A novel solid-state NMR method for the investigation of trivalent lanthanide sorption on amorphous silica at low surface loadings.

The modelling of radionuclide transport in the subsurface depends on a comprehensive understanding of their interactions with mineral surfaces. Spectroscopic techniques provide important insight into these processes directly, but at high concentrations are sometimes hindered by safety concerns and limited solubilities of many radionuclides, especially the actinides. Here we use Eu(iii) as a surrogate for trivalent actinide species, and study Eu(iii) sorption on the silica surface at pH 5 where sorption is fairly limited. We have applied a novel, surface selective solid-state nuclear magnetic resonance (NMR) technique to provide information about Eu binding at the silica surface at estimated surface loadings ranging from 0.1 to 3 nmol m(-2) (<0.1% surface loading). The NMR results show that inner sphere Eu(iii) complexes are evenly distributed across the silica surface at all concentrations, but that at the highest surface loadings there are indications that precipitates may form. These results illustrate that this NMR technique may be applied in solubility-limited systems to differentiate between adsorption and precipitation to better understand the interactions of radionuclides at solid surfaces.

Technical Note: Experimental results from a prototype high-field inline MRI-linac.

PURPOSE: The pursuit of real-time image guided radiotherapy using optimal tissue contrast has seen the development of several hybrid magnetic resonance imaging (MRI)-treatment systems, high field and low field, and inline and perpendicular configurations. As part of a new MRI-linac program, an MRI scanner was integrated with a linear accelerator to enable investigations of a coupled inline MRI-linac system. This work describes results from a prototype experimental system to demonstrate the feasibility of a high field inline MR-linac. METHODS: The magnet is a 1.5 T MRI system (Sonata, Siemens Healthcare) was located in a purpose built radiofrequency (RF) cage enabling shielding from and close proximity to a linear accelerator with inline (and future perpendicular) orientation. A portable linear accelerator (Linatron, Varian) was installed together with a multileaf collimator (Millennium, Varian) to provide dynamic field collimation and the whole assembly built onto a stainless-steel rail system. A series of MRI-linac experiments was performed to investigate (1) image quality with beam on measured using a macropodine (kangaroo) ex vivo phantom; (2) the noise as a function of beam state measured using a 6-channel surface coil array; and (3) electron contamination effects measured using Gafchromic film and an electronic portal imaging device (EPID). RESULTS: (1) Image quality was unaffected by the radiation beam with the macropodine phantom image with the beam on being almost identical to the image with the beam off. (2) Noise measured with a surface RF coil produced a 25% elevation of background intensity when the radiation beam was on. (3) Film and EPID measurements demonstrated electron focusing occurring along the centerline of the magnet axis. CONCLUSIONS: A proof-of-concept high-field MRI-linac has been built and experimentally characterized. This system has allowed us to establish the efficacy of a high field inline MRI-linac and study a number of the technical challenges and solutions.

The Scheibe cochlea deformity with macrocephaly: a case for single channel implantation.

An 11-year-old congenitally deaf child with bilateral primitive common cavity (Scheibe type) cochleosaccular dysplasia and benign familial macrocephaly was implanted with an extracochlear single channel device with an ear level speech processor. This paper describes the assessment, findings, dilemmas in decision making, surgical procedure and the favourable outcome after implanting. The relevant literature has been reviewed and our case is presented for the unusual combination of features.

Cochlear implant failure due to unexpected absence of the eighth nerve--a cautionary tale.

We present a case of bilateral absence of the eighth cranial nerve in the internal auditory meatus (IAM). This caused total failure of responses after cochlear implantation in a six-year-old patient with congenital deafness. Pre-operative magnetic resonance (MR) imaging is important to show not only the anatomy of the middle and inner ears but also the structures in the IAM.

Reed beds: constructed wetlands for municipal wastewater treatment plant sludge dewatering.

Reed beds are an alternative technology wastewater treatment system that mimic the biogeochemical processes inherent in natural wetlands. The purpose of this project was to determine the effectiveness of a reed bed sludge treatment system (RBSTS) in southern New England after a six-year period of operation by examining the concentrations of selected metals in the reed bed sludge biomass and by determining the fate of solids and selected nutrients. Parameters assessed in both the reed bed influent and effluent: total suspended solids, biochemical oxygen demand, nitrate-nitrogen and total phosphorus. In addition, the following metals were studied in the reed bed influent, effluent and Phragmites plant tissue and the sludge core biomass: boron, cadmium, chromium, copper, iron, lead, manganese, molybdenum, nickel, and zinc. The removal efficiencies for sludge dewatering, total suspended solids and biochemical oxygen demand were all over 90%. Nitrate and total phosphorus removal rates were 90% and 80% respectively. Overall metals removal efficient was 87%. Copper was the only metal in the sludge biomass that exceeded the standards set by the Massachusetts Department of Environmental Protection for land disposal of sludge. The highest metal concentrations, for the most part, tended to be in the lower tier of the sludge profile. The exception was boron, which was more concentrated in the middle tier of the sludge profile. The data and results presented in this paper support the notion that reed bed sludge treatment systems and the use of reed beds provide an efficient and cost effective alternative for municipal sludge treatment.

Effect of light source instability on uniformity of 3D reconstructions from a cone beam optical CT scanner.

Temporally varying light intensity during acquisition of projection images in an optical CT scanner can potentially be misinterpreted as physical properties of the sample. This work investigated the impact of LED light source intensity instability on measured attenuation coefficients. Different scenarios were investigated by conducting one or both of the reference and data scans in a 'cold' scanner, where the light source intensity had not yet stabilised. Uniform samples were scanned to assess the impact on measured uniformity. The orange (590 nm) light source decreased in intensity by 29 % over the first 2 h, while the red (633 nm) decreased by 9 %. The rates of change of intensity at 2 h were 0.1 and 0.03 % respectively over a 5 min period-corresponding to the scan duration. The normalisation function of the reconstruction software does not fully account for the intensity differences and discrepancies remain. Attenuation coefficient inaccuracies of up to 8 % were observed for data reconstructed from projection images acquired with a cold scanner. Increased noise was observed for most cases where one or both of the scans was acquired without sufficient warm-up. The decrease in accuracy and increase in noise were most apparent for data reconstructed from reference and data scans acquired with a cold scanner on different days.

SU-E-J-179: Requirements for the Accuracy of Electron Density Data Planning for MRI Based Cervix Cancer Treatment Planning.

PURPOSE: A sensitivity analysis of the effect of variations in electron density data (ED) on dose calculation accuracy for MRI based cervical cancer treatment planning. METHODS: Five cervical cancer patients were analysed in this work. Planning CT scans represented gold standard ED data. Standard four field 3DCRT plans (prescription 45Gy) were designed on these CT scans. The CT data was then manipulated to simulate the following methods of assigning ED to MRI; (1) homogenous bulk density corrections, (2) Bulk density correction to bones, (3) rigid image registration of CT to MR, and (4) regression analysis based pseudo CT. Plans were then generated on the manipulated data sets, and compared to the plans generated on the original. Dose was analysed using Chi analysis and equivalent uniform dose (EUD). Data was analysed to quantify (A) the effect on plan design (called optimisation error), and (B) the effect on dose calculation accuracy (systematic error). RESULTS: Analysis of the averaged patient results showed that for 3DCRT, the use of imperfect electron density data had minimal impact on plan design for all tested data sets. Analysis of systematic error showed minimal errors for cases (1), (2) and (3), where average errors of less than 0.3 Gy in EUD were recorded and Chi analysis showed that over 95% of points within the high dose region (D>36Gy) were within 2% or 2mm of the original dose. For case (4), errors greater than .5 Gy in EUD were recorded; these were not considered acceptable errors. CONCLUSIONS: Using imperfect electron density data for 3DCRT treatment planning for cervical cancer patients is feasible for appropriately considered choices of electron density assignment. Further analysis is needed to test this result for IMRT, and is ongoing.

Stomatal Behavior and Water Status of Maize, Sorghum, and Tobacco under Field Conditions: I. At High Soil Water Potential.

Diurnal changes in the vertical profiles of irradiance incident upon the adaxial leaf surface (I), stomatal resistance (r(s)), leaf water potential (psi), osmotic potential (pi), and turgor potential (P) were followed concurrently in crops of maize (Zea mays L. var. Pa 602A), sorghum (Sorghum bicolor [L.] Moench var. RS610), and tobacco (Nicotiana tabacum L. var. Havanna Seed 211) on several days in 1968 to 1970 when soil water potentials were high. In all three crops the r(s), measured with a ventilated diffusion porometer, the psi, measured with the pressure chamber, the pi, measured with a vapor pressure osmometer, and the calculated P, decreased from sunrise to reach minimum values near midday and then increased again in the afternoon. The diurnal range of all the variables was greater for leaves in the upper canopy than for those in the lower canopy. P was observed to decrease with decreasing psi, but never became zero. Sorghum had a higher P at a psi of, say -10 bars, than did maize, and maize had a higher P than tobacco at the same psi. Moreover, at the same psi the upper leaves in all canopies had a higher P than the lower leaves. When compared at high irradiances, r(s) did not increase as psi declined to -13, -15, and -10 bars or as P declined to 0.3, 3.5, and 1.2 bars in maize, sorghum, and tobacco, respectively. The relation between r(s) and I in the upper, nonsenescent leaves of all three crops fits a hyperbolic curve, but the response varied with species and leaf senescence. The adaxial and abaxial epidermises had the same response of r(s) to I in maize and sorghum, whereas in tobacco the adaxial epidermis had a higher r(s) than the abaxial epidermis at all values of I. At equal values of I, tobacco had the lowest leaf resistance (r(l)) and maize had the highest r(l). Senescent maize leaves had nonfunctional stomata, whereas the lowermost sorghum leaves had higher stomatal resistances on average than the other leaves.

Water potential gradients in field tobacco.

A pressure chamber was used to establish the vertical gradients of leaf water potential (Psi(Leaf)) and stem water potential (Psi(Stem)) in field-grown tobacco (Nicotiana tabacum L. var. Havanna seed 211) at three different times of day. Leaves enclosed in polyethylene bags and aluminum foil the previous afternoon and left to equilibrate overnight were used to determine Psi(Stem). The greatest difference between Psi(Leaf) and Psi(Stem) occurred in the upper part of the plant at 1100 hours Eastern Standard Time and was 5.5 bars. The largest vertical gradient in Psi(Stem) occurred at 1300 hours. The soil water potential (Psi(Soil)), extrapolated from the potential of leaves on a completely enclosed plant, was higher than -1 bar. The vertical gradient in Psi(Stem) and the difference between Psi(Leaf) and Psi(Stem) showed the existence of a resistance to water movement within the stem (r(stem)) and a further resistance between the stem and leaf (r(petiole)). The r(petiole) and root resistance (r(root)) were estimated to be 931 and 102 bars seconds per cubic centimeter, respectively. The r(stem) was low (94 bars seconds per cubic centimeter) at 1100 hours but increased to 689 bars seconds per cubic centimeter at 1300 hours.