Multislice T1 relaxation time measurements in the brain using IR-EPI: Reproducibility, normal values, and histogram analysis in patients with multiple sclerosis

T1 and ADC histogram parameters may be an in vivo biomarker for predicting the grade, subtype, and proliferative activity of meningioma

OBJECTIVE

To investigate the value of histogram analysis of T1 mapping and diffusion-weighted imaging (DWI) in predicting the grade, subtype, and proliferative activity of meningioma.

METHODS

This prospective study comprised 69 meningioma patients who underwent preoperative MRI including T1 mapping and DWI. The histogram metrics, including mean, median, maximum, minimum, 10th percentiles (C10), 90th percentiles (C90), kurtosis, skewness, and variance, of T1 and apparent diffusion coefficient (ADC) values were extracted from the whole tumour and peritumoural oedema using FeAture Explorer. The Mann-Whitney U test was used for comparison between low- and high-grade tumours. Receiver operating characteristic (ROC) curve and logistic regression analyses were performed to identify the differential diagnostic performance. The Kruskal-Wallis test was used to further classify meningioma subtypes. Spearman's rank correlation coefficients were calculated to analyse the correlations between histogram parameters and Ki-67 expression.

RESULTS

High-grade meningiomas showed significantly higher mean, maximum, C90, and variance of T1 (p = 0.001-0.009), lower minimum, and C10 of ADC (p = 0.013-0.028), compared to low-grade meningiomas. For all histogram parameters, the highest individual distinctive power was T1 C90 with an AUC of 0.805. The best diagnostic accuracy was obtained by combining the T1 C90 and ADC C10 with an AUC of 0.864. The histogram parameters differentiated 4/6 pairs of subtype pairs. Significant correlations were identified between Ki-67 and histogram parameters of T1 (C90, mean) and ADC (C10, kurtosis, variance).

CONCLUSION

T1 and ADC histogram parameters may represent an in vivo biomarker for predicting the grade, subtype, and proliferative activity of meningioma.

KEY POINTS

• The histogram parameter based on T1 mapping and DWI is useful to preoperatively evaluate the grade, subtype, and proliferative activity of meningioma. • The combination of T1 C90 and ADC C10 showed the best performance for differentiating low- and high-grade meningiomas.

Silent 3D MR sequence for quantitative and multicontrast T1 and proton density imaging

This study aims to develop a silent, fast and 3D method for T1 and proton density (PD) mapping, while generating time series of T1-weighted (T1w) images with bias-field correction. Undersampled T1w images at different effective inversion times (TIs) were acquired using the inversion recovery prepared RUFIS sequence with an interleaved k-space trajectory. Unaliased images were reconstructed by constraining the signal evolution to a temporal subspace which was learned from the signal model. Parameter maps were obtained by fitting the data to the signal model, and bias-field correction was conducted on T1w images. Accuracy and repeatability of the method was accessed in repeated experiments with phantom and volunteers. For the phantom study, T1 values obtained by the proposed method were highly consistent with values from the gold standard method, R² = 0.9976. Coefficients of variation (CVs) ranged from 0.09% to 0.83%. For the volunteer study, T1 values from gray and white matter regions were consistent with literature values, and peaks of gray and white matter can be clearly delineated on whole-brain T1 histograms. CVs ranged from 0.01% to 2.30%. The acoustic noise measured at the scanner isocenter was 2.6 dBA higher compared to the in-bore background. Rapid and with low acoustic noise, the proposed method is shown to produce accurate T1 and PD maps with high repeatability by reconstructing sparsely sampled T1w images at different TIs using temporal subspace. Our approach can greatly enhance patient comfort during examination and therefore increase the acceptance of the procedure.

Multiple sclerosis pathogenesis: missing pieces of an old puzzle

Traditionally, multiple sclerosis (MS) was considered to be a CD4 T cell-mediated CNS autoimmunity, compatible with experimental autoimmune encephalitis model, which can be characterized by focal lesions in the white matter. However, studies of recent decades revealed several missing pieces of MS puzzle and showed that MS pathogenesis is more complex than the traditional view and may include the following: a primary degenerative process (e.g. oligodendroglial pathology), generalized abnormality of normal-appearing brain tissue, pronounced gray matter pathology, involvement of innate immunity, and CD8 T cells and B cells. Here, we review these findings and discuss their implications in MS pathogenesis.

Myelin water imaging to detect demyelination and remyelination and its validation in pathology

Damage to myelin is a key feature of multiple sclerosis (MS) pathology. Magnetic resonance imaging (MRI) has revolutionized our ability to detect and monitor MS pathology in vivo. Proton density, T1 and T2 can provide qualitative contrast weightings that yield superb in vivo visualization of central nervous system tissue and have proved invaluable as diagnostic and patient management tools in MS. However, standard clinical MR methods are not specific to the types of tissue damage they visualize, and they cannot detect subtle abnormalities in tissue that appears otherwise normal on conventional MRIs. Myelin water imaging is an MR method that provides in vivo measurement of myelin. Histological validation work in both human brain and spinal cord tissue demonstrates a strong correlation between myelin water and staining for myelin, validating myelin water as a marker for myelin. Myelin water varies throughout the brain and spinal cord in healthy controls, and shows good intra- and inter-site reproducibility. MS plaques show variably decreased myelin water fraction, with older lesions demonstrating the greatest myelin loss. Longitudinal study of myelin water can provide insights into the dynamics of demyelination and remyelination in plaques. Normal appearing brain and spinal cord tissues show reduced myelin water, an abnormality which becomes progressively more evident over a timescale of years. Diffusely abnormal white matter, which is evident in 20%-25% of MS patients, also shows reduced myelin water both in vivo and postmortem, and appears to originate from a primary lipid abnormality with relative preservation of myelin proteins. Active research is ongoing in the quest to refine our ability to image myelin and its perturbations in MS and other disorders of the myelin sheath.

Magnetic resonance imaging relaxation time in Alzheimer's disease

The magnetic resonance imaging (MRI) relaxation time constants, T1 and T2, are sensitive to changes in brain tissue microstructure integrity. Quantitative T1 and T2 relaxation times have been proposed to serve as non-invasive biomarkers of Alzheimer's disease (AD), in which alterations are believed to not only reflect AD-related neuropathology but also cognitive impairment. In this review, we summarize the applications and key findings of MRI techniques in the context of both AD subjects and AD transgenic mouse models. Furthermore, the possible mechanisms of relaxation time alterations in AD will be discussed. Future studies could focus on relaxation time alterations in the early stage of AD, and longitudinal studies are needed to further explore relaxation time alterations during disease progression.

A 24-month advanced magnetic resonance imaging study of multiple sclerosis patients treated with alemtuzumab

Background:

Tissue damage in both multiple sclerosis (MS) lesions and normal-appearing white matter (NAWM) are important contributors to disability and progression. Specific aspects of MS pathology can be measured using advanced imaging. Alemtuzumab is a humanised monoclonal antibody targeting CD52 developed for MS treatment.

Objective:

To investigate changes over 2 years of advanced magnetic resonance (MR) metrics in lesions and NAWM of MS patients treated with alemtuzumab.

Methods:

A total of 42 relapsing–remitting alemtuzumab-treated MS subjects were scanned for 2 years at 3 T. T1 relaxation, T2 relaxation, diffusion tensor, MR spectroscopy and volumetric sequences were performed. Mean T1 and myelin water fraction (MWF) were determined for stable lesions, new lesions and NAWM. Fractional anisotropy was calculated for the corpus callosum (CC) and N-acetylaspartate (NAA) concentration was determined from a large NAWM voxel. Brain parenchymal fraction (BPF), cortical thickness and CC area were also calculated.

Results:

No change in any MR measurement was found in lesions or NAWM over 24 months. BPF, cortical thickness and CC area all showed decreases in the first year followed by stability in the second year.

Conclusion:

Advanced MR biomarkers of myelin (MWF) and neuron/axons (NAA) show no change in NAWM over 24 months in alemtuzumab-treated MS participants.

T1 relaxation maps allow differentiation between pathologic tissue subsets in relapsing-remitting and secondary progressive multiple sclerosis

In an attempt to clarify whether T1 relaxation time mapping may assist in characterizing the pathological brain tissue substrate of multiple sclerosis (MS), we compared the T1 relaxation times of lesions, areas of normal-appearing white matter (NAWM) located proximal to lesions, and areas of NAWM located distant from lesions in 12 patients with the relapsing-remitting and 12 with the secondary progressive (SP) subtype of disease. Nine healthy volunteers served as controls. Calculated mean T1 values were averaged across all patients within each clinical group, and comparisons were made by means of the Mann-Whitney U-test. Significant differences were found between all investigated brain regions within each clinical subgroup. Significant differences were also detected for each investigated brain region among clinical subgroups. While T1 values of NAWM were significantly higher in patients with SP disease than in normal white matter (NWM) of controls, no differences were detected when corresponding brain areas of patients with RR MS were compared with NWM of controls. T1 maps identify areas of the brain that are damaged to a different extent in patients with MS, and may be of help in monitoring disease progression.

The Effect of Inversion Time on the Relationship Between Iron Oxide Nanoparticles Concentration and Signal Intensity in T1-Weighted MR Images

Background:

Magnetic nanoparticles have been widely applied in recent years for biomedical applications. Signal intensity (SI) of magnetic resonance (MR) images depends on the concentration of nanoparticles. It is important to find the minimum concentration of iron oxide nanoparticles that produces maximum SI and determines the minimum injection dose for clinical studies.

Objectives:

This study was performed to determine the relationship between the iron oxide nanoparticle concentration and SI using inversion recovery (IR) sequence in T₁-weighted MR images.

Materials and Methods:

Different concentrations of carboxydextran-coated iron oxide nanoparticles 20 nm in size were prepared. In vitro MR imaging was performed with inversion times (TI) of 100-400 ms (interval of 20 ms) and IR Turbo-FLASH (Turbo fast low angle shot) pulse sequence using a 1.5 T MRI system. Then the SI produced by each concentration of nanoparticles was measured and the minimum nanoparticle concentration that led to the maximum SI was determined. Coil non-uniformity was also considered for measuring the accurate SI of each image.

Results:

The results indicate that SI depended on the concentration of nanoparticles and TI. In addition, SI increased by increasing the TIs ranging from 200 to 400 ms for all studied concentrations. The linear relationship between the nanoparticle concentrations and SI that gave a square correlation coefficient (R²) equal to 0.99 was seen up to 76.83 µmol Fe/L in 400 ms for long TI and 239.16 µmol Fe/L in 200 ms for short TI.

Conclusions:

TI is an important parameter to consider in the relationship between SI and nanoparticle concentrations. An increase in TI leads to a decrease in the range of linearity.

Diffusely abnormal white matter in multiple sclerosis: further histologic studies provide evidence for a primary lipid abnormality with neurodegeneration

Although multiple sclerosis (MS) lesions have been studied extensively using histology and magnetic resonance imaging (MRI), little is known about diffusely abnormal white matter (DAWM). Diffusely abnormal white matter, regions with reduced mild MRI hyperintensity and ill-defined boundaries, show reduced myelin water fraction, and decreased Luxol fast blue staining of myelin phospholipids, with relative preservation of myelin basic protein and 2',3'-cyclic-nucleotide 3'-phosphohydrolase. Because DAWM may be important in MS disability and progression, further histologic characterization is warranted. The MRI data were collected on 14 formalin-fixed MS brain samples that were then stained for myelin phospholipids, myelin proteins, astrocytes and axons. Diffusely abnormal white matter showed reduced myelin water fraction (-30%, p < 0.05 for 13 samples). Myelin phospholipids showed the most dramatic and consistent histologic reductions in staining optical density (-29% Luxol fast blue and -24% Weil's, p < 0.05 for 13 and 14 samples,respectively) with lesser myelin protein involvement (-11% myelin-associated glycoprotein, -10% myelin basic protein, -8% myelin-oligodendrocyte glycoprotein, -7% proteolipid protein, -5% 2',3'-cyclic-nucleotide 3'-phosphohydrolase, p < 0.05 for 3, 3, 1, 2, and 3 samples, respectively). Axonal involvement was intermediate. Diffusely abnormal white matter lipid and protein reductions occurred independently. These findings suggest a primary lipid abnormality in DAWM that exceeds protein loss and is accompanied by axonal degeneration. These phenomena may be important in MS pathogenesis and disease progression, which is prominent in individuals with DAWM.

Blood-brain barrier permeability of normal appearing white matter in relapsing-remitting multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) affects the integrity of the blood-brain barrier (BBB). Contrast-enhanced T1 weighted magnetic resonance imaging (MRI) is widely used to characterize location and extent of BBB disruptions in focal MS lesions. We employed quantitative T1 measurements before and after the intravenous injection of a paramagnetic contrast agent to assess BBB permeability in the normal appearing white matter (NAWM) in patients with relapsing-remitting MS (RR-MS).

METHODOLOGY/PRINCIPAL FINDINGS

Fifty-nine patients (38 females) with RR-MS undergoing immunomodulatory treatment and nine healthy controls (4 females) underwent quantitative T1 measurements at 3 tesla before and after injection of a paramagnetic contrast agent (0.2 mmol/kg Gd-DTPA). Mean T1 values were calculated for NAWM in patients and total cerebral white matter in healthy subjects for the T1 measurements before and after injection of Gd-DTPA. The pre-injection baseline T1 of NAWM (945±55 [SD] ms) was prolonged in RR-MS relative to healthy controls (903±23 ms, p = 0.028). Gd-DTPA injection shortened T1 to a similar extent in both groups. Mean T1 of NAWM was 866±47 ms in the NAWM of RR-MS patients and 824±13 ms in the white matter of healthy controls. The regional variability of T1 values expressed as the coefficient of variation (CV) was comparable between the two groups at baseline, but not after injection of the contrast agent. After intravenous Gd-DTPA injection, T1 values in NAWM were more variable in RR-MS patients (CV = 0.198±0.046) compared to cerebral white matter of healthy controls (CV = 0.166±0.018, p = 0.046).

CONCLUSIONS/SIGNIFICANCE

We found no evidence of a global BBB disruption within the NAWM of RR-MS patients undergoing immunomodulatory treatment. However, the increased variation of T1 values in NAWM after intravenous Gd-DTPA injection points to an increased regional inhomogeneity of BBB function in NAWM in relapsing-remitting MS.

Relaxation time mapping in multiple sclerosis

Several relaxation mapping techniques have been proposed to quantitatively assess disease-related brain tissue changes in multiple sclerosis. Newer developments also account for the distribution of hydrogen protons in different tissue compartments, and therefore provide markers for myelin and macromolecular content. This article will cover the broad spectrum of the pulse sequences and analysis techniques related to this topic that are currently available. Various technical and practical limitations linked with specific approaches will be discussed. These include acquisition time, accuracy and precision, radiofrequency absorption and limited coverage of the brain. Finally, the application of these techniques in the context of multiple sclerosis will be reviewed.

Lesion detection at seven Tesla in multiple sclerosis using magnetisation prepared 3D-FLAIR and 3D-DIR

Objectives

To examine the feasibility and value of 7 T 3D T2-weighted Fluid Attenuated Inversion Recovery (FLAIR) and Double Inversion Recovery (DIR) MR sequences for lesion detection in multiple sclerosis (MS).

Methods

High-resolution 3D-FLAIR and 3D-DIR MR sequences at 7 T were obtained using magnetisation preparation (MP), and compared with 2D-T2-weighted and 3D-T1-weighted sequences in 10 MS patients and five healthy controls. We determined contrast ratios and counted lesions according to anatomical location.

Results

MR imaging at 7 T was safe and allowed multi-contrast imaging within clinically acceptable imaging times. Lesion to white matter (WM) and grey matter (GM) contrast ratios were higher in 3D-MP-FLAIR and 3D-MP-DIR compared with 2D-T2 and 3D-T1. Cortical (mixed+intra-cortical) and total lesion counts were 97/592 on 3D-MP-FLAIR and 100/558 on 3D-MP-DIR compared with 84/384 on 2D-T2 and 42/442 on 3D-T1. More juxta-cortical lesions were seen with 3D-MP-FLAIR (205) and 3D-MP-DIR (133) than with 2D-T2 (125) and 3D-T1 (70). Finally, higher numbers of lesions were found for deep WM lesions: 176 for 3D-MP-FLAIR and 196 for 3D-MP-DIR vs. 155 for 2D-T2 and 131 for 3D-T1.

Conclusions

Near isotropic 3D-MP-FLAIR and 3D-MP-DIR allows high quality T2-weighted MR imaging in MS at 7 T, improving (cortical) lesion detection.

Key Points

• Magnetization prepared 3D-FLAIR and 3D-DIR 7 T MRI provide high quality isotropic images.

• MS lesions are well demonstrated by 3D-MP-FLAIR and 3D-MP-DIR at 7 T MRI.

• 3D-MP-FLAIR and 3D-MP-DIR at 7 T MRI show many more Virchov-Robin spaces.

Current concepts in the neuropathology and pathogenesis of multiple sclerosis

Multiple sclerosis (MS) has been classically regarded as an inflammatory demyelinating disease of the central nervous system. In recent years, the classification and pathogenesis of the disease have become controversial, particularly with respect to whether an individual patient demonstrates a single or multiple pathogenetic mechanisms in the establishment of the focal plaque of MS. It is also becoming increasingly apparent that there is a significant neurodegenerative component in the disease, involving not only plaques but the non-plaque parenchyma as well. Magnetic resonance imaging, together with histopathologic studies, will continue to shed light on the pathogenesis of these focal and diffuse abnormalities in MS.

A head phantom prototype to verify subdural electrode localization tools in epilepsy surgery

When planning epilepsy surgery, the position of subdural electrodes in relation to the cortex is crucial. Electrodes may dislocate after implantation. Neurosurgeons are highly interested in the accuracy of methods that visualize these electrodes. In order to determine the accuracy of an electrode visualization method, we have developed a physical head phantom and evaluated our new method of subdural electrode localization. This method projects automatically segmented electrodes of a preimplantation computed tomography (CT) data set onto the segmented brain surface of a postimplantation magnetic resonance imaging (MRI) data set within 2 to 5 min. The phantom consists of a skull, an adipose layer for skin replication, and a deformable brain. It further contains gyri and sulci structures, composed of gelatin and different additives used as phantom material for white matter, gray matter, and cerebrospinal fluid. The phantom allows a well-defined displacement of an "implanted" electrode grid perpendicular to the brain surface. By using the phantom data, we demonstrated that our electrode visualization tool did in fact function accurately. The image contrasts between different phantom materials in MRI and CT phantom data sets were similar to patient data sets. The phantom appears suitable for obtaining a more complex patient data replication, as well as for simulating different deformation scenarios.

Hypothalamic involvement assessed by T1 relaxation time in patients with relapsing—remitting multiple sclerosis

Recent work in multiple sclerosis, focusing on neuropathological abnormalities, found a frequent and severe hypothalamic involvement. The possible clinical implications are disturbances in sleep and sexual activity, depression, memory impairment and fatigue. Despite this there are no magnetic resonance imaging studies focusing on in vivo hypothalamic pathology in multiple sclerosis. Our objective was to investigate magnetic resonance imaging-detectable abnormalities related to pathological changes in the hypothalamus of patients with multiple sclerosis, and to subsequently explore the relationship with fatigue. We used T1 relaxation time as a sensitive measure of pathology. Using region of interest analysis, median T1 values in the hypothalamus were measured in 44 relapsing—remitting multiple sclerosis patients and in 13 healthy controls. Fatigue was assessed using the Fatigue Severity Scale, and patients were divided in two subgroups, fatigued and non-fatigued, according to Fatigue Severity Scale scores. We found a significantly higher T1 relaxation time in the hypothalamus of multiple sclerosis patients compared with controls ( p = 0.027). There was a significant correlation between T1 values and fatigue severity (rho 0.437, p = 0.008), and median T1 values were different among the study groups. Our results show that pathological involvement of the hypothalamus in relapsing—remitting multiple sclerosis is detectable using magnetic resonance imaging, and that the pathology measured by quantitative T1 might reflect fatigue.

Improvement of brain segmentation accuracy by optimizing non-uniformity correction using N3

Smoothly varying and multiplicative intensity variations within MR images that are artifactual, can reduce the accuracy of automated brain segmentation. Fortunately, these can be corrected. Among existing correction approaches, the nonparametric non-uniformity intensity normalization method N3 (Sled, J.G., Zijdenbos, A.P., Evans, A.C., 1998. Nonparametric method for automatic correction of intensity nonuniformity in MRI data. IEEE Trans. Med. Imag. 17, 87-97.) is one of the most frequently used. However, at least one recent study (Boyes, R.G., Gunter, J.L., Frost, C., Janke, A.L., Yeatman, T., Hill, D.L.G., Bernstein, M.A., Thompson, P.M., Weiner, M.W., Schuff, N., Alexander, G.E., Killiany, R.J., DeCarli, C., Jack, C.R., Fox, N.C., 2008. Intensity non-uniformity correction using N3 on 3-T scanners with multichannel phased array coils. NeuroImage 39, 1752-1762.) suggests that its performance on 3 T scanners with multichannel phased-array receiver coils can be improved by optimizing a parameter that controls the smoothness of the estimated bias field. The present study not only confirms this finding, but additionally demonstrates the benefit of reducing the relevant parameter values to 30-50 mm (default value is 200 mm), on white matter surface estimation as well as the measurement of cortical and subcortical structures using FreeSurfer (Martinos Imaging Centre, Boston, MA). This finding can help enhance precision in studies where estimation of cerebral cortex thickness is critical for making inferences.

MR relaxation in multiple sclerosis

This article provides an overview of relaxation times and their application to normal brain and brain and cord affected by multiple sclerosis. The goal is to provide readers with an intuitive understanding of what influences relaxation times, how relaxation times can be accurately measured, and how they provide specific information about the pathology of MS. The article summarizes significant results from relaxation time studies in the normal human brain and cord and from people who have multiple sclerosis. It also reports on studies that have compared relaxation time results with results from other MR techniques.

Magnetic resonance imaging of myelin

The ability to measure myelin in vivo has great consequences for furthering our knowledge of normal development, as well as for understanding a wide range of neurological disorders. The following review summarizes the current state of myelin imaging using MR. We consider five MR techniques that have been used to study myelin: 1) conventional MR, 2) MR spectroscopy, 3) diffusion, 4) magnetization transfer, and 5) T2 relaxation. Fundamental studies involving peripheral nerve and MR/histology comparisons have aided in the interpretation and validation of MR data. We highlight a number of important findings related to myelin development, damage, and repair, and we conclude with a critical summary of the current techniques available and their potential to image myelin in vivo.

Gray and normal-appearing white matter in multiple sclerosis: an MRI perspective

Besides focal white matter lesions, multiple sclerosis brain tissue also displays abnormalities in the gray matter and the normal-appearing white matter. Recent advances in magnetic resonance imaging studies of both types of tissue are discussed. Herein, normal-appearing white matter abnormalities are being found in quantitative magnetic resonance investigations, consistent with a limited degree of axonal damage and/or demyelination, and an increase of glial cells, but the specific nature of the histopathological changes underlying the quantitative magnetic resonance abnormalities remains unclear. Gray matter studies have demonstrated that much of the disease process remains undetected by conventional magnetic resonance imaging. Although newly developed techniques, such as 3D double-inversion recovery, may greatly improve detection of cortical pathology, it remains important to investigate the resultant effects on the cortical tissue alongside this, by studying integrity of normal-appearing cortical tissue through quantitative magnetic resonance studies, as well as the net neurodegenerative effect through measurements of cortical thickness and cortical atrophy (rates). To improve our understanding of normal-appearing white and gray matter changes, their mutual relations, and their relations to clinical changes, further in vivo magnetic resonance imaging studies are required. Specifically, it is proposed that more spatially specific investigations, ideally utilizing subject-specific anatomical information from, for example, diffusion fiber-tracking techniques, could be used to gain more insight into the relations between normal-appearing white matter changes, cortical changes, magnetic resonance visible focal-lesions, and physical and cognitive deficits.

T1 relaxation in in vivo mouse brain at ultra-high field

Accurate knowledge of relaxation times is imperative for adjustment of MRI parameters to obtain optimal signal-to-noise ratio (SNR) and contrast. As small animal MRI studies are extended to increasingly higher magnetic fields, these parameters must be assessed anew. The goal of this study was to obtain accurate spin-lattice (T(1)) relaxation times for the normal mouse brain at field strengths of 9.4 and 17.6 T. T(1) relaxation times were determined for cortex, corpus callosum, caudate putamen, hippocampus, periaqueductal gray, lateral ventricle, and cerebellum and varied from 1651 +/- 28 to 2449 +/- 150 ms at 9.4 T and 1824 +/- 101 to 2772 +/- 235 ms at 17.6 T. A field strength-dependent increase of T(1) relaxation times is shown. The SNR increase at 17.6 T is in good agreement with the expected SNR increase for a sample-dominated noise regime.

Human gray matter: feasibility of single-slab 3D double inversion-recovery high-spatial-resolution MR imaging

The purpose of this study was to develop and prospectively evaluate the feasibility of a single-slab three-dimensional (3D) double inversion-recovery, or DIR, sequence for magnetic resonance imaging at 1.5 T. The study was approved by the local ethics committee, and informed consent was obtained from six healthy control subjects (one woman, five men; age range, 26-47 years) and two patients with multiple sclerosis (one woman, aged 39; one man, aged 56). Gray matter (GM)-only images were obtained by selectively suppressing cerebrospinal fluid (CSF) and white matter (WM) signals. Whole-brain high-spatial-resolution 3D images (1.2 x 1.2 x 1.3 mm) were acquired within 10 minutes. Cortical and deep GM structures were clearly delineated from WM and CSF, and there were regional differences in GM signal intensity. No flow artifacts from blood or CSF were observed. These GM images with high spatial resolution are suitable to identify cortical pathologic conditions and can potentially be used for segmentation purposes to determine cortical thickness or volume.

Rapid MRI method for mapping the longitudinal relaxation time

A novel method for mapping the longitudinal relaxation time in a clinically acceptable time is developed based on a recent proposal [J.-J. Hsu, I.J. Lowe, Spin-lattice relaxation and a fast T1-map acquisition method in MRI with transient-state magnetization, J. Magn. Reson. 169 (2004) 270-278] and the speed of the spiral pulse sequence. The method acquires multiple curve-fitting samples with one RF pulse train. It does not require RF pulses of specific flip angles (e.g., 90 degrees or 180 degrees ), nor are the long recovery waiting time and the measurement of the magnetization at thermal equilibrium needed. Given the value of the flip angle, the curve fitting is semi-logarithmic and not computationally intensive. On a heterogeneous phantom, the average percentage difference between measurements of the present method and those of an inversion-recovery method is below 2.7%. In mapping the human brain, the present method, for example, can obtain four curve-fitting samples for five 128 x 128 slices in less than 3.2s and the results are in agreement with other studies in the literature.

Reproducibility and reliability of MR measurements in white matter: clinical implications

The purpose of this study was to determine the reproducibility and reliability of five MRI-derived measurements, namely, total water content (WC), myelin water content (MWC), mean T2 relaxation time (GMT2), T1 relaxation time (T1) and magnetization transfer ratio (MTR). Five controls were scanned 5 times over 1 year. The five MR measurements were made for 5 white matter regions. All measurements were found to be highly reproducible. MTR had a low reliability coefficient because all individual values were similar. Therefore, MTR would be most sensitive in detecting changes from normal. WC had a high reliability coefficient in all regions. For MWC, GMT2 and T1, the overall reliability coefficients were high but for some individual regions were low. The high coefficients suggest that these measurements, although different between normal subjects, are consistent over time. They could be used to explore natural differences in the normal population, but due to the large spread in normal values, larger sample sizes are needed to detect pathological changes.

Deep gray matter and fatigue in MS: a T1 relaxation time study

Fatigue in multiple sclerosis (MS) occurs commonly, sometimes as the earliest symptom. Some MS patients consider fatigue to be their most troublesome complaint, and it has been shown to be an independent predictor of impaired quality of life. Several reports have demonstrated that subcortical gray matter pathology is related to fatigue. We hypothesized that MRI detectable changes in the deep gray matter of MS patients may correlate with fatigue severity. Our objective was: to assess the relationship between fatigue severity and detectable changes on magnetic resonance imaging (MRI), quantified using the mean T1 relaxation time (T1), in deep gray matter structures in relapsing remitting multiple sclerosis (RRMS). Using region of interest analysis, T1 values were measured for the thalamus, putamen and caudate nucleus in 52 RRMS patients and 19 healthy volunteers. Fatigue was assessed using the Fatigue Severity Scale.

RESULTS

The median T1 in the thalamus and the putamen were significantly higher in the patient cohort than in the healthy controls; the median T1 in the caudate was also higher in the MS patients but did not reach statistical significance. There was a significant correlation between fatigue severity and the T1 of the thalamus (rho = 0.418; p = 0.014). Furthermore, the median T1 in the thalamus was significantly higher in patients with fatigue compared with those without (p = 0.018). Our results provide further evidence for the role of subcortical gray matter structures in the pathogenesis of multiple sclerosis (MS)-related fatigue. This study also demonstrates that T1 relaxation time measurement is a suitable technique for detecting abnormalities of the deep gray matter in RRMS and presents further support of gray matter involvement in MS.

Human myocardium: single-breath-hold MR T1 mapping with high spatial resolution--reproducibility study

A prospective study approved by the local ethics committee was performed to establish the normal range and reproducibility of myocardial T1 values as assessed with single-breath-hold T1 mapping with high spatial resolution. With a 1.5-T magnetic resonance (MR) imaging system, baseline and contrast material-enhanced modified Look-Locker inversion recovery, or MOLLI, imaging was performed in 15 healthy volunteers who had given written informed consent. Image quality scores and myocardial T1 values were derived for standard short-axis segments and sections. Results were compared with those from a second MR imaging study performed on the same day (baseline only) and those from a third study performed on a different day (baseline and contrast enhanced; eight volunteers). Intra- and interobserver agreement were determined. Myocardial T1 maps were obtained rapidly in a reproducible fashion. A normal range for baseline and postcontrast myocardial T1 was established (baseline mean T1 in short-axis sections, 980 msec +/- 53 [standard deviation]; 95% confidence interval: 964, 997; number of sections, 43). This technique could enable direct quantification of changes in tissue characteristics in ischemic and inflammatory myocardial diseases.