Browsing by Author "Koivunen, V."
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Item CHRONIC LIMB THREATENING ISCHEMIA AND DIABETES MELLITUS: THE SEVERITY OF TIBIAL ATHEROSCLEROSIS AND OUTCOME AFTER INFRAPOPLITEAL REVASCULARIZATION(Finnish Surgical Society, 2021-12) Koivunen, V.; Juonala, M.; Mikkola, Kimmo; Hakovirta, H. H.; Department of Computer Science; Turku University Hospital; University of TurkuBackground and Aims: Diabetes mellitus associates with poor outcomes in chronic limb threatening ischemia but data on different hypoglycemic regimens and outcomes are lacking. We analyzed insulin-treated diabetes mellitus, non-insulin-treated diabetes mellitus, and patients without diabetes mellitus. Materials and Methods: All patients with peripheral artery disease and/or diabetes mellitus and infrapopliteal revascularization in the Department of Vascular Surgery, Turku University Hospital during 2007–2015 were included. Tibial atherosclerosis was categorized into crural index classes of I–IV. Results: Of the 497 patients, 180 were insulin-treated diabetes mellitus, 94 non-insulin-treated diabetes mellitus, and 223 patients without diabetes mellitus groups (diabetes mellitus 55.1%). Insulin-treated diabetes mellitus was the most ill, youngest (insulin-treated diabetes mellitus—median: 72.4, interquartile range: 64.0–79.5 versus non-insulin-treated diabetes mellitus—76.0, interquartile range: 67.9–83.6 versus patients without diabetes mellitus—77.3, interquartile range: 68.5–83.7, p < 0.001), had the highest body mass index (insulin-treated diabetes mellitus—median: 27.7, interquartile range: 24.0–31.8 versus non-insulin-treated diabetes mellitus—26.3, interquartile range: 23.2–30.3 versus patients without diabetes mellitus—23.9, interquartile range: 21.5–26.9, p < 0.001), and Charlson comorbidity index (insulin-treated diabetes mellitus—65.6% versus non-insulin-treated diabetes mellitus—46.8% versus patients without diabetes mellitus—10.8%, p < 0.001). After endovascular revascularization, limb salvage was poorer for insulin-treated diabetes mellitus (p = 0.046) and non-insulin-treated diabetes mellitus groups (p = 0.011) compared to surgery, but not for patients without diabetes mellitus (p = 0.15). Patients with crural index IV in insulin-treated diabetes mellitus (p = 0.001) and non-insulin-treated diabetes mellitus (p = 0.013) had higher mortality after revascularization. Crural index IV was a risk factor for limb loss (hazard ratio: 1.37, 95% confidence interval: 1.08–1.74, p = 0.008). Conclusion: Limb salvage after bypass is better for insulin and non-insulin diabetics, compared to the endovascular approach. Extensive tibial atherosclerosis is an independent risk factor for limb loss. It associates with increased mortality in both insulin and non-insulin diabetics.Item Cooperative Energy Detection with Heterogeneous Sensors under Noise Uncertainty: SNR Wall and use of Evidence Theory(Institute of Electrical and Electronics Engineers, 2018-09) Gohain, P. B.; Chaudhari, S.; Koivunen, V.; Dept Signal Process and Acoust; Visa Koivunen Group; International Institute of Information Technology HyderabadThe analyzed system model in this paper is a distributed parallel detection network in which each secondary user (SU) evaluates the energy-based test statistic from the received observations and sends it to a fusion center (FC), which makes the final decision. Uncertainty in the noise variance at each SU is modeled as an unknown constant in a certain interval around the nominal noise variance. It is assumed that the SUs are heterogeneous in that the nominal noise variances and the uncertainty intervals can be different for different SUs. Moreover, the received signal power at each SU may be different. For the considered system model, the paper presents important results for two inter-related themes on cooperative energy detection (CED) in the presence of noise uncertainty (NU). First, the expressions for generalized SNR walls are derived for the classical CED fusion rule, i.e., sum of energies from all SUs. Second, a Dempster-Shafer theory (DST) based CED is proposed in the presence of NU with heterogeneous sensors. In the proposed scheme, the test statistic from each SU is the energy-based basic mass assignment (BMA) values, which are first discounted depending on the uncertainty level associated with the SU and then fused at the FC using the Dempster rule of combination to arrive at the global decision. It is shown that the proposed scheme outperforms the traditional sum fusion rule in terms of detection performance as well as the location of SNR wall.Item Multicarrier Radar-communications Waveform Design for RF Convergence and Coexistence(2019-05-01) Bică, M.; Koivunen, V.; Dept Signal Process and Acoust; Visa Koivunen GroupRF convergence where the same transceiver is used for communications and sensing purposes is taking place. In this paper, a dual-use radar-communications multicarrier waveform is proposed, where different subcarriers are assigned to different subsystems. Two algorithms for subcarrier assignment and optimal power allocation for the radar and communications subsystems are developed. A compound mutual information (MI) based objective function is used for optimizing the power allocation of each subsystem in both design algorithms. The first proposed design algorithm assumes priority for the radar subsystem and it is called radar selfish design. The second proposed design algorithm is called cooperative design, in which both subsystems are jointly optimized by maximizing a compound MI based objective function.