共查询到20条相似文献,搜索用时 31 毫秒
1.
Conrad Rockel Alireza Akbari Dinesh A. Kumbhare Michael D. Noseworthy 《Magma (New York, N.Y.)》2017,30(2):127-138
Object
To assess post-exercise recovery of human calf muscles using dynamic diffusion tensor imaging (dDTI).Materials and methods
DTI data (6 directions, b = 0 and 400 s/mm2) were acquired every 35 s from seven healthy men using a 3T MRI, prior to (4 volumes) and immediately following exercise (13 volumes, ~7.5 min). Exercise consisted of 5-min in-bore repetitive dorsiflexion-eversion foot motion with 0.78 kg resistance. Diffusion tensors calculated at each time point produced maps of mean diffusivity (MD), fractional anisotropy (FA), radial diffusivity (RD), and signal at b = 0 s/mm2 (S0). Region-of-interest (ROI) analysis was performed on five calf muscles: tibialis anterior (ATIB), extensor digitorum longus (EDL) peroneus longus (PER), soleus (SOL), and lateral gastrocnemius (LG).Results
Active muscles (ATIB, EDL, PER) showed significantly elevated initial MD post-exercise, while predicted inactive muscles (SOL, LG) did not (p < 0.0001). The EDL showed a greater initial increase in MD (1.90 × 10?4mm2/s) than ATIB (1.03 × 10?4mm2/s) or PER (8.79 × 10?5 mm2/s) (p = 7.40 × 10?4), and remained significantly elevated across more time points than ATIB or PER. Significant increases were observed in post-exercise EDL S0 relative to other muscles across the majority of time points (p < 0.01 to p < 0.001).Conclusions
dDTI can be used to differentiate exercise-induced changes between muscles. These differences are suggested to be related to differences in fiber composition.2.
Aguor EN Arslan F van de Kolk CW Nederhoff MG Doevendans PA van Echteld CJ Pasterkamp G Strijkers GJ 《Magma (New York, N.Y.)》2012,25(5):369-379
Object
Imaging of myocardial infarct composition is essential to assess efficacy of emerging therapeutics. T 2 * mapping has the potential to image myocardial hemorrhage and fibrosis by virtue of its short T 2 * . We aimed to quantify T 2 * in acute and chronic myocardial ischemia/reperfusion (I/R) injury in mice.Materials and methods
I/R-injury was induced in C57BL/6 mice (n?=?9). Sham-operated mice (n?=?8) served as controls. MRI was performed at baseline, and 1, 7 and 28?days after surgery. MRI at 9.4?T consisted of Cine, T 2 * mapping and late-gadolinium-enhancement (LGE). Mice (n?=?6) were histologically assessed for hemorrhage and collagen in the fibrotic scar.Results
Baseline T 2 * values were 17.1?±?2.0?ms. At day 1, LGE displayed a homogeneous infarct enhancement. T 2 * in infarct (12.0?±?1.1?ms) and remote myocardium (13.9?±?0.8?ms) was lower than at baseline. On days 7 and 28, LGE was heterogeneous. T 2 * in the infarct decreased to 7.9?±?0.7 and 6.4?±?0.7?ms, whereas T 2 * values in the remote myocardium were 14.2?±?1.1 and 15.6?±?1.0?ms. Histology revealed deposition of iron and collagen in parallel with decreased T 2 * .Conclusion
T 2 * values are dynamic during infarct development and decrease significantly during scar maturation. In the acute phase, T 2 * values in infarcted myocardium differ significantly from those in the chronic phase. T 2 * mapping was able to confirm the presence of a chronic infarction in cases where LGE was inconclusive. Hence, T 2 * may be used to discriminate between acute and chronic infarctions. 相似文献3.
Nis Elbrønd Larsen Søren Haack Lars Peter Skovgaard Larsen Erik Morre Pedersen 《Magma (New York, N.Y.)》2013,26(5):431-442
Object
Diffusion weighted imaging (DWI) of the liver suffers from low signal to noise making 3 Tesla (3 T) an attractive option, but 3 T data is scarce. It was the aim to study the influence of different b values and respiratory compensation methods (RCM) on the apparent diffusion coefficient (ADC) level and on ADC reproducibility at 3 T.Materials and methods
Ten healthy volunteers and 12 patients with malignant liver lesions underwent repeated (2–22 days) breathhold, free-breathing and respiratory triggered DWI at 3 T using b values between 0 and 1,000 s/mm2.Results
The ADCs changed up to 150 % in healthy livers and up to 48 % in malignant lesions depending on b value combinations. Best ADC reproducibility in healthy livers were obtained with respiratory triggering (95 % limits of agreement: ±0.12) and free-breathing (±0.14). In malignant lesions equivalent reproducibility was obtained with less RCM dependence. The use of a lower maximum b value (b = 500) decreased reproducibility (±0.14 to ±0.32) in both normal liver and malignant lesions.Conclusion
Large differences in absolute ADC values and reproducibility caused by varying combinations of clinically realistic b values were demonstrated. Different RCMs caused smaller differences. Lowering maximum b value to 500 increased limits of agreement up to a factor of two. Serial ADC changes larger than approximately 15 % can be detected confidently on an individual basis in both malignant lesions and normal liver parenchyma at 3 T using appropriate b values and respiratory compensation. 相似文献4.
Object
The nuclear magnetic resonance (NMR) mobile-universal-surface-explorer (MOUSE) was evaluated in a pilot study to determine its ability to detect physiological changes in human skin caused by physical or pharmacological interventions.Materials and methods
The left lower arm skin thicknesses of ten male subjects were measured five times using a Profile NMR-MOUSE? (1H, 19?MHz) before and after a venous occlusion manoeuvre. In five of the subjects, the T2eff relaxation times were derived from a bi-exponential fitting and were determined in the dermis and subcutis before and after applying a salve containing capsaicin.Results
The dermis (including the epidermis) showed rather homogeneous signal amplitudes. The subcutis was characterised by higher and more variable amplitudes. The full-skin thickness values were affirmed by ultrasound imaging. The NMR profiles did not show significant skin swelling due to venous occlusion. In the dermis, capsaicin caused significant (p?<?0.05) decreases in both components of T 2eff (100?±?19?ms?C19?±?10?ms; 9.5?±?0.5?ms?C7.2?±?1.6?ms). In the subcutis, the T 2eff was not affected.Conclusion
In principle, NMR-MOUSE profiles are capable of detecting skin structure. However, precise measurements are jeopardised by poor reproducibility, long acquisition times, and incompatibility between the geometries of the sensitive area of the instrument and the non-planar structure of the skin. In the dermis, T 2eff contrast could be used to detect the changes in tissue composition caused by inflammatory reactions. 相似文献5.
João Pedro Filipe Luís Curvo-Semedo João Casalta-Lopes Maria Cristina Marques Filipe Caseiro-Alves 《Magma (New York, N.Y.)》2013,26(3):303-312
Object
By measuring the apparent diffusion coefficient (ADC) of liver parenchyma and focal hepatic lesions (FHL) we proposed to investigate the utility of ADC in the differential diagnosis of hepatic disease and to determine the influence of region of interest (ROI) characteristics in those measurements.Materials and methods
Ninety-three patients with at least one supracentimetric FHL, or parenchymal abnormality, were retrospectively evaluated. Diagnosis was based on histopathologic data or, alternatively, on a combination of consensus between imaging methods and 24 months of follow-up. Ninety lesions were evaluated with respiratory-triggered diffusion-weighted imaging (b values: 50 and 700 s/mm2): 14 hepatocellular carcinomas, 18 metastases, 10 focal nodular hyperplasias, four adenomas, 30 hemangiomas and 14 cysts. ADC of hepatic parenchyma was measured by placing ROIs in four different segments, and in FHLs by using three circular 1 cm2 ROIs and one ROI encompassing the full lesion. Data was statistically analyzed (p < 0.05 considered significant), and a receiver operating characteristic curve was assessed to evaluate the accuracy for the diagnosis of malignancy.Results
Our measurements showed that parenchyma ADC was significantly higher in segment II and that ADCs of malignant lesions were significantly lower than those of benign lesions (p < 0.001). There was significant overlap between benign solid lesions and malignant lesions and the area under the curve for malignancy was 0.939 (sensitivity 89.7 %, specificity 90.6 %), using a cutoff of 1.43 × 10?3 mm2/s. No significant difference was found between ROIs of different characteristics.Conclusion
ADC measurements can help to characterize FHLs and differentiate normal from pathological parenchyma. Any ROI above 1 cm2 can provide accurate ADC measurements in homogenous lesions. 相似文献6.
Christian Eberhardt Moritz C. Wurnig Andrea Wirsching Cristina Rossi Markus Rottmar Pinar S. Özbay Lukas Filli Mickael Lesurtel Andreas Boss 《Magma (New York, N.Y.)》2016,29(5):751-763
Objective
Diffusion-weighted magnetic resonance imaging (DW-MRI) combined with intravoxel incoherent motion (IVIM) analysis may be applied for assessment of organ lesions, diffuse parenchymal pathologies, and therapy monitoring. The aim of this study was to determine IVIM reference parameters of abdominal organs for translational research in a large cohort of C57Bl/6 laboratory mice.Materials and methods
Anesthetized mice (n = 29) were measured in a 4.7 T small-animal MR scanner with a diffusion-weighted echo-planar imaging sequence at the \(b\)-values 0, 13, 24, 55, 107, 260, 514, 767, 1020 s/mm2. IVIM analysis was conducted on the liver, spleen, renal medulla and cortex, pancreas, and small bowel with computation of the true tissue diffusion coefficient \(D_{\text{t}}\), the perfusion fraction \(f_{\text{p}}\), and the pseudodiffusion coefficient \(D_{\text{p}}\). Microvessel density (MVD) was assessed by immunohistochemistry (IHC) against panendothelial cell antigen CD31.Results
Mean values of the different organs [\(D_{\text{t}}\) (10?3 mm2/s); \(f_{\text{p}}\) (%); \(D_{\text{p}}\) (10?3 mm2/s); MVD (MV/mm2)]: liver 1.15 ± 0.14; 14.77 ± 6.15; 50.28 ± 33.21, 2008.48 ± 419.43, spleen 0.55 ± 0.12; 9.89 ± 5.69; 24.46 ± 17.31; n.d., renal medulla 1.50 ± 0.20; 14.63 ± 4.07; 35.50 ± 18.01; 1231.88 ± 290.61, renal cortex 1.34 ± 0.18; 10.83 ± 3.70; 16.74 ± 6.74; 810.09 ± 193.50, pancreas 1.23 ± 0.22; 20.12 ± 7.46; 29.35 ± 17.82, 591.15 ± 86.25 and small bowel 1.06 ± 0.13; 16.48 ± 3.63; 15.31 ± 7.00; 420.50 ± 168.42. Unlike \(D_{\text{t}}\) and \(f_{\text{p}}\), \(D_{\text{p}}\) correlates significantly with MVD (r = 0.90, p = 0.037).Conclusion
This systematic evaluation of murine abdominal organs with IVIM and MVD analysis allowed to establish reference parameters for future DW-MRI translational research studies on small-animal disease models.7.
Jana Taron Petros Martirosian Nina F. Schwenzer Michael Erb Thomas Kuestner Jakob Weiß Ahmed Othman Mike Notohamiprodjo Konstantin Nikolaou Christina Schraml 《Magma (New York, N.Y.)》2016,29(5):739-749
Objective
To evaluate simultaneous multislice (sms) accelerated diffusion-weighted imaging (DWI) of the liver in comparison to conventional sequences.Materials and methods
Ten volunteers underwent DWI of the liver at 1.5 T. Four different sms-accelerated sequences with monopolar and bipolar gradient preparation (MP, BP) and acceleration factors 2 and 3 (sms2-DWI, sms3-DWI) were compared to conventional DWI (c-DWI). Image quality criteria rated on a 5-point Likert scale (5 = excellent), image quality sum scores (maximum 120), and ADC were compared using Friedman test and Dunn-Bonferroni post hoc test. Bland–Altman plots were calculated for ADC comparison. p values <0.05 were considered significant.Results
Sms2-DWI offered scan time minimization of 67 % without significant difference in image quality (sum score: sms2-DWI MP/BP: 97 ± 8/92 ± 9; c-DWI MP/BP: 99 ± 8/97 ± 8). Sms3-DWI offered slight additional scan time minimization with significantly inferior image quality (sum score: sms3-DWI MP/BP: 75 ± 14/69 ± 14; p < 0.001). MP preparation provided slightly higher image quality in sms-DWI without statistical significance. ADC in sms-DWI were significantly lower (sms2-DWI MP 1.01 × 10?3 mm2/s; c-DWI MP 1.20 × 10?3 mm2/s; p < 0.001).Conclusion
Sms2-DWI provides considerable scan time minimization without significant shortcomings in image quality. Sms3-DWI provides significantly inferior image quality without further scan time minimization. Potentially lower ADC in sms-DWI should be considered in clinical routine.8.
Ulrich Grosse Roland Syha Dimitrios Papanikolaou Petros Martirosian Gerd Grözinger Christoph Schabel Fritz Schick Fabian Springer 《Magma (New York, N.Y.)》2013,26(6):555-564
Object
Due to an increasing scientific interest in MR-imaging of carious lesions and teeth, an accurate signal characterization of dental restoration materials is necessary for optimization of MR sequence protocols and evaluation of material degradation. Therefore, signal yield and relaxation behavior of common dental restoration materials in comparison to those of dentine of extracted human teeth were assessed in vitro by ultrashort echo time (UTE) sequences.Materials and methods
Eighteen material samples and dentine of two freshly extracted human teeth were investigated on a 3T whole-body clinical MR-scanner. Transverse (T2*) and longitudinal relaxation times (T1) were quantified using a recently published modified Ernst equation that takes relevant in-pulse relaxation effects into account.Results
All investigated samples could be successfully visualized but maximum signal yield was highly variable between samples. T1-values of the investigated dental restoration materials ranged between 28 and 365 ms, whereas T2*-values ranged between 96 and 917 μs. In contrast, T1-values of dentine (T1 = 545 ms ± 299 ms) were higher, while T2*-values (T2* = 478 μs ± 271 μs) showed similar values.Conclusions
Dental restoration materials and dentine of extracted human teeth can be visualized by UTE sequences and show a broad range of signal yield and relaxation times. 相似文献9.
In vivo chlorine and sodium MRI of rat brain at 21.1 T 总被引:1,自引:1,他引:0
Victor D. Schepkin Malathy Elumalai Jason A. Kitchen Chunqi Qian Peter L. Gor’kov William W. Brey 《Magma (New York, N.Y.)》2014,27(1):63-70
Object
MR imaging of low-gamma nuclei at the ultrahigh magnetic field of 21.1 T provides a new opportunity for understanding a variety of biological processes. Among these, chlorine and sodium are attracting attention for their involvement in brain function and cancer development.Materials and methods
MRI of 35Cl and 23Na were performed and relaxation times were measured in vivo in normal rat (n = 3) and in rat with glioma (n = 3) at 21.1 T. The concentrations of both nuclei were evaluated using the center-out back-projection method.Results
T 1 relaxation curve of chlorine in normal rat head was fitted by bi-exponential function (T 1a = 4.8 ms (0.7) T 1b = 24.4 ± 7 ms (0.3) and compared with sodium (T 1 = 41.4 ms). Free induction decays (FID) of chlorine and sodium in vivo were bi-exponential with similar rapidly decaying components of $ T_{{2{\text{a}}}}^{*} = 0.4 $ ms and $ T_{{2{\text{a}}}}^{*} = 0.53 $ ms, respectively. Effects of small acquisition matrix and bi-exponential FIDs were assessed for quantification of chlorine (33.2 mM) and sodium (44.4 mM) in rat brain.Conclusion
The study modeled a dramatic effect of the bi-exponential decay on MRI results. The revealed increased chlorine concentration in glioma (~1.5 times) relative to a normal brain correlates with the hypothesis asserting the importance of chlorine for tumor progression. 相似文献10.
E. E. Sigmund S. H. Baete K. Patel D. Wang D. Stoffel R. Otazo P. Parasoglou J. Bencardino 《Magma (New York, N.Y.)》2018,31(5):599-608
Objectives
We describe measurement of skeletal muscle kinetics with multiple echo diffusion tensor imaging (MEDITI). This approach allows characterization of the microstructural dynamics in healthy and pathologic muscle.Materials and methods
In a Siemens 3-T Skyra scanner, MEDITI was used to collect dynamic DTI with a combination of rapid diffusion encoding, radial imaging, and compressed sensing reconstruction in a multi-compartment agarose gel rotation phantom and within in vivo calf muscle. An MR-compatible ergometer (Ergospect Trispect) was employed to enable in-scanner plantar flexion exercise. In a HIPAA-compliant study with written informed consent, post-exercise recovery of DTI metrics was quantified in eight volunteers. Exercise response of DTI metrics was compared with that of T2-weighted imaging and characterized by a gamma variate model.Results
Phantom results show quantification of diffusivities in each compartment over its full dynamic rotation. In vivo calf imaging results indicate larger radial than axial exercise response and recovery in the plantar flexion-challenged gastrocnemius medialis (fractional response: nT2w?=?0.385?±?0.244, nMD?=?0.163?±?0.130, nλ1?=?0.110?±?0.093, nλrad?=?0.303?±?0.185). Diffusion and T2-weighted response magnitudes were correlated (e.g., r?=?0.792, p?=?0.019 for nMD vs. nT2w).Conclusion
We have demonstrated the feasibility of MEDITI for capturing spatially resolved diffusion tensor data in dynamic systems including post-exercise skeletal muscle recovery following in-scanner plantar flexion.11.
Yukihisa Takayama Akihiro Nishie Masaaki Sugimoto Osamu Togao Yoshiki Asayama Kousei Ishigami Yasuhiro Ushijima Daisuke Okamoto Nobuhiro Fujita Akira Yokomizo Jochen Keupp Hiroshi Honda 《Magma (New York, N.Y.)》2016,29(4):671-679
Objective
To evaluate the utility of amide proton transfer (APT) imaging in estimating the Gleason score (GS) of prostate cancer (Pca).Materials and methods
Sixty-six biopsy-proven cancers were categorized into four groups according to the GS: GS-6 (3 + 3); GS-7 (3 + 4/4 + 3); GS-8 (4 + 4) and GS-9 (4 + 5/5 + 4). APT signal intensities (APT SIs) and apparent diffusion coefficient (ADC) values of each GS group were compared by one-way analysis of variance with Tukey’s HSD post hoc test.Results
The mean and standard deviation of the APT SIs (%) and ADC values (×10?3 mm2/s) were as follows: GS-6, 2.48 ± 0.59 and 1.16 ± 0.26; GS-7, 5.17 ± 0.66 and 0.92 ± 0.18; GS-8, 2.56 ± 0.85 and 0.86 ± 0.17; GS-9, 1.96 ± 0.75 and 0.85 ± 0.18, respectively. The APT SI of the GS-7 group was highest, and there were significant differences between the GS-6 and GS-7 groups and the GS-7 and GS-9 groups (p < 0.05). The ADC value of the GS-6 group was significantly higher than each value of the GS-7, GS-8, and GS-9 groups (p < 0.05), but no significant differences were obtained among the GS-7, GS-8, and GS-9 groups.Conclusion
The mean APT SI in Pca with a GS of 7 was higher than that for the other GS groups.12.
Stefan Haneder Henrik J. Michaely Simon Konstandin Lothar R. Schad John N. Morelli Bernhard K. Krämer Stefan O. Schoenberg Alexander Lammert 《Magma (New York, N.Y.)》2014,27(1):47-52
Purpose
The purpose of this prospective study was to assess physiologic changes in the renal corticomedullary 23Na-concentration ([23Na]) gradient with 23Na-MRI at 3.0T in patients with central diabetes insipidus (CDI) before and after intranasal administration of 20 μg desmopressin (DDAVP).Methods and materials
Four patients with CDI (all male, mean age 60.2 years) were included in this IRB-approved study. For 23Na-imaging, a 3D density adapted, radial GRE-sequence (TE = 0.55 ms; TR = 120 ms; projections = 8,000; spatial resolution = 5 × 5 × 5 mm3) was used in combination with a dedicated 23Na-coil and reference phantoms. The corticomedullary [23Na] gradient (in mmol/L/mm) was calculated pixel-by-pixel along a linear region-of-interest (ROI) spanning from the renal cortex in the direction of the medulla. Mean ± SDs of [23Na] were calculated for each patient as well as for the entire group.Results
Mean [23Na] increased along the corticomedullary gradient from the cortex (pre-DDAVP 38.0 ± 6.3 mmol/L vs. post-DDAVP 30.7 ± 3.5 mmol/L) to the medulla (pre-DDAVP 71.6 ± 14.8 mmol/L vs. post-DDAVP 59.7 ± 10.8 mmol/L). The overall mean decrease of [23Na] after DDAVP administration was 17.1 ± 1.1 %.Conclusion
23Na-MRI with state-of-the-art techniques at 3T depicts the physiologic renal response to the administration of desmopressin in patients with central diabetes insipidus. 相似文献13.
Stefan Haneder Paul Kettnaker Simon Konstandin John N. Morelli Lothar R. Schad Stefan O. Schoenberg Henrik J. Michaely 《Magma (New York, N.Y.)》2013,26(6):501-509
Objectives
The purpose of this prospective study was to assess the normal physiologic ranges of the renal corticomedullary 23Na-concentration ([23Na]) gradient at 3.0T in healthy volunteers. The corticomedullary [23Na] gradient was correlated with other functional MR imaging parameters—blood oxygenation level dependent (BOLD) and diffusion-weighted imaging (DWI)—and to individual and physiologic parameters—age, gender, estimated glomerular filtration rate (eGFR), body mass index (BMI), and blood serum sodium concentration ([23Na]serum).Methods and materials
50 healthy volunteers (30 m, 20 w; mean age: 29.2 years) were included in this IRB-approved study, without a specific a priori preparation in regard to water or food intake. For 23Na-imaging a 3D density adapted, radial gradient echo (GRE)-sequence (spatial resolution = 5 × 5 × 5 mm3) was used in combination with a dedicated 23Na-coil and 23Na-reference phantoms. [23Na] values of the corticomedullary [23Na] gradient were measured by placement of a linear region of interest (20 × 1 mm2) from the renal cortex in the direction of the renal medulla. By using external standard reference phantoms, [23Na] was calculated in mmol/L of wet tissue volume (mmol/l WTV). Axial diffusion-weighted images (spatial resolution = 1.7 × 1.7 × 5.0 mm3) and 2D GRE BOLD images (spatial resolution = 1.2 × 1.2 × 4.0 mm3) were acquired. Mean values ± standard deviations for [23Na], apparent diffusion coefficient (ADC) values, and R2* values were computed for each volunteer. The corticomedullary 23Na-concentration gradient (in mmol/l/mm) was calculated along the area of linear concentration increase from the cortex in the direction of the medulla. Correlations between the [23Na] and DWI, BOLD, and the physiologic parameters were assessed with Pearson correlation coefficients.Results
The mean corticomedullary [23Na] for all healthy volunteers increased from the renal cortex (58 ± 17 mmol/l WTV) in the direction of the medulla (99 ± 18 mmol/l WTV). The inter-individual differences ranged from respective cortical and medullary values of 27 and 63 mmol/L WTV to 126 and 187 mmol/L WTV. No statistically significant differences in renal [23Na] were found based on differences in individual or physiologic parameters (age, gender, [23Na]serum, BMI, GFR). No ADC or R2* gradients were identified, and [23Na] did not correlate with these parameters.Conclusion
Renal corticomedullary [23Na] values increase from the cortex in the direction of the medullary pyramid, demonstrating wide inter-individual ranges and no significant correlations with age, gender, [23Na]serum, BMI, GFR, ADC, or R2* values. For future clinical evaluations, an approach relying on renal stimulation (e.g. pharmacologically induced diuresis) may be applicable to account for wide inter-individual ranges of normal [23Na]. 相似文献14.
Jessica Schulz Thomas Siegert Enrico Reimer Christian Labadie Julian Maclaren Michael Herbst Maxim Zaitsev Robert Turner 《Magma (New York, N.Y.)》2012,25(6):443-453
Object
Prospective motion correction using data from optical tracking systems has been previously shown to reduce motion artifacts in MR imaging of the head. We evaluate a novel optical embedded tracking system.Materials and methods
The home-built optical embedded tracking system performs image processing within a 7T scanner bore, enabling high speed tracking. Corrected and uncorrected in vivo MR volumes are acquired interleaved using a modified 3D FLASH sequence, and their image quality is assessed and compared.Results
The latency between motion and correction of the slice position was measured to be (19?±?5)?ms, and the tracking noise has a standard deviation no greater than 10???m/0.005° during conventional MR scanning. Prospective motion correction improved the edge strength by 16?% on average, even though the volunteers were asked to remain motionless during the acquisitions.Conclusion
Using a novel method for validating the effectiveness of in vivo prospective motion correction, we have demonstrated that prospective motion correction using motion data from the embedded tracking system considerably improved image quality. 相似文献15.
Chlorine and sodium chemical shift imaging during acute stroke in a rat model at 9.4 Tesla 总被引:1,自引:1,他引:0
Sebastian Baier Philipp Krämer Saskia Grudzenski Marc Fatar Stefan Kirsch Lothar R. Schad 《Magma (New York, N.Y.)》2014,27(1):71-79
Object
A triple-resonant coil setup with an 1H linear resonator and a double-tuned 23Na/35Cl surface coil was used to study the evolution of T 2 * and M 0 for 35Cl and 23Na in a rat stroke model during the acute phase at 9.4 Tesla.Materials and methods
In vivo measurements were performed 1.5–7 h after onset of stroke (n = 2), ten days after onset (n = 1) and on a healthy control rat by a chemical shift imaging sequence. Measurement times were 15 min (23Na) and 57 min (35Cl).Results
The relaxation times ten days after onset [T 2 * = 14.3 ± 1.8 ms (23Na) and 6.0 ± 1.3 ms (35Cl)] are clearly prolonged in comparison to a healthy rat [T 2 * = 4.8 ± 0.6 ms (23Na) and 2.1 ± 0.3 ms (35Cl)] and the acute phase [T 2 * = 5.6 ± 0.2 ms (23Na) and 1.9 ± 0.1 ms (35Cl)].Conclusion
M 0 in the infarcted region clearly rises later and slower for chlorine than for sodium. To the best of our knowledge, these are the first combined proton, sodium, and chlorine measurements in an animal stroke model during the acute phase. 相似文献16.
Edyta Blaszczyk Agnieszka Töpper Luisa Schmacht Felix Wanke Andreas Greiser Jeanette Schulz-Menger Florian von Knobelsdorff-Brenkenhoff 《Magma (New York, N.Y.)》2017,30(1):85-91
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.17.
Peter T. While Jose R. Teruel Igor Vidić Tone F. Bathen Pål Erik Goa 《Magma (New York, N.Y.)》2018,31(3):425-438
Objective
To explore the relationship between relative enhanced diffusivity (RED) and intravoxel incoherent motion (IVIM), as well as the impact of noise and the choice of intermediate diffusion weighting (b value) on the RED parameter.Materials and methods
A mathematical derivation was performed to cast RED in terms of the IVIM parameters. Noise analysis and b value optimization was conducted by using Monte Carlo calculations to generate diffusion-weighted imaging data appropriate to breast and liver tissue at three different signal-to-noise ratios.Results
RED was shown to be approximately linearly proportional to the IVIM parameter f, inversely proportional to D and to follow an inverse exponential decay with respect to D*. The choice of intermediate b value was shown to be important in minimizing the impact of noise on RED and in maximizing its discriminatory power. RED was shown to be essentially a reparameterization of the IVIM estimates for f and D obtained with three b values.Conclusion
RED imaging in the breast and liver should be performed with intermediate b values of 100 and 50 s/mm2, respectively. Future clinical studies involving RED should also estimate the IVIM parameters f and D using three b values for comparison.18.
Sheryl L. Herrera Morgan E. Mercredi Richard Buist Melanie Martin 《Magma (New York, N.Y.)》2018,31(5):609-620
Object
Most early methods to infer axon diameter distributions using magnetic resonance imaging (MRI) used single diffusion encoding sequences such as pulsed gradient spin echo (SE) and are thus sensitive to axons of diameters > 5 μm. We previously simulated oscillating gradient (OG) SE sequences for diffusion spectroscopy to study smaller axons including the majority constituting cortical connections. That study suggested the model of constant extra-axonal diffusion breaks down at OG accessible frequencies. In this study we present data from phantoms to test a time-varying interstitial apparent diffusion coefficient.Materials and Methods
Diffusion spectra were measured in four samples from water packed around beads of diameters 3, 6 and 10 μm; and 151 μm diameter tubes. Surface-to-volume ratios, and diameters were inferred.Results
The bead pore radii estimates were 0.60±0.08 μm, 0.54±0.06 μm and 1.0±0.1 μm corresponding to bead diameters ranging from 2.9±0.4 μm to 5.3±0.7 μm, 2.6±0.3 μm to 4.8±0.6 μm, and 4.9±0.7 μm to 9±1 μm. The tube surface-to-volume ratio estimate was 0.06±0.02 μm?1 corresponding to a tube diameter of 180±70 μm.Conclusion
Interstitial models with OG inferred 3-10 μm bead diameters from 0.54±0.06 μm to 1.0±0.1 μm pore radii and 151 μm tube diameters from 0.06±0.02 μm?1 surface-to-volume ratios.19.
Martin S?gaard Anja Bieberle-H��tter Peter Vang Hendriksen Mogens Mogensen Harry Louis Tuller 《Journal of Electroceramics》2011,27(3-4):134-142
Electrical conductivity relaxation measurements were carried out on thin films of (La0.6Sr0.4)0.99 FeO3????? deposited on MgO (100) substrates by pulsed laser deposition in order to determine the surface exchange coefficient, k Ex, of the oxygen incorporation process in the temperature range 550?C700°C. The composition of the films was verified using wavelength dispersive x-ray and Rutherford backscattering spectroscopy. Scanning electron microscopy showed small triangular crystallites with the largest dimension 80 nm and the smallest dimension 10 nm. X-ray diffraction showed a cubic perovskite structure and significant texturing. At a constant temperature, k Ex was found to be a function only of the final $p_{\mathrm{O_{2}}}$ of the $p_{\mathrm{O_{2}}}$ -changes the sample was subjected to during conductivity relaxation experiments, confirming that the magnitude of the exchange coefficient was not influenced by changes in ionic defect concentrations. The k Ex-values determined for these thin films were significantly lower than for bulk samples. A value of 3.6 × 10???6 cm s???1 was obtained at 702°C and a final $p_{\mathrm{O_{2}}}$ of 0.048 atm, approximately a factor of six lower than that obtained for bulk samples. An activation energy of 282 ± 20 kJ mol???1 was found for the surface exchange coefficient at $p_{\mathrm{O_{2}}}$ =?0.048 atm. Possible reasons for the reduced magnitude of k Ex are discussed including the role of thermal history in influencing surface morphology and chemistry. 相似文献
20.
Juana Martín-Sitjar Teresa Delgado-Go?i Miquel E. Caba?as Jason Tzen Carles Arús 《Magma (New York, N.Y.)》2012,25(6):487-496