Monitoring of in-vitro ultrasonic stimulation of cells by numerical modeling.

Ultrasound stimulation of living tissues is a promising technique that can be safely applied for regenerative treatments. However, the ultrasound-induced mechanotransduction is still not well understood because of the large number of parameters involved at different scales and their difficult experimental accessibility. In this context, in-vitro studies may help to gain insight into the interaction between ultrasound and cells. Nevertheless, to conduct a reliable analysis of ultrasound effects on cell culture, the monitoring of the acoustic intensity delivered to the cells is of prime interest. Thanks to the development of an innovative custom experimental set-up inspired from ultrasound stimulation of bone regeneration conditions, major disturbing phenomena such as multiple reflections and standing wave formation inside the Petri dish are eliminated. Thus, the level of ultrasound stimulation, especially, in terms of spatial average temporal average intensity (ISATA), delivered to the cells can be monitored. Then, to properly estimate the level of ultrasound stimulation, a finite element model representing the experimental in-vitro configuration is developed. The numerical model manages on capturing the characteristics of the experimentally measured acoustic intensity distribution as illustrated by the experimental and numerical ISATA values of 42.3 and 45.8 mW/cm2 respectively, i.e. a relative difference of 8%. The numerical model would therefore allow exploring data inaccessible to experimental measurement and parametric studies to be carried out and facilitates the investigation of different virtual experimental configurations.

Morphological Analysis of Healthy Aortic Arch.

OBJECTIVE/BACKGROUND: This study aimed to describe an arch morphology protocol in a healthy population, and to assess the impact of age and sex. METHODS: A retrospective morphology evaluation was conducted in a population with no personal history of thoracic aorta surgery or pathology, through computed tomography (CT) imaging analysis, using a standardised protocol. Based on centreline three dimensional coordinates, a single investigator calculated a series of parameters in the arch zones and in the total arch, using Matlab scripts. These were categorized as: (i) morphometric data: diameter, length and aortic angle of each zone, total arch angle, and length; (ii) geometric data: tortuosity index (TI), arch width, assimilated curvature radius (CRi), and attachment zone angles. Student or Mann-Whitney tests were used to compare parameter means. Their variability with age and sex was assessed through univariate and multivariate regression analysis. RESULTS: CT images from 123 subjects (mean ± SD age 53 ± 19 years) were reviewed. Significant correlation between age and morphology was found. The aorta expanded homogeneously and stretched heterogeneously with age because of posterior arch elongation. TI decrease, CRi, and attachment zone angle increase were also observed with aging. Age remained significantly associated with these morphological parameters, independently of body surface area and hypertension. Sex also affected morphology: longer total arch length and higher CRarch in men; lower zone 3 attachment angle in women CONCLUSION: Using mathematical algorithms, and with a view to improving endovascular arch treatment, this study provides a standardised arch morphology protocol and objectively identifies both age related evolution and sex related variation in the different zones.

Risk Factor Analysis for the Mal-Positioning of Thoracic Aortic Stent Grafts.

OBJECTIVE: The present study aimed at quantifying mal-positioning during thoracic endovascular aortic repair and analysing the extent to which anatomical factors influence the exact stent graft positioning. METHODS: A retrospective review was conducted of patients treated between 2007 and 2014 with a stent graft for whom proximal landing zones (LZ) could be precisely located by anatomical fixed landmarks, that is LZ 1, 2, or 3. The study included 66 patients (54 men; mean age 51 years, range 17-83 years) treated for traumatic aortic rupture (n = 27), type B aortic dissection (n = 21), thoracic aortic aneurysm (n = 8), penetrating aortic ulcer (n = 5), intramural hematoma (n = 1), and floating aortic thrombus (n = 4). Pharmacologic hemodynamic control was systematically obtained during stent graft deployment. Pre- and post-operative computed tomographic angiography was reviewed to quantify the distance between planned and achieved LZ and to analyze different anatomical factors: iliac diameter, calcification degree, aortic angulation at the proximal deployment zone, and tortuosity index (TI). RESULTS: Primary endoleak was noted in seven cases (10%): five type I (7%) and two type II (3%). Over a mean 35 month follow up (range 3-95 months), secondary endoleak was detected in two patients (3%), both type I, and stent graft migration was seen in three patients. Mal-positioning varied from 2 to 15 mm. A cutoff value of 11 mm was identified as an adverse event risk. Univariate analysis showed that TI and LZ were significantly associated with mal-positioning (p = .01, p = .04 respectively), and that aortic angulation tends to reach significance (p = .08). No influence of deployment mechanism (p = .50) or stent graft generation (p = .71) or access-related factors was observed. Multivariate analysis identified TI as the unique independent risk factor of mal-positioning (OR 241, 95% CI 1-6,149, p = .05). A TI >1.68 was optimal for inaccurate deployment prediction. CONCLUSION: TI calculation can be useful to anticipate difficulties during stent graft deployment and to reduce mal-positioning.

Risk Factor Analysis of Bird Beak Occurrence after Thoracic Endovascular Aortic Repair.

OBJECTIVES: The aim was to analyze the role played by anatomy and stent graft in the incidence of incomplete apposition to aortic arch. METHODS: Between 2007 and 2014 data including available and suitable computed tomographic angiography (CTA) imaging of patients who had undergone thoracic endovascular aortic repair were reviewed. The study included 80 patients (65 men, 54 ± 21 years) treated for traumatic aortic rupture (n = 27), thoracic aortic aneurysm (n = 15), type B aortic dissection (n = 24), penetrating aortic ulcer (n = 5), intramural hematoma (n = 2), aorto-oesophageal fistula (n = 2), and aortic mural thrombus (n = 5). Pre- and post-operative CTA images were analyzed to characterize bird beak in terms of length and angle, and to calculate aortic angulation within a 30 mm range at the proximal deployment zone. RESULTS: Bird beak configuration was detected in 46 patients (57%): mean stent protrusion length was 16 mm (range: 8-29 mm) and mean bird beak angle was 20° (range: 7-40°). The bird beak effect was significantly more frequent after traumatic aortic rupture treatment (p = .05) and in landing zone 2 (p = .01). No influence of either stent graft type or generation, or degree of oversizing was observed (p = .29, p = .28, p = .81 respectively). However, the mean aortic angle of patients with bird beak was higher in the Pro-form group than that in the Zenith TX2 group (62° vs. 48°, p = .13). Multivariate analysis identified the aortic angle of the deployment zone as the unique independent risk factor of malapposition (HR = 1.05, 95% CI 1-1.10, p = .005). The cutoff value of 51° was found to be predictive of bird beak occurrence with a sensitivity of 58% and a specificity of 85%. CONCLUSIONS: Assessment of proximal landing zone morphology to avoid deployment zones generating an aortic angle of over 50° can be recommended to improve aortic curvature apposition with the current available devices.

Computed tomography, histological and ultrasonic measurements of adolescent scoliotic rib hump geometrical and material properties.

In Adolescent Idiopathic Scoliosis (AIS), numerical models can enhance orthopaedic or surgical treatments and provide reliable insights into the mechanism of progression. Computational methods require knowledge of relevant parameters, such as the specific geometrical or material properties of the AIS rib, about which there is currently a lack of information. The aim of our study was to determine the geometrical and material properties (Young's modulus [E] and Poisson's ratio [ν]) for AIS rib bones. Twelve ribs extracted during gibbectomy on 15 and 17 year old girls were tested using computed tomography (CT) scanner, histology and ultrasonic scanner. The mean porosity (± standard deviation (SD)) is 1.35 (±0.52)% and the mean (±SD) bone mineral density is 2188 (±19)mmHA/cc. The cortical part of the AIS rib hump is found to be thicker than physiological values in the literature. To mimic the rib hump for an AIS girl, our results suggest that ribs should be modeled as hollow circular cylinders with a 10.40 (±1.02)mm external radius and 7.56mm (±0.75) internal radius, and material properties with a mean E of 14.9GPa (±2.6) and a mean ν of 0.26 (±0.08).