NMR imaging of the brain

Accelerated multislice MRI with patterned excitation

PURPOSE

Accelerate multislice 2D MRI by using RF pulses that simultaneously act on different slices to combine contrast preparation and image acquisition.

THEORY AND METHODS

MRI applications often require the use of multiple RF pulses to generate desired contrast and prepare the signal for readout. Examples are the use of inversion prepulses to generate T1 contrast, or the use of spin-echo preparations to generate T2 or diffusion contrast. In multislice MRI, this separation of contrast preparation and readout can render scans time-inefficient and lengthy. We introduce a class of pulse sequences that overcomes this inefficiency by combining contrast preparation and signal readout. This is accomplished by using RF pulses that manipulate the magnetization of multiple slices simultaneously and a gradient crusher scheme that selects a target slice for readout.

RESULTS

Feasibility of the method was demonstrated for spin echo-based measurement of water diffusion and tissue pulsation in human brain at 3 T. Increases in time-efficiency and reductions in scan time were highly dependent on specific implementation and reached as high as 25% and 53%, respectively.

CONCLUSION

A novel approach to multislice MRI is demonstrated that reduces scan time for specific applications.

Myelin and Modeling: Bootstrapping Cortical Microcircuits

Histological studies of myelin-stained sectioned cadaver brain and in vivo myelin-weighted magnetic resonance imaging (MRI) show that the cerebral cortex is organized into cortical areas with generally well-defined boundaries, which have consistent internal patterns of myelination. The process of myelination is largely driven by neural experience, in which the axonal passage of action potentials stimulates neighboring oligodendrocytes to perform their task. This bootstrapping process, such that the traffic of action potentials facilitates increased traffic, suggests the hypothesis that the specific pattern of myelination (myeloarchitecture) in each cortical area reveals the principal cortical microcircuits required for the function of that area. If this idea is correct, the observable sequential maturation of specific brain areas can provide evidence for models of the stages of cognitive development.

Mobile phones, cordless phones and rates of brain tumors in different age groups in the Swedish National Inpatient Register and the Swedish Cancer Register during 1998-2015

We used the Swedish Inpatient Register (IPR) to analyze rates of brain tumors of unknown type (D43) during 1998–2015. Average Annual Percentage Change (AAPC) per 100,000 increased with +2.06%, 95% confidence interval (CI) +1.27, +2.86% in both genders combined. A joinpoint was found in 2007 with Annual Percentage Change (APC) 1998–2007 of +0.16%, 95% CI -0.94, +1.28%, and 2007–2015 of +4.24%, 95% CI +2.87, +5.63%. Highest AAPC was found in the age group 20–39 years. In the Swedish Cancer Register the age-standardized incidence rate per 100,000 increased for brain tumors, ICD-code 193.0, during 1998–2015 with AAPC in men +0.49%, 95% CI +0.05, +0.94%, and in women +0.33%, 95% CI -0.29, +0.45%. The cases with brain tumor of unknown type lack morphological examination. Brain tumor diagnosis was based on cytology/histopathology in 83% for men and in 87% for women in 1980. This frequency increased to 90% in men and 88% in women in 2015. During the same time period CT and MRI imaging techniques were introduced and morphology is not always necessary for diagnosis. If all brain tumors based on clinical diagnosis with CT or MRI had been reported to the Cancer Register the frequency of diagnoses based on cytology/histology would have decreased in the register. The results indicate underreporting of brain tumor cases to the Cancer Register. The real incidence would be higher. Thus, incidence trends based on the Cancer Register should be used with caution. Use of wireless phones should be considered in relation to the change of incidence rates.

Advanced MRI strategies for assessing spinal cord injury

Advanced magnetic resonance (MR) approaches permit the noninvasive quantification of macromolecular, functional, and physiological properties of biological tissues. In this chapter, we review the application of advanced MR techniques to the spinal cord. Macromolecular properties of the spinal cord can be studied using magnetization transfer (MT) MR, diffusion tensor imaging (DTI), Q-space diffusion spectroscopy, and selective detection of myelin water. The functional and metabolic status of the spinal cord can be studied using functional MRI (fMRI), perfusion imaging, and magnetic resonance spectroscopy (MRS). Finally, we consider the outlook for advanced MR studies in persons in whom metal hardware has been implanted to stabilize the cord. In spite of the spinal cord's diminutive size, its location deep within the body, and constant motion, recent work shows that the spinal cord can be studied using these advanced MR approaches.

Advanced MRI strategies for assessing spinal cord injury

Advanced magnetic resonance (MR) approaches permit the noninvasive quantification of macromolecular, functional, and physiological properties of biological tissues. In this chapter, we review the application of advanced MR techniques to the spinal cord. Macromolecular properties of the spinal cord can be studied using magnetization transfer (MT) MR, diffusion tensor imaging (DTI), Q-space diffusion spectroscopy, and selective detection of myelin water. The functional and metabolic status of the spinal cord can be studied using functional MRI (fMRI), perfusion imaging, and magnetic resonance spectroscopy (MRS). Finally, we consider the outlook for advanced MR studies in persons in whom metal hardware has been implanted to stabilize the cord. In spite of the spinal cord's diminutive size, its location deep within the body, and constant motion, recent work shows that the spinal cord can be studied using these advanced MR approaches.

Negative fluid-attenuated inversion recovery imaging identifies acute ischemic stroke at 3 hours or less

OBJECTIVE

To evaluate the use of fluid-attenuated inversion recovery (FLAIR) imaging as surrogate marker of lesion age within the first 6 hours of ischemic stroke.

METHODS

e analyzed FLAIR and diffusion-weighted imaging (DWI) sequences performed within 6 hours of symptom onset in 120 consecutive patients with ischemic stroke with known symptom onset. The visibility of acute ischemic lesions on FLAIR images was judged in two steps (on FLAIR alone and with knowledge of DWI) and compared with DWI.

RESULTS

egative FLAIR in the case of positive DWI allocated ischemic lesions to a time window 3 hours or less with a high specificity (0.93) and a high positive predictive value (0.94), whereas sensitivity (0.48) and negative predictive value (0.43) were low. Lesion visibility on FLAIR images alone (35.6%) and with knowledge of DWI (62.5%) was lower than on DWI (97.1%). The sensitivity of FLAIR increased with increasing time from symptom onset from 27.0/50.0% <or= 3 hours to 56.7/93.3% after 3 to 6 hours (FLAIR alone/with knowledge of DWI). Multivariate regression analysis spotted longer time from symptom onset and larger size of the ischemic lesion as independent predictors of lesion visibility on FLAIR images.

INTERPRETATION

"mismatch" between positive DWI and negative FLAIR allows the identification of patients that are highly likely to be within the 3-hour time window. Within the first 6 hours of stroke, the sensitivity of FLAIR sequences for acute ischemic lesions increases with time from symptom onset elapsing, approximating 100% after 3 to 6 hours.

T2 detection of tumor invasion within segmented components of glioblastoma multiforme

PURPOSE

To use T2-weighted images to detect tumor invasion when comparing normal individuals to groups of gliomablastoma multiforme (GBM) patients with varying levels of CXCR4, a chemokine receptor that promotes tumor migration.

MATERIALS AND METHODS

T2-weighted images were acquired preoperatively in 22 treatment-naïve GBM patients. Two groups were formed based on the expression levels of CXCR4. A third group of normal volunteers was used for comparison. Each image was segmented to obtain four different clusters for tissue types identified as white matter, basal ganglia, gray matter/edema and cerebrospinal fluid (CSF)/tumor. Signal intensity histograms were formed for each cluster and compared between groups.

RESULTS

In every cluster the GBM groups displayed significantly higher standard deviations of intensity distributions when compared to normal subjects. Significant differences in skewness were found between normal subjects and GBM patients in the white matter, basal ganglia, and CSF/tumor. Further, when the two groups of GBM patients were compared the CXCR4-high group was found to have a significant shift in the median intensity values in the cluster containing gray matter and peritumoral edema.

CONCLUSION

T2 signal intensity histograms in normal subjects differ significantly from those obtained from GBM groups, suggesting widespread dissemination of disease.

Susceptibility-weighted imaging: technical aspects and clinical applications, part 1

Susceptibility-weighted imaging (SWI) is a new neuroimaging technique, which uses tissue magnetic susceptibility differences to generate a unique contrast, different from that of spin density, T1, T2, and T2*. In this review (the first of 2 parts), we present the technical background for SWI. We discuss the concept of gradient-echo images and how we can measure local changes in susceptibility. Armed with this material, we introduce the steps required to transform the original magnitude and phase images into SWI data. The use of SWI filtered phase as a means to visualize and potentially quantify iron in the brain is presented. Advice for the correct interpretation of SWI data is discussed, and a set of recommended sequence parameters for different field strengths is given.

MRI texture analysis on texture test objects, normal brain and intracranial tumors

Texture analysis was performed in three different MRI units on T1 and T2-weighted MR images from 10 healthy volunteers and 63 patients with histologically confirmed intracranial tumors. The goal of this study was a multicenter evaluation of the usefulness of this quantitative approach for the characterization of healthy and pathologic human brain tissues (white matter, gray matter, cerebrospinal fluid, tumors and edema). Each selected brain region of interest was characterized with both its mean gray level values and several texture parameters. Multivariate statistical analyses were then applied in order to discriminate each brain tissue type represented by its own set of texture parameters. Texture analysis was previously performed on test objects to evaluate the method dependence on acquisition parameters and consequently the interest of a multicenter evaluation. Even obtained on different sites with their own acquisition routine protocol, MR brain images contain textural features that can reveal discriminant factors for tissue classification and image segmentation. It can also offer additional information in case of undetermined diagnosis or to develop a more accurate tumor grading.

Stereotactic anatomy of the posterior cranial fossa. A study of the transcerebellar approach to the brainstem

The stereotactic transcerebellar (suboccipital) approach to the brainstem is one of the most accessible routes to reach targets located in the pons or in the medulla oblongata. Its use requires a perfect knowledge of the stereotactic anatomy of the posterior cranial fossa, and a standard reference system related to structures of the brainstem itself which can easily be visualized by Nuclear Magnetic Resonance. The present work consists in a three-dimensional variability study of the human posterior cranial fossa with its main contents, based on the investigation of 30 normal specimens (hemifossae). A new stereotactic reference system is proposed for the pons and the medulla, comprising three orthogonal** planes: the midsagittal plane, the IVth ventricular floor plane and the pontomedullary junction plane. A standard "safety access tunnel" was defined for the transcerebellar approach to the pons and, with some limitations, to the medulla. A complementary investigation, based upon angiographic studies, was carried out to define a safe "entry zone" to the posterior cranial fossa of the occipital bone beneath the transverse venous sinus.

Controversies in the management of subdural empyema. A study of 41 cases with review of literature

Forty one cases of subdural empyema treated between 1977 and 1988 at the Postgraduate Institute of Medical Education and Research. Chandigarh, have been analysed. The patients ranged from 9 days to 80 years of age. There were 22 children, including 11 infants. Fever, altered sensorium and seizures were the most common symptoms present for 1 day to 6 months. Otogenic infection was the commonest aetiological factor followed by postoperative and posttraumatic causes. Thirty seven patients had supratentorial empyemas, including 4 with parafalcine collections, three had infratentorial empyemas, and in one there was extension of the empyema from the supratentorial to the infratentorial compartment. Therapeutic modalities used included percutaneous needle aspirations in infants and burr hole evacuation and craniotomies in adults. A wide spectrum of organisms was detected. Mortality in this series was 24%, which was mainly attributable to the deteriorated neurological status prior to treatment. A detailed review of the literature has been given, highlighting various controversies in the management of SDE. Important prognostic factors and a treatment plan are suggested.

Computed tomography versus magnetic resonance imaging of the brain. A collaborative interinstitutional study

A retrospective study (1983-1984) of magnetic resonance imaging (MRI) and computed tomography (CT) examinations in 471 patients with known pathology in the brain and craniocervical junction was conducted in order to determine the relative efficacy of MRI versus CT. All MRI examinations involved slice thickness greater than 10 mm, and only single-slice single-echo or multislice single-echo imaging techniques were available. These studies were evaluated independently by two neuroradiologists from a panel of six for anatomic abnormalities, lesion contrast, and radiologist's impression. Results, which excluded microadenomas of the pituitary and approximately 9% of studies in which consensus was not achieved by the readers, were as follows: (1) 14% of the studies were positive on MRI but normal on CT; (2) in 55% of the studies, MRI was better than CT; (3) MRI was equal or better than CT in 95% of the studies; and (4) CT was better than MRI in 5% (21/421) of the examinations. There were no patients in this series where CT was positive but MRI missed the abnormality.

Subcortical arteriosclerotic encephalopathy--a controlled psychometric study

Eleven patients with subcortical arteriosclerotic encephalopathy (SAE) were assessed psychometrically, and the results compared with control subjects without neurological disorders and patients with a single cerebral vascular lesion (CVL). The groups were matched for sex, age, years of education, and in addition for the CVL group, the nature, site and size of the discrete vascular lesion. The SAE patients had mild to moderate impairment in intellectual, memory, receptive language and constructional functions, but individual performance ranged from near normality to severe impairment. The differences between the performance of SAE patients and the controls were significant in the majority of tests. The SAE patients had lower scores than CVL patients on all tests, but in many of these the difference was not significant.

MRI parameters in multiple sclerosis patients

Magnetic resonance imaging (MRI) findings of 20 patients with clinically definite multiple sclerosis (MS) are presented. The studies were performed on a 0.5 Tesla magnet using spin-echo technique. Analysis of the MRI findings included detailed linear measurements of the ventricular and the subarachnoid spaces and reading of the intensity of the grey and white matter and intensity of the MS plaques. The plaques were sorted according to their number and size. The younger patients (20-40 years) had overall more plaques than the older ones (over 40 years). The small plaques were the most numerous and the large ones were the least common. Statistically significant association was found between the number of plaques and the cella media width. The intensity ratios between the non-plaque white matter/grey matter showed a significant correlation with the ventricular score. A significant negative correlation was found between the antero-posterior diameter of the spinal cord and the number of MS plaques in the brain. The plaque/white matter ratio had a significantly negative correlation with the cervical cord's width.

Mental changes in subcortical arteriosclerotic encephalopathy

We describe six patients with chronic hypertension, atherosclerotic vascular disease and periventricular leukoencephalopathy (PVL) on CT. PVL was combined with cortical infarcts in one and with lacunar infarcts in five patients. On neuropsychological examination all patients showed the characteristic features of a subcortical type of mental deterioration. Clinico-radiologic correlation suggests a direct association of PVL and subcortical dementia, and it is argued that prominent cortical features in the dementia of patients with vascular disease and PVL suggest the concomitant presence of Alzheimer's disease.

Magnetic resonance imaging of colloid cysts of the third ventricle

Two cases of colloid cyst of the third ventricle are reported. Their computed tomographic (CT), magnetic resonance (MR) and neuropathological features are presented. The MR findings were different in the two cases for reasons not yet fully explained, full biochemical and biophysical analyses of the cyst contents not being available. Neuropathologically, the only significant difference was the abundant presence of cholesterin crystals in the colloid of case 1 and their absence in case 2. One of our cases is also peculiar from a CT point of view, since it was primarily hypodense and did not enhance on intravenous contrast administration.

T1 and T2 proton nuclear magnetic resonance (N.M.R.) relaxation times in vitro and human intracranial tumours. Results from 98 patients

137 samples of intracranial tumours have been studied in proton NMR spectroscopy. T1 and T2 relaxation times are above those of normal grey and white matter. Differential diagnosis between benign and malignant brain tumours does not seem feasible upon proton T1 and T2 alone. Histological correlations allowed us to specify secondary changes accounting for T1 and T2 variations (oedema, microcyst, stroma reaction, necrosis).

A description of a low field resistive magnetic resonance imaging system and its application in imaging midline central nervous system pathology

A commercial low field magnetic resonance imaging (MRI) system installed in the Royal Infirmary, Edinburgh at the end of 1983 has since been used for the clinical investigation of over 1000 patients. This system uses an interlaced saturation recovery and inversion recovery pulse sequence which yields four types of clinical image. AT1 weighted image has been found to be the most sensitive for the detection of pathology. Several examples of pathology with negative X-ray computed tomography examinations including three examples of a syrinx and two cases of tonsillar herniation have been demonstrated using this system. It is suggested that the system could provide a routine clinical service for imaging the central nervous system.

Magnetic resonance imaging in the evaluation of intracranial tumors of childhood

Magnetic resonance imaging (MRI) is a noninvasive imaging technique that demonstrates intracranial anatomy without the use of ionizing irradiation and intravenous contrast agents. Image quality is dependent on various factors, including field strength, scanning sequence, and imaging time. Although there is currently no concensus as to how to visualize intracranial lesions optimally, MRI has already been shown to be sensitive in the detection of brain tumors. It can detect many different types of tumors; however, its specificity is unclear. Intracranial tumor extent is extremely well-demonstrated by MRI. The advantages and disadvantages of MRI compared with computerized tomography are reviewed.

Nuclear magnetic resonance imaging (NMR), (MRI), of brain stem tumours

The NMR scans of twenty-six patients who were referred with the clinically suspected or histologically verified diagnoses of brain stem tumour were reviewed. Twenty-one patients (eleven children and ten adults) had scans that were positive for tumour. Nine of these had histological confirmation. Eleven were irradiated without histology on the basis of the clinical diagnosis. The remaining patient was treated expectantly. The other five patients (two children and three adults) had CT and NMR scans that were negative for tumours. Clinical follow-up of these five cases for 9 to 29 months disclosed no further evidence of tumour. All but one tumour had evidence of an increased T1 and T2. Mass effects were seen in all but one case (not the same as the first exception). Multiplanar imaging was useful in determining intra- or extra-axial location as well as tumour extent. Intravenous Gadolinium-DTPA (a paramagnetic contrast agent) showed tumour enhancement in the two patients in whom it was used. NMR showed more extensive abnormality than CT in nineteen patients and similar abnormality to CT in two patients. CT demonstrated calcification better than NMR in the three cases in which it was observed.

The role of neurologists in pediatric neuro-oncology

Because of advances in the diagnosis and management of brain tumors, the opportunity for neurologists to participate in the care of children with central nervous system neoplasms has greatly increased. Data developed by various study groups has allowed a more systematic approach to childhood brain tumors. Much more information will become available. New data must be reviewed and recommendations for therapy made by individuals with clinical neuroscience experience and training. The training needs of such individuals must be met in neurology training programs.

Cerebral NMR: diagnostic evaluation of brain tumors by partial saturation technique with resistive NMR

One hundred and forty patients with cerebral neoplasms were examined in a 0.12-Tesla prototype resistive NMR proton imaging device by partial saturation technique. NMR was superior to CT in tumor and edema localization and equal to CT in tumor and edema detection. NMR, however, was not able to clearly separate tumor from edema, a separation that contrast enhanced CT achieved.

Radiology of intracranial empyemas, with special reference to computed tomography

Intracranial empyemas are collections of pus, which usually develop in the subdural or extradural space; the former is more frequent. They are not common lesions, forming about one fifth to one third of reported series of intracranial abscesses [1, 2]. In the preantibiotic era, they were commonly fatal [3], but a review of series reported since widespread use of antibiotics indicated a continuing mortality rate of 25% [4]. Their radiological interest resides not only in their importance, but also in the problems of early diagnosis. Negative results have been reported with a number of techniques, including radionuclide imaging [5], computed tomography (CT) [2, 4, 6, 7] and cerebral angiography [8, 9]. A recent neurosurgical review concluded balefully that "no reassurance can be obtained from negative investigations". The present study is an examination of the possible ways in which such negative studies, particularly CT, can be avoided.

Nuclear magnetic resonance diagnosis of an anaplastic astrocytoma

A patient presented with an 8-month history of a progressive left homonymous visual field deficit, left hemiparesis, and a left thalamocortical sensory deficit that was not detectable by repeated conventional neurodiagnostic evaluations. Proton nuclear magnetic resonance (NMR) imaging revealed a right parietal lesion characterized by a prolonged T2 (spin-spin relaxation time). At surgery, the mass proved to be an anaplastic astrocytoma. NMR appears to be more sensitive than x-ray computerized tomography scanning in some patients with malignant gliomas and offers the clinician an additional probe with which to evaluate these patients.

Nuclear magnetic resonance imaging in central nervous system disease

From the preliminary work of many investigators, it appears that proton nuclear magnetic resonance (NMR) imaging will have wide application in the diagnostic assessment (and potential management) of patients with vascular, neoplastic, and demyelinating diseases of the central nervous system (CNS). Findings in isolated cases and small series suggest that NMR imaging may play a role in the evaluation of patients with other CNS conditions including hydrocephalus, malformations, infections, developmental and metabolic disorders, and degenerative processes. Because of the dynamic nature of disease processes involving the CNS, the precise meaning of NMR image parameters (rho, T1, and T2) remains unclear. A comprehensive study correlating NMR images in neurologic disease with precise neuropathologic examination is required. In the future, with accurate quantitative measurements of these NMR parameters, in vivo imaging may provide insight into the dynamic nature of neurologic disease.

NMR anatomy of the brain using inversion-recovery sequences

The use of NMR inversion-recovery (IR) sequences to demonstrate brain anatomy is illustrated. The high level of grey-white matter contrast is of value in localising anatomical structures and demonstrating myelination during childhood. While the resemblance of IR scans to gross anatomical sections in different planes is close, it is limited by the spatial resolution of the NMR scanner, artefacts and partial volume effects.

Nuclear magnetic resonance imaging of the orbit

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