Intravascular ultrasound for valve frame expansion and orifice area measurement as well as paravalvular leak assessment during transcatheter aortic valve replacement

Introduction Valve frame expansion (measured outer valve frame area/nominal valve dimension), but not oversizing (nominal valve dimension/annulus area, %) determines pattern of restored blood flow after transcatheter aortic valve replacement (TAVR). There is no online measure of frame expansion, and error in current echocardiographic assessment of effective orifice area (EOA) and paravalvular leak (PVL) are common. Purpose To evaluate large imaging field intravascular ultrasound (IVUS) during TAVR for measuring valve geometry [frame expansion, minimal geometric orifice area (min GOA), and mechanism of PVL] with transthoracic echo and angio-CT serving for comparative measures, along with the nominal EOA as established by Hahn et al. Methods After successful TAVR either a 10MHz Vision PV 0.035" (60mm imaging field) or 20MHz Vision PV 0.018" (24mm imaging field plus Chr omaFlo) IVUS catheter (Philips) was slowly pulled from the left ventricle outflow (LVOT) to the aorta with continuous imaging of the aortic root. Results There were 16 pts (80.8±7.1 yrs, 8 female) treated for de novo aortic stenosis (n=15) or failed bioprosthesis (n=1), 7 of whom were treated with balloon-expandable TAVR. PV 0.35" catheters were used in 8 pts (including valve-in-valve) and allowed complete geometry assessment of 26.6±2.7mm nominal prosthesis Ø (Figure 1A) whereas PV 0.018" allowed complete geometry assessment in only 4 of 8 pts with nominal prosthesis Ø of 26.1±2.8mm (Figure 1B). Actual % valve inflow expansion (IVUS outer frame/valve nominal dimension) was significantly smaller than % valve oversizing (80%±19% vs 125±19%, p=0.005). Min GOA was substantially bigger than corresponding nominal EOA and EOA calculated using the post-procedural LVOT diameter (272±84mm2 vs 174±25mm2 vs 181±59mm2, p=0.001 correspondingly). However, min GOA was similar to EOA calculated using baseline LVOT area (272±84mm2 vs 230±90mm2; r=0.713, p=0.009). IVUS and angio-CT measurements of outer prosthesis frame area were similar for inflow, coaptation site, and outflow (460±143mm2 vs 454±134mm2 and 455±134mm2 vs 447±114mm2 and 722±174mm2 vs 725±180; p≤0.001 for all paired correlations). Inflow expansion (IVUS outer frame/baseline CT annulus area) tended to be smaller among valves with ≥mild vs no PVL (95±14% vs 107±11%, p=0.156), with clear ChromaFlo signal seen in the space between the aortic annulus wall and outer-valve frame surface (Figure 1C). Conclusions Large imaging field IVUS during TAVR allows for peri-procedural assessment of actual valve geometry that differs substantially from nominal. IVUS offers online tomographic perspective and highest accuracy in anatomy evaluation corresponding with valve function. FUNDunding Acknowledgement Type of funding sources: None. Figure 1

Unconditional convergence constants of g-frame expansions

In this paper, we prove that the unconditional constants of the g-frame expansion in a Hilbert space are bounded by [Formula: see text], where [Formula: see text], [Formula: see text] are the frame bounds of the g-frames. It follows that tight g-frames have unconditional constant one. Then we generalize this to a classification of such g-frames by showing that a g-Bessel sequence has unconditional constant one if it is an orthogonal sum of g-tight frames. We also obtain a new result under which a g-Bessel sequence is a g-frame from the view of unconditional constant. Finally, we prove similar results for cross g-frame expansions as long as the cross g-frame expansions stay uniformly bounded away from zero.

Optimal Gabor-Frame-Expansion-Based Intermittent-Clutter-Filtering Method for Radar Wind Profiler

Intermittent clutter signals are frequently observed by radar wind profilers during the seasonal bird migration. A novel statistical filtering algorithm based on a simultaneous time–frequency analysis of the profiler’s raw data was recently proposed to address shortcomings of existing methods. The foundation of this method is a Gabor frame expansion of the complex time series of the demodulated receiver voltage. In this paper, two objective criteria are suggested to obtain an optimal setup for the discrete Gabor frame expansion from the multitude of possibilities: first, the choice of almost-tight frames for a predefined maximum redundancy and second, the requirement that the analyzing bandwidth of the used Gaussian window function should provide a simultaneously sparse representation of both atmospheric signal components and intermittent clutter. The question of optimal sampling settings, especially dwell time, for a maximum reduction of bird interference is also discussed. Using data obtained during intense bird migration events it is shown that a combination of filtering and quality control of the result is required to prevent the occurrence of significant systematic and correlated errors in the final wind measurement.