(1)H-MR spectroscopy in the human spinal cord.

SUMMARY: MR spectroscopy allows insight into the chemical composition of human tissue noninvasively. Thereby it can help to better characterize pathologic processes affecting the spinal cord and may provide important clinical markers for differential diagnosis. However, due to technical challenges, it has been rarely applied to the spinal cord. The aim of this review was to summarize the technical development and clinical studies using MR spectroscopy in the spinal cord. Main challenges of applying MR spectroscopy in the spinal cord are discussed, and a description of a state-of-the-art scan protocol is given. In conclusion, MR spectroscopy is a promising tool for research and diagnosis of the spinal cord because it can provide additional information complementary to other noninvasive imaging methods. However, the application of MR spectroscopy in the spinal cord is not straightforward, and great care is required to attain optimal spectral quality.

Diffusion-weighted imaging of the entire spinal cord.

In spite of their diagnostic potential, the poor quality of available diffusion-weighted spinal cord images often restricts clinical application to cervical regions, and improved spatial resolution is highly desirable. To address these needs, a novel technique based on the combination of two recently presented reduced field-of-view approaches is proposed, enabling high-resolution acquisition over the entire spinal cord. Field-of-view reduction is achieved by the application of non-coplanar excitation and refocusing pulses combined with outer volume suppression for removal of unwanted transition zones. The non-coplanar excitation is performed such that a gap-less volume is acquired in a dedicated interleaved slice order within two repetition times. The resulting inner volume selectivity was evaluated in vitro. In vivo diffusion tensor imaging data on the cervical, thoracic and lumbar spinal cord were acquired in transverse orientation in each of four healthy subjects. An in-plane resolution of 0.7 x 0.7 mm(2) was achieved without notable aliasing, motion or susceptibility artifacts. The measured mean +/- SD fractional anisotropy was 0.69 +/- 0.11 in the thoracic spinal cord and 0.75 +/- 0.07 and 0.63 +/- 0.08 in cervical and lumbar white matter, respectively.

Preliminary experience with visualization of intracortical fibers by focused high-resolution diffusion tensor imaging.

BACKGROUND AND PURPOSE: The inherent low anisotropy of gray matter and the lack of adequate imaging sensitivity and resolution has, so far, impeded depiction of axonal fibers to their intracortical origin or termination. We tested the hypothesis that an experimental approach with high-resolution diffusion tensor imaging (DTI) provides anisotropic data for fiber tractography with sufficient sensitivity to visualize in vivo the fine distribution of white matter bundles at the intracortical level. MATERIALS AND METHODS: We conducted phantom measurements of signal-to-noise ratio (SNR) and obtained diffusion tensor maps of the occipital lobe in 6 healthy volunteers using a dedicated miniature phased array detector at 3T. We reconstructed virtual fibers using a standard tracking algorithm. RESULTS: The coil array provided a SNR of 8.0 times higher at the head surface compared with a standard quadrature whole head coil. Diffusion tensor maps could be obtained with an in-plane resolution of 0.58 x 0.58 mm(2). The axonal trajectories reconstructed from the diffusion data penetrate into the cortical ribbon perpendicular to the pial surface. This is the expected pattern for the terminations of thalamocortical afferent fibers to the middle layers of the occipital cortex and is consistent with the known microstructural organization of the mammalian cerebral cortex. CONCLUSION: High-resolution DTI reveals intracortical anisotropy with a distinct parallel geometrical order, perpendicular to the pial surface, consistent with structures that may be identified as the terminal afferents in cortical gray matter.

Lipoma of the parotid gland.

We describe three cases of parotid gland lipoma, a relatively rare, asymptomatic, slow growing, freely movable, soft tissue mass. Preoperative clinical diagnosis is generally difficult but MRI using fat saturation techniques provides accurate diagnostic information regarding this benign parotid gland tumor, enabling better treatment planning.

Reduced field-of-view MRI using outer volume suppression for spinal cord diffusion imaging.

A spin-echo single-shot echo-planar imaging (SS-EPI) technique with a reduced field of view (FOV) in the phase-encoding direction is presented that simultaneously reduces susceptibility effects and motion artifacts in diffusion-weighted (DW) imaging (DWI) of the spinal cord at a high field strength (3T). To minimize aliasing, an outer volume suppression (OVS) sequence was implemented. Effective fat suppression was achieved with the use of a slice-selection gradient-reversal technique. The OVS was optimized by numerical simulations with respect to T(1) relaxation times and B(1) variations. The optimized sequence was evaluated in vitro and in vivo. In simulations the optimized OVS showed suppression to <0.25% and approximately 3% in an optimal and worst-case scenario, respectively. In vitro measurements showed a mean residual signal of <0.95% +/- 0.42 for all suppressed areas. In vivo acquisition with 0.9 x 1.05 mm(2) in-plane resolution resulted in artifact-free images. The short imaging time of this technique makes it promising for clinical studies.

MR-spectroscopic imaging during visual stimulation in subgroups of migraine with aura.

Migraine pathophysiology possibly involves deficient mitochondrial energy reserve and diminished cortical habituation. Using functional magnetic resonance spectroscopic imaging (fMRSI), we studied cortical lactate changes during prolonged visual stimulation to search for different pathophysiological mechanisms in clinically distinct subgroups of migraine with aura. Eleven healthy volunteers (HV) and 10 migraine patients were investigated interictally: five with visual aura (MA) and five with visual symptoms and at least one of the following: paraesthesia, paresis or dysphasia (MAplus). Using MRSI (Philips, 1.5 T) (1)H-spectra were repeatedly obtained from a 25 mm-thick slice covering visual and non-visual cortex, with the first and fifth measurements in darkness and the second to fourth with 8-Hz checkerboard stimulation. In MAplus lactate increased only during stimulation, only in visual cortex; in MA resting lactate was high in visual cortex, without further increase during stimulation. This is compatible with an abnormal metabolic strain during stimulation in MAplus, possibly due to dishabituation, and a predominant mitochondrial dysfunction in MA.

Normal brain activation in hemiatrophy due to multiple sclerosis: a functional MRI case study.

Evidence from recent functional magnetic resonance imaging studies suggests that adaptive cortical changes ('plasticity') could participate in the maintenance of function in multiple sclerosis (MS). Here, we addressed the impact of brain atrophy on the pattern of cerebral activation in an MS patient with a relapsing-remitting course. This patient showed mildly disabling hemiparesis of the left side (EDSS 2.0), and corresponding brain hemiatrophy (15% volume reduction) of the right hemisphere. The clinical syndrome was considered to result from a lesion in the corona radiata involving corticospinal fibers. Motor-evoked potential recordings confirmed substantial axonal damage to the pyramidal tract arising from that hemisphere. Irrespective of these asymmetries, normal brain activation was found for hand and foot movements for both brain sides. This demonstrates that brain atrophy itself does not necessarily induce cortical adaptive changes, even if mild disability is present. On the other hand, significantly disabling distinct clinical syndromes e.g. arising from spinal cord lesions may evoke cortical changes irrespective of brain atrophy. This issue has to be studied in longitudinal investigations.

Extensive spherical amyloid deposition presenting as a pituitary tumor.

A 71-yr-old man was admitted for further evaluation and trans-sphenoidal surgery of a pituitary tumor. He complained of impotence and decreased libido over a period of about 40 yr. Thirty-eight yr ago he was treated for bilateral gynecomastia with galactorrhea. Endocrinological investigation at presentation revealed only mild hyperprolactinemia and hypogonadotropic hypogonadism. Pituitary magnetic resonance imaging (MRI) showed a tumor up to 2.5 cm in diameter with infiltration of the sphenoid sinus and right cavernous sinus. The tumor exhibited a heterogeneous hyperintense signal on T1-weighted images and hypointense signal on T2-weighted images. Standard trans-sphenoidal surgery was performed and a brownish mass was found inside the sella, which was removed. Histological examination of the mass revealed extensive spherical amyloid deposits with strongly positive immunohistochemical staining for prolactin. Therefore, a prolactinoma with extensive spherical amyloid deposition was diagnosed. Extensive spherical amyloid deposition is a rare finding in prolactin-secreting pituitary adenomas. So far, characteristic radiological findings by MRI have been described only twice. Due to characteristic MRI findings, the diagnosis of extensive intrasellar amyloid deposition can be entertained pre-operatively. Trans-sphenoidal surgical resection is essential to confirm the diagnosis histologically and because of the potential lack of tumor shrinkage under dopaminagonist therapy in this type of prolactinoma.

Somatomotor functional MRI in a large congenital arachnoid cyst.

The immature human brain, when damaged, is able to reorganise functionally. We performed functional MRI during eight different movements in a patient found incidentally to have an extensive, frontal, congenital arachnoid cyst, looking at which neural substrates contribute to motor control. Significant changes from the normal pattern of activation were seen in cortical and cerebellar areas which could not be accounted for by the space-occupying effect of the cyst alone. These findings in this asymptomatic patient with a congenital anomaly demonstrate an alternative organisation of the central motor system, with a preservation of neurological function.

Identification of the ascending middle cerebral artery branches on digital subtraction angiography.

We aimed to establish a method for identifying the ascending convexity branches of the middle cerebral artery on digital subtraction arteriography. We reviewed 100 randomly chosen lateral internal carotid arteriograms of patients with aneurysms. After identifying the Sylvian triangle, the posterior internal frontal, paracentral, superior internal parietal and pericallosal arteries, we formulated templates in order to assess the position of the angular, posterior parietal, central, precentral and prefrontal arteries. Using the Sylvian triangle as a template, we identified the angular and posterior parietal arteries in 91% and 96% of cases, respectively. Using a combination of the posterior internal frontal, paracentral, superior internal frontal and pericallosal arteries a template could be formulated in 87% of cases. This was successfully used to identify the central arteries. A template derived from the pericallosal artery and Sylvian triangle was used to identify the prefrontal arteries in 83% of cases. Templates can be formulated on the basis of the Sylvian triangle and anterior cerebral artery branches for consistent identification of branches of the ascending complex of the middle cerebral artery on digital subtraction angiography.

Dynamic changes during evacuation of a left temporal abscess in open MRI: technical case report.

We demonstrate the usefulness of "near real-time" neuro-navigation by open MRI systems for guidance of stereotactic evacuation of intracranial abscesses. A 70-year-old patient was referred to our institution with an intracranial left temporal abscess. He presented with headache, senso-motor aphasia and mild right hemiparesis. The abscess (35 x 25 mm) was stereotactically evacuated under MRI guidance, and a recurrence of a daughter abscess was again evacuated on the 9th postoperative day. "Near real-time" imaging showed an indentation of the abscess wall of 11 mm along the trajectory. A thermosensitive MRI protocol demonstrated a higher temperature around the abscess capsule than in the brain tissue more distant to the capsule, demonstrating the inflammatory process. The patient had 6 weeks of antibiotic therapy for gram-negative bacteria and was discharged with improved clinical symptoms 5 weeks after admission. Follow-up CT 2 months postoperatively showed a complete resolution of the abscess. Open MRI-guided interventions with "near real-time" imaging demonstrate the anatomical changes during an ongoing procedure and can be accommodated for enhancing the overall precision of stereotactic procedures. Thermosensitive MRI protocols are capable of revealing temperature gradients around inflammatory processes.

Proton magnetic resonance spectroscopy characteristics of a focal cortical dysgenesis during status epilepticus and in the interictal state.

We report the magnetic resonance imaging and proton magnetic resonance spectroscopic findings ((1)HMRS) in a patient with a focal cortical dysgenesis in the right superior frontal gyrus during intermittent frontal status epilepticus (IFSE) with simple partial seizures, and after she had become seizure free. During the status epilepticus, demonstrated by simultaneous behavioural and electroencephalographic telemetric long-term monitoring with scalp electrodes and ictal SPECT, we performed a single voxel spectroscopy of the dysgenic cortex. The(1)HMRS was repeated after 20 days when the patient's seizures were controlled. The N-acetyl-aspartate concentration in the focal dysgenic cortex was decreased in the interictal state but more during IFSE. The creatine/phosphocreatine concentration was normal in both instances. There was a clear lactate signal during IFSE, which was no longer visible in the interictal state. To our knowledge this is the first report of a(1)HMRS study of a focal cortical dysgenesis during an intermittent status epilepticus. We interpret the observed changes as signs of histopathological changes inherent to a cortical malformation and of an impaired energy metabolism due to the partial status epilepticus.

Identification of multiple nonprimary motor cortical areas with simple movements.

The human cortex reportedly contains at least five nonprimary motor areas: in the frontolateral convexity, the dorsal and ventral premotor cortex (PMd and PMv), and in the frontomesial wall, the presupplementary and supplementary motor areas (pre-SMA and SMA), and the rostral, dorsal and ventral cingulate areas (CMAr, CMAd, and CMAv). Activation of these regions in neuroimaging studies has been generally associated either with the performance of complex motor tasks or with reorganization occurring with motor recovery in the presence of pathology. Recent evidence from neuroimaging studies suggests that the same areas are activated with well controlled simple movements in healthy subjects providing support to the observation that their contribution may be more quantitative rather than exclusively specific to a certain aspect of motor behaviour. An important consequence of this observation is that activation of multiple nonprimary motor areas during simple motor tasks should not be considered unique to patients with upper or lower motoneuron lesions but rather as a normal physiological process.

Evaluation of the anatomical and functional properties of deglutition with various kinetic high-speed MRI sequences.

We evaluated various fast MR sequences for obtaining anatomical and dynamic functional information during deglutition. Seven healthy volunteers underwent MRI of the oropharynx during swallowing of an oral positive-contrast agent. Single-slice imaging was performed in the median sagittal plane while subjects were in a supine position. Twenty serial images were obtained using EPI, FLASH, and turbo-FLASH sequences. The dynamic (movement-related) information and the anatomical resolution of the soft tissues were evaluated during deglutition. The FLASH sequence provided high-quality images at rest. During swallowing, however, the images were significantly degraded by movement artifacts and had inferior temporal resolution. The EPI evidenced better temporal resolution, but was degraded by strong distortions and movement artifacts. The turbo-FLASH sequence provided the best temporal resolution and sufficient spatial resolution during motion. This sequence proved optimal for the investigation of swallowing function, and is expected to be of value for the documentation of functional disturbances in patients with oropharyngeal pathology.

Interactive magnetic resonance imaging-guided management of intracranial cystic lesions by using an open magnetic resonance imaging system.

OBJECT: The authors present their experience with neurosurgical procedures requiring real-time imaging feedback such as aspiration of a cystic structure or abscess cavity, decompression of hydrocephalic ventricles, management of arachnoid cysts, and installation of permanent or temporary drainage conduits, in which interactive magnetic resonance (MR) imaging guidance was used to monitor structural alterations associated with the procedure. METHODS: Drainage of eight intraparenchymal brain abscesses in seven patients, decompression of space-occupying cystic or necrotic brain tumors in four patients, and endoscopic management of hydrocephalus associated with arachnoid cysts in three patients were performed using MR imaging-guided frameless stereotaxy in an open-configuration 0.5-tesla superconducting MR imaging system. Intraoperative MR imaging guidance provided accurate information on the course of the surgical procedure and associated intraoperative changes in tissue position, such as the degree of cyst aspiration, the presence or absence of hemorrhage or induced swelling, and changes associated with decompression of adjacent brain parenchyma and the ventricular system. No clinically significant complications were encountered in any patient. There were no targeting errors, and procedural objectives were accomplished in all cases. CONCLUSIONS: Drainage of brain abscesses, punctures of cystic or necrotic intracranial lesions with subsequent aspiration, and management of hydrocephalus can be performed safely and accurately by monitoring the procedure using real-time MR imaging to obtain immediate feedback on associated dynamic tissue changes.

Neuroimaging of cerebellar liponeurocytoma. Case report.

Cerebellar liponeurocytoma is a newly recognized, rare clinicopathological entity. It manifests with posterior fossa symptoms in adults and is characterized histopathologically by advanced neuronal and focal lipomatous differentiation with a low level of mitotic activity. The authors analyzed the computerized tomography (CT) and magnetic resonance (MR) imaging findings in two patients with histopathologically proven cerebellar liponeurocytomas and review the literature. Cerebellar liponeurocytoma may be suspected on the basis of neuroimaging findings that demonstrate an intraaxial neoplasm with the propensity for exophytic growth into the adjacent subarachnoid spaces. On CT scans, the tumor commonly presents as a hypointense mass with intermingled areas exhibiting the attenuation values of fatty tissue. On T1-weighted MR images, the tumor is hypointense with scattered foci of hyperintense signal and displays moderate contrast enhancement. On T1-weighted MR images, the tumor is slightly hyperintense to cortex, and edema is usually absent. Areas of fat density as assessed on CT scans and of T1 hyperintensity seen on MR images help to distinguish this rare neoplasm from the more common adult medulloblastomas or ependymomas. The available follow-up data indicate a favorable clinical prognosis; therefore, knowledge and precise characterization of this tumor is important to avoid unnecessary adjuvant radio- or chemotherapy.

MRI in tick-borne encephalitis.

The tick-borne encephalitis (TBE) virus gives rise to epidemic encephalitis. Mild forms usually manifest as influenza-like episodes or are clinically silent. MRI is usually normal in TBE. We describe severe TBE in a patient who presented with fever and altered mental status after a tick bite and a specific antibody response to TBE. MRI revealed pronounced signal abnormalities in the basal ganglia and thalamus, without contrast enhancement. These findings coincide well with neuropathological studies of severe nerve cell degeneration with inflammatory cell infiltrates, neuronophagia and reactive astrocytosis in the deep grey matter. We review the literature and discuss the relevant differential diagnosis.