Systematic review and meta-analysis of the diagnostic accuracy of ultrasonography for deep vein thrombosis

Background Ultrasound (US) has largely replaced contrast venography as the definitive diagnostic test for deep vein thrombosis (DVT). We aimed to derive a definitive estimate of the diagnostic accuracy of US for clinically suspected DVT and identify study-level factors that might predict accuracy. Methods We undertook a systematic review, meta-analysis and meta-regression of diagnostic cohort studies that compared US to contrast venography in patients with suspected DVT. We searched Medline, EMBASE, CINAHL, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Controlled Trials Register, Database of Reviews of Effectiveness, the ACP Journal Club, and citation lists (1966 to April 2004). Random effects meta-analysis was used to derive pooled estimates of sensitivity and specificity. Random effects meta-regression was used to identify study-level covariates that predicted diagnostic performance. Results We identified 100 cohorts comparing US to venography in patients with suspected DVT. Overall sensitivity for proximal DVT (95% confidence interval) was 94.2% (93.2 to 95.0), for distal DVT was 63.5% (59.8 to 67.0), and specificity was 93.8% (93.1 to 94.4). Duplex US had pooled sensitivity of 96.5% (95.1 to 97.6) for proximal DVT, 71.2% (64.6 to 77.2) for distal DVT and specificity of 94.0% (92.8 to 95.1). Triplex US had pooled sensitivity of 96.4% (94.4 to 97.1%) for proximal DVT, 75.2% (67.7 to 81.6) for distal DVT and specificity of 94.3% (92.5 to 95.8). Compression US alone had pooled sensitivity of 93.8 % (92.0 to 95.3%) for proximal DVT, 56.8% (49.0 to 66.4) for distal DVT and specificity of 97.8% (97.0 to 98.4). Sensitivity was higher in more recently published studies and in cohorts with higher prevalence of DVT and more proximal DVT, and was lower in cohorts that reported interpretation by a radiologist. Specificity was higher in cohorts that excluded patients with previous DVT. No studies were identified that compared repeat US to venography in all patients. Repeat US appears to have a positive yield of 1.3%, with 89% of these being confirmed by venography. Conclusion Combined colour-doppler US techniques have optimal sensitivity, while compression US has optimal specificity for DVT. However, all estimates are subject to substantial unexplained heterogeneity. The role of repeat scanning is very uncertain and based upon limited data

High-order modulation formats, constellation design, and DSP for high-speed transmission systems

The capacity of optical fiber communication networks is limited by the Kerr effect inherent to transmission using optical fibers. The signal degradations due to the nonlinear distortions limit the achievable transmission distances and become more significant in systems with larger transmission bandwidths, closer channel spacing, and higher order modulation formats. Optical fiber nonlinearities are seen as the major bottleneck to the performance of optical transmission networks. This chapter describes the theoretical and experimental investigations into a series of techniques developed to unlock the capacity of optical communications and to overcome the barriers in transmission over nonlinear fiber channels. It covers three key areas for combatting optical fiber nonlinearities to increasing the overall throughput of the optical fiber channels in the nonlinear regime that have been the focus of research over the recent years. These are (1) digital nonlinearity compensation technique, such as digital backpropagation, to partially “undo” the nonlinearity and improve signal performance, (2) digital nonlinearity compensation in presence of laser phase noise, and (3) signal design techniques, making use of coded modulation and constellation shaping in optical communications. This chapter aims to review and quantify examples of digital signal processing-based nonlinearity compensation and further possible increases in the achievable capacity and transmission distances, depending on the modulation format used, that come from the combination of nonlinearity compensation and signal constellation shaping