<p>Accurately assessing the risk and growth of rupture among intracranial aneurysms (IA) remains a challenging task for clinicians. Hemodynamic factors are known to play a critical role in the development of IAs, but the specific mechanisms are not well understood. Many studies have sought to correlate specific flow metrics to risk of growth and rupture but have reported conflicting findings. Computational fluid dynamics (CFD) has predominantly been the methodology used to study IA hemodynamics. Yet, CFD assumptions and limitations coupled with the lack of CFD validation has precluded clinical acceptance of IA hemodynamic assessments and likely contributed to the contradictory results among previous studies. Experimental particle image velocimetry (PIV) studies have been noticeably limited in both scope and number among IA studies, in part due to the complexity associated with such experiments. Moreover, the limited understanding of the robustness of hemodynamic metrics across varying flow and measurement environments and the effect of transitional flow in IAs also remain open issues. In this work, techniques to enhance IA PIV capabilities were developed and the first volumetric pulsatile IA PIV study was performed. A novel blood analog solution—a mixture of water, glycerol and urea— was developed and an autonomous methodology for reducing experimental noise in velocity fields was introduced and demonstrated. Both of these experimental techniques can also be used in PIV studies extending beyond IA applications. Further, the onset and development of transitional flow in physiological, pulsatile waveforms was explored. The robustness of hemodynamic metrics such as wall shear stress, oscillatory shear index, and relative residence time across varying modalities, spatiotemporal resolutions, and flow assumptions was explored. Additional hemodynamic metrics which have been demonstrated to be influential in other cardiovascular flows but yet to be tested in IA studies were also identified and considered. Ultimately this work provides a framework for future IA PIV studies as well as insight on using hemodynamic evaluations to assess the risk of growth and rupture of an IA, thereby taking steps towards enhancing the clinical utility of such analysis.</p>

Es wurde die Bedeutung der intravaskulären Ultraschalluntersuchung (IVUS) bei Diagnostik (1) und interventioneller Therapie (2) der koronaren Herzerkrankung am Beispiel der Transplantatvaskulopathie (TVP) untersucht. 1. Bei 321 Patienten post-HTx-Patienten ohne relevante Stenosen im Koronarangiogramm wurde eine dreidimensionale Rekonstruktion des Ramus interventricularis anterior (LAD) und des linkskoronaren Hauptstammes aus den mittles manueller Katheterrückzugstechnik aquirierten IVUS-Bildern durchgeführt und die intrakoronare Plaqueverteilung und die mittlere Plaquelast der einzelnen Koronarsegmente analysiert. Bei 296 Patienten (92%) fanden angiographisch nicht sichtbare frühe Plaquebildung. 48% dieser Patienten zeigten ein fokal,polyfokale, 52% ein diffuses Plaqueverteilungsmuster. Unabhängige Prädiktoren für das Auftreten einer diffusen TVP waren männliches Geschlecht des Empfängers, das Zeitintervall zwischen HTx und IVUS-Untersuchung (Transplantationszeit) und das Spenderalter. In beiden morphologischen Untergruppen war ein häufigere und stärkere Plaquebildung in den proximalen Koronarsegmenten nachweisbar. Ein distaler Gefäßbefall war bei diffuser Plaquebildung signifikant häufiger und zeigte eine steigende Inzidenz mit zunehmender Transplantationszeit. Somit stellt das longitudinale Plaqueverteilungsmuster und der distale Gefäßbefall einen zusätzlichen morphologischen Marker für den Schweregrad einer beginnenden Transplantatvaskulopathie dar. 2. Bei 36 post-HTx Patienten wurden 62 Stenosen prospektiv mit einer IVUS-gesteuerten, gefäßgrößen-adaptierten Stentimplantation erfolgreich versorgt. Die Stentgröße wurde dem Mittelwert aus Lumen- und Gefäßdurchmessers im proximalen Referenzsegment angepaßt. Nach Vordilatation fand sich ein Lumengewinn von 1.26± 0.16 auf 1.95 ± 0.27mm, nach abschließender Stentimplantation auf 2.94 ± 0.37mm. Nach 6 Monaten betrug die binäre In-Stent-Restenosierungsrate 21.8%, eine Re-PTCA wurde bei 10.9 % durchgeführt. / The role of intravascular ultrasound imaging in diagnosis of coronary disease (1) and guiding percutaneous coronary intervention (2) was evaluated in patients with transplant vasculopathy. 1. In 321 post-HTx-patients without angiographic evidence of coronary disease, three-dimensional intravascular ultrasound imaging of the left anterior descending coronary artery (LAD) and the left main coronary artery was performed. Intracoronary plaque distribution and plaque burden was evaluated for each coronary segment. In 296 patients (92%) angiographically silent plaque was detected by IVUS. 48% of these patients showed a focal,polyfocal and 52% a diffuse plaque distribution pattern. Independent predictors of diffuse plaque formation were male gender of the recipient, transplantation time and donor age. In both morphological subgroups of plaque distribution the incidence and magnitude of plaque formation was highest in the proximal LAD segment. Plaque formation in the distal LAD was more frequent in diffuse plaque formation and increased significantly with time after transplantation. Therefore longitudinal plaque distribution pattern and distal vessel involvment are useful additional morphological markers for staging of beginning transplant vasculopathy. 2. In 36 post-HTx-patients 62 coronary stenosis were successfully treated by vessel-size adapted stenting by use of intravascular ultrasound guidance. The stent size was adapted to the proximal reference segment´s mean of lumen/vessel diameter. After pre-dilatataion the minimal lumen diameter increased from 1.26± 0.16 to 1.95 ± 0.27mm and to 2.94 ± 0.37mm after final stent implantation. After 6 months, binary in-stent-restenosis rate was 21.8% and target vessel revascularization rate 10.9%, respectively.