On MR imaging of atheromatous lipids in human arteries

Pro-resolving mediators in the regulation of periodontal disease

Periodontitis is an inflammatory disease of the supporting structures of the dentition that is initiated by bacteria that form a biofilm on the surface of the teeth. The pathogenesis of the disease is a result of complex interactions between the biofilm and the host response that results in dysbiosis of the microbiome and dysregulation of the inflammatory response. Current data suggest that the excess inflammation associated with periodontitis is due to a failure of resolution of inflammation pathways. In this review, the relationship between inflammation and microbial dysbiosis is examined in the context of pro-inflammation and pro-resolution mediators and their ability to modify the course of disease. The impact of local oral inflammation on systemic inflammation and the relationship of periodontitis to other inflammatory diseases, including type 2 diabetes and cardiovascular disease is reviewed. Active resolvers of inflammation, including the lipoxins and resolvins, show great promise as therapeutics for the treatment of periodontitis and other inflammatory diseases.

Characterization of signal properties in atherosclerotic plaque components by intravascular MRI

Magnetic resonance imaging (MRI) is capable of distinguishing between atherosclerotic plaque components solely on the basis of biochemical differences. However, to date, the majority of plaque characterization has been performed by using high-field strength units or special coils, which are not clinically applicable. Thus, the purpose of the present study was to evaluate MRI properties in histologically verified plaque components in excised human carotid endarterectomy specimens with the use of a 5F catheter-based imaging coil, standard acquisition software, and a clinical scanner operating at 0.5 T. Human carotid endarterectomy specimens from 17 patients were imaged at 37 degrees C by use of an opposed solenoid intravascular radiofrequency coil integrated into a 5F double-lumen catheter interfaced to a 0.5-T General Electric interventional scanner. Cross-sectional intravascular MRI (156x250 microm in-plane resolution) that used different imaging parameters permitted the calculation of absolute T1and T2, the magnetization transfer contrast ratio, the magnitude of regional signal loss associated with an inversion recovery sequence (inversion ratio), and regional signal loss in gradient echo (gradient echo-to-spin echo ratio) in plaque components. Histological staining included hematoxylin and eosin, Masson's trichrome, Kossa, oil red O, and Gomori's iron stain. X-ray micrographs were also used to identify regions of calcium. Seven plaque components were evaluated: fibrous cap, smooth muscle cells, organizing thrombus, fresh thrombus, lipid, edema, and calcium. The magnetization transfer contrast ratio was significantly less in the fibrous cap (0.62+/-13) than in all other components (P<0.05) The inversion ratio was greater in lipid (0.91+/-0.09) than all other components (P<0.05). Calcium was best distinguished by using the gradient echo-to-spin echo ratio, which was lower in calcium (0.36+/-0.2) than in all plaque components, except for the organizing thrombus (P<0.04). Absolute T1 (range 300+/-140 ms for lipid to 630+/-321 ms for calcium) and T2 (range 40+/-12 ms for fresh thrombus to 59+/-21 ms for smooth muscle cells) were not significantly different between groups. In vitro intravascular MRI with catheter-based coils and standard software permits sufficient spatial resolution to visualize major plaque components. Pulse sequences that take advantage of differences in biochemical structure of individual plaque components show quantitative differences in signal properties between fibrous cap, lipid, and calcium. Therefore, catheter-based imaging coils may have the potential to identify and characterize those intraplaque components associated with plaque stability by use of existing whole-body scanners.

Effects of temperature and histopathologic preparation on the size and morphology of atherosclerotic carotid arteries as imaged by MRI

Using magnetic resonance imaging the effects of temperature, formalin fixation, and decalcification on the size and morphology of atherosclerotic arteries were evaluated. Ten ex vivo carotid arteries were scanned fresh at body and room temperature and formalin-fixed and decalcified at room temperature. Different spin-echo pulse sequences were used and absolute T2 values calculated. During processing for histopathology, the contrast between the arterial layers increased. From body to room temperature there were significant increases in size (4%-7%), T2 of media (60--> 68 msec), and fibrous plaque component (95--> 110 msec). Formalin fixation caused significant increases in size (2%-3%) and media T2 (68--> 74 msec). Decalcification caused significant shrinkage (2%-5%) and decrease in T2 of media (74--> 53 msec) and fibrous plaque component (118--> 76 msec). Thus temperature and preparation have profound effects on contrast, size, and T2 of atherosclerotic arteries. Ex vivo experiments should be performed on fresh specimens at body temperature. J. Magn. Reson. Imaging 1999;10:876-885.

Intravascular magnetic resonance imaging of aortic atherosclerotic plaque composition

Magnetic resonance imaging (MRI) may be an excellent tool to define atherosclerotic plaque composition, but surface MRI (SMRI) suffers from a low signal-to-noise ratio and low resolution of arterial images. Intravascular MRI (IVMRI) represents a potential solution for acquiring high-quality in vivo images of atherosclerotic plaques. Isolated segments of 11 thoracic human aortas obtained at autopsy were imaged by IVMRI using an intravascular receiver catheter coil designed and built at our institution. Images obtained by IVMRI were compared with corresponding images obtained by SMRI and with histopathological aortic cross sections. The intensity of intimal thickness and plaque components was graded by IVMRI and histopathology using a score of 1 for mild, 2 for moderate, and 3 for severe intensity. IVMRI had an agreement of 75% with histopathology in fibrous cap grading (37.5% expected, kappa = 0.60, P < 0.001) and of 74% in necrotic core grading (39% expected, kappa = 0.57, P < 0.001). Intraplaque calcification was correctly graded by IVMRI in six of the eight plaques in which histopathology recognized calcium. The analysis of intimal thickness showed 80% agreement between IVMRI and histopathology (52% expected, kappa = 0.59, P < 0.001). IVMRI image features were similar to those of SMRI. In addition, IVMRI accurately determined atherosclerotic plaque size in comparison with histopathology and SMRI (slope = 1.25 cm2, r = 0.99, P < 0.001 for luminal area by IVMRI vs histopathology; slope = 0.97 cm2, r = 0.996, P < 0.001 for luminal area by IVMRI vs SMRI). IVMRI has the potential to provide important prognostic information in patients with atherosclerosis because of its ability to accurately assess both plaque composition and size.

In vitro and in situ magnetic resonance imaging signal features of atherosclerotic plaque-associated lipids

The goal of this study was to evaluate magnetic resonance imaging (MRI) signal features of the different types of lipids found in human atherosclerotic plaques. A 1.5-T SIGNA scanner was used to acquire T1-, T2-, and proton density-weighted data at four different temperatures for individual lipids and lipid mixtures designed to replicate the proportions of lipids found in plaques. Individual lipids and lipid mixtures were scanned both in a test tube and after implantation in the media of normal porcine aortas. Each of the three broad classes of lipids (triglycerides, unesterified and esterified cholesterol, and phospholipids) had different and distinct MR signal patterns, which allowed discrimination of these classes of lipids in vitro. Further, lipid implantation studies demonstrated that these distinct MR signal patterns could be used to readily distinguish each lipid type from surrounding porcine aortic media. MR signals from lipid mixtures demonstrated marked regional heterogeneity, similar to the heterogeneous lipid distribution characteristic of human atherosclerotic plaques. In summary, MR signals from lipid mixtures that mimic plaque lipid proportions can be detected at body temperature, especially in those mixtures with an increased percentage of cholesteryl esters. These studies raise the possibility that with further advances in technology, MRI may become a useful tool for determining the lipid content and composition of human atherosclerotic plaques in vivo.