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Both the silver halide and gelatin in the emulsion Film is used as a detector for measuring personal play an integral part in the photochemical action cheap aygestin 5mg mastercard pregnancy nose. The radiation dose but suffers since it is not tissue equiv- X- or gamma photon ionizes the silver halide (AgBr) alent generic aygestin 5 mg otc 6272 menopause. The bromine ion is absorbed by the gelatin and the silver ion migrates to a sensitive region in the crystal buy discount aygestin 5mg on line menstrual joy. This effect can be used to measure radiation dose (film density Only a small amount of energy is required to ionize being proportional to radiation dose) or form a radio- gas effective aygestin 5 mg women's health center hershey pa. Unlike ‘tissue equivalent’ detectors (see later) AgBr where Q is the number of ion pairs and m is mass of has two K edges that fall within the diagnostic range chamber gas. Film gas atoms and the collection of the induced charge by response (sensitivity) to photon energy decreases at electrodes as shown diagrammatically in Fig. The signal current is extremely small silver halide (Ag(I)Br) and has a density of 1. There is very lit- tle change in signal output for change in applied voltage over this range. The amplitude of the signal depends detector and uses the simple design illustrated in Fig. The region between the plates is filled with air the applied voltage between the plates. Air requires an average energy of 34 eV voltage does, however, influence the speed of ion col- to produce an ion pair so for a 100 keV photon lection. The ion chamber has a very slow response approximately 3000 ions or electrons are formed. Radiation level is measured as a current which is dependent on both source activity or X-ray inten- sity and energy of the radiation. Maximum efficiency is achieved by capturing the majority of emissions in a 4 geometry which has been described in Chapter 1. Charge In order to increase efficiency still further a dense gas amplifier filling is used, either nitrogen, argon or xenon under pressure: ( 10 atmospheres). They are manufactured as a single Geiger channel divided into many hundreds (700–800) of separate individual chambers with electrodes. The xenon gas is under pres- sure to increase density and so efficiency, which is of Proportional the order of 50–60%. Factors which increase current density are: 137Cs • Xenon density is 5 that of air (Table 6. The chamber can be calibrated in either radiation dose ( Gy, mGy) or dose rate ( Gy or mGy min 1). The sensitivity of a survey/monitoring ion chamber is 10 100 1000 related to gas volume or the size of the chamber itself (b) Photon energy (keV) but very small (thimble) ion chambers are valuable Figure 6. The very small current given by the ionization Common isotope gamma energies are marked on the event is amplified electronically to give a useful sig- curve. The tiny signals require good cabling Gas detectors 147 and connectors; cable movement can induce noise signals that spoil measurements. As a consequence this signal is a slowly changing voltage which is propor- tional to activity level. The resulting larger electric field accelerates the electrons in the chamber Air 1. Both A typical large surface area contamination moni- counters use xenon to improve efficiency. The high tor operating at proportional region is xenon filled voltage is between 1000 and 2000 V. Since the sensi- with a 100 cm2 to 200 cm2 surface detector area with tivity varies with applied voltage, proportional a 6 mg cm 2 titanium foil window. Butane offers a cheap high density ered that if the electric field in an ion chamber is gas but requires frequent replenishment. There is no proportionality as all incident its original state, ready for the next event. The operating voltage is much quench ion avalanche so that after each ionization higher (900 to 1200 V) which increases gas amplifica- the ion cascade quickly stops; this improves the long tion considerably. The most common additive is collisions gives a very strong signal for each ionization bromine and these tubes can be operated at a lower event. Their response can be dampened electronically so Central 1 electrode that radiation levels can be measured in Gy h or mGy h 1. Luminescent phos- phors still occupy an essential place in diagnostic Geiger tube imaging. Gamma or X-radiation interacts with the phosphor or scintillator producing a light event whose intensity is proportional to the photon energy deposited. Light production can be instantaneous or delayed and the duration of the light signal can be measured in nano-seconds (10 9s) or tenths of seconds (10 1s). Properties of a good scintillator are: • Transparency to emitted light • Large light output • High photon absorption for gamma and X-rays • Available in large sizes Figure 6. Its name is 0 100 200 300 400 500 given to a wide range of phenomena which result in (b) Photon energy (keV) light being produced after stimulation by either pho- Figure 6. The incident photon energy is deposited in the (b) the energy response curve for a Geiger counter which outer valency orbits which causes electrons to jump peaks over the diagnostic range. NaI, CsI) with impurity If impurity traps are present in the forbidden zone atoms. Examples of doped crystals, commonly used in the electrons can be caught; their fate then depends radiology, would be NaI:Tl, CsI:Na and Gd2O2S:Tb. The term luminescence covers three the doping materials are responsible for trap- major phosphor types that are commonly found in ping centers in the forbidden zone which give the radiology and used for both imaging and radiation phosphor its unique properties (light spectrum and dose measurement such as counters or storage devices. Radiation ejects electrons from the valency band into the con- duction band from where they attempt to return Conduction band again to the valency band but are caught by trap defects in the forbidden zone. They eventually leave these traps falling into the vacant ‘holes’ in the valency band and in so doing they emit light. Light output can continue for some time after stimulation by radiation Trap Forbidden zone since electrons from the traps are periodically excited into the conduction band. The valency band shows the presence of tion band fall into empty traps in the forbidden an electron and the absence (hole). The tors can be improved by impurity activation (dop- time between (c) and (d) determines the period ing). The added impurity probably occupies interstitial of emission (10 4 to many seconds). Thallium is a common impurity Phosphorescent materials are ideal for video monitor added in concentrations of 0. Cesium iodide is also found immediately after photon irradiation; in practice a as a scintillation material in radiology. The common finite dead time (afterglow) does exist but this is very applications for fluorescent detectors (scintillators) short and measured in nano-seconds. Summarizing that are found throughout radiology are: the reactions associated with fluorescence in Fig.
Put your fngers on the back of the neck buy aygestin 5mg on line breast cancer uggs boots, in the midline generic aygestin 5mg without prescription breast cancer 4 stage, and feel for the ligamentum nuchae discount aygestin 5mg overnight delivery breast cancer 6s jordans. When the fngers are run down the midline they reach the spine of the 7th cervical vertebra discount 5 mg aygestin free shipping breast cancer medication. Place a fnger just above the upper border of the manubrium sterni and pass it upwards for about one inch. To mark the trachea, draw two vertical lines parallel to each other, and about 2 cm apart, starting just below the cricoid cartilage and ending at the level of the sternal angle. The trachea ends at this level by dividing into the right and left principal bronchi. The upper end of the right principal bronchus lies, more or less in the midline, at the level of the sternal angle. The bronchus is marked by drawing two lines 1 cm apart, running downwards and to the right, joining these two levels. Before trying to mark this bronchus remember that, as compared to the right bronchus, it is twice as long (5 cm), and is placed more transversely. Its lower end lies over the left third costal cartilage, 4 cm from the median plane. The upper end of the oesophagus lies at the lower border of the cricoid cartilage that can be located as described for the trachea. These lines should be drawn so that at the level of the cricoid cartilage and at the level of the sternal angle, the oesophagus is seen to be in the middle line. To mark the part of the oesophagus that lies in the posterior mediastinum continue the same lines downwards, but with a distinct inclination to the left side. The lowest half inch of the oesophagus marked as described above outlines the abdominal part. The upper end of this artery lies in the neck, 1 cm above the sternal end of the clavicle, 3. The line joining these two points runs downwards behind the upper six costal cartilages and lies about 1. It lies transversely, partly behind the left third costal cartilage and partly behind the sternum. From here draw two vertical parallel lines upwards to the level of the left second intercostal cartilage. This gives us the level at which the pulmonary trunk divides into the right and left pulmonary arteries. The frst point to remember is that this vessel lies entirely in the middle mediastinum. This valve is placed obliquely behind the left half of the body of the sternum at the level of the third intercostal space. From the ends of the line representing the valve draw two parallel lines passing upwards and to the right to reach the sternal angle (right half). Arch of the Aorta the projection of the arch onto the anterior wall of the thorax is shown in 21. The lower end of the arch of the aorta corresponds to the upper end of the ascending aorta described above. In other words, the anterior end of the arch lies behind the right half of the sternal angle. It lies partly behind the left half of the sternal angle and partly behind the second left costal cartilage. Do not forget that the posterior end really lies against the posterior wall of the thorax, at the level of the lower border of the fourth thoracic vertebra. The summit of the arch reaches up to the level of the middle of the manubrium sterni. When viewed from the front the arch looks much smaller than it actually is because of foreshortening. To mark the convex upper border of the arch begin, the line at the right end of the sternal angle and carry it upwards and to the left with a curve that reaches the middle of the manubrium sterni. From there, continue the convexity downwards and to the left to end over the second left costal cartilage near the sternal margin. You can draw the lower border in the form of a sharply convex short line as shown in 21. The upper end of the descending thoracic aorta corresponds to the lower end of the arch of the aorta. Its projection onto the anterior wall of the thorax lies over the left part of the sternal angle and the adjoining part of the second left costal cartilage. In other words, the upper end of the descending aorta lies to the left of the midline. The lower end has to be marked at the level of the lower border of the twelfth vertebra. As the vessel descends it gradually passes from the left side to a median position. These are the brachiocephalic artery, the left common carotid artery and the left subclavian artery. Therefore, to mark any of these arteries frst mark the upper border of the arch of the aorta as described above. Its origin from the arch of the aorta lies just to the left of the centre of the manubrium (i. From here it passes upwards and to the left to reach the left sternoclavicular joint. To mark the artery join the two levels by two parallel line about one-fourth inch (8 mm) apart. The origin of this artery from the arch of the aorta is to the left of that of the left common carotid i. The artery is marked by two parallel, vertical, lines that extend to the left sternoclavicular joint. This vessel lies partly in the superior mediastinum and partly in the middle mediastinum. Its surface projection is, therefore, partly above the level of the sternal angle and partly below this level. Its upper end (beginning) lies over the lower border of the frst right costal cartilage. Its lower end (termination) is at the level of the upper border of the third right costal cartilage. The lower end (termination) of this vein corresponds to the upper end of the superior vena cava (and lies over the lower border of the frst right costal cartilage).
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So increasing the resolution of is increased although it is not a limiting factor even in this examination since the intensifying screens Table 8 buy 5mg aygestin fast delivery womens health rights. In all cases the light output varies according to X-ray intensity and energy so the continuous X-ray spec- trum gives a range of light intensities discount 5 mg aygestin mastercard premier women's health yakima. Screen thickness (from 100 • Intensifying screens in film cassettes to 500 m) is normally quoted as a weight per unit Image intensifier input and output screens area: 100 to 165 mg cm 2 is a typical range cheap 5mg aygestin amex women's health clinic ne calgary. Sensitivity • • Large single crystal detectors for nuclear medicine increases with thickness due to improved absorption gamma cameras but resolution becomes poorer 5 mg aygestin menopause weight gain. The increased sensitivity achieved by using X- or gamma radiation directly into light photons, but intensifying screens decreases patient radiation dose the image plate requires a secondary energy source by a factor of 15 to 20 and the consequent shorter (infrared laser) in order to release stored energy in exposure times reduce movement unsharpness. Image intensifier tubes use sodium doped increases it penetrates further into the phosphor cesium iodide (CsI:Na), since this material has a good causing diffusion of the deeper light event so there is absorption for X-ray photons and its needle-like a significant geometrical broadening when it reaches crystal structure reduces light scatter which maintains the film emulsion at the phosphor surface. Image plates use complex barium fluoro- sequence conventional film screens have a typical resolution of 5 to 8 Lp mm 1. The television or video information using thermoluminescence principles; display is an analog image but, unlike film, breaks up their light emission occurs at depth within the phos- image information into a sequence of scan lines which phor so degrading image resolution which is typically degrade the original X-ray image data, particularly 5Lpmm 1. For this reason the beam enters the Time for one scan line film back so photon interaction occurs near the film Peak white 1 V emulsion. Image detector surface 195 synchronization pulses which indicate the ‘end-of- numbers (up to 2000 to 3000 in some high definition line’. The time per scan line will differ according to displays) require a much higher frame rate in order the video standard. The scanning pattern is identical between camera and display maintaining overall synchronization. Original radiology requirement for high speed electronics was reduced by display systems used domestic television standards employing a method of scan-line interlacing. Half the but most recent video displays now utilize high defi- image was transmitted at a time as alternate fields (odd nition line standards of 1024, 1249, and 2048 lines then even-line numbers); combining each field gave a using a non-interlaced format. Since 25 or 30 frames s 1 (fps) are adequate, it is only necessary to transmit this rate so the complete Video bandwidth can be calculated from the for- line count (525 or 625) is transmitted in two halves, mula: r s f where r equals the resolution odd lines then even lines, as shown in Fig. The along the line (normally symmetrical with the line interlacing patterns shown in Fig. Frequency restrictions in domestic television are not a serious problem in radio- 500 512 30 7. The line scanning for a video system (as transmitted or using a closed cir- cuit) is synchronized between camera and display with a common time base, shown in Fig. For moving pictures it is necessary to display a frame rate which takes advan- tage of vision persistence and high enough to prevent flicker. For historical reasons the frame rate is dictated by (a) Flicker frequency (Hz) the mains line frequency; 525 lines uses a frame rate Figure 8. Analog image Resolution (Lp mm 1) Film Chest (35 43cm) 5 Mammography (24 18cm) 20 Video ( scan lines ) 1024 3. Image quality should be able to reproduce faithfully the machine’s capabili- h ties, i. An image system which is unable to record all the X-ray image information will miss important diagnostic detail; conversely, an image that exceeds the performance figures of the machine will only serve to emphasize noise. Image spatial resolution in the radiographic image is influenced by two fac- These display systems use 70 to 100 frames per tors which degrade resolution giving overall ‘image second eliminating flicker. The ability to displays can use 3000 scan lines in order to give film- distinguish a step change in image density depends like image quality. A good chest radiograph can achieve Although the intensity change across the bound- 5Lpmm 1 and a detail screen about 8 Lp mm 1. High resolu- sity change in the bottom step becomes less visible as tion, progressive scan (non-interlaced) 2000 to 3000 distance d increases although the height h remains the scan line monitors can achieve in excess of 5 Lp mm 1 same. Objects having a gradual change must be larger but film-screen is still able to offer the best image in order to be visible. The central area, called the umbra, has this shadow Magnification also leads to image distortion since penumbra whose size is determined by geometrical anatomy or pathology further away from the detec- factors; this is similar to a light penumbra described tor is magnified compared to the same size objects in Chapter 2. However, intensifying phosphor screens reduce this figure to 2 to 5 Lp mm 1 for conventional 0. The difference between intensities (I1 and I2) is given and film contrast are relative differences; if the above by an absolute difference (subject and visual contrast). Since Ia x I0 x e then e I0 Ia Taking common logs: I0 m x log log(e a ) Ia log max 0. In detail these are: intensity profile taken through two densities on the film, D1 and D2. The profile is a step change complete • Tissue thickness x (in mm or cm) 1 3 with image noise. The densities are measured as the • Tissue density (kg L or kg m ) mean level of the noise variation. As X-ray energy (keV) increases subject contrast becomes more This depends on image viewing conditions and cov- dependent on electron density as the probability of ers all external factors: Compton reactions increases. The noise component small) in order to achieve good low contrast record- of the signal is the standard deviation ( ) of the sig- ing and Fig. The best solution, however, is to decrease the ground intensity (as before), measured by taking a noise itself. Since this depends on photon density quantum noise is inversely propor- 0 (d) tion to patient dose. This stage in image formation and loss 3 of photon density is called the quantum sink. A typical radiographic density would be 1 105 a larger lesion is more visible, (d) noise reduction in photons mm 2. The performance of intensi- When a screen-film is exposed to a uniform X-ray fier screens and film is given in Table 8. The relative exposure the film density, on processing, shows noise figures and sensitivity in terms of dose are given. The film latitude must match these dynamic the influence of scatter on contrast is simplistically ranges to capture the entire contrast range. The dynamic range of the signal itself is the ratio of X-ray intensity with no attenuation to the scatter component S degrades maximum subject X-ray intensity at maximum tissue attenuation. If the values for D1, D2, and S are 12, 3, and 2, respectively, then for contrast without scatter, C: 8. Scatter Since (D S) (D S) D D then is significantly reduced by placing a grid between the 2 1 2 1 patient and the film cassette or imaging surface D (image intensifier). Common focal distances for these grids are 80, 100, 140, and 180 cm for conventional radiology and scatter to primary ratio is plotted against contrast 60 cm for mammography. Parallel grids have their lead strips of Compton scatter is highest at low photon energies arranged in a parallel fashion (they are not focused). Metals Various factors also reduce the effect of scatter on the used in the construction of grids are lead (Z 82), image.
Latent tetany can be elucidated in the absence of renal failure or increased tissue by tapping on the facial nerve (Chvostek’s sign) or leav- breakdown generic aygestin 5mg without a prescription menstrual 2 weeks early, virtually diagnostic of either postsurgi- ing a sphygmomanometer in?ated to above the systolic cal or idiopathic hypoparathyroidism buy aygestin 5 mg fast delivery women's health green coffee. The examina- ism is a rare condition that may be isolated or associ- tion should look for signs of chronic hypocalcemia such ated with familial polyglandular endocrinopathy as hypertension purchase 5mg aygestin free shipping menstruation gas pain, dystonia cheap 5mg aygestin visa women's health clinic lismore, ataxia, dementia, malnutri- type 2 (mucocutaneous candidiasis, Addison’s dis- tion, dry skin, dermatitis, sparse and brittle hair, cata- ease, or hypoparathyroidism). Hypoalbuminemia is associated with lower serum for thyroid or parathyroid diseases, and rarely radia- calcium concentrations but normal ionized calcium tion therapy, can result in transient or sometimes levels. In patients who are critically ill, the differential diagno- Differential diagnoses that should be considered sis of hypocalcemia narrows. Acute hyperphosphatemia include malabsorption states (sprue, short bowel, (caused by acute renal failure, rhabdomyolysis, or tumor regional enteritis), hepatobiliary disease, anticonvulsant lysis, for example) causes acute hypocalcemia directly. Pancreatitis that is suf?ciently severe to cause hypocal- Bisphosphonates can induce hypocalcemia if vitamin cemia (by forming soaps in the pancreatic bed) is usually D stores are low. Treatment includes adequate replacement of calcium, calcium binding to albumin in the blood, reduces ion- magnesium, and vitamin D. Hypomagnese- placement with calcitriol or a similar metabolite is mia is most commonly found in patients with a history necessary. Vitamin D de?ciency syndromes can be of heavy alcohol abuse or malabsorption or in those re- treated with high-dose vitamin D (such as 50,000 U ceiving parenteral nutrition. Consequences and management of hyperphosphatemia in calcium regulation and human disease. Hypercalcemia is frequently encountered by primary also induce hypercalcemia, often in association with an care physicians. Levels >14 mg/dl are considered to be a hypercalce- or if there is excessive action of the 1-alpha-hydroxylase mic crisis and can be lethal. Patients with more severe hyperactive in patients with granulomatous disease such hypercalcemia can present with nonspeci?c symptoms as sarcoidosis and responds well to treatment with gluco- that include nausea, anorexia, constipation, abdominal corticoids while the underlying disease is being treated. Signs Consumption of large amounts of calcium or vitamin A of hypercalcemia include dysrhythmias, hypertension, can lead to hypercalcemia, but it is rare. Primary hyperparathyroidism has a relatively benign not always necessary and can lead to hypokalemia and course. In the United States, pamidronate important long-term consequences that drive early in- and zoledronate are bisphosphonates licensed for use tervention. Hypocalcemia occurs in up to 50% of patients ?ciency, the Z-score on bone densitometry is 2, or treated with bisphosphonates for hypercalcemia of urinary calcium excretion is particularly high. A preop- malignancy, although symptomatic hypocalcemia is erative parathyroid sestamibi scan can assist the endo- rare. Calcitonin is characterized by good tolerability crine surgeon and limit the extent of surgery. However, a major advantage of calcitonin is the be con?dent of the procedure’s success before surgical acute onset of the hypocalcemic effect (reduction of closure. Medical management of primary hyperpara- 1–2 mg/dl within 6 hours), which contrasts with the thyroidism with calcimimetics is currently limited to delayed (approximately 2–4 days) but more pro- clinical trials. However, data are limited, and hyperparathyroidism and can be managed surgically further trials are necessary. Evaluation and treatment of primary hyperparathy- and low urinary calcium excretion. Diagnosis and management of asymptomatic primary hyperparathyroidism: consensus development conference statement. Hypercalcemia of malignancy is usually symptomatic Ann Intern Med 1991;114:593–597. Current management strategies by releasing parathyroid hormone–related protein for hypercalcemia. Palliat Med Bone destruction by metastatic disease or myeloma can 2004;18(5):418–431. The physician must be aware of the diagnos- have Hashimoto’s thyroiditis and no circulating antibodies. Abnormal test Positive antibodies also are found in portions of the gen- results must be interpreted with good clinical judgment. Normal possible to distinguish hyperthyroid from euthyroid pa- percentage uptake varies widely. Can provide information about gland/lobe con- soon be obsolete as new immunoassays for free thyroxine tour. Thyroid function tests: guidelines for inter- 4 pretation in common clinical disorders. Primary g/kg (75–112 g/day in women and 125–200 g/day hypothyroidism refers to intrinsic thyroid failure and in men). A lower dosage should be initiated in the el- accounts for 99% of cases; secondary hypothyroidism derly and titrated. Patients who are obese require refers to hypothyroidism that results from pituitary doses that are approximately 20% higher. The clinical picture of hypothy- thyroxine is requested by some patients but is not roidism is now a good deal milder because thyrotropin supported by the balance of clinical trial data. The most common tuted, 25 g of levothyroxine can be replaced with signs in patients with moderate to severe hypothyroidism 5 g of liothyronine. Desiccated thyroid, liothyronine include bradycardia, delayed ankle re?exes, periorbital alone, and other thyroid preparations are not recom- puf?ness, and coarse hair. Testing for the presence of thyroid peroxidase among older women and is generally permanent. Both iodine de?ciency and excess can cause opment of more severe hypothyroidism, or levothyrox- hypothyroidism. It is the most common Hypothyroidism can be transient when related to cause of hypothyroidism worldwide but is uncommon thyroiditis. In?ammation of the thyroid gland can be in the United States, where iodine is added to salt. Hypothyroidism occurring Acute administration of iodine suppresses thyroxine postpartum is one of the most common presentations (T4) synthesis; however, patients recover their thyroid of thyroiditis. Transient hypothyroidism lasts as long as function after just a few days of treatment. Other drugs 6 months, but the hypothyroidism will have resolved in that cause hypothyroidism include antithyroid medica- a signi?cant majority of patients within 3 months. N Engl J Med maternal euthyroidism for normal fetal cognitive 2001;345(4):260–265. J Clin Endocrinol Metab 2005;90(8): proximately 30% as soon as pregnancy is con?rmed. Management of subclinical itored and the levothyroxine dosage should be ad- hypothyroidism. Hyperthyroidism can also be tissues, although the clinical importance of this func- caused by overreplacement with exogenous thyroid hor- tion is uncertain. In particular, the thyroid function is suggested for approximately every 6 presentation in older patients can be highly variable. Many Characteristic symptoms include anxiety, tremor, palpita- patients can ultimately be controlled at a low dosage.