Aneurysm Volume Research Articles

TU-A-218-03: Effect of the Flow Diverter Resistance on the Aneurysm Angiographic Time Density Curves

Purpose: Flow diverters (FD) are new stent like devices used for selected intracranial aneurysms treatment. The devices are in their initial clinical use and the relation between device parameters, physiological implications and treatment outcome needs to be further investigated. Flow resistance is a parameter which could be used to characterize the device flow induced modifications. The purpose of this study is to investigate the relation between FD flow resistance and physiological aneurysmal blood flow modification using time density curves (TDC's) derived from high speed angiograms. Material and Methods: Six bifurcation aneurysm phantoms were treated with stainless steel wire meshes to simulate various FD's. The FD resistance was calculated using a semi-empirical model dependent on the device porosity, flow conditions and device strut diameter. Contrast time density curves (TDC's) were measured in a region-of-interest which included the entire aneurysm volume, using high-speed x-ray angiographic image sequences. In each TDC we measured bolus peak, input flow slope (IFS), the mean transit time (MTT), and time to peak (TTP). The treated aneurysm TDC's parameters were normalized to the untreated case. The flow model assumes that the ratio of the pressure drop and velocity square is proportional with the resistance. The model validity was demonstrated by verifying the linear dependence of TDC parameters of the inverse square root of the device flow resistance. Results: The observed flow changes correlated linearly with the FD flow resistance. For flow resistances larger than 20 the contrast entering the aneurysm was negligible. The linear fit results yielded R̂2 values of 0.99 for the peak, 0.93 for the IFS, 0.93 for TTP and 0.94 for the MTT. Conclusions: The FD flow resistance correlates strongly with all TDC parameters, indicating that it could be used to predict blood flow physiological changes in aneurysms treated with FD's. NIH Grants R01-EB008425, R01-EB002873 and an equipment grant from Toshiba Medical Systems Corp.

Aneurysm Volume in the Rabbit Bifurcation Model-Calculation with Cylindric Volume Formula versus Multiplanar Reconstruction-Volumetry in Contrast-Enhanced Magnet Resonance Angiography

Aneurysm Volume in the Rabbit Bifurcation Model-Calculation with Cylindric Volume Formula versus Multiplanar Reconstruction-Volumetry in Contrast-Enhanced Magnet Resonance Angiography

Endovascular Treatment of a Large Partially Thrombosed Basilar Tip Aneurysm

Despite the remarkable developments in neurosurgical and neuro-interventional procedures, the optimal treatment for large or giant partially thrombosed aneurysms with a mass effect remains controversial. The authors report a case of a partially thrombosed aneurysm with a mass effect, which was successfully treated by stent-assisted coil embolization. A 41-year-old man presented with headache. Brain computed tomography depicted an 18×18 mm sized thrombosed aneurysm in the interpeducular cistern. More than 80% of the aneurysm volume was filled with thrombus and the canalized portion beyond its neck measured 6.8×5.6 mm by diagnostic cerebral angiography. Stent-assisted endovascular coiling was performed on the canalized sac and the aneurysm was completely obliterated. Furthermore, most of the thrombosed aneurysm disappeared in the interpeduncular cistern was clearly visualized follow-up brain magnetic resonance imaging conducted at 21 months. The authors report a case of selective coiling of a large, partially thrombosed basilar tip aneurysm.

Matrix2Coils in Embolization of Intracranial Aneurysms: 1-Year Outcome and Comparison with Bare Platinum Coil Group in a Single Institution

The endosaccular occlusion by using BPC has been useful in the treatment of intracranial aneurysms, but its limited durability remains a deep-seated drawback. The Matrix² coil, one of the bioactive-coated coils, had been developed to improve this limited durability. To evaluate durability of Matrix² coils after embolization of intracranial aneurysms, we retrospectively compared 1-year outcomes with that of BPC groups. A group of 121 aneurysms in 114 patients were embolized by using Matrix² coils between April 2006 and September 2008. The BPC group consisted of 151 aneurysms in 137 patients embolized by using BPCs alone between October 2007 and October 2008. The initial outcomes including packing densities, occlusion grades, and periprocedural complications, and the 1-year outcomes on MR angiography were retrospectively compared between the 2 groups. The Matrix² coil group and BPC group with similar baseline demographic characteristics revealed comparable initial outcomes. The rates of overall recurrence, major recanalization, and retreatment were 17.4%, 14.0%, and 10.7% versus 7.3%, 5.3%, and 4.6%, respectively (P = .066). However, the rates of subgroups with aneurysm volumes between 50 and 200 mm³ were 23.7%, 13.1%, and 10.5% versus 2.2%, 0%, and 0% (P = .022), respectively. The rates of subgroups with packing attenuation <30% were 38.3%, 31.9%, and 23.4% versus 13.3%, 11.7%, and 10% (P = .025), respectively. There were no differences in packing attenuation (P = .152), initial occlusion grade (P = .098), and 1-year outcomes (P = .209) according to the length of Matrix² coils used. Overall, initial and 1-year outcomes of the Matrix² coil group were comparable to those of the BPC group. However, in certain subgroups of aneurysm volume and packing attenuation, the 1-year durability of Matrix² coils was inferior to that of the BPC group.

Embolization of Intracranial Aneurysms with HydroSoft Coils: Results of the Korean Multicenter Study

Various modifications of detachable coils have been attempted to reduce recurrence rates in aneurysmal coil embolization and HydroSoft coil is one of them. The authors report their experience using HydroSoft coils in the treatment of cerebral aneurysms. The present study is a prospective multicenter observational series of 127 aneurysms in 120 patients treated with HydroSoft coils. Ten centers participated in this study, and there were 92 (72%) unruptured and 35 ruptured aneurysms. Aneurysm volumes were ≥ 100 mm³ in 21 (17%) and < 100 mm³ in 106 (83%) (mean, 56 mm³; range, 5-249 mm³). The average percentage length of HydroSoft coils detached in treated aneurysms was 67% (range, 42%-100%). Immediate postprocedural angiography demonstrated complete aneurysm occlusion in 69% (87/127 aneurysms), residual neck in 20% (25/127), and residual sac in 12% (15/127). Procedure-related adverse events occurred in 4.7% (6/127 aneurysms), including procedural bleeding (5/127) and thromboembolism (2/127), and immediate procedure-related morbidity and mortality rates were 0.8% and 0%. Conventional angiography or MRA follow-up was performed in 83% (105/127) at ≥ 6 months after treatment (mean interval, 11 months; range, 6-24 months). The overall recanalization rate was 3% (3/105 aneurysms; 2 major and 1 minor recanalizations). Progression to complete aneurysmal occlusion was noted in 20 of 27 aneurysms (74%) during the follow-up. The safety profile of HydroSoft coils appears acceptable. In terms of initial occlusion rates and durability, embolization by using HydroSoft coils seems to be favorable compared with most large series of pure platinum or coated coils.

O-019 Accuracy of 3D rotational angiography, mathematical modeling, and angiosuite in determining aneurysm volumes

IntroductionThe ability to assess packing density during endovascular treatment of aneurysms is limited by multiple factors. Algorithms to quickly predict the effect of coil choice on packing density are not...

P-006 AngioSuite-Neuro edition

Introduction/PurposeDespite continuous improvements in imaging quality and therapeutic options, there has been no satisfactory method to easily calculate aneurysm volumes, packing densities or occlusion grades. Previous models have been simplistic...

Volumetric analysis of the aneurysmal sac with computed tomography in the follow-up of abdominal aortic aneurysms after endovascular treatment

Our aim was to assess the usefulness of volumetric analysis for the follow-up of abdominal aortic aneurysms after endovascular repair (EVAR) and operator independence of the method. We retrospectively evaluated 99 computed tomography (CT) exams of 33 patients. Two blinded operators assessed the volume before treatment and after EVAR at 1-3 and 12-24 months. Friedman's statistical test was used to assess the reproducibility of the method. The time required for postprocessing by the two operators was compared. One patient was excluded. Twenty-one patients showed no endoleak: 12/21 showed a volume reduction at both follow-up scans (9.7% and 19.5%, respectively); 8/21 showed an early volume increase (9.8%) with a late reduction (10.5%); 1/21 patient showed a volume increase at both follow-up scans (endotension). Eleven patients had an endoleak (one type I, nine type II and one type III); 4/9 type II endoleaks showed a volume reduction at both post-EVAR scans (8.5% and 19.5%). All other cases showed a volume increase after EVAR (type II 15.4%/16.8%, type I 24.1%/9.1%, type III 8%/10.7%). The Friedman statistical test assessed operator independence with p < 0.001. Mean difference between the two operators was 0.9% (0-4.3%). CT volume analysis is an accurate and reproducible modality for the follow-up of abdominal aortic aneurysms after EVAR. At early follow-up, contrast-enhanced CT remains mandatory to identify small endoleaks. For later follow-up, volumetric analysis would eliminate the need for contrast material in asymptomatic patients with stable or decreasing aneurysm volume.

Comparison of Cerebral Aneurysm Volumes as Determined by Digitally Measured 3D Rotational Angiography and Approximation from Three Diameters

This study compared digital measurement of aneurysm volume by 3D rotational angiography (3D-RA) with an approximation technique using three diameters of an aneurysm to re-interpret previously reported optimal packing densities (volume embolization ratio, VER) in coil embolization of intracranial aneurysms. Estimation of the volume of saccular aneurysms is important for calculation of the VER, which is in turn reported to be useful for prediction of coil compaction. The conventional formula for the volume estimation is V=4/3 π(A/2) (B/2) (C/2), where A, B, and C are the aneurysmal height, length, and width measured on 3D-RA image respectively. Using 3D rotational angiography data from 74 aneurysms, the approximated volume generated using the conventional formula was directly compared with the digitally measured volume. The digitally measured volume varied from 0.003 ml to 7.935 ml, and the dome-to-neck ratio (D/N) from 0.79 up to 4.62. We found that the conventional formula almost systematically underestimated the volume by up to 50 %, particularly when the neck was large relative to the dome (D/N<2). On average, digitally measured volume was 1.26~1.29 times larger than the approximated volume obtained using the conventional formula.Conventional 2D angiography based aneurysm volume calculation tends to underestimate an aneurysm volume, so the so-called VER (volume embolization ratio) could be overestimated.

Measurements and detection of abdominal aortic aneurysm growth: Accuracy and reproducibility of a segmentation software

PurposeTo validate the reproducibility and accuracy of a software dedicated to measure abdominal aortic aneurysm (AAA) diameter, volume and growth over time. Materials and methodsA software enabling AAA segmentation, diameter and volume measurement on computed tomography angiography (CTA) was tested. Validation was conducted in 28 patients with an AAA having 2 consecutive CTA examinations. The segmentation was performed twice by a senior radiologist and once by 3 medical students on all 56 CTAs. Intra and inter-observer reproducibility of D-max and volumes values were calculated by intraclass correlation coefficient (ICC). Systematic errors were evaluated by Bland–Altman analysis. Differences in D-max and volume growth were compared with paired Student's t-tests. ResultsMean D-max and volume were 49.6±6.2mm and 117.2±36.2ml for baseline and 53.6±7.9mm and 139.6±56.3ml for follow-up studies. Volume growth (17.3%) was higher than D-max progression (8.0%) between baseline and follow-up examinations (p<.0001). For the senior radiologist, intra-observer ICC of D-max and volume measurements were respectively estimated at 0.997 (≥0.991) and 1.000 (≥0.999). Overall inter-observer ICC of D-max and volume measurements were respectively estimated at 0.995 (0.990–0.997) and 0.999 (>0.999). Bland–Altman analysis showed excellent inter-reader agreement with a repeatability coefficient <3mm for D-max, <7% for relative D-max growth, <6ml for volume and <6% for relative volume growth. ConclusionSoftware AAA volume measurements were more sensitive than AAA D-max to detect AAA growth while providing an equivalent and high reproducibility.

Toward accurate volumetry of brain aneurysms: Combination of an algorithm for automatic thresholding with a 3D eraser tool

The present study describes a new approach for aneurysm volume quantification on three-dimensional angiograms, which focuses on solving three common technical problems: the variability associated with the use of manual thresholds, the irregular morphology of some aneurysms, and the imprecision of the limits between the parent artery and the aneurysm sac. The method consists of combining an algorithm for automatic threshold determination with a spherical eraser tool that allows the user to separate the image of the aneurysm from the parent artery. The accuracy of volumetry after automatic thresholding was verified with an in vitro experiment in which 57 measurements were performed using four artificial aneurysms of known volume. The reliability of the method was compared to that obtained with the technique of ellipsoid approximation in a clinical setting of 15 real angiograms and 150 measurements performed by five different users. The mean error in the measurement of the artificial aneurysms was 7.23%. The reliability of the new approach was significantly higher than that of the ellipsoid approximation. Limits of agreement between two measurements were determined with Bland–Altman plots and ranged from −14 to 13% for complex and from −10.8 to 11.03% for simple-shaped sacs. The reproducibility was lower (>20% of variation) for small aneurysms (<70 mm 3) and for those presenting a very wide neck (dome-to-neck ratio < 1). The method is potentially useful in the clinical practice, since it provides relatively precise, reproducible, volume quantification. A safety coiling volume can be established in order to perform sufficient but not excessive filling of the aneurysm pouch.

Follow-up of abdominal aortic aneurysm after endovascular aortic repair: Comparison of volumetric and diametric measurement

To determine the correlation of maximal diameter measurements with volumetric evaluation of size after endovascular aortic repair (EVAR) of abdominal aortic aneurysms (AAA) using computed tomography angiography (CTA) and to survey its applicability for clinical follow-up. 73 consecutive patients (2 females, 71 males; age 38-84 years; mean age, 69.1 ± 8 years) with AAA were treated with percutaneous EVAR in a single institution. For follow-up, CTA was performed periodically after EVAR. Images were evaluated for maximal diameter in consensus by two experienced radiologists. Using OsirixTM, volumetric measurements were done by one radiologist, including the entire infrarenal abdominal aorta. In 73 patients 220 CTA examinations were performed after EVAR with a mean follow-up of 17.3 months (range, 1.8-42.7 months). The mean postinterventional volume of aneurysm was 165.63 ml ± 93.29 ml (range, 47.94-565.67 ml). The mean maximal postinterventional diameter was 5.91 ± 1.52 cm (range, 3.72-13.82 cm). At large over the entire observation period a slight, non-significant decrease of 1.6% (2.58ml ± 69.05 ml, range 82.82-201.92 ml) in volumes and a 9.3% (mean 0.55 cm ± 1.22 cm, range 2.85-1.93cm) in diameters were observed. For all examinations a high correlation of volume and diameter was calculated (r = 0.813-0.905; α<0.01). For follow-up of abdominal EVAR using CTA there is a high correlation between volumetric and diametric measurements of aneurysm. Based on a daily clinical routine setting, measurements of maximal diameters in cross sectional imaging of AAA after EVAR seems to be sufficient to exclude post interventional enlargement.

Temporal Stability of Dysmorphic Fusiform Aneurysms of the Intracranial Internal Carotid Artery

Purpose Estimation of the stability of dysmorphic fusiform aneurysms of the intracranial internal carotid artery requires precise monitoring of their volumes. This report describes a method of magnetic resonance (MR) imaging and three-dimensional postprocessing to study the evolution of these aneurysms in a prospective cohort of patients not immediately suitable for surgery or endovascular treatment. Materials and Methods Ten patients with fusiform aneurysms of the intracranial internal carotid artery underwent serial MR studies. Five patients were studied at two time points and the remainder at multiple time points (mean delay between studies, 12.6 mo ± 3.8). For each patient, studies from all time points were coregistered. The volumes of each vessel component were calculated. Results Mean aneurysm volume was 833 mm 3 ± 878. Mean annual rate of volume progression was 1.37% ± 2.09. All aneurysms were thrombus-free. Conclusions This study indicates that, given the relatively low rate of progression of dysplastic fusiform aneurysms and the complexity of their shape, three-dimensional quantitative volumetric methods can be helpful in monitoring whether any growth has occurred.

Comparative Morphological Analysis of the Geometry of Ruptured and Unruptured Aneurysms

The risk of aneurysm rupture appears to be related to multiple factors such as topology, morphology, size, perianeurysmal environment, and blood flow hemodynamics. To evaluate aneurysm morphology and to quantitatively compare the volumetric parameters between ruptured and unruptured aneurysms from our clinical database at the UCLA Medical Center. Novel algorithms that automatically compute aneurysm geometry were tested on the basis of voxel data obtained from angiographic images, and measurements of aneurysm morphology were automatically recorded. We studied a total of 50 aneurysms (25 ruptured and 25 unruptured) with sizes ranging from 3 to 26 mm. To compare the geometric characteristics between ruptured and unruptured groups, we examined measurements, including volume and surface area, and the ratios of these measurements to the minimal bounding sphere around each aneurysm. More than 65% of ruptured aneurysms had a ratio of aneurysm volume to bounding sphere volume (AVSV) of > 0.5. More than 70% of ruptured aneurysms had a ratio of aneurysm surface to bounding sphere surface (AASA) of < 1. A trend differentiating ruptured and unruptured aneurysms was observed in AVSV (P = .07) and AASA (P = .04). Classification and regression trees analysis showed 68% correct classification with rupture for AVSV and 70% for AASA. By comparing aneurysm geometry with the bounding sphere, we found a trend associating the ratios of aneurysm volume and surface area with rupture. These geometric parameters may be useful for understanding the influence of morphology on the risk of aneurysm rupture.

Mural destabilization after aneurysm treatment with a flow-diverting device: a report of two cases

BackgroundFlow-diverting stents have demonstrated great promise for the treatment of cerebral aneurysms; however, clinical experience with the devices remains very preliminary. We present two cases of spontaneous delayed complications—one fatal...

Aortic volume as an indicator of disease progression in patients with untreated infrarenal abdominal aneurysm

The maximal diameter of an abdominal aortic aneurysm (AAA) and the change in diameter over time reflect rupture risk and are used for surgical planning. However, evidence has emerged that aneurysm volume may be a better indicator of AAA remodeling. The purpose of this study was to assess the relationship between the volume and maximal diameter of the abdominal aorta in patients with untreated infrarenal AAA. This was a retrospective study of 100 patients with infrarenal AAA who were followed for more than 6 months. We examined 2 sets of computed tomography images for each patient, acquired ≥ 6 months apart. The maximal diameter and volume of the infrarenal abdominal aorta were determined by semiautomated segmentation software. At baseline, mean maximal infrarenal diameter was 5.1 ± 1.0 cm and mean aortic volume was 139 ± 72 mL. There was good correlation between the maximal diameter and aortic volume at baseline (r(2) = 0.55; P<0.001). The mean change in maximal diameter between studies was 0.2 ± 0.3 cm and the mean volume change was 19 ± 19 mL. However, the correlation between diameter change and volume change was modest (r(2) = 0.34; P=0.001). Most patients (n = 64) had no measurable change in maximal diameter between studies (≤ 2 mm), but the change in volume was found to vary widely (-2 to 69 mL). In patients with untreated infrarenal AAA, a change in aortic volume can occur in the absence of a significant change in maximal diameter. Additional work is needed to examine the relationship between change in AAA volume and outcomes in this patient group.

Complex Bilobular, Bisaccular, and Broad-Neck Microsurgical Aneurysm Formation in the Rabbit Bifurcation Model for the Study of Upcoming Endovascular Techniques

Despite rapid advances in the development of materials and techniques for endovascular intracranial aneurysm treatment, occlusion of large broad-neck aneurysms remains a challenge. Animal models featuring complex aneurysm architecture are needed to test endovascular innovations and train interventionalists. Eleven adult female New Zealand rabbits were assigned to 3 experimental groups. Complex bilobular, bisaccular, and broad-neck venous pouch aneurysms were surgically formed at an artificially created bifurcation of both CCAs. Three and 5 weeks postoperatively, the rabbits underwent 2D-DSA and CE-3D-MRA, respectively. Mortality was 0%. We observed no neurologic, respiratory, or gastrointestinal complications. The aneurysm patency rate was 91% (1 aneurysm thrombosis). There was 1 postoperative aneurysm hemorrhage (9% morbidity). The mean aneurysm volumes were 176.9 ± 63.6 mm(3), 298.6 ± 75.2 mm(3), and 183.4 ± 72.4 mm(3) in bilobular, bisaccular, and broad-neck aneurysms, respectively. The mean operation time was 245 minutes (range, 175-290 minutes). An average of 27 ± 4 interrupted sutures (range, 21-32) were needed to create the aneurysms. This study demonstrates the feasibility of creating complex venous pouch bifurcation aneurysms in the rabbit with low morbidity, mortality, and high short-term aneurysm patency. The necks, domes, and volumes of the bilobular, bisaccular, and broad-neck aneurysms created are larger than those previously described. These new complex aneurysm formations are a promising tool for in vivo animal testing of new endovascular devices.

Analysis of aneurysm rupture in relation to the geometric indices: aspect ratio, volume, and volume-to-neck ratio

Geometric indices of cerebral aneurysms have been widely studied to determine rupture risk. However, most of these parameters were evaluated based on two-dimensional (2D) images and could have a measurement bias. We propose a new three-dimensional geometric index, an aneurysm volume-to-neck area ratio (VNR). To determine whether the VNR of ruptured aneurysms is different from that of unruptured aneurysms, we compared VNR with other 2D geometric indices in discriminative capacity for aneurysm rupture status. Two hundred fourteen aneurysms in 195 patients (mean age, 57.44 ± 11.21 years; males, 69; females, 126) were retrospectively evaluated. There were 105 ruptured and 109 unruptured aneurysms. The five geometric indices [aspect ratio (AR), bottleneck ratio (BR), height-width ratio (HWR), volume, and VNR] were calculated from angiographic data and assessed to determine correlation with aneurysm rupture (t test). Receiver operating characteristic (ROC) curve analysis was used for comparison of discriminative capacity between different indices. AR, BR, HWR, and VNR were correlated with rupture status. Areas under the ROC curve of the aspect ratio and VNR were significantly larger than that of the HWR, BR, and volume. However, AR and VNR did not show a significant difference. A larger aneurysm volume in proportion to the neck could be one of the geometric indices of aneurysms that indicate a higher rupture risk. This characteristic is represented by the aspect ratio.

Gelling process differences in reverse emulsion, in situ gelling polymeric materials for intracranial aneurysm embolization, formulated with injectable contrast agents

The use of liquid-to-solid curing materials for brain aneurysm embolization has become increasingly attractive, as liquid embolics can be delivered noninvasively and can potentially achieve a higher degree of aneurysm volume occlusion. This study was aimed at characterizing differences in the gelling process of a reverse emulsion, crosslinking polymer system formulated with different types of injectable contrast agents. The polymeric system consists of poly(propylene glycol) diacrylate (PPODA) and pentaerythritol tetrakis(3-mercaptopropionate) (QT). These monomers undergo Michael-type addition upon initiation by a basic, aqueous solution. Conray™ and Omnipaque™ 300, commercially available contrast agents, were pH-adjusted to basic conditions and used as initiating solutions with the PPODA-QT system. Material characteristics were identified through rheology and scanning electron microscopy (SEM). Results showed that Conray- and Omnipaque-formulated materials progress through the gelling process uniquely, evidenced by distinctly different viscosity profiles and droplet distributions. These results indicate that Conray is more miscible with the PPODA-QT organic phase. Greater solubility in the organic phase allows Conray-formulated gels to have faster and more widespread reaction initiation kinetics when Conray and Omnipaque have the same pH. Omnipaque-formulated gels require a higher pH for the material to solidify in a time frame comparable to Conray-formulated gels. This discrepancy arises because the majority of reaction initiation sites in Omnipaque-formulated gels occur at phase boundaries via hydroxide ion flux from emulsified droplets rather than from hydroxide ions that are solubilized and integrated within the PPODA-QT organic phase.

Quantification of recurrence volumes after endovascular treatment of cerebral aneurysm as surrogate endpoint for treatment stability

New coils with unproven clinical benefit enlarge the armamentarium for endovascular aneurysm treatment continuously. Large patient numbers needed to detect benefits of such new techniques prevent timely evaluation of efficacy. We propose measuring the volume of aneurysm recurrences as surrogate endpoint for coil stability. We hypothesize that this method allows detecting effects of new materials with reduced sample sizes in comparison to conventional studies with dichotomous endpoints. Institutional review board approval and informed consent were obtained. Fifty-nine patients with decreasing aneurysm size and at least two available follow-up time-of-flight magnetic resonance angiographies (ToF-MRAs) were included. Newly developed software for measuring aneurysm volume differences based on ToF-MRA images was used. Based on the observed recurrence volumes and retreatment rates, the sample size for future studies comparing standard versus "new coils" were calculated. Mean recurrence volume was 38.92μl (SD110.85μl). To show a 50% reduction of retreatment rate to control (p = 0.05; power 80%) in a regular study (dichotomous endpoint), the required sample size would be n = 356 compared with n = 78 if using the continuous surrogate endpoint "recurrence volume". When extrapolating our data to data given in the literature, sample sizes could be reduced from n = 948 to n = 74 without loss of statistical power. Further studies on new materials using volumetric analysis based on ToF-MRA as surrogate endpoint could substantially decrease sample size and allow a more timely assessment of possible benefit of new materials with a fraction of the cost.