Electronic screening-enhanced hole pairing in two-leg spin ladders studied by high-resolution resonant inelastic x-ray scattering at Cu M edges.

We study the electronic screening mechanisms of the effective Coulomb on-site repulsion in hole-doped Sr(14)Cu(24)O(41) compared to undoped La(6)Ca(8)Cu(24)O(41) using polarization dependent high-resolution resonant inelastic x-ray scattering at Cu M edges. By measuring the energy of the effective Coulomb on-site repulsion and the spin excitations, we estimate superexchange and hopping matrix element energies along rungs and legs, respectively. Interestingly, hole doping locally screens the Coulomb on-site repulsion reducing it by as much as 25%. We suggest that the increased ratio of the electronic kinetic to the electronic correlation energy contributes to the local superexchange mediated pairing between holes.

Observation of Leggett's collective mode in a multiband MgB2 superconductor.

We report observation of Leggett's collective mode in a multiband MgB2 superconductor with Tc=39 K arising from the fluctuations in the relative phase between two superconducting condensates. The novel mode is observed by Raman spectroscopy at 9.4 meV in the fully symmetric scattering channel. The observed mode frequency is consistent with theoretical considerations based on first-principles computations.

Gaplike excitations in the superconducting state of Bi2Sr2CaCu2O8 studied by resonant Raman scattering.

We report on the response of the electronic continuum from inelastic light-scattering experiments over an extended energy range between 1.970 and 4.504 eV in the superconducting state of Bi2Sr2CaCu2O8. The formation of a substantial Raman feature at shifts below twice the superconducting gap as well as the additional weight above this energy are found to be strongly dependent on the incident photon energy. For excitation wavelengths observed in ultraviolet, we find an enhancement of the integrated spectral weight below T(c). The resulting composite feature shows three distinct resonances at 2.5, 3.3, and 3.8 eV. We strongly suggest that the superconductivity-induced changes are the result of both the opening of a superconducting gap and the appearance of a collective mode.

MR imaging of vertebrobasilar vascular disease.

Sixteen patients with vascular lesions of the vertebral and basilar arteries were studied with magnetic resonance imaging. The vascular abnormalities included seven cases of atherosclerotic disease with partial or complete thrombosis, six aneurysms, two cases of vertebrobasilar dolichoectasia, and one basilar artery dissection. Magnetic resonance effectively demonstrated vascular thrombosis with occlusion as high signal intensity on spin echo (SE) sequences with absence of flow void and no flow enhancement on gradient echo (GRE) images. Nonthrombosed aneurysms exhibited mixed signal intensity on SE images and hyperintensity on GRE images. Intraluminal thrombus also appeared heterogeneous, with variable signal intensity depending on the specific components of hemorrhage present. Correlation of the SE and GRE scans was helpful for distinguishing stasis and turbulent flow from thrombus. Compression of cranial nerves by vascular structures was clearly depicted in both cases of dolichoectasia. Basilar artery dissection was displayed as a focal area of flow void surrounded by a thrombosed false lumen. Magnetic resonance is an effective noninvasive method for evaluating vascular pathology of the vertebrobasilar system.

MR imaging of the temporomandibular joint: a cadaver study of the value of coronal images.

Recent studies comparing cryosectional anatomy of the temporomandibular joint (TMJ) to its MR appearance have shown that the assessment of disk displacement is inaccurate when based on the sagittal plane alone. This article describes the MR appearance of the normal and abnormal (positional and osseous changes) TMJ in the coronal plane and compares these findings with their cryosectional anatomy. Twenty-two TMJs from unselected frozen cadavers were embedded in paraffin. Coronal and sagittal MR imaging was performed; specimens were then cut in the same plane as the coronal images. Disk position by cryosection was normal in 14 cases and abnormal in eight cases. Coronal MR images alone correctly depicted the TMJ disk position in 17 cases (77%) (13 normal, four abnormal). Complementary sagittal images were necessary for diagnosing anterior displacement in two cases (9%). MR was inaccurate in three cases (14%) of severe degenerative joint disease. Bone condition was correctly diagnosed on the basis of coronal images alone in all cases. Our study shows that coronal MR imaging alone of the TMJ in cadavers accurately shows disk position in 77% of cases. Complementary sagittal images were of benefit in the diagnosis of an additional 9% with anterior displacement. Disk position was assessed inaccurately in either plane in patients with severe degenerative joint disease. For a full MR assessment of the TMJ for disk position and bone condition, we recommend imaging in both coronal and sagittal planes.

Primary myxoma of the posterior fossa.

A rare case of primary intracranial myxoma of the posterior fossa is described in a 32-year old woman. The patient presented with a history of headaches, disequilibrium, nausea and abnormal vision for several months. Computed tomography (CT) showed a well-demarcated hypodense mass. After contrast administration the mass appeared as an inhomogeneously enhancing lesion surrounded by a small rim of edema. The mass was surgically excised with histological examination revealing a true myxoma. Echocardiography revealed no evidence of a cardiac myxoma. The CT appearance of other case reports of non-cardiac myxomas in the literature is reviewed.

Clinical experience with routine Gd-DTPA administration for MR imaging of the brain.

A retrospective analysis of intracranial magnetic resonance (MR scans of 514 patients who underwent nonselective Gd-DTPA enhanced MR imaging was performed to determine the efficacy of this protocol for Gd-DTPA administration. This report reviews the frequency and clinical significance of abnormally enhancing areas that were entirely undetectable on precontrast images or would have been missed without the retrospective knowledge of enhancement. Fifty-seven patients (11% of the 514 patients studied) showed enhancing lesions, with 16 (3.1% of the total) of these patients demonstrating one or more lesions identifiable only on postcontrast images. Of those 16 patients, 8 had other focal abnormalities on precontrast studies, whereas the remaining 8 (1.6% of the total) had negative precontrast studies. The new diagnoses affected clinical management directly in five patients and in another nine contributed potentially significant information. Considerations regarding a selective versus nonselective protocol for Gd-DTPA administration for intracranial MR imaging and the use of clinical information to augment these protocols are discussed.

Heterotopic brain in the middle ear: CT findings.

A soft tissue mass was found by CT in the mesotympanum of the left middle ear of a 4-year-old boy. This lesion was without radiologic or surgical evidence of associated bony defect or communication with the intracranial cavity. Pathological examination revealed heterotopic brain tissue. Although heterotopic brain tissue in the middle ear is rare, it should be considered in the differential diagnosis of soft tissue middle ear masses.

Mucocele of the anterior clinoid process: CT and MR findings.

A patient with biopsy-proven primary mucocele of the anterior clinoid process is presented. Gadolinium-DTPA enhanced magnetic resonance imaging revealed a nonenhancing lesion isointense to gray matter. Computed tomography revealed well corticated bony margins without direct involvement of the sphenoid sinus.