Cortico-limbic interactions and carotid atherosclerotic burden during chronic stress exposure.

BACKGROUND AND AIMS: Chronic stress associates with cardiovascular disease, but mechanisms remain incompletely defined. Advanced imaging was used to identify stress-related neural imaging phenotypes associated with atherosclerosis. METHODS: Twenty-seven individuals with post-traumatic stress disorder (PTSD), 45 trauma-exposed controls without PTSD, and 22 healthy controls underwent 18F-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging (18F-FDG PET/MRI). Atherosclerotic inflammation and burden were assessed using 18F-FDG PET (as maximal target-to-background ratio, TBR max) and MRI, respectively. Inflammation was assessed using high-sensitivity C-reactive protein (hsCRP) and leucopoietic imaging (18F-FDG PET uptake in spleen and bone marrow). Stress-associated neural network activity (SNA) was assessed on 18F-FDG PET as amygdala relative to ventromedial prefrontal cortex (vmPFC) activity. MRI diffusion tensor imaging assessed the axonal integrity (AI) of the uncinate fasciculus (major white matter tract connecting vmPFC and amygdala). RESULTS: Median age was 37 years old and 54% of participants were female. There were no significant differences in atherosclerotic inflammation between participants with PTSD and controls; adjusted mean difference in TBR max (95% confidence interval) of the aorta 0.020 (-0.098, 0.138), and of the carotids 0.014 (-0.091, 0.119). Participants with PTSD had higher hsCRP, spleen activity, and aorta atherosclerotic burden (normalized wall index). Participants with PTSD also had higher SNA and lower AI. Across the cohort, carotid atherosclerotic burden (standard deviation of wall thickness) associated positively with SNA and negatively with AI independent of Framingham risk score. CONCLUSIONS: In this study of limited size, participants with PTSD did not have higher atherosclerotic inflammation than controls. Notably, impaired cortico-limbic interactions (higher amygdala relative to vmPFC activity or disruption of their intercommunication) associated with carotid atherosclerotic burden. Larger studies are needed to refine these findings.

Semi-Automatic Graphical Tool for Measuring Coronary Artery Spatially Weighted Calcium Score from Gated Cardiac Computed Tomography Images.

The current standard for measuring coronary artery calcification to determine the extent of atherosclerosis is by calculating the Agatston score from computed tomography (CT). However, the Agatston score disregards pixel values less than 130 Hounsfield Units (HU) and calcium regions less than 1 mm2. Due to this thresholding, the score is not sensitive to small, weakly attenuating regions of calcium deposition and may not detect nascent micro-calcification. A recently proposed metric called the spatially weighted calcium score (SWCS) also utilizes CT but does not include a threshold for HU and does not require elevated signals in contiguous pixels. Thus, the SWCS is sensitive to weakly attenuating, smaller calcium deposits and may improve the measurement of coronary heart disease risk. Currently, the SWCS is underutilized owing to the added computational complexity. To promote translation of the SWCS into clinical research and reliable, repeatable computation of the score, the aim of this study was to develop a semi-automatic graphical tool that calculates both the SWCS and the Agatston score. The program requires gated cardiac CT scans with a calcium hydroxyapatite phantom in the field of view. The phantom allows for deriving a weighting function, from which each pixel's weight is adjusted, allowing for the mitigation of signal variations and variability between scans. With all three anatomical views visible simultaneously, the user traces the course of the four main coronary arteries by placing points or regions of interest. Features such as scroll-to-zoom, double-click to delete, and brightness/contrast adjustment, along with written guidance at every step, make the program user-friendly and easy to use. Once tracing the arteries is complete, the program generates reports, which include the scores and snapshots of any visible calcium. The SWCS may reveal the presence of subclinical disease, which may be used for early intervention and lifestyle changes.

Self-gated, dynamic contrast-enhanced magnetic resonance imaging with compressed-sensing reconstruction for evaluating endothelial permeability in the aortic root of atherosclerotic mice.

High-risk atherosclerotic plaques are characterized by active inflammation and abundant leaky microvessels. We present a self-gated, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) acquisition with compressed sensing reconstruction and apply it to assess longitudinal changes in endothelial permeability in the aortic root of Apoe-/- atherosclerotic mice during natural disease progression. Twenty-four, 8-week-old, female Apoe-/- mice were divided into four groups (n = 6 each) and imaged with self-gated DCE-MRI at 4, 8, 12, and 16 weeks after high-fat diet initiation, and then euthanized for CD68 immunohistochemistry for macrophages. Eight additional mice were kept on a high-fat diet and imaged longitudinally at the same time points. Aortic-root pseudo-concentration curves were analyzed using a validated piecewise linear model. Contrast agent wash-in and washout slopes (b1 and b2 ) were measured as surrogates of aortic root endothelial permeability and compared with macrophage density by immunohistochemistry. b2 , indicating contrast agent washout, was significantly higher in mice kept on an high-fat diet for longer periods of time (p = 0.03). Group comparison revealed significant differences between mice on a high-fat diet for 4 versus 16 weeks (p = 0.03). Macrophage density also significantly increased with diet duration (p = 0.009). Spearman correlation between b2 from DCE-MRI and macrophage density indicated a weak relationship between the two parameters (r = 0.28, p = 0.20). Validated piecewise linear modeling of the DCE-MRI data showed that the aortic root contrast agent washout rate is significantly different during disease progression. Further development of this technique from a single-slice to a 3D acquisition may enable better investigation of the relationship between in vivo imaging of endothelial permeability and atherosclerotic plaques' genetic, molecular, and cellular makeup in this important model of disease.

Measuring Visceral Adipose Tissue Metabolic Activity in Sleep Apnea Utilizing Hybrid 18F-FDG PET/MRI: A Pilot Study.

PURPOSE: Visceral adipose tissue (VAT) is proinflammatory and is associated with cardiovascular (CV) disease. We investigated the relationship between obstructive sleep apnea (OSA) and visceral adipose tissue (VAT) metabolic activity in a pilot group of patients using positron-emission tomography/magnetic resonance imaging (PET/MRI) with 18F-fluorodeoxyglucose (FDG) tracer as a novel marker of adipose tissue inflammation. PATIENTS AND METHODS: We analyzed patients from an ongoing study, recruiting those with newly diagnosed, untreated OSA (Respiratory Disturbance Index [RDI] ≥ 5), using home sleep apnea testing (WatchPAT-200 Central-Plus). PET/MRI scans were acquired before continuous positive airway pressure (CPAP)-initiation, and after 3 months of CPAP therapy. Adipose tissue metabolic activity (18F-FDG-uptake) was measured using standardized uptake values (SUV) within the adipose tissue depots. The primary outcome was VAT SUVmean, and secondary outcomes included VAT volume, and subcutaneous adipose tissue (SAT) volume/SUVmean. Reproducibility and reliability of outcome measures were analyzed using intraclass correlation coefficients (ICC). Multivariable linear regression was used to evaluate the association between OSA and primary/secondary outcomes. RESULTS: Our analytical sample (n = 16) was 81% male (mean age 47 ± 15 years, mean BMI of 29.9 ± 4.8kg/m2). About 56% had moderate to severe OSA (mean RDI 23 ± 6 events/hour), and 50% were adherent to CPAP. We demonstrated excellent inter/intra-rater reliability and reproducibility for the primary and secondary outcomes. Patients with moderate-to-severe OSA had a higher VAT SUV mean compared to those with mild OSA (0.795 ± 0.154 vs 0.602 ± 0.19, p = 0.04). OSA severity was positively associated with VAT SUVmean (primary outcome), adjusted for age and BMI (B [SE] = 0.013 ± 0.005, p = 0.03). Change in VAT volume was inversely correlated with CPAP adherence in unadjusted analysis (B [SE] = -48.4 ± 18.7, p = 0.02). CONCLUSION: Derangements in VAT metabolic activity are implicated in adverse cardiometabolic outcomes and may be one of the key drivers of CV risk in OSA. Our results are hypothesis-generating, and suggest that VAT should be investigated in future studies using multi-modal imaging to understand its role as a potential mediator of adverse cardiometabolic risk in OSA.

Review of radiographic findings in COVID-19.

The purpose of this study is to review the published literature for the range of radiographic findings present in patients suffering from coronavirus disease 2019 infection. This novel corona virus is currently the cause of a worldwide pandemic. Pulmonary symptoms and signs dominate the clinical picture and radiologists are called upon to evaluate chest radiographs (CXR) and computed tomography (CT) images to assess for infiltrates and to define their extent, distribution and progression. Multiple studies attempt to characterize the disease course by looking at the timing of imaging relative to the onset of symptoms. In general, plain CXR show bilateral disease with a tendency toward the lung periphery and have an appearance most consistent with viral pneumonia. Chest CT images are most notable for showing bilateral and peripheral ground glass and consolidated opacities and are marked by an absence of concomitant pulmonary nodules, cavitation, adenopathy and pleural effusions. Published literature mentioning organ systems aside from pulmonary manifestations are relatively less common, yet present and are addressed in this review. Similarly, publications focusing on imaging modalities aside from CXR and chest CT are sparse in this evolving crisis and are likewise addressed in this review. The role of imaging is examined as it is currently being debated in the medical community, which is not at all surprising considering the highly infectious nature of Severe Acute Respiratory Syndrome coronavirus 2.

Segmentation of carotid arterial walls using neural networks.

BACKGROUND: Automated, accurate, objective, and quantitative medical image segmentation has remained a challenging goal in computer science since its inception. This study applies the technique of convolutional neural networks (CNNs) to the task of segmenting carotid arteries to aid in the assessment of pathology. AIM: To investigate CNN's utility as an ancillary tool for researchers who require accurate segmentation of carotid vessels. METHODS: An expert reader delineated vessel wall boundaries on 4422 axial T2-weighted magnetic resonance images of bilateral carotid arteries from 189 subjects with clinically evident atherosclerotic disease. A portion of this dataset was used to train two CNNs (one to segment the vessel lumen and the other to segment the vessel wall) with the remaining portion used to test the algorithm's efficacy by comparing CNN segmented images with those of an expert reader. RESULTS: Overall quantitative assessment between automated and manual segmentations was determined by computing the DICE coefficient for each pair of segmented images in the test dataset for each CNN applied. The average DICE coefficient for the test dataset (CNN segmentations compared to expert's segmentations) was 0.96 for the lumen and 0.87 for the vessel wall. Pearson correlation values and the intra-class correlation coefficient (ICC) were computed for the lumen (Pearson = 0.98, ICC = 0.98) and vessel wall (Pearson = 0.88, ICC = 0.86) segmentations. Bland-Altman plots of area measurements for the CNN and expert readers indicate good agreement with a mean bias of 1%-8%. CONCLUSION: Although the technique produces reasonable results that are on par with expert human assessments, our application requires human supervision and monitoring to ensure consistent results. We intend to deploy this algorithm as part of a software platform to lessen researchers' workload to more quickly obtain reliable results.

Imaging-assisted nanoimmunotherapy for atherosclerosis in multiple species.

Nanomedicine research produces hundreds of studies every year, yet very few formulations have been approved for clinical use. This is due in part to a reliance on murine studies, which have limited value in accurately predicting translational efficacy in larger animal models and humans. Here, we report the scale-up of a nanoimmunotherapy from mouse to large rabbit and porcine atherosclerosis models, with an emphasis on the solutions we implemented to overcome production and evaluation challenges. Specifically, we integrated translational imaging readouts within our workflow to both analyze the nanoimmunotherapeutic's in vivo behavior and assess treatment response in larger animals. We observed our nanoimmunotherapeutic's anti-inflammatory efficacy in mice, as well as rabbits and pigs. Nanoimmunotherapy-mediated reduction of inflammation in the large animal models halted plaque progression, supporting the approach's translatability and potential to acutely treat atherosclerosis.

Reproducibility of thrombus volume quantification in multicenter computed tomography pulmonary angiography studies.

AIM: To evaluate reproducibility of pulmonary embolism (PE) clot volume quantification using computed tomography pulmonary angiogram (CTPA) in a multicenter setting. METHODS: This study was performed using anonymized data in conformance with HIPAA and IRB Regulations (March 2015-November 2016). Anonymized CTPA data was acquired from 23 scanners from 18 imaging centers using each site's standard PE protocol. Two independent analysts measured PE volumes using a semi-automated region-growing algorithm on an FDA-approved image analysis platform. Total thrombus volume (TTV) was calculated per patient as the primary endpoint. Secondary endpoints were individual thrombus volume (ITV), Qanadli score and modified Qanadli score per patient. Inter- and intra-observer reproducibility were assessed using intra-class correlation coefficient (ICC) and Bland-Altman analysis. RESULTS: Analyst 1 found 72 emboli in the 23 patients with a mean number of emboli of 3.13 per patient with a range of 0-11 emboli per patient. The clot volumes ranged from 0.0041 - 47.34 cm3 (mean +/- SD, 5.93 +/- 10.15cm3). On the second read, analyst 1 found the same number and distribution of emboli with a range of volumes for read 2 from 0.0041 - 45.52 cm3 (mean +/- SD, 5.42 +/- 9.53cm3). Analyst 2 found 73 emboli in the 23 patients with a mean number of emboli of 3.17 per patient with a range of 0-11 emboli per patient. The clot volumes ranged from 0.00459-46.29 cm3 (mean +/- SD, 5.91 +/- 10.06 cm3). Inter- and intra-observer variability measurements indicated excellent reproducibility of the semi-automated method for quantifying PE volume burden. ICC for all endpoints was greater than 0.95 for inter- and intra-observer analysis. Bland-Altman analysis indicated no significant biases. CONCLUSION: Semi-automated region growing algorithm for quantifying PE is reproducible using data from multiple scanners and is a suitable method for image analysis in multicenter clinical trials.

Effect of varying computed tomography acquisition and reconstruction parameters on semi-automated clot volume quantification.

AIM: To examine effects of computed tomography (CT) image acquisition/reconstruction parameters on clot volume quantification in vitro for research method validation purposes. METHODS: This study was performed in conformance with HIPAA and IRB Regulations (March 2015-November 2016). A ten blood clot phantom was designed and scanned on a dual-energy CT scanner (SOMATOM Force, Siemens Healthcare GmBH, Erlangen, Germany) with varying pitch, iterative reconstruction, energy level and slice thickness. A range of clot and tube sizes were used in an attempt to replicate in vivo emboli found within central and segmental branches of the pulmonary arteries in patients with pulmonary emboli. Clot volume was the measured parameter and was analyzed by a single image analyst using a semi-automated region growing algorithm implemented in the FDA-approved Siemens syngo.via image analysis platform. Mixed model analysis was performed on the data. RESULTS: On the acquisition side, the continuous factor of energy showed no statistically significant effect on absolute clot volume quantification (P = 0.9898). On the other hand, when considering the fixed factor of pitch, there were statistically significant differences in clot volume quantification (P < 0.0001). On the reconstruction side, with the continuous factor of reconstruction slice thickness no statistically significant effect on absolute clot volume quantification was demonstrated (P = 0.4500). Also on the reconstruction side, with the fixed factor of using iterative reconstructions there was also no statistically significant effect on absolute clot volume quantification (P = 0.3011). In addition, there was excellent R2 correlation between the scale-measured mass of the clots both with respect to the CT measured volumes and with respect to volumes measure by the water displacement method. CONCLUSION: Aside from varying pitch, changing CT acquisition parameters and using iterative reconstructions had no significant impact on clot volume quantification with a semi-automated region growing algorithm.

Combined PET/DCE-MRI in a Rabbit Model of Atherosclerosis: Integrated Quantification of Plaque Inflammation, Permeability, and Burden During Treatment With a Leukotriene A4 Hydrolase Inhibitor.

OBJECTIVES: The authors sought to develop combined positron emission tomography (PET) dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) to quantify plaque inflammation, permeability, and burden to evaluate the efficacy of a leukotriene A4 hydrolase (LTA4H) inhibitor in a rabbit model of atherosclerosis. BACKGROUND: Multimodality PET/MRI allows combining the quantification of atherosclerotic plaque inflammation, neovascularization, permeability, and burden by combined 18F-fluorodeoxyglucose (18F-FDG) PET, DCE-MRI, and morphological MRI. The authors describe a novel, integrated PET-DCE/MRI protocol to noninvasively quantify these parameters in aortic plaques of a rabbit model of atherosclerosis. As proof-of-concept, the authors apply this protocol to assess the efficacy of the novel LTA4H inhibitor BI691751. METHODS: New Zealand White male rabbits (N = 49) were imaged with integrated PET-DCE/MRI after atherosclerosis induction and 1 and 3 months after randomization into 3 groups: 1) placebo; 2) high-dose BI691751; and 3) low-dose BI691751. All animals were euthanized at the end of the study. RESULTS: Among the several metrics that were quantified, only maximum standardized uptake value and target-to-background ratio by 18F-FDG PET showed a modest, but significant, reduction in plaque inflammation in rabbits treated with low-dose BI691751 (p = 0.03), whereas no difference was detected in the high-fat diet and in the high-dose BI691751 groups. No differences in vessel wall area by MRI and area under the curve by DCE-MRI were detected in any of the groups. No differences in neovessel and macrophage density were found at the end of study among groups. CONCLUSIONS: The authors present a comprehensive, integrated 18F-FDG PET and DCE-MRI imaging protocol to noninvasively quantify plaque inflammation, neovasculature, permeability, and burden in a rabbit model of atherosclerosis on a simultaneous PET/MRI scanner. A modest reduction was found in plaque inflammation by 18F-FDG PET in the group treated with a low dose of the LTA4H inhibitor BI691751.

In Vivo PET Imaging of HDL in Multiple Atherosclerosis Models.

OBJECTIVES: The goal of this study was to develop and validate a noninvasive imaging tool to visualize the in vivo behavior of high-density lipoprotein (HDL) by using positron emission tomography (PET), with an emphasis on its plaque-targeting abilities. BACKGROUND: HDL is a natural nanoparticle that interacts with atherosclerotic plaque macrophages to facilitate reverse cholesterol transport. HDL-cholesterol concentration in blood is inversely associated with risk of coronary heart disease and remains one of the strongest independent predictors of incident cardiovascular events. METHODS: Discoidal HDL nanoparticles were prepared by reconstitution of its components apolipoprotein A-I (apo A-I) and the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine. For radiolabeling with zirconium-89 ((89)Zr), the chelator deferoxamine B was introduced by conjugation to apo A-I or as a phospholipid-chelator (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-deferoxamine B). Biodistribution and plaque targeting of radiolabeled HDL were studied in established murine, rabbit, and porcine atherosclerosis models by using PET combined with computed tomography (PET/CT) imaging or PET combined with magnetic resonance imaging. Ex vivo validation was conducted by radioactivity counting, autoradiography, and near-infrared fluorescence imaging. Flow cytometric assessment of cellular specificity in different tissues was performed in the murine model. RESULTS: We observed distinct pharmacokinetic profiles for the two (89)Zr-HDL nanoparticles. Both apo A-I- and phospholipid-labeled HDL mainly accumulated in the kidneys, liver, and spleen, with some marked quantitative differences in radioactivity uptake values. Radioactivity concentrations in rabbit atherosclerotic aortas were 3- to 4-fold higher than in control animals at 5 days' post-injection for both (89)Zr-HDL nanoparticles. In the porcine model, increased accumulation of radioactivity was observed in lesions by using in vivo PET imaging. Irrespective of the radiolabel's location, HDL nanoparticles were able to preferentially target plaque macrophages and monocytes. CONCLUSIONS: (89)Zr labeling of HDL allows study of its in vivo behavior by using noninvasive PET imaging, including visualization of its accumulation in advanced atherosclerotic lesions. The different labeling strategies provide insight on the pharmacokinetics and biodistribution of HDL's main components (i.e., phospholipids, apo A-I).

Three-dimensional dynamic contrast-enhanced MRI for the accurate, extensive quantification of microvascular permeability in atherosclerotic plaques.

Atherosclerotic plaques that cause stroke and myocardial infarction are characterized by increased microvascular permeability and inflammation. Dynamic contrast-enhanced MRI (DCE-MRI) has been proposed as a method to quantify vessel wall microvascular permeability in vivo. Until now, most DCE-MRI studies of atherosclerosis have been limited to two-dimensional (2D) multi-slice imaging. Although providing the high spatial resolution required to image the arterial vessel wall, these approaches do not allow the quantification of plaque permeability with extensive anatomical coverage, an essential feature when imaging heterogeneous diseases, such as atherosclerosis. To our knowledge, we present the first systematic evaluation of three-dimensional (3D), high-resolution, DCE-MRI for the extensive quantification of plaque permeability along an entire vascular bed, with validation in atherosclerotic rabbits. We compare two acquisitions: 3D turbo field echo (TFE) with motion-sensitized-driven equilibrium (MSDE) preparation and 3D turbo spin echo (TSE). We find 3D TFE DCE-MRI to be superior to 3D TSE DCE-MRI in terms of temporal stability metrics. Both sequences show good intra- and inter-observer reliability, and significant correlation with ex vivo permeability measurements by Evans Blue near-infrared fluorescence (NIRF). In addition, we explore the feasibility of using compressed sensing to accelerate 3D DCE-MRI of atherosclerosis, to improve its temporal resolution and therefore the accuracy of permeability quantification. Using retrospective under-sampling and reconstructions, we show that compressed sensing alone may allow the acceleration of 3D DCE-MRI by up to four-fold. We anticipate that the development of high-spatial-resolution 3D DCE-MRI with prospective compressed sensing acceleration may allow for the more accurate and extensive quantification of atherosclerotic plaque permeability along an entire vascular bed. We foresee that this approach may allow for the comprehensive and accurate evaluation of plaque permeability in patients, and may be a useful tool to assess the therapeutic response to approved and novel drugs for cardiovascular disease.

Inhibiting macrophage proliferation suppresses atherosclerotic plaque inflammation.

Inflammation drives atherosclerotic plaque progression and rupture, and is a compelling therapeutic target. Consequently, attenuating inflammation by reducing local macrophage accumulation is an appealing approach. This can potentially be accomplished by either blocking blood monocyte recruitment to the plaque or increasing macrophage apoptosis and emigration. Because macrophage proliferation was recently shown to dominate macrophage accumulation in advanced plaques, locally inhibiting macrophage proliferation may reduce plaque inflammation and produce long-term therapeutic benefits. To test this hypothesis, we used nanoparticle-based delivery of simvastatin to inhibit plaque macrophage proliferation in apolipoprotein E deficient mice (Apoe-/- ) with advanced atherosclerotic plaques. This resulted in rapid reduction of plaque inflammation and favorable phenotype remodeling. We then combined this short-term nanoparticle intervention with an eight-week oral statin treatment, and this regimen rapidly reduced and continuously suppressed plaque inflammation. Our results demonstrate that pharmacologically inhibiting local macrophage proliferation can effectively treat inflammation in atherosclerosis.

A Multicenter MRI Protocol for the Evaluation and Quantification of Deep Vein Thrombosis.

We evaluated a magnetic resonance venography (MRV) approach with gadofosveset to quantify total thrombus volume changes as the principal criterion for treatment efficacy in a multicenter randomized study comparing edoxaban monotherapy with a heparin/warfarin regimen for acute, symptomatic lower extremities deep vein thrombosis (DVT) treatment. We also used a direct thrombus imaging approach (DTHI, without the use of a contrast agent) to quantify fresh thrombus. We then sought to evaluate the reproducibility of the analysis methodology and applicability of using 3D magnetic resonance venography and direct thrombus imaging for the quantification of DVT in a multicenter trial setting. From 10 randomly selected subjects participating in the edoxaban Thrombus Reduction Imaging Study (eTRIS), total thrombus volume in the entire lower extremity deep venous system was quantified bilaterally. Subjects were imaged using 3D-T1W gradient echo sequences before (direct thrombus imaging, DTHI) and 5 min after injection of 0.03 mmol/kg of gadofosveset trisodium (magnetic resonance venography, MRV). The margins of the DVT on corresponding axial, curved multi-planar reformatted images were manually delineated by two observers to obtain volumetric measurements of the venous thrombi. MRV was used to compute total DVT volume, whereas DTHI was used to compute volume of fresh thrombus. Intra-class correlation (ICC) and Bland Altman analysis were performed to compare inter and intra-observer variability of the analysis. The ICC for inter and intra-observer variability was excellent (0.99 and 0.98, p <0.001, respectively) with no bias on Bland-Altman analysis for MRV images. For DTHI images, the results were slightly lower (ICC = 0.88 and 0.95 respectively, p <0.001), with bias for inter-observer results on Bland-Altman plots. This study showed feasibility of thrombus volume estimation in DVT using MRV with gadofosveset trisodium, with good intra- and inter-observer reproducibility in a multicenter setting.

Pharmaceutical development and preclinical evaluation of a GMP-grade anti-inflammatory nanotherapy.

The present study describes the development of a good manufacturing practice (GMP)-grade liposomal nanotherapy containing prednisolone phosphate for the treatment of inflammatory diseases. After formulation design, GMP production was commenced which yielded consistent, stable liposomes sized 100nm±10nm, with a prednisolone phosphate (PLP) incorporation efficiency of 3%-5%. Pharmacokinetics and toxicokinetics of GMP-grade liposomal nanoparticles were evaluated in healthy rats, which were compared to daily and weekly administration of free prednisolone phosphate, revealing a long circulatory half-life with minimal side effects. Subsequently, non-invasive multimodal clinical imaging after liposomal nanotherapy's intravenous administration revealed anti-inflammatory effects on the vessel wall of atherosclerotic rabbits. The present program led to institutional review board approval for two clinical trials with patients with atherosclerosis. FROM THE CLINICAL EDITOR: In drug discovery, bringing production to industrial scale is an essential process. In this article the authors describe the development of an anti-inflammatory nanoparticle according to good manufacturing practice. As a result, this paves the way for translating laboratory studies to clinical trials in humans.

Prednisolone-containing liposomes accumulate in human atherosclerotic macrophages upon intravenous administration.

Drug delivery to atherosclerotic plaques via liposomal nanoparticles may improve therapeutic agents' risk-benefit ratios. Our paper details the first clinical studies of a liposomal nanoparticle encapsulating prednisolone (LN-PLP) in atherosclerosis. First, PLP's liposomal encapsulation improved its pharmacokinetic profile in humans (n=13) as attested by an increased plasma half-life of 63h (LN-PLP 1.5mg/kg). Second, intravenously infused LN-PLP appeared in 75% of the macrophages isolated from iliofemoral plaques of patients (n=14) referred for vascular surgery in a randomized, placebo-controlled trial. LN-PLP treatment did however not reduce arterial wall permeability or inflammation in patients with atherosclerotic disease (n=30), as assessed by multimodal imaging in a subsequent randomized, placebo-controlled study. In conclusion, we successfully delivered a long-circulating nanoparticle to atherosclerotic plaque macrophages in patients, whereas prednisolone accumulation in atherosclerotic lesions had no anti-inflammatory effect. Nonetheless, the present study provides guidance for development and imaging-assisted evaluation of future nanomedicine in atherosclerosis. FROM THE CLINICAL EDITOR: In this study, the authors undertook the first clinical trial using long-circulating liposomal nanoparticle encapsulating prednisolone in patients with atherosclerosis, based on previous animal studies. Despite little evidence of anti-inflammatory effect, the results have provided a starting point for future development of nanomedicine in cardiovascular diseases.

Atherosclerotic plaque targeting mechanism of long-circulating nanoparticles established by multimodal imaging.

Atherosclerosis is a major cause of global morbidity and mortality that could benefit from novel targeted therapeutics. Recent studies have shown efficient and local drug delivery with nanoparticles, although the nanoparticle targeting mechanism for atherosclerosis has not yet been fully elucidated. Here we used in vivo and ex vivo multimodal imaging to examine permeability of the vessel wall and atherosclerotic plaque accumulation of fluorescently labeled liposomal nanoparticles in a rabbit model. We found a strong correlation between permeability as established by in vivo dynamic contrast enhanced magnetic resonance imaging and nanoparticle plaque accumulation with subsequent nanoparticle distribution throughout the vessel wall. These key observations will enable the development of nanotherapeutic strategies for atherosclerosis.

Registration of dynamic contrast-enhanced MRI of the common carotid artery using a fixed-frame template-based squared-difference method.

PURPOSE: This study examines template-based squared-difference registration for motion correction in dynamic contrast-enhanced (DCE) MRI studies of the carotid artery wall and compares the results of fixed-frame template-based registration with a previously proposed consecutive-frame registration method. MATERIALS AND METHODS: Ten T1-weighted black-blood, turbo spin-echo DCE-MRI studies of the carotid artery wall were used to test template-based squared-difference registration. An intermediate image from each series was selected as the fixed-frame template for registration. Squared-difference minimization was used to align each image and template. Time-intensity curves generated from data aligned with template-based squared-difference registration were compared with gold standard curves created by drawing regions of interest on each image in the series. The results were also compared with unregistered data and data after consecutive-frame squared-difference registration. RESULTS: An analysis of variance test of root mean-square error values between gold standard curve and curves from unregistered data and data registered with consecutive-frame and fixed-frame template-based methods was significant (P < 0.005) with template-based squared-difference registration producing curves that most closely matched the gold standard. CONCLUSION: A fixed-frame template-based squared-difference registration method was proposed and validated for alignment of DCE-MRI of carotid arteries.

The complementary roles of dynamic contrast-enhanced MRI and 18F-fluorodeoxyglucose PET/CT for imaging of carotid atherosclerosis.

PURPOSE: Inflammation and neovascularization in vulnerable atherosclerotic plaques are key features for severe clinical events. Dynamic contrast-enhanced (DCE) MRI and FDG PET are two noninvasive imaging techniques capable of quantifying plaque neovascularization and inflammatory infiltrate, respectively. However, their mutual role in defining plaque vulnerability and their possible overlap has not been thoroughly investigated. We studied the relationship between DCE-MRI and (18)F-FDG PET data from the carotid arteries of 40 subjects with coronary heart disease (CHD) or CHD risk equivalent, as a substudy of the dal-PLAQUE trial (NCT00655473). METHODS: The dal-PLAQUE trial was a multicenter study that evaluated dalcetrapib, a cholesteryl ester transfer protein modulator. Subjects underwent anatomical MRI, DCE-MRI and (18)F-FDG PET. Only baseline imaging and biomarker data (before randomization) from dal-PLAQUE were used as part of this substudy. Our primary goal was to evaluate the relationship between DCE-MRI and (18)F-FDG PET data. As secondary endpoints, we evaluated the relationship between (a) PET data and whole-vessel anatomical MRI data, and (b) DCE-MRI and matching anatomical MRI data. All correlations were estimated using a mixed linear model. RESULTS: We found a significant inverse relationship between several perfusion indices by DCE-MRI and (18)F-FDG uptake by PET. Regarding our secondary endpoints, there was a significant relationship between plaque burden measured by anatomical MRI with several perfusion indices by DCE-MRI and (18)F-FDG uptake by PET. No relationship was found between plaque composition by anatomical MRI and DCE-MRI or (18)F-FDG PET metrics. CONCLUSION: In this study we observed a significant, weak inverse relationship between inflammation measured as (18)F-FDG uptake by PET and plaque perfusion by DCE-MRI. Our findings suggest that there may be a complex relationship between plaque inflammation and microvascularization during the different stages of plaque development. (18)F-FDG PET and DCE-MRI may have complementary roles in future clinical practice in identifying subjects at high risk of cardiovascular events.

SHILO, a novel dual imaging approach for simultaneous HI-/LOw temporal (Low-/Hi-spatial) resolution imaging for vascular dynamic contrast enhanced cardiovascular magnetic resonance: numerical simulations and feasibility in the carotid arteries.

BACKGROUND: Dynamic contrast enhanced (DCE) cardiovascular magnetic resonance (CMR) is increasingly used to quantify microvessels and permeability in atherosclerosis. Accurate quantification depends on reliable sampling of both vessel wall (VW) uptake and contrast agent dynamic in the blood plasma (the so called arterial input function, AIF). This poses specific challenges in terms of spatial/temporal resolution and matched dynamic MR signal range, which are suboptimal in current vascular DCE-CMR protocols. In this study we describe a novel dual-imaging approach, which allows acquiring simultaneously AIF and VW images using different spatial/temporal resolution and optimizes imaging parameters for the two compartments. We refer to this new acquisition as SHILO, Simultaneous HI-/LOw-temporal (low-/hi-spatial) resolution DCE-imaging. METHODS: In SHILO, the acquisition of low spatial resolution single-shot AIF images is interleaved with segments of higher spatial resolution images of the VW. This allows sampling the AIF and VW with different spatial/temporal resolution and acquisition parameters, at independent spatial locations. We show the adequacy of this temporal sampling scheme by using numerical simulations. Following, we validate the MR signal of SHILO against a standard 2D spoiled gradient recalled echo (SPGR) acquisition with in vitro and in vivo experiments. Finally, we show feasibility of using SHILO imaging in subjects with carotid atherosclerosis. RESULTS: Our simulations confirmed the superiority of the SHILO temporal sampling scheme over conventional strategies that sample AIF and tissue curves at the same time resolution. Both the median relative errors and standard deviation of absolute parameter values were lower for the SHILO than for conventional sampling schemes. We showed equivalency of the SHILO signal and conventional 2D SPGR imaging, using both in vitro phantom experiments (R2 =0.99) and in vivo acquisitions (R2 =0.95). Finally, we showed feasibility of using the newly developed SHILO sequence to acquire DCE-CMR data in subjects with carotid atherosclerosis to calculate plaque perfusion indices. CONCLUSIONS: We successfully demonstrate the feasibility of using the newly developed SHILO dual-imaging technique for simultaneous AIF and VW imaging in DCE-CMR of atherosclerosis. Our initial results are promising and warrant further investigation of this technique in wider studies measuring kinetic parameters of plaque neovascularization with validation against gold standard techniques.