Receiver selection for multi-target tracking in multi-static Doppler radar systems

This paper presents a novel receiver selection method for multi-target tracking in multi-static Doppler radar systems. The assumption is that in the surveillance volume of interest, a single transmitter with a known frequency is active and several spatially distributed radar receivers collect and report Doppler-only measurements. The Doppler measurements are not only affected by the additive noise but also contaminated by false and missed detections. In this paper, multi-target tracking is obtained by modeling the multi-target state as a labeled multi-Bernoulli random finite set and receiver selection is implemented during tracking. Receiver selection is solved under the partially observed Markov decision framework, and the variance of the cardinality estimate is used as the selection criterion. To increase the diversity of the selected sensors and overcome the low observability of the Doppler measurement, the receivers selected at previous time steps are taken into account by adding a window. Simulation studies demonstrate the tracking performance of the proposed method with different window lengths. The results show that the observability of the target state is a crucial factor in determining the performance of receiver selection. The proposed method with a suitable window length can effectively improve the tracking accuracy.

An integrated approach based on advanced CTG parameters and Doppler measurements for late growth restriction management

Background The clinical diagnosis of late Fetal Growth Restriction (FGR) involves the integration of Doppler ultrasound data and Fetal Heart Rate (FHR) monitoring through computer assisted computerized cardiotocography (cCTG). The aim of the study was to evaluate the diagnostic power of combined Doppler and cCTG parameters by contrasting late FGR –and healthy controls. Methods The study was conducted from January 2018 to May 2020. Only pregnant women who had the last Doppler measurement obtained within 1 week before delivery and cCTG performed within 24 h before delivery were included in the study. Two hundred forty-nine pregnant women fulfilling the inclusion criteria were enrolled in the study; 95 were confirmed as late FGR and 154 were included in the control group. Results Among the extracted cCTG parameters, Delta Index, Short Term Variability (STV), Long Term Variability (LTV), Acceleration and Deceleration Phase Rectified Slope (APRS, DPRS) values were lower in the late FGR participants compared to the control group. In the FGR cohort, Delta, STV, APRS, and DPRS were found different when stratifying by MCA_PI (MCA_PI <5th centile or > 5th centile). STV and DPRS were the only parameters to be found different when stratifying by (UA_PI >95th centile or UA_PI <95th centile). Additionally, we measured the predictive power of cCTG parameters toward the identification of associated Doppler measures using figures of merit extracted from ROC curves. The AUC of ROC curves were accurate for STV (0,70), Delta (0,68), APRS (0,65) and DPRS (0,71) when UA_PI values were > 95th centile while, the accuracy attributable to the prediction of MCA_PI was 0.76, 0.77, 0.73, and 0.76 for STV, Delta, APRS, and DPRS, respectively. An association of UA_PI>95th centile and MCA_PI<5th centile with higher risk for NICU admission, was observed, while CPR < 5th centile resulted not associated with any perinatal outcome. Values of STV, Delta, APRS, DPRS were significantly lower for FGR neonates admitted to NICU, compared with the uncomplicated FGR cohort. Conclusions The results of this study show the contribution of advanced cCTG parameters and fetal Doppler to the identification of late FGR and the association of those parameters with the risk for NICU admission. Trial registration Retrospectively registered.

Perioperative Doppler measurements of renal perfusion are associated with acute kidney injury in patients undergoing cardiac surgery

Acute kidney injury (AKI) is a frequent and severe complication in cardiac surgery. Normal renal function is dependent on adequate renal perfusion, which may be altered in the perioperative period. Renal perfusion can be assessed with Doppler measurement. We aimed to determine the association between Doppler measurements of renal perfusion and the development of AKI. This was a prospective, observational study of 100 patients with ≥ one risk factor for postoperative AKI undergoing open-heart surgery. Doppler ultrasound examinations were performed before surgery and on the first and fourth postoperative day. AKI was defined according to the KDIGO criteria and subdivided into mild (KDIGO stage 1) and severe AKI (KDIGO stage 2 + 3). Thirty-three patients developed AKI, 25 developed mild and eight developed severe AKI. Abnormal renal venous flow pattern on the first postoperative day was significantly associated with the development of severe AKI (OR 8.54 (95% CI 1.01; 72.2), P = 0.046), as were portal pulsatility fraction (OR 1.07 (95% CI 1.02; 1.13), P = 0.005). Point-of-care Doppler ultrasound measurements of renal perfusion are associated with the development of AKI after cardiac surgery. Renal and portal Doppler ultrasonography can be used to identify patients at high risk or very low risk of AKI after cardiac surgery.

Large Amplitude Harmonic Vibration under Pulse Doppler Measurement

A flow velocity or tissue motion can be measured by pulse Doppler method. However, when the method is applied to a sinusoid motion or harmonic vibration, the estimation result is deviated. In this paper, the generalized theory of pulse Doppler measurement to the sinusoid motion is explained and the relation between the estimation deviation and the real value is given. Furthermore, a special case of binary velocity estimation is expanded and simulated with different parameters. This simulation result suggested that different selection of parameters may fundamentally affect the output of pulse Doppler estimation.

Acute Hemodynamic Improvement by Thermal Vasodilation inside the Abdominal and Iliac Arterial Segments of Young Sedentary Individuals

<b><i>Objective:</i></b> To study the hemodynamic response to lower leg heating intervention (LLHI) inside the abdominal and iliac arterial segments (AIAS) of young sedentary individuals. <b><i>Methods:</i></b> A Doppler measurement of blood flow was conducted for 5 young sedentary adults with LLHI. Heating durations of 0, 20, and 40 min were considered. A lumped parameter model (LPM) was used to ascertain the hemodynamic mechanism. The hemodynamics were determined via numerical approaches. <b><i>Results:</i></b> Ultrasonography revealed that the blood flow waveform shifted upwards under LLHI; in particular, the mean flow increased significantly (<i>p</i> &#x3c; 0.05) with increasing heating duration. The LPM showed that its mechanism depends on the reduction in afterload resistance, not on the inertia of blood flow and arterial compliance. The time-averaged wall shear stress, time-averaged production rate of nitric oxide, and helicity in the external iliac arteries increased more significantly than in other segments as the heating duration increased, while the oscillation shear index (OSI) and relative residence time (RRT) in the AIAS declined with increasing heating duration. There was a more obvious helicity response in the bilateral external iliac arteries than the OSI and RRT responses. <b><i>Conclusion:</i></b> LLHI can effectively induce a positive hemodynamic environment in the AIAS of young sedentary individuals.