The successful suppression of clutter arising from stationary or slowly moving tissue is one of the key issues in medical ultrasound color blood imaging. Remaining clutter may cause bias in the mean blood frequency estimation and results in a potentially misleading description of blood-flow. In this paper, based on the principle of general wall-filter, the design process of three classes of filters, infinitely impulse response with projection initialization (Prj-ⅡR), polynomials regression (Pol-Reg), and eigen-based filters are previewed and analyzed. The performance of the filters was assessed by calculating the bias and variance of a mean blood velocity using a standard autocorrelation estimator. Simulation results show that the performance of Pol-Reg filter is similar to Prj-ⅡR filters. Both of them can offer accurate estimation of mean blood flow speed under steady clutter conditions, and the clutter rejection ability can be enhanced by increasing the ensemble size of Doppler vector. Eigen-based filters can effectively remove the non-stationary clutter component, and further improve the estimation accuracy for low speed blood flow signals. There is also no significant increase in computation complexity for eigen-based filters when the ensemble size is less than 10.
ObjectiveTo systematically evaluate the outcomes of drug-eluting balloon (DEB) in treating coronary artery in-stent restenosis (ISR) by using meta-analysis and trial sequential analysis (TSA). MethodsWe searched PubMed, EMbase, The Cochrane Library（Issue 4, 2016）, CNKI, CBM, VIP and WanFang Data to collect randomized controlled trials (RCTs) regarding the treatment of ISR by DEB from inception to April 2016. After two reviewers independently screened citations, extracted data and assessed the bias risk of included studies, we carried out meta-analysis and TSA analysis by using RevMan 5.3 version and TSA v0.9 respectively. ResultsA total of 10 RCTs involving 1909 patients were included. Seven-hundred and forty-seven patients were included with regard to the comparison between DEB and POBA, 1162 patients were recruited to compare DEB and drug-eluting stents (DES). The results of meta-analysis revealed that DEB was associated with decreased mortality (OR=0.36, 95%CI 0.14 to 0.93, P=0.04), compared with that of plain old balloon angioplasty (POBA). And TSA showed that cumulative Z-curve strode the conventional threshold value but not the TSA threshold value which suggested a false positive result of meta-analysis. In comparison with that of POBA, DEB had a lower incidence of target lesion revascularization (TLR) (OR=0.16, 95%CI 0.07 to 0.38, P＜0.01). And the result of TSA displayed that the cumulative Z-curve strode both the conventional and TSA threshold value which validated the result of meta-analysis. Besides, the results of meta-analysis showed that there were no significant differences in mortality (OR=0.84, 95%CI 0.41 to 1.72, P=0.63) and TLR (OR=1.55, 95%CI 0.76 to 3.16, P=0.22) between DEB and DES. However, the result of TSA revealed that the cumulative Z-curve did not strode both the conventional and TSA threshold value, and the included sample size less was than required information size which suggested that the reliability of the meta-analysis needed more studies to confirm. While the subgroup analysis of EES revealed that DEB had a higher incidence of TLR than that of DEB (OR=3.37, 95%CI 1.59 to 7.15, P＜0.01). And the result of TSA displayed that the cumulative Z-curve strode both the conventional and TSA threshold value which validated the result of meta-analysis. ConclusionCurrent evidence shows, EES is superior to DEB in decreasing the incidence of TLR in patients with ISR, while DEB is superior to POBA. However, the comparison of DEB and other strategies on reducing of mortality in patients with ISR still needed more studies to prove.