bluuebunny/crossref_metadata_2025 huggingface dataset:
Futility Clarified
Authors: Chwang Eric
Published: August 2009

Futility has had a rough time in recent medical ethics literature. From about 1987 to 1996, various writers and groups tried to define futility within the context of medical treatment, but without success. Baruch Brody and Amir Halevy give an excellent summary of the morass in their 1995 article “Is Futility a Futile Concept?” where they argue that none of the then-proposed definitions succeed. While a smattering of other attempted definitions have appeared since then, for the most part writers about futility have found it more profitable to stop trying to define futility and instead move in a different direction, that of figuring out how to resolve disputes where patient families want more treatment which clinicians think is futile. This is, for example, the approach taken by the Texas Advance Directives Act (1999), which was the first futility legislation in North America and is often seen as an appropriate template. The idea embodied in this influential legislation is that our energies should be focused on creating a process which we can use to resolve difficult cases, and which everyone finds legitimate, rather than in trying to find a definition which everyone finds legitimate.
Health Insurance Exchanges: Legal Issues
Authors: Jost Timothy Stoltzfus
Published: August 2009

This “Legal Solutions in Health Reform” paper identifies and analyzes the legal issues raised by health insurance exchanges. Like all Legal Solutions papers, it does not purport to provide a concrete proposal as to how health insurance exchanges should be organized or even whether they should play a role in health care reform. Rather, it attempts simply to describe the legal issues that health insurance exchanges raise, and to propose alternative solutions to legal problems where useful. More specifically, it analyzes and offers alternative solutions to the legal problems raised by proposals to establish insurance exchanges by the federal government, by state governments, and by private entities or associations. Because the focus of this project and paper is on legal issues, discussion of policy and design issues is attenuated. Nevertheless, some attention to policy issues is unavoidable because law is the realization of policy.
The Purchase of Insurance across State Lines in the Individual Market
Authors: Kanwit Stephanie
Published: August 2009

This paper analyzes the legal issues associated with the leading and much-debated proposals that aim to revitalize state regulatory competition and allow individuals to purchase insurance across state lines (PASL). These proposals seek to reverse decades-old principles of state preeminence in the regulation of individual health insurance and instead create “jurisdictional competition” in the individual market by allowing an insurer to choose the state under whose law it wishes to be regulated, subject to certain consumer protections. Advocates say this type of jurisdictional competition would reform perceived problems in the individual market and lower the costs of individual health insurance by imposing the regulatory authority of only the insurer’s selected “home” state.
A Program in Contemplative Self‐Healing
Authors: Loizzo Joseph , Charlson Mary , Peterson Janey
Published: August 2009

This paper reviews current behavioral health interventions and introduces a self‐healing program based on the Indo‐Tibetan tradition. While most work on behavior change emphasizes cognition and motivation, this review highlights stress‐reactivity as a rate‐limiting resistance to learning. Surveying cognitive‐behavioral theories, it finds these limited in modeling stress‐reactivity. Reviewing current interventions that address stress by integrating relaxation, mindfulness, imagery, or movement with cognitive‐behavioral education, it attributes their limited effectiveness to the limits of their model of stress and their strategy of eclectically mixing techniques. Next, the article explores the Indic model of stress‐cessation and self‐healing assumed by mindfulness practice, concluding that it more fully reflects current findings on stress and learning. It reviews the theory and practice of mindfulness and of two less known contemplative “vehicles” preserved in Tibet, using more advanced techniques and insights better suited to lay lifestyles and secular cultures. It suggests that the Tibetan tradition of integrating all three vehicles of contemplative insight and skill in one self‐healing practice should maximize coherence and effectiveness while minimizing confounding variables caused by eclecticism. Finally, the paper introduces an intervention that integrates mindfulness with techniques of cognitive analysis, affect modulation, motivational imagery, and reinforcing breathing, tailored over centuries into a complete, threefold path of self‐healing. A pilot study of this intervention in women treated for breast and other gynecologic cancers suggests that the whole spectrum of Indo‐Tibetan mind/body practices can be readily mastered and effectively used by Westerners to reduce stress and enhance learning and quality of life.
Caloric Restriction and Longevity
Authors: Mehta Linda Hotchkiss , Roth George S.
Published: August 2009

Aging involves a gradual increase in disorder of the systems that sustain living. Although stress is a major driver of this process, one stressor, caloric restriction (CR), is the only intervention proven to extend life span in multiple species as well as extend the persistence of those characteristics that are associated with youth. CR has been used since ancient times to enhance many of those characteristics: principally, increased activity levels and heightened levels of mental acuity. Religious ascetics, often living in monastic communities, have provided long‐term opportunities to observe the effects of CR, or fasting, in humans. Tibetan medicine has made use of observations, which include that of enhanced immune function, in its dietary prescriptions. In the hopes of reaping these benefits for the general population, scientists focusing their research on the aging process have sought mimetics that will deliver the benefits of CR without requiring the discipline of fasting. The search begins with discovering the processes that make CR work.
From the Global to the Local
Authors: Bushell William C. , Spector Novera Herbert , Theise Neil D.
Published: August 2009

While skepticism regarding the possibilities for a productive meeting (metaphorically or actual) between Western medicine and biology and older healing and health practices of traditional cultures may be prevalent, there are many theoretical points of meeting and much experimental data to suggest that cognitive‐behavioral practices (C‐Bp) of the latter may induce testable and reproducible phenomena for the former. Such modulation or modification of tissue regeneration by C‐Bp presumably must work through systemic signaling of some kind. Several possible mechanisms for such signaling are recognized and will be reviewed here: humoral, neurological, cell trafficking, and bioelectromagnetic/energy mediated. Nonetheless, while cultures and techniques may be varied, human bodies are more alike than dissimilar. We indicate that great profit may be had for all participating cultures in establishing a common language, shared criteria for designing experiments and interpreting data, and cooperative goals for the promotion of tissue integrity and regeneration.
Current Concepts in Limb Regeneration
Authors: Wicker Jordan , Kamler Kenneth
Published: August 2009

Cognitive‐behavioral practices such as meditation and yoga have long been viewed as methods of reaching states of peace and relaxation, but recent research has focused on the role of these practices in reducing endogenous mediators of stress and inflammation that would otherwise be harmful to our bodies. Further, these stress‐related factors play major roles in inflammation, acting as barriers to wound healing and tissue regeneration. Fractures, denervation, tendon and ligament rupture, and cartilage degradation are morbidities associated with injury and often act as an impediment for healing. Studies of human fingertip regeneration exist; however, the underlying molecular and environmental changes have yet to be completely elucidated. Studying the regenerative capabilities of lower organisms and fetal wound healing has allowed scientists to understand the mechanisms behind regeneration, coming closer to a human application. Much research relies on the idea that the developing embryo shares a great deal in common with regenerating appendages of organisms such as the salamander. This review will cover historical perspectives of regeneration biology and current topics in limb regeneration, with particular interest given to the upper extremity, including the commonalities between human embryological development and amphibian regeneration, growth factors and pathways that show correlation with development and regeneration, recently discovered differences in fetal and adult wound healing, and current research and knowledge regarding human extremity tissue regeneration. With a greater understanding of the mechanisms and mediators involved in regeneration, the application of cognitive‐behavioral practices may assist in seeing the future goals of regeneration come to fruition.
Protection throughout the Life Span
Authors: Olivo Erin L.
Published: August 2009

The Indo‐Tibetan tradition claims that proficiency in the suggested longevity practices of meditation, diet, and physical exercise (yoga), will result in profound anti‐aging, stress‐mediating and health enhancing effects. Western biomedical research has begun to demonstrate that the psychobiological states induced and cultivated by cognitive behavioral practices which are emblematic of those contained within the Indo‐Tibetan tradition (hypnosis, meditation, visualization, systematic relaxation), indeed do have a profound impact on the body's protective and regulatory systems. Although continued study is necessary, much of the early research illuminating the mechanisms responsible for the life‐span extending and health‐enhancing effects of these cognitive behavioral practices points to the importance of their anti‐inflammatory, anti‐stress, and antioxidant effects as well as their impact in enhancing the production of endogenous substances that possess general longevity‐enhancing, regenerative properties.
Tibetan Medicine and Regeneration
Authors: Dhondup Lobsang , Husted Cynthia
Published: August 2009

An overview of the concept of regeneration in Tibetan medicine is presented with descriptions of detoxification and tonification longevity protocols. The body must be fortified before receiving stronger treatments for regeneration. All disease is brought into balance with understanding of the interplay of the five elements, three humors, and their qualities and locations. The example of multiple sclerosis (MS) is given. The macroscopic three‐humor interpretation of MS agrees with the microscopic three‐humor description of demyelination, providing a new framework for the understanding and treatment of MS. Treatments for MS and other chronic conditions are based on age, season, time of day, and the individual's three‐humor and hot (excess) and cold (deficiency) balance. Treatments to promote regeneration include nutrition, gentle exercise, herbal formulas, accessory therapies such as herbal baths and oils, and meditation. It is built into the theory of Tibetan medicine to have predictions about outcome and distinguish different disease patterns in patients with MS and other disorders. Taking into account daily and seasonal variations coupled with the changing nature of MS, it is critical to frequently evaluate people with MS and other chronic conditions for monitoring and adjustment of treatment for regeneration.
Toward a Unified Field of Study: Longevity, Regeneration, and Protection of Health through Meditation and Related Practices
Authors: Bushell William C. , Theise Neil D.
Published: August 2009

The orientation of this volume and the Longevity and Optimal Health: Integrating Eastern and Western Perspectives conference is that there is abundant evidence in the scientific and medical literatures that the diligent practice of certain yoga‐meditational regimens can lead to a spectrum of health enhancements, ranging from modest to profound, and that these can be investigated in a scientifically rigorous fashion. This overview will summarize these possibilities regarding improved human longevity, regeneration, and protection of health and serve to introduce the perspectives of conference participants from all of the traditions represented.
Beyond early intervention: can we adopt alternative narratives like ‘Woodshedding’ as pathways to recovery in schizophrenia?
Authors: Shiers David , Rosen Alan , Shiers Ann
Published: August 2009

Aim:To consider how early intervention in psychosis can support a recovery paradigm.

Methods:Significant numbers of those developing a first episode of psychosis are on a path to a persisting and potentially life long condition. Constituting the schizophrenia spectrum disorders, such conditions demand the particular qualities and attitudes inherent within recovery‐based practice.

This paper explores some of these qualities and attitudes by examining the tension between a traditional ‘clinical’ narrative used by many health providers and a ‘human’ narrative of users of services and their families.

Results:We draw out key features and constructs of recovery practice as they relate to the EI paradigm. These include: woodshedding, turning points, discontinuous improvement models, therapeutic optimism, gradualism and narratives of story telling. We also highlight the role of family members and other close supporters and believe their potential contribution requires greater consideration.

Conclusions:The early intervention (EI) paradigm can resonate and indeed offer a stronghold for recovery‐based practice where traditional mental health services have sometimes struggled. Conversely, failure of caregivers to provide such an approach in the early phase of illness can cause unnecessary and sometimes disastrous consequences.
Substance misuse over the first 18 months of specialized intervention for first episode psychosis
Authors: Carr Jason A. R. , Norman Ross M. G. , Manchanda Rahul
Published: August 2009

Aim: Examine substance misuse over the first 18 months of first‐episode psychosis treatment.

Method: Clinicians rated alcohol and drug (mostly cannabis) misuse for 243 individuals followed prospectively. Assessments were completed at baseline and after 3, 6 and 18 months. Interventions relating to substance misuse included ongoing assessment of use, education and counselling to avoid.

Results: Alcohol and drug misuse declined significantly between baseline and 3 months, especially among patients with a substance abuse or dependence diagnosis at baseline. Overall, these reductions were maintained over the 18‐month follow‐up period. The exception was worsening alcohol misuse over time among patients with alcohol abuse or dependence on entry.

Conclusions: With good usual care, education and support, alcohol and drug misuse declined significantly during the first months of psychosis treatment. The improvements in drug misuse were generally maintained over the 18‐month follow‐up, and worsening alcohol misuse over time may be the greater issue.
Comparison of Three Pebble Count Protocols (EMAP, PIBO, and SFT) in Two Mountain Gravel‐Bed Streams1
Authors: Bunte Kristin , Abt Steven R. , Potyondy John P. , Swingle Kurt W.
Published: August 2009

Abstract:  Although the term ``pebble count'' is in widespread use, there is no standardized methodology used for the field application of this procedure. Each pebble count analysis is the product of several methodological choices, any of which are capable of influencing the final result. Because there are virtually countless variations on pebble count protocols, the question of how their results differ when applied to the same study reach is becoming increasingly important. This study compared three pebble count protocols: the reach‐averaged Environmental Monitoring and Assessment Program (EMAP) protocol named after the EMAP developed by the Environmental Protection Agency, the habitat‐unit specific U.S. Forest Service’s PACFISH/INFISH Biological Opinion (PIBO) Effectiveness Monitoring Program protocol, and a data‐intensive method developed by the authors named Sampling Frame and Template (SFT). When applied to the same study reaches, particle‐size distributions varied among the three pebble count protocols because of differences in sample locations within a stream reach and along a transect, in particle selection, and particle‐size determination. The EMAP protocol yielded considerably finer, and the PIBO protocol considerably coarser distributions than the SFT protocol in the pool‐riffle study streams, suggesting that the data cannot be used interchangeably. Approximately half of the difference was due to sampling at different areas within the study reach (i.e., wetted width, riffles, and bankfull width) and at different locations within a transect. The other half was attributed to using different methods for particle selection from the bed, particle‐size determination, and the use of wide, nonstandard size classes. Most of the differences in sampling outcomes could be eliminated by using simple field tools, by collecting a larger sample size, and by systematically sampling the entire bankfull channel and all geomorphic units within the reach.
Rhaponticoidesaytachii sp. nov. (Asteraceae) from south Anatolia, Turkey
Authors: Doğu Süleyman , Bağcı Yavuz , Dinç Muhittin
Published: August 2009

A new species of Rhaponticoides Vaill., Rhaponticoidesaytachii Y. Bağcı, Doğu & Dinç sp. nov. collected by the authors from south Anatolia, is described and illustrated. The new species is restricted to deprived Quercus forest openness around Dumlugöze‐Sarıveliler (C4 Karaman). Diagnostic morphological characters from R. amplifolia (Boiss. & Heldr.) M.V. Agab. & Greuter are discussed. The ecology, biogeography and conservation status of the new species is also presented.
Dynamic Assessment of Advanced Second Language Learners
Authors: Antón Marta
Published: August 2009

Abstract: This article reports on the implementation of diagnostic assessment in an advanced Spanish language program at the university level. Particular attention is given to the use of dynamic assessment practices as a way to assess language abilities, intervene in learning, and document learners' growth. Dynamic assessment is conceptually based on sociocultural theory, specifically on Vygotsky's notion of Zone of Proximal Development (Lantolf & Thorne, 2006; Minick, 1987). Assessment procedures conducted with third‐year Spanish language majors are described with the purpose of illustrating the potential of dynamic assessment for second language learning contexts. Students took a five‐part diagnostic test. Two parts of the test, the writing and speaking sections, were conducted following dynamic assessment procedures. A qualitative analysis of the results shows that dynamic assessment allows for a deeper and richer description of learners' actual and emergent abilities, which enables programs to devise individualized instructional plans attuned to learners' needs.
Student Attitudes Toward Native and Non‐Native Language Instructors
Authors: Hertel Tammy Jandrey , Sunderman Gretchen
Published: August 2009

Abstract: This study investigates students' attitudes toward native and nonnative speaking instructors of Spanish. A quantitative questionnaire was administered to 292 students enrolled in three different levels of undergraduate Spanish courses at a U.S. university. Participants were asked to rate Likert scale items related to native versus nonnative speaking instructors' knowledge and teaching ability, as well as their own potential to learn from the instructors. Results indicate that students perceive native speaking instructors to possess advantages over nonnative speaking instructors with regard to pronunciation and culture, but not with regard to the teaching of grammar or vocabulary. Proficiency level and the native language of a participant's current instructor also influenced opinions.
Less Commonly Taught Language and Commonly Taught Language Students: A Demographic and Academic Comparison
Authors: Brown Alan V.
Published: August 2009

Abstract: Efforts to fund the teaching of critical languages, along with increasing enrollments in less commonly taught language (LCTL) classes, have evidenced a renewed interest in LCTL pedagogy. While much is known about enrollment trends, materials development, and professional training, far less research has compared LCTL and commonly taught language (CTL) students. Students from 83 classes (nine different languages) at a large university completed a questionnaire containing items requesting demographic and academic information. The results of a chi‐square analysis demonstrated that LCTL learners were older, expected higher grades, reported higher GPAs, found their courses more difficult, and had studied a third language at a much higher rate. Although far from conclusive, these data begin to identify differences that may exist between LCTL and CTL students, specifically in university, introductory‐level courses.
An Elaborate Data Set Characterizing the Mechanical Response of the Foot
Authors: Erdemir Ahmet , Sirimamilla Pavana A. , Halloran Jason P. , van den Bogert Antonie J.
Published: August 2009

Mechanical properties of the foot are responsible for its normal function and play a role in various clinical problems. Specifically, we are interested in quantification of foot mechanical properties to assist the development of computational models for movement analysis and detailed simulations of tissue deformation. Current available data are specific to a foot region and the loading scenarios are limited to a single direction. A data set that incorporates regional response, to quantify individual function of foot components, as well as the overall response, to illustrate their combined operation, does not exist. Furthermore, the combined three-dimensional loading scenarios while measuring the complete three-dimensional deformation response are lacking. When combined with an anatomical image data set, development of anatomically realistic and mechanically validated models becomes possible. Therefore, the goal of this study was to record and disseminate the mechanical response of a foot specimen, supported by imaging data. Robotic testing was conducted at the rear foot, forefoot, metatarsal heads, and the foot as a whole. Complex foot deformations were induced by single mode loading, e.g., compression, and combined loading, e.g., compression and shear. Small and large indenters were used for heel and metatarsal head loading, an elevated platform was utilized to isolate the rear foot and forefoot, and a full platform compressed the whole foot. Three-dimensional tool movements and reaction loads were recorded simultaneously. Computed tomography scans of the same specimen were collected for anatomical reconstruction a priori. The three-dimensional mechanical response of the specimen was nonlinear and viscoelastic. A low stiffness region was observed starting with contact between the tool and foot regions, increasing with loading. Loading and unloading responses portrayed hysteresis. Loading range ensured capturing the toe and linear regions of the load deformation curves for the dominant loading direction, with the rates approximating those of walking. A large data set was successfully obtained to characterize the overall and the regional mechanical responses of an intact foot specimen under single and combined loads. Medical imaging complemented the mechanical testing data to establish the potential relationship between the anatomical architecture and mechanical responses and to further develop foot models that are mechanically realistic and anatomically consistent. This combined data set has been documented and disseminated in the public domain to promote future development in foot biomechanics.
Effect of Strain Rate on the Tensile Material Properties of Human Placenta
Authors: Manoogian Sarah J. , Bisplinghoff Jill A. , McNally Craig , Kemper Andrew R. , Santago Anthony C. , Duma Stefan M.
Published: August 2009

Automobile crashes are the largest cause of injury death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. Computational models, useful tools to evaluate the risk of fetal loss in motor vehicle crashes, are based on a limited number of quasistatic material tests of the placenta. This study presents a total of 64 uniaxial tensile tests on coupon specimens from six human placentas at three strain rates. Material properties of the placental tissue were evaluated at strain rates of 0.07/s, 0.70/s, and 7.00/s. The test data have average failure strains of 0.34, 0.36, and 0.37, respectively. Failure stresses of 10.8 kPa, 11.4 kPa, and 18.6 kPa correspond to an increase in strain rate from 0.07/s to 7.0/s. The results indicate rate dependence only when comparing the highest strain rate of 7.0/s to either of the lower rates. There is no significant rate dependence between 0.07/s and 0.70/s. When compared with previous testing of placental tissue, the current study addresses the material response to more strain rates as well as provides a much larger set of available data. In summary, tensile material properties for the placenta have been determined for use in computational modeling of pregnant occupant kinematics in events ranging from low impact activities to severe impacts such as in motor vehicle crashes.
Measuring Viscoelasticity of Soft Samples Using Atomic Force Microscopy
Authors: Tripathy S. , Berger E. J.
Published: August 2009

Relaxation indentation experiments using atomic force microscopy (AFM) are used to obtain viscoelastic material properties of soft samples. The quasilinear viscoelastic (QLV) model formulated by Fung (1972, “Stress Strain History Relations of Soft Tissues in Simple Elongation,” in Biomechanics, Its Foundation and Objectives, Prentice-Hall, Englewood Cliffs, NJ, pp. 181–207) for uniaxial compression data was modified for the indentation test data in this study. Hertz contact mechanics was used for the instantaneous deformation, and a reduced relaxation function based on continuous spectrum is used for the time-dependent part in the model. The modified QLV indentation model presents a novel method to obtain viscoelastic properties from indentation data independent of relaxation times of the test. The major objective of the present study is to develop the QLV indentation model and implement the model on AFM indentation data for 1% agarose gel and a viscoelastic polymer using spherical indenter.
Bone Resorption Induced by Fluid Flow
Authors: Johansson Lars , Edlund Ulf , Fahlgren Anna , Aspenberg Per
Published: August 2009

A model where bone resorption is driven by stimulus from fluid flow is developed and used as a basis for computer simulations, which are compared with experiments. Models for bone remodeling are usually based on the state of stress, strain, or energy density of the bone tissue as the stimulus for remodeling. We believe that there is experimental support for an additional pathway, where an increase in the amount of osteoclasts, and thus osteolysis, is caused by the time history of fluid flow velocity, fluid pressure, or other parameters related to fluid flow at the bone/soft tissue interface of the porosities in the bone.
Effects of Ga+ milling on InGaAsP quantum well laser with mirrors milled by focused ion beam
Authors: Vallini F. , Figueira D. S. L. , Jarschel P. F. , Barea L. A. M. , Von Zuben A. A. G. , Frateschi N. C.
Published: August 2009

InGaAsP/InP quantum well ridge waveguide lasers were fabricated for the evaluation of Ga+ focused ion beam milling of mirrors. Electrical and optical properties were investigated. A 7% increment in the threshold current, a 17% reduction in the external quantum efficiency, and a 15 nm blueshift in the emission spectrum were observed after milling as compared to the as-cleaved facet result. Annealing in inert atmosphere partially reverts these effects, resulting in a 4% increment in the threshold current, an 11% reduction in the external efficiency, and a 13 nm blueshift with the as-cleaved result. The current-voltage behavior after milling and annealing shows a very small increase in leakage current, indicating that optical damage is the main effect of the milling process.
EGSnrc‐based Monte Carlo dosimetry of CSA1 and CSA2 brachytherapy source models
Authors: Selvam T. Palani , Sahoo S. , Vishwakarma R. S.
Published: August 2009

Purpose:

AAPM TG‐56 recommends the use of a specific dosimetric dataset for each brachytherapy source model. In this study, a full dosimetric dataset for indigenously developedsource models, namely, the CSA1 and CSA2, in accordance with the AAPM TG‐43U1 formalism is presented. The study includes calculation of dose‐to‐kerma ratioin water around these sources including stainless steel encapsulatedsources such as RTR, 3M, and selectron/LDR.

Methods:

The Monte Carlo–based EGSnrcMP code system is employed for modeling the sources in vacuum and in water. Calculations of air‐kerma strength,for the investigated sources and collision kerma in water along the transverse axis of the RTR source are based on the FLURZnrc code. Simulations of water‐kerma and dose in water for the CSA1, CSA2, RTR, 3M, and selectron/LDRsources are carried out using the DOSRZnrc code. In DOSRZnrc calculations, water‐kerma and dose are scored in a cylindrical water phantom having dimensions of.

Results:

The calculated dose‐rate constants for the CSA1 and CSA2 sources are 0.945(1) and 1.023(1) cGy/(h U), respectively. The calculated value ofper unit source activity,for the CSA1 and CSA2 sources is. The EGSnrcMP‐based collision kerma rates for the RTR source along the transverse axis (0.25–10 cm) agree with the correspondingGEANT4‐based published values within 0.5%. Anisotropy profiles of the CSA1 and CSA2 sources are significantly different from those of other sources. For the selectron/LDR single pelletspherical source (modeled as a cylindrical pellet with dimensions similar to the seed selectron), the values ofat 1 and 1.25 mm from the capsule are 1.023(1) and 1.029(1), respectively. The value ofat 1 mm from the CSA1, CSA2, RTR, and 3Msource capsules (all sources have an external radius of 1.5 mm) is 1.017(1) and this ratio is applicable to axial positionsto. This is in contrast to a publishedGEANT4‐based Monte Carlo dosimetric study on RTR and 3Msources wherein the authors have assumed that collision kerma is approximately equal to absorbed dose at 1 mm from the source capsules. Collision kerma is approximately equal to absorbed dose for distancesfrom source capsules as opposed toreported in published studies. A detailed electron transport is necessary up to 2 mm from source capsules.

Conclusions:

The Monte Carlo–calculated dose‐rate data for the CSA1 and CSA2 sources can be used as input data for treatment planning or to verify the calculations by radiotherapy treatment planning system.
Measurements of dose discrepancies due to inhomogeneities and radiographic contrast in balloon catheter brachytherapy
Authors: Oh Seungjong , Scott Jacob , Shin Dong Hoon , Suh Tae‐Suk , Kim Siyong
Published: August 2009

Recently, a device called MammoSite®, consisting of a balloon and a catheter, was developed to perform partial‐breast irradiation using a high‐dose‐rate (HDR) brachytherapy unit with ease and reproducibility. However, the actual dose to the skin does not agree well with the calculated dose by the treatment planning system because of the difference between the calculation condition and the real treatment condition (i.e., homogeneous water and full scatter condition vs contrast solution and lack of full scatter condition). In this study, the authors experimentally estimated dose discrepancies due to contrast and lack of full scatter in breast HDR brachytherapy with MammoSite®. Using metal‐oxide‐semiconductor field‐effect transistor detectors and a breast phantom, the dose discrepancies between the calculation and the treatment conditions were measured according to contrast concentration (10% and 20% volume ratios), balloon size (35 and ), and source to detector distance ranging from 25 to 50 mm. The source was an Ir‐192 isotope from Nucletron HDR unit. The dose discrepancies from the calculation condition due to both contrast and lack of full scatter combined ranged from about to in the studied cases (error bound is in two sided confidence interval of 80% based on Student's distribution). In all cases, the effect of lack of full scatter was dominant to that of contrast and significant dose discrepancies existed between the calculation and the real treatment conditions, indicating that the actual skin dose is less than that which is currently calculated.
A general analytical solution to the geometrical problem of field matching in radiotherapy
Authors: Hernandez V. , Arenas M. , Pons F. , Sempau J.
Published: August 2009

Purpose:

Several authors studied the problem of geometrical matching of fields produced by medical linear accelerators. However, a general solution has yet to be published. Currently available solutions are based on parallelism arguments. This study provides a general solution, considering not only parallelism but also field sizes.

Methods:

A fixed field with arbitrary field size, gantry, collimator, and couch angle is considered, and another field with a fixed gantry angle is matched to it. A single reference system attached to the treatment couch is used, and two approaches are followed. In the first approach, fixed field sizes are assumed and parallelism of the adjacent field‐side planes is imposed. In the second approach, fixed isocenter positions are considered and both parallelism and coincidence between field‐side planes are required.

Results:

When fixed field sizes are assumed, rotation angles are obtained; however, the isocenters may need to be shifted to make side planes coincident and therefore achieve a proper match. When fixed isocenter positions are considered, solutions for all parameters, including the field size, are obtained and an exact geometrical match is achieved.

Conclusions:

General expressions to the field‐matching problem are found for the two approaches followed, fixed field sizes, and fixed isocenter positions. These results can be applied to any treatment technique and can easily be implemented in modern treatment planning systems.
An evaluation of ionization chambers for the relative dosimetry of kilovoltage x‐ray beams
Authors: Hill Robin , Mo Zhao , Haque Mamoon , Baldock Clive
Published: August 2009

In this work, the authors have evaluated ten different ionization chambers for the relative dosimetry of kilovoltage x‐ray beams in the energy range of 50–280 kVp. Percentage depth doses in water and relative detector response (in Solid Water and in air) were measured for each of the x‐ray beams studied using a number of chambers. Measured depth dose data were compared with Monte Carlo calculated depth doses using the EGSnrc Monte Carlo package and the BEAMnrc user code. The accuracy of the phase space files generated by BEAMnrc was verified by calculating the half‐value layer and comparing with the measured half‐value layer of each x‐ray beam. The results indicate that the Advanced Markus, Markus, NACP, and Roos parallel plate ionization chambers were suitable for the measurement of depth dose data in this beam quality range with an uncertainty of less than 3%, including in the regions close to the water surface. While the relative detector response of the Farmer and scanning thimble chambers exhibited a better energy response, they were not suitable for depth dose measurements in the first 5 mm below the water surface with differences of up to 12% in the surface dose measurement for the 50 kVp x‐ray beam. These differences were due to dose artifacts generated by the chamber size and the dose gradient. However, at depths greater than 5 mm, the Farmer and thimble scanning chambers gave uncertainties of less than 3% for the depth dose measurements for all beam energies. The PTW PinPoint 31006 chamber was found to give varying dose differences of up to 8% depending on the x‐ray beam energy; this was attributed to the steel central electrode. The authors recommend that one of the parallel plate ionization chambers investigated be used to determine depth dose data for kilovoltage x‐ray beams in the energy range studied and give correct dose information close to the surface and at depth in the water phantom.
Scintillator avalanche photoconductor with high resolution emitter readout for low dose x‐ray imaging: Lag
Authors: Li Dan , Zhao Wei , Nanba Masakazu , Egami Norifomi
Published: August 2009

Purpose:

A new concept of indirect conversion flat‐panel imager with avalanche gain and field emitter array (FEA) readout is being investigated. It is referred to as scintillator avalanche photoconductor with high resolution emitter readout (SAPHIRE). The present work investigates the temporal performance, i.e., lag, of SAPHIRE.

Methods:

Since the temporal performance of the x‐ray detection materials, i.e., the structured scintillator and avalanche amorphous selenium photoconductor, has been studied previously, the investigation is focused on lag due to the FEA readout method. The principle of FEA readout is similar to that of scanning electron beam readout used in camera tubes, where the dominant source of lag is the energy spread of electrons. Since the principles of emission and beam focusing methods for FEA are different from thermionic emission used in camera tubes, its electron beam energy spread and hence lag is expected to be different. In the present work, the energy spread of the electrons emitted from a FEA was investigated theoretically by analyzing different contributing factors due to the FEA design and operations: The inherent energy spread of field emission, the FEA driving pulse delay, and the angular distribution of emitted electrons. The electron energy spread determined the beam acceptance characteristic curve of the photoconductive target, i.e., the accepted beam current as a function of target potential , from which lag could be calculated numerically. Lag calculation was performed using FEA parameters of two prototype HARP‐FEA image sensors, and the results were compared with experimental measurements. Strategies for reducing lag in SAPHIRE were proposed and analyzed.

Results:

The theoretical analysis shows that the dominant factor for lag is the angular distribution of electrons emitted from the FEA. The first frame lags for two prototype sensors with 4 and HARP layer thicknesses were 62.1% and 9.1%, respectively. A lag clearance procedure can be implemented by turning on all the FEA pixels simultaneously between subsequent frames without negative impact of readout speed. For large‐area SAPHIRE, the bias electrode for the HARP needs to be divided into strips to allow parallel readout. With typical cardiac detector parameters, SAPHIRE with 128 parallel strips can provide real‐time readout (30 frames/s) with first frame lag of .

Conclusions:

The investigation of lag in SAPHIRE shows that the angular distribution of emitted electrons from FEA can result in substantial lag if the readout was performed pixel by pixel. Effective strategies for reducing lag include dividing the bias electrode into multiple strips to allow parallel readout and the incorporation of rapid charge clearance procedure between subsequent frames or rows.
Spatial analysis of magnetic resonance and relaxation times improves classification between subjects with and without osteoarthritis
Authors: Carballido‐Gamio Julio , Stahl Robert , Blumenkrantz Gabrielle , Romero Adan , Majumdar Sharmila , Link Thomas M.
Published: August 2009

Purpose:

Studies have shown that functional analysis of knee cartilage based on magnetic resonance (MR) relaxation times is a valuable tool in the understanding of osteoarthritis (OA). In this work, the regional spatial distribution of knee cartilage and relaxation times based on texture and laminar analyses was studied to investigate if they provide additional insight compared to global mean values in the study of OA.

Methods:

Knee cartilage of 36 subjects, 19 healthy controls and 17 with mild OA, was divided into 16 compartments. and relaxation times were studied with first order statistics, eight texture parameters with four different orientations using gray‐level co‐occurrence matrices and by subdividing each compartment into two different layers: Deep and superficial. Receiver operating characteristic curve analysis was performed to evaluate the potential of each technique to correctly classify the populations.

Results:

Although the deep and superficial cartilage layers had in general significantly different and relaxation times, they performed similarly in terms of subject discrimination. The subdivision of lateral and medial femoral compartments into weight‐bearing and non‐weight‐bearing regions did not improve discrimination. Also it was found that the most sensitive region was the patella and that discriminated better than . The most important finding was that with respect to global mean values, laminar and texture analyses improved subject discrimination.

Conclusions:

Results of this study suggest that spatially assessing MR images of the knee cartilage relaxation times using laminar and texture analyses could lead to better and probably earlier identification of cartilage matrix abnormalities in subjects with OA.
On the speckle‐free nature of photoacoustic tomography
Authors: Guo Zijian , Li Li , Wang Lihong V.
Published: August 2009

Purpose:

A long‐standing conundrum is why photoacoustic tomography (PAT) possesses the unique ability to produce images devoid of speckle artifacts while all other coherent imaging technologies do not.

Methods:

In this paper, we explain the inherent mechanism that suppresses speckle in PAT, and the analysis was validated by simulations based on an experimental PAT system.

Results:

We found that the speckle‐free feature of PAT results directly from the optical absorption contrast.

Conclusions:

All optical absorbers expand on laser excitation, and therefore all initial photoacoustic pressure rises are positive, which engenders strong correlations among the photoacoustic waves from the absorbers. As a result, prominent boundaries always build up in photoacoustic images and suppress the interior speckle.
Mass preserving nonrigid registration of CT lung images using cubic B‐spline
Authors: Yin Youbing , Hoffman Eric A. , Lin Ching‐Long
Published: August 2009

The authors propose a nonrigid image registration approach to align two computed‐tomography (CT)‐derived lung datasets acquired during breath‐holds at two inspiratory levels when the image distortion between the two volumes is large. The goal is to derive a three‐dimensional warping function that can be used in association with computational fluid dynamics studies. In contrast to the sum of squared intensity difference (SSD), a new similarity criterion, the sum of squared tissue volume difference (SSTVD), is introduced to take into account changes in reconstructed Hounsfield units (scaled attenuation coefficient, HU) with inflation. This new criterion aims to minimize the local tissue volume difference within the lungs between matched regions, thus preserving the tissue mass of the lungs if the tissue density is assumed to be relatively constant. The local tissue volume difference is contributed by two factors: Change in the regional volume due to the deformation and change in the fractional tissue content in a region due to inflation. The change in the regional volume is calculated from the Jacobian value derived from the warping function and the change in the fractional tissue content is estimated from reconstructed HU based on quantitative CT measures. A composite of multilevel B‐spline is adopted to deform images and a sufficient condition is imposed to ensure a one‐to‐one mapping even for a registration pair with large volume difference. Parameters of the transformation model are optimized by a limited‐memory quasi‐Newton minimization approach in a multiresolution framework. To evaluate the effectiveness of the new similarity measure, the authors performed registrations for six lung volume pairs. Over 100 annotated landmarks located at vessel bifurcations were generated using a semiautomatic system. The results show that the SSTVD method yields smaller average landmark errors than the SSD method across all six registration pairs.
Monte Carlo simulations of the count rate performance of a clinical whole‐body MR/PET scanner
Authors: Delso Gaspar , Martinez Maria‐Jose , Torres Irene , Ladebeck Ralf , Michel Christian , Nekolla Stephan , Ziegler Sibylle I.
Published: August 2009

The combination of MR and PET scanners can provide a powerful tool for clinical diagnosis and investigation. Among the existing approaches, the most challenging is that of complete hardware integration of both scanners. Such an integrated tomograph would allow simultaneous acquisition of both modalities, which could help solve issues such as cardiac and respiratory motion. Full integration imposes restrictions on the design of the PET part, such as detector configuration and maximum ring diameter. Furthermore, MR components surrounding the PET detector ring may cause gamma ray interactions, thus affecting PET performance. The purpose of this article is to assess the performance of a hypothetical whole‐body integrated MR/PET scanner using Monte Carlo simulation techniques and compare it to state‐of‐the‐art PET/CT devices used in clinical routine. The Monte Carlo simulation toolkit used for this study is the GEANT4 application for emission tomography. A hypothetical whole‐body MR/PET tomograph fully integrated at hardware level and positioned between gradient and local coils of the MR scanner has been modeled. The NEMA 2‐2001 protocol has been used to configure the simulations in order to measure sensitivity, scatter fraction, count losses, and random detections. Global sensitivity values as a function of the lower‐level discriminator (LLD) energy are provided for time resolutions of 5 and 2.25 ns. In addition, the scatter fraction of the system is studied as a function of the LLD for energy resolution values of 10%, 15%, and 20%. Finally, true, scatter, random, and noise equivalent count rate curves as a function of activity concentration are given for dead‐time values of 136, 432, and 1150 ns and for time resolution values of 2.25 and 5 ns. The influence on the count rate performance of the integrated PET scanner of the new geometry and interfering MR elements has been measured. The results show that the interference of the MR components has a much lower impact than the reduction in the detector ring diameter. Due to the larger solid angle coverage, the sensitivity is higher than that measured for a clinical PET/CT system (6200–10 900 cps/MBq at the center of the scanner) but not enough to compensate the degradation of the noise equivalent count rate due to increased scatter detection. The simulations prove the viability of an integrated MR/PET system and suggest that priority has to be given to either the improvement of the temporal resolution or the correction of triple coincidences if competitive performance is to be achieved.