Vascular hypoperfusion in acute optic neuritis is a potentially new neurovascular model for demyelinating diseases.

PURPOSE: Optic neuritis is highly correlated with multiple sclerosis and is a major cause of acute visual loss and long-term neuronal degeneration. Primary cerebral hypoperfusion has been reported in brain demyelinating diseases. This study investigated whether peripapillary perfusion is changed in patients with acute optic neuritis (AON). METHODS: This three-year cohort study was conducted from September 1 2012, to August 31, 2015. Two hundred and forty-one patients with non-glaucomatous acute optic neuropathy were screened, and 42 non-highly myopic patients who had suffered their first episode of unilaterally idiopathic AON were studied. All cases received spectral-domain optical coherence tomography (OCT) examination, general survey, and standard corticosteroid therapy. OCT images were analyzed using a customized MATLAB program for measuring peripapillary choroidal thickness (PCT). Multivariate regression models were constructed to identify factors that are significantly related to peripapillary perfusion. RESULTS: Decreased PCT was found in eyes experiencing AON combined with disc swelling (the ratio of lesion eye PCT/fellow eye PCT was 0.87 ± 0.08; range, from 0.75 to 1.00). In comparison to the healthy fellow eyes, approximately every 26% increase in the thickness of the retinal nerve fiber layer due to axonal swelling was associated with a 10% decreased thickness of PCT. Thinner PCT is also correlated with poorer trough vision, which may lead to poorer final vision. These findings were obvious in patients with optic papillitis but not in patients with retrobulbar neuritis. CONCLUSIONS: Peripapillary vascular hypoperfusion was found in patients experiencing AON combined with disc swelling. These findings are unlike those for other ocular inflammatory diseases but are consistent with cerebral hypoperfusion, which is found in brain demyelinating diseases; thus, these findings may represent a new neurovascular model in this field.

Detecting changes in ultrasound backscattered statistics by using Nakagami parameters: Comparisons of moment-based and maximum likelihood estimators.

The Nakagami distribution is an approximation useful to the statistics of ultrasound backscattered signals for tissue characterization. Various estimators may affect the Nakagami parameter in the detection of changes in backscattered statistics. In particular, the moment-based estimator (MBE) and maximum likelihood estimator (MLE) are two primary methods used to estimate the Nakagami parameters of ultrasound signals. This study explored the effects of the MBE and different MLE approximations on Nakagami parameter estimations. Ultrasound backscattered signals of different scatterer number densities were generated using a simulation model, and phantom experiments and measurements of human liver tissues were also conducted to acquire real backscattered echoes. Envelope signals were employed to estimate the Nakagami parameters by using the MBE, first- and second-order approximations of MLE (MLE1 and MLE2, respectively), and Greenwood approximation (MLEgw) for comparisons. The simulation results demonstrated that, compared with the MBE and MLE1, the MLE2 and MLEgw enabled more stable parameter estimations with small sample sizes. Notably, the required data length of the envelope signal was 3.6 times the pulse length. The phantom and tissue measurement results also showed that the Nakagami parameters estimated using the MLE2 and MLEgw could simultaneously differentiate various scatterer concentrations with lower standard deviations and reliably reflect physical meanings associated with the backscattered statistics. Therefore, the MLE2 and MLEgw are suggested as estimators for the development of Nakagami-based methodologies for ultrasound tissue characterization.