High-magnification Faraday rotation imaging and analysis of X-pinch implosion dynamics.

An X-pinch load driven by an intense current pulse (>100 kA in ∼100 ns) can result in the formation of a small radius, runaway compressional micro-pinch. A micro-pinch is characterized by a hot (>1 keV), current-driven (>100 kA), high-density plasma column (near solid density) with a small neck diameter (1-10 µm), a short axial extent (<1 mm), and a short duration (≲1 ns). With material pressures often well into the multi-Mbar regime, a micro-pinch plasma often radiates an intense, sub-ns burst of sub-keV to multi-keV x rays. A low-density coronal plasma immediately surrounding the dense plasma neck could potentially shunt current away from the neck and thus reduce the magnetic drive pressure applied to the neck. To study the current distribution in the coronal plasma, a Faraday rotation imaging diagnostic (1064 nm) capable of producing simultaneous high-magnification polarimetric and interferometric images has been developed for the MAIZE facility at the University of Michigan. Designed with a variable magnification (1-10×), this diagnostic achieves a spatial resolution of ∼35 µm, which is useful for resolving the ∼100-µm-scale coronal plasma immediately surrounding the dense core. This system has now been used on a reduced-output MAIZE (100-200 kA, 150 ns) to assess the radial distribution of drive current immediately surrounding the dense micro-pinch neck. The total current enclosed was found to increase as a function of radius, r, from a value of ≈50±25 kA at r ≈ 140 µm (at the edge of the dense neck) to a maximal value of ≈150±75 kA for r ≥ 225 µm. This corresponds to a peak magnetic drive pressure of ≈75±50 kbar at r ≈ 225 µm. The limitations of these measurements are discussed in the paper.

Implementation of extreme ultraviolet spectroscopy on a sheared-flow-stabilized Z pinch.

A diagnostic for extreme ultraviolet spectroscopy was fielded on the sheared-flow-stabilized (SFS) fusion Z-pinch experiment (FuZE-Q) for the first time. The spectrometer collected time-gated plasma emission spectra in the 5-40 nm wavelength (30-250 eV) range for impurity identification, radiative power studies, and for plasma temperature and density measurements. The unique implementation of the diagnostic included fast (10 ns risetime) pulsed high voltage electronics and a multi-stage differential pumping system that allowed the vacuum-coupled spectrometer to collect three independently timed spectra per FuZE-Q shot while also protecting sensitive internal components. Analysis of line emission identifies oxygen (N-, C-, B-, Be-, Li-, and He-like O), peaking in intensity shortly after maximum current (>500 kA). This work provides a foundation for future high energy spectroscopy experiments on SFS Z-pinch devices.

Negative pressure wound therapy in elective stoma reversal surgery: results of a UK district general hospital pilot.

The role of negative pressure wound therapy in stoma reversal surgery remains unknown. To evaluate this, a retrospective, non-randomized, single-institution, pilot study was conducted. Surgeon preference determined type of wound closure and application of the single-brand negative wound pressure device. No patient in the intervention group suffered wound complications, but five of the thirty-six patients in the control group suffered surgical site infection-related complications. Primary closure and negative pressure wound therapy use decreases wound complications in stoma reversal surgery, thereby alleviating the wound-management burden in hospitals and in the community. This has cost-saving implications, but further studies are needed.

Optimization of switch diagnostics on the MAIZE linear transformer driver.

The MAIZE Linear Transformer Driver consists of 40 capacitor-switch-capacitor "bricks" connected in parallel. When these 40 bricks are charged to ±100-kV and then discharged synchronously, the MAIZE facility generates a 1-MA current pulse with a 100-ns rise time into a matched load impedance. Discharging each of the capacitors in a brick is carried out by the breakdown of a spark-gap switch, a process that results in the emission of light. Monitoring this output light with a fiber optic coupled to a photomultiplier tube (PMT) and an oscilloscope channel provides information on switch performance and timing jitter-whether a switch fired early, late, or in phase with the other switches. However, monitoring each switch with a dedicated detector-oscilloscope channel can be problematic for facilities where the number of switches to be monitored (e.g., 40 on MAIZE) greatly exceeds the number of detector-oscilloscope channels available. The technique of using fibers to monitor light emission from switches can be optimized by treating a PMT as a binary digit or bit and using a combinatorial encoding scheme, where each switch is monitored by a unique combination of fiber-PMT-oscilloscope channels simultaneously. By observing the unique combination of fiber-PMT-oscilloscope channels that are turned on, the prefiring or late-firing of a single switch on MAIZE can be identified by as few as six PMT-oscilloscope channels. The number of PMT-oscilloscope channels, N, required to monitor X switches can be calculated by 2N = X + 1, where the number "2" is selected because the PMT-oscilloscope acts as a bit. In this paper, we demonstrate the use of this diagnostic technique on MAIZE. We also present an analysis of how this technique could be scaled to monitor the tens of thousands of switches proposed for various next generation pulsed power facilities.

Evaluation of microtitre plate-based Haemoglobin estimation.

INTRODUCTION: Haemoglobin estimation is one of the most important clinical investigations. Many techniques are available to measure haemoglobin; still there is a need for a haemoglobin assay technique which is cheap, robust and simple and can be used in field conditions very quickly using figure prick sample. We evaluated a cyanmethaemoglobin-based haemoglobin estimation using a microtitre plates for the purpose. METHODS: Microtitre plate-based haemoglobin estimation was developed using cyanmethaemoglobin-based assay and was compared with standard haematology analyser-based haemoglobin estimation in a large number of samples from a population of voluntary blood donors. Various tests were performed to evaluate the stability of colour, variation of the results during duplicate assay on the same days and on different days as well as linearity of the test was performed against broad range of haemoglobin values for the new microtitre plate-based technique. Standard statistical test of significance was applied to validate the assay. RESULTS: Total 200 samples from in-house and field conditions were evaluated. 10 µL blood sample in 300 µL Drabkin's solution provided optimum and comparable results after 10 minutes of incubation. The colour was stable up to 6 hours, the coefficient of variation was less than 3%, and the cost per test including everything was less than 3 cent/2P. Turnaround time for 90 samples was only 30 minutes. CONCLUSION: Cyanmethaemoglobin-based assay in microtitre plate is feasible, robust, rapid, cheap and cost-effective method for haemoglobin estimation in field conditions.

Skeletal absorbed fractions for electrons in the adult male: considerations of a revised 50-microm definition of the bone endosteum.

In 1995, the International Commission on Radiological Protection (ICRP) issued ICRP Publication 70 which provided an extensive update to the physiological and anatomical reference data for the skeleton of adults and children originally issued in ICRP Publication 23. Although ICRP Publication 70 has been a valuable document in the development of reference voxel computational phantoms, additional guidance is needed for dose assessment in the skeletal tissues beyond that given in ICRP Publication 30. In this study, a computed tomography (CT) and micro-CT-based model of the skeletal tissues is presented, which considers (1) a 50-microm depth in marrow for the osteoprogenitor cells, (2) electron escape from trabecular spongiosa to the surrounding cortical bone, (3) cortical bone to trabecular spongiosa cross-fire for electrons and (4) variations in specific absorbed fraction with changes in bone marrow cellularity for electrons. A representative data set is given for electron dosimetry in the craniofacial bones of the adult male.

Role of TrkB in the anxiolytic-like and antidepressant-like effects of vagal nerve stimulation: Comparison with desipramine.

A current hypothesis regarding the mechanism of antidepressant (AD) action suggests the involvement of brain-derived neurotrophic factor (BDNF). Consistent with this hypothesis, the receptor for BDNF (and neurotrophin 4/5 (NT-4/5)), Tropomyosin-related kinase B (TrkB), is activated in rodents by treatment with classical AD drugs. Vagal nerve stimulation (VNS), a therapy for treatment resistant depression (TRD), also activates TrkB in rodents. However, the role of this receptor in the therapeutic effects of VNS is unclear. In the current study, the involvement of TrkB in the effects of VNS was investigated in rats using its inhibitor, K252a. Anxiolytic-like and AD-like effects were analyzed using the novelty suppressed feeding test (NSFT) and forced swim test (FST), respectively. K252a blocked the anxiolytic-like effect of chronic VNS treatment and the AD-like effect of acute VNS treatment. By contrast, blocking TrkB did not prevent either the anxiolytic-like or AD-like effect of chronic treatment with desipramine (DMI), a selective noradrenergic reuptake inhibitor; it did, however, block the acute effect of DMI in the FST. To examine whether the activation of TrkB caused by either VNS or DMI is ligand-dependent, use was made of TrkB-Fc, a molecular scavenger for ligands of TrkB. Intraventricular administration of TrkB-Fc blocked the acute activation of TrkB induced by either treatment, indicating that treatment-induced activation of this receptor is ligand-dependent. The behavioral results highlight differences in the involvement of TrkB in the chronic effects of an AD drug and a stimulation therapy as well as its role in acute versus chronic effects of DMI.

Voxel size effects in three-dimensional nuclear magnetic resonance microscopy performed for trabecular bone dosimetry.

An important problem in internal dosimetry is the assessment of energy deposition by beta particles within trabecular regions of the skeleton. Recent dosimetry methods for trabecular bone are based on Monte Carlo particle transport simulations within three-dimensional (3D) images of real human bone samples. Nuclear magnetic resonance (NMR) microscopy is a 3D imaging technique of choice due to the large signal differential between bone tissue and the water-filled marrow cavities. Image voxel sizes currently used in NMR microscopy are between 50 microm and 100 microm, but the images are time consuming to acquire and can only be performed at present for in vitro samples. It is therefore important to evaluate what resolution is best suitable in order to properly characterize the trabecular microstructure, to adequately predict the tissue dosimetry, and to minimize imaging time. In this work, a mathematical model of trabecular bone, composed of a distribution of spherical marrow cavities, was constructed. The mathematical model was subsequently voxelized with different voxel sizes (16 microm to 1,000 microm) to simulate 3D NMR images. For each image, voxels are assigned to either bone or marrow according to their enclosed marrow fraction. Next, the images are coupled to the EGS4 electron transport code and absorbed fractions to bone and marrow are calculated for a marrow source of monoenergetic electrons. Radionuclide S values are also determined for the voxelized images with results compared to data calculated for the pure mathematical sample. The comparison shows that for higher energy electrons (>400 keV), good convergence of the results is seen even within images of poor resolution. Above 400 keV, a voxel resolution as large as 300 microm results in dosimetry errors below 5%. For low-energy electrons and high-resolution images, the self-dose to marrow is also determined to within 5% accuracy. Nevertheless, increased voxelization of the image overestimates the surface area of the bone-marrow interface leading to errors in the cross-dose to bone as high as 25% for some low-energy beta emitters.

Surface area overestimation within three-dimensional digital images and its consequence for skeletal dosimetry.

The most recent methods for trabecular bone dosimetry are based on Monte Carlo transport simulations within three-dimensional (3D) images of real human bone samples. Nuclear magnetic resonance and micro-computed tomography have been commonly used as imaging tools for studying trabecular microstructure. In order to evaluate the accuracy of these techniques for radiation dosimetry, a previous study was conducted that showed an overestimate in the absorbed fraction of energy for low-energy electrons emitted within the marrow space and irradiating the bone trabeculae. This problem was found to be related to an overestimate of the surface area of the true bone-marrow interface within the 3D digital images, and was identified as the surface-area effect. The goal of the present study is to better understand how this surface-area effect occurs in the case of single spheres representing individual marrow cavities within trabecular bone. First, a theoretical study was conducted which showed that voxelization of the spherical marrow cavity results in a 50% overestimation of the spherical surface area. Moreover, this overestimation cannot be reduced through a reduction in the voxel size (e.g., improved image resolution). Second, a series of single-sphere marrow cavity models was created with electron sources simulated within the sphere (marrow source) and outside the sphere (bone trabeculae source). The series of single-sphere models was then voxelized to represent 3D digital images of varying resolution. Transport calculations were made for both marrow and bone electron sources within these simulated images. The study showed that for low-energy electrons (<100 keV), the 50% overestimate of the bone-marrow interface surface area can lead to a 50% overestimate of the cross-absorbed fraction. It is concluded that while improved resolution will not reduce the surface area effects found within 3D image-based transport models, a tenfold improvement in current image resolution would compensate the associated errors in cross-region absorbed fractions for low-energy electron sources. Alternatively, other methods of defining the bone-marrow interface, such as with a polygonal isosurface, would provide improvements in dosimetry without the need for drastic reductions in image voxel size.

Site-specific variability in trabecular bone dosimetry: considerations of energy loss to cortical bone.

With continual advances in radionuclide therapies, increasing emphasis is being placed on improving the patient specificity of dose estimates to marrow tissues. While much work has been focused on determining patient-specific assessments of radionuclide uptake in the skeleton, few studies have been initiated to explore the individual variability of absorbed fraction data for electron and beta-particle sources in various skeletal sites. The most recent values of radionuclide S values used in clinical medicine continue to utilize a formalism in which electrons are transported under a trabecular bone geometry of infinite extent. No provisions are thus made for the fraction of energy lost to the cortical bone cortex of the skeletal site and its surrounding tissues. In the present study, NMR microscopy was performed on trabecular bone samples taken from the femoral head and humeral proximal epiphysis of three subjects: a 51-year male, an 82-year female, and an 86-year female. Following image segmentation and coupling to EGS4, electrons were transported within macrostructural models of the various skeletal sites that explicitly include the spatial extent of the spongiosa, as well as the thickness of the surrounding cortical bone. These energy-dependent profiles of absorbed fractions to marrow tissues were then compared to transport simulations made within an infinite region of spongiosa. Ratios of mean absorbed fraction, as weighted by the beta energy spectra, under both transport methodologies were then assembled for the radionuclides 32P and 90Y. These ratios indicate that corrections to existing radionuclide S values for 32P can vary by as much as 5% for the male, 6% for the 82-year female, and 8% for the 86-year female. For the higher-energy beta spectrum of 90Y, these same corrections can reach 8%, 10%, and 11%, respectively.

A hyperboliod representation of the bone-marrow interface within 3D NMR images of trabecular bone: applications to skeletal dosimetry.

Recent advances in physical models of skeletal dosimetry utilize high-resolution NMR microscopy images of trabecular bone. These images are coupled to radiation transport codes to assess energy deposition within active bone marrow irradiated by bone- or marrow-incorporated radionuclides. Recent studies have demonstrated that the rectangular shape of image voxels is responsible for cross-region (bone-to-marrow) absorbed fraction errors of up to 50% for very low-energy electrons (<50 keV). In this study, a new hyperboloid adaptation of the marching cube (MC) image-visualization algorithm is implemented within 3D digital images of trabecular bone to better define the bone-marrow interface, and thus reduce voxel effects in the assessment of cross-region absorbed fractions. To test the method, a mathematical sample of trabecular bone was constructed, composed of a random distribution of spherical marrow cavities, and subsequently coupled to the EGSnrc radiation code to generate reference values for the energy deposition in marrow or bone. Next, digital images of the bone model were constructed over a range of simulated image resolutions, and coupled to EGSnrc using the hyperboloid MC (HMC) algorithm. For the radionuclides 33P, 117mSn, 131I and 153Sm, values of S(marrow<--bone) estimated using voxel models of trabecular bone were shown to have relative errors of 10%, 9%, <1% and <1% at a voxel size of 150 microm. At a voxel size of 60 microm, these errors were 6%, 5%, <1% and <1%, respectively. When the HMC model was applied during particle transport, the relative errors on S(marrow<--bone) for these same radionuclides were reduced to 7%, 6%, <1% and <1% at a voxel size of 150 microm, and to 2%, 2%, <1% and <1% at a voxel size of 60 microm. The technique was also applied to a real NMR image of human trabecular bone with a similar demonstration of reductions in dosimetry errors.

Voxel effects within digital images of trabecular bone and their consequences on chord-length distribution measurements.

Chord-length distributions through the trabecular regions of the skeleton have been investigated since the early 1960s. These distributions have become important features for bone marrow dosimetry; as such, current models rely on the accuracy of their measurements. Recent techniques utilize nuclear magnetic resonance (NMR) microscopy to acquire 3D images of trabecular bone that are then used to measure 3D chord-length distributions by Monte Carlo methods. Previous studies have shown that two voxel effects largely affect the acquisition of these distributions within digital images. One is particularly pertinent as it dramatically changes the shape of the distribution and reduces its mean. An attempt was made to reduce this undesirable effect and good results were obtained for a single-sphere model using minimum acceptable chord (MAC) methods (Jokisch et al 2001 Med. Phys. 28 1493-504). The goal of the present work is to extend the study of these methods to more general models in order to better quantify their consequences. First, a mathematical model of a trabecular bone sample was used to test the usefulness of the MAC methods. The results showed that these methods were not efficient for this simulated bone model. These methods were further tested on a single voxelized sphere over a large range of voxel sizes. The results showed that the MAC methods are voxel-size dependent and overestimate the mean chord length for typical resolutions used with NMR microscopy. The study further suggests that bone and marrow chord-length distributions currently utilized in skeletal dosimetry models are most likely affected by voxel effects that yield values of mean chord length lower than their true values.

Skeletal dosimetry via NMR microscopy: investigations of sample reproducibility and signal source.

Nuclear magnetic resonance microscopy has been used for several years as a means of quantifying the 3D microarchitecture of the cancellous regions of the skeleton. These studies were originally undertaken for the purpose of developing non-invasive techniques for the early detection of osteoporosis and other bone structural changes. Recently, nuclear magnetic resonance microscopy has also been used to acquire this same 3D data for the purpose of both (1) generating chord length data across bone trabeculae and marrow cavities and (2) generating 3D images for direct coupling to Monte Carlo radiation transport codes. In both cases, one is interested in the reproducibility of the dosimetric data obtained from nuclear magnetic resonance microscopy. In the first of two studies, a trabecular bone sample from the femoral head of a 51-y-old male cadaver was subjected to repeated image acquisition, image processing, image coupling, and radiation transport simulations. The resulting absorbed fractions at high electron energies (4 MeV) were shown to vary less than 4% among four different imaging sessions of the same sample. In a separate study, two femoral head samples were imaged under differing conditions of the NMR signal source. In the first case, the samples were imaged with intact marrow. These samples were then subjected to marrow digestion and immersed in Gd-doped water, which then filled the marrow cavities. Energy-dependent absorbed fraction profiles for both the marrow-intact and marrow-free samples showed essentially equivalent results. These studies thus provide encouragement that skeletal dosimetry models of improved patient specificity can be achieved via NMR microscopy in vivo.

A dosimetric analysis comparing electron beam with the MammoSite brachytherapy applicator for intact breast boost.

INTRODUCTION: Electron beam radiation is the modality most often used to deliver an operative bed boost to breast cancer patients after completing whole breast radiation. However, electrons can potentially provide inadequate coverage. The MammoSite breast brachytherapy applicator may provide dosimetric advantages in the delivery of an operative bed boost and its role in this setting is not yet defined. MATERIALS AND METHODS: The study population consisted of 15 patients with early stage breast cancer treated with partial breast irradiation (PBI) using the MammoSite device. For each patient, a theoretical boost plan using electrons and a second theoretical boost plan using the MammoSite applicator were created. To assess the adequacy of each boost plan, the PTV V90, PTV V95, and PTV V100 were calculated. To assess dose to normal tissues, the ipsilateral breast V50, ipsilateral lung V30, and heart V20 were calculated. RESULTS: The mean PTV V100 for the MammoSite boost was 95.5%, compared to 77.4% for the electron boost (p<0.001). The mean PTV V95 was 97.8%, compared to 93.3% for the electron boost (p=0.02). The mean PTV V90, mean breast V50, mean lung V30, and mean heart V20 were not statistically different for MammoSite compared to electrons. CONCLUSIONS: A tumor bed boost using the MammoSite breast brachytherapy applicator provides superior target coverage and delivers similar doses to the ipsilateral breast and lung compared to a boost delivered with electrons. More investigation into the role of balloon brachytherapy in the delivery of a breast boost is warranted.