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Purpose Artificial intelligence in computer vision has been increasingly adapted in clinical application since the implementation of neural networks, potentially providing incremental information beyond the mere detection of pathology. As its algorithmic approach propagates input variation, neural networks could be used to identify and evaluate relevant image features. In this study, we introduce a basic dataset structure and demonstrate a pertaining use case. Methods A multidimensional classification of ankle x-rays (n = 1493) rating a variety of features including fracture certainty was used to confirm its usability for separating input variations. We trained a customized neural network on the task of fracture detection using a state-of-the-art preprocessing and training protocol. By grouping the radiographs into subsets according to their image features, the influence of selected features on model performance was evaluated via selective training. Results The models trained on our dataset outperformed most comparable models of current literature with an ROC AUC of 0.943. Excluding ankle x-rays with signs of surgery improved fracture classification performance (AUC 0.955), while limiting the training set to only healthy ankles with and without fracture had no consistent effect. Conclusion Using multiclass datasets and comparing model performance, we were able to demonstrate signs of surgery as a confounding factor, which, following elimination, improved our model. Also eliminating pathologies other than fracture in contrast had no effect on model performance, suggesting a beneficial influence of feature variability for robust model training. Thus, multiclass datasets allow for evaluation of distinct image features, deepening our understanding of pathology imaging.

Background Intraoperative incorporation of radiopaque fiducial markers at the tumor resection surface can provide useful assistance in identifying the tumor bed in postoperative imaging for RT planning and radiological follow-up. Besides titanium clips, iodine containing injectable liquid fiducial markers represent an option that has emerged more recently for this purpose. In this study, marking oral soft tissue resection surfaces, applying low dose injections of a novel Conformité Européenne (CE)-marked liquid fiducial marker based on sucrose acetoisobutyrate (SAIB) and iodinated SAIB (x-SAIB) was investigated. Methods Visibility and discriminability of low dose injections of SAIB/x-SAIB (10 µl, 20 µl, 30 µl) were systematically studied at different kV settings used in clinical routine in an ex-vivo porcine mandible model. Transferability of the preclinical results into the clinical setting and applicability of DE-CT were investigated in initial patients. Results Markers created by injection volumes as low as 10 µl were visible in CT imaging at all kV settings applied in clinical routine (70–120 kV). An injection volume of 30 µl allowed differentiation from an injection volume of 10 µl. In a total of 118 injections performed in two head and neck cancer patients, markers were clearly visible in 83% and 86% of injections. DE-CT allowed for differentiation between SAIB/x-SAIB markers and other hyperdense structures. Conclusions Injection of low doses of SAIB/x-SAIB was found to be a feasible approach to mark oral soft tissue resection surfaces, with injection volumes as low as 10 µl found to be visible at all kV settings applied in clinical routine. With the application of SAIB/x-SAIB reported for tumors of different organs already, mostly applying relatively large volumes for IGRT, this study adds information on the applicability of low dose injections to facilitate identification of the tumor bed in postoperative CT and on performance of the marker at different kV settings used in clinical routine.

BACKGROUND AND AIMS Chronic kidney disease (CKD) affects around 10% of adults worldwide and an estimated 13–17% in Germany1. Imaging is a novel, promising approach to identify additional markers of kidney function and CKD2. Within a large, population-based cohort study, the German National Cohort study (NAKO/GNC), 30 000 participants underwent a whole-body MRI protocol3. The goal of our project was to develop an automated kidney segmentation workflow and to examine distributions of the segmented kidneys and kidney sub-compartments. METHOD Data from the first 11 207 participants were used to develop a robust image processing pipeline for kidney segmentation and apply it to participants’ abdominal MRI images. After importing 3D gradient echo and 2D haste images into the imaging platform NORA (www.nora-imaging.org), an in-house ‘patchwork’-framework (https://bitbucket.org/reisert/patchwork) based on deep-learning convolutional neural networks was trained on data from 300 persons to automatically segment different kidney compartments (cortex, hilus, medulla and cysts). After an initial training round, the model was improved over four iterations by a loop of prediction, manual correction and retraining. The final model was then applied to the full dataset of 11 207 abdominal MR images, followed by manual quality control prior to statistical analysis. Volumetric parameters for total kidney volume [TKV, defined as cortex + medulla] and compartments were calculated from the segmentations. Values were calculated in absolute units of mL and normalized to body-surface-area (BSA) defined as sqrt(weight in kg*height in cm)/3600. RESULTS TKV and the kidney compartments cortex, medulla and hilus could be segmented robustly with the trained network (Fig. 1A). After exclusion of approximately 10% of images because of insufficient segmentation quality due to initial imaging artifacts or poor image quality, the mean (SD) TKV was 364 (±60) mL for men and 290 (±51) mL for women. This difference was markedly attenuated after normalisation to BSA (Fig. 1B). The right kidney was systematically smaller than the left kidney by approximately 5% (Fig. 1C). There was a strong association between participants’ BSA with TKV (Fig. 1D). The normalized kidney sub-compartment volumes showed different patterns across age, with medullary volume decreasing and hilus increasing (Fig. 2). CONCLUSION The developed framework enables robust segmentation of kidneys in abdominal MRI data from a nonspecific clinical routine protocol of a large cohort study. Basic parameters such as TKV and sub-compartment volumes of the kidney show correlations with participants’ height, weight, sex and age that are consistent with prior knowledge and may enable an estimation of ‘kidney age’. This is an optimal starting point to identify more advanced imaging biomarkers of kidney function and CKD.

Cannulas with multi-staged side holes are the method of choice for femoral cannulation in extracorporeal therapies today. A variety of differently designed products is available on the market. While the preferred tool for the performance assessment of such cannulas are pressure-flow curves, little is known about the flow and velocity distribution. Within this work flow and velocity patterns of a femoral venous cannula with multi-staged side holes were investigated. A mock circulation loop for cannula performance evaluation was built and reproduced using a computer-aided design system. With computational fluid dynamics, volume flows and fluid velocities were determined quantitatively and visually with hole-based precision. In order to ensure the correctness of the flow simulation, the results were subsequently validated by determining the same parameters with four-dimensional flow-sensitive magnetic resonance imaging. Measurement data and numerical solution differed 7% on average throughout the data set for the examined parameters. The highest inflow and velocity were detected at the most proximal holes, where half of the total volume flow enters the cannula. At every hole stage a Y-shaped inflow profile was detected, forming a centered stream in the middle of the cannula. Simultaneously, flow separation creates zones with significant lower flow velocities. Numerical simulation, validated with four-dimensional flow-sensitive magnetic resonance imaging, is a valuable tool to examine flow and velocity distributions of femoral venous cannulas with hole-based accuracy. Flow and velocity distribution in such cannulas are not ideal. Based on this work future cannulas can be effectively optimized.

Objective To evaluate a novel liquid fiducial marker for intraoperative marking of the tumour resection surface in oral cancer patients to facilitate precise postoperative delineation of the interface between the tumour resection border and reconstructed tissue for intensity-modulated radiation therapy. Methods A total of 200 markers were created by injecting the volumes of 10 µl, 20 µl, 30 µl, 40 µl and 50 µl of a liquid marker composed of sucrose acetoisobutyrate (SAIB) and iodinated sucrose acetoisobutyrate (x-SAIB) into the soft tissue of porcine mandible segments. Visibility of the resulting markers was quantified by threshold-based segmentation of the marker volume in CT- and CBCT imaging and by a comparison of signal intensities in MRI. Results Even the lowest volume of SAIB-/x-SAIB investigated (10 µl) resulted in a higher visibility (CTSoft tissue: 88.18 ± 13.23 µl; CTBone: 49.55 ± 7.62 µl; CBCT: 54.65 ± 12.58 µl) than observed with the incorporation of titanium ligature clips (CTSoft tissue: 50.15 ± 7.50 mm3; CTBone: 23.90 ± 3.39 mm3; CBCT: 33.80 ± 9.20 mm3). Markers created by the injection of 10 µl and 20 µl could reliably be delineated from markers created by the injection of higher volumes. Conclusion SAIB/x-SAIB, which has recently become available as a Conformité Européenne (CE)-marked fiducial marker, provides an option for fast and reliable production of markers with excellent visibility in imaging modalities used in oral cancer radiation therapy (RT) planning routine.

A 58-year-old man with progressive dyspnea and recurrent extensive left-sided pleural effusion underwent pulmonary ventilation/perfusion SPECT/CT, which showed a pronounced mismatched perfusion deficit of the entire, normally ventilated left lung. As unilateral perfusion deficits of an entire lobe are generally not due to pulmonary embolism, further CT angiography and cardiac MRI were conducted. These examinations revealed high-grade left pulmonary vein stenosis (PVS) caused by pulmonary vein isolation performed for atrial fibrillation 3 and 4 years earlier. Thus, in addition to, for example, neoplastic processes or pulmonary congenital vascular abnormalities, PVS must be considered as a differential diagnosis and possible pitfall in ventilation/perfusion SPECT/CT in dyspneic patients with prior pulmonary vein isolation.

The development and successful implementation of cutting-edge imaging technologies to visualise cardiac anatomy and function is a key component of effective diagnostic efforts in cardiology. Here, we describe a number of recent exciting advances in the field of cardiology spanning from macro- to micro- to nano-scales of observation, including magnetic resonance imaging, computed tomography, optical mapping, photoacoustic imaging, and electron tomography. The methodologies discussed are currently making the transition from scientific research to routine clinical use, albeit at different paces. We discuss the most likely trajectory of this transition into clinical research and standard diagnostics, and highlight the key challenges and opportunities associated with each of the methodologies.

The impact of specific blood flow patterns within ascending aortic and/or aortic root aneurysms on aortic morphology is unknown. We investigated the interrelation of ascending aortic flow compression/peripheralization and aneurysm morphology with respect to sinotubuar junction (STJ) definition.Thirty-one patients (aortic root/ascending aortic aneurysm45 mm) underwent flow-sensitive 4D magnetic resonance thoracic aortic flow measurement at 3 Tesla (Siemens, Germany) at two different institutions (Freiburg, Germany, and San Francisco, CA, USA). Time-resolved image data post-processing and visualization of mid-systolic, mid-ascending aortic flow were performed using local vector fields. The Flow Compression Index (FCI) was calculated individually as a fraction of the area of high-velocity mid-systolic flow over the complete cross-sectional ascending aortic area. According to aortic aneurysm morphology, patients were grouped as (i) small root, eccentric ascending aortic aneurysm (STJ definition) and (ii) enlarged aortic root, non-eccentric ascending aortic aneurysm with diffuse root and tubular enlargement.The mean FCI over all patients was 0.47 ± 0.5 (0.37-0.99). High levels of flow compression/peripheralization (FCI0.6) were linked to eccentric aneurysm morphology (Group A, n = 11), while low levels or absence of aortic flow compression/peripheralization (FCI0.8) occurred more often in Group B (n = 20). The FCI was 0.48 ± 0.05 in Group A and 0.78 ± 0.14 in Group B (P0.001). Distribution of bicuspid aortic valve (P = 0.6) and type of valve dysfunction (P = 0.22 for aortic stenosis) was not found to be different between groups.Irrespective of aortic valve morphology and function, ascending aortic blood flow patterns are linked to distinct patterns of ascending aortic aneurysm morphology. Implementation of quantitative local blood flow analyses might help to improve aneurysm risk stratification in the future.

Purpose Cardiovascular diseases remain the number one death cause worldwide. Preclinical 4D flow phase contrast magnetic resonance imaging can provide substantial insights in the analysis of aortic pathophysiologies in various animal models. These insights may allow a better understanding of pathophysiologies, therapy monitoring, and can possibly be translated to humans. This study provides a framework to acquire the velocity field within the aortic arch. It analyses important flow values at different locations within the aortic arch. Imaging parameters with high temporal and spatial resolution are provided, that still allow combining this time-consuming method with other necessary imaging-protocols. Methods A new setup was established where a prospectively gated 4D phase contrast sequence is combined with a highly sensitive cryogenic coil on a preclinical magnetic resonance scanner. The sequence was redesigned to maintain a close to steady state condition of the longitudinal magnetization and hence to overcome steady state artifacts. Imaging parameters were optimized to provide high spatial and temporal resolution. Pathline visualizations were generated from the acquired velocity data in order to display complex flow patterns. Results Our setup allows data acquisition with at least two times the rate than that of previous publications based on Cartesian encoding, at an improved image quality. The "steady state" sequence reduces observed artifacts and provides uniform image intensity over the heart cycle. This made possible quantification of blood speed and wall shear stress (WSS) within the aorta and its branches. The highest velocities were observed in the ascending aorta with 137.5 ± 8 cm/s. Peak velocity values in the Brachiocephalic trunk were 57 ± 12 cm/s. Quantification showed that the peak flow occurs around 20 ms post R-wave in the ascending aorta. The highest mean axial wall shear stress was observed in the analysis plane between the left common carotid artery (LCCA) and the left subclavian artery. A stable image quality allows visualizing complex flow patterns by means of streamlines and for the first time, to the best of our knowledge, pathline visualizations from 4D flow MRI in mice. Conclusion The described setup allows analyzing pathophysiologies in mouse models of cardiovascular diseases in the aorta and its branches with better image quality and higher spatial and temporal resolution than previous Cartesian publications. Pathlines provide an advanced analysis of complex flow patterns in the murine aorta. An imaging protocol is provided that offers the possibility to acquire the aortic arch at sufficiently high resolution in less than one hour. This allows the combination of the flow assessment with other multifunctional imaging protocols.

Technical variations of the David reimplantation valve-sparing aortic root replacement (V-SARR) procedure have been proposed to be advantageous in patients with connective tissue disease, such as the Marfan syndrome (MFS). We report results of a Marfan cohort treated exclusively with the non-modified David I procedure.Forty-eight Marfan patients (25 males, mean age 33 ± 12 years, range 15-62 years) underwent the original variant of the David V-SARR (David I) between 1997 and 2013. Forty-two operations (88%) were performed as elective procedures for aortic root aneurysms and six for acute dissections (12%). Seventeen had aortic regurgitation (AR) grades ≥2+ preoperatively, and 3 had AR2+. No patients with severe AR (4+) were selected for V-SARR. Three full or hemi-arch replacements were performed. Patients who were operated on using a variation of the David I or David II procedure were excluded.Mean prosthesis size was 28 ± 3 mm (18-30 mm). Mean clinical and echocardiographic follow-up (98% complete) was 3.8 ± 3.7 years with a cumulative follow-up of 178 patient-years. The early mortality rate was 2% (one hospital death). The survival rate was 98% (95% confidence 84-99%) at 4 years and 90% (57-98%) at 8 years with 5 patients at risk at 10 years. The rate of freedom from root or valve reoperation was 97% (79-99%) and 97% (79-99%) at 4 and 8 years, respectively. Only one patient required mechanical aortic valve replacement for progression of AR.Despite potential theoretical drawbacks of the David I V-SARR technique without neo-sinuses or a neo-sinotubular junction, it results in a favourable mid-term outcome in Marfan patients and compares well with reported results of different modifications of David V-SARR.

Purpose To evaluate influence of variation in spatio-temporal resolution and scan-rescan reproducibility on three-dimensional (3D) visualization and quantification of arterial and portal venous (PV) liver hemodynamics at four-dimensional (4D) flow MRI. Methods Scan-rescan reproducibility of 3D hemodynamic analysis of the liver was evaluated in 10 healthy volunteers using 4D flow MRI at 3T with three different spatio-temporal resolutions (2.4 × 2.0 × 2.4 mm3, 61.2 ms; 2.5 × 2.0 × 2.4 mm3, 81.6 ms; 2.6 × 2.5 × 2.6 mm3, 80 ms) and thus different total scan times. Qualitative flow analysis used 3D streamlines and time-resolved particle traces. Quantitative evaluation was based on maximum and mean velocities, flow volume, and vessel lumen area in the hepatic arterial and PV systems. Results 4D flow MRI showed good interobserver variability for assessment of arterial and PV liver hemodynamics. 3D flow visualization revealed limitations for the left intrahepatic PV branch. Lower spatio-temporal resolution resulted in underestimation of arterial velocities (mean 15%, P < 0.05). For the PV system, hemodynamic analyses showed significant differences in the velocities for intrahepatic portal vein vessels (P < 0.05). Scan-rescan reproducibility was good except for flow volumes in the arterial system. Conclusion 4D flow MRI for assessment of liver hemodynamics can be performed with low interobserver variability and good reproducibility. Higher spatio-temporal resolution is necessary for complete assessment of the hepatic blood flow required for clinical applications. Magn Reson Med 72:477–484, 2014. © 2013 Wiley Periodicals, Inc.

To evaluate the feasibility of time-resolved flow-sensitive four-dimensional (4D) MRI for the visualization and quantification of splanchnic arterial and portal venous hemodynamics in patients with cirrhosis and in controls.We applied flow-sensitive 4D MRI to evaluate arterial and portal venous three-dimensional blood flow in patients with advanced liver cirrhosis (n=5) and in healthy controls (n=10) using 3T MRI (spatial resolution=1.7×2.1×2.4 mm, temporal resolution=62.4 ms). The qualitative flow was analyzed using three-dimensional streamlines and time-resolved particle traces. Retrospective flow was quantified in nine predefined anatomic regions evaluating maximum and mean velocities, the flow volume, the vessel lumen area, pulsatility indices, and resistance indices. Doppler ultrasound (US) was our reference standard.Flow-sensitive 4D MRI visualized liver hemodynamics successfully in 91% of patients and 96% of volunteers with limitations for the patients' extrahepatic vessels (one case of splenic and superior mesenteric veins each) and intrahepatic portal vein branches (in five vessels). Healthy control individuals revealed reduced velocities and larger vessel areas in MRI than in Doppler US. We found no significant differences in the flow volume, pulsatility indices, and resistance indices on comparing MRI with US. Regional flow quantification within the splanchnic system of healthy volunteers and liver cirrhosis patients revealed an increase in the inflow (up to 65%), but a decrease in the patients' outflow (up to 37%).Flow-sensitive 4D MRI is feasible for profound evaluation of arterial and portal venous hemodynamics in liver cirrhosis patients, providing additional information on the pathophysiology of the altered splanchnic system.

Purpose To evaluate spatiotemporal parallel imaging with R = 5 in comparison to conventional parallel imaging with R = 2 applied to phase contrast (PC) magnetic resonance imaging (MRI). This was motivated by the fact that scan times for PC imaging often exceed breath-hold capabilities of patients even with standard parallel imaging using typical reduction factors of R = 2. Materials and Methods K-t generalized autocalibrating partially parallel acquisition (GRAPPA) acquisition was validated in phantom measurements and then applied in 10 volunteer and three patient examinations. Due to the higher reduction factor compared to conventional GRAPPA, k-t GRAPPA measurements could be performed during breath-hold with high spatial and temporal resolution. K-t GRAPPA scans were compared to GRAPPA acquired during free-breathing with navigator respiration control. In addition, spatiotemporally accelerated PC imaging was acquired during free-breathing for comparison of k-t-accelerated breath-held scans. Results Substantial improvements in image quality for the breath-hold measurements were observed. Significantly reduced peak velocities were found for the GRAPPA protocol compared to the k-t-accelerated breath-hold scans for both flow (8%) and myocardial motion (up to 30%) measurements. Conclusion Spatiotemporal acceleration allows the performance of high temporal or spatial resolution PC imaging during breath-hold while providing high image quality and robust acquisition of functional information that cannot be achieved during breath-hold with standard techniques. J. Magn. Reson. Imaging 2013;38:1054–1062. © 2013 Wiley Periodicals, Inc.

OBJECTIVES: Left ventricular assist devices (LVADs) have become an important treatment option for heart failure patients. However, altered blood flow patterns are suspected to affect perfusion in the aorta or cause structural changes to the aortic root, leading to regurgitation and valve dysfunction or thrombus formation. The purpose of this study was to evaluate flow patterns in a realistic in vitro model system using four-dimensional flow-sensitive magnetic resonance imaging. METHODS: A magnetic resonance compatible model system was developed consisting of an aorta connected to a VAD simulating the pulsatile flow of the native heart. An LVAD was connected to the aorta model via three different cannula positions. Flow patterns in the entire system as well as flow rates in predefined positions for reduced and zero cardiac output were evaluated. RESULTS: Cannula position influences flow patterns and flow rates in the entire thoracic aorta. For a residual cardiac output, a larger anastomosis and a decreased flow rate of the LAVD result in a higher flow rate and smaller retrograde flow in the ascending aorta when compared with a smaller anastomosis or a cannula position in the descending aorta. Pronounced flow turbulences in the aorta were observed for the cannula position in the descending aorta. CONCLUSIONS: In the setting of reduced cardiac output, as commonly observed in patients on LVAD therapy, a large anastomosis to the ascending aorta for the outflow cannula induces the least-adverse flow patterns in the aortic root. Our approach may aid in a better understanding of LVAD-induced flow-pattern changes. Optimization of the cannula position and anastomosis may help to prevent the progression of aortic valve-regurgitation and thrombus formation.

OBJECTIVES :C on flicting results have been reported on late aortic growth and complication rates of the descending thoracic aorta in patients with Marfan syndrome (MFS) after proximal aortic surgery. METHODS: Of 198 Marfan patients followed up regularly, 121 (43% David-I, 7% David-II, 11% supracoronary replacement, 52% mechanical conduit, 8% arch replacement) were analysed after proximal aortic surgery retrospectively. 97% had MFS1, 3% MFS2 (Loeys-Dietz-Syndrome); 56% were male and the mean age was 35 ± 13 years. 65% were initially operated on for root/ascending aortic aneurysm and 35% for aortic dissections. Using automated computed tomography angiography and magnetic resonance angiography cross-sectional analyses, the mean diameters of the distal arch, mid-descending and distal supradiaphragmatic descending thoracic aorta were measured at early and late follow-up (mean 6.3 years for aneurysms and 4.7 years for dissections). The mean duration of clinical follow-up was 7.6 years and the cumulative clinical follow-up comprised 894 patient-years. RESULTS: At 20 years, overall freedom from distal aortic complications and/or reintervention was 76% (51–86%) for aneurysms and 52% (28–71%) for dissections (P= 0.03). In non-dissected aortas, distal aortic growth was significant, but minimal: arches grew from 25.2 ± 0.6 to 26.3 ± 0.8 mm (P= 0.01), mid-descending aortas from 22.2 ± 0.5 to 24.9 ± 1.2 mm (P= 0.05) and distal descending aortas from 22.1 ± 0.7 to 24.2 ± 1.4 (P= 0.02, 0.58 mm/year ± 0.5 mm). Dissected distal aortas increased by a mean of 0.3 ± 0.5 mm/year. Dissection (P< 0.001), urgent procedure (P= 0.02) and hypertension (0.052) were associated with larger distal aortic diameters at late follow-up and more significant aortic growth over time. CONCLUSIONS: Late distal complication rates are low for patients initially presenting with aneurysms. The risk of late distal reoperation is dictated by the initial pathology and by the presence of an initial dissection and not by faster distal aortic growth. Strategies to completely restore a non-dissected anatomy might improve late surgical outcome in Marfan’s syndrome.

It was the aim to analyse the impact of age, aortic arch geometry, and size on secondary flow patterns such as helix and vortex flow derived from flow-sensitive magnetic resonance imaging (4D PC-MRI). 62 subjects (age range = 20–80 years) without circumscribed pathologies of the thoracic aorta (ascending aortic (AAo) diameter: 3.2 ± 0.6 cm [range 2.2–5.1]) were examined by 4D PC-MRI after IRB-approval and written informed consent. Blood flow visualisation based on streamlines and time-resolved 3D particle traces was performed. Aortic diameter, shape (gothic, crook-shaped, cubic), angle, and age were correlated with existence and extent of secondary flow patterns (helicity, vortices); statistical modelling was performed. Helical flow was the typical pattern in standard crook-shaped aortic arches. With altered shapes and increasing age, helicity was less common. AAo diameter and age had the highest correlation (r = 0.69 and 0.68, respectively) with number of detected vortices. None of the other arch geometric or demographic variables (for all, P ≥ 0.177) improved statistical modelling. Substantially different secondary flow patterns can be observed in the normal thoracic aorta. Age and the AAo diameter were the parameters correlating best with presence and amount of vortices. Findings underline the importance of age- and geometry-matched control groups for haemodynamic studies. • Secondary blood flow patterns (helices, vortices) are commonly observed in the aorta • Secondary flow patterns predominantly depend on patient age and aortic diameter • Geometric factors show a lesser impact on blood flow patterns than age and diameter • Future analyses of flow patterns should incorporate age- and diameter dependencies

Purpose To assess the distribution and regional differences of flow and vessel wall parameters such as wall shear stress (WSS) and oscillatory shear index (OSI) in the entire thoracic aorta. Materials and Methods Thirty-one healthy volunteers (mean age = 23.7 ± 3.3 years) were examined by flow-sensitive four-dimensional (4D)-MRI at 3T. For eight retrospectively positioned 2D analysis planes distributed along the thoracic aorta, flow parameters and vectorial WSS and OSI were assessed in 12 segments along the vascular circumference. Results Mean absolute time-averaged WSS ranged between 0.25 ± 0.04 N/m2 and 0.33 ± 0.07 N/m2 and incorporated a substantial circumferential component (–0.05 ± 0.04 to 0.07 ± 0.02 N/m2). For each analysis plane, a segment with lowest absolute WSS and highest OSI was identified which differed significantly from mean values within the plane (P < 0.05). The distribution of atherogenic low WSS and high OSI closely resembled typical locations of atherosclerotic lesions at the inner aortic curvature and supraaortic branches. Conclusion The normal distribution of vectorial WSS and OSI in the entire thoracic aorta derived from flow-sensitive 4D-MRI data provides a reference constituting an important perquisite for the examination of patients with aortic disease. Marked regional differences in absolute WSS and OSI may help explaining why atherosclerotic lesions predominantly develop and progress at specific locations in the aorta. J. Magn. Reson. Imaging 2009;30:77–84. © 2009 Wiley-Liss, Inc.

Modern phase contrast MR imaging at 3 Tesla allows the depiction of 3D morphology as well as the acquisition of time-resolved blood flow velocities in 3 directions. In combination with state-of-the-art visualization and data processing software, the qualitative and quantitative analysis of hemodynamic changes associated with vascular pathologies is possible. The 4D nature of the acquired data permits free orientation within the vascular system of interest and offers the opportunity to quantify blood flow and derived vessel wall parameters at any desired location within the data volume without being dependent on predefined 2D slices. The technique has the potential of overcoming the limitations of current diagnostic strategies and of implementing new diagnostic parameters. In light of the recent discussions regarding the influence of the wall shear stress and the oscillatory shear index on the genesis of arteriosclerosis and dilatative vascular processes, flow-sensitive 4D MRI may provide the missing diagnostic link. Instead of relying on experience-based parameters such as aneurysm size, new hemodynamic considerations can deepen our understanding of vascular pathologies. This overview reviews the underlying methodology at 3T, the literature on time-resolved 3D MR velocity mapping, and presents case examples. By presenting the pre- and postoperative assessment of hemodynamics in a thoracic aortic aneurysm and the detailed analysis of blood flow in a patient with coarctation we underline the potential of time-resolved 3D phase contrast MR at 3T for hemodynamic assessment of vascular pathologies, especially in the thoracic aorta.

The anatomy of the aorta changes in the course of life. Up to the age of 15, its diameter and length increase relatively swiftly. It continues to grow in adulthood: the diameter of the ascending aorta is 20 to 30% greater in 70-year-olds than in 20-year-olds (1). Rapid growth of the aorta—usually segmental—causes an aneurysm. Three quarters of all aneurysms occur in the abdominal aorta. The annual incidence of abdominal aortic aneurysm (diameter >3.0 cm) is 40 in every 100 000 population. Six times more men than women are affected (2– 4). Intervention is required (aneurysmal diameter >5.0 cm) in 10% of patients with a diagnosed abdominal aortic aneurysm (3). In up to 55% of these persons the aneurysm is not amenable to insertion of a conventional tube graft or Y-graft (5). The annual incidence of thoracic aneurysm is 10–15 per 100 000 (6, 7). Men are 1.8 times more frequently affected than women. No population studies of the incidence of thoracic abdominal aneurysm have been published. The pathological aorta can be treated surgically or via the endovascular route. One crucial advantage of the endovascular approach is the minimally invasive access with relatively low strain on the cardiovascular system and thus lower perioperative mortality. In a total of 22 830 patients, mortality was 1.2% for endovascular treatment and 4.8% for open surgery (8, 9). Not every affected aorta is amenable to insertion of a thoracic tube stent graft or infrarenal Y-stent graft. In patients with a juxtarenal or thoracoabdominal aneurysm there is no proximal or distal zone for anchorage (landing zone) and therefore conventional tube and Y-grafts cannot be safely attached. These patients therefore often undergo open surgery. Relatively young and otherwise healthy patients recover comparatively quickly from an open thoracic, thoracoabdominal, or abdominal intervention. However, patients with vascular disease are usually of advanced age and not uncommonly have numerous comorbidities. One of the endovascular treatment options in such cases is the chimney technique. Chimney grafts are placed in the visceral vessels so that their aortic segments lie parallel to the aortic stent graft. However, use of this technique is limited by the elevated risk of leakage between the chimney graft, the aortic stent graft, and the aorta (10, 11). The very first implantation of a stent graft into the thoracic aorta was performed by Volodos in 1987 (12). The first such interventions in Germany—in centers including Freiburg (13)—were carried out in 1995. There have been rapid developments in stent grafts, pre- and intraoperative diagnostic procedures, endovascular instrumentation, catheter techniques, and many other relevant areas. Preoperative diagnostic, high-resolution computed tomography, three-dimensional (3-D) reconstruction of the aorta, preoperative simulation of the intraoperative angiographic visualization, the possibility of treatment in hybrid operating suites, and printing of 3-D models all help in planning the intervention and now form part of standard management. Hydrophilic coating and reduced diameter of the insertion port permit access via distinctly sclerosed vessels. The first fenestrated endovascular aneurysm repair (fEVAR) was carried out by Park in 1996 (14). Fenestrated (Figures 1a ​,, ​,2)2) and branched stent grafts (bEVAR) (Figure 1b) were developed for treatment of patients with juxtarenal, perirenal, or thoracoabdominal aneurysms. Now, with the sole exceptions of the aortic root and the proximal ascending aorta, all segments of the aorta are amenable to endovascular treatment with standard stent grafts. Figure 1 Stent grafts Figure 2 Treatment of a juxtarenal abdominal aortic aneurysm with a fenestrated stent graft

Background Reoperations on the aortic root and distal thoracic aorta late after initial root surgery in patients with Marfan syndrome might carry high periprocedural risks and be associated with adverse early and midterm clinical outcome. Methods Overall clinical follow-up was 13.0 ± 7.6 years and 3.7 ± 3 years after secondary aortic procedures. Cumulative follow-up was a total of 148 patient-years. Kaplan-Meier, log-rank, and multiple logistic regression calculations were performed to identify risk factors for mortality. Results Of 122 patients with Marfan syndrome who underwent aortic root surgery from 1998 to 2013, 40 (21 men; age, 33 ± 12 years) underwent subsequent open thoracic aortic or endovascular secondary procedures between 1998 and 2013. Initial aortic root procedures were performed for aneurysmal disease (n = 16, 40%) or acute or subacute Stanford type A dissection (n = 24, 60%). Secondary interventions were performed on the aortic arch or descending thoracic or thoracoabdominal aorta (n = 18, 45%; n = 8 stent grafts) and aortic valve, root, or ascending aorta (n = 22, 60%) 9.3 ± 6.7 years (range, 0.06 to 24 years) after initial root surgery. Survival at 5 and 10 years after secondary aortic surgery was 80% (range, 65% to 90%) and 66% (range, 35% to 85%), respectively (n = 13 and n = 5 remaining at risk at 5 and 10 years). No difference between stent graft and conventional procedures was detected ( p = 0.756). Actuarial freedom from stroke was 89% at 5 and 10 years (range, 69% to 96%; stent graft versus no stent graft log-rank p = 0.47). Four patients had tertiary aortic procedures. The presence of a chronic dissection or root or valve disease was not associated with adverse outcomes after secondary procedures. The only strong predictor of mortality after reoperations was acute dissection at the time of the initial treatment. Conclusions Aortic reoperations in patients with Marfan syndrome can be performed with acceptable midterm outcomes. Performed as a bailout procedure, stent grafting was not associated with increased mortality. The only strong predictor of mortality after reoperations is acute dissection at the time of the initial treatment.

To evaluate spatiotemporal parallel imaging with R = 5 in comparison to conventional parallel imaging with R = 2 applied to phase contrast (PC) magnetic resonance imaging (MRI). This was motivated by the fact that scan times for PC imaging often exceed breath-hold capabilities of patients even with standard parallel imaging using typical reduction factors of R = 2.K-t generalized autocalibrating partially parallel acquisition (GRAPPA) acquisition was validated in phantom measurements and then applied in 10 volunteer and three patient examinations. Due to the higher reduction factor compared to conventional GRAPPA, k-t GRAPPA measurements could be performed during breath-hold with high spatial and temporal resolution. K-t GRAPPA scans were compared to GRAPPA acquired during free-breathing with navigator respiration control. In addition, spatiotemporally accelerated PC imaging was acquired during free-breathing for comparison of k-t-accelerated breath-held scans.Substantial improvements in image quality for the breath-hold measurements were observed. Significantly reduced peak velocities were found for the GRAPPA protocol compared to the k-t-accelerated breath-hold scans for both flow (8%) and myocardial motion (up to 30%) measurements.Spatiotemporal acceleration allows the performance of high temporal or spatial resolution PC imaging during breath-hold while providing high image quality and robust acquisition of functional information that cannot be achieved during breath-hold with standard techniques.

Background Continuous blood flow from left ventricular assist devices (LVAD) has become an important treatment option for heart failure patients. However, recent reports indicate that the complex geometric alterations of the vascular system associated with LVAD implantation as well as the introduction of constant flow into the aorta may alter blood flow patterns. These can potentially affect perfusion patterns to the supra-aortic vessels or cause structural changes to the aortic root leading to regurgitation and valve dysfunction. The purpose of this study was to evaluate the feasibility of flow-sensitive 4D MRI for the investigation of such blood flow alterations in an in-vitro model simulating 3D blood in a physiological model of the left ventricle, aortic valve and aorta.

Purpose: To evaluate the feasibility of time-resolved flow-sensitive MRI for the three-dimensional (3D) visualization and quantification of normal and pathological portal venous (PV) hemodynamics. Materials and Methods: Portal venous hemodynamics were evaluated in 18 healthy volunteers and 5 patients with liver cirrhosis. ECG- and adaptive respiratory navigator gated flow-sensitive 4D MRI (time-resolved 3D MRI with three-directional velocity encoding) was performed on a 3 Tesla MR system (TRIO, Siemens, Germany). Qualitative flow analysis was achieved using 3D streamlines and time-resolved particle traces originating from seven emitter planes precisely placed at anatomical landmarks in the PV system. Quantitative analysis included retrospective extraction of regional peak and mean velocities and vessel area. Results were compared with standard 2D flow-sensitive MRI and to the reference standard Doppler ultrasound. Results: Qualitative flow analysis was successfully used in the entire PV system. Venous hemodynamics in all major branches in 17 of 18 volunteers and 3 of 5 patients were reliably depicted with good interobserver agreement (kappa = 0.62). Quantitative analysis revealed no significant differences and moderate agreement for peak velocities between 3D MR and 2D MRI (r = 0.46) and Doppler ultrasound (US) (r = 0.35) and for mean velocities between 3D and 2D MRI (r = 0.41). The PV area was significantly (P < 0.01) higher in 3D and 2D MRI compared with US. Conclusion: We successfully applied 3D MR velocity mapping in the PV system, providing a detailed qualitative and quantitative analysis of normal and pathological hemodynamics. J. Magn. Reson. Imaging 2010;32:466–475. © 2010 Wiley-Liss, Inc.

Rationale and Objectives Gadofosveset trisodium is a blood-pool contrast agent (BPA) that shows a less pronounced r1 relaxivity advantage over gadobenate dimeglumine at 3T than at 1.5T. However, there are few data on image quality during first-pass imaging of the thoracic vasculature with gadofosveset trisodium at 3 T. Therefore, it was the aim of this study to compare first-pass imaging characteristics of gadofosveset trisodium to gadobenate dimeglumine during time-resolved contrast-enhanced three-dimensional magnetic resonance angiography (CE MRA) at 3 T. Materials and Methods Twenty volunteers underwent time-resolved CE MRA on a 3 T magnetic resonance (MR) system with a standard eight-channel phased-array surface coil, receiving either gadofosveset trisodium (blood pool agent [BPA], n = 10) or gadobenate dimeglumine (standard contrast agent, [SCA], n = 10). Image quality was assessed by two independent readers using a Likert scale ranging from 0 = poor quality to 3 = excellent quality, and relative signal-to-noise and contrast-to-noise ratios were calculated. Results Equally good to excellent first-pass image quality was confirmed for time-resolved CE MRA using BPA and SCA (arteries, 2.8 ± 0.2 and 2.6 ± 0.4; veins, 2.5 ± 0.3 and 2.2 ± 0.4; artifacts, 2.4 ± 0.2 and 2.3 ± 0.1). Signal-to-noise and contrast-to-noise ratios showed nonsignificant differences, except for left subclavian artery values. There was an overall nonsignificant superiority in signal-to-noise and contrast-to-noise ratios for standard contrast agent in arterial values and BPA regarding venous values. Conclusions Despite a markedly decreased r1/r2 relaxivity ratio, first-pass imaging characteristics of gadofosveset trisodium and gadobenate dimeglumine are equally well suited for first pass time-resolved CE MRA at 3 T.

Ziele: Es war das Ziel, mittels fluss-sensitiver 4D MRT und farbkodierter Visualisierung die Abhangigkeit der aortalen Hamodynamik vom Aortendurchmesser auszuwerten und nachzuweisen, dass ektatische Aorten einen deutlichen veranderten Blutfluss zeigen. Methode: Die Messungen wurden an einem 3T-Scanner (TRIO, Siemens) mit einer 8-Kanal Oberflachenspule nach Aufklarung und Einverstandnis an 62 Patienten (50,6±18,9 Jahre, 73,1±10,6kg, 25 Frauen) durchgefuhrt. Eine 3-direktional fluss-sensitive 3-dimensionale Gradientenechosequenz wurde mit den Parametern: Geschwindigkeitssensitivitat=150cm/s, Ortsauflosung=(2.71–2.93×1.58–1.69×2.60–3.0)mm3, zeitliche Auflosung=48.8ms angewendet. Die Visualisierung und Platzierung von 8 Auswerteschichten in der Aorta erfolgte mittels Ensight (CEI, USA). Ermittelt wurden: Durchmesser der Aorta ascendens (AAo), Helizitat des Fluss, Vortexbildung, -dauer und –lokalisation, Lokalisation und Zeit zum maximalen arteriellen Fluss (TTP) je positionierter Schicht und Dauer des retrograden Fluss. Als Gruppierungsmerkmal diente der Durchmesser der AAo in kleine Aortendiameter (KAD-Gruppe ≤3,5cm, MW 2,8±0,4cm) und erweiterte Diameter (EAD-Gruppe >3,5cm, MW 3,8±0,4cm) Ergebnis: Die KAD-Gruppe zeigte eine signifikant geringere Zahl an deutlich kurzer nachweisbaren Vortices (KAD=1,3±1,1; EAD 2,3±0,9; p3,5cm) signifikante Anderungen der Hamodynamik erfahren. Mit Hinblick auf das flussinduzierte arterielle Remodeling wird damit verdeutlicht, dass der Analyse der Hamodynamik bei geometrischen Veranderungen der Aorta zukunftig eine grosere Bedeutung zum therapeutischen Prozedere zukommen konnte. Korrespondierender Autor: Frydrychowicz A Universitatsklinikum Freiburg, Diagnostische Radiologie, Hugstetter Str. 55, 79106 Freiburg E-Mail: alex.frydrychowicz@uniklinik-freiburg.de