Imaging Approaches to the Diagnosis of Vascular Diseases.

PURPOSE OF REVIEW: Vascular imaging is a complex field including numerous modalities and imaging markers. This review is focused on important and recent findings in atherosclerotic carotid artery plaque imaging with an emphasis on developments in magnetic resonance imaging (MRI) and computed tomography (CT). RECENT FINDINGS: Recent evidence shows that carotid plaque characteristics and not only established measures of carotid plaque burden and stenosis are associated independently with cardiovascular outcomes. On carotid MRI, the presence of a lipid-rich necrotic core (LRNC) has been associated with incident cardiovascular disease (CVD) events independent of wall thickness, a traditional measure of plaque burden. On carotid MRI, intraplaque hemorrhage (IPH) presence has been identified as an independent predictor of stroke. The presence of a fissured carotid fibrous cap has been associated with contrast enhancement on CT angiography imaging. Carotid artery plaque characteristics have been associated with incident CVD events, and advanced plaque imaging techniques may gain additional prominence in the clinical treatment decision process.

Postprandial effects on arterial stiffness parameters in healthy young adults.

Postprandial lipemia has been associated with acute endothelial dysfunction. Endothelial dysfunction, in turn, is associated with increased arterial stiffness. However, the relationship between postprandial lipemia and acute changes in arterial stiffness has not been extensively investigated. Therefore, we conducted a pilot study on the effects of postprandial lipemia on arterial stiffness in 19 healthy young adults before and after consumption of a high-fat mixed meal. Arterial stiffness was assessed locally with echo-tracking carotid arterial strain (CAS) and globally with carotid-femoral pulse wave velocity (PWV). As assessed by these two benchmark parameters, arterial stiffness did not differ significantly postprandially. However, the arterial distension period (ADP) was significantly lower 2 hours after mixed meal ingestion. In addition, slopes of carotid artery area (CAA) curves were significantly steeper postprandially. Therefore, we concluded that ADP may be a more sensitive marker of arterial stiffness in healthy young adults when compared to PWV and CAS.

Distribution of calcification in carotid endarterectomy tissues: comparison of micro-computed tomography imaging with histology.

BACKGROUND: Calcification in atherosclerotic plaques has been viewed as a marker of plaque stability, but whether calcification accumulates in specific anatomic sites in the carotid artery is unknown. We determined the burden and distribution of calcified plaque in carotid endarterectomy (CEA) tissues. METHODS: A total of 22 CEA tissues were imaged with high-resolution micro-computed tomography (micro-CT). Total plaque burden and total calcium score using the Agatston method were quantified. The Agatston score (AS) was also normalized for tissue size. Plaque and calcium distribution were analyzed separately for three CEA regions: common segment (CS), bulb segment (BS), and internal/external segments (IES). RESULTS: The average CEA tissue length was 40.83 (interquartile range [IQR] 33.31-42.41) mm with total plaque burden of 103.45 (IQR: 78.84-156.81) mm(3) and total AS of 38.58 (IQR 11.59-89.97). Total plaque volume was 21.02 (IQR: 14.47-25.42) mm(3) in the CS, 37.89 (22.59-48.32) mm(3) in the BS, and 54.05 (36.87-74.52) mm(3) in the IES. Of the 22 tissues, 15 had no calcium in the CS compared with three in the bulb and two in the IES. Normalized calcified plaque was most prevalent in the BS, the IES and was least prevalent in the CS. The overall correlation of calcification between histology sections and matched micro-CT images was 0.86 (p<0.001). CONCLUSIONS: Calcified plaque is heterogeneously distributed in CEA tissues with most in the bulb and IES regions. The amount of calcification in micro-CT slices shows a high correlation with matched histology sections.

Convolutional Neural Networks to Study Contrast-Enhanced Magnetic Resonance Imaging-Based Skeletal Calf Muscle Perfusion in Peripheral Artery Disease.

Peripheral artery disease (PAD) is associated with impaired blood flow in the lower extremities and histopathologic changes of the skeletal calf muscles, resulting in abnormal microvascular perfusion. We studied the use of convolution neural networks (CNNs) to differentiate patients with PAD from matched controls using perfusion pattern features from contrast-enhanced magnetic resonance imaging (CE-MRI) of the skeletal calf muscles. We acquired CE-MRI based skeletal calf muscle perfusion in 56 patients (36 patients with PAD and 20 matched controls). Microvascular perfusion imaging was performed after reactive hyperemia at the midcalf level, with a temporal resolution of 409 ms. We analyzed perfusion scans up to 2 minutes indexed from the local precontrast arrival time frame. Skeletal calf muscles, including the anterior muscle, lateral muscle, deep posterior muscle group, and the soleus and gastrocnemius muscles, were segmented semiautomatically. Segmented muscles were represented as 3-dimensional Digital Imaging and Communications in Medicine stacks of CE-MRI perfusion scans for deep learning (DL) analysis. We tested several CNN models for the 3-dimensional CE-MRI perfusion stacks to classify patients with PAD from matched controls. A total of 2 of the best performing CNNs (resNet and divNet) were selected to develop the final classification model. A peak accuracy of 75% was obtained for resNet and divNet. Specificity was 80% and 94% for resNet and divNet, respectively. In conclusion, DL using CNNs and CE-MRI skeletal calf muscle perfusion can discriminate patients with PAD from matched controls. DL methods may be of interest for the study of PAD.

A machine learning-based approach to identify peripheral artery disease using texture features from contrast-enhanced magnetic resonance imaging.

Diagnosing and assessing the risk of peripheral artery disease (PAD) has long been a focal point for medical practitioners. The impaired blood circulation in PAD patients results in altered microvascular perfusion patterns in the calf muscles which is the primary location of intermittent claudication pain. Consequently, we hypothesized that changes in perfusion and increase in connective tissue could lead to alterations in the appearance or texture patterns of the skeletal calf muscles, as visualized with non-invasive imaging techniques. We designed an automatic pipeline for textural feature extraction from contrast-enhanced magnetic resonance imaging (CE-MRI) scans and used the texture features to train machine learning models to detect the heterogeneity in the muscle pattern among PAD patients and matched controls. CE-MRIs from 36 PAD patients and 20 matched controls were used for preparing training and testing data at a 7:3 ratio with cross-validation (CV) techniques. We employed feature arrangement and selection methods to optimize the number of features. The proposed method achieved a peak accuracy of 94.11% and a mean testing accuracy of 84.85% in a 2-class classification approach (controls vs. PAD). A three-class classification approach was performed to identify a high-risk PAD sub-group which yielded an average test accuracy of 83.23% (matched controls vs. PAD without diabetes vs. PAD with diabetes). Similarly, we obtained 78.60% average accuracy among matched controls, PAD treadmill exercise completers, and PAD exercise treadmill non-completers. Machine learning and imaging-based texture features may be of interest in the study of lower extremity ischemia.

Contrast-Enhanced Magnetic Resonance Imaging Based T1 Mapping and Extracellular Volume Fractions Are Associated with Peripheral Artery Disease.

BACKGROUND: Extracellular volume fraction (ECV), measured with contrast-enhanced magnetic resonance imaging (CE-MRI), has been utilized to study myocardial fibrosis, but its role in peripheral artery disease (PAD) remains unknown. We hypothesized that T1 mapping and ECV differ between PAD patients and matched controls. METHODS AND RESULTS: A total of 37 individuals (18 PAD patients and 19 matched controls) underwent 3.0T CE-MRI. Skeletal calf muscle T1 mapping was performed before and after gadolinium contrast with a motion-corrected modified look-locker inversion recovery (MOLLI) pulse sequence. T1 values were calculated with a three-parameter Levenberg-Marquardt curve fitting algorithm. ECV and T1 maps were quantified in five calf muscle compartments (anterior [AM], lateral [LM], and deep posterior [DM] muscle groups; soleus [SM] and gastrocnemius [GM] muscles). Averaged peak blood pool T1 values were obtained from the posterior and anterior tibialis and peroneal arteries. T1 values and ECV are heterogeneous across calf muscle compartments. Native peak T1 values of the AM, LM, and DM were significantly higher in PAD patients compared to controls (all p < 0.028). ECVs of the AM and SM were significantly higher in PAD patients compared to controls (AM: 26.4% (21.2, 31.6) vs. 17.3% (10.2, 25.1), p = 0.046; SM: 22.7% (19.5, 27.8) vs. 13.8% (10.2, 19.1), p = 0.020). CONCLUSIONS: Native peak T1 values across all five calf muscle compartments, and ECV fractions of the anterior muscle group and the soleus muscle were significantly elevated in PAD patients compared with matched controls. Non-invasive T1 mapping and ECV quantification may be of interest for the study of PAD.

Longitudinal Magnetic Resonance Imaging-Based Superficial Femoral Artery Velocity Measurements in Diabetic and Nondiabetic Patients With Peripheral Artery Disease.

BACKGROUND: Longitudinal associations of noninvasive 2-dimensional phase-contrast magnetic resonance imaging (2D-PC-MRI) velocity markers of the superficial femoral artery (SFA) were analyzed along with the characteristics of peripheral artery disease (PAD). We hypothesized that the 2-year differences in MRI-based measures of SFA velocity were associated with longitudinal changes in markers of PAD. METHODS: A total of 33 (11 diabetic, 22 nondiabetic) patients with PAD with baseline and 2-year follow-up MRI scans were included in this secondary analysis of the Effect of Lipid Modification on Peripheral Artery Disease after Endovascular Intervention Trial (ELIMIT). Electrocardiographically gated 2D-PC-MRI was performed at a proximal and a distal location of the distal SFA territory. SFA lumen, wall, and total vessel volumes and the normalized wall index (NWI) were analyzed. RESULTS: Baseline characteristics did not differ between diabetic and nondiabetic PAD patients. Maximum proximal and distal SFA velocity measures did not differ between baseline and 2 years (41.98 interquartile range (IQR) (23.58-72.6) cm/s vs. 40.31 IQR (26.69-61.29) cm/s; P = 0.30). Pooled analysis (N = 33) showed that the 24-month change in the NWI was inversely associated with the 24-month change in the proximal maximal SFA velocity (beta = -168.36, R2 = 0.150, P value = 0.03). The 24-month change of the maximum velocity differences between the proximal and distal SFA locations was inversely associated with the 24-month changes in peak walking distance (beta = -0.003, R2 = 0.360, P value = 0.011). CONCLUSION: The 2-year change of SFA plaque burden is inversely associated with the 2-year change of proximal peak SFA blood flow velocity. 2D-PC-MRI measured SFA velocity may be of interest in assessing PAD longitudinally.

Magnetic Resonance Imaging-Derived Microvascular Perfusion Modeling to Assess Peripheral Artery Disease.

Background Computational fluid dynamics has shown good agreement with contrast-enhanced magnetic resonance imaging measurements in cardiovascular disease applications. We have developed a biomechanical model of microvascular perfusion using contrast-enhanced magnetic resonance imaging signal intensities derived from skeletal calf muscles to study peripheral artery disease (PAD). Methods and Results The computational microvascular model was used to study skeletal calf muscle perfusion in 56 individuals (36 patients with PAD, 20 matched controls). The recruited participants underwent contrast-enhanced magnetic resonance imaging and ankle-brachial index testing at rest and after 6-minute treadmill walking. We have determined associations of microvascular model parameters including the transfer rate constant, a measure of vascular leakiness; the interstitial permeability to fluid flow which reflects the permeability of the microvasculature; porosity, a measure of the fraction of the extracellular space; the outflow filtration coefficient; and the microvascular pressure with known markers of patients with PAD. Transfer rate constant, interstitial permeability to fluid flow, and microvascular pressure were higher, whereas porosity and outflow filtration coefficient were lower in patients with PAD than those in matched controls (all P values ≤0.014). In pooled analyses of all participants, the model parameters (transfer rate constant, interstitial permeability to fluid flow, porosity, outflow filtration coefficient, microvascular pressure) were significantly associated with the resting and exercise ankle-brachial indexes, claudication onset time, and peak walking time (all P values ≤0.013). Among patients with PAD, interstitial permeability to fluid flow, and microvascular pressure were higher, while porosity and outflow filtration coefficient were lower in treadmill noncompleters compared with treadmill completers (all P values ≤0.001). Conclusions Computational microvascular model parameters differed significantly between patients with PAD and matched controls. Thus, computational microvascular modeling could be of interest in studying lower extremity ischemia.

Magnetic resonance imaging based superficial femoral artery velocity measurements in peripheral artery disease.

Peripheral artery disease (PAD) causes lower extremity dysfunction and is associated with an increased risk of cardiovascular mortality and morbidity. In this study, we analyzed how non-invasive 2-dimensional-phase-contrast magnetic resonance imaging (2D-PC-MRI) measured velocity markers of the distal superficial femoral artery (SFA) are associated with clinical and functional characteristics of PAD. A total of 70 (27 diabetic and 43 non-diabetic) PAD patients were included in this secondary analysis of data collected from the Effect of Lipid Modification on Peripheral Artery Disease after Endovascular Intervention Trial (ELIMIT). Electrocardiographically (ECG)-gated 2D-PC-MRI was performed at a proximal and a distal imaging location of the distal SFA. Baseline characteristics did not differ between diabetic and non-diabetic PAD patients. Claudication onset time (COT) was shorter in diabetic PAD patients compared to non-diabetics (0.56 (inter quartile range (IQR): 0.3, 2.04) minutes vs. 1.30 (IQR: 1.13, 2.15) minutes, p = 0.025). In a pooled analysis of all 70 PAD patients, maximum velocity was significantly higher in the proximal compared with the distal SFA segment (43.97 (interquartile range (IQR): 20.4, 65.2) cm/s; vs. 34.9 (IQR: 16.87, 51.71) cm/s; p < 0.001). The maximum velocities in both the proximal and distal SFA segments were significantly higher in diabetic PAD patients compared with non-diabetics (proximal: 53.6 (IQR: 38.73, 89.43) cm/s vs. 41.49 (IQR: 60.75, 15.9) cm/s, p = 0.033; distal: 40.8 (IQR: 23.7, 71.90) cm/s vs. 27.4 (IQR: 41.67, 12.54) cm/s, p = 0.012). Intra-observer variability, as assessed by intraclass correlation (ICC) analysis, was excellent for SFA mean and maximum velocities (0.996 (confidence interval [CI]: 0.996, 0.997); 0.999 (CI: 0.999, 0.999)). In conclusion, 2D-PC-MRI SFA velocity measures are reproducible and may be of interest in assessing diabetic and non-diabetic PAD patients.

Comparison of Longitudinal Skeletal Thigh Muscle Findings With Magnetic Resonance Imaging in Patients With Peripheral Artery Disease With-Versus-Without Diabetes Mellitus.

The aim of this secondary analysis of ELIMIT (The Effect of Lipid Modification on Peripheral Artery Disease after Endovascular Intervention Trial) was to determine longitudinal changes over 24 months in skeletal thigh muscle volumes and individual muscle compartments in patients with peripheral artery disease (PAD) with and without diabetes. A total of 48 patients with available magnetic resonance imaging of the distal superficial femoral artery at baseline and 2 years were included in this analysis. Muscle volumes and superficial femoral artery wall, lumen, and total vessel volumes were quantified. Intrareader reproducibility of muscle tracings was assessed with the intraclass correlation coefficient using a 2-way model. Baseline characteristics were similar between patients with PAD with and without diabetes, except for smoking history (p = 0.049), cholesterol levels (p <0.050), and calf walking pain (p = 0.049). Interobserver reproducibility of the muscle volume tracings was excellent for all muscle groups (all intraclass correlation coefficients >0.86, confidence interval 0.69 to 0.94). Total muscle and total leg volumes increased significantly between baseline and 24 months among patients with PAD without diabetes (31 ± 6.4 cm3 vs 32 ± 7.0 cm3, p <0.001; 18 ± 4.4 cm3 vs 19 ± 4.8 cm3, p = 0.045), whereas there was no change in patients with PAD and diabetes. Total muscle volume was inversely associated with age and body mass index in patients with PAD both with and without diabetes (p <0.05). In conclusion, magnetic resonance imaging-quantified thigh muscle volumes are highly reproducible and may be of interest in assessing PAD patients with and without diabetes.

Simultaneous bilateral magnetic resonance imaging of the femoral arteries in peripheral arterial disease patients.

PURPOSE: To image the femoral arteries in peripheral arterial disease (PAD) patients using a bilateral receive coil. MATERIALS AND METHODS: An eight-channel surface coil array for bilateral MRI of the femoral arteries at 3T was constructed and evaluated. RESULTS: The bilateral array enabled imaging of a 25-cm segment of the superficial femoral arteries (SFA) from the profunda to the popliteal. The array provided improved the signal-to-noise ratio (SNR) at the periphery and similar SNR in the middle of a phantom compared to three other commercially available coils (4-channel torso, quadrature head, whole body). Multicontrast bilateral images of the in vivo SFA with 1 mm in-plane resolution made it possible to directly compare lesions in the index SFA to the corresponding anatomical site in the contralateral vessel without repositioning the patient or coil. A set of bilateral time-of-flight, T1-weighted, T2-weighted, and proton density-weighted images was acquired in a clinically acceptable exam time of ≈45 minutes. CONCLUSION: The developed bilateral coil is well suited for monitoring dimensional changes in atherosclerotic lesions of the SFA.

Relation of Magnetic Resonance Imaging Based Arterial Signal Enhancement to Markers of Peripheral Artery Disease.

Peripheral artery disease (PAD) is associated with impaired lower extremity function. We hypothesized that contrast-enhanced magnetic resonance imaging (CE-MRI) based arterial signal enhancement (SE) measures are associated with markers of PAD. A total of 66 participants were enrolled, 10 were excluded due to incomplete data, resulting in 56 participants for the final analyses (36 PAD, 20 matched controls). MR imaging was performed postreactive hyperemia using bilateral thigh blood-pressure cuffs. First pass-perfusion images were acquired at the mid-calf region with a high-resolution saturation recovery gradient echo pulse sequence, and arterial SE was measured for the lower extremity arteries. As expected, peak walking time (PWT) was reduced in PAD patients compared with controls (282 [248 to 317] sec, vs 353 [346 to 360] sec; p = 0.002), and postexercise ankle brachial index (ABI) decreased in PAD patients but not in controls (PAD: 0.75 ± 0.2, 0.60 [0.5 to 0.7]; p <0.001; vs Controls: 1.17 ± 0.1, 1.19 [1.1 to 1.2]; p = 0.50). Intraclass correlation coefficients were excellent for inter- and intraobserver variability of arterial tracings (n = 10: 0.95 (95%-confidence interval [CI]: 0.94 to 0.96), n = 9: 1.0 (CI: 1.0 to 1.0). Minimum arterial SE was reduced in PAD patients compared with matched controls (128 [110 to 147] A.U. vs 192 [149 to 234] A.U., p = 0.003). Among PAD patients but not in controls the maximum arterial SE was associated with the estimated glomerular filtration rate (eGFR), a marker of renal function (n = 36, ß = 1.37, R2 = 0.12, p = 0.025). In conclusion, CE-MRI first-pass arterial perfusion is impaired in PAD patients compared with matched controls and associated with markers of lower extremity ischemia.

Associations Between Carotid Artery Plaque Burden, Plaque Characteristics, and Cardiovascular Events: The ARIC Carotid Magnetic Resonance Imaging Study.

Importance: It remains unknown whether in an asymptomatic community-based cohort magnetic resonance imaging (MRI) measures of plaque characteristics are independently associated with incident cardiovascular disease (CVD) events when adjusted for carotid artery (CA) wall thickness, a measure of plaque burden. Objective: To assess associations of CA MRI plaque characteristics with incident CVD events. Design, Setting, and Participants: The Atherosclerosis Risk in Communities (ARIC) study is a prospective epidemiologic study of the incidence of CVD in 15 792 adults of which 2066 women and men were enrolled in the ARIC Carotid MRI substudy. ARIC participants were enrolled from 1987 to 1989, and the substudy was conducted between January 2004 and December 2005. Analysis began January 2017 and ended August 2020. Exposures: Incident CVD events during a median (interquartile range [IQR]) follow-up time of 10.5 (8.1-10.9) years were assessed. Main Outcomes and Measures: Proportional hazards Cox analyses were performed to ascertain associations between MRI variables of CA plaque burden and plaque characteristics. Results: Of 15 792 ARIC participants, 2066 were enrolled in the substudy, of whom 1256 (701 women [55.8%]) had complete data and were eligible for incident CVD analyses. Carotid artery plaques in participants with incident CVD events (172 [13.7%]) compared with those without (1084 [86.3%]) had a higher normalized wall index (median [IQR], 0.48 [0.36-0.62] vs 0.43 [0.34-0.55]; P = .001), maximum CA wall thickness (median [IQR], 2.22 [1.37-3.52] mm vs 1.96 [1.29-2.85] mm; P = .01), maximum CA stenosis (median [IQR], 5% [0%-22%] vs 0% [0%-13%]; P < .001), and when present, a larger lipid core volume (median [IQR], 0.05 [0.02-0.11] mL vs 0.03 [0.01-0.07] mL; P = .03), respectively. The presence of a lipid core was independently associated with incident CVD events when adjusted for traditional CVD risk factors and maximum CA wall thickness (hazard ratio, 2.48 [95% CI, 1.36-4.51]; P = .003), whereas the presence of calcification was not. The frequency of intraplaque hemorrhage presence in this population of individuals free of CVD at baseline who were not recruited for carotid stenosis was too small to draw any meaningful conclusions (intraplaque hemorrhage presence: 68 of 1256 participants [5.4%]). Carotid artery lumen area and maximum stenosis, which were overall low, were independently associated with incident CVD events when adjusted for traditional CVD risk factors, as anticipated. Conclusions and Relevance: The presence of a CA lipid core on MRI is associated with incident CVD events independent of maximum CA wall thickness in asymptomatic participants.

Magnetic resonance imaging based modeling of microvascular perfusion in patients with peripheral artery disease.

Peripheral artery disease (PAD) is associated with an increased risk of adverse cardiovascular events, impaired lower extremity blood flow and microvascular perfusion abnormalities in the calf muscles which can be determined with contrast-enhanced magnetic resonance imaging (CE-MRI). We developed a computational model of the microvascular perfusion in the calf muscles. We included 20 patients (10 PAD, 10 controls) and utilized the geometry, mean signal intensity and arterial input functions from CE-MRI calf muscle perfusion scans. The model included the microvascular pressure (pv), outflow filtration coefficient (OFC), transfer rate constant (kt), porosity (φ), and the interstitial permeability (Ktissue). Parameters were fitted and the simulations were compared across PAD patients and controls. Intra-observer reproducibility of the simulated mean signal intensities was excellent (intraclass correlation coefficients >0.995). kt and Ktissue were higher in PAD patients compared with controls (4.72 interquartile range (IQR) 3.33, 5.56 vs. 2.47 IQR 2.10, 2.85; p = 0.003; and 3.68 IQR 3.18, 4.41 vs. 1.81 IQR 1.81, 1.81; p < 0.001). Conversely, porosity (φ) was lower in PAD patients compared with controls (0.52 IQR 0.49, 0.54 vs. 0.61 IQR 0.58, 0.64; p = 0.016). Porosity (φ) was correlated with the ankle brachial index (r = 0.64, p = 0.011). The proposed computational microvascular model is robust and reproducible, and essential model parameters differ significantly between PAD patients and controls.

Myocardial Extracellular Volume Fraction Adds Prognostic Information Beyond Myocardial Replacement Fibrosis.

BACKGROUND: Cardiac magnetic resonance techniques permit quantification of the myocardial extracellular volume fraction (ECV), representing a surrogate marker of reactive interstitial fibrosis, and late gadolinium enhancement (LGE), representing replacement fibrosis or scar. ECV and LGE have been independently linked with heart failure (HF) events. In deriving ECV, coronary artery disease type LGE, but not non-coronary artery disease type LGE, has been consistently excluded. We examined the associations between LGE, global ECV derived from myocardial tissue segments free of any detectable scar, and subsequent HF events. METHODS: Mid short-axis T1 maps were divided into 6 cardiac segments, each classified as LGE absent or present. Global ECV was derived from only segments without LGE. ECV was considered elevated if >30%, the upper 95% bounds of a reference group without known cardiac disease (n=28). Patients were divided into 4 groups by presence of elevated ECV and of any LGE. Subsequent HF hospitalization and any death were ascertained. Their relationship with ECV was examined separately and as a composite with Cox proportional hazard models. RESULTS: Of 1604 serial patients with T1 maps, 1255 were eligible after exclusions and followed over a median 26.3 (interquartile range, 15.9-37.5) months. Patients with elevated ECV had increased risk for death (hazard ratio [HR] 2.45 [95% CI, 1.76-3.41]), HF hospitalization (HR, 2.45 [95% CI, 1.77-3.40]), and a combined end point of both outcomes (HR, 2.46 [95% CI, 1.94-3.14]). After adjustments for covariates including LGE, the relationship persisted for death (HR, 1.82 [95% CI, 1.28-2.59]), hospitalization (HR, 1.60 [95% CI, 1.12-2.27]), and combined end points (HR, 1.73 [95% CI, 1.34-2.24]). CONCLUSIONS: ECV measures of diffuse myocardial fibrosis were associated with HF outcomes, despite exclusion of replacement fibrosis segments from their derivation and even among patients without any scar. ECV may have a synergistic role with LGE in HF risk assessment.

Patient-Specific Flow Descriptors and Normalized wall index in Peripheral Artery Disease: a Preliminary Study.

BACKGROUND AND AIMS: MRI-based hemodynamics have been applied to study the relationship between time-averaged wall shear stresses (TAWSS), oscillatory shear index (OSI) and atherosclerotic lesions in the coronary arteries, carotid artery, and human aorta. However, the role of TAWSS and OSI are poorly understood in lower extremity arteries. The aim of this work was to investigate the feasibility of hemodynamic assessment of the superficial femoral artery (SFA) in patients with peripheral artery disease (PAD) and we hypothesized that there is an association between TAWSS and OSI, respectively, and atherosclerotic burden expressed as the normalized wall index (NWI). METHODS: Six cases of 3D vascular geometries of the SFA and related inlet/outlet flow conditions were extracted from patient-specific MRI data including baseline, 12 and 24 months. Blood flow simulations were performed to compute flow descriptors, including TAWSS and OSI, and NWI. RESULTS: NWI was correlated positively with TAWSS (correlation coefficient: r = 0.592; p < 0.05). NWI was correlated negatively with OSI (correlation coefficient: r = -0.310, p < 0.01). Spatially averaged TAWSS and average NWI increased significantly between baseline and 24-months, whereas OSI decreased over 2-years. CONCLUSIONS: In this pilot study with a limited sample size, TAWSS was positively associated with NWI, a measure of plaque burden, whereas OSI showed an inverse relationship. However, our findings need to be verified in a larger prospective study. MRI-based study of hemodynamics is feasible in the superficial femoral artery.

Preparative chromatography with supercritical fluids. Comparison of simulated moving bed and batch processes.

Preparative chromatography is a key technology for the separation of fine chemicals in production scale. Most of the published studies are carried out using liquid solvents as mobile phase. However, the used organic solvents can often be replaced by supercritical fluids. A reduction or renouncement of organic solvents does not only correspond to the trend of the so-called green chemistry--a sustainable, environmentally friendly production of chemical products. But a changeover to chromatography with supercritical fluids can also be reasonable under economic criteria. In this contribution a comparison between the Batch-supercritical fluid chromatography (Batch-SFC) process and the simulated moving bed (SMB)-SFC process is presented. Because of the minor importance of solvent consumption and solvent recovery in SFC, the separation systems were optimized primarily in terms of their specific productivity. For three of the four investigated model systems, the specific productivity of the SMB process is significantly higher than the productivity of the Batch process. Due to the fact, that the process with the higher specific productivity is not inevitably the more economical process, supplementary the costs of the process were considered. Therefore the comparison of the two processes was done from an economic point of view considering the minimum product price that has to be realized to fulfill the defined economic aim. It was found that although the optimized specific productivities of the SMB process were significantly higher than the productivities of the Batch process, the Batch process is the more profitable process for the investigated production rate range between 0.4 and 5t/a.

Magnetic Resonance Venous Volume Measurements in Peripheral Artery Disease (from ELIMIT).

The relation between the arterial and venous systems in patients with impaired lower extremity blood flow remains poorly described. The objective of this secondary analysis of the Effectiveness of Intensive Lipid Modification Medication in Preventing the Progression on Peripheral Artery Disease Trial was to determine the association between femoral vein (FV) volumes and measurements of peripheral artery disease. FV wall, lumen, and total volumes were quantified with fast spin-echo proton density-weighted magnetic resonance imaging scans in 79 patients with peripheral artery disease over 2 years. Reproducibility was excellent for FV total vessel (intraclass correlation coefficient 0.924, confidence interval 0.910 to 0.935) and lumen volumes (intraclass correlation coefficient 0.893, confidence interval 0.873 to 0.910). Baseline superficial femoral artery volumes were directly associated with FV wall (r = 0.46, p <0.0001), lumen (r = 0.42, p = 0.0001), and total volumes (r = 0.46, p <0.0001). The 2-year change in maximum walking time was inversely associated with the 24-month change in FV total volume (r = -0.45, p = 0.03). In conclusion, FV volumes can be measured reliably with fast spin-echo proton density-weighted magnetic resonance imaging, and baseline superficial femoral artery plaque burden is positively associated with FV volumes, whereas the 2-year change in FV volumes and leg function show an inverse relation.

Calf muscle perfusion as measured with magnetic resonance imaging to assess peripheral arterial disease.

We hypothesized that skeletal muscle perfusion is impaired in peripheral arterial disease (PAD) patients compared to healthy controls and that perfusion patterns exhibit marked differences across five leg muscle compartments including the anterior muscle group (AM), lateral muscle group (LM), deep posterior muscle group (DM), soleus (SM), and the gastrocnemius muscle (GM). A total of 40 individuals (26 PAD patients and 14 healthy controls) underwent contrast-enhanced magnetic resonance imaging (CE-MRI) utilizing a reactive hyperemia protocol. Muscle perfusion maps were developed for AM, LM, DM, SM, and GM. Perfusion maps were analyzed over the course of 2 min, starting at local pre-contrast arrival, to study early-to-intermediate gadolinium enhancement. PAD patients had a higher fraction of hypointense voxels at pre-contrast arrival for all five muscle compartments compared with healthy controls (p < 0.0005). Among PAD patients, the fraction of hypointense voxels of the AM, LM, and GM were inversely correlated with the estimated glomerular filtration rate (eGFR; r = -0.509, p = 0.008; r = -0.441, p = 0.024; and r = -0.431, p = 0.028, respectively). CE-MRI-based skeletal leg muscle perfusion is markedly reduced in PAD patients compared with healthy controls and shows heterogeneous patterns across calf muscle compartments.

Morphometric analysis of calcification and fibrous layer thickness in carotid endarterectomy tissues.

BACKGROUND: Advanced atherosclerotic lesions are commonly characterized by the presence of calcification. Several studies indicate that extensive calcification is associated with plaque stability, yet recent studies suggest that calcification morphology and location may adversely affect the mechanical stability of atherosclerotic plaques. The underlying cause of atherosclerotic calcification and the importance of intra-plaque calcium distribution remains poorly understood. METHOD: The goal of this study was the characterization of calcification morphology based on histological features in 20 human carotid endarterectomy (CEA) specimens. Representative frozen sections (10µm thick) were cut from the common, bulb, internal and external segments of CEA tissues and stained with von Kossa׳s reagent for calcium phosphate. The morphology of calcification (calcified patches) and fibrous layer thickness were quantified in 135 histological sections. RESULTS: Intra-plaque calcification was distributed heterogeneously (calcification %-area: bulb segment: 14.2±2.1%; internal segment: 12.9±2.8%; common segment: 4.6±1.1%; p=0.001). Calcified patches were found in 20 CEAs (patch size: <0.1mm(2) to >1.0mm(2)). Calcified patches were most abundant in the bulb and least in the common segment (bulb n=7.30±1.08; internal n=4.81±1.17; common n=2.56±0.56; p=0.0007). Calcified patch circularity decreased with increasing size (<0.1mm(2): 0.77±0.01, 0.1-1mm(2): 0.62±0.01, >1.0mm(2): 0.51±0.02; p=0.0001). A reduced fibrous layer thickness was associated with increased calcium patch size (p<0.0001). CONCLUSIONS: In advanced carotid atherosclerosis, calcification appears to be a heterogeneous and dynamic atherosclerotic plaque component, as indicated by the simultaneous presence of few large stabilizing calcified patches and numerous small calcific patches. Future studies are needed to elucidate the associations of intra-plaque calcification size and distribution with atherothrombotic events.