Optimized digital backward propagation for phase modulated signals in mixed-optical fiber transmission link.

The parametric optimization of Digital Backward Propagation (DBP) algorithm for mitigating fiber transmission impairments is proposed and numerically demonstrated for phase modulated signals in mixed-optical fiber transmission link. The optimization of parameters i.e. dispersion (D) and non-linear coefficient (γ) offer improved eye-opening (EO). We investigate the optimization of iterative and non-iterative symmetric split-step Fourier method (S-SSFM) for solving the inverse non-linear Schrödinger equation (NLSE). Optimized DBP algorithm, with step-size equal to fiber module length i.e. one calculation step per fiber span for obtaining higher computational efficiency, is implemented at the receiver as a digital signal processing (DSP) module. The system performance is evaluated by EO-improvement for diverse in-line compensation schemes. Using computationally efficient non-iterative symmetric split-step Fourier method (NIS-SSFM) upto 3.6 dB referenced EO-improvement can be obtained at 6 dBm signal launch power by optimizing and modifying DBP algorithm parameters, based on the characterization of the individual fiber types, in mixed-optical fiber transmission link.

Efficacy of stent angioplasty for symptomatic stenoses of the proximal vertebral artery.

BACKGROUND: To evaluate the safety and efficacy of stent angioplasty in the treatment of symptomatic arteriosclerotic stenoses of the proximal vertebral artery (VA). METHODS: Thirty-eight symptomatic stenoses of the vertebral origin were treated with flexible balloon-expandable coronary stents. Angiographic and clinical follow-up examinations were obtained in 26 patients at a mean of 11 months. RESULTS: The immediate post-procedural angiographic results showed no residual stenosis in 33 vessels and mild residual stenoses in five vessels. Periprocedurally, there were two asymptomatic technical complications and one TIA. During follow-up re-stenosis could be detected in 10 cases (36%), and vessel occlusions in two patients. Two stents were broken. One of the restenosis caused a TIA within the follow-up period. CONCLUSIONS: Flexible balloon-expandable coronary stents proved to be save and effective in preventing vertebrobasilar stroke but were incapable to preserve the proximal vertebral artery lumen. For the VA origine an adequate stent, self-expanding, bioresorbable, or drug-eluting has to be found.

Perfusion MRI before and after acetazolamide administration for assessment of cerebrovascular reserve capacity in patients with symptomatic internal carotid artery (ICA) occlusion: comparison with 99mTc-ECD SPECT.

INTRODUCTION: Impaired cerebral vascular reserve (CVR) in patients with symptomatic internal carotid artery (ICA) occlusion is regarded as a possible indication for performing extra-/intracranial (EC/IC) bypass surgery. As perfusion MR imaging (MRI) can demonstrate cerebral haemodynamics at capillary level, our hypothesis was that perfusion MRI could be used in these patients for the evaluation of CVR following acetazolamide challenge in a similar way to single photon emission CT (SPECT) and might provide additional information. METHODS: Enrolled in the study were 12 patients (mean age 61.3 years; 11 male, 1 female) with symptomatic unilateral ICA occlusion proven by angiography. Both perfusion MRI and 99m-technetium-ethyl-cysteinate dimer ((99m)Tc-ECD) SPECT were performed before and after injection of acetazolamide (Diamox ,1000 mg i.v.). CVR parameters including regional cerebral blood flow (rCBF) and volume (rCBV), and mean transit times (MTT) were measured by perfusion MRI. RESULTS: The patients with impaired CVR proven by SPECT (n = 9) had a negative mean rCBF increment (-46.52%), negative rCBV increment (-13.5%) and delayed MTT (mean +2.98 s), respectively, on the occluded side (Student's t-test all P < 0.05). The patients with sufficient CVR (n = 3) had a mean rCBF increment of 1.2%, a decrement of rCBV of 10.46%, and a mean MTT shortening of 0.27 s following the acetazolamide injection. CONCLUSIONS: Perfusion MRI before and after acetazolamide administration compares favourably with (99m)Tc-ECD SPECT for the detection of impaired CVR. The impact that perfusion MRI studies (before and after acetazolamide administration) might have on the treatment decision in patients with ICA occlusion has yet to be determined by a prospective study.