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1.
We previously reported cerebellar and putaminal transverse relaxation time (T2) differences in children with ADHD and in adults with childhood trauma. As brain T2 can be altered by deoxyhemoglobin concentration ([dHb]) and because [dHb] is proportional to regional cerebral blood volume (rCBV), at steady state we attributed those differences to rCBV changes. Studies in other species have established a correlation between T2 and rCBV; however this has yet to be demonstrated in human brain. Echo planar imaging (EPI) T2 relaxometry and dynamic susceptibility-contrast (DSC) MRI were used to measure T2 and rCBV in 11 healthy adults. Significant T2-rCBV correlations were observed in both cerebellar vermis and putamen ( r=0.759, p=0.007; r=0.782, p=0.004, respectively). These correlations predict 9±3% and 10±3% rCBV changes, respectively, for each 1-msec change in T2. Consequently, brain T2 measurements may be useful for estimating steady-state rCBV. 相似文献
2.
Object To determine the single spin-echo T 2 relaxation times of uncoupled and J-coupled metabolites in rat brain in vivo at 14.1 T and to compare these results with those previously obtained at 9.4 T. Materials and methods Measurements were performed on five rats at 14.1 T using the SPECIAL sequence and TE-specific basis-sets for LCModel analysis. Results and conclusion The T 2 of singlets ranged from 98 to 148 ms and T 2 of J-coupled metabolites ranged from 72 ms (glutamate) to 97 ms (myo-inositol). When comparing the T 2s of the metabolites measured at 14.1 T with those previously measured at 9.4 T, a decreasing trend was found ( p < 0.0001). We conclude that the modest shortening of T 2 at 14.1 T has a negligible impact on the sensitivity of the 1H MRS when performed at TE shorter than 10 ms. 相似文献
3.
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
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.
ObjectiveOur aim was to study the influence of small variations in spatial resolution and contrast agent dosage on myocardial T1 relaxation time.Materials and methodsTwenty-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.ResultsNative 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).ConclusionRelated 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. 相似文献
6.
Objective To compare measurements of the arterial blood volume (aBV), a perfusion parameter calculated from arterial spin labelling
(ASL), and cerebral blood volume (CBV), calculated from dynamic susceptibility contrast (DSC) MRI. In the clinic, CBV is used
for grading of intracranial tumours. 相似文献
7.
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
8.
Object The recently developed vascular space occupancy (VASO) fMRI technique is gaining popularity as it facilitates the measurement
of cerebral blood volume (CBV) changes concomitant with brain activation, without the use of contrast agents. Thus far, VASO
fMRI has only been used in conjunction with a GE-EPI (gradient-echo echo planar imaging) sequence, which is proceeded by an
inversion recovery (IR) experiment to selectively null the blood signal. The use of GE-EPI has potential disadvantages: (a)
the non-zero TE may lead to BOLD contamination and (b) images suffer from the EPI-typical inhomogeneity artefacts.
Materials and methods Here, we propose the use of VASO based on an IR-HASTE (inversion recovery half-Fourier acquisition single-shot turbo spin
echo) sequence.
Results Results from a visual stimulation study ( n = 8) show a 43% higher functional contrast-to-noise (CNR) of HASTE compared to EPI, with a strongly increased count of active
voxels at the same significance threshold. Sensitivity to inflow effects was investigated and found to be similar for both
methods.
Conclusion As HASTE VASO yields essentially artefact-free images, it appears to be the method of choice for measuring relative CBV changes
with VASO. 相似文献
9.
Myocardial iron deposition occurs as a result of blood transfusion therapy in b-thalassemia major patients. Since this deposition causes various cardiac complications, it is of interest to assess the iron content of the myocardium in relation to the clinical picture of the patients. Two different MRI indices were used to achieve this purpose: the T2 relaxation time and the heart/skeletal muscle signal intensity ratio. ECG gated spin echo images were obtained from 54 adult thalassemic patients, with a mean age of 26 (18–44) years, at TE = 22 ms and 60 ms, using a 1.5 T system. Patients were divided into 2 groups (A and B), according to their serum ferritin levels (> or < 2000 ng ml -1). Results were compared with nine controls, with a mean age of 25 (18–43) years. Heart T2 relaxation time in controls (44.3 ± 3.5 ms) was higher than in group A (29.9 ± 5.7 ms, P< 0.001) and group B (33.4 ± 6.8 ms, P < 0.01). T2 was measurable in 66% of group A and 83% of group B patients. The heart/muscle signal intensity ratio in group A (0.45 ± 0.27) was lower than in group B (0.82 ± 0.33, P < 0.001) and the controls (1.15 ± 0.20, P < 0.001). The heart/muscle signal intensity ratio was measurable in 94% of the patients and demonstrated an inverse relationship with the serum ferritin levels (r = - 0.52, P<0.01). This study indicates that the heart/muscle ratio is a sensitive index of iron overload and it can be measured in the majority of patients, irrespective of tissue iron concentration, thereby offering an advantage over the use of T2 relaxation time. © 1998 Elsevier Science B.V. All rights reserved. 相似文献
10.
This study reports proton relaxation times of water and metabolites in soleus and tibialis anterior muscles of young healthy volunteers at 3 T. The results are in agreement with data reported for 1.5 and 4 T, showing a steady increase of spin-lattice relaxation times of water, creatine and lipids with B0 and no effect of B0 on spin–spin relaxation. Comparison between muscles revealed a longer spin–spin relaxation time of water in soleus than in tibialis anterior muscle (31±1 ms vs. 28±1 ms, p<0.05). These data can be applied to relaxation correction for the absolute quantification of skeletal muscle metabolite concentrations and further sequence optimization. 相似文献
13.
Magnetic resonance (MR) microimaging of the human is becoming increasingly common for studies of tissue microstructure and microfunction. In this study, we consider the constraints that such experiments place on the design of radio-frequency (rf) coils, and describe the advantages of multiring coils, which offer a locally uniform B 1 field. We show that these coils are particularly suitable for high-field imaging of a restricted region of larger experimental animals or humans, offering the same simplicity and efficient use of rf power as a simple surface coil but without requiring sequence modifications such as adiabatic pulses. Imaging results are shown from human brain and from the abdominal aorta of an experimental animal. Acknowledgements. We thank Dr. S. King for his helpful assistance. 相似文献
14.
ObjectivePartial volume (PV) correction is an important step in arterial spin labeling (ASL) MRI that is used to separate perfusion from structural effects when computing the mean gray matter (GM) perfusion. There are three main methods for performing this correction: (1) GM-threshold, which includes only voxels with GM volume above a preset threshold; (2) GM-weighted, which uses voxel-wise GM contribution combined with thresholding; and (3) PVC, which applies a spatial linear regression algorithm to estimate the flow contribution of each tissue at a given voxel. In all cases, GM volume is obtained using PV maps extracted from the segmentation of the T1-weighted (T1w) image. As such, PV maps contain errors due to the difference in readout type and spatial resolution between ASL and T1w images. Here, we estimated these errors and evaluated their effect on the performance of each PV correction method in computing GM cerebral blood flow (CBF).Materials and methodsTwenty-two volunteers underwent scanning using 2D echo planar imaging (EPI) and 3D spiral ASL. For each PV correction method, GM CBF was computed using PV maps simulated to contain estimated errors due to spatial resolution mismatch and geometric distortions which are caused by the mismatch in readout between ASL and T1w images. Results were analyzed to assess the effect of each error on the estimation of GM CBF from ASL data.ResultsGeometric distortion had the largest effect on the 2D EPI data, whereas the 3D spiral was most affected by the resolution mismatch. The PVC method outperformed the GM-threshold even in the presence of combined errors from resolution mismatch and geometric distortions. The quantitative advantage of PVC was 16% without and 10% with the combined errors for both 2D and 3D ASL. Consistent with theoretical expectations, for error-free PV maps, the PVC method extracted the true GM CBF. In contrast, GM-weighted overestimated GM CBF by 5%, while GM-threshold underestimated it by 16%. The presence of PV map errors decreased the calculated GM CBF for all methods.ConclusionThe quality of PV maps presents no argument for the preferential use of the GM-threshold method over PVC in the clinical application of ASL. 相似文献
15.
Object The goal of the study was to determine blood T 1 and T 2 values as functions of oxygen saturation ( Y), temperature (Temp) and hematocrit (Hct) at an ultrahigh MR field (11.7?T) and explore their impacts on physiological measurements, including cerebral blood flow (CBF), blood volume (CBV) and oxygenation determination. Materials and methods T 1 and T 2 were simultaneously measured. Temperature was adjusted from 25 to 40°C to determine Temp dependence; Hct of 0.17?C0.51 to evaluate Hct dependence at 25 and 37°C; and Y of 40?C100% to evaluate Y dependence at 25 and 37°C. Comparisons were made with published data obtained at different magnetic field strengths ( B 0). Results T 1 was positively correlated with Temp, independent of Y, and negatively correlated with Hct. T 2 was negatively correlated with Temp and Hct, but positively correlated with Y, in a non-linear fashion. T 1 increased linearly with B 0, whereas T 2 decreased exponentially with B 0. Conclusion This study reported blood T 1 and T 2 measurements at 11.7?T for the first time. These blood relaxation data could have implications in numerous functional and physiological MRI studies at 11.7?T. 相似文献
16.
Inadequate blood supply relative to metabolic demand, a haemodynamic condition termed as misery perfusion, often occurs in
conjunction with acute ischaemic stroke. Misery perfusion results in adaptive changes in cerebral physiology including increased
cerebral blood volume (CBV) and oxygen extraction ratio (OER) to secure substrate supply for the brain. It has been suggested
that the presence of misery perfusion may be an indication of reversible ischaemia, thus detection of this condition may have
clinical impact in acute stroke imaging. The ability of single spin echo T 2 to detect misery perfusion in the rat brain at 1.5 T owing to its sensitivity to blood oxygenation level dependent (BOLD)
contrast was studied both theoretically and experimentally. Based on the known physiology of misery perfusion, tissue morphometry
and blood relaxation data, T 2 behaviour in misery perfusion was simulated. The interpretation of these computations was experimentally assessed by quantifying
T 2 in a rat model for cerebral misery perfusion. CBF was quantified with the H 2 clearance method. A drop of CBF from 58 ± 8 to 17 ± 3 ml/100 g min in the parieto-frontal cortex caused shortening of T 2. from 66.9 ± 0.4 to 64.6 ± 0.5 ms. Under these conditions, no change in diffusion MRI was detected. In contrast, the cortex
with CBF of 42 ± 7 ml/100 g min showed no change in T 2. Computer simulations accurately predicted these T 2, responses. The present study shows that the acute drop of CBF by 70% causes a negative BOLD that is readily detectable by
T 2 MRI at 1.5 T. Thus BOLD may serve as an index of misery perfusion thus revealing viable tissue with increased OER. 相似文献
17.
A standard fast imaging sequence, rapid acquisition with relaxation enhancement (RARE), has been applied to human magnetic
resonance at 8 T. RARE is known for its speed, good contrast and high RF power content. Highly T
2 weighted images, the hallmark of RARE imaging, were acquired from the human brain. It is demonstrated that while T
2 values may be reduced at 8 T, high quality RARE images could still be acquired at this field strength. Most importantly however,
it is demonstrated that RARE images could be acquired without violating specific absorption rate (SAR) guidelines. Since it
is well known that T
2 weighted images are of significant value in clinical diagnosis, the implementation of RARE at this field strength will provide
ultra high field MRI (UHFMRI) with a valuable imaging protocol at this field strength without exceeding SAR limitations. 相似文献
18.
Purpose Increased T2 signal intensity (SI) can be regularly observed in myocardial infarction. However, there are controversial reports
about the relationship of elevated T2 SI to myocardial viability and some authors propose that high T2 SI serves as a sign
of irreversible myocardial injury. This study investigates increased T2 SI compared to myocardial function in patients with
reperfused subacute myocardial infarction. Preserved function was used as criterion for viability.
Methods Ten healthy volunteers and 17 patients with myocardial infarction and patent inlarct related coronary artery were examined
on a 1.5 T Magnetom Vision system (Siemens). For T2-weighted MR imaging a breath-hold STIR sequence with dark-blood preparation
was used. Cine FLASH 2D imaging was applied to assess myocardial function. Signal-to-noise (S/N) in STIR T2 images was measured
in normal and infarcted regions and subsequently identified by two independent observers. Based on a 20 segment model of the
left ventricle findings were compared to regional myocardial function.
Results Elevated STIR T2 SI was found in all 17 patients and observed in 27% (204/754) of segments. S/N of normal myocardium was 5.1
±0.7 in volunteers and 4.9 ± 0.8 in patients (P=NS). Infarcted myocardium presented with significantly-increased S/N 12.8 ± 1.9 ( P < 0.0001). Significant transmural elevation of T2 SI was noted in 32% of segments with preserved systolic function.
Conclusion Increased STIR T2 SI can be observed transmurally in post-ischemic myocardial regions with preserved function. It therefore
cannot be used as an exclusive marker for the non-viable region. 相似文献
19.
Cerebral infarcts initially showing as markedly hyperintense on magnetic resonance (MR) T
2-weighted images decreased in intensity and became nearly isointense to normal brain tissue in subsequent MR studies. This MR fogging was observed in 7 (23%) out of 31 cases of cortical infarct and 4 (20%) out of 20 cases of perforator infarct in the second to sixth weeks of the disease. In all fogging cases, significant contrast enhancement (CE) was seen in the fogging area after intravenous administration of MR contrast agent. The CE study is recommended in MR of cerebral infarct during the subacute and early chronic stage. 相似文献
20.
Abstract Ferroelectric Random Access Memory (FeRAM) provides some advantages such as non-volatility, high endurance on write/read cycles, high radiation hardness and low power consumption compared to conventional memories. However, in order to realize a commercial FeRAM, it is important to overcome the limitation in various reliability items such as retention, imprint, and fatigue failure at high operation temperature. In this paper, the retention characteristic of FeRAM related with imprint degradation of ferroelectric capacitors at high temperature is evaluated on the level of 8” wafer. Both cell configurations of 2T/2C and 1T/1C are discussed in terms of imprint reliability. General reliability items of the FeRAM after TSOP-I type package, such as fatigue endurance, early failure rate (EFR), humidity acceleration stress test (HAST), and temperature cycle (TC), are also evaluated. 相似文献
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