Quantitative nuclear magnetic resonance imaging: characterisation of experimental cerebral oedema

Evaluation of acute brain edema using quantitative magnetic resonance imaging: effects of pretreatment with dexamethasone

We developed a quantitative magnetic resonance imaging method to permit a rapid assessment of brain water content during osmotic brain edema produced by intraperitoneal (ip) injection of distilled water. Fifteen minutes after water injection, the normalized mean image intensity (MIn) from a spin-echo pulse sequence (TE = 80 ms, TR = 1085 ms) was the same as that measured from control animals not injected with water. Sixty minutes after the water injection, the mean +/- SEM brain image MIn had increased by 10.8 +/- 2.4% compared to 3.4 +/- 0.7% in control animals (P less than 0.05). Blood plasma osmolality decreased by 6-10% during this time interval. A subsequent ip injection of hypertonic NaCl solution (100 gm/liter) caused the blood plasma osmolality and brain image MIn to return toward their initial values. MIn of cerebral gray matter correlated with tissue water content measured in parallel studies. Animals pretreated with 0.25 mg/(kg day) dexamethasone had cerebral gray matter MIn values during osmotic edema which were lower than those of untreated animals.

In vivo evaluation of the reproducibility of T1 and T2 measured in the brain of patients with multiple sclerosis

The precision (reproducibility) of relaxation times derived from magnetic resonance images of patients with multiple sclerosis (MS) were investigated. Measurements of 10 MS patients were performed at 1.5 T on two occasions within 1 wk. T1 and T2 was measured using a partial saturation inversion recovery sequence (6 points) and a Carr-Purcell-Meiboom-Gill phase alternating-phase shift multiple spin-echo sequence with 32 echoes. Regions of interest (ROI) were placed both in apparently normal white matter and plaques. The precision (+/- 1.96 SD) and the confidence intervals for T1 and T2 for white matter and plaques were calculated. The precision of T1 for white matter and plaques was respectively +/- 94 msec and +/- 208 msec. The precision of T2 for white matter and plaques was respectively +/- 18 msec and +/- 26 msec. For all measurements the coefficient of variation was about 9%. Judging from our own study and others as well, a precision better than 10% for T1 and T2 would seem unrealistic at present.

Nuclear magnetic resonance T2 relaxation times in multiple sclerosis

An original method was used to carry out the mathematical analysis of T2 transverse magnetization decay curves and the measure of T2 relaxation times on multiple sclerosis (MS) patients. The presumably normal white matter (WM) of these patients presented higher T2 relaxation times (98.6 msec), in comparison with that found in a population sample (88 msec). In this case, magnetization decay curves remain mostly monoexponential and are characterized by a single T2. On the other hand, areas of increased signal (AIS) curves are always better fitted by a biexponential function characterized by a short (82 msec) and a long (greater than 200 msec) T2. The spreading out of long T2 varies from one AIS to another in the same patient and among different patients; values of long T2 also vary with time, but without any correlation with the clinical state. In fact, no correlation was been established between relaxation times and clinical parameters. Quantitative MRI therefore enables a different approach to interpret MRI images; results suggest that several histobiochemical parameters play a role in the pathogenesis of an AIS and that MS is a dynamic and constantly evolving disease.

Diffusion-weighted imaging of kainic acid lesions in the rat brain

We present T2-weighted and diffusion-weighted images of kainic acid lesions in the rat brain. Our observations show improved image contrast between edematous lesions and unaffected tissue using diffusion-weighted imaging. Furthermore, we show that the anisotropic intensity changes associated with this sequence can be used to highlight white matter tracts and to provide information concerning their orientation in the rat brain.

Cognitive abnormalities in multiple sclerosis: a psychometric and MRI study

This study reports the cognitive abnormalities of a group of 58 patients with definite multiple sclerosis (MS). The psychometric functions measured were: 'IQ deficit', verbal and visual memory, abstracting ability, visual and auditory attention and naming ability. The presence of brain pathology was investigated using magnetic resonance imaging (MRI). A group of 46 physically disabled controls without significant brain disease was used for comparison. Normative MRI data were obtained from a group of 40 normal volunteers. The psychometric performance of the MS group was compared to the previously reported findings in patients with clinically isolated syndromes. MS patients had widespread cognitive deficits sparing naming ability and affecting verbal memory less severely than other intellectual functions. The overall performance on psychometric tests was related to the severity of the MRI abnormalities and to the duration of the illness, but was not significantly influenced by the presence of psychiatric morbidity or the degree of physical disability. Patients with clinically isolated syndromes occupied an intermediate position between MS patients and disabled controls in terms of cognitive and MRI abnormalities.

In vivo determination of multiexponential T2 relaxation in the brain of patients with multiple sclerosis

In vivo measurement of T2 relaxation times in multiple sclerosis (MS) lesions by magnetic resonance imaging (MRI) is potentially useful for the evaluation of the disease activity. Seven patients with definite MS were investigated over a period of three years (19 examinations), using a whole-body MRI scanner operating at 0.15 T with a specially designed high-power radio-frequency head coil. A modified CPMG sequence with a 180 degree pulse interval of TE = 6 msec and 128 echoes was used for the T2 relaxation measurement of the areas of increased signal (AIS) and white matter (WM). A biexponential T2 analysis of each pixel of the spin-echo images was computed. The T2 relaxation processes were found to be a monoexponential function in WM. The T2 relaxation times of apparently normal white matter in MS patients was significantly longer than in control subjects. The T2 relaxation curves of the AIS were found in most cases to fit a biexponential function characterized by a short and a long T2. T2 long relaxation times of AIS were spread out over a wide range (150-560 msec). The study of T2 long histograms shows that some AIS can be divided into two or three parts depending on the T2 long values. Each of these parts may correspond to a pathological process such as edema, demyelination and gliosis. Evolution of T2 relaxation times over a period of time cannot as yet be correlated with modifications in the clinical state.

Major differences in the dynamics of primary and secondary progressive multiple sclerosis

In patients with primary and secondary progressive multiple sclerosis (MS), major differences in the pattern and extent of abnormality on cerebral magnetic resonance imaging (MRI) between the two groups have recently been demonstrated. In the present study, 24 patients, matched for age, sex, duration of disease, and disability, had serial gadolinium diethylenetriaminepentaacetic acid-enhanced MRI over a 6-month period. The 12 patients in the secondary progressive group had a total of 109 new lesions over this time (18.2 lesions per patient per year) and 87% of these enhanced. Enhancement also occurred within and at the edge of preexisting lesions. In contrast, only 20 new lesions were seen in the primary progressive group (3.3 lesions per patient per year) and only one of these enhanced. There was no difference in the degree of clinical deterioration between the two groups over the 6-month period. These findings may indicate a difference in the dynamics of disease activity between the two forms of progressive MS, particularly in relation to the inflammatory component of the lesions, and have important implications for the selection of patients and the monitoring of disease activity in therapeutic trials.

Characterization of periventricular edema in normal-pressure hydrocephalus by measurement of water proton relaxation times

The magnetic resonance longitudinal relaxation time (T1) and transverse relaxation time (T2) of the water proton of the periventricular white and cortical gray matter were measured for 17 control patients and 21 patients with suspected normal-pressure hydrocephalus (NPH). Of the latter group, 14 showed good response to shunting (true-NPH group) and seven showed no response (false-NPH group). In the true-NPH group, both the T1 and the T2 of the periventricular white matter were significantly prolonged compared to the control values, and slowly shortened after cerebrospinal fluid (CSF) shunting. The true-NPH group showed significantly longer T1 and T2 of the white matter than did the false-NPH group. The T1 and T2 of the white matter were longer than those of the gray matter in this group, which was the reverse of the relationship observed in the control patients. In the white matter of the false-NPH group, there was a significant prolongation of T1 only; no difference was seen in the T2 compared to control values. There was no change in either T1 or T2 of this region after CSF shunting. The false-NPH group showed no significant difference in either T1 or T2 between the white and the gray matter. There was no difference in either T1 or T2 of the gray matter between the false-NPH and control groups or between preshunt and postshunt measurements in each patient group. It is suggested that a distinction between true- and false-NPH, which cannot be made from the radiographic appearance alone, may be possible from measurement of relaxation times. The mechanism of varied relaxation behavior between two entities may be explained by a difference in properties of the biological water and its environment.

Rebound of ICP after brain compression. An MRI study in dogs

The rebound of intracranial pressure (ICP) occurring after decompression of an intracranial mass lesion was studied in an epidural balloon compression model. Intracranial morphology and brain tissue water content were assessed with magnetic resonance imaging (MRI). Fast and slow components of the transverse relaxation time (T2) were used as indicators of brain oedema development. During balloon compression a progressive prolongation of both the fast and the slow T2 components took place. Following deflation of the balloon both components increased rapidly, particularly the slow-T2. The MR scans displayed progressive occlusion of the aqueduct, and obliteration of the ambient and pontine cisterns. The changes in morphology and in water content after decompression had largely the same time course as the development of the rebound of ICP. In contrast, no changes in morphology and tissue water content occurred after hydrostatic brain compression achieved by subarachnoid fluid infusion. The findings suggest that the intracranial pressure rebound is caused by cerebral oedema accumulated during and particularly in the recirculation phase after an ischaemic injury of adequate intensity and adequate duration.

Magnetic resonance imaging in asymptomatic disseminated vasculomyelinopathy

Two cases of disseminated vasculomyelinopathy (one of acute disseminated encephalomyelitis (ADEM), the other of acute transverse myelitis), are reported because of the persistence, 3 years and 5 months respectively, of abnormalities of magnetic resonance imaging (MRI). These abnormalities remained although in the first case the disease had been essentially asymptomatic from the onset except for one seizure, the patient remaining neurologically intact, whereas in the second case, the patient had made a complete recovery from very serious neurologic dysfunction. The first case illustrates the fact that ADEM may rarely occur without any symptoms, even in the presence of severe imaging abnormalities in both CT and MRI. Neither the persistence of a blood-brain barrier permeability alteration nor gliosis can satisfactorily explain the MRI changes, and thus the pathological significance of areas of increased signal intensity in MRI remains poorly understood and a matter of uncertainty. This report emphasizes the futility of attempting to correlate any kind of clinical observation, laboratory parameter, or effect of therapeutic regimens with changes, or lack thereof, in the MRI in multiple sclerosis and disseminated vasculomyelinopathy.

The role of MRI scanning in neuro-ophthalmology

The role of high resolution magnetic resonance imaging (MRI) in the assessment of optic atrophy, chiasmal compression, and posterior fossa lesions is demonstrated. Good spatial resolution, absence of bony artifact and multiplanar imaging are significant advantages over CT scanning in these areas, as is the ability to detect areas of demyelination. Orbital MRI offers future potential but at present we think that CT scanning provides better spatial resolution and is more cost effective for the orbit.

Assessment of demyelination, edema, and gliosis by in vivo determination of T1 and T2 in the brain of patients with acute attack of multiple sclerosis

This study intended to investigate the possibility of magnetic resonance (MR) to characterize the acute plaque due to multiple sclerosis (MS). To obtain information, in vivo measurements of relaxation processes were performed in 10 patients with known acute MS plaques, using a whole-body superconductive MR-scanner, operating at 1.5 T. The measurements were repeated several times, from onset of the disease and during remission by use of six-point partial saturation inversion recovery and 32-echo multiple spin-echo sequences, giving T1 and T2, respectively. We also focused on the issue, whether T1 and T2 relaxation processes in fact were monoexponential. The results of the first T1 and T2 measurements of the acute plaques were not clearly different from T1 and T2 of presumably chronic plaques obtained in a group of chronic MS patients previously (H.B.W. Larsson, J. Frederiksen, L. Kjär, O. Hendriksen, and J. Olesen, Magn. Reson. Med. 7, 43 (1988)). In some of the acute plaques a slight initial increase in T1 and T2 was seen, when the measurement was repeated in about 10 days. Thereafter T1 decreased slowly in all but one patient as a function of days. In all cases the T1 relaxation process followed a monoexponential course. The T2 relaxation process was a monoexponential function in the acute plaques, when measured within 20 days from onset of disease. After an average of 78 days, however, the T2 relaxation process clearly became biexponential in all but two patients. Later some of the relaxation curves changed back toward monoexponentiality. Thus, the study shows that it is possible to detect significant changes in MR parameters during the evolution of the disease, and these changes are discussed in relation to knowledge of pathoanatomical events in MS.

The value of T1-weighted images in the differentiation between MS, white matter lesions, and subcortical arteriosclerotic encephalopathy (SAE)

The aim of the study was to define reliable criteria for the differentiation of MR imaging between patients with MS and with "vascular" white matter lesions/SAE. We examined 35 patients with proven MS according to the Poser criteria and 35 patients with other white matter lesions and/or SAE. The result is that with MR a differentiation can be achieved provided that T1-weighted spin-echo sequences are included and the different pattern of distribution is considered. MS plaques are predominantly located in the subependymal region, vascular white matter lesions are mainly located in the water-shed of the superficial middle cerebral branches and the deep perforating long medullary vessels in the centrum semiovale. Infratentorial lesions are more often seen in MS. Confluence at the lateral ventricles is frequently accompanied by confluent abnormalities around the third ventricle, Sylvian aqueduct, and fourth ventricle, which is uncommon in SAE. In MS many lesions visible on T2-weighted images have a cellular or intracellular composition that renders them visible also on T1-weighted ones as regions with low signal intensity and more or less distinct boundary. "Vascular" white matter lesions and SAE mainly represent demyelination and can therefore be seen on T2-weighted images, but corresponding low signal intensity lesions on T1-weighted images are uncommon. In some exceptions there are such lesions with low signal representing lacunar infarcts or widened Virchow-Robin-spaces.

Magnetic resonance imaging in Leber's optic neuropathy

Thirteen males with Leber's optic neuropathy had magnetic resonance imaging (MRI) of the brain, and in eight the optic nerves were imaged using STIR (Short Time Inversion Recovery) sequences. All optic nerve scans were abnormal. In seven with bilateral visual loss four showed bilateral increased optic nerve signal and three unilateral increase. The involvement was of the mid and posterior intra-orbital sections over three 5 mm slices or more with sparing of the anterior portion. One patient with unilateral visual loss had increased signal only on the affected side. Brain MRI was normal, in marked contrast to the findings in clinically isolated optic neuritis in which multiple white matter lesions are seen in the majority.

Improved sensitivity of MRI in multiple sclerosis by use of extensive standardized procedures

The relative value of two different MRI procedures for the assessment of infratentorial extension in multiple sclerosis (MS) was studied. Multislice spin-echo techniques were used overall. Procedure A consisted of parasagittal T1-weighted images (500/30) and axial T2-weighted images (2500/30, 2500/120). Procedure B consisted of parasagittal T2-weighted images (1600/35, 1600/90). In the parasagittal T2-weighted images clear visualization of MS lesions is achieved because signal intensities of CSF and normal nervous tissue are nearly identical. All images were performed with a 0.5 Tesla MR system. Data were obtained in 98 patients with definite (N = 30) or probable MS (N = 68). Areas with abnormal signal intensity in the infratentorial regions (brainstem, cerebellum, and/or cervical spinal cord) were identified in 44% of the patients with procedure A and in 64% with procedure B. The standard application of the combination of both procedures improves the sensitivity of the MR examination for the diagnosis of MS, the delineation of infratentorial lesions and the correlation between clinical and MR data without excessively increasing imaging time.

One-year MR imaging follow-up of patients with multiple sclerosis under cortisone therapy

Twenty patients with relapsing/remitting course of MS were studied four times with MR imaging over the course of one year. First MR was undertaken during the acute relapse, afterwards patients were given cortisone therapy for four to six weeks. The second MR study followed 4-6 weeks after the first, the patients at this time being in remission. The third MR study was carried out 4 months after the first, the last scan one year after the first. The total number of lesions varied, though not greatly, over the whole follow-up, but there was an influence of the clinical course of MS on the pattern of lesions in MR imaging, mostly in respect to the number of confluences and the size of the lesions. Follow-up over one year showed that the inflammatory process produced an increase in the number of plaques, independent of the fact that most patients stayed in remission. A delayed effect of the cortisone therapy on the size, number, and confluence of plaques is suggested whilst clinical signs improved in most cases immediately after the beginning of drug therapy. Independent of the clinical course of the disease in some cases plaques previously seen vanished and others appeared in one and the same examination.

Proton magnetic resonance studies of triethyltin-induced edema during perinatal brain development in rabbits

To better understand the role of myelin-associated water in the differentiation of white and gray matter in magnetic resonance (MR) imaging, changes in MR relaxation processes were studied in rabbits during myelination and after induction of cytotoxic edema with triethyltin (TET). Normal rabbits were killed at various age intervals ranging from premature (28 days' gestation) to adult, and changes in MR relaxation times (T1 and T2) and in water and electrolyte content were determined for various areas of brain and muscle. Similar measurements were made in rabbits of comparable age exposed to TET. Light and electron microscopy and MR imaging were used to follow myelin development and morphological changes induced by TET. During the first 30 postnatal days, both T1 and T2 declined by 50% in normal rabbits, a fall that paralleled the loss in brain water and sodium that occurred during the same period. Exposure to TET prolonged T1 and T2 in white but not gray matter, reflecting the accumulation of sodium and water (edema fluid) in white matter areas. Multiexponential analysis revealed a second, longer component in T2 magnetization decay of TET-exposed white matter, presumably attributable to accumulation of non-ordered water within intramyelinic vacuoles, a supposition consistent with electron microscopic and MR imaging findings. In contrast to reports by others, changes in T1 (but not T2) closely correlated with alterations in brain water (r = 0.93, df = 39). The absence of tissue disruption in the animals in the present study may account for these differences, but further studies will be required both to resolve this question and to fully understand MR images of white matter edema in mature and immature brain.

Magnetic resonance imaging of silastic-induced canine hydrocephalus

Nine adult beagle dogs underwent magnetic resonance imaging in a 2-Tesla small-bore unit. Six surviving dogs were followed up serially with magnetic resonance imaging after induction of hydrocephalus by injection of Silastic into the prepontine cistern or fourth ventricle. Ventricular size (Y) measured as percentage cross-sectional area of an anterior frontal slice was related to postoperative day (X) as Y = 1.54 + 4.21 x ln(X), r = 0.9596. Periventricular edema appeared initially in the superlateral angles of the frontal horns in an area that corresponded histologically to the subcallosal fasciculus. T1 relaxation time of normal white matter of 979.32 msec increased to 1813.90 msec in the area of the edema (p less than 0.0001). The T2 relaxation time of normal white matter of 83.39 msec increased to 238.26 msec in the area of the edema (p less than 0.0001). Histological changes included expansion of the extracellular space in an area comparable to the region of increased signal intensity on T2-weighted images, as well as diffuse astrocytosis in the chronically hydrocephalic dogs.

A magnetic resonance imaging study of experimental cerebral edema and its response to dexamethasone

Vasogenic edema following cortical freezing, and its response to dexamethasone were studied in cats. The time course of the edema shown by MRI was the same as that observed by invasive techniques. Dexamethasone retards early edema formation and may reduce its total volume, but does not accelerate its disappearance.

MR brain scanning in patients with vasculitis: differentiation from multiple sclerosis

We performed MR (magnetic resonance) brain imaging on 24 patients with a systemic vasculitis. MRI proved to be a sensitive method for detecting brain lesions (clinically silent or manifest) in these patients. The most frequent abnormalities were periventricular lesions seen in 12 cases. Such changes are not specific for vascular disease, and are often seen in multiple sclerosis. However, additional changes were commonly seen which suggested the correct diagnosis.