Search

To compare quantitative parameters for assessing the degree of eccentric systolic blood flow in the ascending thoracic aorta (AsAo).Forty-one patients were studied with three-dimensional (3D), cine phase-contract MRI (4D Flow). Analysis was performed at peak systole for a cross-sectional plane in the AsAo just distal to the sinotubular junction. AsAo flow was graded as normal, mildly, or markedly eccentric based on qualitative visual assessment. For quantitative analysis, flow jet angle and normalized flow displacement from the vessel center were calculated.Patients with normal AsAo systolic flow (n = 25) had an average flow jet angle of 13.7 degrees and flow displacement 0.04. These parameters were significantly elevated for patients with mild eccentric systolic flow (n = 6): 24.6 degrees (P = 0.012) and 0.12 (P = 0.001), respectively. However, for patients with marked eccentric flow (n = 10), only flow displacement was significantly elevated compared with the mild eccentric group (0.18; P = 0.04); flow angle was 25.7 degrees.Flow displacement is a more reliable quantitative parameter for measuring eccentric AsAo systolic flow than flow jet angle, and should be evaluated in studies investigating the role of eccentric flow in the promotion of aortic pathology.

To quantify small amounts of iron-labeled cells in mouse brains with magnetic resonance imaging (MRI).Iron-labeled cells (from 500 to 7,500) were stereotaxically transplanted into the brain of living mice that were subsequently imaged with MRI at 4.7 T. We compared four quantitative methods: (1) T2 relaxometry, (2) T2* relaxometry, (3) the volume of the cloverleaf hypointense artifact generated on T2*-weighted images, and (4) the volume of the cloverleaf hyperintense artifact generated on positive contrast images.The methods based on relaxometry, whether T2 or T2*, did not correlate with the number of injected cells. By contrast, those based on measurement of cloverleaf artifact volume, whether using negative or positive enhancement, showed a significant linear relationship for the given range of cells (R [0.92-0.95], p 0.05).T2* artifact volume imaging (negative or positive) appears promising for the quantification of magnetically labeled cells following focal injection in the brain.

Objective: Inflammation within atherosclerotic lesions increases the risk for plaque rupture and thrombosis. A functional approach to plaque analysis is the intravenous administration of ultrasmall superparamagnetic particles of iron oxide (USPIO) that enables visualization of macrophages residing in the plaques. In this study, we sought to characterize the age-related inflammatory status associated with atherosclerosis lesion progression in ApoE ―/― mice using USPIO-enhanced magnetic resonance imaging (MRI). Materials and Methods: A total of 24 ApoE ―/― mice were divided in 4 groups (N = 6) and were given a high cholesterol diet from 6 weeks of age to the end of the protocol. One group per MR time point was investigated at 10, 16, 24, and 34 weeks of age. Each MR examination was performed on a 4.7 T scanner and consisted of baseline and 48 hours post-USPIO administration imaging sessions. P904, a USPIO contrast agent (Guerbet, Paris, France) with a potential for plaque macrophage targeting, was used. Vessel wall area measurements were performed on high resolution spin echo transverse images. Multi-echo gradient-echo images acquired with the same geometry were used to calculate T2 * maps of the vessel wall using a pixel-by-pixel monoexponential fit. A one-way analysis of variance was performed to characterize the temporal variation of vessel wall area, susceptibility artifact area, baseline, and post-USPIO T2 * values. MR measurements were correlated with the histologic findings. Results: A significant increase was found in the aortic wall area from 1.4 ± 0.2 at 10 weeks to 2.0 ± 0.3 mm 2 at 34 weeks of age (P < 0.05). Concerning the post-USPIO MRI, signal loss regions, with patterns spanning from focal to the complete disappearance of the vessel wall, were observed on all postcontrast images. A significant increase in the size of the susceptibility artifact was observed from 0.5 ± 0.2 to 2.4 ± 1.0 at 24 weeks (P < 0.05) and to 2.0 ± 0.9 mm 2 at 34 weeks (P < 0.05). The T2 * values calculated on the 48 hours post-USPIO images were shorter compared with baseline. The decrease was 34% ± 16% at 10 weeks, 57% ± 11% at 16 weeks, 57% ± 16% at 24 weeks, and 48% ± 13% at 34 weeks. The Pearson's correlation test between measurement of aortic wall area performed on both MR images and histologic analysis showed a statistically significant correlation (r = 0.695 and P < 0.05). A correlation was also obtained between the signal loss area and the macrophages covered area (r = 0.68 and P < 0.05). Conclusions: This study demonstrated the feasibility of USPIO-enhanced MRI in assessing the inflammatory status related to the temporal progression of the atherosclerosis plaque in ApoE ―/― transgenic mice model of atherosclerosis. In our experimental conditions, the vascular inflammation peak, for the ApoE ―/― mice feeding high-fat/high-cholesterol diet is measured between 16 and 24 weeks of age.

To evaluate the use of a recently developed fast-clearing ultrasmall superparamagnetic iron oxide (USPIO) for detection of vascular inflammation in atherosclerotic plaque.The study protocol was approved by the animal experimentation ethics committee. A recently introduced USPIO, P904, and a reference-standard USPIO, ferumoxtran-10, were tested in a rabbit model of induced aortic atherosclerosis. In vivo magnetic resonance (MR) angiography and T2*-weighted plaque MR imaging were performed at baseline and after administration of P904 and ferumoxtran-10 (administered dose for both, 1000 micromol of iron per kilogram of body weight) in 26 hyperlipidemic New Zealand white rabbits. The variation in vessel wall area over time was evaluated with nonparametric testing. Ex vivo MR imaging findings were compared with iron content at linear regression analysis.With in vivo MR imaging, plaque analysis was possible as early as 24 hours after P904 injection. The authors observed a 27.75% increase in vessel wall area due to susceptibility artifacts on day 2 (P = .04) and a 38.81% increase on day 3 (P = .04) after P904 administration compared with a 44.5% increase in vessel wall area on day 7 (P = .04) and a 34.8% increase on day 10 (P = .22) after ferumoxtran-10 administration. These susceptibility artifacts were correlated with intraplaque iron uptake in the corresponding histologic slices. The number of pixels with signal loss on the ex vivo MR images was linearly correlated with the logarithm of the iron concentration (P = .0001; R(2) = 0.93).Plaque inflammation in rabbits can be detected earlier with P904 than with ferumoxtran-10 owing to the faster blood pharmacokinetics and the early uptake of P904 in the reticuloendothelial system.http://radiology.rsnajnls.org/cgi/content/full/252/2/401/DC1.

Purpose To assess the efficacy of a modified electrocardiograph (EKG)-triggered black-blood T1W (T1W) spin-echo sequence in improving contrast on post-gadolinium high-resolution carotid plaque imaging by implementing heart-rate–independent contrast preparation. Materials and Methods We used a standard EKG-triggered double inversion-recovery (DIR) turbo spin-echo (TSE) sequence modified with the addition of an extra saturation (90°) radio frequency (RF) pulse placed immediately after the DIR module, shortening the repetition time to a fixed value of 400 msec. A total of 10 patients with atherosclerotic disease were included in the study. Postinjection intraplaque contrast measurements were performed on each patient for the standard and the modified sequence. Results Post-gadolinium-injection intraplaque contrast was 31.7 ± 12.8% with the standard T1W sequence (nT1-TSE), and 45.3 ± 17.2% with the modified T1W sequence (mT1-TSE), showing a significant contrast enhancement of 13.6% (P < 0.001) without significant image quality modification. Conclusion The addition of a RF pulse to the standard EKG-triggered T1W TSE sequence increased intraplaque contrast without increasing sequence acquisition time. Furthermore, it appeared to be a robust technique, easy to implement on clinical scanners. J. Magn. Reson. Imaging 2008;28:533–537. © 2008 Wiley-Liss, Inc.

To the Editor: Is the aortic dilation that is commonly seen with bicuspid aortic valve (BAV) related to intrinsic aortic wall fragility or altered systolic hemodynamics? Recent publications on the topic favor the intrinsic fragility hypothesis. But recent advancements in imaging show very abnormal

Author(s): Sigovan, Monica; Hope, Michael D; Wrenn, Jarrett; Dyverfeldt, Petter; Saloner, David

Background 3D cine phase-contrast CMR ("4D Flow”) permits quantitative assessment of anomalous alterations of aortic blood flow. Two hemodynamic parameters that have been used for this purpose is the wall shear stress (WSS), which is known to regulate endothelial cell function, and the normalized flow displacement from the vessel center, which was recently shown to correlate with increased growth rates of ascending aortic dilation [1,2]. Analysis of these hemodynamic parameters requires that a user 1) positions a 2D plane of interest in the volumetric 4D Flow dataset and 2) delineates the contour of the vascular lumen in this 2D plane. We set out to assess the reproducibility of 4D Flow-based estimation of WSS and normalized flow displacement at these two critical levels of user-interaction. Furthermore, we assessed which of the parameters correlate best with aortic growth.

Objectifs En imagerie haute resolution vasculaire, l’intensite de la ponderation T1 des sequences Turbo Spin Echo synchronisees a l’ECG est limitee par la frequence cardiaque du patient. Nous proposons une methode simple pour accroitre la ponderation T1 de ces sequences afin d’ameliorer le contraste entre les differents elements de la plaque atheromateuse carotidienne apres injection de Gadolinium. Materiels et methodes Ajout a la sequence 2D TSE avec double inversion-recuperation et synchronisation ECG d’un pulse de 90 ° entre le module de double inversion-recuperation et le module de lecture TSE de facon a rendre le temps de repetition de la sequence plus court et independant du rythme cardiaque. Validation de la sequence par une etude incluant 10 patients consecutifs presentant une plaque carotidienne avec mesure, par deux observateurs independants, du contraste intra-plaque 5 minutes apres injection intraveineuse de Gadolinium. Resultats Le contraste intra-plaque etait de 31,7 ± 12,8 % avec la sequence standard contre 45,3 ± 17,2 % avec la sequence modifiee soit un gain en contraste de 13,6 % (p Conclusion L’ajout d’un pulse de 90 a a la sequence 2D TSE synchronisee a l’ECG est une methode simple, couramment utilisable, permettant d’accroitre le contraste intra-plaque sans augmenter le temps d’acquisition.

Diagnostic imaging of hepatocellular carcinoma (HCC) requires a liver CT or MRI multiphase acquisition protocol. Patients would benefit from a high-resolution imaging method capable of performing multi-phase imaging in a single acquisition without an increase in radiation dose. Spectral Photon-Counting Computed Tomography (SPCCT) has recently emerged as a novel and promising imaging modality in the field of diagnostic radiology. SPCCT is able to distinguish between two contrast agents referred to as multicolor imaging because, when measuring in three or more energy regimes, it can detect and quantify elements with a K-edge in the diagnostic energy range. Based on this capability, we tested the feasibility of a dual-contrast multi-phase liver imaging protocol via the use of iodinated and gadolinated contrast agents on four healthy New Zealand White (NZW) rabbits. To perform a dual-contrast protocol, we injected the agents at different times so that the first contrast agent visualized the portal phase and the second the arterial phase, both of which are mandatory for liver lesion characterization. We demonstrated a sensitive discrimination and quantification of gadolinium within the arteries and iodine within the liver parenchyma. In the hepatic artery, the concentration of gadolinium was much higher than iodine (8.5 ± 3.9 mg/mL versus 0.7 ± 0.1 mg/mL) contrary to the concentrations found in the liver parenchyma (0.5 ± 0.3 mg/mL versus 4.2 ± 0.3 mg/mL). In conclusion, our results confirm that SPCCT allows in-vivo dual contrast qualitative and quantitative multi-phase liver imaging in a single acquisition.

The advent of new X-ray detectors, i.e. photon-counting detectors, introduced in spectral photon-counting computed tomography (SPCCT) systems allow analysis of the energy composition of the transmitted X-ray spectrum. By dividing the spectrum into well-chosen energy-based datasets, the specific and quantitative « multicolor » imaging of materials (such as gadolinium and gold), also known as K-edge imaging, is possible with such systems. Meanwhile, the field of nanoparticle contrast agents for CT has expanded rapidly over the past decade, with the greatest number of publications focusing on gold nanoparticles (AuNP). It turns out that AuNP are a good candidate for K-edge imaging, du to their high K-edge energy (~80.3 keV). In addition, they have the potential to circulate longer than iodinated contrast agents for improved blood pool imaging and to be highly biocompatible. The main objective of this thesis work is to evaluate in vitro and in vivo K-edge imaging using a preclinical prototype SPCCT system in combination with pegylated AuNP and clinically approved contrast agents based on iodine and gadolinium for imaging of the lumen and arterial wall in healthy and atherosclerotic rabbits. Our main contribution is to demonstrate that K-edge imaging is feasible in vivo in combination with AuNP to improve the specific assessment of the atherosclerotic arterial wall in comparison to conventional imaging via the quantification of its macrophage burden, as well as to perform « bicolor » imaging (i.e. simultaneous imaging of two agents) for specific differentiation between enhancement of the lumen with one iodinated contrast agent and enhancement of the aortic wall with K-edge AuNP., L'avènement de nouveaux détecteurs, dits à comptage photonique, appliqués à la tomodensitométrie aux rayons X permet l'analyse de la composition énergétique du spectre de rayons X transmis. En divisant le spectre en plusieurs fenêtres énergétiques, l’imagerie « multicouleur » spécifique et quantitative de matériaux (tels que le gadolinium et l'or), également appelée imagerie K-edge, est possible. Parallèlement, les nanoparticules d'or s'avèrent de bonnes candidates pour l'imagerie K-edge en raison de leur énergie K-edge élevée (~80.3 keV). De plus, elles ont le potentiel de circuler plus longtemps que les agents de contraste iodés pour une meilleure imagerie du compartiment vasculaire et d'être biocompatibles pour des applications in vivo. L'objectif principal de ce travail de thèse est d'évaluer l'imagerie K-edge in vitro et in vivo, permise par un prototype préclinique de tomodensitométrie spectrale à comptage photonique, en combinaison avec des nanoparticules d'or pégylées et des produits de contraste approuvés cliniquement à base d'iode et de gadolinium pour l'imagerie de la lumière et de la paroi artérielle chez le lapin sain et athéromateux. Notre principale contribution a été de démontrer que l'imagerie K-edge est réalisable in vivo en combinaison avec des nanoparticules d'or pour améliorer l'évaluation spécifique de la paroi artérielle athéromateuse en comparaison à l'imagerie conventionnelle via la quantification de sa charge macrophagique, ainsi que pour réaliser une imagerie spécifique « bicouleur » de la lumière artérielle marquée par un produit de contraste iodé et la plaque marquée par les nanoparticules d'or.