Noninvasive evaluation of cerebral arteriovenous malformations by 4D-MRA for preoperative planning and postoperative follow-up in 56 patients: comparison with DSA and intraoperative findings.

BACKGROUND AND PURPOSE: 4D-MRA is a promising technique in the diagnosis and follow-up of cAVMs. The purpose of this study was to compare 4D-MRA in the pre- and postoperative evaluation of cAVMs with DSA or intraoperative findings as the standards of reference regarding qualitative and quantitative parameters. MATERIALS AND METHODS: Fifty-six consecutive patients with cAVMs (30 women) underwent both 4D-MRA and DSA. Preoperative 4D-MRA was excluded from analysis in 1 patient (movement artifacts). Twenty-five patients underwent surgery on cAVMs and underwent both imaging modalities pre- and postoperatively. 4D-MRA was performed with either 0.5-mol/L gadolinium-diethylene-triamine pentaacetic acid (group 1: voxel size, 1.1 × 1.1 × 1.4 mm(3); 608 ms/dynamic frame; 19 patients) or 1.0-mol/L gadobutrol (group 2: voxel size, 1.1 × 1.1 × 1.1 mm(3); 572 ms/dynamic frame; additional alternating view sharing; 37 patients). Two readers independently reviewed 4D-MRA and DSA regarding the Spetzler-Martin classification, arterial feeders, and postoperative residual filling. Vessel sharpness, vessel diameter, and VBC of 4D-MRA were quantified. RESULTS: Preoperative Spetzler-Martin classification 4D-MRA and DSA ratings matched in 55/55 patients (Spetzler-Martin grades: I, 12; II, 22; III, 15; IV, 5; V, 1), and 93/100 arterial feeders were correctly identified by preoperative 4D-MRA (7 additional arterial feeders identified by DSA only: group 1, 3/19; group 2, 4/36). Postoperative 4D-MRA and DSA matched in 25/25 patients (residual filling, 1/25). Vessel sharpness and diameters did not differ substantially between the 2 groups. VBC was significantly higher in group 2 (P < .005). CONCLUSIONS: 4D-MRA is a reliable tool that allows predicting Spetzler-Martin classification and postoperative residual filling; it hence allows substituting DSA in the pre- and postoperative evaluation of patients with cerebral AVMs.

Electret ion chamber-based passive radon-thoron discriminative monitors.

Electret ion chambers (EICs), commercially available under brand name E-PERM(®), are widely used for measuring indoor and outdoor (222)Rn concentrations in air. These are designed to respond only to (222)Rn and not to (220)Rn by restricting diffusional entry area. Such radon EIC (R EIC) monitors are modified by increasing the entry area to allow (220)Rn, in addition to (222)Rn. Such modified units are called RT EIC. When a set of R and RT EICs are collocated, it is possible to discriminate and measure both radon and thoron concentrations, using appropriate calibration factors (CFs) and algorithms. The EICs come in different volumes, providing different sensitivities. The thoron CFs for 58-, 210- and 960-ml volume R and RT pairs are, respectively, 2.8-, 18.7- and 89-V drop per (kBq m(-3) d ), respectively. These provide much wider sensitivities and ranges compared to alpha track-based passive radon-thoron discriminative monitors.

Annual average indoor radon variations over two decades.

Long-term exposure to elevated radon (222Rn) concentrations has been linked to increased lung cancer risk. Year-long measurements of contemporary radon concentrations have been the "gold standard" for epidemiologists trying to reconstruct past radon exposures and for homeowners trying to estimate future radon exposure. Random variations and persistent temporal trends can affect remedial action decisions and risk coefficients derived from epidemiological studies. Temporal fluctuations are possible when changes occur in a home's structure, climate, environment, or occupants. The annual-average temporal radon behavior was studied at 196 sites in 98 Minnesota houses. Seventeen hundred year-long indoor radon measurements were made from 1983 to 2000 to determine year-to-year radon fluctuations and long-term temporal trends. Ten year-long measurements over a span of 13 years were made at the typical site. The median radon concentration was 120 Bq m-3. The median radon concentration of the group of houses showed little year-to-year variation and no persistent temporal trends. At individual sites, year-to-year radon variations ranged from 3 to 110%. The median variation was 26%. Climate, exposure to wind, and radon concentration affected year-to-year variation, but house age, construction, or measurement floor did not. Some individual sites showed significantly larger radon changes when modifications were made to the house structure and heating-ventilation systems. Year-long radon measurements on the first floor provided better estimates of cumulative radon exposure than screening measurements. The radon variations observed in this study provide uncertainty estimates for year-long measurements that could help improve remediation decision protocols and refine risk estimates from epidemiological studies.

210Po implanted in glass surfaces by long term exposure to indoor radon.

Recent epidemiologic investigations of the relationship between residential radon gas exposure and lung cancer relied on contemporary radon gas measurements to estimate past radon gas exposures. Significant uncertainties in these exposure estimates can arise from year-to-year variation of indoor radon concentrations and subject mobility. Surface implanted 210Po has shown potential for improving retrospective radon gas exposure estimates. However, in previous studies, the ability of implanted 210Po activity to reconstruct cumulative radon gas exposure was not tested because glass was not available from homes with known radon-gas concentration histories. In this study, we tested the validity of the retrospective radon gas reconstruction using implanted 210Po surface activity by measuring glass surfaces from homes whose annual-average radon gas concentrations had been measured almost every year during two decades. Regression analysis showed a higher correlation between measured surface activity and cumulative radon gas exposure in these homes (R2>0.8) than was observed in homes where only contemporary radon gas measurements were available. The regression slope (0.57 ky m(-1)) was consistent with our earlier retrospective results. Surface activity measurements were as reliable for retrospective radon gas exposure reconstruction as yearlong gas measurements. Both methods produced estimates that were within 25% of the long-term average radon gas concentrations in a home. Surface measurements can be used for home screening tests because they can provide rapid, reliable estimates of past radon gas concentrations. Implanted 210Po measurements are also useful in retrospective epidemiologic studies that include participants who may have been exposed to highly variable radon concentrations in previously occupied or structurally modified homes.

Observation of chaos-assisted tunneling between islands of stability.

We report the direct observation of quantum dynamical tunneling of atoms between separated momentum regions in phase space. We study how the tunneling oscillations are affected as a quantum symmetry is broken and as the initial atomic state is changed. We also provide evidence that the tunneling rate is greatly enhanced by the presence of chaos in the classical dynamics. This tunneling phenomenon represents a dramatic manifestation of underlying classical chaos in a quantum system.

The Iowa radon lung cancer study--phase I: Residential radon gas exposure and lung cancer.

Exposure to high concentrations of radon (222Rn) progeny produces lung cancer in both underground miners and experimentally-exposed laboratory animals. The goal of the study was to determine whether or not residential radon exposure exhibits a statistically significant association with lung cancer in a state with high residential radon concentrations. A population-based, case-control epidemiologic study was conducted examining the relationship between residential radon gas exposure and lung cancer in Iowa females who occupied their current home for at least 20 years. The study included 413 incident lung cancer cases and 614 age-frequency-matched controls. Participant information was obtained by a mailed-out questionnaire with face-to-face follow-up. Radon dosimetry assessment consisted of five components: (1) on-site residential assessment survey; (2) on-site radon measurements; (3) regional outdoor radon measurements; (4) assessment of subjects' exposure when in another building; and (5) linkage of historic subject mobility with residential, outdoor, and other building radon concentrations. Histologic review was performed for 96% of the cases. Approximately 60% of the basement radon concentrations and 30% of the first floor radon concentrations of study participants' homes exceeded the US Environmental Protection Agency action level of 150 Bq m(-3) (4 pCi l(-1)). Large areas of western Iowa had outdoor radon concentrations comparable to the national average indoor value of 55 Bq m(-3) (1.5 pCi l(-1)). Excess odds of 0.24 (95% CI = -0.05-0.92) and 0.49 (95% CI = 0.03-1.84) per 11 WLM(5-19) were calculated using the continuous radon exposure estimates for all cases and live cases, respectively. Slightly higher excess odds of 0.50 (95% CI = 0.004-1.80) and 0.83 (CI = 0.11-3.34) per 11 WLM(5-19) were noted for the categorical radon exposure estimates for all cases and the live cases. A positive association between cumulative radon gas exposure and lung cancer was demonstrated using both categorical and continuous analyses. The risk estimates obtained in this study indicate that cumulative radon exposure presents an important environmental health hazard.

Shape of the quantum diffusion front.

We show that quantum diffusion has well-defined front shape. After an initial transient, the wave packet front (tails) is described by a stretched exponential P(x,t) = A(t)exp(-absolute value of [x/w](gamma)), with 1 < gamma < infinity, where w(t) is the spreading width which scales as w(t) approximately t(beta), with 0 < beta < or = 1. The two exponents satisfy the universal relation gamma = 1/(1-beta). We demonstrate these results through numerical work on one-dimensional quasiperiodic systems and the three-dimensional Anderson model of disorder. We provide an analytical derivation of these relations by using the memory function formalism of quantum dynamics. Furthermore, we present an application to experimental results for the quantum kicked rotor.

Recovery of classically chaotic behavior in a noise-driven quantum system.

The quantum kicked rotor is studied in a regime of high amplitude noise. A transition to diffusive behavior is observed as dynamical localization, characterized by suppressed diffusion and exponential momentum distributions, is completely destroyed by noise. With increasing noise amplitude, further transition to classical behavior is shown through an accurate quantitative analysis, which demonstrates that both the energy growth and the momentum distributions are reaching their classical limits. The importance of short-time correlations in the recovery of classically chaotic behavior is discussed.

Residential radon gas exposure and lung cancer: the Iowa Radon Lung Cancer Study.

Exposure to high concentrations of radon progeny (radon) produces lung cancer in both underground miners and experimentally exposed laboratory animals. To determine the risk posed by residential radon exposure, the authors performed a population-based, case-control epidemiologic study in Iowa from 1993 to 1997. Subjects were female Iowa residents who had occupied their current home for at least 20 years. A total of 413 lung cancer cases and 614 age-frequency-matched controls were included in the final analysis. Excess odds were calculated per 11 working-level months for exposures that occurred 5-19 years (WLM(5-19)) prior to diagnosis for cases or prior to time of interview for controls. Eleven WLM(5-19) is approximately equal to an average residential radon exposure of 4 pCl/liter (148 Bq/m3) during this period. After adjustment for age, smoking, and education, the authors found excess odds of 0.50 (95% confidence interval: 0.004, 1.81) and 0.83 (95% percent confidence interval: 0.11, 3.34) using categorical radon exposure estimates for all cases and for live cases, respectively. Slightly lower excess odds of 0.24 (95 percent confidence interval: -0.05, 0.92) and 0.49 (95 percent confidence interval: 0.03, 1.84) per 11 WLM(5-19) were noted for continuous radon exposure estimates for all subjects and live subjects only. The observed risk estimates suggest that cumulative ambient radon exposure presents an important environmental health hazard.

Intercomparison of retrospective radon detectors.

We performed both a laboratory and a field intercomparison of two novel glass-based retrospective radon detectors previously used in major radon case-control studies performed in Missouri and Iowa. The new detectors estimate retrospective residential radon exposure from the accumulation of a long-lived radon decay product, (210)Pb, in glass. The detectors use track registration material in direct contact with glass surfaces to measure the alpha-emission of a (210)Pb-decay product, (210)Po. The detector's track density generation rate (tracks per square centimeter per hour) is proportional to the surface alpha-activity. In the absence of other strong sources of alpha-emission in the glass, the implanted surface alpha-activity should be proportional to the accumulated (210)Po, and hence to the cumulative radon gas exposure. The goals of the intercomparison were to a) perform collocated measurements using two different glass-based retrospective radon detectors in a controlled laboratory environment to compare their relative response to implanted polonium in the absence of environmental variation, b) perform collocated measurements using two different retrospective radon progeny detectors in a variety of residential settings to compare their detection of glass-implanted polonium activities, and c) examine the correlation between track density rates and contemporary radon gas concentrations. The laboratory results suggested that the materials and methods used by the studies produced similar track densities in detectors exposed to the same implanted (210)Po activity. The field phase of the intercomparison found excellent agreement between the track density rates for the two types of retrospective detectors. The correlation between the track density rates and direct contemporary radon concentration measurements was relatively high, considering that no adjustments were performed to account for either the residential depositional environment or glass surface type. Preliminary comparisons of the models used to translate track rate densities to average long-term radon concentrations differ between the two studies. Further calibration of the retrospective detectors' models for interpretation of track rate density may allow the pooling of studies that use glass-based retrospective radon detectors to determine historic residential radon exposures.

Exposure to atmospheric radon.

We measured radon (222Rn) concentrations in Iowa and Minnesota and found that unusually high annual average radon concentrations occur outdoors in portions of central North America. In some areas, outdoor concentrations exceed the national average indoor radon concentration. The general spatial patterns of outdoor radon and indoor radon are similar to the spatial distribution of radon progeny in the soil. Outdoor radon exposure in this region can be a substantial fraction of an individual's total radon exposure and is highly variable across the population. Estimated lifetime effective dose equivalents for the women participants in a radon-related lung cancer study varied by a factor of two at the median dose, 8 mSv, and ranged up to 60 mSv (6 rem). Failure to include these doses can reduce the statistical power of epidemiologic studies that examine the lung cancer risk associated with residential radon exposure.

Retrospective temporal and spatial mobility of adult Iowa women.

Human exposure assessments require a linkage between toxicant concentrations in occupied spaces and the receptor's mobility pattern. Databases reporting distinct populations' mobility in various parts of the home, time outside the home, and time in another building are scarce. Temporal longitudinal trends in these mobility patterns for specific age and gender groups are nonexistent. This paper describes subgroup trends in the spatial and temporal mobility patterns within the home, outside the home, and in another building for 619 Iowa females that occupied the same home for at least 20 years. The study found that the mean time spent at home for the participants ranged from a low of 69.4% for the 50-59 year age group to a high of 81.6% for the over 80-year-old age group. Participants who lived in either one- or two- story homes with basements spent the majority of their residential occupancy on the first story. Trends across age varied for other subgroups by number of children, education, and urban/rural status. Since all of these trends were nonlinear, they indicate that error exists when assuming a constant, such as a 75% home occupancy factor, which has been advocated by some researchers and agencies. In addition, while aggregate data, such as presented in this report, are more helpful in deriving risk estimates for population subgroups, they cannot supplant good individual-level data for determining risks.

Spatial variation of residential radon concentrations: the Iowa Radon Lung Cancer Study.

Homeowners and researchers frequently estimate the radon concentrations in various areas of the home from a single radon measurement often performed in the home's basement. This study describes the spatial variation of radon concentrations both between floors and between rooms on the same floor. The geometric mean basement and first floor radon concentrations for one-story homes were 13.8% and 9.0% higher, respectively, as compared to their counterparts in two-story homes. The median first floor/basement ratio of radon concentrations for one-story homes was 0.60. The median ratios between first floor/basement and second floor/basement for two-story homes were 0.51 and 0.62, respectively. The mean coefficient of variation for detectors placed on the same floor was 9.5%, which was only 2.6% higher than the mean coefficient of variation found for collocated (duplicate) quality control detectors. The wide individual variations noted in radon concentrations serve as a reminder of the importance of performing multiple radon measurements in various parts of the home when estimating home radon concentrations.

Temporal and spatial variation of waterborne point-of-use 222Rn in three water distribution systems.

Three water supply systems in Iowa were studied to examine temporal variation of 222Rn at the point of entry and the point of use. For the three towns, 71, 9, and 0% of the maximum point-of-use 222Rn concentrations were significantly higher than the point-of-entry 222Rn concentrations. Homes connected to older water mains in two of the towns had higher 222Rn concentrations than those connected to newer water mains. In one town, the waterborne 222Rn concentrations in the home were related to the home's location along an old water main. The increase in 222Rn concentrations, after the water leaves the water plant, were attributed to radium deposits in the water distribution system. In addition, the water plant's radium laden iron filters contributed 7 Bq L-1 and 60 Bq L-1 of 222Rn to the finished water in What Cheer, Iowa, and Wellman, Iowa, respectively. Backwashing schedules in the water treatment systems greatly affected point-of-entry 222Rn concentrations. The results of this study have important implications for 222Rn sampling, required for regulatory compliance.

Residential radon-222 exposure and lung cancer: exposure assessment methodology.

Although occupational epidemiological studies and animal experimentation provide strong evidence that radon-222 (222Rn) progeny exposure causes lung cancer, residential epidemiological studies have not confirmed this association. Past residential epidemiological studies have yielded contradictory findings. Exposure misclassification has seriously compromised the ability of these studies to detect whether an association exists between 222Rn exposure and lung cancer. Misclassification of 222Rn exposure has arisen primarily from: 1) detector measurement error; 2) failure to consider temporal and spatial 222Rn variations within a home; 3) missing data from previously occupied homes that currently are inaccessible; 4) failure to link 222Rn concentrations with subject mobility; and 5) measuring 222Rn gas concentration as a surrogate for 222Rn progeny exposure. This paper examines these methodological dosimetry problems and addresses how we are accounting for them in an ongoing, population-based, case-control study of 222Rn and lung cancer in Iowa.

Long-term radon concentrations estimated from 210Po embedded in glass.

Measured surface-alpha activity on glass exposed in radon chambers and houses has a linear correlation to the integrated radon exposure. Experimental results in chambers and houses have been obtained on glass exposed to radon concentrations between 100 Bq m-3 and 9 MBq m-3 for periods of a few days to several years. Theoretical calculations support the experimental results through a model that predicts the fractions of airborne activity that deposit and become embedded or adsorbed. The combination of measured activity and calculated embedded fraction for a given deposition environment can be applied to most indoor areas and produces a better estimate for lifetime radon exposure than estimates based on short-term indoor radon measurements.

Spatial and temporal indoor radon variations.

This paper examines the ability of standard radon measurement protocols to predict long-term radon concentrations in houses located in the upper Midwest. It was observed that: (1) significant radon variations can occur on a spatial scale as small as a single floor; (2) radon measurements that integrate for periods less than 3 mo are reliable only to within a factor of 2 or more; and (3) contemporary, short-term measurements within existing structures may not accurately reflect past radon concentrations. Two-hundred forty-three occupied houses located in 40 towns were monitored for at least 1 y using alpha-track detectors. If lifetime radon exposure estimates need to be determined accurately, then long-term, integrating radon detectors should be placed in several rooms of each house. In radon atmospheres that may not be stable for long periods of time, it is suggested that multiple, year-long measurements or surface alpha activity measurements in combination with year-long alpha-track measurements are needed for an accurate lifetime radon assessment.