Proton induced activation studies in the carbon steel composites.

The number of accelerator installations has increased significantly in the last decade and requirements are consistently increasing. In these facilities neutrons and high energy charge particle induced reactions are possible with the metallic enclosures made up of natural Fe or steel composites used as structural components or shielding materials. Present study aims to generate a dose rate profile of the induced activations and quantify the induced radionuclide concentrations in the low carbon steel composites. A comparison of the radionuclide concentrations generated in the metallic Fe and SS-304 composite is also presented for a judicious material selection to minimise the radiation concerns.

Calcium scoring in low-dose ungated chest CT scans using convolutional long-short term memory networks.

We aimed to develop a novel deep-learning based method for automatic coronary artery calcium (CAC) quantification in low-dose ungated computed tomography attenuation correction maps (CTAC). In this study, we used convolutional long-short -term memory deep neural network (conv-LSTM) to automatically derive coronary artery calcium score (CAC) from both standard CAC scans and low-dose ungated scans (CT-attenuation correction maps). We trained convLSTM to segment CAC using 9543 scans. A U-Net model was trained as a reference method. Both models were validated in the OrCaCs dataset (n=32) and in the held-out cohort (n=507) without prior coronary interventions who had CTAC standard CAC scan acquired contemporarily. Cohen's kappa coefficients and concordance matrices were used to assess agreement in four CAC score categories (very low: <10, low:10-100; moderate:101-400 and high >400). The median time to derive results on a central processing unit (CPU) was significantly shorter for the conv-LSTM model- 6.18s (inter quartile range [IQR]: 5.99, 6.3) than for UNet (10.1s, IQR: 9.82, 15.9s, p<0.0001). The memory consumption during training was much lower for our model (13.11Gb) in comparison with UNet (22.31 Gb). Conv-LSTM performed comparably to UNet in terms of agreement with expert annotations, but with significantly shorter inference times and lower memory consumption.

Directional distribution of the ambient neutron dose equivalent from 145-MeV ¹9F projectiles incident on thick Al target.

The directional distribution of the ambient neutron dose equivalent from 145-MeV (19)F projectiles bombarding a thick aluminium target is measured and analysed. The measurements are carried out with a commercially available dose equivalent meter at 0°, 30°, 60° and 90° with respect to the beam direction. The experimental results are compared with calculated doses from EMPIRE nuclear reaction code and different empirical formulations proposed by others. The results are also compared with the measured data obtained from an earlier experiment at a lower projectile energy of 110 MeV for the same target-projectile combination.

Spatio-temporal variations in adult density, abdominal status & indoor resting pattern of Culex quinquefasciatus Say in Panaji, Goa, India.

BACKGROUND & OBJECTIVES: Goa is one of the filariasis endemic states of India. However, information on density pattern and resting behavior of Culex quinquefasciatus Say, the principal vector of filariasis in Goa is lacking. Therefore, current longitudinal study was undertaken to investigate these aspects. METHODS: Panaji was divided into six zones and a total of 240 man hours were spent in 60 fixed catching sites to collect the adult Cx. quinquefasciatus mosquitoes on fortnightly basis from indoor resting sites during 2005-06. The female mosquitoes were classified as unfed, fed, semi-gravid and gravid to ascertain the resting behavior of Cx. quinquefasciatus adults. The data were analysed to evaluate the spatio-temporal variations in adult density, abdominal status and indoor resting sites and linked to meteorological variables like temperature, relative humidity, rainfall and number of rainy days. RESULTS: Cx. quinquefasciatus adults were prevalent perennially in Panaji with highest per man hour density of females (48.6) in February and the lowest density (6.6) in September. Monthly variations in the densities between different months was significant (F=15.3; P<0.05). Rainfall significantly influenced the population of Cx. quinquefasciatus (t=2.63; P<0.05). Fed group and semi-gravid group showed a strong correlation with the relative humidity (P<0.05), rain fall (P<0.05) and number of rainy days (P<0.05). 62.4 per cent of females and 65.1 per cent of males preferred to rest on hanging objects. Spatio-temporal variations in the number of Cx. quinquefasciatus females and males resting on different sites and also the variations in different sites (P<0.05) were significant. INTERPRETATION & CONCLUSION: The density of female Cx. quinquefasciatus encountered in all the months was higher than the estimated tolerated level of density of 34 per ten man hours up to which there is no risk of filariasis transmission. The strong correlation between the abdominal conditions and relative humidity, rainfall and number of rainy days imply that these meteorological variables significantly influenced the feeding and fecundity of the species. 85.3 per cent of the indoor resting population comprising of fed, semi-gravid and gravid females confirmed the endophilic nature of the species. The preferential resting behavior of both females and males on hanging objects suggest that use of insecticide treated long-lasting bed nets as personal protective measure can be exploited to reduce the density of the vector species.

Direction distribution of ambient neutron dose equivalent from 20 MeV protons incident on thick Be and Cu targets.

Ambient neutron dose equivalent from 20 MeV protons incident on thick Be and Cu targets are measured at 0 degrees, 30 degrees, 60 degrees and 90 degrees with respect to the beam direction using a conventional dose equivalent meter. The neutron spectra calculated using nuclear reaction model codes ALICE, PRECO and earlier reported empirical expressions are converted to the ambient dose equivalent using the ICRP fluence-to-dose conversion coefficients and are compared with the measured values. The experimental energy spectra reported in the literature for 19.08 MeV protons incident on a thick Be target are also converted to ambient neutron dose equivalent and are compared with the present experimental results. It is observed that the values estimated from the neutron spectra obtained from the nuclear reaction codes are unable to predict the measured values. The results obtained from the reported experimental energy spectra compare well with the results obtained here. An empirical relation that was used to calculate the directional dependence of the measured neutron dose equivalent from heavy ion-induced reactions is used in this study to check its effectiveness for proton-induced reactions.

Metabolite and enzyme profiles of glycogen metabolism in Methanococcoides methylutens.

When a buffered anaerobic cell suspension of Methanococcoides methylutens was maintained under methanol-limited conditions, intracellular glycogen and hexose phosphates were consumed rapidly and a very small amount of methane formed at 4 h of a starvation period. When methanol was supplemented after a total of 20 h of starvation, a reverse pattern was observed: the glycogen level and the hexose phosphate pool increased, and formation of methane took place after a lag period of 90 min. A considerable amount of methane was formed in 120 min after its detection with a rate of 0.18 micromol mg(-1) protein min(-1). When methane formation decreased after 270 min of incubation and finally came to a halt, probably due to complete assimilation of supplemented methanol, the levels of glycogen and hexose monophosphates decreased once again. However fructose 1,6-diphosphate levels showed a continuous increase even after exhaustion of methane formation. In contrast to the hexose phosphate pool, levels of other metabolites showed a small increase after addition of methanol. The enzyme profile of glycogen metabolism showed relatively high levels of triose phosphate isomerase. Glyceraldehyde 3-phosphate dehydrogenase reacted with NADPH with a three-fold higher activity as compared to that with NADH.

Quantitative analysis of ultrahigh molecular weight polyethylene (UHMWPE) wear debris associated with total knee replacements.

The size and morphology of particulate wear debris retrieved from tissues around 18 failed total knee replacements (TKR) were characterized. Interfacial membranes from nine cemented and nine uncemented TKR were harvested from below the tibial components during revision surgery. Wear debris were extracted using papain and potassium hydroxide digestion. Ultrahigh molecular weight polyethylene (UHMWPE) particles from around cemented or uncemented TKR were similar in size and morphology. The mean size was 1.7 +/- 0. 7 microm with a range of 0.1-18 microm. Thirty-six percent of the particles were less than 1 microm and 90% were less than 3 microm. Morphologically the particles were predominantly spherical with occasional fibrillar attachments and flakes. Particles from TKR were greater than threefold larger than previously characterized particles from total hip replacements, which were 0.5 microm in mean size. Differences in joint conformity and wear patterns between the hip and knee articulations may explain the disparity in size of the wear debris. Since particle size represents an important variable influencing the magnitude of the biological response, it is possible that in vivo the larger TKR debris results in a diminished mediator release, which in turn may account for the lower incidence of osteolysis and aseptic loosening in some designs of TKR.

Short-term effects of bisphosphonates on the biomechanical properties of canine bone.

Periprosthetic osteolysis and aseptic loosening of total joint replacements are believed to be initiated often by abnormal bone resorption induced by prosthetic wear debris. Bisphosphonates can inhibit bone resorption and have been successfully used clinically to treat osteoporosis and Paget's disease. In a recent study it also was shown that a third generation bisphosphonate (alendronate) is effective in preventing wear debris-induced periprosthetic osteolysis. Since inhibition of bone resorption by alendronate may disrupt the delicate balance between bone resorption and formation in normal bone remodeling, it is possible that continuous alendronate therapy may have an adverse effect on the biomechanical properties of bone. Thus the purpose of the present study was to examine the effects of systemic alendronate administration on the biomechanical properties of normal bone using a canine total hip arthroplasty model. We evaluated the biomechanical properties of femora from canines that had received total hip replacements on one side and had been given oral alendronate daily for 23 weeks. The biomechanical properties assessed were fracture toughness, elastic modulus, tensile strength, microhardness, porosity, and weight fractions of the mineral and organic phases of bone. Also, bone microstructure was examined using optical microscopy. Our results indicate that in the short term alendronate therapy does not have any adverse effects on the intrinsic biomechanical properties of canine bone. However, the long-term effects of alendronate therapy still need to be investigated.

Fabrication of submicron titanium-alloy particles for biological response studies.

Biologic response to generated wear particles and subsequent aseptic loosening is a critical factor limiting the long-term survival of total hip replacements. To better understand the sequence of events leading to aseptic loosening and the role of the individual material components, fabricating metal particles similar to those present clinically is very important. We describe a simple milling technique to generate significant amounts of fine titanium-alloy (TiAlV) debris. A TiAlV rod was milled against a TiAlV plate in distilled water supplemented with antibiotics. The resulting debris were sedimented in alcohol and the fine debris were separated. Scanning electron microscopy analysis and particle size analysis demonstrated that the mean size of particles was 1.1 +/- 0.9 microm (range 0.2-4.2 microm). Sixty-two percent were smaller than 1.0 microm, and 85% were smaller than 2.0 microm. The particles generated had varying shapes, including angular or shard-like shapes with jagged and irregular outlines.

Nitric oxide release by macrophages in response to particulate wear debris.

At the interface between a prosthetic implant and bone, macrophage interaction with particulate wear debris is a key event in the initiation of localized bone resorption, leading to aseptic loosening of the prostheses. Numerous investigators have reported that macrophages release a variety of cytokines and mediators including tumor necrosis factor, interleukin-1, prostaglandin E2, and interleukin-6 when they are stimulated with particulate wear debris. In this study, we have demonstrated that macrophages stimulated with particulate debris are also capable of releasing in copious amounts a key inflammatory chemical, nitric oxide. This release of nitric oxide was dependent upon the period of culture and the type and dosage of the challenging particles. Titanium-alloy particles were the most stimulatory, followed by commercially pure titanium and polymethyl-methacrylate. While the role of nitric oxide in osteolysis is not clearly understood, the literature suggests that it may be a key mediator in inhibiting DNA synthesis, in cell proliferation, and in stimulating PGE2 release. This finding enhances our understanding of the sequence of events occurring at the bone-implant interface during wear debris-mediated osteolysis, and exposes potential avenues to interrupt this sequence.

Pathogenesis of bone loss after total hip arthroplasty.

Bone loss with or without evidence of aseptic loosening is a long term complication after total hip arthroplasty (THA). It occurs with all materials and in all prosthetic systems in use or that have been used to date. Bone loss after THA can be a serious problem in revision surgery because bone deficiencies may limit reconstructive options, increase the difficulty of surgery, and necessitate autogenous or allogenic bone grafting. There are three factors adversely affecting maintenance of bone mass after THA: (1) bone loss secondary to particulate debris; (2) adaptive bone remodeling and stress shielding secondary to size, material properties, and surface characteristics of contemporary prostheses; and (3) bone loss as a consequence of natural aging. This chapter reviews the mechanisms of the primary causes of bone loss after THA.

The John Charnley Award. Inhibition of wear debris mediated osteolysis in a canine total hip arthroplasty model.

In this study the efficacy of an oral bisphosphonate therapy to inhibit wear debris mediated bone resorption was evaluated in a canine total hip replacement model. Adult canines were randomized to three groups (n = 8 each) with a right uncemented total hip replacement performed on each animal. Group I (control) received no particulate debris. In Groups II and III, a mixture of 1 x 10(9) particles were introduced into the proximal femoral gap intraoperatively. The particle mixture consisted of fabricated ultra high molecular weight polyethylene (mean 2.3 microns, 90% by number), titanium alloy (mean 3.1 microns, 5%), and cobalt chrome alloy (mean 0.8 micron, 5%). Group III canines additionally received oral drug therapy (5 mg once a day, alendronate sodium) which was begun on postoperative Day 7 and continued until the time of sacrifice. Postoperatively, all animals were allowed 24 weeks of full ambulation before euthanasia. Radiographs obtained preoperatively, postoperatively, and at time of sacrifice were evaluated for periprosthetic osteolysis. Interfacial tissues were examined histologically and placed in organ culture and the supernatants were assayed for prostaglandin E2 and interleukin-1. One animal receiving debris (Group II) suffered a periprosthetic fracture and was sacrificed from the study. Radiographically, one of eight Group I (control) and six of seven canines from Group II (debris) had periprosthetic radiolucencies with endosteal scalloping develop. In contrast, only one of eight animals from Group III (debris + alendronate) had periprosthetic radiolucencies develop. Whereas tissues from control animals were mostly fibrous and acellular, tissues from both experimental groups had significant macrophage infiltration. Levels of prostaglandin E2 and interleukin-1 were elevated significantly in periprosthetic tissues from both experimental groups compared with controls. Continuous administration of alendronate effectively inhibited bone lysis for the 24-week duration of the study. This is consistent with the literature indicating that alendronate is incorporated in the mineralizing matrix making it refractory to osteoclastic resorption. This report has significant clinical implications for controlling the most common cause of implant failure.

Effects of particles on fibroblast proliferation and bone resorption in vitro.

An in vitro study was conducted to determine the ability of particle challenged human peripheral monocytes to modulate fibroblast proliferation and bone resorption. The effects of commercially pure titanium, titanium-aluminum-vanadium, and ultrahigh molecular weight polyethylene wear debris, either fabricated or retrieved from patients with failed total hip arthroplasties, were examined as a function of the composition, size, and dose of particles. In vitro generated particles were selected to be matched closely in particle size distribution to that found in vivo. Dosages were controlled by standardizing the ratio of particle surface area to mean monocyte surface area. The results support the hypothesis that, in vitro, challenge of monocytes by particulate wear debris results in a biphasic dose response. For the metal particles, fibrogenesis was observed over the range of 1x to 10x surface area ratio (the surface area of particles to the surface area of cells), although for metallic and polyethylene particles, saturated doses of 10x surface area ratio were required to stimulate bone resorption. In addition, metallic particles were able to stimulate fibrogenesis at doses at which simulated and retrieved polyethylene were ineffective. Although there may be a nonosteolytic chronically tolerable annual dose of ultrahigh molecular weight polyethylene wear debris corresponding to approximately 1x surface area ratio, lower doses, especially of metallic debris, may produce reactive fibroblast proliferation and fibroplasia that may contribute to implant loosening and failure.

Technique for generating submicrometer ultra high molecular weight polyethylene particles.

Ultra high molecular weight polyethylene wear debris is believed to have a major role in aseptic loosening of prosthetic joints. In order to study the cellular and host response to this and other such particulate debris, a source of fine ultra high molecular weight polyethylene debris is needed. We have described a technique to fracture the GUR 4150 primary ultra high molecular weight polyethylene grain, which reproducibly generated particles less than 1 micron in size. Furthermore, the particle morphology was similar to that of ultra high molecular weight polyethylene particles generated in vivo and retrieved from interfacial tissues. The fabricated polyethylene particles ranged from 0.1 to 33 microns in diameter, with a mean of 2.3 +/- 0.2 micron. Sixty percent of the particles were smaller than 1 micron and 90% were smaller than 7 microns. Using filtration and sedimentation, it is possible to acquire finer particle fractions. These particles are currently being used for biological response studies.

Aseptic loosening in uncemented total hip arthroplasty in a canine model.

An in vivo canine model was developed to investigate the histologic and biochemical parameters associated with aseptic loosening. Thirty-eight canines had cementless total hip arthroplasty. Experimental groups were designed specifically to investigate the relative contributions of implant motion and particulate debris (cobalt chrome alloy, titanium aluminum vanadium, and polyethylene) on the resultant periprosthetic tissues. Tissues from a stable, well-ingrown prosthesis provided a control. Importantly, the histologic and biochemical characteristics of the experimentally induced membranes consistently correlated with previous in vitro reports of tissues retrieved at revision surgery for aseptic loosening. Implant motion and all 3 particulate debris groups resulted in increased numbers of macrophages in the periprosthetic membranes. The histologic findings paralleled the increase in levels of biochemical mediators of bone resorption as measured by collagenase, gelatinase, prostaglandin E2, and interleukin-1 activity. The most striking results were seen in the histology and biochemistry of the particle groups with highly cellular membranes showing increased biochemical activity when compared with controls. The clinical relevance of this work lies in the description of an in vivo model of aseptic loosening that can be used to investigate the effects of numerous variables implicated in aseptic loosening. Ultimately, the model may serve as a basis for developing therapeutic interventions.

Human monocyte response to particulate biomaterials generated in vivo and in vitro.

We studied the ability of four clinically relevant particle species to stimulate human peripheral blood monocytes to release bone-resorbing agents, including interleukin-1 (both interleukin-1 alpha and interleukin-1 beta), interleukin-6, and prostaglandin E2. The species studied were titanium-6% aluminum-4% vanadium (TiAlV), commercially pure titanium, fabricated ultrahigh molecular weight polyethylene, and polyethylene retrieved from interfacial membranes of failed uncemented total hip arthroplasties. For all species, the mean size was less than 1 micron. Human peripheral blood monocytes were challenged with these particles in a uniform manner on the basis of surface area. Phorbol 12-myristate acetate, zymosan, and nonphagocytosable titanium particles served as controls. Stimulation of human monocytes is a function of the composition and concentration of particles. In this study, TiAlV particles appeared to be the most competent to elicit the synthesis and release of inflammatory mediators. Particles of commercially pure titanium and of fabricated ultrahigh molecular weight polyethylene also could induce the release of various cellular mediators, albeit at a lower level, whereas the particles of polyethylene retrieved from interfacial membranes were less stimulatory in these short-term in vitro experiments.

Cellular mediators secreted by interfacial membranes obtained at revision total hip arthroplasty.

The interfacial membrane between implant and host-bone in aseptically loose total hip arthroplasties has a potential role in the etiology of local bone resorption and loosening of the prosthetic component. Inflammatory/potential "bone-resorbing" agents (cytokines/mediators) released by the cells of the interfacial membranes of loosened uncemented and cemented total hip arthroplasties were measured. Synovial tissues from patients with acute femoral neck fractures, patients with osteoarthritis, and cadavers without joint disorders were used as control subjects. Control synovial tissue from osteoarthritic patients secreted the highest levels of prostaglandin E2, interleukin-8, and tumor necrosis factor alpha. Interleukin-1 alpha was the only cytokine whose levels were elevated as much as 4-fold around uncemented implants compared with cemented implants, and up to 16-fold compared with control synovial tissue. An apparent inverse relation between interleukin-1 alpha and interleukin-6 interfacial membranes of total hip arthroplasties compared with control synovial tissues suggests a complex cellular mechanism through a cytokine/prostaglandin cascade; this may regulate the observed bone resorption in aseptic loosening.

Wear Debris in Total Joint Replacements.

In vivo degradation of prosthetic implant materials is increasingly recognized as a major factor limiting the durability of total joint arthroplasty. In vivo degradation occurs primarily by means of wear processes that can generate large quantities of particulate debris. This debris can stimulate an adverse local host response leading to periprosthetic bone loss, which can compromise implant fixation and bone stock. The authors review the basic mechanisms of implant degradation and the host response to particulate degradation products, particularly in the context of the pathogenesis of osteolysis. Submicron polyethylene particles (mean size, 0.5 um) are the dominant type of wear particle present in periprosthetic tissues associated with uncemented hip replacements. Polyethylene wear can be minimized by improving the quality of the polyethylene, avoiding use of large-diameter (greater than 28 mm) femoral heads in total hip arthroplasty, and improving the design and fabrication of modular connections, which can be important sources of three-body wear particles. Advances in the understanding of the basic mechanisms of osteolysis are critical to the development of preventive measures that will minimize the clinical impact of this phenomenon.