Small Vessel Disease, a Marker of Brain Health: What the Radiologist Needs to Know

Small vessel disease, a disorder of cerebral microvessels, is an expanding epidemic and a common cause of stroke and dementia. Despite being almost ubiquitous in brain imaging, the clinicoradiologic association of small vessel disease is weak, and the underlying pathogenesis is poorly understood. The STandards for ReportIng Vascular changes on nEuroimaging (STRIVE) criteria have standardized the nomenclature. These include white matter hyperintensities of presumed vascular origin, recent small subcortical infarcts, lacunes of presumed vascular origin, prominent perivascular spaces, cerebral microbleeds, superficial siderosis, cortical microinfarcts, and brain atrophy. Recently, the rigid categories among cognitive impairment, vascular dementia, stroke, and small vessel disease have become outdated, with a greater emphasis on brain health. Conventional and advanced small vessel disease imaging markers allow a comprehensive assessment of global brain heath. In this review, we discuss the pathophysiology of small vessel disease neuroimaging nomenclature by means of the STRIVE criteria, clinical implications, the role of advanced imaging, and future directions.

The α-β phase transition in volcanic cristobalite

Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α-β phase transition in volcanic cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic cristobalite exists in the α form and has a larger cell volume than synthetic α-cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic cristobalite exhibits a lower degree of thermal expansion than synthetic cristobalite, and it also has a lower α-β transition temperature (∼473 K) compared with synthetic cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures.

The surface reactivity and implied toxicity of ash produced from sugarcane burning

Sugarcane combustion generates fine-grained particulate that has the potential to be a respiratory health hazard because of its grain size and composition. In particular, conversion of amorphous silica to crystalline forms during burning may provide a source of toxic particles. In this study, we investigate and evaluate the toxicity of sugarcane ash and bagasse ash formed from commercial sugarcane burning. Experiments to determine the main physicochemical properties of the particles, known to modulate biological responses, were combined with cellular toxicity assays to gain insight into the potential reactions that could occur at the particle-lung interface following inhalation. The specific surface area of the particles ranged from ∼16 to 90 m(2) g(-1) . The samples did not generate hydroxyl- or carbon-centered radicals in cell-free tests. However, all samples were able to 'scavenge' an external source of hydroxyl radicals, which may be indicative of defects on the particle surfaces that may interfere with cellular processes. The bioavailable iron on the particle surfaces was low (2-3 μmol m(-2) ), indicating a low propensity for iron-catalyzed radical generation. The sample surfaces were all hydrophilic and slightly acidic, which may be due to the presence of oxygenated (functional) groups. The ability to cause oxidative stress and membrane rupture in red blood cells (hemolysis) was found to be low, indicating that the samples are not toxic by the mechanisms tested. Cytotoxicity of sugarcane ash was observed, by measuring lactate dehydrogenase release, after incubation of relatively high concentrations of ash with murine alveolar macrophage cells. All samples induced nitrogen oxide release (although only at very high concentrations) and reactive oxygen species generation (although the bagasse samples were less potent than the sugarcane ash). However, the samples induced significantly lower cytotoxic effects and nitrogen oxide generation when compared with the positive control.

Automated mineralogical analysis of PM10: new parameters for assessing PM toxicity

This work provides the first automated mineralogical/phase assessment of urban airborne PM10 and a new method for determining particle surface mineralogy (PSM), which is a major control on PM toxicity in the lung. PM10 was analyzed on a TEOM filter (Aug.-Sept. 2006 collection) from the London Air Quality Network Bexley, East London, U.K. A cross-section of the filter was analyzed using a QEMSCAN automated mineralogical analysis system which provided 381,981 points of analysis for 14,525 particles over a period of 9 h 54 min. The method had a detection limit for individual mineral components of 0.05 ppm (by area). Particle shape and mineralogical characteristics were determined for particles in the size ranges PM(10-4), PM(4-2.5), and PM(2.5-0.8). The PM(2.5-0.8) fraction contained 2 orders of magnitude more mineral particles than the PM(10-4) and PM(4-2.5) fractions, however the PM(10-4) fraction forms 94% and 79% of the mineral mass and surface area, respectively. PSM of the PM10 was dominated by gypsum (36%), plagioclase (16%), Na sulphates (8%), and Fe-S-O phases (8%) in the PM(10-2.5), which may be important in explaining the toxicity of the coarse fraction. The wider implications of the study are discussed.

Generation of crystalline silica from sugarcane burning

Sugarcane leaves contain amorphous silica, which may crystallise to form crystalline silica polymorphs (cristobalite or quartz), during commercial sugarcane harvesting where sugarcane plants are burned. Respirable airborne particulate containing these phases may present an occupational health hazard. Following from an earlier pilot study (J. S. Le Blond, B. J. Williamson, C. J. Horwell, A. K. Monro, C. A. Kirk and C. Oppenheimer, Atmos. Environ., 2008, 42, 5558-5565) in which experimental burning of sugarcane leaves yielded crystalline silica, here we report on actual conditions during sugarcane burning on commercial estates, investigate the physico-chemical properties of the cultivated leaves and ash products, and quantify the presence of crystalline silica. Commercially grown raw sugarcane leaf was found to contain up to 1.8 wt% silica, mostly in the form of amorphous silica bodies (with trace impurities e.g., Al, Na, Mg), with only a small amount of quartz. Thermal images taken during several pre-harvest burns recorded temperatures up to 1056 degrees C, which is sufficient for metastable cristobalite formation. No crystalline silica was detected in airborne particulate from pre-harvest burning, collected using a cascade impactor. The sugarcane trash ash formed after pre-harvest burning contained between 10 and 25 wt% SiO(2), mostly in an amorphous form, but with up to 3.5 wt% quartz. Both quartz and cristobalite were identified in the sugarcane bagasse ash (5-15 wt% and 1-3 wt%, respectively) formed in the processing factory. Electron microprobe analysis showed trace impurities of Mg, Al and Fe in the silica particles in the ash. The absence of crystalline silica in the airborne emissions and lack of cristobalite in trash ash suggest that high temperatures during pre-harvest burning were not sustained long enough for cristobalite to form, which is supported by the presence of low temperature sylvite and calcite in the residual ash. The occurrence of quartz and cristobalite in bagasse ash is significant as the ash is recycled onto the fields where erosion and/or mechanical disturbance could break down the deposits and re-suspend respirable-sized particulate. Appropriate methods for treatment and disposal of bagasse ash must, therefore, be employed and adequate protection given to workers exposed to these dusts.

The lichen transplant methodology in the source apportionment of metal deposition around a copper smelter in the former mining town of Karabash, Russia

The lichen transplant monitoring methodology has been tested for source apportionment of metal deposition around the Cu smelter and former mining town of Karabash. Transplants of the lichen Hypogymnia physodes (L.) Nyl., collected from a 'control' site in July 2001, were set up at 10 stations along a 60 km NE-SW transect centred on Karabash. Samples were collected after 2 and 3 month monitoring periods and analysed using established wet-chemical techniques. The sources of particulate investigated were the smelter blast furnace and converter, floatation tailings, metallurgical slags, local road dusts, top soils and ambient airborne total suspended particulate. From multi-element least-squares modelling the blast furnace was the main source of particulate in transplants close to the smelter (<10 km). Particulate from the converter, with relatively high Pb and Zn, was found to be more widely dispersed, being finer-grained and so having a longer atmospheric residence time. Ambient airborne particulate, sampled in Karabash town using air-pump apparatus, was almost entirely derived from the converter, very different to the lichen transplants from the same area which mainly contained blast furnace particulate. It is proposed that lichens close to the smelter mainly trapped larger blast furnace-derived particulate as they have a low capture efficiency for smaller (converter) particles. The study demonstrates the utility of lichen transplants for monitoring atmospheric deposition and highlights the caution required in their use to assess ambient air quality in human health studies.

Biogeochemical signatures in the lichen Hypogymnia physodes in the mid Urals

Multi-element content and uranium (U) isotopes were investigated in the lichen Hypogymnia physodes (native and transplants) sampled across a 60-km transect, centred on Karabash smelter town, from Turgoyak Lake (SW) to Kyshtym (NE) to investigate the origin of U. Kyshtym was the site of a major nuclear accident in 1957. (234)U/(238)U activity ratios in native thalli sampled during July 2001 were within the natural isotopic ratio in minerals. Uranium/thorium (U/Th) ratios were higher in native thalli towards the NE (average 0.73) than those in the SW (average 0.57). Element signatures in native thalli and transplants suggest U was derived from fossil fuel combustion from Karabash and sources lying further to the east. Systematic and significant U enrichment indicative of a nuclear fuel cycle source was not detected in any sample. Element signatures in epiphytic lichen transplants and native thalli provide a powerful method to evaluate U deposition.

Lead isotopes in lichen transplants around a Cu smelter in Russia determined by MC-ICP-MS reveal transient records of multiple sources

Transplants of the lichen Hypogymnia physodes, which is relatively tolerant to SO2 and heavy metals, were deployed for 3 months over a 60 km long SW-NE transect centered on a highly polluting Cu smelter and its adjoining town of Karabash, southern Urals, Russia. The abundance of 206Pb, 207Pb, 208Pb, and 204Pb were determined by MC-ICP-MS. The measurement of 204Pb revealed critical features, which would otherwise remain concealed: (i) The precise isotope ratios referenced to 204Pb allowed several different sources to be resolved even within the small area covered: (a) the obvious pollutant source of the Karabash Cu smelter; (b) two dispersed sources, likely to include soil with lower and different contributions of thorogenic and uranogenic lead; and (c) one anthropogenic source with higher contribution of 235U derived Pb. (ii) In part of the transect, the Pb isotope composition changed while the Pb concentrations remained the same. This indicates that the Pb content of the transplantation material from the background site was largely replaced and that the transplants provide a transient record reflecting a continuous accumulation and loss of environmental Pb, probably mainly in the form of extracellular particles. Overall, the method of lichen transplantation coupled with Pb isotope ratio determinations proved effective in assessing the usefulness of lichens in biomonitoring and in resolving different sources of atmospheric deposition.

Characterisation of airborne particulate pollution in the Cu smelter and former mining town of Karabash, South Ural Mountains of Russia

Airborne total suspended particulates (TSP), dusts from smelter blast furnace and converter stacks, and filtrates of snow melt waters have been characterised in the Cu smelter and former mining town of Karabash, Russia. TSP was collected at sites up- and downwind of the smelter and large waste and tailings dumps (Oct. 2000 and July 2001). Methods for particle size, mineralogical and elemental determinations have been tested and described, and a new PSD-MicroSOURCE XRD technique developed for the mineralogical analysis of microsamples on filter substrates. TSP in downwind samples has a mean equivalent spherical diameter of 0.5 microm (s.d. = 0.2) and was found to be 100% respirable. The main element of human health/environmental concern, above Russian maximum permitted levels (1 microg m(-3), average over any time period), was Pb which was measured at 16-30 microg m(-3) in downwind samples. Individual particulates mainly consisted of complex mixtures of anglesite (PbSO4), Zn2SnO4 and poorly ordered Zn sulphates. From experimental and theoretical considerations, a high proportion of contained Pb, Zn, Cd and As in this material is considered to be in a readily bioavailable form. Chemical and mineralogical differences between the TSP, stack dusts and snow samples are discussed, as well as the implications for human and regional environmental health.

Lichen biomonitoring near Karabash smelter town, ural mountains, Russia, one of the most polluted areas in the world

Biogeochemical signatures were investigated in transplanted and native lichens near a major pollution source using sensitive multi-element chemical analysis. Transplants were established across a 60 km transect centred on the smelter town of Karabash, Ural Mountains, Russia. Statistically significant trends in element concentrations were recorded, some below one part per million. Fine metal particles are accumulated from pollution aerosols. Prolonged exposure may lead to cellular damage and enhanced accumulation or element loss. 206Pb: 207Pb isotope ratios are similar to those associated with airborne particles in Europe and Russia; an outlier near Kyshtym with a lower ratio indicates a source with a higher 235U : 238U ratio. The method is discrete, sensitive, able to detect short-term pollution episodes and useful for understanding element cycling, which is of critical importance for human and environmental health.

SEM-EDX analysis in the source apportionment of particulate matter on Hypogymnia physodes lichen transplants around the Cu smelter and former mining town of Karabash, South Urals, Russia

Scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX) of particulate matter on lichen transplant thalli (Hypogymnia physodes) was assessed as a complementary technique to wet chemical analysis for source apportionment of airborne contaminants. Transplants (2 month exposure) stationed in the Cu smelter and former mining town of Karabash were compared with those from a control site 30 km south. Particulate matter in Karabash samples (715 analyses) showed higher levels of S, Pb, Cu, Sn and Zn compared with the control (598 analyses). Complex element associations among the particles confounded detailed mineralogical identifications, and therefore a simplified particle classification scheme was devised for source apportionment. Karabash samples contained high levels of particles classified as mining-related (MRP), and these were also identified in control samples, indicating wide spatial dispersion from the smelter and highlighting the sensitivity of the method. It was noted that MRP <2.5-microm diameter were poorly represented on lichen surfaces suggesting this may limit the usefulness of Hypogymnia transplants as proxies when assessing human health impacts from airborne particulates. Analyses of the lichen thallus surface (away from surface particulates) revealed high levels of Cu, Zn, Fe and Pb associated with organics in the Karabash samples compared with the control, with a proportionate loss of K, interpreted as being due to a stress-related increase in cell membrane permeability. This type of analysis may provide a novel SEM-EDX-based method for assessing lichen vitality. The techniques developed are presented and further implications of the study are discussed.

Bioaccumulation of lead by the lichen Acarospora smaragdula from smelter emissions

Accumulation of lead in the crustose lichen Acarospora smaragdula sensu lato is reported in the vicinity of an ore- processing plant where it is subjected to acidification and metal particulate fallout. A combination of light microscopy, X-ray element mapping, field emission scanning electron microscopy (FESEM) and other analytical techniques identifies Pb accumulation within specific fungal tissues derived from smelter particles (PM10s). No Pb was detected within the photobiont layer. Our studies suggest that Pb is highly mobile under the prevailing acidic conditions, and is fixed within the lichen cortex and melanized apothecia. Lead is also accumulated within the medulla and at the rock-lichen interface where it may precipitate as amorphous botryoidal encrustations on medullary hyphae and iron-rich particles. Modern FESEMs and microprobes enable analysis of minute quantities of material, and are important tools in understanding the fate of metals within lichens necessary to develop their use as predictive and sensitive bioindicators of aerial particulate contaminants. We suggest that crustose lichens, hitherto largely ignored in metal pollution studies, may be useful bioindicators of aerial particulate contaminants in polluted areas where macrolichens are absent.

Absolute quinidine bioavailability

The absolute bioavailability of quinidine was studied in 11 hospitalized patients. A 400-mg dose of quinidine gluconate was administered to each patient by intravenous infusion and as an oral solution. Drug treatments were separated by a 72-hr period. In 8 patients, peak plasma quinidine concentrations were reached in 65 min after the oral dose; in the remaining 3 subjects, peak concentrations were reached later. From the ratio of the total area under the plasma concentration-time curves (AUCoral/AUCir), the absolute bioavailability of quinidine ranged from 44% to 89% (mean, 72). In 8 patients, the ratio of the total amount of quinidine excreted in the urine in 48 hr (AUinfinity oral/AUinfinity ir) indicated that the extent of quinidine bioavailability varied form 47% to 96% (mean, 73). The predicted bioavailability of quindine due to first-pass effects was 76+/-11%. It is concluded that absorption after the oral solution was rapid and that the reduction of quinidine bioavailability was due to first-pass hepatic drug removal.

Disposition kinetics of dihydroquinidine following quinidine administration

The disposition kinetics of dihydroquinidine, a known impurity in drug grade quinidine, was studied in 7 patients who were hospitalized for control of cardiac arrhythmias. Quinidine gluconate injection containing 5.4 to 6.2 percent dihydroquinidine was used. Following an overnite fast, dihydroquinidine doses of 0.16 to 0.31 mg/kg base were infused intravenously over 22 min. Plasma samples were collected at various times for 12 hr and analyzed for dihydroquinidine by a thin layer chromatography-fluorometric assay procedure. Postinfusion plasma dihydroquinidine concentration decline was described by a biexponential equation which suggested that the impurity distributes within the body in two kinetically distinguishable pools. The volume of the central pool (Vc) and steady-state volume of distribution (Vdss) were 0.67 +/- 0.15 L/kg and 2.76 +/- 0.63 L/kg, respectively. The halflife of the fast (t1/2alpha) and slow (t1/2beta) disposition processes were 4.71 +/- 0.26 min and 5.71 +/- 1.00 hr. Total plasma clearance was 4.17 +/- 0.68 ml/min/kg. Renal excretion of intact dihydroquinidine accounted for 16 percent of the administered dose. The corresponding value for renal dihydroquinidine clearance (Clr) was 0.61 +/- 0.08 ml/min/kg. The results of this study indicated that there were no significant differences in the distribution and elimination characteristics of dihydroquinidine and quinidine.

Disposition kinetics of quinidine

The disposition kinetics of quinidine in 12 hospitalized patients in whom oral quinidine therapy was to be initiated is described. Quinidine in doses of 2.6 to 5.2 mg/kg base were infused intravenously over 22 min. Plasma samples were collected during the postinfusion for 24 hr and analyzed by a specific and sensitive assay procedure. In the 12 hr after administration, postinfusion plasma quinidine concentration decay was described by a biexponential equation. Attempts to include the 24-hr data point in the fitting procedures resulted in poorer agreements between the theoretical and experimental curves. A 2-compartment open model is proposed to describe the disposition of quinidine. The volume of the central pool (Vc) and steady-state volume of distribution (Vdss) were 0.91 +/- 0.11 L/kg and 3.03 +/- 0.25 L/kg, respectively, and indicate that quinidine distribution is predominantly extravascular. Quinidine distribution was quite rapid (t1/2alpha = 7.19 +/- 0.70 min), while the apparent elimination half-life (t1/2beta) was considerably longer, 6.333 +/- 0.47 hr. Total body plasma clearance ranged from 1.49 to 7.15 ml/min/kg (mean 4.70) and is primarily associated with nonrenal mechanisms of drug elimination. Urine specimens collected for 48 hr indicated that 17% of the dose is excreted intact and that urinary excretion was essentially complete within 24 hr. Renal clearance (Clr) was 0.80 +/- 0.18 ml/min/kg. The study demonstrated that there is substantial interpatient variability with respect to quinidine disposition.