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The collimator is attached to a detector whose midplane is at a distance c from the back surface of the collimator buy diabecon 60 caps low price diabetes type 1 update. Also buy 60 caps diabecon with amex diabetes mellitus type 2 nih, the collimator resolution deteriorates with increasing source-to-collimator distance, b, and is best at the collimator face. Therefore, in nuclear medi- cine studies, patients should be placed as close to the collimator as possi- ble to provide the best resolution. Septal pen- etration of g-rays plays an important role in the collimator resolution and depends on the g-ray energy. High-energy photons from outside the field of view can cross the septum and yet interact in the detector, thus blurring the image. Because of this, g-rays of only ~50–300keV are suitable for com- Spatial Resolution 121 monly used collimators, the most preferable photon energy being 150keV. At energies below ~50keV, photons are absorbed in the body tissue, whereas at energies above ~300keV septal penetration of the photons can occur. Current collimators are made with appropriate septal thickness for specific photon energies to limit septal penetration. Parallel-hole colli- mators are classified as low-energy collimators with a few tenths of a milli- meter septal thickness (for up to 150-keV g-rays) and medium-energy collimators with a few millimeter thickness (up to 400-keV photons) (Cherry et al. Currently very high energy collimators are available for counting 511-keV photons. It is understandable that for a given diame- ter collimator, the number of holes are greater in low-energy collimators than in high-energy collimators. Normally, high-energy collimators have poorer efficiency and resolution than low-energy collimators. In another classification, collimators are termed high-sensitivity and high- resolution collimators. Often, these collimators are made with an identical number of holes with identical diameters but with different thicknesses. Thus, the collimator with longer holes is called the high-resolution colli- mator and that with shorter holes is called the high-sensitivity collimator. The spatial resolution for the high-sensitivity collimator deteriorates sharply with the source-to-collimator distance. All-purpose, or general- purpose, collimators are designed with intermediate values of resolution and sensitivity. The collimator resolution for pinhole, diverging, and converging colli- mators is expressed by similar but somewhat complex equations, and their details are available in reference books on nuclear physics and instrumen- tation. For pinhole and converging collimators, best resolution is obtained when the object is at the focal plane. The overall system resolutions of different collimators are illustrated in Figure 10. Fan-beam collimators give better spatial resolution but poorer sensitivity than parallel-hole collimators. Scatter Resolution Radiations are scattered by interaction with tissue in patients and with the detector. The effect of scatter resolution is essentially the same for all col- limators (Rollo and Harris, 1977). Effect of source-to-collimator distance on overall system resolution for various types of collimators. Bar phantoms consist of four sets of parallel lead bar strips arranged perpen- dicular to each other in four quadrants in a lucite holder (Fig. The widths and spacings of the strips are the same within each quadrant but differ in different quadrants. The Hine–Duley phantom consists of five groups of lead strips of different thicknesses and spacings arranged in par- allel fashion in a lucite holder (Fig. In all bar phantoms, the thick- ness of lead should be sufficient to stop photons of a given energy for which spatial resolution is being estimated. A 57Co flood source (described later under Quality Control) is placed on the top of it and an image is taken.

This type of experiment generic diabecon 60 caps free shipping diabetes in dogs symptoms panting, however discount diabecon 60caps online blood sugar 450, could offer to know whether this can also be done following long-term insights into the feasibility of integration and survival of donor damage. By drawing information from other systems and the limited studies in the ear so far, it could be suggested that a more suc- cessful approach would be obtained when stem cells, regardless of their origin, are exposed in vitro to specific signals that would Stem cell–based therapy holds trigger the initial programs of differentiation. Transplanted “naïve” stem cells, although homing and surviving into the dif- promise, but many challenges ferent regions of the cochlea, may not produce the diversity of lie ahead fully differentiated cell types needed. It is likely that the neces- sary signals and cues to drive a particular lineage are no longer The application of stem cells to the development of therapies in place in the adult cochlea and the cells would need to be for deafness is creating hopes and expectations. Gene therapy cells pretransplantation would be particularly important with for instance aims to replace or correct a single defective gene. The main targets for transplantation have ondary degeneration of several cell types (74–77). Although been Parkinson’s disease, Huntington’s disease, epilepsy, and exciting results including restoration of auditory function have stroke (80). In these cases, clinical trials have been based been obtained by replacing the math1 gene into acutely deaf- mainly upon the use of primary foetal neural tissue, a rather ill ened guinea pigs (78), this kind of approach alone may not defined and controversial source. Successful experiments with work in many chronic conditions where the general cytoarchi- retinal tissue have been discussed earlier. A cell-based ther- replacement of hair cells by transplantation is probably harder apy could contribute not only to restoring the critical hair cells than replacement of brain cells, retinal cells, or pancreatic cells. A con- need to be placed with micron accuracy to be coupled to the siderable number of transplanted cells were located in the scala sound stimulus. This kind of intervention would be most constructive in conjunction with cochlear implants. In the same context, it may be easier to replace or Xenotransplantation regenerate spiral ganglion neurons. To transfer this technology to a clinical application, sources for stem cells will need to be scrutinised, not only in terms of tissue How to deliver them? The use of animal tissue as donors for transplantation into humans, or xenotransplanta- The delivery of stem cells will very likely require improvement tion, is certainly a possibility. Pig cells, for instance, have been and sophistication of current surgical techniques. A potential used to treat certain conditions such as diabetes (85) and way of access could involve the round window, a route increas- Parkinson’s disease (86). This approach, although attractive for ingly used for drug administration (81), or a cochleostomy in its the relatively availability of the source, is saddled with several proximity, as normally performed to place the array of elec- limitations. Xenotransplants elicit a significant immune rejec- trodes in a cochlear implant (82). Experiments performed so far tion both from the acquired and from the innate systems. This have delivered the cells into the modiolus (69,83) or into the is a formidable obstacle to overcome, requiring substantial perilymphatic space by drilling a small hole either into the scala immmunosuppression, even considering that the inner ear may tympani at the basal cochlear turn (73) or into the lateral semi- be an immunoprivileged organ. These ways of delivery should be appropri- pathogens crossing across species is a certain risk. Porcine ate for neurons, but for the replacement of the sensory endogenous retrovirus, for instance, has been shown to infect epithelium, cells would ideally have to be injected directly into human cells (87), and more control experiments and closely the scala media. Stem cells in the inner ear 285 of) all these limitations, an increased resistance is building up 3. The morphology and growth of a pluripo- diabetes type 1, more than 70% of the patients interviewed tent teratocarcinoma cell line and its derivatives in tissue culture. The end of the beginning for pluripotent minimised by the use of human stem cells. Isolation of a pluripotent cell line from early mouse develop a human-based system. Basic differences in the biology embryos cultured in medium conditioned by teratocarcinoma stem of human stem cells are becoming more apparent when cells. Nature 2001; (93,94) as well as by massively parallel signature sequencing 414:88–91.

First order diabecon 60caps without prescription diabetes mellitus drugs, some procedures organize the scores so that we can more clearly see any patterns in the data effective 60caps diabecon managing diabetes in school. We don’t need to examine each of the hundreds of scores that may be obtained in a study. Instead, a summary—such as the average score—allows us to quickly and easily understand the general characteristics of the data. Researchers have created techniques and rules for this and, because everyone uses the same rules, it is much easier for us to communicate with each other, especially in published research reports. All behavioral research is designed to answer a question about a behavior and, ultimately, we must decide what the data tell us about that behavior. Even if you are not interested in becoming a researcher, statistics are necessary for comprehending other people’s research. You hear of a new therapy that says the way to “cure” people of some psychological problem is to scare the living daylights out of them. This sounds crazy but what is important is the research that does or does not support this therapy. As a responsible professional, you would evaluate the research supporting this therapy before you would use it. This book is written for students who have not yet studied how to conduct research. When we discuss each statistic, we also discuss simple studies that employ the procedure, and this will be enough. Later, when you study research methods, you will know the appropriate statistical procedures to use. We will discuss some research tools that happen to involve mathematical operations. But it is simple math: adding, subtracting, multiplying, dividing, finding square roots, and drawing simple graphs. Best of all, statisticians have already developed the statistics we’ll discuss, so we won’t be deriving formulas, performing proofs, or doing other “mystery” math. We will simply learn when to use the procedure that statisticians say is appropriate for a given situation, then compute the answer and then determine what it tells us about the data. First, there are not all that many procedures to learn, and these fancy sounding “procedures” include such simple things as computing an average or drawing a graph. A mechanic does not need to be an expert wrencher who loves to wrench, and you do not need be an expert statistician Why is It Important to Learn Statistics (and How Do You Do That? Rather, in the same way that a mechanic must understand how to correctly use a wrench, your goal is to be able to correctly use statistics. But these are simply the shorthand “code” for communicating statistical results and for simplifying statistical formulas. Think of it this way: To understand research you must speak the language, and you are about to learn the language of statistics. Once you speak this language, much of the mystery surrounding statistics evaporates. What makes some formulas appear difficult is that they are written in a code that communicates a sequence of operations: You first might square the scores, then add them together, then divide by some other number, and so on. However, most chapters begin with a section called “New Statistical Notation,” which explains the symbols that you’ll encounter, and then each formula is presented with example data and step-by-step instructions on how to work through it. With practice the formu- las become easy, and then the rest of the mystery surrounding statistics will evaporate. Ultimately you want to make sense of data, and to do that, you must compute the appropriate statistic and then correctly interpret it. More than anything else, you need to learn when and why to use each pro- cedure and how to interpret its answer. At first glance, you might think that this book was written before the invention of computers.

Yet to suggest that Erasistratus and Herophilus were ‘Aristotelians’ would do grave injustice to their highly original ideas and the innovative aspects of their empirical research diabecon 60 caps otc diabetes insipidus bedwetting, such as Herophilus’ discovery of the nervous system and Erasistratus’ dissections of the brain and the valves of the heart diabecon 60 caps with mastercard diabetes type 1 diarrhea. It also ignores their connections with developments in other sciences, notably mechanics, and with other philosophical movements, such as Scepticism (in particular regarding whether causes can be known) and Stoicism. The Hellenistic period was also the time in which the medical ‘sects’ came into being: Empiricism, Dogmatism and Methodism. What separated these groups was in essence philosophical issues to do with the nature of medical knowledge, how it is arrived at and how it is justified. The precise chronological sequence of the various stages in this debate is difficult to reconstruct, but the theoretical issues that were raised had a major impact on subsequent medical thinking, especially on the great medical systems of late antiquity, namely Galen’s and Methodism. Galen is one of those authors who have been rediscovered by classicists and students of ancient philosophy alike, be it for his literary output, his mode of self-presentation and use of rhetoric, the picture he sketches of the intellectual, social and cultural milieus in which he works and of the traditions in which he puts himself, and the philosophical aspects of his thought – both his originality and his peculiar blends of Platonism, Hippocratism and Aristotelianism. Galen’s work, voluminous in size as well as in substance, represents a great synthesis of earlier thinking and at the same time a systematicity of enormous intellectual power, breadth and Introduction 29 versatility. In chapter 10, I shall consider Galen’s theoretical considerations about pharmacology, and in particular his views on the relationship between reason and experience. Although in the field of dietetics and pharmacology he is particularly indebted to the Empiricists, his highly original notion of ‘qualified experience’ represents a most fortunate combination of reason and experience; and one of Galen’s particular strengths is his flexibility in applying theoretical and experiential approaches to different domains within medical science and practice. Among Galen’s great rivals were the Methodists, a group of medical thinkers and practitioners that was founded in the first century bce but came to particular fruition in the first and second centuries ce, especially under their great leader Soranus. Although their approach to medicine was emphatically practical, empirical and therapy-oriented, their views present interesting philosophical aspects, for example in epistemology and in the as- sumption of some kind of corpuscular theory applied to the human body. Regrettably, most works written by the Methodists survive only in frag- ments, and much of the evidence is biased by the hostile filter of Galen’s perception and rhetorical presentation. Caelius has long been dismissed as an unoriginal author who simply translated the works of Soranus into Latin. However, recent scholarship has begun to appreciate Caelius’ originality and to examine his particular version of Methodism. This overlap not only concerned the ideas, concepts and method- ologies they entertained, but also the ways and forms in which they ex- pressed and communicated these ideas, the modalities of dissemination and persuasion, and the settings in which they had to work and present 32 For a collection of the fragments of the Methodists see now Tecusan (2004). I touch here on a further aspect in which the study of ancient medicine – and philosophy – has recently been contextualised, and in this case the impetus has come from a third area of research we need to consider briefly because of its particular relevance to the papers collected in this volume, namely the field of textual studies or, to use a more recent and specific term,‘discourse analysis’. One only needs to point to the twenty-two volumes of Kuhn’s¨ edition of the works of Galen or the ten tomes of Littre’s´ edition of the works of Hippocrates to realise that ancient medical literature has been remarkably well preserved, at least compared with many other areas of classical Greek and Latin literature. While much philological spade-work has been done to make these texts more accessible, especially in projects such as the Corpus Medicorum Graecorum or the Collection des Universites de France´ , many parts of this vast corpus of literature, to which newly discovered texts continue to be added, still await further investigation. There still is, of course, a great basic demand for textual studies, edi- tions, translations, commentaries and interpretative analyses – and in this respect, the triennial conferences on Greek and Latin medical texts have proved remarkably fruitful. Yet apart from this, there is an increasing in- terest being taken in medical, scientific and philosophical texts, not just because of their intellectual contents but also from the point of view of linguistics, literary studies, discourse analysis, narratology, ethnography of literature (orality and literacy), rhetoric and communication studies. This is related to a growing scholarly awareness of the communicative and com- petitive nature of Greek medicine and science. Greek doctors, philosophers, astronomers and mathematicians had to impress their audiences, to per- suade them of their competence and authority, to attract customers and to reassure them that they were much better off with them than with their rivals. Medical, scientific and philosophical texts functioned in a specific setting, with a particular audience and purpose, and served as vehicles not only for the transmission of ideas but also for the assertion of power and authority. These developments have given rise to a whole new field of studies and questions regarding the ways in which knowledge was expressed and com- municated in the ancient world: the modes of verbal expression, technical idioms, stylistic registers and literary genres that were available to people who laid a claim to knowledge (healers, scientists, philosophers) in order to convey their views to their fellows, colleagues and their wider audiences; the rhetorical strategies they employed in order to make their ideas intel- ligible, acceptable, or even fashionable; the circumstances in which they Introduction 31 had to present their ideas, and the audio-visual means (writing facilities, diagrams, opportunities for live demonstration) they had at their disposal; the interests and the expectations of their audiences, and the ways in which these influenced the actual form of their writings; and the respects in which ‘scientific’, or ‘technical’, or ‘expert’ language or ‘discourse’ differed from ‘ordinary’ and ‘literary’ language and ‘discourse’. After many years of considerable neglect, the last two decades have thus seen a significant increase in attention being given to the forms of ancient scientific writing, especially among students of the Hippocratic Corpus, but also, for example, on Latin medical literature, with some studies focusing on ‘strictly’ linguistic and textual characteristics, while others have attempted to relate such characteristics to the wider context in which the texts were produced. First, general trends in the study of rhetoric and discourse analysis, in particular the study of ‘non-literary’ texts such as advertisements, legal proceedings, minutes of meetings, political pamphlets and medical reports, the study of rhetoric and persuasive strategies in apparently ‘neutral’ scien- tific writings, and the development of genre categories based on function rather than form have led to a growing awareness among classicists that even such seemingly ‘unartistic’, non-presumptuous prose writings as the extant works of Aristotle, the Elements of Euclid and the ‘notebook-like’ Hippocratic Epidemics do have a structure which deserves to be studied in its own right, if only because they have set certain standards for the emergence and the subsequent development of the genre of the scientific treatise (‘tractatus’) in Western literature. It is clear, for example, to any student of Aristotle that, however impersonal the tone of his works may be and however careless the structure of his argument may appear, his writings nonetheless contain a hidden but undeniable rhetoric aimed at making the reader agree with his conclusions, for example in the subtle balance be- tween confident explanation and seemingly genuine uncertainty, resulting in a careful alternation of dogmatic statements and exploratory suggestions. The study of these formal characteristics has further been enriched by a growing appreciation of the role of non-literal, or even non-verbal as- pects of communication (and conversely, the non-communicative aspects of language).