Linac-integrated kV-cone beam CT polymer gel dosimetry.

X-ray CT polymer gel dosimetry (PGD) remains a promising tool for three dimensional verification of high-dose treatment deliveries such as non-coplanar stereotactic irradiations. Recent demonstrations have shown a proof-of-principle application of linac-integrated cone beam CT-imaged (LI-CBCT) PGDs for 3D dose verification. LI-CBCT offers advantages over previous CT based PGD, including close to real-time imaging of the irradiated dosimeter, as well as the ability to maintain the dosimeter in the same physical location for irradiation and imaging, thereby eliminating spatial errors due to dosimeter re-positioning for read-out that may occur for other systems. However the dosimetric characteristics of a LI-CBCT PGD system remain to be established. The work herein determines the dosimetric properties and critical parameters needed to perform cone beam PGD. In particular, we show that imaging the dosimeter 20-30 min post irradiation offers excellent recovery of maximum polymerization yield ([Formula: see text]90%), averaging with as few as 10 image averages can provide ∼90% gamma pass rates (3%, 3 mm) as compared to treatment planning, and that eliminating outlier averaging points can improve the precision and signal to noise ratio of resultant images. In summary, with appropriate methodology LI-CBCT PGD can provide dosimetric data capable of verification of complex high dose radiation deliveries in three dimensions and may find use in commissioning and validation of novel complex treatments.

Evaluation of an x-ray CT polymer gel dosimetry system in the measurement of deformed dose.

This study is an evaluation of the use of a N-isopropylacrylamide (NIPAM)-based x-ray CT polymer gel dosimetry (PGD) system in the measurement of deformed dose. This work also compares dose that is measured by the gel dosimetry system to dose calculated by a novel deformable dose accumulation algorithm, defDOSXYZnrc, that uses direct voxel tracking. Deformable gels were first irradiated using a single 3.5 × 5 cm2 open field and the static dose was compared to defDOSXYZnrc as a control measurement. Gel measurement was found to be in excellent agreement with defDOSXYZnrc in the static case with gamma passing rates of 94.5% using a 3%/3 mm criterion and 93.3% using a 3%/2 mm criterion. Following the static measurements, a deformable gel was irradiated with the same single field under an external compression of 25 mm and then released from this compression for dosimetric read out. The measured deformed dose was then compared to deformed dose calculated by defDOSXYZnrc based on deformation vectors produced by the Velocity AI deformable image registration (DIR) algorithm. In the deformed dose distribution there were differences in the measured and calculated field position of up to 0.8 mm and differences in the measured in calculated field size of up to 11.9 mm. Gamma pass rates were 60.0% using a 3%/3 mm criterion and 56.8% using a 3%/2 mm criterion for the deforming measurements representing a decrease in agreement compared to the control measurements. Further analysis showed that passing rates increased to 86.5% using a 3%/3 mm criterion and 70.5% using a 3%/2 mm criterion in voxels within 5 mm of fiducial markers used to guide the deformable image registration. This work represents the first measurement of deformed dose using x-ray CT polymer gel dosimetry. Overall these results highlight some of the challenges in the calculation and measurement of deforming dose and provide insight into possible strategies for improvement.

Introduction of a deformable x-ray CT polymer gel dosimetry system.

This study introduces the first 3D deformable dosimetry system based on x-ray computed tomography (CT) polymer gel dosimetry and establishes the setup reproducibility, deformation characteristics and dose response of the system. A N-isopropylacrylamide (NIPAM)-based gel formulation optimized for x-ray CT gel dosimetry was used, with a latex balloon serving as the deformable container and low-density polyethylene and polyvinyl alcohol providing additional oxygen barrier. Deformable gels were irradiated with a 6 MV calibration pattern to determine dosimetric response and a dosimetrically uniform plan to determine the spatial uniformity of the response. Wax beads were added to each gel as fiducial markers to track the deformation and setup of the gel dosimeters. From positions of the beads on CT images the setup reproducibility and the limits and reproducibility of gel deformation were determined. Comparison of gel measurements with Monte Carlo dose calculations found excellent dosimetric accuracy, comparable to that of an established non-deformable dosimetry system, with a mean dose discrepancy of 1.5% in the low-dose gradient region and a gamma pass rate of 97.9% using a 3%/3 mm criterion. The deformable dosimeter also showed good overall spatial dose uniformity throughout the dosimeter with some discrepancies within 20 mm of the edge of the container. Tracking of the beads within the dosimeter found that sub-millimetre setup accuracy is achievable with this system. The dosimeter was able to deform and relax when externally compressed by up to 30 mm without sustaining any permanent damage. Internal deformations in 3D produced average marker movements of up to 12 mm along the direction of compression. These deformations were also shown to be reproducible over 100 consecutive deformations. This work has established several important characteristics of a new deformable dosimetry system which shows promise for future clinical applications, including the validation of deformable dose accumulation algorithms.

Reciprocal regulation of RhoA and RhoC characterizes the EMT and identifies RhoC as a prognostic marker of colon carcinoma.

Understanding how RhoC expression and activation are regulated is essential for deciphering its contribution to tumorigenesis. Here, we report that RhoC expression and activation are induced by the epithelial to mesenchymal transition (EMT) of colon carcinoma. Using LIM 1863 colon cancer cells, RhoC protein expression and subsequent activation were detected coincident with the loss of E-cadherin and acquisition of mesenchymal characteristics. Several Ets-1 binding sites were identified in the RhoC promoter, and evidence was obtained using chromatin immunoprecipitation that Ets-1 can regulate RhoC expression during the EMT. Interestingly, a marked decrease in RhoA activation associated with the EMT was observed that corresponds to the increase in RhoC expression. Use of shRNA established that RhoA inhibits and RhoC promotes post-EMT cell migration, demonstrating functional significance for their coordinate regulation. To assess the importance of RhoC expression in colon cancer, immunohistochemistry was performed on 566 colorectal tumors with known clinical outcome. The level of RhoC ranged from no expression to high expression, and statistical analysis revealed that elevated RhoC expression correlates with poor outcome as well as aberrant expression and localization of E-cadherin. These data provide one mechanism for how RhoC expression is regulated in colon carcinoma and substantiate its utility as a prognostic marker.

Consumption of untreated tank rainwater and gastroenteritis among young children in South Australia.

BACKGROUND: Tank rainwater is a source of untreated drinking water in Australia and elsewhere. The aim of this study was to determine whether the risk of gastroenteritis among children who drank tank rainwater differed from that of children who drank treated public mains water. METHODS: A cohort study of 1,016 4- to 6-year old children who drank rainwater or treated mains water in rural South Australia was undertaken in 1999. Parents kept a daily diary of their child's gastrointestinal symptoms and water consumption for a period of 6 weeks. Data on respiratory illness and other risk factors for gastroenteritis were also collected. RESULTS: The incidence of gastroenteritis among children was 3.8-5.3 episodes per child-year, but most episodes (60%) lasted just 1 day. No increase in odds of gastroenteritis was observed among children who drank rainwater compared with treated mains water. The adjusted odds ratio for gastroenteritis associated with rainwater consumption compared with mains consumption was 0.84 (95% confidence interval 0.63-1.13). CONCLUSIONS: Gastroenteritis was found to be a significant cause of morbidity among young children. Young children, who were regular consumers of tank rainwater, were at no greater odds of gastroenteritis than those who drank treated public mains water.

Trial-by-trial discrimination of three enantiomer pairs by neural ensembles in mammalian olfactory bulb.

Populations of output neurons in the mammalian olfactory bulb (OB) exhibit distinct, widespread spatial and temporal activation patterns when stimulated with odorants. However, questions remain as to how ensembles of mitral/tufted (M/T) neurons in the mammalian OB represent odorant information. In this report, the single-trial encoding limits of random ensembles of putative single- and multiunit M/T cells in the anesthetized rat OB during presentations of enantiomers of limonene, carvone, and 2-butanol are investigated using simultaneous multielectrode recording techniques. The results of these experiments are: the individual constituents of our recorded ensembles broadly represent information about the presented odorants, the ensemble single-trial response of small spatially distributed populations of M/T neurons can readily discriminate between six different odorants, and the most consistent odorant discrimination is attained when the ensemble consists of all available units and their responses are integrated over an entire breathing cycle. These results suggest that small differences in spike counts among the ensemble members become significant when taken within the context of the entire ensemble. This may explain how ensembles of broadly tuned OB neurons contribute to olfactory perception and may explain how small numbers of individual units receiving input from distinct olfactory receptor neurons can be combined to form a robust representation of odorants.

High-resolution analysis of the spatio-temporal activity patterns in rat olfactory bulb evoked by enantiomer odors.

Understanding how mammals process olfactory stimuli has motivated the development of tools and techniques which permit the simultaneous study of finely structured spatial and temporal patterns of neural activity. A technique is described that uses an array of 32 penetrating microelectrodes implanted bilaterally into the dorsal aspect of rat olfactory bulb to investigate the responses of mitral and tufted neurons to stimulation with simple enantiomer odor pairs at a number of concentrations. It is shown that stable, simultaneous recordings from up to 49 single- and multi-units can be performed for periods of up to 14 h. We show that such odors evoke unique spatial and fast-temporal activity patterns which may subserve odor discrimination. This technique is extensible to other systems neuroscience investigations of olfactory sensory processing.

Exercise-induced HSP27, HSP70 and MAPK responses in human skeletal muscle.

AIM: The present work examined protein and messenger RNA (mRNA) expression of intramuscular heat shock protein 27 (HSP27), heat shock cognate (HSC70) and HSP70 in human biceps brachii (BB) and vastus lateralis (VL) subsequent to two different exercises. METHODS: Untrained subjects performed 50 high-force eccentric contractions with their non-dominant BB and ran downhill (-10 degrees) for 30 min. The 48-h PX stress response was evaluated with immunoblotting and reverse transcriptase-polymerase chain reaction (RT-PCR). Muscle damage was indicated indirectly at 48 h post-exercise (PX) [loss of mobility, muscle soreness and serum creatine kinase (CK) activity]. RESULTS: On the protein level, HSP27 and HSP70 increased significantly PX in the BB (384 and 227%, respectively; P < 0.01), but there were no significant HSP changes in the VL or in HSC70 in either muscle. The RT-PCR data complemented these findings: BB HSP27 and HSP70C mRNA levels increased (135 and 128%, respectively; P < 0.05); in the VL only HSP70B increased (206%; P < 0.05). Phosphorylation of e-jun NH2-terminal kinase (JNK) and extracellular regulated kinase (ERK) increased significantly in the BB (226 and 200%, respectively; P < 0.05) but not in the VL, indicating activation of these pathways only after the resistance exercise. CONCLUSION: These data indicate that the PX HSP and mitogen-activated protein kinase responses are exercise-specific and local, not systemic. Further, only the resistance exercise induced HSP expression (protein and mRNA) and JNK/ERK activation at 48 h PX, suggesting that these molecules may be important to long-term skeletal muscle adaptations such as hypertrophy.

Catalytic coupling of the active sites in acetyl-CoA synthase, a bifunctional CO-channeling enzyme.

Acetogenic bacteria contain acetyl-CoA synthase (ACS), an enzyme with two distinct nickel-iron-sulfur active sites connected by a tunnel through which CO migrates. One site reduces CO2 to CO, while the other synthesizes acetyl-CoA from CO, CoA, and the methyl group of another protein (CH3-CP). Rapid binding of CO2 and a two-electron reduction activates ACS. When CoA and CH3-CP bind ACS, CO is rerouted through the tunnel to the synthase site, and kinetic parameters at the reductase site are altered. Under these conditions, the rates of CO2 reduction and acetyl-CoA synthesis are synchronized by an ordered catalytic mechanism.

Visual prostheses.

The development of man-made systems to restore functional vision in the profoundly blind has recently undergone a renaissance that has been fueled by a combination of celebrity and government interest, advances in the field of bioengineering, and successes with existing neuroprosthetic systems. This chapter presents the underlying physiologic principles of artificial vision, discusses three contemporary approaches to restoring functional vision in the blind, and concludes by presenting several relevant questions to vision prostheses. While there has been significant progress in the individual components constituting an artificial vision system, the remaining challenge of integrating these components with each other and the nervous system does not lie strictly in the realm of neuroscience, medicine, or engineering but at the interface of all three. In spite of the apparent complexity of an artificial vision system, it is not unreasonable to be optimistic about its eventual success.

Kinetic mechanism of acetyl-CoA synthase: steady-state synthesis at variable Co/Co2 pressures.

Steady-state initial rates of acetyl-CoA synthesis (upsilon/[E(tot)]) catalyzed by acetyl-CoA synthase from Clostridium thermoaceticum (ACS) were determined at various partial pressures of CO and CO2. When [CO] was varied from 0 to 100 microM in a balance of Ar, rates increased sharply from 0.3 to 100 min(-1). At [CO] > 100 microM, rates declined sharply and eventually stabilized at 10 min(-1) at 980 microM CO. Equivalent experiments carried out in CO2 revealed similar inhibitory behavior and residual activity under saturating [CO]. Plots of upsilon/[E(tot)] vs [CO2] at different fixed inhibitory [CO] revealed that Vmax/[E(tot)] (kcat) decreased with increasing [CO]. Plots of upsilon/[E(tot)] vs [CO2] at different fixed noninhibitory [CO] showed that Vmax/[E(tot)] was insensitive to changes in [CO]. Of eleven candidate mechanisms, the simplest one that fit the data best had the following key features: (a) either CO or CO2 (at a designated reductant level and pH) activate the enzyme (E' + CO right arrow over left arrow E, E' + CO2/2e-/2H+ right arrow over left arrow E); (b) CO and CO2 are both substrates that compete for the same enzyme form (E + CO right arrow over left arrow ECO, E + CO2/2e-/2H+ right arrow over left arrow ECO, and ECO --> E + P); (c) between 3 and 5 molecules of CO bind cooperatively to an enzyme form different from that to which CO2 and substrate CO bind (nCO + ECO right arrow over left arrow (CO)nECO), and this inhibits catalysis; and (d) the residual activity arises from either the (CO)nECO state or a heterogeneous form of the enzyme. Implications of these results, focusing on the roles of CO and CO2 in catalysis, are discussed.

Head louse infection: a health promotion activity.

Head lice are the most common human ectoparasite. Although an infectious disease, louse infection rarely cause physical problems other than an itchy scalp. Social stigma surrounding infection induces feelings of shame, anger and embarrassment for families. Preventative health education and promotion via screening can effectively reduce the incidences of lice infection. The Mosaic Model of Treatment is recommended as the most up-to-date treatment regime, suitable for use on all children.

A technique to prevent dural adhesions to chronically implanted microelectrode arrays.

Minimizing relative movements between neural tissues and arrays of microelectrodes chronically implanted into them is expected to greatly enhance the capacity of the microelectrodes to record from single cortical neurons on a long-term basis. We describe a new surgical technique to minimize the formation of adhesions between the dura and an implanted electrode array using a 12 microm (0.5 mil) thick sheet of Teflon film positioned between the array and the dura. A total of 15 cats were implanted using this technique. Gross examination of 12 implant sites at the time of sacrifice failed to find evidence of adhesions between the arrays and the dura when the Teflon(R) film remained in its initial position. In six implants from which recordings were made, an average of nine of the 11 (81%) connected electrodes in each array recorded evoked neural activity after 180 days post implantation. Further, on average, two separable units were identified on each of the implanted electrodes in these arrays. No significant change was found in the density of cell bodies around implanted electrodes of four of the implanted electrode arrays. However, histological evaluation of the implant sites revealed evidence of meningeal proliferation beneath the arrays. The technique described is shown to be effective at preventing adhesions between implanted electrode arrays and improve the characteristics of chronic recordings obtained with these structures.

Neuronal interactions improve cortical population coding of movement direction.

Interactions among groups of neurons in primary motor cortex (MI) may convey information about motor behavior. We investigated the information carried by interactions in MI of macaque monkeys using a novel multielectrode array to record simultaneously from 12-16 neurons during an arm-reaching task. Pairs of simultaneously recorded cells revealed significant correlations in their trial-to-trial firing rate variation when estimated over broad (600 msec) time intervals. This covariation was only weakly related to the preferred directions of the individual MI neurons estimated from the firing rate and did not vary significantly with interelectrode distance. Most significantly, in a portion of cell pairs, correlation strength varied with the direction of the arm movement. We evaluated to what extent correlated activity provided additional information about movement direction beyond that available in single neuron firing rate. A multivariate statistical model successfully classified direction from single trials of neural data. However, classification was consistently better when correlations were incorporated into the model as compared to one in which neurons were treated as independent encoders. Information-theoretic analysis demonstrated that interactions caused by correlated activity carry additional information about movement direction beyond that based on the firing rates of independently acting neurons. These results also show that cortical representations incorporating higher order features of population activity would be richer than codes based solely on firing rate, if such information can exploited by the nervous system.

A neural interface for a cortical vision prosthesis.

The development of a cortically based vision prosthesis has been hampered by a lack of basic experiments on phosphene psychophysics. This basic research has been hampered by the lack of a means to safely stimulate large numbers of cortical neurons. Recently, a number of laboratories have developed arrays of silicon microelectrodes that could enable such basic studies on phosphene psychophysics. This paper describes one such array, the Utah electrode array, and summarizes neurosurgical, physiological and histological experiments that suggest that such an array could be implanted safely in visual cortex. We also summarize a series of chronic behavioral experiments that show that modest levels of electrical currents passed into cortex via this array can evoke sensory percepts. Pending the successful outcome of biocompatibility studies using such arrays, high count arrays of penetrating microelectrodes similar to this design could provide a useful tool for studies of the psychophysics of phosphene perception in human volunteers. Such studies could provide a proof-of-concept for cortically based artificial vision.

Changes in airborne lead particulate in port pirie, South Australia, 1986-1996.

Port Pirie is 230 km north of Adelaide, the capital of South Australia. The major industry in the city is a lead smelter owned by Pasminco. Fume, dust, and fugitive emissions from the smelter have been deposited in and around Port Pirie over the past 100 years. The results presented in this paper are from an air monitoring station situated at the southeast entrance of the smelter, approximately 600 m from the blast furnace. Measurements include total suspended particulate (TSP) and total suspended particulate lead (TSPL) reported as concentrations (microgram/m3). Data are available from 1986 to 1996 and consist of 548 measurements. Analysis of geometric mean concentration levels by wind direction showed that while for TSP there was little relationship with wind direction, TSPL increased substantially as the wind came from the direction of the smelter. An analysis of geometric mean concentration levels by wind speed showed that TSP was significantly correlated with wind speed for all wind sectors apart from winds coming from the smelter production area. The lack of correlation between TSP and wind speed when the wind blows from the direction of the smelter is probably due to the dilution effect of particulate from a point source as wind speed increases. TSPL was significantly correlated with wind speed for all wind sectors apart from winds coming from the city. As expected, both TSP and TSPL concentrations were significantly lower on days when rain fell. Both mean geometric TSP and TSPL concentrations were lower in the period 1993-1996 than in 1986-1992. Multiple linear regression analysis was used to demonstrate that this decline was statistically significant after adjusting for weather conditions. Wind directions were divided into four sectors: winds from the smelter production area; winds from the smelter nonproduction area; winds from the zinc wharf and east of the city; and winds from the city. Structural equation models for each sector were used to demonstrate that the decline in geometric mean TSPL concentrations over the two periods were of a similar order of magnitude for all four sectors. The relevance of this to the lead abatement programs that have been undertaken both within the city of Port Pirie and inside the smelter itself is discussed.

The Utah intracortical Electrode Array: a recording structure for potential brain-computer interfaces.

We investigated the potential of the Utah Intracortical Electrode Array (UIEA) to provide signals for a brain-computer interface (BCI). The UIEA records from small populations of neurons which have an average signal-to-noise ratio (SNR) of 6:1. We provide specific examples that show the activities of these populations of neurons contain sufficient information to perform control tasks. Results from a simple stimulus detection task using these signals as inputs confirm that the number of neurons present in a recording is significant in determining task performance. Increasing the number of units in a recording decreases the sensitivity of the response to the stimulus; decreasing the number of units in the recording, however, increases the variability of the response to the stimulus. We conclude that recordings from small populations of neurons, not single units, provide a reliable source of sufficiently stimulus selective signals which should be suitable for a BCI. In addition, the potential for simultaneous and proportional control of a large number of external devices may be realized through the ability of an array of microelectrodes such as the UIEA to record both spatial and temporal patterns of neuronal activation.

Single unit recording capabilities of a 100 microelectrode array.

We have developed a three-dimensional silicon electrode array which provides 100 separate channels for neural recording in cortex. The device is manufactured using silicon micromachining techniques, and we have conducted acute recording experiments in cat striate cortex to evaluate the recording capabilities of the array. In a series of five acute experiments, 58.6% of the electrodes in the array were found to be capable of recording visually evoked responses. In the most recent acute study, the average signal-to-noise ratio for recordings obtained from 56 of the electrodes in the array was calculated to be 5.5:1. Using standard window discrimination techniques, an average of 3.4 separable spikes were identified for each of these electrodes. In order to compare the two-dimensional mapping capabilities of the array with those derived from other technologies, orientation preference and ocular dominance maps were generated for each of the evoked responses. Histological evaluation of the implant site indicates some localized tissue insult, but this is likely due to the perfusion procedure since high signal-to-noise ratio neural responses were recorded. The recording capabilities of the Utah Intracortical Electrode Array in combination with the large number of electrodes available for recording make the array a tool well suited for investigations into the parallel processing mechanisms in cortex.

A new educational approach for supporting the professional development of third-year medical students.

This paper describes a new course designed to support the professional development of third-year medical students. The course runs through the clinical clerkships, and has several additional features: it includes a multidisciplinary faculty; it is centrally based in the medical school; it addresses students' values and attitudes in addition to their knowledge and skills; and it makes use of small-group learning methods, and faculty, student, and group continuity during the year. The curriculum, which addresses ethical, social, and communicative issues in medicine, plus the evaluation of students and of the course, are described.