High-resolution 3D X-ray imaging of intracranial nitinol stents

Introduction To assess an optimized 3D imaging protocol for intracranial nitinol stents in 3D C-arm flat detector imaging. For this purpose, an image quality simulation and an in vitro study was carried out. Methods Nitinol stents of various brands were placed inside an anthropomorphic head phantom, using iodine contrast. Experiments with objects were preceded by image quality and dose simulations. We varied X-ray imaging parameters in a commercially interventional X-ray system to set 3D image quality in the contrast–noise–sharpness space. Beam quality was varied to evaluate contrast of the stents while keeping absorbed dose below recommended values. Two detector formats were used, paired with an appropriate pixel size and X-ray focus size. Zoomed reconstructions were carried out and snapshot images acquired. High contrast spatial resolution was assessed with a CT phantom. Results We found an optimal protocol for imaging intracranial nitinol stents. Contrast resolution was optimized for nickel–titanium-containing stents. A high spatial resolution larger than 2.1 lp/mm allows struts to be visualized. We obtained images of stents of various brands and a representative set of images is shown. Independent of the make, struts can be imaged with virtually continuous strokes. Measured absorbed doses are shown to be lower than 50 mGy Computed Tomography Dose Index (CTDI). Conclusion By balancing the modulation transfer of the imaging components and tuning the high-contrast imaging capabilities, we have shown that thin nitinol stent wires can be reconstructed with high contrast-to-noise ratio and good detail, while keeping radiation doses within recommended values. Experimental results compare well with imaging simulations

High-resolution 3D X-ray imaging of intracranial nitinol stents

Abstract Introduction To assess an optimized 3D imaging protocol for intracranial nitinol stents in 3D C-arm flat detector imaging. For this purpose, an image quality simulation and an in vitro study was carried out. Methods Nitinol stents of various brands were placed inside an anthropomorphic head phantom, using iodine contrast. Experiments with objects were preceded by image quality and dose simulations. We varied X-ray imaging parameters in a commercially interventional X-ray system to set 3D image quality in the contrast-noise-sharpness space. Beam quality was varied to evaluate contrast of the stents while keeping absorbed dose below recommended values. Two detector formats were used, paired with an appropriate pixel size and X-ray focus size. Zoomed reconstructions were carried out and snapshot images acquired. High contrast spatial resolution was assessed with a CT phantom. Results We found an optimal protocol for imaging intracranial nitinol stents. Contrast resolution was optimized for nickel-titanium-containing stents. A high spatial resolution larger than 2.1 lp/mm allows struts to be visualized. We obtained images of stents of various brands and a representative set of images is shown. Independent of the make, struts can be imaged with virtually continuous strokes. Measured absorbed doses are shown to be lower than 50 mGy Computed Tomography Dose Index (CTDI). Conclusion By balancing the modulation transfer of the imaging components and tuning the high-contrast imaging capabilities, we have shown that thin nitinol stent wires can be reconstructed with high contrast-to-noise ratio and good detail, while keeping radiation doses within recommended values. Experimental results compare well with imaging simulations

Intra-Section Analysis of Human Coronary Arteries Reveals a Potential Role for Micro-Calcifications in Macrophage Recruitment in the Early Stage of Atherosclerosis

Vascular calcification is associated with poor cardiovascular outcome. Histochemical analysis of calcification and the expression of proteins involved in mineralization are usually based on whole section analysis, thereby often ignoring regional differences in atherosclerotic lesions. At present, limited information is available about factors involved in the initiation and progression of atherosclerosis.This study investigates the intra-section association of micro-calcifications with markers for atherosclerosis in randomly chosen section areas of human coronary arteries. Moreover, the possible causal relationship between calcifying vascular smooth muscle cells and inflammation was explored in vitro.To gain insights into the pathogenesis of atherosclerosis, we performed analysis of the distribution of micro-calcifications using a 3-MeV proton microbeam. Additionally, we performed systematic analyses of 30 to 40 regions of 12 coronary sections obtained from 6 patients including histology and immuno-histochemistry. Section areas were classified according to CD68 positivity. In vitro experiments using human vascular smooth muscle cells (hVSMCs) were performed to evaluate causal relationships between calcification and inflammation.From each section multiple areas were randomly chosen and subsequently analyzed. Depositions of calcium crystals at the micrometer scale were already observed in areas with early pre-atheroma type I lesions. Micro-calcifications were initiated at the elastica interna concomitantly with upregulation of the uncarboxylated form of matrix Gla-protein (ucMGP). Both the amount of calcium crystals and ucMGP staining increased from type I to IV atherosclerotic lesions. Osteochondrogenic markers BMP-2 and osteocalcin were only significantly increased in type IV atheroma lesions, and at this stage correlated with the degree of calcification. From atheroma area type III onwards a considerable number of CD68 positive cells were observed in combination with calcification, suggesting a pro-inflammatory effect of micro-calcifications. In vitro, invasion assays revealed chemoattractant properties of cell-culture medium of calcifying vascular smooth muscle cells towards THP-1 cells, which implies pro-inflammatory effect of calcium deposits. Additionally, calcifying hVSMCs revealed a pro-inflammatory profile as compared to non-calcifying hVSMCs.Our data indicate that calcification of VSMCs is one of the earliest events in the genesis of atherosclerosis, which strongly correlates with ucMGP staining. Our findings suggest that loss of calcification inhibitors and/or failure of inhibitory capacity is causative for the early precipitation of calcium, with concomitant increased inflammation followed by osteochondrogenic transdifferentiation of VSMCs

Calcifying VSMCs <i>in Vitro</i> display a pro-inflammatory and not an osteochondrogenic phenotype.

<p>qPCR of calcifying human primary VSMCs show a significant decrease in MGP as compared to control VSMCs. No differences were found in the expression of the osteochondrogenic markers Runx2, BMP-2 and osteocalcin. The pro-inflammatory cytokines MCP1, IL1b and IFNy were significantly increased in calcifying VSMCs indicative that calcifying VSMCs can initiate local vascular inflammation and promote macrophage migration towards the vascular wall.</p

<i>In vitro</i> model for chemoattractant properties of calcifying VSMCs on macrophages.

<p>The effect of calcifying VSMCs on the attraction of inflammatory cells was tested via invasion assays using PMA-stimulated THP-1 cells (macrophages). Conditioned medium of both control and calcifying VSMCs was used and calcium was added to control medium to obtain equal concentration of calcium in both conditions. Medium from calcifying VSMCs increased the invasion of macrophages significantly, indicating that VSMCs that calcify produce chemoattractants for inflammatory cells. Results were normalised to cell number at start. *P < 0.05, **P < 0.001 significance was assessed unpaired non-parametric t-test (Mann-Whitney).</p

Model showing the potential mechanism of initiation and progression of calcification of the vascular wall.

<p>1) Contractile VSMCs in the thickened intima change phenotype towards synthetic VSMCs. Synthetic VSMCs start secreting extracellular vesicles into the extracellular environment. In case of shortage of vitamin K, a vitamin required for the conversion of ucMGP into the active form cMGP, extracellular vesicles are loaded with ucMGP which is unable to prevent nucleation of calcium-phosphate. 2) Calcifying vesicles provide the first nidus for mineralisation and microcalcifications will be formed. These microcalcifications induce an inflammatory response in VSMCs. 3) VSMCs start secreting pro-inflammatory cytokines that will attract macrophages. 4) Macrophages start fueling the inflammation process by phagocytosing mcirocalcifications and secreting pro-inflammatory cytokines. 5) Pro-inflammatory macrophages affect synthetic VSMCs which will in turn produce BMP2. Synthetic VSMCs will transdifferentiate towards osteochondrogenic VSMCs that subsequently will produce bone-forming proteins such as osteocalcin. 6) Macrocalcifications are the final result of the osteochondrogenic environment in the atherosclerotic plaque.</p

Representative images of type I, II, III and IV regions.

<p>Representative images of regions classified as type I, II, III and IV with the corresponding calcium yield scan and (immuno-)histochemical staining of von Kossa, αSMA, ucMGP, cMGP, BMP-2 and osteocalcin (OC) in adjacent sections. Arrows indicate calcification close to the internal elastic lamina. Scale bars are 200μm.</p

Regional differentiation of atherosclerotic lesion types.

<p>An overview of a human coronary artery section, depicting atherosclerotic stages I to IV, is shown in the left panel, with enlargements of the selected regions at the right panel. The regions of coronary lesions classified as types I, II, III, and IV, based on CD68 positivity, are shown in 1A, with corresponding regions in the calcium yield scan in 1B.</p

Microcalcifications in Early Intimal Lesions of Atherosclerotic Human Coronary Arteries

Although calcium (Ca) precipitation may play a pathogenic role in atherosclerosis, information on temporal patterns of microcalcifications in human coronary arteries, their relation to expression of calcification-regulating proteins, and colocalization with iron (Fe) and zinc (Zn) is scarce. Human coronary arteries were analyzed post mortem with a proton microprobe for element concentrations and stained (immuno)histochemically for morphological and calcification-regulating proteins. Microcalcifications were occasionally observed in preatheroma type I atherosclerotic intimal lesions. Their abundance increased in type II, III, and IV lesions. Moreover, their appearance preceded increased expression of calcification-regulating proteins, such as osteocalcin and bone morphogenetic protein-2. In contrast, their presence coincided with increased expression of uncarboxylated matrix Gla protein (MGP), whereas the content of carboxylated MGP was increased in type III and IV lesions, indicating delayed posttranslational conversion of biologically inactive into active MGP. Ca/phosphorus ratios of the microcalcifications varied from 1.6 to 3.0, including amorphous Ca phosphates. Approximately 75% of microcalcifications colocalized with the accumulation of Fe and Zn. We conclude that Ca microprecipitation occurs in the early stages of atherosclerosis, inferring a pathogenic role in the sequel of events, resulting in overt atherosclerotic lesions. Microcalcifications may be caused by local events triggering the precipitation of Ca rather than by increased expression of calcification-regulating proteins. The high degree of colocalization with Fe and Zn suggests a mutual relationship between these trace elements and early deposition of Ca salts