As Aristotle makes no mention of a mixture of humours anywhere else cheap cefpodoxime 200 mg otc treatment for uti back pain, but does mention a particular mixture of heat and cold as the basis for a healthy physical constitution discount cefpodoxime 200 mg without prescription bacteria resistant to antibiotics,46 it is appropriate to think of a mixture of qualities discount 200 mg cefpodoxime mastercard antibiotic 93 3196. In this theory 100mg cefpodoxime mastercard virus jumping species, melancholics are characterised by a mixture of heat and cold (either too cold or too hot) that is permanently out of balance, something which Aristotle clearly regards as a sign of disease. Further details about this physiological basis can be found in the only passage entirely devoted to bile (chole¯), in Part. According to Aristotle, bile is a residue (perittoma¯ ) without purpose (oÉc nek tinov), and although nature sometimes makes good use of residues, this does not imply that we should expect everything to have a purpose. After all, there are many things that are necessarily by-products of things that do serve a purpose, but are themselves without purpose. On bile as a perittoma¯ Aristotle says a few lines further on (677 a 25): ‘when the blood is not entirely pure, bile will be generated as a residue, for residue is the opposite of food’. Bile appears to be a ‘purifying secretion’ (apokatharma), which is con- ﬁrmed by the saying in antiquity that people live longer if they do not have bile. Ogle (1910) is correct in translating chole¯as ‘gall bladder’ and whether it should not be understood as ‘bile’ until later. This characterisation returns several times in Aristotle’s writings on biology: Part. The chapter in Parts of Animals clearly states that the residues are themselves without purpose, but that nature sometimes uses them for a good purpose. This characterisation of yellow and black bile and phlegm54 as perittomata¯ plays a pivotal part in the question whether Aristotle adopted the Hippo- cratic theory of the four humours. However, there is no indication that these ﬂuids in any combination form a kind of humoral system similar to the theory of the four humours in On the Nature of Man; the only place where three are mentioned together (viz. This itself shows that it is unlikely that Aristotle assigned them a role as important bodily ﬂuids on which hu- man health depends. In addition, it should be pointed out that the notion of perittoma¯ does not appear in the Hippocratic Corpus and was probably not introduced into Greek medicine until the second half of the fourth century bce (perhaps by Aristotle himself, or by one of his students), after 52 Louis (1956) 189 n. Aristotle uses the Hippocratic typology phlegmatodes – cholodes¯ ¯ ¯ ¯ once, though not in a biological context (and in a passage of dubious authenticity: Metaph. We may conclude that the texts do not give detailed information on the physiological basis of Aristotle’s use of the term hoi melancholikoi. Yet it seems clear that such a concept does exist in Aristotle’s work: hoi melan- cholikoi are melancholics by nature (ten¯ phusin), that is, as a result of a physiological constitution, which, however, is diseased and permanently in need of a cure. It is impossible to say with certainty whether melancholics are characterised (1) by the very presence of black bile in them (for, as Part. This is probably due to the fact that Aristotle pays limited attention to medical matters when he writes in his capacity of phusikos: he only discusses the principles of health and disease, that is to say, the role of heat and cold in the body and the balance between them. Thivel states that in Aristotle, by contrast to the later Anonymus Londiniensis, the perittoma¯ has not yet become a ‘principe de maladie’. For the notion of perittoma¯ in Aristotle see also On Length and Shortness of Life (De longitudine et brevitate vitae) 466 b 5–9 and Peck’s Loeb edition of On the Generation of Animals, lxv–lxvii, as well as Harig (1977) 81–7. However, the objection must be made that Aristotle’s statement may well refer only to the methodical process employed in his writings on physics (phusike philosophia¯ , including his clearly planned but perhaps never written On Health and Disease). Aristotle may have discussed medical facts in greater detail elsewhere, for instance in the Iatrika which Diogenes Laertius (5. For a more extensive discussion of this passage see van der Eijk (1994) 271–80 [and ch. Aristotle on melancholy 155 difﬁcult to assess his dependence on sources in general and his attitude towards the Hippocratic writings in particular. For this reason, and in view of our limited knowledge of fourth-century medicine in general, it is virtu- ally impossible to say anything with certainty on the sources of Aristotle’s concept of melancholy. At any rate, there is no indication that Aristotle made a connection between the ‘constitutional type’ of the melancholic, well-known from the early writings of the Hippocratic Corpus, and the later, similarly Hippocratic embedding of black bile in the theory of the four humours of On the Nature of Man (which, after all, does not mention the melancholic type). In fact, the notion of melancholy as an abnormal predisposition and a disease, and the fact that black bile is considered a perittoma¯ , makes any possible Hippocratic inﬂuence rather unlikely. The concept of the melancholic, with the associated psycho-physical and ethi- cal characteristics seems to be a predominantly independent and genuine invention of Aristotelian philosophy. In view of the extensive scholarly literature on this chapter60 I will, rather than giving a summary, start with some interpretative observations that I consider of paramount importance for assessing the Aristotelian character of the theory. First of all, it should be said that I certainly do not intend to reinstate Aristotle as the author of this text: as far as the issue of the authorship of the Problemata is concerned I concur entirely with Hellmut Flashar’s view (1962, 303–16) that the Problemata are most probably not the same as the Problemata that Aristotle wrote (or planned to write). With regard to the opening question, ‘Why is it that all men who have made extraordinary achievements in the ﬁelds of philosophy or politics or poetry or the arts turn out to be melancholics? However, there are still numerous passages in this text that have not been fully explained in the existing interpretations. The subsequent discussion of the heroes Heracles, Aias and Bellerophontes and the poets and philosophers Empedocles, Socrates and Plato shows that the presupposition implied in the question is apparently based on a rather speciﬁc notion of melancholy. Epilepsy, bouts of ecstasy, prophetic powers, but also depressions, extreme fear of people, and suicidal inclinations are all attributed to the same disease. Apparently, this aim lies ﬁrst of all in the explanation that this attribution actually has a physiological justiﬁcation, that is, that the very different, at times even contrasting characteristics of the melancholic are all based on one coherent physiological condition; secondly, the author intends to explain the in itself paradoxical connection between melancholy as a disease (953 a 13, 15: arrosthema¯ ¯ ; 16: nosos; 18: helke¯; 29: nosemata¯ ; 31: pathe¯) and the extraordinary political, philosophical and poetic achievements (ta peritta) by means of this physiological basis. This second aim has correctly been understood as readopting the Platonic theory of mania. Answering the opening question of the chapter is in fact only attempted in the context of the second aim; the largest part of the text is devoted to answering the other question of why the ways in which melancholy manifests itself differ so much. The opening question is referred to on just two occasions: in 954 a 39–b 4 and, very brieﬂy, in 954 b 27–8. This division is also followed in the structure of the ﬁnal summary of the chapter (955 a 29ff. Boyance(´ 1936, 191) presumes that a certain divine inﬂuence is implied in the role of the pneuma, yet there is no indication of this in the text of the chapter (on the role of the pneuma see n. Aristotle on melancholy 157 between melancholy and extraordinary achievement (36ff. The basis for achieving both aims lies in the fact that the author distin- guishes between disease (nosos, nosema, arrosthema¯ ¯ ¯ ) and natural disposition (phusis); in this respect it is striking that the ‘natural melancholics’ are also affected by ‘melancholic diseases’ and that they apparently are more prone to this than other people (953 a 12–15 and 29–31). To explain its effects, the au- thor employs the analogy between the melancholic nature and wine (this analogy returns in statements made by Aristotle). Muri (¨ 1953, 25) only implicitly alludes to it when he states ‘indem die Disposition da, wo es not tut (z. The text says:¨ ¨ peª d’ sti kaª eÎkraton e²nai tn nwmal©an kaª kaläv pwv cein, kaª Âpou de± qermotran e²nai tn diqesin kaª plin yucrn, £ toÉnant©on di t¼ Ëperboln cein, perittoª mn e«si pntev o¬ melagcoliko©, oÉ di n»son, ll di fÅsin. As the author presents this sentence as a summary of something previously discussed, the question arises what kaª Âpou de± refers to, for in this sentence the eukrasia that underlies the melancholic’s peritton does not seem to be referring to a balance of heat and cold (as in 954 b 1), but to a certain ability to adapt this balance to the conditions required by each individual situation (hopou dei). Signiﬁcant in this context are the differences between the translations of Klibansky et al. Another difﬁculty here is the interpretation of di tn Ëperboln cein: what would this ‘surfeit’ precisely be? This contradiction could only be solved by understanding perittos here in the ﬁnal sentence as a neutral notion and therefore synonymous with ektopos (‘eccentric’). This is to a certain extent justiﬁed by the fact that no speciﬁcation as to the precise ﬁeld (£ filosof©an ktl. However, as the causal subclause refers to a healthy balance (eukraton), perittos must be understood in a positive sense. At ﬁrst sight it seems that 953 a 29–31 speaks about a difference between ‘disease’ (nosema¯ ) and ‘nature’ (phusis), but in fact it says that many melancholics actually get melancholy-related diseases, while others are only very prone to getting these disorders. Nevertheless, as the next sentence shows, both groups belong to the ‘natural melancholics’ (phusei melancholikoi).
The bone marrow biopsy is about 50 to 60% sensitive for amyloid order cefpodoxime 200 mg with amex xnl antibiotic, but it would allow evaluation of the percent of plasma cells in the bone marrow and allow the diagnosis of multiple myeloma to be made generic cefpodoxime 100mg line virus removal tool. Light chains most commonly deposit systemically in the heart cheap 100 mg cefpodoxime amex antibiotic resistance risk factors, kidneys purchase cefpodoxime 100 mg with amex bacteria nintendo 64, liver, and nervous system, causing organ dysfunction. In these organs, biopsy would show the classic eosinophilic material that, when exposed to Congo red stain, has a characteristic apple-green birefringence. Rheumatoid factor is occasionally positive in relapsing polychondritis but is usu- ally low titer when present. Saddle-nose deformity, which is present in 25% of patients with relapsing polychondritis, may be confused with Wegener’s granulomatosis. The bacteria of septic arthritis usually enter the joint via hematogenous spread through synovial capillaries. The concurrent presence of pseudogout does not preclude the diag- nosis of septic arthritis. Antibiotics, prompt surgical evaluation of possible arthro- scopic drainage, and blood cultures to rule out bacteremia are all indicated. Prompt local and systemic treatment of infection can prevent destruction of cartilage, joint instability, or deformity. If the smear shows no organisms, a third-generation cephalosporin is reasonable empirical therapy. In the presence of Gram-positive cocci in clusters, antistaphylococcal therapy should be instituted based on community prevalence of methicillin resistance or recent hospitalization (which would favor empirical vancomycin). Nonsteroidal anti-inﬂammatory agents might be a possi- bility depending on the patient’s renal function and gastrointestinal history. Usually this occurs in the absence of intrinsic shoulder disease, in- cluding osteoarthritis and avascular necrosis. It is, however, more common in patients who have had bursitis or tendinitis previously as well as patients with other systemic illnesses, such as chronic pulmonary disease, ischemic heart disease, and diabetes mellitus. The etiology is not clear, but adhesive capsulitis appears to develop in the setting of prolonged immobility. On physical examination, the affected joint is tender to palpa- tion, with a restricted range of motion. The gold standard for diagnosis is arthrography with limitation of the amount of injectable contrast to less than 15 mL. In most patients, adhesive capsulitis will regress spontaneously within 1 to 3 years. This autoimmune disorder is associated with lymphocytic inﬁltration of exocrine glands that results in decreased tear and saliva production as the most prominent symptoms. Sjögren’s syndrome affects women nine times more frequently than men and usually pre- sents in middle age. Other autoimmune diseases often have associated xerostomia and dry eyes (secondary Sjögren’s syndrome). High titers of antibodies to Ro and La are associated with longer disease duration, salivary gland enlargement, and the development of extra- glandular involvement, especially cutaneous vasculitis and demyelinating syndromes. One- third of patients with Sjögren’s syndrome have extraglandular involvement of the disease, most commonly in the lungs and kidneys. In this patient with acidemia and hypokalemia, the possibility of renal disease due to Sjögren’s syndrome should be considered. Interstitial nephritis is a common manifestation of Sjögren’s syndrome in the kidneys. Distal (type I) renal tubular acidosis is also frequent, occurring in 25% of individuals with Sjögren’s syn- drome. Diagnosis could be conﬁrmed by obtaining urine electrolytes to demonstrate a pos- itive urine anion gap. Treatment does not require immunosuppression as the acidemia can be treated with bicarbonate replacement. Diar- rhea could cause similar electrolyte abnormalities with a non-anion gap acidosis, but the patient would be symptomatic. Furthermore, gastrointestinal symptoms do not commonly occur in Sjögren’s syndrome. Purging in anorexia nervosa could result in hypokalemia and increased risk of dental caries, but it would be associated with metabolic alkalosis rather than acidosis. The clinical syndrome is a rheuma- tologic one, with joint effusions, arthropathy, and cystic bone lesions predominating. The β2-microglobulin can be found in joint synovium, and the joint ﬂuid is usually nonin- ﬂammatory. Serum amyloid A (secondary amyloid) is associated with chronic infections or inﬂammatory conditions. Transthyretin is associated with a familial form of amyloidosis that is transmitted in an au- tosomal dominant fashion. One variant of transthyretin amyloid has a carrier frequency of up to 4% in African Americans and is associated with a late-onset cardiomyopathy. The patient reports difﬁculty with everyday tasks requiring the use of proximal muscles, such as getting up from a chair and climbing steps. In addition to the musculoskeletal ﬁndings, there are numerous extramuscular manifestations. This pa- tient may have systemic symptoms of fever, malaise, weight loss, and Raynaud’s phenom- enon. Involvement of the striated muscles and the upper esophagus may lead to dysphagia. Although dermatomyositis is linked with an increased incidence of cancer, poly- myositis does not seem to be associated with an increased incidence. Diuretics result in hyperuricemia through enhanced urate reabsorption in the proximal tubule of the kidney in the setting of volume depletion. Hyperuricemia re- mains asymptomatic in many individuals but may manifest as acute gout. While any joint may be af- fected, the initial presentation of gout is often in the great toe at the metatarsophalangeal joint. A typ- ical patient will complain that the pain is so great that they are unable to wear socks or allow sheets or blankets to cover the toes. The diagnosis of gout is conﬁrmed by the demonstration of monosodium urate crystals seen both extracellularly and intracellularly within neutrophils. Monosodium urate crystals appear strongly negatively birefringent under polarized light microscopy and have a typical needle- and rod-shaped appearance. Likewise, very low glucose levels and a positive Gram stain are not manifestations of acute gout but are common in septic arthritis. Calcium pyrophosphate dihydrate crystals appear as weakly positively birefringent rhomboidal crystals and are seen in pseudogout. The scalp lesion is consistent with discoid lupus erythematosus, which can be a benign condition if presenting as an isolated condition. Indi- viduals with anti-Sm antibodies often also have antibodies to ribonucleoprotein as well. The level of rheumatoid factor in this patient falls within the equivocal range and is not di- agnostic of rheumatoid arthritis. Further, the patient’s discoid rash and photosensitivity as well as positive serologies would further eliminate rheumatoid arthritis from the differen- tial diagnosis. Behçet’s disease presents with oral and genital ulcerations, and 50% will also have nonerosive arthritis.
Improved filler forming methods have already been introduced into phases order 100mg cefpodoxime free shipping antimicrobial hand soap, bonding agents and toughened polymer both clinical and dental laboratory settings cheap cefpodoxime 200 mg mastercard script virus. It is matrixes are being investigated to improve wear and anticipated that advanced process development will structural behavior and add remineralizing capabil- continue buy cheap cefpodoxime 100mg online antibiotics for uti otc. Much focus will remain on the optimiza- ity (Antonucci et al buy generic cefpodoxime 200 mg line antibiotics japan over counter, 1991; Stansbury and Anto- tion of current materials, minimizing contraindica- nucci, 1992; Skrtic et al, 1996; Schumacher et al, tions and broadening use of esthetic materials for 1997; Stansbury and Antonucci, 1999; and Xu et al, posterior restorations. Novel posterior restorative materials are are under development that combines diagnostic, being developed, including mercury-free, condensa- restorative and therapeutic (controlled release) ble silver fillings and esthetic interpenetrating-phase capability. Work continues on improving adhesive composites (non-shrinking), based on the resin infil- chemistries and on mercury-free restorative materi- tration of porous, three-dimensional ceramic skele- als. Increased focus is being given to the develop- tons (Dariel et al, 1995; Eichmiller et al, 1996; ment of laboratory tests that validly reproduce clin- Giordano et al, 1997; Kelly and Antonucci, 1997; ical behavior. Biomimetic approaches are becomes available regarding intraoral damage mech- being investigated, as are tissue engineering con- anisms and microstructure-property relationships. Surface chemistries ening the use of titanium in fixed prosthodontics, par- and topologies of implantable materials are being ticularly with respect to improving the interface with studied to enhance cellular interactions. Advanced forming systems, almost all involving Many academicians recognize the need for a more some computer control, will (1) broaden the range robust evidence base to guide clinical decisions of currently available materials that can be used in involving comparisons among materials and the dental practice, (2) improve the precision and auto- rational development of clinical indications for new mate dental laboratory fabrication, (3) foster devel- materials (Laskin, 2000). Investigations are being opment of novel prostheses and craniofacial called for to identify the relative technique sensitivi- implants, and (4) provide routes to novel materials. Research is anticipated in the development involves three-dimensional printing of powder/ of in vitro test methodologies predictive of clinical binder combinations followed by sintering to form behavior to evaluate dental biomaterials and assist solid objects from ceramics or alloys (Cima, 1996). Future analysis) of too large a percentage of published den- research will form an improved definition of genet- tal clinical trials (Kelly, 1999; and Palmer and Sendi, ic, environmental, and microbial risk factors for 1999). Rather than focusing on component materi- periodontitis that will lead to development of a pro- al properties, dental prostheses are being evaluated file for patients at risk for advanced disease. It can be antici- and cellular processes with implanted materials pated that subtraction radiography will be intro- remains a research focus to both enhance the clini- duced as part of patient management, but may be cal application of titanium dental implants and to limited to specialized treatment centers. The development possible that this area of investigation will see and microstructure of tissues continues to be studied renewed interest because of the growing body of evi- with the hope that biological processes can be mim- dence linking periodontal diseases and various sys- icked in the fabrication of biomimetic prosthetic temic diseases. These tests will likely be formatted materials (Marshall et al, 2001; White et al, 2001; in a user-friendly style, utilizing saliva or blood to Kamat et al, 2000; and Kirkham et al, 2000). Research in this area will be tissue engineering research as initial carriers of cells, linked to studies of the relationship of periodontal growth factors and molecular species designed to diseases and cardiovascular disease, cerebrovascular direct and enhance defect repair, especially in bone disease, pre-term low birth weight babies, and dia- (Ma and Choi, 2001; Loty et al, 2000; Reddi, 2000; betes mellitus. Tissue engineering as a means of reducing the risk for these medical dis- approaches may also provide clinicians with the orders will also be explored. As an example, a specific mutation on chromosome Periodontal Disease Risk Assessment and 11q14 associated with the gene encoding of the Diagnosis enzyme cathepsin C was detected in a consanguineous family with prepubertal periodontitis (Hart et al, The diagnosis of periodontal disease will continue 2000). Clinicians will begin of periodontal disease research, in tandem with the to identify individuals who are at risk for active peri- general emphasis on using information about varia- odontal diseases using genetic tests and biologic tests tions in the human genome, and the protein products that identify specific microorganisms in subgingival of those genes, to explain human diseases. In addition, digital radiography Periodontal Disease Management will be used more in periodontal diagnosis, and prac- tical systems will be introduced to perform subtrac- The improved understanding of the pathogenesis of tion radiography in the dental office. The use of systemic antibiotics to general health as other risk factors, such as smok- will be reserved for the most aggressive forms of dis- ing or high cholesterol levels. Considerable research expected to be active participants in the management effort has focused on the use of newer anti-inflamma- of patients with certain systemic diseases, and to tory agents for treatment of periodontitis. While sys- broadly consider how medical management of patients temically delivered agents have been used in both ani- will influence dental health and dental care. For exam- mal and human studies, topical delivery of these agents ple, longitudinal medical studies have demonstrated (mouth rinses, toothpastes) seems the most logical that good glycemic control limits the onset and preva- approach for the future. When indicated, dentists be employed as anti-inflammatory agents (Graves et al, should be checking hemoglobin A1c. Periodontal dis- 1998), and, in the case of diabetes-associated periodon- eases are the sixth complication of diabetes mellitus. Advances in treatment of periodontitis will focus If, in the near future, multicentered, randomized, on procedures to induce regeneration of lost peri- controlled clinical trials confirm that periodontal odontal tissues. Among the specific mediators being disease causes systemic conditions, several issues studied for application in periodontal therapy are will confront the dental profession: recombinant bone morphogenetic proteins and combinations of growth factors. The success of x Studies will need to be conducted to determine these therapies will depend on the identification of the effectiveness of screening patients in the dental the appropriate biological mediator and the appro- office for certain diseases with obvious ramifications priate delivery system. If effective, these pro- grams will enhance the oral health and general Although there are a few negative findings (Hujoel health status of patients. Oral infections are suspected to be a risk lic and physicians that dentistry can no longer be factor for certain systemic diseases (that is, cardiovas- considered solely a luxury, elective health care. Increased x The recognition of the medical necessity for peri- communication by dentists with other health care odontal care will increase the perceived impor- professionals can be expected. Thus, the larger problems are strating a systemic therapeutic benefit from peri- the perception among health care professionals, the odontal therapy, there is no concrete evidence to jus- nature and system by which health care is delivered, tify a change in oral health care policy or current and access and utilization. Future research in humans should more demiological, basic science, social science and clinical thoroughly evaluate the maternal genotype in addition to trial research will enable them to participate more that of the fetus in determining risk of this birth defect. Current research efforts are point- ing the way to promising directions, especially in the x Continued efforts should target the identification areas of etiology/prevention and outcomes. Basic research should also work towards obtaining a x Family studies have for many years demonstrated better understanding of the molecular pathways that inherited genetic variation has a very large effect on that are disrupted by mutations at these genes. This will move us towards an era of genetics, promise to reveal their basic causes with "individualized medicine" where risk of orofacial continued investment. However, the nature of clini- clefting can be much more accurately predicted cal research requires very long-term commitments based on the "genetic blueprint" of the parents. The of major resources for patient recruitment and eval- human genome project has now produced the uation, laboratory assays, and data management tools and knowledge in the form of millions of single and statistical analysis. Groups around the world cur- tective dietary factors such as vitamins and folate rently focused on this research effort will need con- are needed to better understand the role of envi- tinued support for many years to achieve major suc- ronmental factors in both nonsyndromic and some cess. Clinical trials of new means of prevention for forms of syndromic orofacial clefting. Some recent research and initia- up a network of nearly all cleft/craniofacial teams in tives have begun to address these issues and can be used Europe to establish standards for recording and as guidelines for planning future directions. Dental specialists have played a major attempts to comprehensively compare treatment role in the creation of this organization. As with the outcomes from different centers, each with widely Craniofacial Outcomes Registry, the Eurocleft Project differing treatment protocols. Using multidiscipli- has the potential for providing collective information nary outcome measures and strict research method- on cleft/craniofacial treatment outcomes which will ology, these studies not only demonstrated the fact enable more productive future research efforts to iden- that outcomes can vary considerably based on the tify the most effective treatment regimes. Europe indicated that there were 194 different These long-term research efforts need to receive primary surgical protocols. Few randomized control trials have been car- ried out in the cleft/craniofacial field, and these are As a result of these developments, the potential essential in order to objectively determine the rela- future impact of the dental profession on improve- tive merits of different treatment methods. Since many of the projects moving results of treatment has led to several recent towards globalization of the research effort are still initiatives having the potential to greatly facilitate early in planning stages, dental professionals have a future outcomes research. For example, the great opportunity to shape these efforts to ensure Craniofacial Outcomes Registry is an attempt to that dental concerns in cleft/craniofacial care are establish standard outcome measures for all properly addressed. Appropriate training of dental aspects of cleft care, and to provide a centralized scientists in the execution of valid and reliable out- repository where individual cleft/craniofacial centers come studies and randomized control trials will can register patients online and then subsequently facilitate the development and use of evidence-based submit treatment information and out-come meas- treatment decisions by future cleft/craniofacial ures. Future research of a high caliber should final- making significant contributions to this effort, both ly allow for the scientifically-based elimination of in terms of participation in the establishment of valid treatment methods which fail to produce outcomes and reliable outcome measures, and also through and benefits necessary to justify their continued use. Finally, there is also a need clusion, such as osteodistraction and implant/ onplant- for the development of outcome measures which based anchorage, arise from basic research in biomate- incorporate the potentially more meaningful issues rials/bioengineering/biomimetics. In the future, a com- of patient/parent expectations, satisfaction, and bination of biological and biomechanical signals may quality of life evaluations (e. Furthermore, it should be advantageous to induce tooth development Research on human genetic variation that influ- in areas of tooth agenesis (Nuckolls et al, 1999).
The prime objective of these scanners is to display the images of the activity distribution in different sections of the object at dif- ferent depths cheap cefpodoxime 200 mg visa virus removal tool kaspersky. The principle of tomographic imaging in nuclear medicine is based on the detection of radiations from the patient at different angles around the patient discount 100 mg cefpodoxime with visa antimicrobial nail solution. In contrast cheap cefpodoxime 200 mg on-line oral antibiotics for acne how long, in transmission tomography generic cefpodoxime 100mg with visa virus definition update, a radi- ation source (x-rays or a radioactive source) projects an intense beam of radiation photons through the patient’s body, and the transmitted beam is detected by the detector and further processed for image formation. Single Photon Emission Computed Tomography 155 The detector head rotates around the long axis of the patient at small angle increments (3° to 10°) for collection of data over 180° or 360°. The data are collected in the form of pulses at each angular position and normally stored in a 64 × 64 or 128 × 128 matrix in the computer for later reconstruction of the images of the planes of interest. Transverse (short axis), sagittal (vertical long axis), and coronal (horizontal long axis) images can be gen- erated from the collected data. Multihead gamma cameras collect data in several projections simultaneously and thus reduce the time of imaging. For example, a three-head camera collects a set of data in about one third of the time required by a single-head camera for 360° data acquisition. Data Acquisition The details of data collection and storage such as digitization of pulses, use of frame mode or list mode, choice of matrix size, etc. Data are acquired by rotating the detector head around the long axis of the patient over 180° or 360°. Although 180° data collection is commonly used (particularly in cardiac studies), 360° data acquisition is preferred by some investigators, because it minimizes the effects of attenuation and vari- ation of resolution with depth. In some situations, the arithmetic mean (A1 + A2)/2 or the geometric mean (A × A )1/2 of the counts,A and A , of the two heads 1 2 1 2 are calculated to correct for attenuation of photons in tissue. However, in 180° collection, a dual-head camera with heads mounted at 90° angles to each other has the advantage of shortening the imaging time required to sample 180° by half (Table 12. Dual-head cameras with heads mounted at 90° or 180° angles to each other and triple-head cameras with heads ori- ented at 120° to each other are commonly used for 360° data acquisition and offer shorter imaging time than a one-head camera for this type of angular sampling. The sensitivity of a multihead system increases with the number of heads depending on the orientation of the heads and whether 180° or 360° acquisition is made. Older cameras were initially designed to rotate in circular orbits around the body. Relationship of sensitivity and time of imaging for 180° and 360° acqui- sitions for different camera head conﬁgurations. This causes loss of data and hence loss of spatial resolution in these projections. Data collection can be made in either continuous motion or “step-and- shoot” mode. In continuous acquisition, the detector rotates continuously at a constant speed around the patient, and the acquired data are later binned into the number of segments equal to the number of projections desired. In the step-and-shoot mode, the detector moves around the patient at selected incremental angles (e. Image Reconstruction Data collected in two-dimensional projections give planar images of the object at each projection angle. To obtain information along the depth of the object, tomographic images are reconstructed using these projections. Two common methods of image reconstruction using the acquired data are the backprojection method and the iterative method, of which the former is the more popular, although lately the latter is gaining more attention. Simple Backprojection The principle of simple backprojection in image reconstruction is illustrated in Figure 12. In the two-dimensional data acquisi- tion, each pixel count in a projection represents the sum of all counts along the straight-line path through the depth of the object (Fig. Recon- struction is performed by assigning each pixel count of a given projection in the acquisition matrix to all pixels along the line of collection (perpen- dicular to the detector face) in the reconstruction matrix (Fig. This Single Photon Emission Computed Tomography 157 is called simple backprojection. When many projections are backprojected, a ﬁnal image is produced as shown in Figure 12. Backprojection can be better explained in terms of data acquisition in the computer matrix. Suppose the data are collected in a 4 × 4 acquisition matrix, as shown in Figure 12. In this matrix, each row represents a slice, projection, or proﬁle of a certain thickness and is backprojected individu- ally. Counts in each pixel are considered to be the sum of all counts along the depth of the view. Similarly, counts from pixels B1,C, and D1 1 are added to each pixel of the second, third, and fourth columns of the reconstruction matrix, respectively. Next, suppose a lateral view (90°) of the same object is taken, and the data are again stored in a 4 × 4 acquisition matrix. The ﬁrst row of pixels (A2,B,C, and D2 2 2) in the 90° acquisition matrix is shown in Figure 12. Counts from pixel A2 are added to each pixel of the ﬁrst row of the same reconstruction matrix, counts from pixel B2 to the second row, counts from pixel C2 to the third row, and so on. If more views are taken at angles between 0° and 90°, or any other angle greater than 90° and stored in 4 × 4 acquisition matrices, then the ﬁrst row data of all these views can be Fig. Each pixel count in a projection represents the sum of all counts along the straight-line path through the depth of the object. An illustration of the backprojection technique using the data from an acquisition matrix into a reconstruction matrix. This type of back- projection results in superimposition of data in each projection, thereby forming the ﬁnal transverse image with areas of increased or decreased activity (Fig. Similarly, backprojecting data from the other three rows of the 4 × 4 matrix of all views, four transverse cross-sectional images (slices) can be produced. Therefore, using 64 × 64 matrices for both acquisition and recon- struction, 64 transverse slices can be generated. From transverse slices, appropriate pixels are sorted out along the horizontal and vertical long axes, and used to form sagittal and coronal images, respectively. It is a common practice to lump several slices together to increase the count density in the individual slices to reduce statistical ﬂuctuations. Single Photon Emission Computed Tomography 159 Filtered Backprojection The simple backprojection has the problem of “star pattern” artifacts (Fig. Because the blurring effect decreases with distance (r) from the object of interest, it can be described by a 1/r function (Fig. It can be considered as a spillover of certain counts from a pixel of interest into neighboring pixels, and the spillover decreases from the nearest pixels to the farthest pixels. This blurring effect is minimized by applying a “ﬁlter” to the acquisition data, and the ﬁltered projections are then backprojected to produce an image that is more representative of the original object. There are in general two methods of ﬁl- tered backprojection: the convolution method in the spatial domain and the Fourier method in the frequency domain, both of which are described below. The Convolution Method The blurring of reconstructed images caused by simple backprojection is eliminated by the convolution method in which a function, termed “kernel,” is convolved with the projection data, and the resultant data are then back- projected. The application of a kernel is a mathematical operation that essentially removes the l/r function by taking some counts from the neigh- boring pixels and putting them back into the central pixel of interest. Math- ematically, a convolved image f′(x, y) can be expressed as N N fx′ y ∑ ∑ ij fxij iy j (12.
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