A patient-specific study of type-B aortic dissection: evaluation of true-false lumen blood exchange

BACKGROUND Aortic dissection is a severe pathological condition in which blood penetrates between layers of the aortic wall and creates a duplicate channel - the false lumen. This considerable change on the aortic morphology alters hemodynamic features dramatically and, in the case of rupture, induces markedly high rates of morbidity and mortality. METHODS In this study, we establish a patient-specific computational model and simulate the pulsatile blood flow within the dissected aorta. The k-ω SST turbulence model is employed to represent the flow and finite volume method is applied for numerical solutions. Our emphasis is on flow exchange between true and false lumen during the cardiac cycle and on quantifying the flow across specific passages. Loading distributions including pressure and wall shear stress have also been investigated and results of direct simulations are compared with solutions employing appropriate turbulence models. RESULTS Our results indicate that (i) high velocities occur at the periphery of the entries; (ii) for the case studied, approximately 40% of the blood flow passes the false lumen during a heartbeat cycle; (iii) higher pressures are found at the outer wall of the dissection, which may induce further dilation of the pseudo-lumen; (iv) highest wall shear stresses occur around the entries, perhaps indicating the vulnerability of this region to further splitting; and (v) laminar simulations with adequately fine mesh resolutions, especially refined near the walls, can capture similar flow patterns to the (coarser mesh) turbulent results, although the absolute magnitudes computed are in general smaller. CONCLUSIONS The patient-specific model of aortic dissection provides detailed flow information of blood transport within the true and false lumen and quantifies the loading distributions over the aorta and dissection walls. This contributes to evaluating potential thrombotic behavior in the false lumen and is pivotal in guiding endovascular intervention. Moreover, as a computational study, mesh requirements to successfully evaluate the hemodynamic parameters have been proposed.

True four-dimensional analysis of thoracic aortic displacement and distension using model-based segmentation of computed tomography angiography.

Previous analyses of aortic displacement and distension using computed tomography angiography (CTA) were performed on double-oblique multi-planar reformations and did not consider through-plane motion. The aim of this study was to overcome this limitation by using a novel computational approach for the assessment of thoracic aortic displacement and distension in their true four-dimensional extent. Vessel segmentation with landmark tracking was executed on CTA of 24 patients without evidence of aortic disease. Distension magnitudes and maximum displacement vectors (MDV) including their direction were analyzed at 5 aortic locations: left coronary artery (COR), mid-ascending aorta (ASC), brachiocephalic trunk (BCT), left subclavian artery (LSA), descending aorta (DES). Distension was highest for COR (2.3 ± 1.2 mm) and BCT (1.7 ± 1.1 mm) compared with ASC, LSA, and DES (p < 0.005). MDV decreased from COR to LSA (p < 0.005) and was highest for COR (6.2 ± 2.0 mm) and ASC (3.8 ± 1.9 mm). Displacement was directed towards left and anterior at COR and ASC. Craniocaudal displacement at COR and ASC was 1.3 ± 0.8 and 0.3 ± 0.3 mm. At BCT, LSA, and DES no predominant displacement direction was observable. Vessel displacement and wall distension are highest in the ascending aorta, and ascending aortic displacement is primarily directed towards left and anterior. Craniocaudal displacement remains low even close to the left cardiac ventricle.

Dear Brand, Please Help me to Become a True-Man Out of the Truman: The Role of Brand Authenticity

Although brand authenticity is gaining increasing interest in academia and managerial practice, empirical studies on its contribution to the branding literature are still limited. The authors therefore conceptually and empirically examine the emergence and outcomes of perceived brand authenticity (PBA). A prior multi-phase scale development process resulted in a 17-item PBA scale to measure its four dimensions of credibility, integrity, symbolism, and longevity. Brand authenticity perceptions are influenced by indexical, existential, and iconic cues, whereby the latter’s influence is moderated by consumers’ level of marketing skepticism. Further, PBA increases emotional brand attachment. This relationship is particularly strong for consumers with a high level of self-authenticity. In addition, PBA effects are stronger in a North American market context compared to a European context.

Schriftliche Prüfungen: Vorteile von Multiple True-False Fragen gegenüber Typ-A Fragen

Fragestellung/Einleitung: Prüfungen sind essentieller Bestandteil in der ärztlichen Ausbildung. Sie liefern wertvolle Informationen über den Entwicklungsprozess der Studierenden und wirken lernbegleitend und lernmodulierend [1], [2]. Bei schriftlichen Prüfungen dominieren derzeit Multiple Choice Fragen, die in verschiedenen Typen verwendet werden. Zumeist werden Typ-A Fragen genutzt, bei denen genau eine Antwort richtig ist. Multiple True-False (MTF) Fragen hingegen lassen mehrere richtige Antworten zu: es muss für jede Antwortmöglichkeit entschieden werden, ob diese richtig oder falsch ist. Durch die Mehrfachantwort scheinen MTF Fragen bestimmte klinische Sachverhalte besser widerspiegeln zu können. Auch bezüglich Reliabilität und dem Informationsgewinn pro Testzeit scheinen MTF Fragen den Typ-A Fragen überlegen zu sein [3]. Dennoch werden MTF Fragen bislang selten genutzt und es gibt wenig Literatur zu diesem Fragenformat. In dieser Studie soll untersucht werden, inwiefern die Verwendung von MTF Fragen die Nutzbarkeit (Utility) nach van der Vleuten (Reliabilität, Validität, Kostenaufwand, Effekt auf den Lernprozess und Akzeptanz der Teilnehmer) [4] schriftlicher Prüfungen erhöhen kann. Um die Testreliabilität zu steigern, sowie den Kostenaufwand für Prüfungen zu senken, möchten wir das optimale Bewertungssystem (Scoring) für MTF Fragen ermitteln. Methoden: Wir analysieren die Daten summativer Prüfungen der Medizinischen Fakultät der Universität Bern. Unsere Daten beinhalten Prüfungen vom ersten bis zum sechsten Studienjahr, sowie eine Facharztprüfung. Alle Prüfungen umfassen sowohl MTF als auch Typ-A Fragen. Für diese Prüfungen vergleichen wir die Viertel-, Halb- und Ganzpunktbewertung für MTF Fragen. Bei der Viertelpunktbewertung bekommen Kandidaten für jede richtige Teilantwort ¼ Punkt. Bei der Halbpunktbewertung wird ½ Punkt vergeben, wenn mehr als die Hälfte der Antwortmöglichkeiten richtig ist, einen ganzen Punkt erhalten die Kandidaten wenn alle Antworten richtig beantwortet wurden. Bei der Ganzpunktbewertung erhalten Kandidaten lediglich einen Punkt wenn die komplette Frage richtig beantwortet wurde. Diese unterschiedlichen Bewertungsschemata werden hinsichtlich Fragencharakteristika wie Trennschärfe und Schwierigkeit sowie hinsichtlich Testcharakteristika wie der Reliabilität einander gegenübergestellt. Die Ergebnisse werden ausserdem mit denen für Typ A Fragen verglichen. Ergebnisse: Vorläufige Ergebnisse deuten darauf hin, dass eine Halbpunktbewertung optimal zu sein scheint. Eine Halbpunktbewertung führt zu mittleren Item-Schwierigkeiten und daraus resultierend zu hohen Trennschärfen. Dies trägt zu einer hohen Testreliabilität bei. Diskussion/Schlussfolgerung: MTF Fragen scheinen in Verbindung mit einem optimalen Bewertungssystem, zu höheren Testreliabilitäten im Vergleich zu Typ A Fragen zu führen. In Abhängigkeit des zu prüfenden Inhalts könnten MTF Fragen einen wertvolle Ergänzung zu Typ-A Fragen darstellen. Durch die geeignete Kombination von MTF und Typ A Fragen könnte die Nutzbarkeit (Utility) schriftlicher Prüfungen verbessert werden.

Do multiple true-false items beat the commonly used one-best-answers questions regarding to the Ottawa Criteria for Good Assessment? Results of a literature review

Background: Multiple True-False-Items (MTF-Items) might offer some advantages compared to one-best-answer-questions (TypeA) as they allow more than one correct answer and may better represent clinical decisions. However, in medical education assessment MTF-Items are seldom used. Summary of Work: With this literature review existing findings on MTF-items and on TypeA were compared along the Ottawa Criteria for Good Assessment, i.e. (1) reproducibility, (2) feasibility, (3) validity, (4) acceptance, (5) educational effect, (6) catalytic effects, and (7) equivalence. We conducted a literature research on ERIC and Google Scholar including papers from the years 1935 to 2014. We used the search terms “multiple true-false”, “true-false”, “true/false”, and “Kprim” combined with “exam”, “test”, and “assessment”. Summary of Results: We included 29 out of 33 studies. Four of them were carried out in the medical field Compared to TypeA, MTF-Items are associated with (1) higher reproducibility (2) lower feasibility (3) similar validity (4) higher acceptance (5) higher educational effect (6) no studies on catalytic effects or (7) equivalence. Discussion and Conclusions: While studies show overall good characteristics of MTF items according to the Ottawa criteria, this type of question seems to be rather seldom used. One reason might be the reported lower feasibility. Overall the literature base is still weak. Furthermore, only 14 % of literature is from the medical domain. Further studies to better understand the characteristics of MTF-Items in the medical domain are warranted. Take-home messages: Overall the literature base is weak and therefore further studies are needed. Existing studies show that: MTF-Items show higher reliability, acceptance and educational effect; MTF-Items are more difficult to produce

Radiomic Texture Analysis Mapping Predicts Areas of True Functional MRI Activity.

Individual analysis of functional Magnetic Resonance Imaging (fMRI) scans requires user-adjustment of the statistical threshold in order to maximize true functional activity and eliminate false positives. In this study, we propose a novel technique that uses radiomic texture analysis (TA) features associated with heterogeneity to predict areas of true functional activity. Scans of 15 right-handed healthy volunteers were analyzed using SPM8. The resulting functional maps were thresholded to optimize visualization of language areas, resulting in 116 regions of interests (ROIs). A board-certified neuroradiologist classified different ROIs into Expected (E) and Non-Expected (NE) based on their anatomical locations. TA was performed using the mean Echo-Planner Imaging (EPI) volume, and 20 rotation-invariant texture features were obtained for each ROI. Using forward stepwise logistic regression, we built a predictive model that discriminated between E and NE areas of functional activity, with a cross-validation AUC and success rate of 79.84% and 80.19% respectively (specificity/sensitivity of 78.34%/82.61%). This study found that radiomic TA of fMRI scans may allow for determination of areas of true functional activity, and thus eliminate clinician bias.