Transition of the craniocaudal velocity of the spinal cord: from cervical segment to lumbar enlargement.

RATIONALE AND OBJECTIVES: The authors investigate the craniocaudal velocity of the spinal cord over its full length by using magnetic resonance imaging. METHODS: A spin-echo pulse sequence with velocity encoding gradients was used to examine five normal volunteers. Oblique-axial phase images at nine levels, from cervical spinal cord to lumbar enlargement, were obtained with prospective electrocardiogram gating. Time-velocity curves were then generated for these levels. RESULTS: Every part of the spinal cord moves first caudally after the R-wave of the electrocardiogram, then cranially. When compared with the cranial levels, peak velocity tend to occur later and their values tend to be smaller at the more caudal levels. CONCLUSIONS: Craniocaudal velocity is transmitted from cervical segment to lumbar enlargement.

Effects of stimulus rate on the auditory cortex using fMRI with 'sparse' temporal sampling.

The purpose of this study was to evaluate the effects of the auditory stimulus presentation rate on signal response during fMRI with a minimal effect of scanner acoustic noise. Six subjects received auditory stimulus with a pure tone (1000 Hz, 30 ms duration) at presentation rates of 0.5, 2, 5, 10 and 20 Hz. Echo planar images were obtained with a long TR of 12 s and clustered multi-slice acquisition. The number of activated pixels and percentage signal change were measured in the transverse temporal gyri, which revealed that these values at 5 Hz were significantly greater than those at 0.5 Hz and at 20 Hz.

Functional mapping of pain-related activation with echo-planar MRI: significance of the SII-insular region.

Activation in numerous regions of the brain is likely to be involved in the complex neural network function of pain perception. To detect the cortical representation during nonpainful and painful stimuli, which were presented using electrical finger stimulation in six normal right-handed male volunteers, we performed echo-planar functional magnetic resonance imaging (fMRI). Using a 1.5-T MR system that scanned the supratentorial region of the brain, we obtained multislice BOLD-based functional MR images with single-shot gradient-echo echo-planar imaging (EPI). The data show that dispersed brain regions are activated during painful stimulation, and especially demonstrate the significance of the SII-insular region in pain perception.

Medial prefrontal cortex generates frontal midline theta rhythm.

Frontal midline theta rhythm (Fm theta) is a distinct theta activity of EEG in the frontal midline area that appears during concentrated performance of mental tasks in normal subjects and reflects focused attentional processing. To tomographically visualize the source current density distributions of Fm theta, we recorded Fm theta by using a 64-channel whole-head MEG system from four healthy subjects, and applied a new analysis method, synthetic aperture magnetometry (SAM), an adaptive beam forming method. Fm theta was observed in the MEG signals over the bilateral frontal regions. SAM analysis showed bilateral medial prefrontal cortices, including anterior cingulate cortex, as the source of Fm theta. This result suggests that focused attention is mainly related to medial prefrontal cortex.

Neuromagnetic fields preceding unilateral movements in dextrals and sinistrals.

Movement-related magnetic fields were recorded with a whole-head magnetoencephalographic system in three dextrals and three sinistrals during right or left index finger extension. The motor field (MF) demonstrated an asymmetrical isofield map pattern with larger field reversal over the contralateral hemisphere for dominant hand movement and an almost symmetrical pattern for non-dominant hand movement in each subject. The equivalent current dipole moment of the MF for the contralateral hemisphere was significantly larger than the ipsilateral hemisphere for dominant hand movement, and almost equal for both hemispheres for non-dominant hand movement. These results were congruent for both dextrals and sinistrals, suggesting a more important role of the hemisphere contralateral to the dominant hand in unilateral voluntary movement, regardless of handedness.

Theta rhythm increases in left superior temporal cortex during auditory hallucinations in schizophrenia: a case report.

Auditory hallucinations (AH), the perception of sounds and voices in the absence of external stimuli, remain a serious problem for a large subgroup of patients with schizophrenia. Functional imaging of brain activity associated with AH is difficult, since the target event is involuntary and its timing cannot be predicted. Prior efforts to image the patterns of cortical activity during AH have yielded conflicting results. In this study, MEG was used to directly image the brain electrophysiological events associated with AH in schizophrenia. We observed an increase in theta rhythm, as sporadic bursts, in the left superior temporal area during the AH states, whereas there was steady theta band activity in the resting state. The present finding suggests strong association of the left superior temporal cortex with the experience of AH in this patient. This is consistent with the hypothesis that AH arises from areas of auditory cortex subserving receptive language processing.

Epidermoid tumor of the cerebellopontine angle: signal loss in the contralateral cistern.

We report a case of an epidermoid tumor of the right cerebellopontine angle (CPA) in which the contralateral CPA cistern showed abnormal, low signal intensity on T2-weighted fast spin-echo MR images. Diffusion-weighted images showed the epidermoid tumor of the right CPA extending to the prepontine cistern. The cause of the abnormal signal intensity was proved to be an artifactual signal loss due to cerebrospinal fluid flow by phase-contrast MR imaging.

MR appearance of Virchow-Robin spaces along lenticulostriate arteries: spin-echo and two-dimensional fast low-angle shot imaging.

PURPOSE: To delineate the appearance of normal Virchow-Robin spaces on routine spin-echo images and demonstrate the lenticulostriate arteries within them with a flow-sensitive fast low-angle shot (FLASH) pulse sequence. METHODS: Seventy subjects, free of cerebrovascular diseases and other neurologic disorders, ranging in age from 1 to 75 years, were examined. On a 1.5-T MR system, axial spin-echo images of 5 mm thickness were obtained in all subjects. In 45 of 70 subjects axial two-dimensional FLASH images of 3 mm thickness were continuously imaged. RESULTS: On T1- and spin density-weighted images Virchow-Robin spaces were detected as small foci of cerebrospinal fluid intensity around the anterior commissure in all subjects (100%), and in the basal ganglia at the level of the foramen of Monro in 40 (57%). T2-weighted images equally showed Virchow-Robin spaces around the anterior commissure but were less sensitive than T1- and spin-density weighted images at the level of the foramen of Monro (14%). Virchow-Robin spaces identified on T2-weighted images should be isointense with cerebrospinal fluid. However, one or two spaces in 11 younger subjects were hypointense relative to adjacent brain tissue. On FLASH images most Virchow-Robin spaces identified on spin-echo images were delineated as high-intensity foci, corresponding to lenticulostriate arteries. CONCLUSIONS: Normal Virchow-Robin spaces along the lenticulostriate arteries are frequently detected on spin-echo images. Their appearance, affected by the flow of associated lenticulostriate arteries, varies from hyper- to hypointensity to brain tissue on T2-weighted images. The two-dimensional FLASH sequence can demonstrate the flow of the arteries, thereby helping confirm that these are truly Virchow-Robin spaces.

Quantitation of flow in the superior sagittal sinus performed with cine phase-contrast MR imaging of healthy and achondroplastic children.

BACKGROUND AND PURPOSE: Cine phase-contrast (PC) MR imaging is a convenient and effective method for measuring volumetric flow rates in vivo. We attempted to evaluate changes in blood flow in the superior sagittal sinus (SSS) in children and to assess the hypothesis that restricted venous outflow attributable to stenosis of the jugular vein causes hydrocephalus in achondroplasia. METHODS: Blood flow in the SSS was measured by using cine PC MR imaging with a 1.5-T scanner. After validation, 35 neurologically healthy children as well as eight children with achondroplasia (five with hydrocephalus) and two children with obstructive hydrocephalus were studied. Average flow velocity over the cardiac cycle and volumetric flow rate in the SSS were obtained. The data for healthy children were plotted as a function of age, and reference values were defined by using a five-point smoothing. RESULTS: In healthy children, flow velocity ranged from 92 to 196 mm/s (mean, 136), and flow rate from 189 to 688 mL/min (mean, 484). The flow rate showed changes statistically related to age. It rapidly increased during the first 2 years and reached a peak by 6 to 8 years of age. The flow velocity showed a similar pattern, but not with significant correlation. In all cases of achondroplasia with hydrocephalus, both flow values were reduced below the reference values minus one standard deviation. In cases of achondroplasia without hydrocephalus, and in obstructive hydrocephalus, the values were not reduced. CONCLUSION: Blood flow in the SSS reflects brain maturation. Hydrocephalus associated with achondroplasia was found to be closely related to reduced flow in the SSS, which supports the hypothesis that restricted venous outflow causes hydrocephalus in cases of achondroplasia.

Neuromas and meningiomas: evaluation of early enhancement with dynamic MR imaging.

PURPOSE: To investigate the role of dynamic MR imaging in the differentiation of neuromas and meningiomas. METHODS: Eleven patients with neuromas and 15 patients with meningiomas underwent dynamic contrast-enhanced MR imaging using a short TE FLASH sequence and a bolus injection of Gd-DTPA. RESULTS: There was no significant difference between these tumors in the signal-enhancement increment at the late phase, which corresponds to the signal-enhancement increment between pre- and postcontrast images in conventional spin-echo imaging. However, the signal enhancement at the vascular phase, ie, the phase where the first passage of Gd-DTPA was recognized both in the arteries and veins, was approximately four times as high in meningiomas as in neuromas. The difference was statistically significant. Furthermore, meningiomas had a wider range of early signal enhancement than did neuromas, reflecting the histologic varieties: two angioblastic meningiomas had the highest values, and three fibroblastic the lowest values comparable with those of neuromas, while meningiomas with other subtypes had intermediate values. CONCLUSIONS: The results of this study indicate that the evaluation of early enhancement with dynamic MR imaging is helpful in the differentiation of neuromas and meningiomas, and possibly in the crude prediction of pathologic subtypes of meningiomas.

MR imaging of middle cerebral artery stenosis and occlusion: value of MR angiography.

PURPOSE: To investigate the effectiveness of MR angiography in conjunction with spin-echo imaging for evaluating vascular patency in patients with middle cerebral artery (MCA) stenosis or occlusion. METHODS: Seven patients with MCA stenosis or occlusion, verified with contrast angiography in five and correlated with transcranial Doppler sonography in two, were examined using two-dimensional and/or three-dimensional time-of-flight MR angiographic techniques as well as conventional spin-echo imaging. RESULTS: Of the seven patients, six demonstrated basal ganglionic and/or cortical infarct in the MCA territory. Except one case with minimal stenosis immediately distal to the MCA origin, all six cases with either severe stenosis or occlusion of the main trunk of the MCA showed the absence of normal flow voids using spin-echo imaging in the sylvian fissure on the affected side. However, it was not possible to discriminate between stenosis and occlusion. Although different mechanisms (ie, flow-induced spin dephasing for the 2-D technique and progressive spin saturation for the 3-D technique) were predominantly responsible for the loss of signal through the area of stenosis, both the 2-D and 3-D MR angiograms clearly depicted the compromised flow of the MCA: a focal discontinuity with decreased vessel caliber corresponded to stenosis, and nonvisualization of distal MCA branches represented occlusion. CONCLUSION: Either 2-D or 3-D time-of-flight MR angiography is a useful adjunct to conventional parenchymal spin-echo imaging for evaluating vascular patency in patients with MCA stenosis or occlusion, although it is important to recognize that each technique has a different basis for the loss of signal through the area of stenosis.

Lateral geniculate nucleus: anatomic and functional identification by use of MR imaging.

BACKGROUND AND PURPOSE: MR imaging has the potential capacity for noninvasively depicting the anatomy and function of thalamic nuclei. The purpose of this study was to identify the lateral geniculate nucleus (LGN), which is the thalamic relay nucleus for vision, with anatomic and functional MR imaging at 1.5 T. METHODS: Three-millimeter-thick axial images were obtained from eight volunteers by using a double-echo turbo spin-echo sequence for proton density- and T2-weighted contrast and a spin-echo 3D gradient-echo sequence for T1-weighted contrast. Each participant underwent a visual activation experiment using gradient-echo echo-planar imaging at the same location as that of the anatomic study. RESULTS: In all cases, the LGN was recognized on proton density-weighted images as a small wedge-shaped area of high signal intensity relative to that of the surrounding white matter tracts. However, it was difficult to identify the LGN on T1- and T2-weighted images because of the smaller contrast-to-noise ratios between the LGN and the adjacent white matter tracts, compared with those of proton density-weighted images (P <.001). Bilateral thalamic activation and activation in the occipital cortex were shown in all participants. Each region of thalamic activation (23 +/- 3 mm2) was localized to the anatomically identified LGN. CONCLUSION: The excellent correspondence between the anatomically and functionally identified LGN confirms that MR imaging is an indispensable method for visualizing functional neuroanatomy in thalamic nuclei.

Asymmetric appearance of intracranial vessels on routine spin-echo MR images: a pulse sequence-dependent phenomenon.

PURPOSE: To determine the cause of right to left signal intensity differences arising from intracranial vessels during routine spin-echo axial MR imaging of the head. METHODS AND RESULTS: Using a normal imaging sequence in which the default directions of the frequency and phase axes were horizontal and vertical, respectively, differences in signal intensity arising from the vertebral arteries were observed in a healthy subject. With the exchange of the frequency and phase axes relative to the normal sequence, no signal intensity differences between the vertebral arteries were recognized. Other pulse sequence modifications, ie, the use of motion-compensating gradients and the reversed polarity of the frequency-encoding gradient, also resulted in variable appearances of the vertebral arteries, indicating that the right-to-left signal asymmetry of the vertebral arteries observed on the normal spin-echo image results from a pulse sequence dependent phenomenon. CONCLUSIONS: Frequency-encoding and slice-selection gradients both produce motion-induced phase shifts. These phase shifts depend on the angle between the direction of flow and that of the effective vector sum of these gradients. The asymmetric appearance of the vertebral arteries during normal spin-echo imaging was found to result from the angle dependence of motion-induced phase shifts. Awareness of this artifactual phenomenon is important to avoid confusing it with conditions such as stenosis/occlusion, dissection, or slow flow.

Proton magnetic resonance spectroscopy of patients with parkinsonism.

We studied cerebral metabolism in 82 patients with nonfamilial parkinsonism, including Parkinson's disease (PD; n = 23), progressive supranuclear palsy (PSP; n = 12), corticobasal degeneration (CBD; n = 19), multiple systemic atrophy (MSA; n = 18) and vascular parkinsonism (VP; n = 10) by using proton magnetic resonance spectroscopy ((1)H-MRS), which allowed noninvasive measurement of signal intensities from N-acetylasparate (NAA), choline-containing compounds (CHO) and creatine plus phosphocreatine (CRE). As compared to normal controls, patients with PSP, CBD, MSA and VP, but not PD, had significant reduction of the NAA/CRE ratio in the frontal cortex, whereas patients with PSP, CBD, MSA and PD, but not VP, had significant reduction of the NAA/CRE ratio in the putamen. Patients with CBD had significant reduction of the NAA/CRE ratio in the frontal cortex and putamen as compared to patients with PD, MSA and VP. Patients with PSP showed a significant reduction of the NAA/CRE ratio in the putamen as compared with patients with PD and MSA. Patients with CBD showed clear asymmetry in the putamen as compared to controls and other patients. The reduction of the NAA/CRE ratio in the putamen correlated well with the severity of parkinsonism. (1)H-MRS may be useful in monitoring patients with various types of parkinsonism.

Effects of stimulus presentation rate on the activity of primary somatosensory cortex: a functional magnetic resonance imaging study in humans.

To investigate the effect of stimulus presentation rate on the activity of primary somatosensory cortex, we performed echo-planar functional magnetic resonance imaging using a 1.5-tesla magnetic resonance system. Eight right-handed normal volunteers underwent functional magnetic resonance imaging during somatosensory stimulation with a 0.2 ms electrical square wave to the left index finger at 1, 4, 8, 16, and 32 Hz at constant intensity. Activated areas were located mainly around 'the hand area' of the right postcentral gyrus. Between 4 and 16 Hz, almost all subjects showed significant activation, but at 1 Hz and 32 Hz, five of eight subjects showed no activation. The average number of activated pixels in this area between 4 and 16 Hz were significantly greater than those at 1 Hz and 32 Hz, and the average percent signal increase had its activation peak at 8 Hz. Our results suggest that the existence of the optimal stimulation rate range may be a common phenomenon to a variety of sensory modalities. The electrical somatosensory stimulation rates from 4 Hz to 16 Hz are advisable to investigate the activation of the primary somatosensory cortex in human subjects.

Computational imaging of cerebral perfusion by real time processing of DSA images. Clinical applications.

Real time and high resolution functional imaging of cerebral perfusion was developed, which displays the color coded image of the cerebral perfusion index (PI) from the serial images of digital subtraction angiography (DSA). The small (3 x 3 pixels) regions of interest (ROI) were set on the images, and the time density curves of the contrast media for each ROI were obtained. The perfusion indices, corresponding to the mean transit time (MTT), were calculated for all the ROIs on the image in real time (5 sec) by the area over height method and then, converted to the PI image. A large ROI (64 x 64 pixels) was also used to estimate the parenchymal perfusion. In the normal subjects, consistent PI values at the various parts of the cerebral arteries were obtained, which reasonably agreed with the published values when converted to the blood flow. Then the study on the pathological subjects were made. Firstly, the alteration in the PI images agreed well with the CBF SPECT study in the case of moyamoya disease with the synangiosis operation. Secondly, even a 5% change of the parenchymal perfusion could be detected with the PI imaging, which was obscure when inspecting the series of DSA images, in the case of intra-arterial papaverine infusion for delayed vasospasm. Thirdly, the vortex inside a large aneurysm could be estimated with the same resolution as DSA. Our method offers real time, high resolution, projection angle independent and semiquantitative imaging of the cerebral perfusion from the conventional DSA images without introducing any new expensive devices. This method could be used to evaluate the therapeutic change and especially to monitor the rapidly changing cerebral perfusion in interventional angiography.

Dysembryoplastic neuroepithelial tumor in the insular cortex. Three dimensional magnetoencephalographic localization of epileptic discharges.

A case of dysembryoplastic neuroepithelial tumor in the left insular cortex manifesting with intractable seizures is presented. The multichannel magnetoencephalography (MEG) localized equivalent current dipoles of epileptic discharges at the cerebral cortex adjacent to the tumor. The total removal of the tumor resulted in complete disappearance of seizures. This case demonstrated that multichannel MEG was useful in the three-dimensional localization of irritative zone in the concealed cortices such as inside the sylvian fissure.

Translucence stereoscopy of interictal magnetoencephalographic epileptiform discharge.

We have developed a translucence stereoscopy method for displaying the distribution of multiple interictal epileptiform discharges within the intracranial space. The epileptiform discharges, measured using a whole-head magnetoencephalography system, were modeled by a least-squares method to obtain the equivalent current dipoles. The dipoles were located in the stereo pair of intracranial images composed of translucent brain slices at several selected levels. The technique demonstrated clearly the distribution of interictal dipoles within the brain in three patients. Three dimensional understanding of the intracranial distribution of multiple dipoles in one image is valuable in analyzing the intracerebral neurophysiological events in epileptic patients.

Proton magnetic resonance spectroscopy (1H MRS) in patients with sporadic cerebellar degeneration.

The authors studied 23 patients with cerebellar degeneration including multiple systemic atrophy (MSA) and cerebellar cortical atrophy (CCA) by proton magnetic resonance spectroscopy (1H-MRS). 1H-MRS allowed noninvasive measurement of the signal intensities derived from N-acetylaspartate (NAA), creatine + phosphocreatine (CRE), and choline-containing compounds (CHO). There was significant reduction of the NAA/CRE level in the frontal cortex, putamen, cerebellar hemisphere and cerebellar vermis of patients with MSA, and in the frontal cortex, cerebellar hemisphere and cerebellar vermis of patients with CCA as compared with those of normal controls. There was significant reduction of the NAA/CRE level also in the putamen of patients with MSA as compared with that of patients with CCA. These results indicated the presence of a degenerative process and/or functional impairment in the frontal cortex and putamen of patients with MSA and in the frontal cortex of patients with CCA, in addition to a degenerative process in the cerebellum. There was a significant correlation between the NAA/CRE level and the severity of clinical signs. 1H-MRS is valuable in providing information regarding the pathophysiology and the progress of cerebellar degenerative diseases.

On-off study of manganese administration to adult patients undergoing home parenteral nutrition: new indices of in vivo manganese level.

BACKGROUND: Recently, there have been reports that magnetic resonance imaging (MRI) reveals high-intensity T1-weighted images (HI) in the basal ganglia (especially in the globus pallidus) of patients receiving total parenteral nutrition (TPN). This finding is presumably due to excess administration of manganese. We investigated the reversibility and reproducibility of these changes by means of an on-off manganese administration study. We also investigated the temporal relationships between the intensity of T1-weighted images (MRI intensity) and the whole-blood and plasma manganese concentrations to evaluate the potential for the MRI intensity to serve as an index of the in vivo manganese level. METHODS: Eleven adult patients undergoing home parenteral nutrition received TPN solutions containing manganese (0 or 20 micromol/d) according to an on-off design. The whole-blood and plasma manganese concentrations were determined at the same time the brain MRI was performed. RESULTS: Both the whole-blood manganese concentration and the MRI intensity in the globus pallidus changed in response to the administration and withdrawal of manganese. It took at least 5 months for HI to disappear when manganese was withdrawn, and this change was reversible and reproducible. The whole-blood manganese concentration showed strong correlations with both the MRI intensity and the T1 value (r = 0.7693, -0.7011). The MRI intensity and the T1 value showed a strong correlation (r = -0.9051). CONCLUSIONS: The whole-blood manganese concentration, the MRI intensity in the globus pallidus and the T1 value, an objective index of the MRI intensity, may be useful indices of the manganese level in the body.