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Furthermore cialis jelly 20 mg fast delivery, Aristotle says explicitly that the explanation offered for these ‘extravagant’ cases of foresight is built on the assumption that they are not due to coincidence (e« mŸ ˆp¼ sumptÛmatov g©netai t¼ proorŽn) purchase on line cialis jelly. Thus he is offering an alternative explanation for cases of foresight which earlier on he attributed to coincidence (463 b 1–11) – and this was apparently also what Democritus was doing purchase generic cialis jelly from india. The experiences mentioned here are clearly derived from sources outside the dreamer’s body buy cialis jelly 20 mg on line, which emit ‘movements’ that, after travelling over a great distance, reach the soul in sleep; and they can do so more easily at night because, Aristotle says, there is less wind 53 See van der Eijk (1994) 310–12 for a discussion and fuller references. Aristotle does not say to which category the dreams discussed here belong, but it seems that, if the category of ‘coincidence’ (sumptoma¯ ) is eliminated, these dreams stand to the events they predict in a relationship of signs (semeia¯ ), and that both the event and the dream go back to a common cause. It is difficult, however, to see how the experiences described here can be accommodated within Aristotle’s theory of sleep and dreams. They clearly do not fulfil the requirements for dreams as posited in On Dreams; nor do they seem to belong to the category of borderline experiences, because, again, Aristotle stipulates that they appear to us stronger than in the waking state. Unless we were to assume that Aristotle is contradicting himself, we might prefer to accept that in addition to dreams and to the borderline experiences of hearing faint sounds and suchlike, he recognises yet another kind of experience during sleep and that, by calling these experiences en- hupnia, he uses the term in a less specific, more general sense than the strict sense in which it was used in On Dreams. After all, as I have said, the word enhupnion basically means ‘something in sleep’, and this could be used both at a more general and at a more specific level. But in that case, very little is left of Aristotle’s initial, a priori assumption that sleep is an incapacitation of the sensitive part of the soul, for it turns out that we are perfectly well capable of perceiving these movements while asleep, provided that the at- mospheric conditions are favourable. Nor is it open here to Aristotle to say that these movements originating from remote places such as the Pillars of Heracles are perceived by us not ‘in so far as’ we are asleep but in so far as we are, in a certain way, already awake: in fact, Aristotle explicitly says that we receive these stimuli ‘because’ we are asleep – indeed, they ‘cause perception because of sleep’ (a­sqhsin poioÓsin di‡ t¼n Ìpnon), which seems in blatant contradiction to everything he has said in On Sleep. A different approach to this problem is to seek an explanation for these apparent inconsistencies in what Charles Kahn has called ‘the progressive nature of the exposition’ in Aristotle’s argument. Instead, he simply goes on, eager to explain as much as he can and carried away by the sub- tlety and explanatory power of his theories, but without bothering to tell us how these explanations fit in with what he has said earlier on. Aristotle on sleep and dreams 203 an argumentative, ‘dialectic’ or perhaps even didactic strategy (we should not forget that Aristotle’s extant works derive from the teaching practice, and that they are very likely to have been supplemented by additional oral elucidation). However this may be, it is undeniable that Aristotle in his works on sleep and dreams, as in his biological works at large, sometimes shows himself an improviser of ad hoc explanations, constantly prepared to adapt his theories to what the phenomena suggest. This inevitably means a lower degree of systematicity than we would perhaps regard as desirable; on the other hand, the elasticity of his explanations, and his readiness to accommodate new empirical observations, are things for which he is to be commended. Lack of systematicity is, to a varying extent, characteristic of many Aris- totelian works and can also be observed in other parts of the Parva naturalia, both within and between the individual treatises that make up the series. But it seems to obtain particularly to On Divination in Sleep,55 which is in general a less technical treatise whose degree of accuracy, both in scien- tific terminology56 and in the description of psycho-physiological details, is rather low in comparison with the other two works. Aristotle approaches the problem of divination in sleep from different perspectives, but he offers neither a definition nor a comprehensive explanatory account. The text has a strongly polemical tone and is for a substantial part devoted to an assessment of current views on the subject, such as the view (referred to and criticised three times) that dreams are sent by the gods, or the view held by the ‘distinguished doctors’, or the theory of Democritus. Yet not too much weight should be attached to these cross-references, as they may easily have been added at a later, editorial stage;besides,theprefacetoOnSleepandWakingpresentsaprogrammeofquestionsthatissomewhat different from what is actually being offered in what follows, and this also applies to On Dreams. Thus the beginning of On Sleep and Waking announces a discussion of the question ‘why people who sleep sometimes dream and sometimes do not dream, or, alternatively, if they always dream, why they cannot always remember their dreams’ (453 b 18–20); but these questions can hardly be regarded as central to On Dreams, where they are addressed only in passing (in 461 a 13) and incompletely (in 462 a 31–b 11, a passage that itself, too, shows signs of a hastily added appendix). Such discrepancies between programme and execution need not, however, be due to later editorial additions, for it is, again, not uncharacteristic of Aristotle’s works for there to be discrepancies between programme and execution. As his discussion shows, and in particular the passage from 463 b 12–18 quoted above, dreams do not have any cognitive or moral significance and do not contribute in any way to the full realisation of human virtues. True, Aristotle concedes that in some cases foresight in sleep is possible, but this is not to be taken in the sense of a special kind of knowledge which some people possess, but rather in the straightforward sense of ‘foreseeing’, in a somewhat accidental and uncontrollable manner, what later actually happens. He does not assign a final cause to dreaming, and the answer to the question of the purpose of dreams is only given in a negative way. In the passage 463 b 14 discussed above, Aristotle says that dreams ‘do not exist for this purpose’, to serve as a kind of medium for divine messages. This lack of a teleological explanation is not something to be surprised at, for as Aristotle himself says, one should not ask for a final cause with everything, for some things simply exist or occur as a result of other things or occurrences. Foresight in sleep is not an intellectual or cognitive virtue in the sense of the Aristotelian notion of excellence (arete¯ ); on the contrary, it occurs with people whose intellectual powers are, for some reason, weakened or inactive. Prophecy in sleep is a matter of luck and belongs to the domain of chance: it escapes human control, and its correctness can only be established afterwards, when the event that was foreseen has actually taken place. Mantic knowledge is not knowledge in the strict sense (for many dreams do not come true, 463 b 22–31), and the insights gained by it, if correct, are at best ‘accidental insights’, which only concern the ‘that’, not the ‘because’: they only point to the existence or occurrence of something without providing an explanation for this. This low estimation provides an additional reason why Aristotle shows so little interest in the contents and the meaning of dreams, which was one of the questions with which this investigation started. It will have become clear that the ‘omissions’ in Aristotle’s discussion of dreams that I mentioned at 57 Part. Aristotle on sleep and dreams 205 the beginning can better be understood both in the light of the framework of the study of nature in which his discussion takes place and in the light of his overall attitude towards the phenomenon in the wider context of his psychology and ethical theory. From this point of view, we can arrive at a more appropriate assessment of Aristotle’s achievement in the study of sleep and dreams. The strength of Aristotle’s treatment lies, in my view, in his highly intelligent and systematic approach, as it is reflected in the shrewd and original questions he asks. His use of empirical material does not, to be sure, always concord with all criteria that we, from a modern point of view, might think desirable for a truly scientific investigation; and his optimistic tone throughout both treatises, suggesting that everything is clear and only waiting to be explained by the master, does not quite do justice to his struggle with the perplexing phenomenon of prophecy in sleep – which he, not surprisingly, is unable to explain satisfactorily. Yet when measuring Aristotle’s achievement in comparison with what was known and believed in his own time, we have good reasons to be impressed. His works on sleep and dreams are without any doubt the most intelligent extant treatment of the subject in classical literature. There also seems to be a general agreement as to the basic consistency of Aristotle’s psychological theory, or at least a tendency to explain apparent contradictions between On the Soul and the Parva naturalia on the one hand, and statements related to the soul in the zoological writings on the other (or between On the Soul and the Parva naturalia, or between different sections of the Parva naturalia) as the result of differences of method, approach, or argumentative strategy of particular treatises or contexts rather than in terms of a development in Aristotle’s psychological ideas. The compatibility of ‘instrumentalism’ and ‘hylomorphism’ was stressed by Kahn (1966); Lefevre (` 1972) and (1978); and for the Parva naturalia by Wiesner (1978); and Wijsenbeek-Wijler (1976). See also 206 Aristotle on the matter of mind 207 This consensus might easily give rise to the view that there is no such thing as an Aristotelian ‘psychology’, or at least that psychology more or less coincides with, or forms part of, biology in that it represents an investigation of animals (and plants) qua living beings, that is, ensouled natural things. Although this view is, in my opinion, not entirely correct (see below), it is in general accordance with Aristotle’s belief that the study of soul ‘contributes greatly’ to the study of nature,3 his definition of soul as ‘the form of the body’4 and his programmatic statement that all psychic ‘affections’ (paqžmata) are ‘forms embedded in matter’ (l»goi ›nuloi). The fact that in On the Soul itself we hear relatively little of these bodily aspects6 might then be explained as a result of a deliberate distribution and arrangement of information over On the soul and the Parva naturalia, which should be seen as complementary parts of a continuous psycho-physiological account which is in its turn complementary to the zoological works. Thus the present chapter will deal with Aristotle’s views on the bodily aspects of think- ing, and it will attempt to show that although thinking, according to Aristotle, is perhaps itself a non-physical process, bodily factors have a much more significant part to play in it than has hitherto been recognised. In their turn, students of Aristotle’s zoological writings might feel an in- creasing need to relate Aristotle’s views on bodily parts and structures of organisms explicitly to the psychic functions they are supposed to serve, Hardie (1964); Tracy (1969) and (1983); Verbeke (1978); Hartman (1977); Modrak (1987). This is not to say that developmental approaches to Aristotle’s psychology have entirely disappeared; on certain specific topics, such as the various discussions in On the Soul and the Parva naturalia of the ‘common sense’ and its physiological aspects, there is still disagreement about how to account for the discrepancies; a developmental explanation is offered by Welsch (1987), a very important book which seems to have gone virtually unnoticed by Anglo-American scholarship on Aristotle’s psychology, and by Block (1988). For, as Aristotle himself indicates, a purely formal description of psychic powers and pro- cesses is insufficient for at least two reasons. First, as he repeatedly stresses (apparently in polemics against the Pythagoreans), the connection of a cer- tain psychic function with a certain bodily structure (an organ such as the eye, a process such as heating) is by no means coincidental; on the contrary, the bodily basis should have a certain nature or be in a certain condition in order to enable the exercise of a certain psychic power (e. These variations may exist, or occur, among different species, but also among in- dividual members of one species, or among types of individuals within one species, or even within one individual organism at different moments or states (e. As this chap- ter will try to show, variations in intellectual capacities and performances among different kinds of animals, among different members of one kind or even within one individual on different occasions are explained by Aristotle with a reference to bodily factors. Are the variations to be explained mechanically or teleologically, and are defects compensated for by other skills? In spite of this pronouncedly biological context, however, there are indi- cations that the study of the soul has, for Aristotle, a special status and is 8 See Part. Aristotle on the matter of mind 209 not completely reducible to the study of nature. His consideration of the – perhaps no more than potential – existence of ‘affections that are peculiar to the soul’ (­dia t¦v yuc¦v) in De an. Likewise unclear is the status of the Parva naturalia, which seem to oc- cupy a kind of middle position between On the Soul and the zoological works and which, as a result, have traditionally, although rather unfortu- nately, been divided into a ‘psychological’ and a ‘biological’ section. Hence it would perhaps be more appropriate to say that for Aristotle psychology and biology, as far as their subject matter is concerned, overlap 11 De an. On the method and scope of the Parva naturalia see van der Eijk (1994) 68–72; for a different view see G. Ross (1906) 1: ‘They [the Parva naturalia] are essays on psychological subjects of very various classes, and there is so much detail in the treatment that, if incorporated in the De Anima, they would have detracted considerably from the unity and the plan of that work. Consequent on the separateness of the subjects in the Parva Naturalia, the method of treatment is much more inductive than in the De Anima. There, on the whole, the author is working outwards from the general definition of soul to the various types and determinations of psychic existence, while here, not being hampered by a general plan which compels him to move continually from the universal to the particular, he takes up the different types of animate activity with an independence and objectivity which was impossible in his central work. In spite of Aristotle’s own characterisation of the scope of the Parva naturalia in the beginning of On Sense Perception, it is not easy to characterise the difference with regard to On the Soul in such a way as to account for the distribution of information over the various treatises.

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Ectopic foci are areas within the conduction system that may buy generic cialis jelly 20mg line, in the diseased state order cialis jelly 20mg without a prescription, develop high rates of intrinsic activity and function as pacemakers generic cialis jelly 20 mg amex. Triggered automaticity results from delayed after-polarizations that reach threshold and are capable of initiating an impulse purchase cialis jelly us. Therapy aims to restore normal pacemaker activity and modify impaired conduction that leads to arrhythmias. Therapeutic effects are achieved by sodium- or calcium-channel blockade, prolongation of effective refractory period, or blockade of sympathetic effects on the heart. Many antiarrhythmic drugs affect depolarized tissue to a greater extent than they affect normally polarized tissue. Class I drugs block fast Na+ channels, thereby reducing the rate of phase 0 depola- rization, prolonging the effective refractory period, increasing the threshold of excitability, and reducing phase 4 depolarization. Quinidine (Quinidex, Duraquin, Cardioquin) (1) Effects and pharmacologic properties (a) At therapeutic levels, direct electrophysiologic effects predominate, including depression of the pacemaker rate and depressed conduction and excitability, pro- longation of Q-T interval, and heart block. Quinidine syncope (dizziness and fainting) may occur as a result of ventricular tachycardia; this condition is associ- ated with a prolonged Q-T interval. Disopyramide (Norpace) (1) Disopyramide has action similar to that of quinidine, but has the longest T1=2 of its class. Lidocaine (Xylocaine) (1) Lidocaine acts exclusively on the sodium channel (both activated and inactivated), and it is highly selective for damaged tissues. Mexiletine (Mexitil) (1) Mexiletine is an agent similar in action to lidocaine, but can be administered orally. Flecainide (Tambocor) and encainide (Enkaid) (1) Flecainide is orally active; it is used for ventricular tachyarrhythmias and maintenance of sinus rhythm in patients with paroxysmal atrial fibrillation and/or atrial flutter. Propafenone (Rythmol) (1) Propafenone has a spectrum of action similar to that of quinidine. Propranolol (Inderal, generic), a nonselective b-adrenoceptor antagonist, and the more selective b1-adrenoceptor antagonists acebutolol (Sectral) and esmolol (Brevibloc) are used to treat ventricular arrhythmias. Esmolol is ultrashort acting, is administered by infusion, and is used to titrate block during surgery. They also are used for a variety of other arrhythmias, including atrial flutter and atrial fibrillation. These drugs act by interfering with outward K currents or + slow inward Na currents. It increases refractoriness, and it also depresses sinus node automaticity and slows conduction. Although electrophysiologic effects may be seen within hours after parenteral administration, effects on abnormal rhythms may not be seen for several days. The antiarrhythmic effects may last for weeks or months after the drug is discontinued. Amiodarone is used for treatment of refractory life-threatening ventricular arrhythmias in preference to lidocaine; additional uses include the treatment of atrial and/or ventricular arrhythmias including conversion of atrial fibrillation and the suppression of arrhythmias in patients with implanted defibrillators; it also possesses antianginal and vasodilatory effects. Serious noncardiac adverse effects include pulmonary fi- brosis and interstitial pneumonitis. Other adverse effects include photosensitivity, ‘‘gray man syndrome,’’ corneal microdeposits, and thyroid disorders (due to iodine in the drug preparation). Solatol prolongs the cardiac action potential, increases the duration of the refractory period, and has nonselective b-adrenoceptor antagonist activity. Uses include treatment of atrial arrhythmias or life-threatening ventricular arrhythmias, and treatment of sustained ventricular tachycardia. Its adverse effects include significant proarrhythmic actions, dyspnea, and dizziness. Dofetilide is approved for the conversion and maintenance of normal sinus rhythm in atrial fibrillation or atrial flutter. Dofetilide is a potent inhibitor of K+-channels and has no effect on conduction velocity. Bretylium inhibits the neuronal release of catecholamines, and it also has some direct anti- arrhythmic action. This drug is used intravenously for severe refractory ventricular tachyarrhythmias and also for prophylaxis and treatment of ventricular fibrillation. These drugs prolong nodal conduction and effective refractory period and have predomi- nate actions in nodal tissues. Verapamil is a phenylalkylamine that blocks both activated and inactivated slow calcium channels. Although verapamil is excreted primarily by the kidney, dose reduction is necessary in the presence of hepatic disease and in the elderly. Bioavailability following oral administration is about 20%; much lower doses are required when administered intravenously. Verapamil is useful in reentrant supraventricular tachycardia, and it can also reduce ven- tricular rate in atrial flutter and fibrillation. Verapamil can pre- cipitate sinus arrest in diseased patients, and it causes peripheral vasodilation. The adverse cardiac effects of verapamil, including sinus bradycardia, transient asystole, and other arrthythmias, may be exacerbated in individuals taking b-adrenoceptor antagonists; this can be reversed by atropine, b-adrenoceptor agonists, or calcium. Verapamil should not be used in patients with abnormal conduction circuits as in Wolff-Parkinson-White syndrome. This hyper- polarizes cardiac cells and decreases the calcium-dependent portion of the action potential. Adenosine is the drug of choice for the treatment of paroxysmal supraventricular tachycar- dia, including those associated with Wolff-Parkinson-White syndrome. Adverse effects are relatively minor, including flushing, dizziness, and headache. Atropine produces adverse effects that include dry mouth, mydriasis, and cycloplegia; it may induce arrhythmias. Isoproterenol stimulates b-adrenoceptors and increases heart rate and contractility. Isoproterenol may cause tachycardia, anginal attacks, headaches, dizziness, flushing, and tremors. The goal of therapy with antianginal agents is to restore the balance between oxygen supply and demand in the ischemic region of the myocardium. Classic angina occurs when oxygen demand exceeds oxy- gen supply, usually because of diminished coronary flow. Vasospastic angina results from reversible coro- nary vasospasm that decreases oxygen supply and occurs at rest. Some individuals have mixed angina, in which both exercise-induced and resting attacks may occur. Nitrates and nitrites are polyol esters of nitric acid and nitrous acid, respectively, and relax vascular smooth muscle. Nitrates and nitrites activate guanylate cyclase and increase cyclic guanine nucleotides. Peripheral venodilation decreases cardiac preload and myo- cardial wall tension; arterial dilation reduces afterload. Redistribution of coronary blood flow to ische- mic regions is increased in nitrate-treated patients. Nitrates and nitrites ameliorate the symptoms of classic angina predominantly through the improvement of hemodynamics. Nitrates and nitrites form nitrosothiol in smooth muscle by reaction with glutathione. These drugs have a large first-pass effect due to the pres- ence of high-capacity organic nitrate reductase in the liver, which inactivates drugs. Nitroglycerin (Cellegesic, Nitrek, others) (1) Nitroglycerin is preferably administered sublingually for rapid delivery and short duration. An unpleasant odor and extensive cutaneous vasodilation render it less desirable than nitroglycerin. Isosorbide dinitrate (Isordil, Sorbitrate, others) (1) Isosorbide dinitrate has active initial metabolites. Timed-release oral preparations are avail- able with durations of action up to 12 hours. Sublingual nitroglycerin is most often used for severe, recurrent Prinzmetal’s angina. Nitrates and nitrites produce vasodilation, which can lead to orthostatic hypotension, reflex tachycardia, throbbing headache (may be dose limiting), blushing, and a burning sensation. Combined therapy with nitrates is often preferred in the treatment of angina pectoris because of the decreased adverse effects of both agents.

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Lesions with low concentrations of p-glycoprotein in the tumours had a slow efflux rate generic 20 mg cialis jelly amex, while the faster efflux rate characterized lesions with high p-glycoprotein buy 20mg cialis jelly otc. T h e authors postulate that these measurements m a y help predict which patients will develop M D R buy 20 mg cialis jelly with amex. C O N C L U S I O N S History repeats itself because no one listens the first time discount 20mg cialis jelly free shipping. T h e trunk is molecular nuclear medicine, regional physiology and regional biochemistry. For the tree to bear fruit, the trunk must be strong and extend into healthy branches. In the old days, w e defined radioisotope scanning as the visualization of previously invisible organs by me a n s of radioactive tracers — an anatomical orientation. Today, nuclear medicine can be defined as topo­ graphic physiological chemistry, resting on an infrastructure of physics, mathematics and communication sciences. Mtg Minneapolis, M N , 1995, Society of Nuclear Medicine, Reston, V A (abstract) (unpublished). I N S T R U M E N T A T I O N A N D D A T A A N A L Y S I S (S e s s i o n 1) Chairperson K. Quantitative emission tomography has been the final goal of much research effort for a number of years in nuclear medicine instrumentation. The detection sensitivity isincreased by the use ofconverging collima­ tors with a fan beam, cone beam or more sophisticated geometry. Transmission measurement for attenuation correction is feasible with rod sources placed at the focal lines of the fan beam collimators. The spatial resolution has increased from 10-15 m m to 3-4 m m fullwidth athalf-maximum inthe last two decades. The true detection sensitivity drastically increases in the 3-D mode by a factor of 5-6, but the scatter fraction also increases by a factor of 3-4. O n the other hand, P E T is suitable for m o r e investigative studies or m o r e detailed diagnosis by virtue of the high image quality, better quanti­ tation and wider variety of available radiopharmaceuticals. Although the P E T system is still expensive, its usefulness in clinical diagnosis has already been recognized and the use of clinical P E T is gradually expanding. T h e imaging properties of S P E C T and P E T have been enhanced by the continuing improvement in imaging devices and rapid progress of computer technology in the last t w o decades. This paper reviews the recent advances in instrumentation for S P E C T and P E T. S P E C T with rotating g a m m a c a m e r a s Currently, the most widely used S P E C T systems involve rotating g a m m a cameras. T h e systems can be used for conventional planar imaging as well as for S P E C T , and do not require a large quantity of funds for a dedicated S P E C T scanner. Progress in the use of the rotating g a m m a camera S P E C T resulted from the dramatic improvement in g a m m a camera performance by the incorporation of microproces­ sors which permit real-time correction of the distortion of the cameras. T h e unifor­ mity, linearity and energy resolution of the cameras w ere greatly improved, which are essential for S P E C T applications. Multi-energy w i n d o w operation m a d e feasible dual isotope studies and the dual or triple energy w i n d o w m e thod for scatter correc­ tion [1]. M o d e m g a m m a cameras have an intrinsic spatial reso­ lution of 3 - 4 m m full width at h a l f -maximum ( F W H M ) , a sensitivity uniformity of less than 3. T h e system resolution of a g a m m a camera equipped with a parallel hole colli­ mator starts from about 5 m m close to the surface of the collimator and degrades with increasing distance f r o m the collimator surface; hence the camera head must be rotated as close as possible to the patient. For torso imaging, most S P E C T sys­ tems can adopt an elliptic rotation of the camera head with respect to the bod y centre. For brain or heart imaging with a L F O V camera, a fan b e a m collimator is use­ ful in improving the utilization of the large detector area. T o increase detection sensitivity, multi-headed S P E C T systems provided with t w o to four camera heads are available (see Fig. A m o n g them, a triangular S P E C T system using three camera heads [2, 3] is attractive because the system can be used for brain imaging with fan b e a m collimators, as well as for bod y imaging with parallel hole collimators (see Fig. Triangular S P E C T systems equipped with fan b e a m collimators have about five times greater sensitivity than a single headed system with a parallel hole collimator. Another merit of triangular S P E C T using fan b e a m collimators is that transmission measurement for attenuation correction can be performed with rod sources placed at the focal lines of the fan b e a m collimators, as s h o w n in Fig. Simultaneous measurement of emission and transmission data is also possible by using one rod source and rotating over 360° [4]. S P E C T with stationary detectors S P E C T systems with stationary cylindrical detectors dedicated for brain studies have been developed. T h e detector consists of a cylindrical array of a n u m b e r of Nal(Tl) crystal rods, and 96 photomultiplier tubes ( P M T s ) are coupled to the outside of the cylinder. T h e detector system is stationary, and a continuously rotating ‘turbo-fan’collimator is provided inside the crystal array. E a c h crystal views an object at various directions along with the rotation of the collimator. Another example is C E R A S P E C T (Digital Scintigraphic) [5], s h o w n in Fig. T h e detector system consists of a single annu­ lar Nal(Tl) crystal (inner diameter 31 cm, height 13 c m and thickness 8 m m ) and a rotating collimator. T h r e e dimensionally converging collimators T h e detection sensitivity of fan b e a m collimators is further improved b y the use of cone b e a m collimators. A typical cone b e a m collimator provides an increase of effi­ ciency of about 2. I m a g e reconstruction with a cone b e a m S P E C T must be handled by a 3 - D reconstruction algorithm. T h e simplest scanning m e t h o d is rotating the camera head in such a w a y that the focal point of the collimator m o v e s along a circular trajectory around the object. T h e single circular orbit, however, can provide a mathematically accurate image only in the vicinity of the plane of the circular orbit, and not in the other part distant fro m the plane. Nevertheless, a relatively simple reconstruction algorithm, the F e l d k a m p algorithm [7], is useful to obtain an approximate image w h e n the angle of the cone b e a m is not so large. T h e algorithm essentially consists of 1-D filtering of observed 2 - D projections along the transaxial direction and 3 - D back projection along the cone b e a m direction. T o acquire sufficient data for accurate 3 - D imaging with the cone b e a m geometry, the scanning trajectory of the focal point must have at least one point of intersection for any plane passing through the reconstructed region of interest [8]. Several focal point trajectories have been suggested which s e e m to be realistic. These are the circle and line orbit, dual orthogonal circular orbit, helical orbit, etc. In using cone b e a m collimators, the activity distribution must be inside the sensitive v o l u m e of the collimator. For easier positioning of an object in the F O V , astigmatic col­ limators [10], as s h o w n in Fig. O n e focal line is parallel to the axis of rotation, while the other is perpendicular. T h e geometry of the astigmatic collimator lies between a fan and a cone b e a m geometry. Recently, a variable focus collimator, the ‘Cardiofocal collimator’(Siemens) [11], has been developed for heart imaging to avoid truncation artefacts (see Fig. T h e focusing of this collimator is strongest at the centre of the collimator and gradually relaxes to nearly parallel hole collimation at the edge of the collimator. S P E C T with pinhole collimators There is an expanding need to localize radiopharmaceuticals in vivo in small laboratory animals such as rats and mice in pre-clinical studies. T h e spatial resolu­ tion achieved with conventional S P E C T imaging with multihole collimators is not adequate for such small animals, and a rotating g a m m a camera equipped with a pin­ hole collimator having an aperture diameter of 1-3 m m can yield significantly better resolution, provided a short imaging distance is used so as to obtain large image magnification. S P E C T i maging of positron emitters It has been well recognized that P E T imaging of 18F-deoxyglucose (18F D G ) is useful for the diagnosis of cardiac, oncological and neurological diseases. Recently, several groups have reported the usefulness of S P E C T imaging of 18F D G with g a m m a camera rotating S P E C T systems using ultrahigh energy collimators designed for 511 keV. For example, with a dual head S P E C T system, a spatial resolution of 17 m m F W H M and a v o lume sensitivity of 2 7 0 (counts/min)/mCi were obtained [13].

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Also known as first meiotic divi- person lifts something, and keeps the intestines and sion and first meiosis. Reed-Sternberg cell A type of cell that is seen recuperate To recover health and strength. If one gets a referral to recurrence The return of a sign, symptom, or ophthalmology, for example, the person is being disease after a remission. The recur in that family, affecting another person or term referral can pertain both to the act of sending persons. For example, a recurrent fever is a fever that has referred pain Pain felt at a site other than where returned after an intermission, a recrudescent fever. For example, the recurrent respiratory papillomatosis See corneal reflex is the blink that occurs upon irritation of the eye. Reflex between laboratories, but is generally in the range sympathetic dystrophy syndrome is associated with of 4. Red cell count can be varying degrees of sweating, warmth and/or cool- expressed in international units as (4. Refractive who has suffered an illness or injury restore lost errors include nearsightedness (myopia), farsight- skills and so regain maximum self-sufficiency. Lenses can be example, rehabilitation work after a stroke may used to control the amount of refraction and correct help the patient walk and speak clearly again. Refsum disease A genetic disorder that affects the metabolism of the fatty acid phytanic acid. For example, a transplanted kid- caused by damage to the cerebellar portion of the ney may be rejected. For example, after an injury, the liver often administered during abdominal surgery to has the capacity to regenerate. A low-salt diet is one type of dietary nancy that facilitates the birth process by causing a regimen. Relaxin also inhibits contractions of the uterus and may play a role in determining the regional lymphadenitis See cat scratch fever. A registry is release, carpal tunnel See carpal tunnel usually organized so that the data in it can be ana- release. For example, analysis of data in a tumor reg- istry maintained at a hospital may show a rise in lung rem In radiation, an international unit of X-ray or cancer among women. These periods occur at intervals of 1 to 2 hours and can vary in regurgitation A backward flowing. A remission can be ate goal is to quickly open blocked arteries and temporary or permanent. Early reperfusion min- imizes the extent of heart muscle damage and pre- remission induction chemotherapy See serves the pumping function of the heart. One of carried out from a great distance using computer the best-known repetitive stress injuries is carpal and robotic technology. For example, supermarket checkers, assembly-line workers, typ- renal cancer is cancer of the kidneys. Common causes of renal artery stenosis include atherosclerosis and thicken- replication A turning back, repetition, duplica- ing of the muscular wall (fibromuscular dysplasia) tion, or reproduction. Reproduction need not be sexual; for example, renal cell carcinoma See cancer, renal cell. This idea has stirred great controversy and has met with almost uniform disapproval. Rendu-Osler-Weber syndrome See hereditary research, controlled A study that compares hemorrhagic telangiectasia. Board certification in all near drowning, heart failure, severe infection, and medical and surgical specialties requires the satis- extreme obesity. In practice, the respiratory rate is usually determined resistance Opposition to something, or the abil- by counting the number of times the chest rises or ity to withstand something. The aim of measuring respiratory forms of the staphylococcus bacterium are resistant rate is to determine whether the respirations are to treatment with antibiotics. Resolution may annual community outbreaks, often lasting 4 to 6 range from low to high. For having a continuous, solid level of antibodies example, when bone is surgically reshaped, it against the virus. Respiratory failure occurs because of the failure of the exchange of oxygen and carbon restless leg syndrome An uncomfortable dioxide in tiny air sacs in the lung (alveoli), failure (creeping, crawling, tingling, pulling, twitching, of the brain centers that control breathing, or fail- tearing, aching, throbbing, prickling, or grabbing) ure of the muscles required to expand the lungs that sensation in the calves that occurs while sitting or can cause respiratory failure. The result is an uncontrollable ical conditions can lead to respiratory failure, urge to relieve the uncomfortable sensation by including asthma, emphysema, chronic obstructive moving the legs. The leg pain typically eases medication, such as cyclosporine, chlorambucil, and with motion of the legs and becomes more notice- cyclophosphamide. A small area called the macula in the retina contains special retinoblastoma A malignant eye tumor usually light-sensitive cells that allow clear perception and seen in children, that arises in cells in the develop- central vision. The retina is filled with tiny blood ing retina that contain cancer-predisposing muta- vessels. The sporadic form of retina has torn, the vitreous liquid can pass through retinoblastoma has later onset and typically leads to the tear and accumulate behind the retina. Retinal vasculitis ranges in sever- often requires removal of the eye (enucleation). Retinal vasculitis by itself is painless, but many of the diseases that cause it can also cause retinoic acid syndrome A disorder due to the painful inflammation elsewhere, such as in the joints. Further definition of fluid around the lungs and heart, and hypoxia (lack the blood vessel condition can be determined with a of oxygen) that develops in some patients receiving special X-ray dye test (angiogram) of the retina. It usually develops within 30 Diseases that cause retinal vasculitis include Behcet’s days of treatment. Steroids and chemotherapy can be syndrome, systemic lupus erythematosus, antiphos- used to treat retinoic acid syndrome. In addition, some retinopathy Any disease of the retina, the light- related diseases require immunosuppression with sensitive membrane at the back of the eye. See retrograde intrarenal surgery A procedure for also dextrocardia; Kartagener syndrome. The approach was to find a gene product and then try to stone can be seen through the scope, manipulated or identify the gene itself. Reye’s syndrome A sudden and sometimes fatal disease of the brain (encephalopathy) that is accom- retropubic prostatectomy Surgical removal of panied by degeneration of the liver. Early diagnosis and control of the increased intracranial pressure can prevent death or brain Rett syndrome A neurological disease that affects damage. Preventing Reye’s syndrome is the reason girls only and is one of the most common causes of why physicians no longer recommend giving chil- mental retardation in females. The hallmark of Rett syndrome Rh factor An antigen found in the red blood cells is the loss of purposeful hand use and its replace- of most people. Other symp- to be Rh positive (Rh+), and those who do not are toms include slowed brain and head growth, Rh negative (Rh-). Rh typing is also important during ity of cases are sporadic and result from a new muta- abortion, miscarriage, pregnancy, and birth, as tion in the girl with Rett syndrome. Organs appear as if in mirror baby that leads to hemolytic disease of the newborn. The patient is felt to muscle is broken down, releasing muscle enzymes have underlying psychological causes for these and electrolytes from inside the muscle cells. Rhabdomyolysis is rel- region, such as chest wall pain, temporomandibular atively uncommon, but it most often occurs as the joint pain, and myofascial pain syndrome pain. Underlying diseases that can also lead to rhabdomyolysis include collagen vascu- rheumatoid arthritis, systemic-onset juvenile lar diseases, such as systemic lupus erythematosus. Treatment includes sur- percent of adults, and a much lower proportion of gery, radiotherapy, chemotherapy, and, most often, a children, who have rheumatoid arthritis. The out- present in patients with other connective-tissue dis- look depends on a number of factors, including the eases, such as systemic lupus erythematosus, and in original location of the tumor.

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