Influence of segmented vessel size due to limited imaging resolution on coronary hyperemic flow prediction from arterial crown volume.

Computational predictions of the functional stenosis severity from coronary imaging data use an allometric scaling law to derive hyperemic blood flow (Q) from coronary arterial volume (V), Q = αV(ß) Reliable estimates of α and ß are essential for meaningful flow estimations. We hypothesize that the relation between Q and V depends on imaging resolution. In five canine hearts, fluorescent microspheres were injected into the left anterior descending coronary artery during maximal hyperemia. The coronary arteries of the excised heart were filled with fluorescent cast material, frozen, and processed with an imaging cryomicrotome to yield a three-dimensional representation of the coronary arterial network. The effect of limited image resolution was simulated by assessing scaling law parameters from the virtual arterial network at 11 truncation levels ranging from 50 to 1,000 µm segment radius. Mapped microsphere locations were used to derive the corresponding relative Q using a reference truncation level of 200 µm. The scaling law factor α did not change with truncation level, despite considerable intersubject variability. In contrast, the scaling law exponent ß decreased from 0.79 to 0.55 with increasing truncation radius and was significantly lower for truncation radii above 500 µm vs. 50 µm (P< 0.05). Hyperemic Q was underestimated for vessel truncation above the reference level. In conclusion, flow-crown volume relations confirmed overall power law behavior; however, this relation depends on the terminal vessel radius that can be visualized. The scaling law exponent ß should therefore be adapted to the resolution of the imaging modality.

Accuracy and precision of pseudo-continuous arterial spin labeling perfusion during baseline and hypercapnia: a head-to-head comparison with ¹5O H2O positron emission tomography.

Measurements of the cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) provide useful information about cerebrovascular condition and regional metabolism. Pseudo-continuous arterial spin labeling (pCASL) is a promising non-invasive MRI technique to quantitatively measure the CBF, whereas additional hypercapnic pCASL measurements are currently showing great promise to quantitatively assess the CVR. However, the introduction of pCASL at a larger scale awaits further evaluation of the exact accuracy and precision compared to the gold standard. (15)O H2O positron emission tomography (PET) is currently regarded as the most accurate and precise method to quantitatively measure both CBF and CVR, though it is one of the more invasive methods as well. In this study we therefore assessed the accuracy and precision of quantitative pCASL-based CBF and CVR measurements by performing a head-to-head comparison with (15)O H2O PET, based on quantitative CBF measurements during baseline and hypercapnia. We demonstrate that pCASL CBF imaging is accurate during both baseline and hypercapnia with respect to (15)O H2O PET with a comparable precision. These results pave the way for quantitative usage of pCASL MRI in both clinical and research settings.

Quantification and visualization of flow in the Circle of Willis: time-resolved three-dimensional phase contrast MRI at 7 T compared with 3 T.

The assessment of both geometry and hemodynamics of the intracranial arteries has important diagnostic value in internal carotid occlusion, sickle cell disease, and aneurysm development. Provided that signal to noise ratio (SNR) and resolution are high, these factors can be measured with time-resolved three-dimensional phase contrast MRI. However, within a given scan time duration, an increase in resolution causes a decrease in SNR and vice versa, hampering flow quantification and visualization. To study the benefits of higher SNR at 7 T, three-dimensional phase contrast MRI in the Circle of Willis was performed at 3 T and 7 T in five volunteers. Results showed that the SNR at 7 T was roughly 2.6 times higher than at 3 T. Therefore, segmentation of small vessels such as the anterior and posterior communicating arteries succeeded more frequently at 7 T. Direction of flow and smoothness of streamlines in the anterior and posterior communicating arteries were more pronounced at 7 T. Mean velocity magnitude values in the vessels of the Circle of Willis were higher at 3 T due to noise compared to 7 T. Likewise, areas of the vessels were lower at 3 T. In conclusion, the gain in SNR at 7 T compared to 3 T allows for improved flow visualization and quantification in intracranial arteries.

Complex flow patterns in a real-size intracranial aneurysm phantom: phase contrast MRI compared with particle image velocimetry and computational fluid dynamics.

The aim of this study was to validate the flow patterns measured by high-resolution, time-resolved, three-dimensional phase contrast MRI in a real-size intracranial aneurysm phantom. Retrospectively gated three-dimensional phase contrast MRI was performed in an intracranial aneurysm phantom at a resolution of 0.2 × 0.2 × 0.3 mm(3) in a solenoid rat coil. Both steady and pulsatile flows were applied. The phase contrast MRI measurements were compared with particle image velocimetry measurements and computational fluid dynamics simulations. A quantitative comparison was performed by calculating the differences between the magnitude of the velocity vectors and angles between the velocity vectors in corresponding voxels. Qualitative analysis of the results was executed by visual inspection and comparison of the flow patterns. The root-mean-square errors of the velocity magnitude in the comparison between phase contrast MRI and computational fluid dynamics were 5% and 4% of the maximum phase contrast MRI velocity, and the medians of the angle distribution between corresponding velocity vectors were 16° and 14° for the steady and pulsatile measurements, respectively. In the phase contrast MRI and particle image velocimetry comparison, the root-mean-square errors were 12% and 10% of the maximum phase contrast MRI velocity, and the medians of the angle distribution between corresponding velocity vectors were 19° and 15° for the steady and pulsatile measurements, respectively. Good agreement was found in the qualitative comparison of flow patterns between the phase contrast MRI measurements and both particle image velocimetry measurements and computational fluid dynamics simulations. High-resolution, time-resolved, three-dimensional phase contrast MRI can accurately measure complex flow patterns in an intracranial aneurysm phantom.

Ethnic differences in resistance artery contractility of normotensive pregnant women.

Black women are at a greater risk to develop hypertension during pregnancy, with a 4.5 times higher rate of fatal preeclampsia than white women. Therefore, it is important to identify factors that may affect this risk. Our group previously proposed that high activity of the central regulatory enzyme of energy metabolism, creatine kinase (CK), may increase ATP-buffering capacity and lead to enhanced vascular contractility and reduced nitric oxide bioavailability. Therefore, we assessed microvascular contractility characteristics in isolated resistance arteries from self-defined black and white normotensive pregnant women using a Mulvany-Halpern myograph. Additionally, morphology was assessed with electron microscopy. Resistance-sized arteries obtained from omentum donated during cesarean sections (11 black women and 20 white women, mean age: 34 yr) studied in series showed similar morphology but significantly greater maximum contractions to norepinephrine (10(-5) M) in blacks [14.0 mN (1.8 SE)] compared with whites [8.9 mN (1.4 SE), P = 0.02]. Furthermore, we found greater residual contractility after the specific CK inhibitor dinitrofluorobenzene (10(-6) M) in black women [55% (6 SE)] compared with white women [28% (4 SE), P = 0.001] and attenuated vasodilation after bradykinin (10(-7) M) in black women [103% (6 SE)] compared with white women [84% (5 SE), P = 0.023], whereas responses to sodium nitroprusside (10(-4) M) and amlodipine (10(-6) M) were similar. We conclude that compared with white women, normotensive pregnant black women display greater resistance artery contractility and evidence of higher vascular CK activity with attenuated nitric oxide synthesis. These findings in normotensives may imply that the black population is at risk for a further incline in pregnancy-related hypertensive disorders.

Effects of shear stress on endothelial cells: possible relevance for ultrasound applications.

This review forms part of a series of papers resulting from a workshop on safety of ultrasound applications. The physical effects of ultrasound include generation of steady streaming in large fluid volumes, and micro-streaming around contrast bubbles. Such streaming induces shear stress acting on the vascular endothelium. This review provides a discussion on the levels of endothelial shear stress associated with diagnostic ultrasound applications, and on the biological effects of shear stress acting on the endothelial cells. Depending on vessel size and ultrasound characteristics, shear stresses associated with streaming and micro-streaming may exceed the physiological levels associated with the flow of blood by many orders of magnitude. The resulting biological effects could range anywhere from activation of normal shear stress sensors such as ion channels, damage of the endothelial surface layer, reversible perforation of the membrane, to cell detachment and lysis. The possible presence of such biological effects does not necessarily mean that the effects are harmful for the individual. However, considering the ever-increasing use of ultrasound, a further investigation into these shear stress-related effects, using both experiments and modelling, is desired. Apart from safety concerns, such effects may provide a base for strategies aimed at targeted delivery of drugs.

Case report: twin-to-twin transfusion syndrome resulting from placental collateral artery development.

BACKGROUND: The twin-to-twin transfusion syndrome (TTTS) is a severe complication of monochorionic twin pregnancies, caused by a net inter-twin transfusion of blood from one fetus (the donor) towards the other fetus (the recipient) through placental anastomoses. TTTS is driven by unidirectional arterio-venous anastomoses, and mitigated by bidirectional arterio-arterial or veno-venous anastomoses which reduce the net inter-twin transfusion. In contrast to these accepted concepts, cases have been described paradoxically devoid of arterio-venous anastomoses but including arterio-arterial anastomoses. We hypothesized that TTTS may develop in such cases as a consequence of a stenosed chorionic artery in the recipient placenta that connects with the arterio-arterial anastomosis. CLINICAL CASES: We describe two cases of monochorionic twin placentae without arterio-venous anastomoses but with only an arterio-arterial and veno-venous anastomosis. In one case severe TTTS developed. There, the arterio-arterial anastomosis connected to a stenosed chorionic artery in the recipient placenta and showed a tortuous appearance. The other case developed uneventful. It lacked a stenosed chorionic artery and the arterio-arterial anastomosis was non-tortuous. CONCLUSION: We present evidence that the arterio-arterial anastomosis represented a functional collateral artery whose outgrowth was driven by an increased shear-stress caused by an increased flow to a lower pressure vascular bed in the placenta of the recipient. The lower arterial pressure occurred from the moment that a chorionic artery which was connected to the anastomosis developed a significant stenosis. The resulting collateral flow through the anastomosis maintained blood supply to the lower pressure placental bed, the beneficial function of collaterals, but also resulted in an increasing net inter-twin transfusion which triggered onset of severe TTTS.

Relation between branching patterns and perfusion in stochastic generated coronary arterial trees.

Biological variation in branching patterns is likely to affect perfusion of tissue. To assess the fundamental consequences of branching characteristics, 50 stochastic asymmetrical coronary trees and one non-stochastic symmetrical branching tree were generated. In the stochastic trees, area growth, A, at branching points was varied: A = random; 1.00; 1.10; 1.13 and 1.15 and symmetry, S, was varied: S = random; 1.00; 0.70; 0.58; 0.50 and 0.48. With random S and A values, a large variation in flow and volume was found, linearly related to the number of vessels in the trees. Large A values resulted in high number of vessels and high flow and volume values, indicating vessels connected in parallel. Lowering symmetry values increased the number of vessels, however, without changing flow, indicating a dominant connection of vessels in series. Both large A and small S values gave more realistic gradual pressure drops compared to the symmetrical non-stochastic branching tree. This study showed large variations in tree realizations, which may reflect real biological variations in tree anatomies. Furthermore, perfusion of tissue clearly depends on the branching rules applied.

Visualisation of intramural coronary vasculature by an imaging cryomicrotome suggests compartmentalisation of myocardial perfusion areas.

A technique is presented for the 3D visualisation of the coronary arterial tree using an imaging cryomicrotome. After the coronary circulation of the excised heart was filled with a fluorescent plastic, the heart was frozen and mounted in the cryomicrotome. The heart was then sliced serially, with a slice thickness of 40 microm, and digital images were taken from each cutting plane of the remaining bulk material using appropriate excitation and emission filters. Using maximum intensity projections over a series of images in the cutting plane and perpendicular plane, the structural organisation of intramural vessels was visualised in the present study. The branching end in the smallest visible vessels, which define tissue areas that are well delineated from each other by 1-2 mm wide bands populated only by vessels less than 40 microm in diameter. The technique presented here allows further quantification in the future of the 3D structure of the coronary arterial tree by image analysis techniques.

Vascular function in preeclampsia.

Preeclampsia is a multisystem disorder peculiar to human pregnancy. It occurs in 4-5% of all pregnancies and remains a leading cause of maternal and neonatal mortality and morbidity. The pathophysiology of this syndrome is not fully understood. Two stages of vascular dysfunction seem to be involved. In the early stage suboptimal development of the placenta and a hemodynamic maladaptation to pregnancy exist. At this stage maternal constitutional factors such as genetic and immunological factors and pre-existing vascular diseases may play a role. Due to this defective placentation a factor is released from the placenta, supposedly under the influence of ischemia. This factor then results in the late vascular dysfunction characterised mainly by a generalised endothelial dysfunction, leading to the clinical syndrome of preeclampsia. This review attempts to unravel the mechanisms that may contribute to preeclampsia-associated changes in vascular function and to indicate the research needed to improve our understanding of this disease.

Microparticles in cardiovascular diseases.

Microparticles are membrane vesicles released from many different cell types. There are two mechanisms that can result in their formation, cell activation and apoptosis. In these two mechanisms, different pathways are involved in microparticle generation. Microparticle generation seems to be a well regulated process. Microparticles vary in size, phospholipid and protein composition. They have a potent pro-inflammatory effect, promote coagulation and affect vascular function. Since these processes are all involved in the pathogenesis of cardiovascular disease and circulating microparticle numbers are altered in many cardiovascular diseases, a role for microparticles in the pathogenesis of cardiovascular diseases is likely. Although hard evidence for a role of microparticles in cardiovascular diseases at present is still only limited, new evidence is accumulating rapidly to support this theory. Elucidation of the microparticle composition and the mechanisms involved in exertion of their effects will supply this evidence and enable us to develop additional intervention strategies for prevention and treatment of cardiovascular diseases.

Intracellular Ca2+ and delay of ischemia-induced electrical uncoupling in preconditioned rabbit ventricular myocardium.

OBJECTIVE: Short periods of ischemia and reperfusion alter myocardial Ca2+ handling and temporarily induce a mild increase of [Ca2+]i. We hypothesized that these alterations are involved in the cardioprotective mechanism of ischemic preconditioning, possibly via a Ca(2+)-dependent activation of protein kinase C (PKC). METHODS AND RESULTS: In arterially perfused rabbit papillary muscles, we determined Ca2+ transients (indo 1) and indicators of the onset of irreversible ischemic damage, including [Ca2+]i rise, electrical uncoupling and contracture. We tested three protocols of ischemic preconditioning (1-3). In addition, the effects of infusion of staurosporine, a blocker of PKC (4), or glibenclamide, a blocker of K+ATP channels (5) were analyzed. Furthermore, pretreatment with phorbol 12-myrisate 13-acetate (PMA), an activator of PKC (6), or cyclopiazonic acid (CPA), an inhibitor of the SR Ca2+ pump (7) was tested. During periods of reperfusion in the preconditioning protocols, the duration of the Ca2+ transient and the diastolic Ca2+ level temporarily increased. Only if sustained ischemia was induced during these changes of the transients, cardioprotection was present. Similar alterations of the Ca2+ transient concurring with cardioprotection were induced by pretreatment with PMA as well as CPA. Staurosporine and glibenclamide antagonized the reperfusion-induced changes of the Ca2+ transients as well as cardioprotection. If reperfusion was extended until the Ca2+ transient had normalized, cardioprotection was also absent. Under all conditions tested, the diastolic Ca2+ elevation or the Ca2+ transient prolongation prior to sustained ischemia correlated with the postponement of ischemic injury. CONCLUSIONS: A pre-ischemic mild increase of [Ca2-]i presents a common effector of preconditioning. Our data suggest that activation of PKC or opening of K+ATP channels may initiate the pathway leading to an alteration of Ca2+ metabolism and a protected status of the myocardium.

The influence of aging and aortic stiffness on permanent dilation and breaking stress of the thoracic descending aorta.

OBJECTIVE: To assess the influence of aging and aortic stiffness on the extent of irreversible deformation and breaking stress of the human thoracic aorta. METHODS: From 14 human heart valve donors without aortic disease (mean age 35 years, range 8-59 years), 14 intact segments of the thoracic descending aorta were studied within 48 h after cardiac arrest. In an experimental setup, the segments were submitted to increasing hydrostatic pressure loads, both statically and dynamically, while radius and wall thickness were monitored echocardiographically. Pressure-radius curves were constructed. Radius and wall thickness were determined at a pressure of 100 mmHg. Radius at elastin resting length and collagen recruitment pressure (Pcol, mmHg) were derived from the pressure-radius relationship and stress-strain curves were constructed to yield Young's moduli of elastin and collagen. Distensibility (D, mmHg-1) was determined while loading the segment with a sinusoidal pressure wave of 120/50 mmHg at both 0.5 and 1 Hz. Subsequently increasing static pressure loads of 400, 800, 1200 and 1600 mmHg were applied. After each pressure load, the increase in aortic radius at a pressure of 100 mmHg (Rinc) was determined. The experiment continued until rupture occurred and breaking stress (sigma break, N m-2) was calculated, donor age and aortic stiffness were correlated with Rinc and sigma break of the aortic segments. RESULTS: Mean breaking stress of the 14 segments was 2.7 x 10(6) N m-2. Breaking stress was negatively correlated with age (r2 = 0.66) and positively with D (r2 = 0.44) and with Pcol (r2 = 0.18). Seven segments survived a pressure load of 800 mmHg, in these vessels, the extent of irreversible dilation was positively correlated with age (r2 = 0.42) and negatively with D (r2 = 0.40) and Pcol (r2 = 0.40). CONCLUSION: Permanent deformation and rupture of the human thoracic aorta following pressure overload are influenced by age, distensibility and collagen recruitment pressure.

Additional Value of Intra-Aneurysmal Hemodynamics in Discriminating Ruptured versus Unruptured Intracranial Aneurysms.

BACKGROUND AND PURPOSE: Hemodynamics are thought to play an important role in the rupture of intracranial aneurysms. We tested whether hemodynamics, determined from computational fluid dynamics models, have additional value in discriminating ruptured and unruptured aneurysms. Such discriminative power could provide better prediction models for rupture. MATERIALS AND METHODS: A cross-sectional study was performed on patients eligible for endovascular treatment, including 55 ruptured and 62 unruptured aneurysms. Association with rupture status was tested for location, aneurysm type, and 4 geometric and 10 hemodynamic parameters. Patient-specific spatiotemporal velocities measured with phase-contrast MR imaging were used as inflow conditions for computational fluid dynamics. To assess the additional value of hemodynamic parameters, we performed 1 univariate and 2 multivariate analyses: 1 traditional model including only location and geometry and 1 advanced model that included patient-specific hemodynamic parameters. RESULTS: In the univariate analysis, high-risk locations (anterior cerebral arteries, posterior communicating artery, and posterior circulation), daughter sacs, unstable inflow jets, impingements at the aneurysm body, and unstable complex flow patterns were significantly present more often in ruptured aneurysms. In both multivariate analyses, only the high-risk location (OR, 3.92; 95% CI, 1.77-8.68) and the presence of daughter sacs (OR, 2.79; 95% CI, 1.25-6.25) remained as significant independent determinants. CONCLUSIONS: In this study population of patients eligible for endovascular treatment, we found no independent additional value of aneurysmal hemodynamics in discriminating rupture status, despite high univariate associations. Only traditional parameters (high-risk location and the presence of daughter sacs) were independently associated with ruptured aneurysms.

Hemodynamic Differences in Intracranial Aneurysms before and after Rupture.

BACKGROUND AND PURPOSE: Rupture risk of intracranial aneurysms may depend on hemodynamic characteristics. This has been assessed by comparing hemodynamic data of ruptured and unruptured aneurysms. However, aneurysm geometry may change before, during, or just after rupture; this difference causes potential changes in hemodynamics. We assessed changes in hemodynamics in a series of intracranial aneurysms, by using 3D imaging before and after rupture. MATERIALS AND METHODS: For 9 aneurysms in 9 patients, we used MRA, CTA, and 3D rotational angiography before and after rupture to generate geometric models of the aneurysm and perianeurysmal vasculature. Intra-aneurysmal hemodynamics were simulated by using computational fluid dynamics. Two neuroradiologists qualitatively assessed flow complexity, flow stability, inflow concentration, and flow impingement in consensus, by using flow-velocity streamlines and wall shear stress distributions. RESULTS: Hemodynamics changed in 6 of the 9 aneurysms. The median time between imaging before and after rupture was 678 days (range, 14-1461 days) in these 6 cases, compared with 151 days (range, 34-183 days) in the 3 cases with unaltered hemodynamics. Changes were observed for flow complexity (n = 3), flow stability (n = 3), inflow concentration (n = 2), and region of flow impingement (n = 3). These changes were in all instances associated with aneurysm displacement due to rupture-related hematomas, growth, or newly formed lobulations. CONCLUSIONS: Hemodynamic characteristics of intracranial aneurysms can be altered by geometric changes before, during, or just after rupture. Associations of hemodynamic characteristics with aneurysm rupture obtained from case-control studies comparing ruptured with unruptured aneurysms should therefore be interpreted with caution.

Differences in sensitivity of rat mesenteric small arteries to agonists when studied as ring preparations or as cannulated preparations.

1. Pharmacological experiments on vascular tissue are normally performed on isometric ring or strip preparations. The aim of this study was to compare the isometric characteristics with the characteristics obtained if vessels were examined under the more physiologically appropriate isobaric condition. 2. Rat mesenteric small arteries were mounted either on two steel wires for isometric force measurement (wire-myograph) or cannulated for measurement of the internal diameter under isobaric conditions (pressure-myograph). 3. The passive pressure-diameter characteristics of the small arteries were similar on the wire- and pressure-myograph (using the Laplace relation to convert wall tension-internal circumference data from the wire-myograph to effective pressure-diameter characteristics). 4. In cumulative concentration-response experiments with noradrenaline and phenylephrine, the threshold concentration was 8-10 times lower, and the EC50-concentration was 4-5 times lower, in the pressure myograph compared to the wire-myograph. Thus vessels were not only more sensitive on the pressure myograph, but the slopes of the concentration-response curves were less steep. Similar experiments with vasopressin also showed this difference in the threshold-concentration and slope, but EC50 concentrations were similar. 5. Cumulative concentration-response experiments with K+ showed no difference either in EC50 or in slope on the wire- and pressure-myographs. 6. On the wire-myograph, some vessels were stretched longitudinally (to mimic the longitudinal stretch which had to be used in the pressure-myograph to avoid buckling). Such stretch did not affect the passive characteristics. 7. The differences between the EC50 determined on the wire- and pressure-myographs as regards noradrenaline and phenylephrine were eliminated when neuronal noradrenaline uptake was inhibited by denervation. However, the slope of the concentration-response curves on the wire-myograph was not affected by denervation.8. When vessels were exposed to cocaine (3 MicroM) the noradrenaline concentration-response curves were the same on the wire- and pressure-myographs as regards both EC50 and slope.9. On the wire-myograph, the calcium antagonist, methoxyverapamil, (D600) reduced the maximal contractile effect of noradrenaline by 50%, but on the pressure-myograph D600 did not affect the maximal response.10. The present results show that results obtained from vascular tissue under isometric conditions may differ substantially from the characteristics which would be obtained under isobaric conditions.

Morphological and functional alterations in glycerol preserved rat aortic allografts.

Glycerol preservation is an effective method for long-term preservation of skin allografts and has a potential use in preserving arterial allografts. We evaluated the effect of glycerol concentration and incubation period on vessel-wall integrity of rat aortic allografts. No significant differences were measured in breaking strength (2.3 +/- 0.3 N) and bursting pressure (223 +/- 32 kPa) between standard glycerolized and control segments (1.7 +/- 0.3 N, 226 +/- 17 kPa). Isometric tension measurements showed complete lack of functional contraction and relaxation capacity in allograft segments prepared according to all preservation protocols. Morphologically, thickness of the vessel-wall media diminished after preservation using low (30/50/75%) or high (70/85/98%) concentrations of glycerol, as compared to control segments (i.e. 81 +/- 2.4 microm, 95 +/- 5.6 microm and 125 +/- 3.5 microm, respectively). Confocal microscopy and Fourier analysis demonstrated that vascular collagen and elastin bundle orientation had remained unaltered. Electron microscopy showed defragmentation of luminal endothelial cells. In conclusion, glycerol preservation of rat aorta resulted in an acellular tissue matrix, which maintained biomechanical integrity and extracellular matrix characteristics. The next step in the investigation will be to test the concept of glycerol preservation of arterial allografts in a vascular transplantation model.

Rupture-associated changes of cerebral aneurysm geometry: high-resolution 3D imaging before and after rupture.

BACKGROUND AND PURPOSE: Comparisons of geometric data of ruptured and unruptured aneurysms may yield risk factors for rupture. Data on changes of geometric measures associated with rupture are, however, sparse, because patients with ruptured aneurysms rarely have undergone previous imaging of the intracranial vasculature. We had the opportunity to assess 3D geometric differences of aneurysms before and after rupture. The purpose of this study was to evaluate possible differences between prerupture and postrupture imaging of a ruptured intracranial aneurysm. MATERIALS AND METHODS: Using high-quality 3D image data, we generated 3D geometric models before and after rupture and compared these for changes in aneurysm volume and displacement. A neuroradiologist qualitatively assessed aneurysm shape change, the presence of perianeurysmal hematoma, and subsequent mass effect exerted on aneurysm and parent vessels. RESULTS: Aneurysm volume was larger in the postrupture imaging in 7 of 9 aneurysms, with a median increase of 38% and an average increase of 137%. Three aneurysms had new lobulations on postrupture imaging; 2 other aneurysms were displaced up to 5 mm and had changed in geometry due to perianeurysmal hematoma. CONCLUSIONS: Geometric comparisons of aneurysms before and after rupture show a large volume increase, origination of lobulations, and displacement due to perianeurysmal hematoma. Geometric and hemodynamic comparison of series of unruptured and ruptured aneurysms in the search for rupture-risk-related factors should be interpreted with caution.

Automatic segmentation of the aortic root in CT angiography of candidate patients for transcatheter aortic valve implantation.

Transcatheter aortic valve implantation is a minimal-invasive intervention for implanting prosthetic valves in patients with aortic stenosis. Accurate automated sizing for planning and patient selection is expected to reduce adverse effects such as paravalvular leakage and stroke. Segmentation of the aortic root in CTA is pivotal to enable automated sizing and planning. We present a fully automated segmentation algorithm to extract the aortic root from CTA volumes consisting of a number of steps: first, the volume of interest is automatically detected, and the centerline through the ascending aorta and aortic root centerline are determined. Subsequently, high intensities due to calcifications are masked. Next, the aortic root is represented in cylindrical coordinates. Finally, the aortic root is segmented using 3D normalized cuts. The method was validated against manual delineations by calculating Dice coefficients and average distance error in 20 patients. The method successfully segmented the aortic root in all 20 cases. The mean Dice coefficient was 0.95 ± 0.03, and the mean radial absolute error was 0.74 ± 0.39 mm, where the interobserver Dice coefficient was 0.95 ± 0.03 and the mean error was 0.68 ± 0.34 mm. The proposed algorithm showed accurate results compared to manual segmentations.

A flow-diverting stent is not a pressure-diverting stent.

The approach for treatment of large and fusiform intracranial aneurysms has evolved from stent-assisted coiling to treatment with flow-diverting stents. The treatment results for these stents are promising; however, early postprocedural aneurysm rupture has been described. The exact cause of rupture is unknown but might be related to intra-aneurysmal flow and pressure changes. We measured intra-aneurysmal pressure before, during, and after placement of a flow-diverting stent by using a dual-sensor guidewire. The pressure inside the aneurysm momentarily decreased during placement but was restored to baseline values within minutes. The flow-diverting stent does not seem to protect the aneurysm from the stress induced by pressure or pressure changes within the lumen.