Detecting human coronary inflammation by imaging perivascular fat

Early detection of vascular inflammation is a long-standing goal that would allow deployment of targeted strategies for the prevention or treatment of multiple disease states. Since vascular inflammation is not detectable with commonly used imaging modalities, we hypothesized that phenotypic changes in perivascular adipose tissue (PVAT) induced by vascular inflammation could be quantified using a new computerized tomography angiography (CTA) methodology. We show that inflamed human vessels release cytokines that prevent lipid accumulation in PVAT-derived preadipocytes in vitro, ex vivo and in vivo. We developed a 3D PVAT analysis method and studied CT images of human adipose tissue explants from 453 patients undergoing cardiac surgery, relating the ex vivo images with in vivo CT scan information on the biology of the explants. We have developed a new imaging biomarker, CT Fat attenuation index (FAI), that describes adipocyte lipid content and size. FAI has excellent sensitivity and specificity for detecting tissue inflammation as assessed by tissue uptake of 18FFDG in positron emission tomography (PET). In a validation cohort of 273 subjects, the FAI gradient around the human coronary arteries identified early subclinical coronary artery disease in vivo, and detected dynamic changes of PVAT in response to variations of vascular inflammation, and inflamed, vulnerable atherosclerotic plaques during acute coronary syndromes. Our study revealed that human vessels exert paracrine effects on the surrounding PVAT, affecting local intracellular lipid accumulation in preadipocytes, which can then be monitored using a CT imaging approach. This methodology can be implemented in clinical practice to allow the non-invasive detection of unstable plaques in the human coronary vasculature

Detecting human coronary inflammation by imaging perivascular fat

Early detection of vascular inflammation is a long-standing goal that would allow deployment of targeted strategies for the prevention or treatment of multiple disease states. Since vascular inflammation is not detectable with commonly used imaging modalities, we hypothesized that phenotypic changes in perivascular adipose tissue (PVAT) induced by vascular inflammation could be quantified using a new computerized tomography angiography (CTA) methodology. We show that inflamed human vessels release cytokines that prevent lipid accumulation in PVAT-derived preadipocytes in vitro, ex vivo and in vivo. We developed a 3D PVAT analysis method and studied CT images of human adipose tissue explants from 453 patients undergoing cardiac surgery, relating the ex vivo images with in vivo CT scan information on the biology of the explants. We have developed a new imaging biomarker, CT Fat attenuation index (FAI), that describes adipocyte lipid content and size. FAI has excellent sensitivity and specificity for detecting tissue inflammation as assessed by tissue uptake of 18FFDG in positron emission tomography (PET). In a validation cohort of 273 subjects, the FAI gradient around the human coronary arteries identified early subclinical coronary artery disease in vivo, and detected dynamic changes of PVAT in response to variations of vascular inflammation, and inflamed, vulnerable atherosclerotic plaques during acute coronary syndromes. Our study revealed that human vessels exert paracrine effects on the surrounding PVAT, affecting local intracellular lipid accumulation in preadipocytes, which can then be monitored using a CT imaging approach. This methodology can be implemented in clinical practice to allow the non-invasive detection of unstable plaques in the human coronary vasculature

Response of mean turbulent energy dissipation rate and spectra to concentrated wall suction

The response of mean turbulent energy dissipation rate and spectra to concentrated suction applied through a porous wall strip has been quantified. Both suction and no suction data of the spectra collapsed reasonably well for Kolmogorov normalised wavenumber k₁* > 0.2. Similar results were also observed for second-order structure functions (not shown) for Kolmogorov normalised radius r* < 10. Although, the quality of collapsed is poorer for transverse component, the result highlights that Kolmogorov similarity hypothesis is reasonably well satisfied. However, the suction results shows a significant departure from the no suction case of the Kolmogorov normalised spectra and second-order structure functions for k₁* < 0.2 and r* > 20, respectively. The departure at the larger scales with collapse at the small scales suggests that suction induce a change in the small-scale motion. This is also reflected in the alteration of mean turbulent energy dissipation rate and Taylor microscale Reynolds number. This change is a result of the weakening of the large-scale structures. The effect is increased as the suction rate is increased

Velocity derivative skewness in isotropic turbulence and its measurement with hot wires

We investigate the effect of the hot wire resolution on the measurement of the velocity derivative skewness in homogeneous isotropic turbulence. Single- and cross-wire configurations (with different lengths and separations of the wires, and temporal sampling resolution) are considered. Predictions of the attenuation on the basis of a model for the energy spectrum are compared to experimental and numerical data in grid and box turbulence, respectively. It is shown that the model-based correction is accurate for the single wire but not for the cross-wire. In the latter case, the effect of the separation between the wires is opposite to that found in the experiments and simulations. Moreover, the attenuation predicted by the numerical data is in good agreement with that observed in the experiment. For both probe configurations, the sampling resolution has a sizeable attenuation effect, but, for the X-probe, the impact of the separation between the wires is more important. In both cases, the length of the wires has only a minor effect, in the non-dimensional range of wire length investigated. Finally, the present experimental data support the conclusion that the skewness is constant with the Reynolds number, in agreement with Kolmogorov's 41 theory