), and inflection point (β)] were measured. Results The sigmoid function fit well to the post-exercise BOLD data (r 2 = 0.95 ± 0.04). The mean response time was 10.5 ± 3.8 seconds, change in baseline BOLD intensity was 0.15 ± 0.068, and time to half-peak was 20.2 ± 8.6 seconds. Conclusion The proposed sigmoid model is a robust method for quantifying quadriceps BOLD response post-exercise without induced ischemia. Extension of this model to evaluate microvascular responses in patients with chronic disease could improve our understanding of exercise intolerance.
      PubDate: 2014-09-24
  • Free-breathing, zero-TE MR lung imaging
    • Abstract: Object The investigation of three-dimensional radial, zero-echo time (TE) imaging for high-resolution, free-breathing magnetic resonance (MR) lung imaging using prospective and retrospective motion correction. Materials and methods Zero-TE was implemented similarly to the rotating-ultra-fast-imaging-sequence, providing 3D, isotropic, radial imaging with proton density contrast. Respiratory motion was addressed using prospective triggering (PT), prospective gating (PG) and retrospective gating (RG) with physiological signals obtained from a respiratory belt and interleaved pencil beam and DC navigators. The methods were demonstrated on four healthy volunteers at 3T. Results 3D, radial zero-TE imaging with high imaging bandwidth and nominally zero echo-time enables efficient capture of short-lived signals from the lung parenchyma and the vessels. Compared to Cartesian encoding, unaccounted for free-breathing respiration resulted in only benign blurring artifacts confined to the origin of motion. Breath holding froze respiration but achieved only limited image resolution (~1.8 mm, 30 s). PT and PG obtained similar quality expiratory-phase images at 1.2 mm resolution in ~6 min scan time. RG allowed multi-phase imaging in ~15 min, derived from eight individually stored averages. Conclusion Zero-TE appears to be an attractive pulse sequence for 3D isotropic lung imaging. Prospective and retrospective approaches provide high-quality, free-breathing MR lung imaging within reasonable scan time.
      PubDate: 2014-09-09
  • Development and performance of a 129-GHz dynamic nuclear polarizer in an
           ultra-wide bore superconducting magnet
    • Abstract: Objective We sought to build a dynamic nuclear polarization system for operation at 4.6 T (129 GHz) and evaluate its efficiency in terms of 13C polarization levels using free radicals that span a range of ESR linewidths. Materials and methods A liquid helium cryostat was placed in a 4.6 T superconducting magnet with a 150-mm warm bore diameter. A 129-GHz microwave source was used to irradiate 13C enriched samples. Temperatures close to 1 K were achieved using a vacuum pump with a 453-m3/h roots blower. A hyperpolarized 13C nuclear magnetic resonance (NMR) signal was detected using a saddle coil and a Varian VNMRS console operating at 49.208 MHz. Samples doped with free radicals BDPA (1,3-bisdiphenylene-2-phenylallyl), trityl OX063 (tris{8-carboxyl-2,2,6,6-benzo(1,2-d:4,5-d)-bis(1,3)dithiole-4-yl}methyl sodium salt), galvinoxyl ((2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy), 2,2-diphenylpicrylhydrazyl (DPPH) and 4-oxo-TEMPO (4-Oxo-2,2,6,6-tetramethyl-1-piperidinyloxy) were assayed. Microwave dynamic nuclear polarization (DNP) spectra and solid-state 13C polarization levels for these samples were determined. Results 13C polarization levels close to 50 % were achieved for [1-13C]pyruvic acid at 1.15 K using the narrow electron spin resonance (ESR) linewidth free radicals trityl OX063 and BDPA, while 10–20 % 13C polarizations were achieved using galvinoxyl, DPPH and 4-oxo-TEMPO. Conclusion At this field strength free radicals with smaller ESR linewidths are still superior for DNP of 13C as opposed to those with linewidths that exceed that of the 1H Larmor frequency.
      PubDate: 2014-08-14
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