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1.
The purpose of this study was to investigate the magnetic resonance imaging (MRI) characteristics of colon cancer metastases in rat liver at 7 T. A dedicated RF microstrip coil of novel design was built in order to increase the signal-to-noise ratio and, in combination with respiratory triggering, to minimize motion artifacts. T 1- and T 2-weighted MR imaging was performed to follow tumor growth. T 1-weighted images provided a good anatomical delineation of the liver structure, while the best contrast between metastases and normal liver tissue was achieved with T 2-weighted images.Measurements of T 1 and T 2 relaxation times were performed with inversion recovery FLASH and Carr–Purcell–Meiboom–Gill and inversion recovery FLASH imaging sequences, respectively, for quantitative MR characterization of metastases. Both the T 1 and T 2 of the metastases were significantly higher than those of normal liver tissue. Further, an increase in the T 1 relaxation time of the metastases was observed with tumor growth. These findings suggest that quantitative in vivo MR characterization provides information on tumor development and possibly response to therapy, though additional studies are needed to elucidate the correlation between the changes in relaxation times and tumor microenvironment. 相似文献
2.
ObjectiveTo implement magnetic resonance fingerprinting (MRF) on a permanent magnet 50 mT low-field system deployable as a future point-of-care (POC) unit and explore the quality of the parameter maps. Materials and methods3D MRF was implemented on a custom-built Halbach array using a slab-selective spoiled steady-state free precession sequence with 3D Cartesian readout. Undersampled scans were acquired with different MRF flip angle patterns and reconstructed using matrix completion and matched to the simulated dictionary, taking excitation profile and coil ringing into account. MRF relaxation times were compared to that of inversion recovery (IR) and multi-echo spin echo (MESE) experiments in phantom and in vivo. Furthermore, B0 inhomogeneities were encoded in the MRF sequence using an alternating TE pattern, and the estimated map was used to correct for image distortions in the MRF images using a model-based reconstruction. ResultsPhantom relaxation times measured with an optimized MRF sequence for low field were in better agreement with reference techniques than for a standard MRF sequence. In vivo muscle relaxation times measured with MRF were longer than those obtained with an IR sequence (T1: 182 ± 21.5 vs 168 ± 9.89 ms) and with an MESE sequence (T2: 69.8 ± 19.7 vs 46.1 ± 9.65 ms). In vivo lipid MRF relaxation times were also longer compared with IR (T1: 165 ± 15.1 ms vs 127 ± 8.28 ms) and with MESE (T2: 160 ± 15.0 ms vs 124 ± 4.27 ms). Integrated ΔB0 estimation and correction resulted in parameter maps with reduced distortions. DiscussionIt is possible to measure volumetric relaxation times with MRF at 2.5 × 2.5 × 3.0 mm3 resolution in a 13 min scan time on a 50 mT permanent magnet system. The measured MRF relaxation times are longer compared to those measured with reference techniques, especially for T2. This discrepancy can potentially be addressed by hardware, reconstruction and sequence design, but long-term reproducibility needs to be further improved. 相似文献
3.
T
1 and T
2 relaxation times were measured on human tissue samples of adipose tissue, muscle, bone marrow and osteolytic skeletal metastases at temperatures ranging from +37°C to –10°C. Relative signal intensities for T
1, proton density and T
2-weighted imaging sequences were also calculated. T
1 and T
2 of adipose tissue decreased almost linearly with decreasing temperature while for muscle, bone marrow and metastases T
1 and T
2 decreased slightly to moderately, with temperature reduction to about –5 °C at which temperature a sudden marked decrease occurred. Calculated signal intensities showed a decrease in image contrast with temperature reduction and reversal of contrast between adipose tissue and the other tested tissues with all imaging sequences at temperatures around 0°C. 相似文献
4.
ObjectiveTo determine T1 and T2 relaxation times of healthy pancreas parenchyma at 7 T using a multi-transmit system. Materials and methodsTwenty-six healthy subjects were scanned with a 7 T MR system using eight parallel transceiver antennas, each with two additional receive loops. A Look-Locker sequence was used to obtain images for T1 determination, while T2 was obtained from spin-echo images and magnetic resonance spectroscopy measurements with different echo times. T1 and T2 times were calculated using a mono-exponential fit of the average magnitude signal from a region of interest in the pancreas and were tested for correlation with age. ResultsThe age range of the included subjects was 21–72 years. Average T1 and T2 relaxation times in healthy pancreas were 896 ± 149 ms, and 26.7 ± 5.3 ms, respectively. No correlation with age was found. ConclusionT1 and T2 relaxation times of the healthy pancreas were reported for 7 T, which can be used for image acquisition optimization. No significant correlations were found between age and T1 or T2 relaxation times of the pancreas. Considering their low standard deviation and no observable age dependence, these values may be used as a baseline to study potentially pancreatic tissue affected by disease. 相似文献
5.
Quantitative proton spectroscopy was performed on 26 volunteers and 9 patients using STEAM. Voxels (8 ml) were localized within white matter or meningioma and water-suppressed spectra acquired with TR=2 s at three echo times. Concentrations were calculated using individual relaxation parameter values with tissue water as an internal reference. Compared to white matter, meningiomas were characterized by an increased choline/creatine ratio, the absence of N-acetylasparate, and the presence of alanine. Further, the T
2 of choline and its concentration were both significantly greater in meningiomas than white matter ( p<0.01). Thus, the high choline/creatine ratio seen in meningioma spectra is the consequence of a greater concentration and a longer T
2. The longer T
2 may reflect differences in the relative proportions of choline-containing compounds. Our data demonstrate that individual measurements of relaxation parameters are important for long echo spectra and may reveal important metabolic information. 相似文献
6.
Previous NMR microimaging studies at 360 MHz have demonstrated a clear differentiation between the nucleus and cytoplasm in isolated single neurons. In particular, the T
2 of the cell nucleus is 2.5 times larger than that of the cytoplasm. In order to determine the magnitude of possible T
2
*
influences on these observations, images of single cells have been obtained at 500 MHz using spin-echo and line-narrowing sequences. Comparison of the images acquired by the two sequences, and of the spin-echo images at 360 and 500 MHz, imply that any T
2
*
contributions are relatively small. Consequently, the measured T
2 differences in spin-echo imaging represent a true difference in the T
2 relaxation in the two cellular compartments. 相似文献
7.
Objective19F MRI requires biocompatible and non-toxic soluble contrast agents with high fluorine content and with suitable 19F relaxation times. Probes based on a DOTP chelate with 12 magnetically equivalent fluorine atoms (DOTP-tfe) and a lanthanide(III) ion shortening the relaxation times were prepared and tested. MethodsComplexes of DOTP-tfe with trivalent paramagnetic Ce, Dy, Ho, Tm, and Yb ions were synthetized and characterized. 19F relaxation times were determined and compared to those of the La complex and of the empty ligand. In vitro and in vivo 19F MRI was performed at 4.7 T. Results19F relaxation times strongly depended on the chelated lanthanide(III) ion. T1 ranged from 6.5 to 287 ms, T2 from 3.9 to 124.4 ms, and T2* from 1.1 to 3.1 ms. All complexes in combination with optimized sequences provided sufficient signal in vitro under conditions mimicking experiments in vivo (concentrations 1.25 mM, 15-min scanning time). As a proof of concept, two contrast agents were injected into the rat muscle; 19F MRI in vivo confirmed the in vivo applicability of the probe. ConclusionDOTP-based 19F probes showed suitable properties for in vitro and in vivo visualization and biological applications. The lanthanide(III) ions enabled us to shorten the relaxation times and to trim the probes according to the actual needs. Similar to the clinically approved Gd3+ chelates, this customized probe design ensures consistent biochemical properties and similar safety profiles. 相似文献
8.
A new magnetic resonance imaging high-resolution sequence is presented that allows for the collection of all data for determination of T
1 and as well as for multiexponential T
2 analysis within one measurement cycle.Noise preprocessing is performed in order to avoid systematic errors in relaxation parameter analysis and to increase the interexperimental reproducibility of the results. For T
2 analysis, an optimized Marquardt algorithm is used, in combination with image processing methods for both automatic detection of voxels with partial volume effects, and for speedup of the iterative nonlinear regression steps. Determination of longitudinal relaxation time is based on a sophisticated signal intensity ratio technique that computes T
1 as the mean of up to eight individual T
1 values, each weighted with its relative T
2 decay. Relative proton density is computed using results of the evaluations of both relaxation times. Validation of the method is accomplished by comparing phantom measurements with reference data acquired with spectroscopic sequences. In vivo examples of the computed parameter images taken from a study of experimental cerebral infarcts in rats are presented.The method allows one to acquire high-resolution parameter images within a measurement time that is tolerable even in clinical routine. Furthermore, the chosen evaluation concepts guarantee a short computation time. Therefore, an on-line computation of the parameter images and, in consequence, their direct use for diagnostic purposes appears feasible. 相似文献
9.
Objective: Nanosized materials of gadolinium oxide can provide high-contrast enhancement in magnetic resonance imaging (MRI). The objective of the present study was to investigate proton relaxation enhancement by ultrasmall (5 to 10 nm) Gd 2O 3 nanocrystals.
Materials and methods: Gd 2O 3 nanocrystals were synthesized by a colloidal method and capped with diethylene glycol (DEG). The oxidation state of Gd 2O 3 was confirmed by X-ray photoelectron spectroscopy. Proton relaxation times were measured with a 1.5-T MRI scanner. The measurements were performed in aqueous solutions and cell culture medium (RPMI).
Results: Results showed a considerable relaxivity increase for the Gd 2O 3–DEG particles compared to Gd-DTPA. Both T
1 and T
2 relaxivities in the presence of Gd 2O 3–DEG particles were approximately twice the corresponding values for Gd–DTPA in aqueous solution and even larger in RPMI. Higher signal intensity at low concentrations was predicted for the nanoparticle solutions, using experimental data to simulate a T 1-weighted spin echo sequence.
Conclusion: The study indicates the possibility of obtaining at least doubled relaxivity compared to Gd–DTPA using Gd 2O 3–DEG nanocrystals as contrast agent. The high T
1 relaxation rate at low concentrations of Gd 2O 3 nanoparticles is very promising for future studies of contrast agents based on gadolinium-containing nanocrystals. 相似文献
10.
1H spin-lattice relaxation curves were acquired for samples of intestinal adenocarcinoma (B) and of uninvolved tissue at the upper (A) and lower (C) resection margin of lengths of intestine taken at surgery from 20 patients. Each sample showed a wide distribution of relaxation times with the order of 90% of the signal in a single peak at long times. Several different single-parameter relaxation times computed from discrete-exponential analysis showed that most of the relaxation times for C and B are in the upper two-thirds of the range of times for A. The mean time for the tumor is about 10% longer (with s p<0.01) than for the upper resection margin. The difference between the tumor and the lower resection margin is not significant. Distribution width parameters associated with A and C were significantly larger than those associated with the tumors. Two-exponential fits indicate that the fast-relaxing component represents a smaller signal fraction for the tumor B than for A or C. 相似文献
11.
Object A novel method of estimating metabolite T
1 relaxation times using MR spectroscopic imaging (MRSI) is proposed. As opposed to conventional single-voxel metabolite T
1 estimation methods, this method investigates regional and gray matter (GM)/white matter (WM) differences in metabolite T
1 by taking advantage of the spatial distribution information provided by MRSI.
Material and methods The method, validated by Monte Carlo studies, involves a voxel averaging to preserve the GM/WM distribution, a non-linear
least squares fit of the metabolite T
1 and an estimation of its standard error by bootstrapping. It was applied in vivo to estimate the T
1 of N-acetyl compounds (NAA), choline, creatine and myo-inositol in eight normal volunteers, at 1.5 T, using a short echo
time 2D-MRSI slice located above the ventricles.
Results WM- T
1,NAA was significantly ( P < 0.05) longer in anterior regions compared to posterior regions of the brain. The anterior region showed a trend of a longer
WM T
1 compared to GM for NAA, creatine and myo-Inositol. Lastly, accounting for the bootstrapped standard error estimate in a group
mean T
1 calculation yielded a more accurate T
1 estimation.
Conclusion The method successfully measured in vivo metabolite T
1 using MRSI and can now be applied to diseased brain. 相似文献
12.
ObjectiveTemperature controlled T1 and T2 relaxation times are measured on NiCl2 and MnCl2 solutions from the ISMRM/NIST system phantom at low magnetic field strengths of 6.5 mT, 64 mT and 550 mT. Materials and methodsThe T1 and T2 were measured of five samples with increasing concentrations of NiCl2 and five samples with increasing concentrations of MnCl2. All samples were scanned at 6.5 mT, 64 mT and 550 mT, at sample temperatures ranging from 10 °C to 37 °C. ResultsThe NiCl2 solutions showed little change in T1 and T2 with magnetic field strength, and both relaxation times decreased with increasing temperature. The MnCl2 solutions showed an increase in T1 and a decrease in T2 with increasing magnetic field strength, and both T1 and T2 increased with increasing temperature. DiscussionThe low field relaxation rates of the NiCl2 and MnCl2 arrays in the ISMRM/NIST system phantom are investigated and compared to results from clinical field strengths of 1.5 T and 3.0 T. The measurements can be used as a benchmark for MRI system functionality and stability, especially when MRI systems are taken out of the radiology suite or laboratory and into less traditional environments.
相似文献
13.
In vivo proton ( 1H) magnetic resonance spectroscopy (MRS) can measure cerebral metabolite concentrations and nuclear relaxation times. Function of the sodium (Na +)/potassium (K +) pump in cell membranes depends on adequate adenosine triphosphate (ATP) levels: intracellular Na + is normally extruded in exchange for extracellular K +. Low ATP will cause pump dysfunction and loss of K + accompanied by influx of Na +and water. Raised intracellular water may increase molecular mobility and this might be detectable as increased apparent transverse relaxation times ( T
2's). 1H-MRS of the brains of newborn piglets during acute hypoxia-ischemia revealed enigmatic increases in the peak area of creatine + phosphocreatine (Cr) relative to those of choline-containing compounds (Cho) and N-acetylaspartate (NAA). Interleaved 1H and phosphorus ( 31P) MRS showed that the T
2's of both Cr and lactate (Lac) increased during acute hypoxia-ischemia and these changes correlated with reductions in nucleotide triphosphate (NTP; largely ATP). Within 50 h of metabolic recovery from the primary insult, as delayed energy failure developed, the T
2's of Cho, Cr, NAA, and Lac increased greatly. These T
2 changes also correlated with NTP depletion. These observations demonstrate important relationships between T
2's and function of the ATP-dependent Na +/K + pump. 相似文献
15.
An oxidative insult can induce severe damage, as in the phenomenon of myocardial ischemia and reperfusion. However, there
are situations in which the damage is not so obvious (e.g., silent ischemia or aging), and the negative effects will be seen
only in time. Our aim was to reveal these small changes in the myofilaments by using the nuclear magnetic resonance (NMR)
technique. We used Wistar rat hearts in a constant-pressure Langendorff system, perfused with oxygenated Krebs-Henseleit buffer
at 37°C. After 15 minutes of stabilization, the hearts were perfused with buffer supplemented with H 2O 2 at 50, 75, or 100 μmol/L for 15 or 30 minutes. Fifteen-minute and 45-minute perfusion controls and unperfused hearts were
also collected. Heart rate (HR) and left ventricular developed pressure (LVDP) were determined with the help of a latex balloon,
inserted in the left ventricle and connected with a pressure transducer. Proton transverse relaxation times ( T
2) were determined at the end of the experiment. T
2 values were measured again in the same tissue fragments after they had been glycerinated and incubated in relaxation and
rigor media. The functional parameters (HR, LVDP, coronary flow) were not significantly changed in control and 50 μmol/L H 2O 2 groups but were increased in the 75 μmol/L H 2O 2 group and significantly decreased in the 100 μmol/L H 2O 2 group. T
2 is significantly decreased in rigor media starting with 50 μmol/L H 2O 2 administrated for 30 minutes and does not correlate with dose and duration of the oxidative insult. T
2 in rigor is shorter than in relaxation media within the groups, and this difference is increased in the treated hearts. 相似文献
16.
Relaxometry revealed changes in the basal ganglia in T 1 and T 2 relaxation times due to liver disease. Manganese is probably responsible for T 1 and T 2 shortening (as the concentration is known to be higher in both the liver and blood due to hepatic cirrhosis). The aim of
this study was to follow possible recovery after liver transplantation by MR relaxometry. Together with a group of 20 healthy
volunteers we scanned 53 patients before and after liver transplantation (some of them repeatedly). Both T 1 and T 2 values were evaluated in the basal ganglia, thalamus, and frontal white matter. T 1, relaxation timewas shortened by approx. 20–25% compared to the control group, probably the result of manganese deposition
in the brain caused by hepatic cirrhosis. After liver transplantation the relaxation time recovered gradually with almost
normal values reached approx. 2 years after surgery. T 1, recovery was observed in all evaluated structures. Similar results were observed with T 2 relaxation in the basal ganglia and thalamus. In the white matter T 2 remained low even 2 years after surgery. 相似文献
17.
Object To evaluate the feasibility of mouse spinal cord MR imaging using echo-planar imaging (EPI).
Materials and methods Optimized multi-shot spin-echo-EPI sequences were compared to conventional spin-echo (c-SE) at 11.75 T and used for high-spatially
resolved acquisitions and relaxation-time measurements.
Results Good quality images were obtained, with clear delineation of gray and white matter. Acquisition-time gain factor was up to
6 (vs. c-SE) and resolution up to 74 × 94 μm 2 was achieved. T
1 and T
2 relaxation times were reliably measured.
Conclusion High-temporally and spatially resolved mouse spinal cord EPI imaging is feasible. This technique should greatly benefit to
long acquisition-time experiments (diffusion imaging) and imaging of rapidly-evolving pathologies.
V. Callot and G. Duhamel equally contributed to this work. 相似文献
18.
The impact-ionization coefficient α
n
at high fields is derived in terms of the electric field ℰ and lattice temperature T
L
, without introducing a priori relations among the parameters. An asymptotic analysis leads to simplifications that validate closed-form expressions of
α
n
. The role of the relaxation times in determining the slope of α
n
(ℰ) is discussed, along with the meaning of the critical field. 相似文献
19.
On-resonant radio frequency (RF) sequences composed of a train of short rectangular pulses of the same kind were optimized in order to obtain selective saturation of protons with short transverse relaxation times for magnetization transfer purposes. It is demonstrated that the sequences regarded allow a good adaptation to different requirements for magnetization transfer examinations on whole-body imagers. The sequences presented here provide relatively strong saturation of protons with very short transverse relaxation times T
250 µs, whereas signals from protons with long T
2 to be recorded are hardly influenced in a broad frequency range. The sequences are especially advantageous for applications in pulse files with limited numbers of support points. 相似文献
20.
Objective The aim of this study is to present a new approach for making quantitative single-voxel T
2 measurements from an arbitrarily shaped region of interest (ROI), where the advantage of the signal-to-noise ratio (SNR)
per unit time of the single-voxel approach over conventional imaging approach can be achieved.
Materials and methods Two-dimensional (2D) spatially selective radiofrequency (RF) pulses are proposed in this work for T
2 measurements based on using interleaved spiral trajectories in excitation k-space (pinwheel excitation pulses), combined with a summed Carr–Purcell Meiboom–Gill (CPMG) echo acquisition. The technique
is described and compared to standard multi-echo imaging methods, on a two-compartment water phantom and an excised brain
tissue.
Results The studies show good agreement between imaging and our method. The measured improvement factors of SNR per unit time of our
single-voxel approach over imaging approach are close to the predicted values.
Conclusion Measuring T
2 relaxation times from a selected ROI of arbitrary shape using a single-voxel rather than an imaging approach can increase
the SNR per unit time, which is critical for dynamic T
2 or multi-component T
2 measurements. 相似文献
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