Three-layered Appearance Research Articles

Intravascular ultrasound imaging of coronary arteries. Is three layers the norm?

The purpose of this study was to evaluate the significance of the three-layered appearance of coronary arteries in adolescence and adults from intravascular ultrasound scans and to correlate these observations with histopathology. Sixteen intact hearts were excised at autopsy from patients with no clinical history of coronary artery disease. The patients' ages ranged from 13 to 55 years. A 30-MHz ultrasound imaging catheter was used to obtain images throughout the epicardial coronary vasculature. A total of 72 image cross sections was marked by epivascular sutures, and the corresponding histological sections were examined. Ultrasound images were classified into two groups: images exhibiting three-layered appearance and images without distinct layering. Histological analysis revealed a significantly greater degree of intimal thickening in segments with three layers (243 +/- 105 microns) than in nonlayered segments (112 +/- 55 microns). Discriminant analysis of these data predicted the threshold between the two groups to be 178 microns. Measurements of medial thickness were not different between these two groups (235 +/- 61 versus 210 +/- 76 microns). In the nonlayered group, the average patient age was 27.1 +/- 8.5 years, whereas in the three-layered groups, the average age was 42.8 +/- 9.8 years. The intracoronary ultrasound image appearance of young, morphologically normal coronary artery walls is homogeneous without layering. A three-layered appearance suggests the presence of at least 178 microns of intimal thickening and is seen more frequently with advancing age.

Atherosclerotic saphenous vein grafts treated with different interventional procedures assessed by intravascular ultrasound

Intravascular ultrasound imaging of saphenous vein grafts may enhance the angiographic interpretation of results following transcatheter interventions. We used intravascular ultrasound to study 18 patients with stenotic vein grafts following balloon angioplasty, atherectomy, or stent placement. In real-time imaging the three-layer appearance was rarely seen, calcification was infrequent (11% of patients), and atheroma were usually mildly echogenic (“soft”). Despite excellent angiographic results (reduction in percent diameter stenosis from 90 ± 8% to 17 ± 8%) and concordant improvement in lumen area by ultrasound regardless of the intervention, there was usually significant retained atheroma at the treatment site. Following balloon angioplasty, ultrasound showed multiple superficial fissures and fractures without discrete dissections. Atherectomy caused a smooth lumen surface without deep dissections or resections, but significant retained atheroma was observed with each one of the atherectomy procedures. Endovascular stents were concentric in the vein with reflective struts above compressed atheroma and an outer echogenic adventitia. Stent expansion was asymmetric axially and longitudinally and evidence of stent recoil was present. Thus intravascular ultrasound may be an important adjunct to angiography in characterizing postintervention results in saphenous vein grafts.

Intravascular ultrasound imaging combined with coronary angioplasty.

A novel catheter combining ultrasound imaging and coronary balloon angioplasty was used in the treatment of 69 coronary-artery lesions in 51 patients. The ultrasound transducer enables real-time cross-sectional imaging and qualitative and quantitative assessment of the vessel wall before and after angioplasty. The combination catheter successfully dilated 67 lesions. There was a characteristic three-layered appearance, representing intima, media, and adventitia, in 60 cases. Intravascular imaging provided information on the vessel wall unobtainable by standard contrast angiography in 28 cases and influenced our management in 6 cases.

Detection and Characterization of Vascular Lesions by Intravascular Ultrasound: An In Vitro Study Correlated with Histology

High-frequency intravascular ultrasound (30 and 40 MHz) was applied to study 112 human vascular specimens. The ultrasound images were compared with histologic cross-sections. In 44 out of 58 of the histologically classified muscular arteries, a hypoechoic middle layer was seen in the vessel wall, giving it a three-layered appearance. In 10 arteries, fibrous degeneration of the muscular media resulted in a homogeneous appearance of the vessel walls, whereas atherosclerotic plaque precluded the visualization of the arterial media in four of the arteries. A three-layered appearance was seen in seven of nine histologically classified transitional arteries, and a homogeneous arterial wall was seen in two of the nine. None of the 33 elastic arteries, veins, venous bypass, and Goretex conduits showed a hypoechoic medial layer. Histologically proved fibrous intimal thickening was echographically detected in 32 of 48 specimens (67%). It was noted that these intimal lesions were easier to detect with 40 MHz than with 30 MHz transducers. Hypoechoic areas of lipid deposition were detected in 32 of 36 specimens (89%) and could be distinguished from fibrous plaques. Histologically evident calcium deposits were detected with intravascular ultrasound in 35 of 36 specimens (97%). Measurement of plaque area was only possible in cross sections with a three-layered appearance. Quantitative analysis showed a significantly larger lumen area measured from ultrasonic images (26.3 +/- 21.3 mm2) than from histologic cross-sections (21.8 +/- 16.6 mm2, p less than 0.001), probably because of tissue shrinkage during processing for histology. A significant correlation (r = 0.96, p less than 0.001) between ultrasonic and histologic measurements of lumen areas was observed, with and a negligible interobserver and intraobserver variability. Plaque area and medial thickness correlated well with histology (r = 0.87, p less than 0.001 and r = 0.93, p less than 0.001, respectively). It appears from this in vitro study that intravascular ultrasound is an accurate technique for detection and characterization of atherosclerotic lesions. Vessel lumen area can be measured in most instances, whereas plaque area and medial thickness can only be reliably assessed in muscular arteries in which the hypoechoic media serves as a reference, and shadowing by calcium or attenuation by fibrous plaque components is absent.

Imaging of post-mortem coronary arteries by 30 MHz intravascular ultrasound

Intravascular ultrasound cross-sectional imaging of the atherosclerotic artery may be employed to guide plaque ablation by spark erosion, atherectomy, laser irradiation or other means. To assess whether in the coronary artery the echolucent zone of the three-layered ultrasound appearance of muscular arteries might be a reliable boundary to halt transluminal ablative angioplasty, epicardial coronary arteries were scanned under pressure over a distance of 4-8 cm at 1 mm intervals. A 5.2F catheter with a 30 MHz transducer rotating at 600 RPM was used. In 419 images from four post-mortem hearts, aged at death 22, 31, 56 and 82 years, the presence of a distinct echolucent zone was scored as percentage of the wall circumference. The median scores were 0%, 0%, 10% and 75%, respectively. In the three youngest hearts, the three-layered appearance was largely absent. In the 82 year old heart, in contrast, the three-layered appearance could generally be identified. Within subjects, the presence of an echolucent zone was variable in location. Qualitatively, neither abundant medial elastin tissue nor a reduced medial thickness could explain the absence of an echolucent zone when the ultrasound image was compared to the corresponding microscopic section. The results show that in the 82 year old heart, 30 MHz intravascular ultrasound discrimination of coronary wall layers would be adequate to guide transluminal plaque ablation. In the younger hearts, guided ablation would fail due to the limited presence of a distinct echolucent zone as an ultrasound landmark of the media. Whether the presence or absence of an echolucent zone is related to age remains to be determined.

Detection of vascular morphology by high frequency intravascular ultrasonic imaging

This study was designed to validate the potential clinical utility of intravascular ultrasonic imaging in vitro and in vivo. In vitro studies were performed to assess the accuracy of dimensional and morphological information. In vitro images of human vessels (n = 75) demonstrated that lesion thickness determined echographically closely related with histological samples (r = 0.83). Morphologically, muscular and elastic arteries could be distinguished echographically based on the echogenicity of the arterial media. Close relation was also found in the morphological subtypes of atherosclerosis.Subsequently, intravascular ultrasound was used percutaneously in vivo in 20 patients to obtain images of the iliac and superficial femoral artery. High quality real-time images were obtained. Normal vessels were seen showing pulsatile circular images with a hypoechoic muscular media resulting in a typical three-layered appearance. Diseased arteries revealed non-obstructive and obstructive lumen. At the site of obstruction thinning of the muscular media was evident. Pulsation was not always present. Following dilatation of the obstructive lesion using balloon angioplasty the ultrasonic cross-sections changed drastically revealing plaque rupture, dissection, plaque-free wall rupture, rest stenosis and oedema.We conclude that intravascular ultrasonic imaging is a promising technique to document accurate dimensional and morphological characteristics of human vascular disease for guidance of therapeutic interventions.

Intravascular ultrasound: significance of the three-layered appearance of normal muscular arteries

Intravascular ultrasound: significance of the three-layered appearance of normal muscular arteries

Ultrastructure of capillary walls in human brain tumors

Changes in capillary walls between human glial, non-glial and metastatic brain tumors were studied with conventional ultrathin section and freeze-fracture replica techniques. The following results were obtained. (1) In glial tumors, ultrathin section studies showed cell junctions of the capillaries were either short or elongate. Moreover, endothelial hyperplasia, surface infolding of endothelial cells, irregularity of the basal lamina and a large extravascular space were observed. Freeze-fracture replicas of capillary endothelium showed tight junctions as two to seven strands. In addition, pinocytotic vesicles had increased markedly and were an average of 25 per microns 2. Both ultrathin and freeze fracture studies showed that, in contrast to malignant gliomas, there were only slight changes in benign astrocytomas. (2) In non-glial tumors, ultrathin sections showed surface infoldings, increased vesicles, many fenestrations of endothelial cells, irregularity of basal lamina and enlarged perivascular space. Freeze-fracture replicas of vascular endothelium, showed that the average number of pinocytotic vesicles and fenestrations were 25 and 22 per microns 2, respectively. Moreover, the tight junction was composed of one or two strands which appeared to be a discontinuous array of particles. (3) In metastatic brain tumors, ultrathin studies showed capillary endothelia were proliferated, had marked infolding, and showed an increased number of pinocytotic vesicles and many fenestrations. Moreover, short and elongate intercellular junctions were presented but no open junction was detected. Finally the basal lamina lost its three-layered appearance and was irregular in width. Freeze-fracture replicas showed pinocytotic vesicles had increased and were 24 per microns 2 on average in four cases, but fenestrations and tight junctions could not be detected. The most fundamental feature of vessels in these three different kinds of tumors was whether they were fenestrated or not. Glial tumors were non-fenestrated, whereas non-glial and metastatic tumors were fenestrated.

Bacterial cell membranes. II. Possible structure of the basal membrane continuum of Micrococcus lysodeikticus.

Treatment of isolated membranes from M. lysodeikitcus with acetone, ethanol, or methanol, but not ethyl acetate, extracts phospholipids and carotenoids. These extracted membranes are not disaggregated by such treatments and retain a three-layered appearance. The extracted membranes can be completely disaggregated by sodium lauryl sulfate, yielding subunits which are primarily protein (stripped subunits). These stripped subunits reaggregate into membranous sheets that also possess a three-layered structure. Conditions for reaggregation of stripped subunits are the same as for unstripped subunits. Extracted phospholipids and carotenoids from M. lysodeikitcus or phospholipids from Erwinia sp. are incorporated into the membranous sheets formed using the stripped subunits from M. lysodeikticus. The composition of the basal membrane continuum from M. lysodeikticus consists primarily of protein; most phospholipids and carotenoids appear to be present as superstructures on the top and bottom of the protein. Membrane protein is basic and does not appear to contain any cysteine. It is speculated that hydrophobic amino acids may be positioned in clusters on the facing sides of the molecules.

Ultrastructure of sporulation in the oyster pathogen Dermocystidium marinum

Electron-microscope studies demonstrate that presporangial cells (hypnospores) of the fungus Dermocystidium marinum are characterized by an apparent lack of mitochondria, by a cell wall homogeneous with respect to electron density, and by an electron-light nucleus. In precleavage sporangia, morphogenesis of mitochondria appears to occur from myelin figures, the cell walls acquire a three-layered appearance, and the nuclei become electron-dense with evidences of condensed chromatin. A discharge pore and tube are formed by rupture of the cell wall and subsequent unfolding of the tube from the innermost part of the cell wall. The pore is blocked by a plug which is a thickened section of the inner cell wall. Sporulation proceeds by successive bipartition of the protoplast involving alternating karyokinesis and cytokinesis. The nuclear membrane persists during karyokinesis. The process terminates with the formation of billagellated planonts, enclosed by two unit membranes. Evaginations of one or both of the membranes form a row of tinsels along one side of the anterior flagellum. Golgi bodies and a previously undescribed, electrondense body are found next to the planont nucleus. D. marinum is concluded to be a member of the Saprolegniales on the basis of planont morphology and previously described stages.

Spherical subunits in photosynthetic membranes of two cyanophyceae and the bacterium Rhodospirillum rubrum.

The photosynthetic lamellae of Oscillatoria amoena and Pseudanabaena catenata appear as a two-dimensional packing of spherical units following permanganate fixation, ultrathin sectioning and high-resolution electron micrography. The usual three-layered appearance is explained as an optical artifact. Quite similar patterns were observed in chromatophore membranes of Rhodospirillum rubrum. Also, the cytoplasmic membrane of R. rubrum shows an identical pattern. Indication is presented that thylakoids of Cyanophyceae can arise as invaginations of the cytoplasmic membrane. The localization of chloroplast lipids in these organisms and the similarity of spherical units and quantasomes is discussed.