Differentiation of Jugular Foramen Paragangliomas versus Schwannomas Using Golden-Angle Radial Sparse Parallel Dynamic Contrast-Enhanced MRI

BACKGROUND AND PURPOSE

Accurate differentiation of paragangliomas and schwannomas in the jugular foramen has important clinical implications because treatment strategies may vary but differentiation is not always straightforward with conventional imaging. Our aim was to evaluate the accuracy of both qualitative and quantitative metrics derived from dynamic contrast-enhanced MR imaging using golden-angle radial sparse parallel MR imaging to differentiate paragangliomas and schwannomas in the jugular foramen.

MATERIALS AND METHODS

A retrospective study of imaging data was performed on patients (n = 30) undergoing MR imaging for jugular foramen masses with the golden-angle radial sparse parallel MR imaging technique. Imaging data were postprocessed to obtain time-intensity curves and quantitative parameters. Data were normalized to the dural venous sinus for relevant parameters and analyzed for statistical significance using a Student t test. A univariate logistic model was created with a binary output, paraganglioma or schwannoma, using a wash-in rate as a variable. Additionally, lesions were clustered on the basis of the wash-in rate and washout rate using a 3-nearest neighbors method.

RESULTS

There were 22 paragangliomas and 8 schwannomas. All paragangliomas demonstrated a type 3 time-intensity curve, and all schwannomas demonstrated a type 1 time-intensity curve. There was a statistically significant difference between paragangliomas and schwannomas when comparing their values for area under the curve, peak enhancement, wash-in rate, and washout rate. A univariate logistic model with a binary output (paraganglioma or schwannoma) using wash-in rate as a variable was able to correctly predict all observed lesions (P < .001). All 30 lesions were classified correctly by using a 3-nearest neighbors method.

CONCLUSIONS

Paragangliomas at the jugular foramen can be reliably differentiated from schwannomas using golden-angle radial sparse parallel MR imaging-dynamic contrast-enhanced imaging when imaging characteristics cannot suffice.

A tunable Fabry-Pérot quantum Hall interferometer in graphene

Electron interferometry with quantum Hall (QH) edge channels in semiconductor heterostructures can probe and harness the exchange statistics of anyonic excitations. However, the charging effects present in semiconductors often obscure the Aharonov-Bohm interference in QH interferometers and make advanced charge-screening strategies necessary. Here we show that high-mobility monolayer graphene constitutes an alternative material system, not affected by charging effects, for performing Fabry-Pérot QH interferometry in the integer QH regime. In devices equipped with gate-tunable quantum point contacts acting on the edge channels of the zeroth Landau level, we observe-in agreement with theory-high-visibility Aharonov-Bohm interference widely tunable through electrostatic gating or magnetic fields. A coherence length of 10 μm at a temperature of 0.02 K allows us to further achieve coherently coupled double Fabry-Pérot interferometry. In future, QH interferometry with graphene devices may enable investigations of anyonic excitations in fractional QH states.

Evolution of inter-layer coupling in artificially stacked bilayer MoS2

In this paper, we show experimentally that for van der Waals heterostructures (vdWh) of atomically-thin materials, the hybridization of bands of adjacent layers is possible only for ultra-clean interfaces. This we achieve through a detailed experimental study of the effect of interfacial separation and adsorbate content on the photoluminescence emission and Raman spectra of ultra-thin vdWh. For vdWh with atomically-clean interfaces, we find the emergence of novel vibrational Raman-active modes whose optical signatures differ significantly from that of the constituent layers. Additionally, we find for such systems a significant modification of the photoluminescence emission spectra with the appearance of peaks whose strength and intensity directly correlate with the inter-layer coupling strength. Our ability to control the intensity of the photoluminescence emission led to the observation of detailed optical features like indirect-band peaks. Our study establishes that it is possible to engineer atomically-thin van der Waals heterostructures with desired optical properties by controlling the inter-layer spacing, and consequently the inter-layer coupling between the constituent layers.

Coherence and Density Dynamics of Excitons in a Single-Layer MoS2 Reaching the Homogeneous Limit

We measure the coherent nonlinear response of excitons in a single layer of molybdenum disulfide embedded in hexagonal boron nitride, forming a h-BN/MoS₂/ h-BN heterostructure. Using four-wave mixing microscopy and imaging, we correlate the exciton inhomogeneous broadening with the homogeneous one and population lifetime. We find that the exciton dynamics is governed by microscopic disorder on top of the ideal crystal properties. Analyzing the exciton ultrafast density dynamics using amplitude and phase of the response, we investigate the relaxation pathways of the resonantly driven exciton population. The surface protection via encapsulation provides stable monolayer samples with low disorder, avoiding surface contaminations and the resulting exciton broadening and modifications of the dynamics. We identify areas localized to a few microns where the optical response is totally dominated by homogeneous broadening. Across the sample of tens of micrometers, weak inhomogeneous broadening and strain effects are observed, attributed to the remaining interaction with the h-BN and imperfections in the encapsulation process.

Weakly Trapped, Charged, and Free Excitons in Single-Layer MoS2 in the Presence of Defects, Strain, and Charged Impurities

Few- and single-layer MoS₂ host substantial densities of defects. They are thought to influence the doping level, the crystal structure, and the binding of electron-hole pairs. We disentangle the concomitant spectroscopic expression of all three effects and identify to what extent they are intrinsic to the material or extrinsic to it, i.e., related to its local environment. We do so by using different sources of MoS₂-a natural one and one prepared at high pressure and high temperature-and different substrates bringing varying amounts of charged impurities and by separating the contributions of internal strain and doping in Raman spectra. Photoluminescence unveils various optically active excitonic complexes. We discover a defect-bound state having a low binding energy of 20 meV that does not appear sensitive to strain and doping, unlike charged excitons. Conversely, the defect does not significantly dope or strain MoS₂. Scanning tunneling microscopy and density functional theory simulations point to substitutional atoms, presumably individual nitrogen atoms at the sulfur site. Our work shows the way to a systematic understanding of the effect of external and internal fields on the optical properties of two-dimensional materials.

Long-term treatment of chronic venous insufficiency of the leg with micronized purified flavonoid fraction in the primary care setting of India

Objective: This study investigates whether micronized purified flavonoid fraction (MPFF) is effective and acceptable without compression or surgical intervention for the management of chronic venous insufficiency of the leg (CVIL) in the primary care setting of a tropical country such as India.

Methods: A prospective observational study on patients with early CVIL drawn from the clinical practice of randomly selected physicians distributed across India. Patients received MPFF 1000 mg/day for six months without compression stockings or surgery. The primary outcome was a change in their CEAP (clinical, aetiological, anatomical, pathophysiological) classification of CVIL severity. Secondary outcomes were changes in leg oedema, symptom intensity and quality of life.

Results: Of the 308 patients recruited by 72 physicians, 166 (53.9%, 95% confidence interval (CI) 48.3-59.5) had regression in the CEAP severity stage. Mean leg circumference in those with oedema decreased by 2 cm (95% CI 1.7-2.3, P <0.05). Patient-assessed mean percentage decrease in symptom intensity was 32.3 for cramps (28.9-35.7, P <0.01); 32.4 for heaviness (29.8-35.7, P <0.01); 28.2 for pain (25.6-30.8, P <0.01); and 21.5 for swelling (18.7-24.3, P <0.01). Quality of life improved by 21.7% (16.9-26.5, P <0.01) in the physical domains, 25.9% (20.8-31.0, P <0.01) in the social domains, and 19.2% (14.7-23.7, P <0.01) in the psychological domains.

Conclusions: When used alone, MPFF was effective and acceptable for the management of CVIL in primary care. This may be useful in tropical climates where compliance with compression stockings is poor and access to surgery limited.

Longitudinal assessment of cardiac diastolic function in HIV-infected patients

Asymptomatic isolated diastolic dysfunction (DD), with normal left ventricular systolic function, may be the first indication of underlying cardiac disease in HIV-negative populations. We previously reported a high prevalence (37%) of DD among asymptomatic HIV-infected patients at low risk for AIDS and cardiovascular disease (CVD). We performed a longitudinal assessment of interval echocardiographic changes in this cohort over a four-year period. Repeat transthoracic echocardiograms (TTEs) utilized standard techniques. Sixty (of the original 91) HIV-infected patients, predominately men, underwent repeat TTE (median follow-up 3.7 years, interquartile range [IQR] 3.5, 4.0). Cohort characteristics (median; IQR) include age 42.0 (36.5, 46.0) years, HIV duration 16.4 years (8.1, 18.9), current CD4 count 572.0 cells/mm(3) (436.5, 839.0), antiretroviral therapy (ART) duration 8.1 years (4.8, 13.4) and Framingham risk score 1.0 (0.0, 2.0). DD was observed in 28/60 patients on re-evaluation (47%, 95% confidence interval [CI] 34%, 60%); 31% (11/36) of patients had new onset DD for an overall incidence of 8.2/100 person-years. On follow-up, subjects with DD were older, had a trend towards higher body mass index, hypertension and longer duration of HIV infection compared with subjects without DD. We confirmed a high prevalence of DD (47%) in asymptomatic HIV-infected patients at low risk for AIDS and CVD.

Recovery from paraplegia following aortic saddle embolism. Case report

An aortic saddle embolus causing paraplegia is rare and even rarer is a documentation of neurological recovery from this event. A 47 year old male presented with absent pulsations in the lower limbs and paraplegia, both of sudden onset. He underwent immediate bilateral transfemoral embolectomy. The postoperative period was stormy. The paraplegia recovered over a period of 2 months and he could walk to his place of work after 6 months. The rare combination of saddle embolus and paraplegia is discussed. An attempt has been made to verify the hypothesis of Dickson et al which states that a low origin of the great radicular artery (GRA) below T12 level may be responsible for paraplegia when obstructed by a saddle embolus. We found the GRA arising at L2 vertebral level in this patient. Postoperative selective spinal arteriogram and magnetic resonance imaging (MRI) of the spinal cord showed a patent GRA and normal spinal cord structure respectively. Early surgical intervention in restoring the blood flow into the GRA may prevent severe histological changes hitherto responsible for nonrecovery from paraplegia in the earlier reports.

Choriocarcinoma presenting as intracavitary tumor in the left atrium

We describe a 27-year-old woman who presented with classical symptoms and signs of left atrial myxoma. Histopathological studies of the excised tumor mass, however, revealed it to be choriocarcinoma. This is the first report of such a presentation of choriocarcinoma.