Aortic Stenosis: Haemodynamic Benchmark and Metric Reliability Study

Aortic stenosis is a condition which is fatal if left untreated. Novel quantitative imaging techniques which better characterise transvalvular pressure drops are being developed but require refinement and validation. A customisable and cost-effective workbench valve phantom circuit capable of replicating valve mechanics and pathology was created. The reproducibility and relationship of differing haemodynamic metrics were assessed from ground truth pressure data alongside imaging compatibility. The phantom met the requirements to capture ground truth pressure data alongside ultrasound and magnetic resonance image compatibility. The reproducibility was successfully tested. The robustness of three different pressure drop metrics was assessed: whilst the peak and net pressure drops provide a robust assessment of the stenotic burden in our phantom, the peak-to-peak pressure drop is a metric that is confounded by non-valvular factors such as wave reflection. The peak-to-peak pressure drop is a metric that should be reconsidered in clinical practice. The left panel shows manufacture of low cost, functional valves. The central section demonstrates circuit layout, representative MRI and US images alongside gross valve morphologies. The right panel shows the different pressure drop metrics that were assessed for reproducibility.

P588Flow profile for a better non-invasive pressure drop in CoA

Introduction

In cardiovascular obstructions, as Coarctation of the Aorta (CoA), guidelines recommend treatment based on a relevant pressure drop (ΔP). Diagnostic ΔP is estimated by simplified Bernoulli (SB) and is measured as peak-to-peak (PtP) ΔP via catheterization. The divergences amid methods are understood, but it is common practice to widely and positively accept both as valid diagnostic. Recently, simplified advective work-energy relative pressure (SAW) to correct SB by considering the full velocity profile for the ΔP computation.

Purpose

To verify the correctness of peak flow derived pressure drop via maximal velocity (SB), and full flow profile (SAW) versus clinical gold-standard PtP ΔP in a CoA phantom.

Methods

An MRI-compatible and pulsatile CoA phantom was built and tested in eight configurations, with four levels of obstruction (9, 11 and 13 mm CoA diameter and no CoA) under two flow regimes (stress and normal). The ΔP was measured via catheterization between ascending and in descending aorta (DA) as instantaneous and as PtP. Also, MRI 4D-flow velocity vector fields were acquired, enabling the ΔP estimation by SB and SAW at effective orifice area (EOA) and DA catheterization locations. at the point of the effective orifice area (EOA) and at DA catheterization location.

Results

The disparity in ΔP illustrate the fundamental differences between methods (figure and table). Catheterised instant and PtP ΔPs are similar for the CoA phantom configurations, where SB and SAW are valid. The lesser the obstruction, the greater is the temporal acceleration contribution to the ΔP and discrepancies between methods arise. As recognised, SB is an overestimation of the catheterization measurements. The most equivalent ΔPs are the catheterization PtP and SAW. Velocity-based ΔPs (SB and SAW) show a drop in performance when the velocity is captured at the DA instead of the right EOA point, illustrating the sensitivity to the acquisition location.

Peak ΔPs per method and per phantom 9mm CoA 11mm CoA 13mm CoA Normal R2 Linear eq. rest stress rest stress rest stress rest stress Instant ΔP 33.4 45.7 11.5 19.6 12.1 14.5 −2.7 −12.2 0.949 y=1.12x PtP ΔP 29.3 43.5 10.0 16.0 5.8 11.2 −1.8 -3.6 – – SB EOA 37.5 52.3 13.4 22.3 6.1 11.4 1.4 1.4 0.988 y=1.23x SB DA 22.6 59.8 10.7 18.6 5.2 8.5 0.9 1.2 0.893 y=1.15x SAW EOA 29.9 51.4 11.3 19.0 4.9 9.7 0.8 0.8 0.972 y=1.11x SAW DA 11.74 28.3 5.5 9.9 2.7 4.5 0.6 0.7 0.911 y=0.56x Linear comparisons were made against gold-standard catheterised PtP ΔP.

Velocity meshes and ΔPs in cardiac cycle

Conclusions

Initial phantom evidence suggests that the non-invasive ΔP assessments based on flow should consider the full flow profile and be acquired at the point of EOA.

Acknowledgement/Funding

PIC project, European Union's Horizon 2020 Marie Skłodowska-Curie ITN Project under grant agreement No 764738

3D Quantification of Wall Shear Stress and Oscillatory Shear Index Using a Finite-Element Method in 3D CINE PC-MRI Data of the Thoracic Aorta

Several 2D methods have been proposed to estimate WSS and OSI from PC-MRI, neglecting the longitudinal velocity gradients that typically arise in cardiovascular flow, particularly on vessel geometries whose cross section and centerline orientation strongly vary in the axial direction. Thus, the contribution of longitudinal velocity gradients remains understudied. In this work, we propose a 3D finite-element method for the quantification of WSS and OSI from 3D-CINE PC-MRI that accounts for both in-plane and longitudinal velocity gradients. We demonstrate the convergence and robustness of the method on cylindrical geometries using a synthetic phantom based on the Poiseuille flow equation. We also show that, in the presence of noise, the method is both stable and accurate. Using computational fluid dynamics simulations, we show that the proposed 3D method results in more accurate WSS estimates than those obtained from a 2D analysis not considering out-of-plane velocity gradients. Further, we conclude that for irregular geometries the accurate prediction of WSS requires the consideration of longitudinal gradients in the velocity field. Additionally, we compute 3D maps of WSS and OSI for 3D-CINE PC-MRI data sets from an aortic phantom and sixteen healthy volunteers and two patients. The OSI values show a greater dispersion than WSS, which is strongly dependent on the PC-MRI resolution. We envision that the proposed 3D method will improve the estimation of WSS and OSI from 3D-CINE PC-MRI images, allowing for more accurate estimates in vessels with pathologies that induce high longitudinal velocity gradients, such as coarctations and aneurisms.

Accelerating dual cardiac phase images using undersampled radial phase encoding trajectories

A three-dimensional dual-cardiac-phase (3D-DCP) scan has been proposed to acquire two data sets of the whole heart and great vessels during the end-diastolic and end-systolic cardiac phases in a single free-breathing scan. This method has shown accurate assessment of cardiac anatomy and function but is limited by long acquisition times. This work proposes to accelerate the acquisition and reconstruction of 3D-DCP scans by exploiting redundant information of the outer k-space regions of both cardiac phases. This is achieved using a modified radial-phase-encoding trajectory and gridding reconstruction with uniform coil combination. The end-diastolic acquisition trajectory was angularly shifted with respect to the end-systolic phase. Initially, a fully-sampled 3D-DCP scan was acquired to determine the optimal percentage of the outer k-space data that can be combined between cardiac phases. Thereafter, prospectively undersampled data were reconstructed based on this percentage. As gold standard images, the undersampled data were also reconstructed using iterative SENSE. To validate the method, image quality assessments and a cardiac volume analysis were performed. The proposed method was tested in thirteen healthy volunteers (mean age, 30years). Prospectively undersampled data (R=4) reconstructed with 50% combination led high quality images. There were no significant differences in the image quality and in the cardiac volume analysis between our method and iterative SENSE. In addition, the proposed approach reduced the reconstruction time from 40min to 1min. In conclusion, the proposed method obtains 3D-DCP scans with an image quality comparable to those reconstructed with iterative SENSE, and within a clinically acceptable reconstruction time.

Cure of experimental Chagas' disease by the bis-triazole DO870 incorporated into 'stealth' polyethyleneglycol-polylactide nanospheres

We have incorporated several inhibitors of sterol biosynthesis into long-circulating polyethyleneglycol-polylactide (PEG-PLA) nanospheres in order to improve the bioavailability of these poorly soluble compounds. Mice infected with CL and Y strains of Trypanosoma cruzi and treated for 30 consecutive days with DO870-loaded nanospheres at doses of 3 mg/kg/day, by the intravenous route, showed a significant cure rate (60-90%) for both strains. The activity was dose dependent and significant activity was observed for doses > or = 0.75 mg/kg/day. No cure was observed in mice treated with unloaded nanoparticles. Ketoconazole and itraconazole failed to induce cure against the Y strain even in the entrapped form.

[Tuberculin reactivity in the elderly. Comparison of PPD-RT23 and PPD-CT68]

BACKGROUND

Tuberculin reactivity varies on the basis of the PPD lot and the population studied.

AIMS

To compare tuberculin reactivity in the elderly following successive applications of PPD from 2 different lots.

POPULATION

Elderly nursing-home residents, from the province of Guadalajara, Spain.

METHODS

The elderly were randomly selected and administered with a first Mantoux intradermoreaction of 2 UT of PPD-RT23 or 2 UT of PPD-CT68. The study was performed in a scaled basis, eliminating the reactors (transversal induration > or = 5 mm at 72 h). The non reactors were restudied with a second and third test in alternative arms at a 7-day interval with the same lot and initial dosis of PPD. At one year the scaled study was repeated with 2 UT of PPD-CT68.

RESULTS

Eight hundred and thirty elderly persons (79 +/- 9 years) were studied, with 410 receiving PPD-RT23 and 420 receiving PPD-CT68. No differences were observed in the percentage of initial reactors (31% vs 29%; p = 0.26) or in the booster reactors (23% vs 20%; p = 0.16). The PPD-RT23 was found to trigger more intensive reactions than the PPD-CT68 leading to a greater frequency of indurations > 14 mm. After one year, the percentage of stable reactions was similar in both groups (50.5% vs 49.5%; NS).

CONCLUSIONS

1) In elderly nursing-home residents 2 UT of PPD-RT23 and 2 UT of PPD-CT68 showed similar results in regard to the number of reactors and the frequency of booster reactions. 2) The proportion of intense reactions was greater with 2 UT of PPD-RT23 than with 2 UT of PPD-CT68. 3) The stability of the reactions at one year was independent of the lot used in the first phase.

The tubulin genes of Trypanosoma cruzi

The organization of the alpha- and beta-tubulin genes in the genome of Trypanosoma cruzi have been analysed by Southern blotting using tubulin probes derived from Trypanosoma brucei. The tubulin array appears to be more complex in this organism than in other members of the same family. Some tubulin genes are tightly clustered in an alternating (alpha-beta)n array with a basic repeat unit length of 4.3 kb. However, other pairs of alternating alpha- and beta-tubulin sequences appear to be physically separated from the basic group. This finding indicates that the tubulin gene cluster present in T. cruzi is less perfectly conserved than in T. brucei. T. (Herpetosoma) rangeli is similar to T. (Schizotrypanum) cruzi in its tubulin gene organization whereas most of these genes are tandemly clustered in the genome of T. (Trypanozoon) evansi, with a basic repeat unit length of 3.6 kb as previously described for T. (Trypanozoon) brucei. Two overlapping recombinant clones containing T. cruzi tubulin sequences have been isolated from a genomic cosmid library of T. cruzi epimastigotes using the T. brucei tubulin probes. Partial sequencing of the T. cruzi beta-tubulin gene has confirmed its identity and shows more than 70% homology with the sea urchin, chicken and T. b. rhodesiense beta-tubulin reported gene sequences. Analysis of tubulin gene organization through the parasite life cycle does not show evidence of major rearrangements within the repeat unit. Several T. cruzi strains and cloned lines whilst sharing the 4.3-kb tubulin repeat unit, exhibited very variable tubulin gene organization with tubulin probes. These striking differences in the organization of this structural gene among T. cruzi strains and cloned lines suggest that the heterogeneity previously reported in parasite populations may be related to a very dynamic, diploid genome.

The water and ionic permeability induced by polyene antibiotics across plasma membrane vesicles from Leishmania sp

An osmotic method has been used to study the effect of the polyene antibiotics amphotericin B, nystatin and candicidin on the water permeability of plasma membranes prepared from Leishmania sp. The effect of amphotericin B on the permeability of Leishmania membranes to a salt such as potassium nitrate was also investigated. A non-linear and saturable enhancement of water and salt permeability was measured with increasing polyene concentrations, which could be adjusted to Hill cooperativity equation. The antibiotic concentrations that induce at 30 degrees C half-maximal effects on the water permeability of Leishmania vesicles were 0.021 microM for candicidin, 0.21 microM for amphotericin B and 1.4 microM for nystatin. At 30 degrees C, the concentration of amphotericin B required to induce half of the maximal effect on the permeability of Leishmania vesicles to potassium nitrate was 1.8 microM. The temperature dependence for amphotericin B, nystatin and candicidin enhancement of the water permeability of Leishmania vesicles was determined by using Q10 data at 20 and 30 degrees C. The estimated activation energies at increasing polyene concentrations display the same general pattern for all three polyene antibiotics investigated, that is, a maximal positive value at about the polyene concentrations required for half-maximal effect. The significance of these results for understanding the mechanisms of action of polyene antibiotics on natural membranes is discussed.

The effect of sulphamethoxypyridazine on liver and plasma levels of vitamin A in rats

1 Long-acting sulphonamides are highly bound to plasma proteins; the present study deals with the effects of this binding property upon a vitamin A compound also transported by plasma proteins. 2 Sulphamethoxypyridazine was administered in rats either orally or by intraperitoneal injection. 3 A significant fall in plasma vitamin A level and an increase in hepatic vitamin A concentration were observed. 4 These results suggest an interference by sulphamethoxypyridazine with the transport of vitamin A, either through competition between the drug and vitamin A for binding sites of plasma proteins, or through altered secretion of the vitamin from the liver.

Proton-enhanced 13C nuclear magnetic resonance of lipids and biomembranes

A recently developed nuclear double resonance technique which permits sensitive detection, together with high resolution, of rare spins in solids or other dipolar-coupled nuclear systems [Pines, Gibby, and Waugh (1973) J. Chem. Phys. 59, 569] has been applied to the study of natural abundance (13)C-nuclear magnetic resonance in lipid mesophases and of selectively labeled carbon sites in bacterial membranes.Detailed microscopic information on the molecular organization and phase transitions of the lipid phases and their interaction with ions and other molecules can be obtained from the study of the chemical shift anisotropies and dynamical aspects of the (13)C NMR spectra of unsonicated lipid dispersions (liposomes). Experiments are reported which demonstrated the feasibility of quantitatively observing the (13)C-nuclear magnetic resonance of specifically labeled sites in unperturbed Escherichia coli membrane vesicles for the study of the physical state of the lipids with the aim of relating it to the known lipid-dependent functional properties of the membranes.