A proton NMR study on the hydration of normal versus psoriatic stratum corneum: linking distinguishable reservoirs to anatomical structures

The NMR behaviour of normal and psoriatic stratum corneum (SC) was investigated as a function of hydration with the aim of obtaining a better understanding of the role of water in the SC structure. Time domain NMR techniques were employed to identify the signal from water and that from nonaqueous components of the SC, such as lipids and proteins. The signals were investigated as a function of water content. The free induction decay was separated into mobile signal (from water and mobile lipids) and solid signal (from protein and 'solid' lipids). Spin-spin relaxation (T(2)) measurements further separated the mobile domains within the SC. The results suggested that, when water is added to dry SC, it first enters the corneocytes; then, at a hydration of 0.24-0.33 g H(2)O/g SC (normal SC) or 0.12-0.24 g H(2)O/g SC (psoriatic SC), water begins to accumulate in hydrated lipid regions. Water was found to exchange between these two domains on the time scale of a few hundred milliseconds. When compared with normal SC, psoriatic SC had a looser corneocyte structure, a larger mobile lipid component at low hydration and a smaller capacity for corneocyte water.

Proton MRS of large multiple sclerosis lesions reveals subtle changes in metabolite T(1) and area

The T(1) values of metabolites were measured in eight subjects with clinically definite multiple sclerosis (MS) having at least one large brain lesion (2.6 ± 0.7 mL) and in eight age- and sex-matched healthy controls. MRS examinations were conducted at 1.5 T using point-resolved spectroscopy (PRESS) (TE = 30 ms, TR = 530, 750, 1200, 1500, 3500, 5000 ms). Spectra were acquired from a voxel placed in the largest lesion in the subject with MS, and in a corresponding voxel (same size and region) in normal white matter (NWM) in the matched control, and were fitted using LCModel. As there are regional variations in metabolite and water T(1) and metabolite signal areas, careful placement of the control voxel was necessary to measure subtle differences between the lesions and NWM. The T(1) and T(1)-corrected signal areas of creatine were the same in MS lesions as in controls. The T(1) values of choline were significantly shorter in MS lesions located in occipital and parietal, but not in frontal, white matter. N-Acetylaspartate (NAA) and myoinositol T(1) values in MS lesions were similar to those in NWM; however, the area of myoinositol correlated directly with lesion water T(1), and the area of NAA correlated inversely with lesion water T(1). MR spectra acquired at short TR require T(1) correction of choline for accurate quantification. Careful voxel placement in controls to match lesion location in subjects with MS enables a clearer view of the subtle changes in lesions.

Pathological basis of diffusely abnormal white matter: insights from magnetic resonance imaging and histology

Background: The pathological basis of diffusely abnormal white matter (DAWM) in multiple sclerosis (MS) has not been elucidated in detail, but may be an important element in disability and clinical progression.

Methods: Fifty-three subjects with MS were examined with T1, multi-echo T2 and magnetization transfer (MT). Twenty-three samples of formalin-fixed MS brain tissue were examined with multi-echo T2 and subsequently stained for myelin phospholipids using luxol fast blue, for axons using Bielschowsky, immunohistochemically for the myelin proteins myelin basic protein (MBP) and 2′,3′-cyclic nucleotide 3′ phosphohydrolase (CNP) and for astrocytes using glial fibrillary acidic protein (GFAP). Regions of interest in DAWM were compared with normal appearing white matter.

Results: Fourteen of 53 subjects with MS in the in vivo study showed the presence of DAWM. Subjects with DAWM were found to have a significantly lower Expanded Disability Status Scale (EDSS) and shorter disease duration (DD) when compared with subjects without DAWM (EDSS: 1.5 versus 3.0, p = 0.031; DD: 5.4 versus 10.3 years, p = 0.045). DAWM in vivo had reduced myelin water and MT ratio, and increased T2 and water content. Histological analysis suggests DAWM, which shows a reduction of the myelin water fraction, is characterized by selective reduction of myelin phospholipids, but with a relative preservation of myelin proteins and axons.

Conclusions: These findings suggest that the primary abnormality in DAWM is a reduction or perturbation of myelin phospholipids that correlates with a reduction of the myelin water fraction.

Two-year study of cervical cord volume and myelin water in primary progressive multiple sclerosis

BACKGROUND

Spinal cord involvement in multiple sclerosis (MS) is common and an important element in disability. Previous studies demonstrated smaller cervical cord area at the C2 level in MS compared to controls, and a decrease in cord area over 12 months, most marked in primary progressive MS (PPMS). A subset of subjects participating in a multicentre, double-blind, placebo-controlled clinical trial evaluating the efficacy of glatiramer acetate in PPMS (PROMiSe trial) were followed for 2 years.

METHODS

24 PPMS subjects, randomized to placebo (n = 9) and glatiramer acetate (n = 15), and 24 matched controls were studied. Cervical cord volume (CCV) at C2-3 was determined using a 3D inversion recovery (IR)-prepared spoiled-gradient echo sequence. Myelin water fraction (MWF) at C2-3 was obtained using a 32-echo IR-prepared relaxation sequence. Scans were repeated at baseline, years 1 and 2.

RESULTS

Baseline CCV was significantly smaller for PPMS than controls [median (interquartile range) 951 (829-1043) vs. 1072 (1040-1129) mm(3), p = 0.0004] and MWF trended to be lower in PPMS cord [median (interquartile range) 0.225 (0.187-0.267) vs. 0.253 (0.235-0.266), p = 0.12]. Baseline CCV correlated with baseline Expanded Disability Status Scale, disease duration, brain white and grey matter volume. In PPMS, CCV was significantly decreased at year 1 (-0.83%, p = 0.04) and year 2 (-1.65%, p = 0.02). Baseline MWF correlated with baseline CCV and brain white and grey matter volume. MWF was significantly decreased from baseline for PPMS at year 2 (-10.5%, p = 0.01). Treatment effect was not detected on change in CCV nor MWF.

CONCLUSIONS

Metrics at the level of the cord, including volume and MWF at C2-3, were lower in PPMS than controls and changed over 2 years only in PPMS.

Reproducibility of myelin water fraction analysis: a comparison of region of interest and voxel-based analysis methods

This study compared region of interest (ROI) and voxel-based analysis (VBA) methods to determine the optimal method of myelin water fraction (MWF) analysis. Twenty healthy controls were scanned twice using a multi-echo T(2) relaxation sequence and ROIs were drawn in white and grey matter. MWF was defined as the fractional signal from 15 to 40 ms in the T(2) distribution. For ROI analysis, the mean intensity of voxels within an ROI was fit using non-negative least squares. For VBA, MWF was obtained for each voxel and the mean and median values within an ROI were calculated. There was a slightly higher correlation between Scan 1 and 2 for the VBA method (R(2)=0.98) relative to the ROI method (R(2)=0.95), and the VBA mean square difference between scans was 300% lower, indicating VBA was the most consistent between scans. For the VBA method, mean MWF was found to be more reproducible than median MWF. As the VBA method is more reproducible and gives more options for visualization and analysis of MWF, it is recommended over the ROI method of MWF analysis.

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.

MR evidence of long T2 water in pathological white matter

PURPOSE

To describe what, if any, specific long T(2)-related abnormalities occur in the white matter of subjects with either phenylketonuria (PKU) or multiple sclerosis (MS).

MATERIALS AND METHODS

The 48-echo T(2) relaxation data (maximum TE = 1.12 sec) were acquired from 15 PKU subjects, 20 MS subjects, and 15 healthy volunteers. Regions of interest were drawn in diffuse white matter hyperintensities (DiffWM), lesions, normal-appearing white matter (NAWM), and normal white matter. Long T(2) maps (200 msec < T(2) < 800 msec) were created for each subject.

RESULTS

A new water reservoir with a markedly prolonged T(2) peak was identified in DiffWM and NAWM in 12 out of 15 subjects with PKU and a long T(2) signal was also seen in 23/97 lesions in 50% of subjects with MS. Additionally, a long T(2) component was observed in the corticospinal tracts of 10 healthy volunteers. The characteristics of the long T(2) signal were unique for each subject group. Potential sources of this signal include vacuolation and increases in extracellular water.

CONCLUSION

This study supports the usefulness of increasing the data acquisition window of the multiecho T(2) relaxation sequence to better characterize the T(2) decay from pathological brain.

Complementary information from multi-exponential T2 relaxation and diffusion tensor imaging reveals differences between multiple sclerosis lesions

While conventional magnetic resonance imaging (MRI) has long been used to study multiple sclerosis (MS), more sensitive and specific approaches to studying both MS lesions and normal appearing white matter (NAWM) are needed to gain a better understanding of the pathogenesis of the disease. Two MRI techniques thought to offer insight regarding myelin and axonal integrity are T(2) relaxation and diffusion tensor imaging (DTI). In this study, metrics obtained from T(2) relaxation (specifically myelin water content (MWC) and long-T(2) fraction) and DTI experiments (in particular the fractional anisotropy, mean diffusivity <D>, parallel diffusivity lambda(||), and perpendicular diffusivity lambda(perpendicular)) were compared for 19 MS patients within both lesion and contralateral NAWM with the goal of better understanding how each of the measures are affected by pathology. In particular, it was successfully determined that the detection of a long-T(2) signal within an MS lesion is indicative of a different underlying pathology than is present in lesions without long-T(2) signal. All of the diffusion metrics were significantly different in lesions with a long-T(2) signal than in those without. While no significant correlations were found between MWC and <D>, lambda(||) or lambda(perpendicular) in NAWM (R(2)=0.02-0.04, p>0.07), and only weak correlations were found in lesions without long-T(2) signal (R(2)=0.05-0.14, p<0.04), strong correlations were observed in lesions exhibiting long-T(2) signal (R(2)=0.54-0.61, p<0.0001).

Long T2 water in multiple sclerosis: what else can we learn from multi-echo T2 relaxation?

Multi-echo T(2) measurements are invaluable in studying brain pathology in multiple sclerosis (MS). In addition to information about myelin water and total water content, the T(2) distribution has the potential to detect additional water reservoirs arising from other sources such as inflammation or edema. The purpose of this study was to better define the T(2) distribution in MS lesions and normal appearing white matter (NAWM) with particular emphasis on the characterisation of longer T(2) components. Magnetisation transfer (MT), T(1) and 48-echo T(2) relaxation data were acquired in 20 MS subjects and regions of interest were drawn in lesions and NAWM. Twenty-seven out of 107 lesions exhibited signal with a markedly prolonged T(2) (200-800 ms). Lesions with a Long-T(2) signal also exhibited a longer geometric mean T(2) (GMT(2)), increased water content (WC), higher T(1), reduced magnetisation transfer ratio (MTR) and decreased myelin water fraction (MWF) than lesions without a Long-T(2) signal. Those subjects with Long-T(2) lesions had a significantly longer disease duration than subjects without this lesion subtype. A strong correlation was observed between T(1) and Long-T(2) fraction, while a slightly weaker relationship was found for GMT(2), MTR and MWF with Long-T(2) fraction. A potential source of the Long-T(2) signal is an increase in extracellular water. This study supports the usefulness of increasing the data acquisition window of the multi-echo T(2) relaxation sequence to better characterise the T(2) decay in MS.

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.

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.

Characterization of the NMR behavior of white matter in bovine brain

In vitro experiments on 15 white matter samples from five bovine brains were performed on a 1H-NMR spectrometer at 24 degrees C and 37 degrees C. The average myelin water fractions (MWFs) were 10.9% and 11.8% for samples at 24 degrees C and 37 degrees C, respectively. The T1 relaxation time at 37 degrees C was found to be 830 ms, exhibiting monoexponential behavior. A four-pool model including intra/extracellular (IE) water, myelin water, nonmyelin tissue, and myelin tissue was proposed to simulate the NMR behavior of bovine white matter. A cross-relaxation correction was introduced to compensate for shifting of the measured data points and T2 times over the duration of the Carr-Purcell-Meiboom-Gill (CPMG) measurement due to cross relaxation. This correction was found to be slight, providing evidence that MWFs measured using a multiecho technique are near physical values. At 24 degrees C the cross-relaxation times between myelin tissue and myelin water, myelin water and IE water, and IE water and nonmyelin tissue were found to be approximately 227, 2064, and 402 ms, respectively. At 37 degrees C these same cross-relaxation times were 158, 1021, and 170 ms, respectively. The exchange rate between myelin water and myelin was found to be 11.8 s-1 at 37 degrees C, while the exchange rate between IE water and nonmyelin tissue was found to be 6.8 s-1. These exchange rates are of similar magnitude, which indicates that the interaction between IE water and nonmyelin tissue cannot be ignored.

Water content and myelin water fraction in multiple sclerosis

BACKGROUND

Measurements of the T2 decay curve provide estimates of total water content and myelin water fraction in white matter in-vivo, which may help in understanding the pathological progression of multiple sclerosis (MS).

METHODS

Thirty-three MS patients (24 relapsing remitting, 8 secondary progressive, 1 primary progressive) and 18 controls underwent MR examinations. T2 relaxation data were acquired using a 32-echo measurement. All controls and 18 of the 33 MS patients were scanned in the transverse plane through the genu and splenium of the corpus callosum. Five white matter and 6 grey matter structures were outlined in each of these subjects. The remaining 15 MS patients were scanned in other transverse planes. A total of 189 lesions were outlined in the MS patients. Water content and myelin water fraction were calculated for all regions of interest and all lesions.

RESULTS

The normal appearing white matter (NAWM) water content was, on average, 2.2% greater than that from controls, with significant differences occurring in the posterior internal capsules, genu and splenium of the corpus callosum, minor forceps and major forceps (p<0.0006). On average, MS lesions had 6.3% higher water content than contralateral NAWM (p<0.0001). Myelin water fraction was 16% lower in NAWM than for controls, with significant differences in the major and minor forceps, internal capsules, and splenium (p<0.05). The myelin water fraction of MS lesions averaged 52 % that of NAWM.

CONCLUSIONS

NAWM in MS has a higher water content and lower myelin water fraction than control white matter. The cause of the myelin water fraction decrease in NAWM could potentially be due to either diffuse edema, inflammation, demyelination or any combination of these features. We present a simple model which suggests that myelin loss is the dominant feature of NAWM pathology.

Abnormalities of myelination in schizophrenia detected in vivo with MRI, and post-mortem with analysis of oligodendrocyte proteins

Schizophrenia unfolds during the late period of brain maturation, while myelination is still continuing. In the present study, we used MRI and T2 relaxation analysis to measure the myelin water fraction in schizophrenia. In schizophrenia (n=30) compared with healthy subjects (n=27), overall white matter showed 12% lower myelin water fraction (P=0.031), with the most prominent effects on the left genu of the corpus callosum (36% lower, P=0.002). The left anterior genu was affected in both first-episode (P=0.035) and chronic patients (P=0.011). In healthy subjects, myelin water fraction in total white matter and in frontal white matter increased with age, and with years of education, indicating ongoing maturation. In patients with schizophrenia, neither relation was statistically significant. Post-mortem studies of anterior frontal cortex demonstrated less immunoreactivity of two oligodendrocyte-associated proteins in schizophrenia (2',3'-cyclic nucleotide 3'-phosphodiesterase by 33%, P=0.05; myelin-associated glycoprotein by 27%, P=0.14). Impaired myelination in schizophrenia could contribute to abnormalities of neural connectivity and persistent functional impairment in the illness.

Evolution of focal and diffuse magnetisation transfer abnormalities in multiple sclerosis

Magnetisation transfer (MT) imaging provides indirect information on tissue structure abnormalities in areas that otherwise may appear normal on conventional MRI. We determined the evolution of MT changes in normal appearing white matter (NAWM) and lesion on serial examination of 9 multiple sclerosis (MS) patients and age matched controls. The mean NAWM MT ratio (MTR) was found to correlate strongly (R = 0.93) with the length of time since the patient's first clinical presentation and was well characterized by a linear decrease of -0.16%/year (p < 0.0001). The time zero intercept of the NAWM MTR regression was 30.7 +/- 0.2%, not different from the average MTR of white matter from controls (30.4 +/- 0.2 %). An additional gradual decrease in NAWM MTR was observed 6 to 12 months before the appearance of a new lesion on conventional MRI, while a more precipitous decrease in MTR was seen 2 to 6 months before the lesion appeared. Those lesions that exhibited pre-lesion MTR decreases showed less MTR recovery than lesions which had no pre-lesion MTR decrease. The data suggest that the MTR of NAWM in MS undergoes a slow progressive decrease that starts at disease onset and accelerates rapidly in focal areas just prior to lesion appearance on conventional MRI.

Normal-appearing white matter in multiple sclerosis has heterogeneous, diffusely prolonged T(2)

T(2) relaxation in normal-appearing white matter (NAWM) of multiple sclerosis (MS) patients was reexamined using more complete sampling and analysis of decay curves, and to assess focal vs. diffuse abnormalities. Nine MS patients and 10 controls were scanned using a single-slice 32-echo pulse sequence with a 10-ms echo spacing. Decay curves from outlined white and gray matter structures were analyzed using non-negative least-squares (NNLS). Resulting T(2) distributions were each summarized by the geometric mean T(2), T(2). Different white matter structures had different mean (over the subjects in a group) T(2). Mean T(2) in NAWM was always greater than that of controls. Differences were not caused by a few voxels with extreme T(2) (i.e., focal lesions), but rather by shifts of the entire T(2) distribution (diffuse prolongation). This T(2) increase suggests diffuse myelin or axonal pathology.

Different magnetization transfer effects exhibited by the short and long T(2) components in human brain

Magnetization transfer ratios (MTRs) were measured separately for the two T(2) components in white matter. For both binomial and off-resonance sinc MT pulses, the MTR was larger for the short T(2) component than for the long T(2) component. This differential MT effect disappeared for delays between the MT pulse and the multi-echo pulse sequence longer than 200 msec, indicating exchange between the two components. When using the sinc MT pulse, the MTR for the short T(2) component was similar for different white matter structures, whereas it varied for different white matter structures when using the binomial pulse-a phenomenon attributed to direct saturation. When the sinc pulse frequency was brought closer to resonance, MTRs in white matter and doped water phantoms increased for both components but more so for the shorter T(2) component. This behavior was consistent with a Bloch equation model of direct saturation.

A pathology-MRI study of the short-T2 component in formalin-fixed multiple sclerosis brain

OBJECTIVE

To determine the pathologic basis of areas not exhibiting signal of the short-T2 component of the T2 relaxation distribution in MS, as studied in formalin-fixed brain.

BACKGROUND

A myelin-specific MRI signal would be of great importance in assessing demyelination in patients with MS. Evidence indicates that the short-T2 (10 to 50 millisecond) component of the T2 relaxation distribution originates from water in myelin sheaths. The authors present two cases of MS in which the anatomic distribution of the short-T2 component was correlated with the pathologic findings in postmortem formalin-fixed brain.

METHOD

One half of the formalin-fixed brain was suspended in a gelatin-albumin mixture cross-linked with glutaraldehyde, and scanned with a 32-echo MRI sequence. The brain was then cut along the center of the 5-mm slices scanned, photographed, dehydrated, and embedded in paraffin. Paraffin sections, stained with Luxol fast blue and immunocytochemically for 2',3'-cyclic nucleotide 3'-phosphohydrolase for myelin and by the Bielschowsky technique for axons, were compared with the distribution of the amplitude of the short-T2 component of the comparable image slices.

RESULTS

The anatomic distribution of the short-T2 component signal corresponded to the myelin distribution. Chronic, silent MS plaques with myelin loss correlated with areas of absence of short-T2 signal. The numbers of axons within lesions were reduced, but many surviving axons were also seen in these areas of complete loss of myelin.

CONCLUSION

In formalin-fixed MS brains the short-T2 component of the T2 relaxation distribution corresponds to the anatomic distribution of myelin. Chronic, silent demyelinated MS plaques show absence of the short-T2 component signal. These results support the hypothesis that the short-T2 component originates from water related to myelin.-1510

A comparison between magnetization transfer ratios and myelin water percentages in normals and multiple sclerosis patients

Magnetization transfer and T2 relaxation data were obtained for five white and six gray matter brain structures from 10 normal volunteers and 9 multiple sclerosis patients. Thirty MS lesions were also analyzed. Magnetization transfer ratios and myelin water percentages were compared. Both techniques showed a significant difference between the average of white and gray matter of the normal volunteers as well as the average of normal-appearing white matter and gray matter of the multiple sclerosis patients. The average magnetization transfer ratio and myelin water percentage for lesions were significantly lower than those of normal-appearing white matter. Myelin water percentages and magnetization transfer ratios were uncorrelated in white and gray matter but showed a small (R = 0.5, P = 0.005) but significant correlation in multiple sclerosis lesions. In summary, the myelin water percentage and the magnetization transfer ratio provide quantifiable but largely independent measures of multiple sclerosis lesion pathology.