Solar Wind Temperature Isotropy.

Reliable models of the solar wind in the near-Earth space environment may constrain conditions close to the Sun. This is relevant to NASA's contemporary innerheliospheric mission Parker Solar Probe. Among the outstanding issues is how to explain the solar wind temperature isotropy. Perpendicular and parallel proton and electron temperatures near 1 AU are theoretically predicted to be unequal, but in situ observations show quasi-isotropy sufficiently below the instability threshold condition. This has not been satisfactorily explained. The present Letter shows that the dynamical coupling of electrons and protons via collisional processes and instabilities may contribute toward the resolution of this problem.

Particle-in-cell Simulations of the Whistler Heat-flux Instability in Solar Wind Conditions.

In collision-poor plasmas from space, e.g., solar wind or stellar outflows, the heat flux carried by the strahl or beaming electrons is expected to be regulated by the self-generated instabilities. Recently, simultaneous field and particle observations have indeed revealed enhanced whistler-like fluctuations in the presence of counter-beaming populations of electrons, connecting these fluctuations to the whistler heat-flux instability (WHFI). This instability is predicted only for limited conditions of electron beam-plasmas, and has not yet been captured in numerical simulations. In this Letter we report the first simulations of WHFI in particle-in-cell setups, realistic for the solar wind conditions, and without temperature gradients or anisotropies to trigger the instability in the initiation phase. The velocity distributions have a complex reaction to the enhanced whistler fluctuations conditioning the instability saturation by a decrease of the relative drifts combined with induced (effective) temperature anisotropies (heating the core electrons and pitch-angle and energy scattering the strahl). These results are in good agreement with a recent quasilinear approach, and support therefore a largely accepted belief that WHFI saturates at moderate amplitudes. In the anti-sunward direction the strahl becomes skewed with a pitch-angle distribution decreasing in width as electron energy increases, which seems to be characteristic of self-generated whistlers and not to small-scale turbulence.

Bremsstrahlung emission and collisional damping rate for Langmuir waves.

The emission of electrostatic Langmuir waves by collisional process, termed electrostatic bremsstrahlung emission, and the collisional damping of Langmuir waves, which can be considered as the inverse electrostatic bremsstrahlung process, are rigorously discussed. Some inaccuracies in the previous formalisms are also corrected. It is shown that the improved formulae in the case of Maxwellian particle distributions are given in forms where they satisfy Kirchhoff's law in the balanced form.

Weak turbulence theory for collisional plasmas.

Plasma is an ionized gas in which the collective behavior dominates over the individual particle interactions. For this reason, plasma is often treated as collisionless or collision-free. However, the discrete nature of the particles can be important, and often, the description of plasmas is incomplete without properly taking the discrete particle effects into account. The weak turbulence theory is a perturbative nonlinear theory, whose essential formalism was developed in the late 1950s and 1960s and continued on through the early 1980s. However, the standard material found in the literature does not treat the discrete particle effects and the associated fluctuations emitted spontaneously by thermal particles completely. Plasma particles emit electromagnetic fluctuations in all frequencies and wave vectors, but in the standard literature, the fluctuations are approximately treated by considering only those frequency-wave number regimes corresponding to the eigenmodes (or normal modes) satisfying the dispersion relations, while ignoring contributions from noneigenmodes. The present paper shows that the noneigenmode fluctuations modify the particle kinetic equation so that the generalized equation includes the Balescu-Lénard-Landau collision integral and also modify the wave kinetic equation to include not only the collisional damping term but also a term that depicts the bremsstrahlung emission of plasma normal modes.

Nonlinear development of streaming instabilities in strongly magnetized plasma.

The nonlinear development of streaming instabilities in the current layers formed during magnetic reconnection with a guide field is explored. Theory and 3D particle-in-cell simulations reveal two distinct phases. First, the parallel Buneman instability grows and traps low velocity electrons. The remaining electrons then drive two forms of turbulence: the parallel electron-electron two-stream instability and the nearly perpendicular lower-hybrid instability. The high velocity electrons resonate with the turbulence and transfer momentum to the ions and low velocity electrons.

Proton heating via nonresonant scattering off intrinsic Alfvénic turbulence.

A novel yet unsophisticated theory is proposed to show that low-beta protons can be efficiently heated by enhanced Alfvén waves. The present research is motivated by a plasma physics issue relevant to the explanation of hot stellar coronas observed with x-ray telescopes. The efficient heating is attributed to nonresonant wave-particle scattering that tends to randomize proton motion in directions transverse to the ambient magnetic field.

Endovascular treatment of intracranial vertebral artery dissections with stent placement or stent-assisted coiling.

BACKGROUND AND PURPOSE: Endovascular treatment with stent placement or stent-assisted coiling was recently introduced as an alternative to parent artery occlusion in intracranial vertebral artery dissections. We describe the efficacy and limitations of this method. METHODS: Fourteen patients with intracranial vertebral artery dissection were treated with stent placement (10 patients) or stent-assisted coiling (4 patients). Double overlapping stents were deployed in 4 of 10 patients with stent placement alone. Angiographic follow-up at 6 to 12 months was available in 13 patients. RESULTS: In 13 patients with dissecting aneurysm, immediate angiographic outcomes were complete occlusion (1 patient), nearly complete (2 patients), and incomplete (10 patients). Follow-up angiograms of 12 of these patients showed complete occlusion (6 patients) and incomplete (6 patients; 1 unstable and 5 stable). Complete occlusion rates in follow-up angiograms were superior in double stent placement (75%) or stent-assisted Guglielmi detachable coil (GDC) embolization to stent placement alone (0%). There were no instances of postprocedural ischemic attacks, new neurologic deficits, and no new minor or major strokes before patient discharge. On the modified Rankin scale applied in follow-up, all patients were assessed as functionally improved or of stable clinical status. CONCLUSIONS: Intracranial vertebral artery dissections were acceptably treated with stent placement or stent-assisted coiling, and the patency could be preserved at follow-up. However, the efficiency of stent placement alone for intracranial vertebral artery dissecting aneurysm was limited. Stent-assisted coil embolization or double stent placements are a viable alternative for complete occlusion of dissecting aneurysms.

Heating of ions by Alfvén waves via nonresonant interactions.

Finite-amplitude intrinsic Alfvén waves exist pervasively in astrophysical and solar-terrestrial environment. It is generally believed that linear wave-particle resonant interaction between thermal protons and Alfvén waves is ineffective when the proton beta is low. However, this Letter demonstrates that the ions can be heated by Alfvén waves via nonresonant nonlinear interaction. Contrary to the customary expectation, it is found that the lower the plasma beta value, the more effective is the heating process. It is also shown that the ion temperature increase is more prominent along perpendicular direction.

Clipping vs coiling of posterior communicating artery aneurysms with third nerve palsy.

The authors investigated the evolution of third nerve palsy in patients with posterior communicating artery aneurysms who underwent coiling vs clipping. There was no statistical difference of complete third nerve palsy recovery in both treatments. Both techniques were of clinical benefit. Older age, diabetes, delayed interventions, and complete third nerve palsy at presentation indicated a poor prognosis for recovery.

Treatment of spontaneous arterial dissections with stent placement for preservation of the parent artery.

BACKGROUND: A wide variety of treatment regimens have been advocated for dissections involving the intracranial arteries. Recently, the stent can be used to exclude the aneurysm from the circulation and preserve the parent artery. We evaluated the safety and efficacy of stent angioplasty for intracranial arterial dissections. METHODS: Ten patients with spontaneous dissections, nine vertebral artery and one internal carotid artery lesions underwent endovascular treatment using stent placement as primary treatment modality. One stent placement was attempted in five patients initially. Three patients were intentionally treated with two overlapping stents which completely covered the aneurysm orifice. Two tandem stents were used in one patient to allow spanning the entire length of the dissection. Stent-assisted coil embolization was performed in one patient. RESULTS: Of the 10 patients in whom stenting was tried, the overall success in reaching the target lesion with stents was 90%. Of the 9 patients treated with stents, stent release and positioning were considered optimal in 7 patients (77.8%) and suboptimal in two. Lesions of 8 patients were improved or stable in angiographic follow-up. However, one pseudo-aneurysm was enlarged, and subsequently, was treated by proximal occlusion using coils. There were no instances of postprocedural ischaemic attacks, new neurological deficits, and no new minor or major strokes prior to patient discharge. All parent arteries of the patient who underwent the successful procedure were preserved. On the modified Rankin scale used for the follow up, all patients were assessed as functionally improved or of stable clinical status. CONCLUSIONS: The success in reducing dissection-induced stenosis or pseudo-aneurysm, the patency rate obtained at follow-up, and the lack of strokes (ischaemic or haemorrhagic) suggest that stent placement offers a viable alternative to complex surgical procedures or deconstructive procedures. The long-term efficacy and durability of stent placement for arterial dissection remains to be determined in a large series.

Temporal changes in reversible cerebral ischemia on perfusion- and diffusion-weighted magnetic resonance imaging: the value of relative cerebral blood volume maps.

Using a transorbital approach we induced the temporal occlusion and reperfusion model in 18 cats. A vascular clamp was placed on the main trunk of the left middle cerebral artery (MCA) for 1 h. Diffusion- and perfusion-weighted MR images were obtained at 1, 3, 6 and 24 h after the clip was released. The cats were killed 24 h after reperfusion, and triphenyl tetrazolium chloride (TTC) staining was performed. After the relative cerebral blood volume (rCBV), time to peak enhancement (TTP) and apparent diffusion coefficient (ADC) maps had been acquired, ROIs were drawn on (1) the area of the infarct produced, (2) the area of high signal intensity on initial diffusion-weighted magnetic resonance imaging (DWI) but normal on TTC staining, e.g., salvaged parenchyma. The ratios of these areas to the normal contralateral cortex were calculated and compared with those of the areas of the final infarct and the salvaged parenchyma. Areas of final infarct showed a temporal increase of rCBV on 3 and 6-h imaging and a final depletion on 24-h imaging. A persistent decrease of ADC value and delayed TTP were observed. Salvaged parenchyma also showed increased rCBV after reperfusion until the last imaging comparing it to the final area of infarct (P < 0.05, 24-h rCBV). The initial decrease in the ADC and delayed TTP normalized on 24-h imaging. In conclusion, rCBV of 24-h imaging was the reliable parameter to predict final infarct. A combination of serial changes on DWI and perfusion-weighted imaging (PWI) can predict ischemic penumbra and outcome.

MRI findings in neuro-behçet's disease.

AIM: To evaluate the pattern and site of involvement in neuro-Behçet's disease (NBD). MATERIALS AND METHODS: Twenty-one patients with NBD were evaluated. Using 1.5T magnetic resonance imaging (MRI), T1-weighted axial and sagittal images, gadolinium enhanced axial and coronal images and T2-weighted axial images were obtained. RESULTS: The brainstem, basal ganglia, cerebral white matter, internal capsule, thalamus and spinal cord were involved in eighteen, nine, nine, seven, six and two patients, respectively. In nine patients with cerebral white matter involvement, four had subcortical involvement and three had periventricular involvement, in addition to two patients with focal deep white matter lesions. Among the brainstem lesions, pons involvement was seen in fourteen patients, all had ventrally located lesions, and nine had tegmental involvement. Midbrain involvement was seen in fourteen patients; the cerebral peduncle was involved in 11 of these. Five patients had brainstem atrophy: two cases were demonstrated at initial MRI, the other three cases were seen on follow-up MRI. Pyramidal signs, the most common neurological signs, were demonstrated in fourteen patients. Follow-up MRI was obtained 10 days to 20 months after the initial MRI in eight cases; all showed changes in size, shape and site of involvement. After gadolinium enhancement, thirteen patients demonstrated mottled non-confluent enhancement in the brainstem (eight patients), posterior limb of the internal capsule (three patients), pachymeninges (two patients) and spinal cord (two patients). CONCLUSION: NBD manifests a reversible course, but chronic NBD may result in brainstem atrophy. Characteristic involvement along the corticospinal tract is well correlated with neurological signs.

Rescue treatment with abciximab in acute ischemic stroke.

In acute ischemic stroke, reocclusion after an initially successful thrombolysis treatment can occur and is associated with increased morbidity and mortality. The authors present the successful use of abciximab, a platelet glycoprotein IIb/IIIa receptor inhibitor, in a patient with a thrombotic occlusion of the proximal middle cerebral artery, which was refractory to combined IV and intra-arterial thrombolysis and percutaneous intracranial balloon angioplasty.

Pituitary adenomas: early postoperative MR imaging after transsphenoidal resection.

BACKGROUND AND PURPOSE: Although there have been several reports on postoperative MR imaging of the sella, immediate postoperative changes (usually within 3 days) have not been extensively analyzed. The purpose of this study was to establish the value of early postoperative MR imaging in differentiating residual tumor from postoperative surgical changes in the sella after transsphenoidal resection of pituitary adenomas. METHODS: Eighty-three patients with surgically proven pituitary adenomas (32 nonfunctioning, 24 prolactin-secreting, 22 growth hormone-secreting, and five prolactin- and growth hormone-secreting tumors) were studied prospectively. All patients underwent dynamic MR imaging within 7 days after surgery. We analyzed the postoperative MR images by focusing on changes in the pituitary gland, signal intensity, resorption of implanted material, and visibility of residual tumor. The patients were divided into four groups according to enhancement pattern of the postoperative pituitary mass: no enhancement, nodular enhancement, peripheral rim enhancement, and a combination of nodular and peripheral rim enhancement. RESULTS: Postoperative changes included resorption of implanted material and reexpansion of the pituitary gland. In 22 patients, residual tumors were found, and all patients showed nodular or combined enhancement. The residual tumors were confirmed by immediate reoperation in three patients, by hormonal assay and follow-up MR images in 11 patients with functioning adenomas, and by growth of the tumor on follow-up MR images in eight patients with nonfunctioning adenomas. Forty-eight patients showed no enhancement and 13 patients showed peripheral rim enhancement. CONCLUSION: Early postoperative dynamic MR imaging after transsphenoidal resection in pituitary adenoma is very effective in differentiating residual tumor from postoperative surgical changes.

Transient MR signal changes in patients with generalized tonicoclonic seizure or status epilepticus: periictal diffusion-weighted imaging.

BACKGROUND AND PURPOSE: Our purpose was to investigate transient MR signal changes on periictal MR images of patients with generalized tonicoclonic seizure or status epilepticus and to evaluate the clinical significance of these findings for differential diagnosis and understanding of the pathophysiology of seizure-induced brain changes. METHODS: Eight patients with MR images that were obtained within 3 days after the onset of generalized tonicoclonic seizure or status epilepticus and that showed seizure-related MR signal changes had their records retrospectively reviewed. T1- and T2-weighted images were obtained of all eight patients. Additional diffusion-weighted images were obtained of five patients during initial examination. After adequate control of the seizure was achieved, follow-up MR imaging was performed. We evaluated the signal changes, location of the lesions, and degree of contrast enhancement on T1- and T2-weighted images and the signal change and apparent diffusion coefficient (ADC) on diffusion-weighted images. We also compared the signal changes of the initial MR images to those of the follow-up MR images. RESULTS: The initial MR images revealed focally increased T2 signal intensity, swelling, and increased volume of the involved cortical gyrus in all eight patients. The lesions were located in the cortical gray matter or subcortical white matter in seven patients and at the right hippocampus in one. T1-weighted images showed decreased signal intensity at exactly the same location (n = 6) and gyral contrast enhancement (n = 4). Diffusion-weighted images revealed increased signal intensity at the same location and focally reduced ADC. The ADC values were reduced by 6% to 28% compared with either the normal structure opposite the lesion or normal control. Follow-up MR imaging revealed the complete resolution of the abnormal T2 signal change and swelling in five patients, whereas resolution of the swelling with residual increased T2 signal intensity at the ipsilateral hippocampus was observed in the other two patients. For one of the two patients, hippocampal sclerosis was diagnosed. For the remaining one patient, newly developed increased T2 signal intensity was shown. CONCLUSION: The MR signal changes that occur after generalized tonicoclonic seizure or status epilepticus are transient increase of signal intensity and swelling at the cortical gray matter, subcortical white matter, or hippocampus on periictal T2-weighted and diffusion-weighted images. These findings reflect transient cytotoxic and vasogenic edema induced by seizure. The reversibility and typical location of lesions can help exclude the epileptogenic structural lesions.

Diffusion-weighted image and MR spectroscopic analysis of a case of MELAS with repeated attacks.

We report the clinical and MR manifestations of an 18 year-old girl with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome. Recurrent status epilepticus caused reversible cytotoxic edema on diffusion-weighted images (DWI). Initial and one month follow-up MR spectroscopy, after seizure control, showed some discrepancies in the ratio of metabolites. N-acetylaspartate (NAA) partially recovered (NAA/creatine (Cr) ratio: 1.27-->1.84). This was because of a normalization of decreased NAA due to cellular dysfunction as a result of status epilepticus. A low ratio of NAA/Cr due to abnormal mitochondria remained in the decreased state. Reversible NAA/Cr ratios in the acute lesion suggested that NAA reflects the neuronal function as well as the level of neuronal structural damage. The altered NAA/Cr ratio better correlated with the abnormal signal intensity area of T2-weighted images (T2WI) and DWI than the lactate (Lac)/Cr ratio. With conservative treatment with anti-epileptics not accompanied by coenzyme Q or sodium dichloroacetate, lactate persistently increased (Lac/Cr ratio: 1.01-->1.21) because of the continued production of lactate in cells with respiratory deficiency, which is the main pathology of MELAS.

Perirolandic hypoperfusion on single-photon emission computed tomography in term infants with perinatal asphyxia: comparison with MRI and clinical findings.

We describe the findings on single-photon emission computed tomography (SPECT) in patients with perinatal asphyxia at term, with perirolandic cortico-subcortical changes on MRI, and to correlate them with clinical features. SPECT of 7 patients was obtained after injection of 185-370 MBq of Tc-99m-ECD (ethyl cysteinate dimer). The patients had spastic quadriplegia (7/7) with perinatal asphyxia (6/7) at term (7/7). The results were correlated with the MRI findings. Hypoperfusion of the perirolandic cortex was clearly seen on SPECT in all patients, even in two with subtle changes on MRI. SPECT demonstrated a more extensive area of involvement than MRI, notably in the cerebellum (in 4), the thalamus (in 7) and basal ganglia (in 5), where MRI failed to show any abnormalities.

The usefulness of the new "double-catheter technique" in the treatment of parent artery incorporated wide-necked aneurysm with guglielmi detachable coils. Technical notes.

SUMMARY: We describe a technique used to treat a widenecked aneurysm in which the neck is incorporated with the parent artery. The patient was a 54-year-old woman who had suffered a grade III subarachnoid haemorrhage. Angiogram and three-dimensional CT showed a large, widenecked aneurysm of the basilar bifurcation area with the right posterior cerebral artery incorporated in the aneurysm sac. A microcatheter was placed in the right posterior cerebral artery (PCA). Another catheter was placed within the aneurysm lumen. When making a first frame with a GDC, we made sure that the frame of the coil did not overlap the PCA positioned microcatheter. Then, with the microcatheter positioned at the PCA, the angiogram was done. The flow pattern and dye-disappearance time were checked. Subsequent coils were introduced, but not beyond the frame of the first coil to maintain PCA flow. This new "double-catheter technique" represents a viable option for treating wide-necked aneurysms, especially when the parent artery is incorporated in a wide-necked aneurysm and the delineation of the parent artery is impossible.

Evaluation of reperfusion and recovery of brain function before and after intracarotid arterial urokinase therapy in acute cerebral infarction with brain SPECT.

PURPOSE: Perfusion defects can be demonstrated reliably at an early stage with regional cerebral blood flow studies using SPECT. The administration of thrombolytic therapy in ischemic stroke is targeted at restoring cerebral perfusion immediately, leading to salvage of ischemic penumbra, smaller infarct size, and improved clinical outcome. This study considered the role of brain perfusion SPECT in the evaluation of reperfusion and brain function recovery of the infarcted area after early recanalization (less than 6 hours) of the occluded artery using intracarotid arterial urokinase therapy (ICAU). METHODS: Intracranial artery occlusion was confirmed in seven patients using emergency carotid angiography performed within the initial 6-hour period. Intracarotid arterial urokinase (500,000 to 800,000 units) was administered into the occluded arterial system (the left middle cerebral artery in four and the right middle cerebral artery in three patients). CT scanning was performed when the patients arrived in the emergency department and was repeated 24 to 48 hours after ICAU and at 7 days or earlier if clinically indicated. All patients had two SPECT studies, the first before urokinase administration and the second 24 or 48 hours later. RESULTS: Complete recanalization of the occluded vessels was seen in one patient after ICAU, effective partial recanalization was achieved in four patients, and minimal recanalization occurred in the other two. Before ICAU, Tc-99m HMPAO brain SPECT showed decreased uptake of the infarcted area in all patients, whereas the follow-up brain SPECT performed 24 or 48 hours after ICAU revealed improvement in the uptake of the recanalized area on qualitative and semiquantitative assessments using an asymmetry index, suggestive of brain function recovery and clinical improvement. Hemorrhagic transformation adjacent to the reperfused regions occurred in two patients with partial recanalization of the left middle cerebral artery. CONCLUSIONS: Reperfusion of the recanalized area and brain function recovery could be achieved if the occluded artery is recanalized within the initial 6-hour period using ICAU, and this was documented using brain perfusion SPECT without a delay in the therapeutic time window. Because the number of patients we studied was limited, further study is necessary to evaluate the effect of ICAU and to determine its prognostic significance.

Perfusion impairments in infantile autism on technetium-99m ethyl cysteinate dimer brain single-photon emission tomography: comparison with findings on magnetic resonance imaging.

The neuro-anatomical substrate of autism has been the subject of detailed investigation. Because previous studies have not demonstrated consistent and specific neuro-imaging findings in autism and most such studies have been performed in adults and school-aged children, we performed a retrospective review in young children in search of common functional and anatomical abnormalities with brain single-photon emission tomography (SPET) using technetium-99m ethyl cysteinate dimer (ECD) and correlative magnetic resonance imaging (MRI). The patient population was composed of 23 children aged 28-92 months (mean: 54 months) who met the diagnostic criteria of autism as defined in the DSM-IV and CARS. Brain SPET was performed after intravenous injection of 185-370 MBq of 99mTc-ECD using a brain-dedicated annular crystal gamma camera. MRI was performed in all patients, including T1, T2 axial and T1 sagittal sequences. SPET data were assessed visually. Twenty patients had abnormal SPET scans revealing focal areas of decreased perfusion. Decreased perfusion of the cerebellar hemisphere (20/23), thalami (19/23), basal ganglia (5/23) and posterior parietal (10/23) and temporal (7/23) areas were noted on brain SPET. By contrast all patients had normal MRI findings without evidence of abnormalities of the cerebellar vermis, cerebellar hemisphere, thalami, basal ganglia or parietotemporal cortex. In conclusion, extensive perfusion impairments involving the cerebellum, thalami and parietal cortex were found in this study. SPET may be more sensitive in reflecting the pathophysiology of autism than MRI. However, further studies are necessary to determine the significance of thalamic and parietal perfusion impairment in autism.