Measurement of T1 and T2 in the cervical spinal cord at 3 tesla

T(1) and T(2) were measured for white matter (WM) and gray matter (GM) in the human cervical spinal cord at 3T. T(1) values were calculated using an inversion-recovery (IR) and B(1)-corrected double flip angle gradient echo (GRE) and show significant differences (p = 0.002) between WM (IR = 876 +/- 27 ms, GRE = 838 +/- 54 ms) and GM (IR = 973 +/- 33 ms, GRE = 994 +/- 54 ms). IR showed significant difference between lateral and dorsal column WM (863 +/- 23 ms and 899 +/- 18 ms, respectively, p = 0.01) but GRE did not (p = 0.40). There was no significant difference (p = 0.31) in T(2) between WM (73 +/- 6 ms) and GM (76 +/- 3 ms) or between lateral and dorsal columns (lateral: 73 +/- 6 ms, dorsal: 72 +/- 7 ms, p = 0.59). WM relaxation times were similar to brain structures with very dense fiber packing (e.g., corpus callosum), while GM values resembled deep GM in brain. Optimized sequence parameters for maximal contrast between WM and GM, and between WM and cerebrospinal fluid (CSF) were derived. Since the spinal cord has rostral-caudal symmetry, we expect these findings to be applicable to the whole cord.     

In vivo magnetic resonance imaging of the human cervical spinal cord at 3 Tesla

PURPOSE: To demonstrate the feasibility of obtaining high-quality magnetic resonance (MR) images of the human cervical spinal cord in vivo at a magnetic field strength of 3 T and to optimize the signal contrast between gray matter, white matter, and cerebrospinal fluid (CSF) on 2D gradient recalled echo (GRE) images of the cervical spinal cord. MATERIALS AND METHODS: Using a custom-built, anatomically molded radio frequency (RF) surface coil, the repetition time and flip angle of a 2D GRE sequence were systematically varied in five volunteers to assess tissue contrast in the cervical spinal cord. RESULTS: The 2D GRE parameters for an optimal balance between gray-white matter and CSF-white matter contrast at 3 T were determined to be a time-to-repetition (TR) of 2000 msec and a flip angle of 45 degrees, with the constant short time-to-echo (TE) of 12 msec used in this study. Excellent tissue contrast and visualization of the internal anatomy of the spinal cord was demonstrated reproducibly in eight subjects using these optimal parameters. CONCLUSION: This study demonstrates that imaging the cervical spinal cord and delineating internal spinal cord structures such as gray and white matter is feasible at 3 T.     

Increased SNR and reduced distortions by averaging multiple gradient echo signals in 3D FLASH imaging of the human brain at 3T

Purpose

To demonstrate how averaging of multiple gradient echoes can improve high‐resolution FLASH (fast low angle shot) magnetic resonance imaging (MRI) of the human brain.

Materials and Methods

3D‐FLASH with multiple bipolar echoes was studied by simulation and in three experiments on human brain at 3T. First, the repetition time (TR) was increased by the square of the flip angle to maintain contrast as derived by theory. Then the number of echoes was increased at constant TR with bandwidths between 110 and 1370 Hz/pixel. Finally, signals of a 12‐echo acquisition train (echo times 4.9–59 msec) were averaged consecutively to study the increase in SNR.

Results

At unchanged contrast, the signal increased proportionally with flip angle and sqrt(TR). Increasing the bandwidth improved delineation of the basal cortex and vessels, while most of the loss in the signal‐to‐noise ratio (SNR) was recovered by averaging. Consecutive averaging increased the SNR to reach maximum efficiency at an echo train length corresponding roughly to T.

Conclusion

SNR is gained efficiently by acquiring additional echoes and increasing TR (and flip angle accordingly to maintain contrast) until the associated T loss in the averaged signal consumes the sqrt(TR) increase in the steady state. A bandwidth of 350 Hz/pixel or higher and echo trains shorter than T are recommended. J. Magn. Reson. Imaging 2009;29:198–204. © 2008 Wiley‐Liss, Inc.     

Quantitative proton magnetic resonance spectroscopy of the human cervical spinal cord at 3 Tesla.

Cervical spinal cord spectroscopy has the potential to add metabolic information to spinal cord MRI and improve the clinical evaluation and research investigation of spinal cord diseases, such as multiple sclerosis (MS) and intraspinal tumors. However, in vivo proton MR spectroscopy ((1)H-MRS) of the spinal cord is difficult to perform due to magnetic field inhomogeneities, physiological movements, and the size of the anatomical region of interest (ROI). For these reasons, few spinal cord (1)H-MRS studies have been undertaken and two preliminary studies on a 3T system were only recently presented as abstracts. In this work we demonstrate the feasibility of cervical spinal cord quantitative (1)H-MRS on a clinical 3T system, propose a study protocol, and report quantification results obtained from healthy volunteers. The main metabolite concentration ratios obtained in 10 healthy subjects, as provided by LCModel, were as follows: total N-acetyl aspartate/creatine (tNAA/Cr) 1.4 +/- 0.3, choline/creatine (Cho/Cr) 0.5 +/- 0.1, and myoinositol/creatine (mI/Cr) 1.7 +/- 0.2. A significant difference was found between spinal cord tNAA, Cr, Cho, and mI concentration ratios and brainstem concentrations previously acquired on the same system.     

Repeatability of ultrashort echo time‐based two‐component T2* measurements on cartilages in human knee at 3 T

Repeatability of in vivo measurement of multicomponent T₂* relaxation in articular cartialges in human knee is important to clinical use. This study evaluated the repeatability of two‐component T₂* relaxation on seven healthy human subjects. The left knee was scanned once a day in three consecutive days, on a clinical 3T MRI scanner with eight‐channel knee coil and ultrashort echo time pulse sequence at 11 echo times = 0.6–40 ms. The intrasubject and intersubject repeatability was evaluated via coefficient of variation (CV = standard deviation/mean) in four typical cartilage regions: patellar, anterior articular, femoral, and tibial regions. It was found that the intrasubject repeatability was good, with CV < 10% for the short‐ and long‐T₂* relaxation time in the layered regions in the four cartilages (with one exception) and CV < 13% for the component intensity fraction (with two exceptions). The intersubject repeatability was also good, with CV ～8% (range 1–15%) for the short‐ and long‐T₂* relaxation time and CV ～10% (range 2–20%) for the component intensity fraction. The long‐T₂* component showed significantly better repeatability (CV ～8%) than the short‐T₂* component (CV～12%) (P < 0.005). These CV values suggest that in vivo measurement of two‐component T₂* relaxation in the knee cartilages is repeatable on clinical scanner at 3 T, with a signal‐to‐noise ratio of 90. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Clinical usefulness of the visibility of the transcerebral veins at 3T on T2*-weighted sequence in acute stroke patients

Objectives

The objective of this work was to investigate the clinical usefulness of the visibility of the transcerebral veins (VTV) in acute ischemic stroke patients at 3 T.

Methods

Sixty consecutive carotid artery territory stroke patients were included retrospectively. Two readers categorized the VTV on T2*-weighted sequence at 3 T for each hemisphere, and asymmetry of this sign was assessed between each hemisphere by an asymmetry index (AI) using a three-item scale. The VTV and AI were correlated with clinical and radiological covariates. Particular interest was focused on patients for whom initial diffusion-weighted imaging alone was inconclusive.

Results

VTV were detected in the stroke hemisphere in 58.3% (n = 35) and in the contralateral side in 10% (n = 6, p < 0.0001). Asymmetry of the VTV between ischemic and contralateral hemispheres was present in 53.3% (n = 32). Intracranial artery occlusion, final infarct volume and symptomatic hemorrhagic transformation were correlated with a higher AI at baseline (ρ = 0.563, ρ = 0.291, and ρ = 0.285, p < 0.05, respectively). Three hyperacute stroke patients with subtle DWI high signal intensity at admission demonstrated VTV.

Conclusions

The pathological value of the VTV seems to reside in its asymmetry between hemispheres, as it was correlated with important clinical parameters. This study also suggests that the VTV could be a supportive finding in stroke diagnosis, especially when DWI is unreliable.     

Oxygen-enhanced proton imaging of the human lung using T2.

Magnetic susceptibility gradients caused by tissue/air interfaces lead to very short T(2)* times in the human lung. These susceptibility gradients are dependent on the magnetic susceptibility of the respiratory gas and therefore should influence T(2)* relaxation. In this work, a technique for quantitative T(2)* mapping of the human lung during one breath hold is presented. Using this method, the lung T(2)* relaxation time was measured under normoxic (room air, 21% O(2)) and hyperoxic (100% O(2)) conditions to verify this assumption. The mean T(2)* difference between room air and 100% O(2) is about 10% and contains ventilation information, since only ventilated regions contribute to signal change due to different susceptibility gradients.     

Proton MR spectroscopic imaging of the medulla and cervical spinal cord

PURPOSE: To demonstrate the feasibility of quantitative, one-dimensional proton MR spectroscopic imaging (1D-MRSI) of the upper cervical spine and medulla at 3.0 Tesla. MATERIALS AND METHODS: A method was developed for 1D-point-resolved spectroscopy sequence (PRESS)-MRSI, exciting signal in five voxels extending from the pontomedullary junction to the level of the C3 vertebra, and performed in 10 healthy volunteers to generate control data. RESULTS: High-resolution 1D-MRSI data were obtained from all 10 subjects. Upper cervical spine concentrations of choline, creatine, and N-acetyl aspartate were estimated to be 2.8 +/- 0.5, 8.8 +/- 1.8, and 10.9 +/- 2.7 mM, respectively, while in the medulla they were 2.6 +/- 0.5, 9.1 +/- 1.7, and 10.8 +/- 0.9 mM. CONCLUSION: Quantitative 1D-MRSI of the upper cervical spine has been shown to be feasible at 3.0 Tesla.     

Simultaneous imaging and R2* mapping using a radial multi-gradient-echo (rMGE) sequence

PURPOSE: To demonstrate a rapid MR technique that combines imaging and R2* mapping based on a single radial multi-gradient-echo (rMGE) data set. The technique provides a fast method for online monitoring of the administration of (super-)paramagnetic contrast agents as well as image-guided drug delivery. MATERIALS AND METHODS: Data are acquired using an rMGE sequence, resulting in interleaved undersampled radial k-spaces representing different echo times (TEs). These data sets are reconstructed separately, yielding a series of images with different TEs used for pixelwise R2* mapping. A fast numerical algorithm implemented on a real-time reconstruction platform provides online estimation of the relaxation rate R2*. Simultaneously the images are summed for the computation of a high-resolution image. RESULTS: Convenient high-resolution R2* maps of phantoms and the liver of a healthy volunteer were obtained. In addition to stable intrinsic baseline maps, the proposed technique provides particularly accurate results for the high relaxation rates observed during the presence of (super-)paramagnetic contrast agents. Assuming that the change in R2* is proportional to the concentration of the agent, the technique offers a rough estimate for dynamic dosage. CONCLUSION: The simultaneous online display of morphological and parametric information permits convenient, quantitative surveillance of contrast-agent administration.     

In vivo quantitative microimaging of rat spinal cord at 7T.

In vivo T(2), ADC, and MT properties of the GM and WM of the rat spinal cord were measured at 7T in the cervical region. The GM T(2), T(2GM) = 43.2 +/- 1.0 msec is significantly reduced compared to the WM T(2), T(2WM) = 57.0 +/- 1.6 msec. Diffusion is anisotropic for both GM and WM, with a larger ADC value along the cord axis (ADC(GM//) = 1.05 +/- 0.09 10(-9) m(2)sec(-1) and ADC(WM//) = 1.85 +/- 0.18 10(-9) m(2)sec(-1)) than perpendicular to this plane (ADC(GM)( perpendicular) approximately 0.50 * 10(-9) m(2)sec(-1) and ADC(WM)( perpendicular) approximately 0.18 * 10(-9) m(2)sec(-1)). The MT properties do not significantly differ between the WM and the GM, but allow one to distinguish the thin CSF layer from the WM. DWI with the sensitizing gradient perpendicular to the cord axis leads to the best contrast between GM and WM in the cervical region.