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what does the filament size affect in a radiograph
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radiology exam one
| Question | Answer |
|---|---|
| characterstics of x-rays | high energy, short wavelength, high frequency can ionize matter (along with gamma rays) possess properties of both waves and particles |
| what does the filament size affect in a radiograph | the size of the focal spot on the anode |
| what does the focal spot size on the anode affect in a radiograph? | detail of the radiographic image |
| differentiate simple phase versus high frequency x-ray machines | simple machines produce 120 x-ray pulses/sec high frequency machines put out almost a constant output of x-rays with no wasted time between pulses, but cost more than single-phase machines |
| advantages of using high frequency x-ray machines | can allow using half the amount of x-ray technique (as single phase) can allow for quicker exposures can make radiographing thicker parts possible |
| possible photon interactions in radiography (4) | scattered away from the film absorbed by the patient transmitted through to film scattered toward the film |
| what is the main thing that happens during radiograph processing? | sivler ions are reduced to metallic silver |
| what does mA control? | quantity or amount of radiation which is used in forming the radiographic image |
| what is the effect of increasing mA? | get a darker/blacker image |
| what is kVp? What does it effect in terms of the radiograph? | the measure of the energy/ penetrating power of x-rays affects quality of the radiograph |
| what does increasing kVp result in? | greater penetrating power of the x-rays creates a darker image difference in contrast |
| what is radiographic density? | how dark/black the radiograph appears |
| three ways to make a radiograph darker | increase mAs increase time of exposure increase kVp |
| how is kVp adjusted to increase darkness? | from the 40-99 kVp range, and increase of 10% doubles the darkness at 100+ kVp, 15% increases double the darkness |
| in addition to darkness, what else does kVp affect? | image contrast the amount of scatter radiation |
| what happens when you increase the distance of the x-ray machine to the radiograph? | the radiation intensity is 1/4 the intensity at the original distance (if the distance is doubled) |
| what are the two types of radiographic contrast? | subject contrast: due to differential absorption radiographic contrast |
| differentiate subject contrast and radiographic contrast | subject: difference in x-ray intensity transmitted through one part of the subject compared to that through another part radiographic: visible difference in film blackness between two adjacent areas on the image |
| factors that affect radiographic contrast (5) | subject contrast (i.e. type of tissue) kVp level amount of scatter radiation (+/- collimation) film type (high vs low contrast) flim fog |
| with what areas of the body should a grid be used when radiographing? | thorax abdomen spine, skull, pelvis large extremities |
| recommended kVp range for the thorax | 80-125 |
| recommended kVp range for the abdomen | 65-90 |
| recommended kVp range for spine, skull, pelvis, large extremities | 60-80 |
| recommended kVp range for small extremities | 40-70 |
| recommended kVp range for small birds and reptiles | 40-60 |
| factors that affect radiographic detail (4) | intensifying screen speed focal spot size focal film distance object film distance |
| how does intensifying film speed affect radiographic detail? | faster speed screens have larger crystals, get less detail |
| how does the focal spot size affect radiographic detail? | larger focal spot: less detail |
| how does focal film distance affect radiographic detail? | longer FFD offers better detail |
| recommended focal film distance for mobile equine work | 24-36 inches |
| recommended focal film distance for small animal radiography | 36-40 inches |
| how does object-film distance affect radiographic detail? | farther away the part is from the film, the greater the magnification and unsharpness |
| differentiate a radiograph produced by a low versus high kVp | low: very black and white, short scale of contrast, high contrast image high: grayer image, long scale of contrast, low contrast image |
| define the grid ratio | height of lead strips/ distance between strips |
| how does grid ratio affect efficiency? | higher the grid ratio, the more efficiency or "clean-up" there is of scattered radiation |
| how does grid ratio affect exposure? | the higher the grid ratio, the more exposure needed to obtain a satisfactory amount of film blackening or photons to the imaging panel or plate |
| what grid ratios are recommended for veterinary use? | 8:1 or 10:1 provide good clean up of scattered radiation while still allowing for reasonable technique settings |
| what is grid frequency? | the number of lead strips in the grid per inch |
| what is the recommended grid frequency? | 103 lines/inch recommended for conventional radiography |
| when would you see grid cut-off? | when the grid is upside down, off center, or off level |
| when should a grid be used? | in general, if the part being radiographed is 10cm or larger up to 15cm is okay with good quality digital radiography |
| how can you control scatter radiation when a grid is not available? | collimation of the primary beam kVp kept to a minimum |
| types of radiation collimators | diaphragm, cone, beam limiting device |
| what are the issues involved in using high kVp? | get longer scale/lower contrast radiographs get more scatter radiation more exposure to personnel |
| order of manual processing of radiographs | developer, wash (sometimes), fixer, wash, air dry |
| what is the main function of developer chemicals? what is a second function? | reduce silver ions to metallic silver also softens the emulsion and makes it jelly-like |
| how does temperature affect manual processing? | as temperature increases, processing time decreases |
| factors that can lead to film underdevelopment (4) | developer too old film not developed long enough improper mixing of chemicals developing films before chemicals are at proper temperature |
| what is the role of the fixer chemicals in processing? (3) | neutralize developer clear away unexposed/undeveloped silver halide crystals shrink and harden gelatin (emulsion) |
| for how long should films be fixed? | twice the development time |
| how do unexposed areas of film that still contain halide crystals appear? | on the viewer, the areas have a cloudy or milky appearance in regular room light, they can look pink, green, or purple depending on original color of emulsion |
| how do underfixed films feel? how does this affect processing? | can feel tacky or sticky due to emulsion being soft can cause films to get stuck in the processor |
| what is the role of washing in the development process? | removes fixer chemicals from the film |
| describe the washing process for manual processing | 15-30 min with plenty of fresh water |
| how does inadequate washing affect film appearance? | flims can look smeary on the surface and smell like chemicals films will turn brown, orange, or yellow as the fixer gets oxidized |
| what affects the color a film turns after inadequate washing? | the amount of fixer left on the film the age of the film |
| define a film artifact | anything that decreases the quality of the radiograph can result in difficult evaluation and interpretation |
| causes of film being too dark (6) | double exposure distance too close overexposure (too much kVp/mAs) overdevelopment overmeasurement machine not calibrated properly |
| causes of film being too light (6) | underexposure (low kVp/mAs) underdevelopment x-ray tube failure incorrect film/screen combination machine not calibrated properly grid cut-off |
| reasons for lack of contrast (film too gray) (6) | lack of grid for parts >10cm kVp too high old, outdated film radiation fog (radiation other than desired) light fog lack of collimation |
| describe light fog on a radiograph | appears as undesired density on the radiograph can manifest in a variety of ways can look black or gray depending on how concentrated the light is and how long the film is exposed to it |
| how can you prevent light fog? (4) | darkroom windows and doors should be light tight boxes of film should be stored in light-tight film bin or with lids be careful when turning on lights and opening doors don't take pagers/cell-phones into the dark room |
| how should you use a safelight? | should be the proper one for your film filter should be in good condition; examine for cracks periodically should be at least 40 inches above work surface 15 watt appliance bulb maximum |
| how can you reduce the motion picked up on the radiographic film? | use screens fast enough that excessive exposure times are not required keep exposure times 1/60th of a second or less for thorax and 1/40th or less for abdomen use sedatives for orthopedic exams and uncooperative patients |
| how should thoracic and abdominal radiographs be taken to avoid motion? | take thorax radiographs on full inspiration take abdominal on full expiration try to stop patient from panting (blow on nose during the exposure or hold mouth and nose shut during the exposure) |
| guidelines for screens used during radiographs | use rare-earth screens (not CaWO4) screens >10yrs old may start requiring more exposure look for missing or inactive screen phosphors |
| how do missing/inactive phosphors of a screen appear? | tiny white specks on the radiograph |
| rough handling artifacts (2) | scratches on the film: can be white or black crescent marks: black crescent-shaped marks when film gets bent by fingertips |
| what are screen artifacts? | white artifacts caused by objects on the screens interfere with light from the screen reaching the film can be anything, but hair, bedding, shavings,and dirt are common |
| ways of preventing screen artifacts | darkroom cleanliness clean screens with commercial screen cleaner or mild dishsoap and water commercial screne cleaner also has antistatic properties to help keep static artifacts to a minimum |
| describe D.R. radiography | sometimes called direct digital flat panel or CCD detector used instead of screen/film computer software is applied to x-ray image |
| describe C.R. radiograph technology | image receptor= CR cassette with imaging plate imaging plate records a latent image made by x-rays cassette is put into a reader, IP is scanned with a laser, and digital image is produced image can be viewed on a monitor |
| How does digital radiography affect image quality? | dependent on imaging software and quality of monitors/printers resolution is less with digital digital radiography offers better contrast and increased latitude (range of material thickness that can be imaged) |
| what is radiographic latitude? | the range of material thickness that can be imaged |
| compare the speed of D.R. versus C.R. | D.R. is faster than C.R. and conventional image available in about 4 sec fewer retakes due to technique C.R. maybe faster than conventional (reduces technique) patient still waits while images are processed in the reader |
| in terms of portable work what are the advantages of C.R. versus D.R. | C.R. can be used stall side, just like conventional C.R. can be used tabletop or with Bucky tray with a grid C.R. can be used for horizontal beam radiography |
| disadvantages of D.R. with portable/remote work | not as practical (connections from detector plate to computer) small animal DR panel is usually installed under the table top and not removeable |
| how do DR and CR compare in terms of durability? | DR plate pricey and fragile (new panel costs 20-50 thousand) CR cassettes are more fragile than conventional cassettes, plate is good for about 10,000 images, new plate costs 1000 |
| what is radiographic planking? | occurs from overexposure... |
| describe paradoxical overexposure | soft tissues and bones that should be white or light gray end up black instead occurs with large overexposures |
| what is border masking? | white border that occurs around the image when the primary beam is collimated greatly some digital machines have automatic border masking (positive) |
| artifacts common to CR and film/screen | hair/debris in cassettes double exposures scatter radiation from cassettes stored or left in x-ray room |
| things to remember with digital radiography | safety rules still need to be followed fewer retakes due to technique, but positioning is still very important collimation is still key |
| what is hyperattenuating (in terms of CT) | white- bone |
| what is hypottenuating (in terms of CT) | black- gas |
| advantages of CT over radiography | CT identifies over 2000 densities (versus 5 for radiograph) CT eliminates superimposition of structures CT can reconstruct images for soft tissue, bone, lungs; in different planes, and in 3D |
| limitations of CT | only acquisition of single plane images (usually transverse plane in CT) Poor contrast of tissues relative to MRI |
| what kind of contrast media is used with CT | iodinated: IV injection, intra-capsular injections for arthrograms, intrathecal injections for myelo-CTs |
| why is IV injection of iodine useful in CT? | get increased uptake in abnormally high vascular tisse (e.g. neoplasia, inflammation) so it can distinguish these areas better sometimes prolonges uptake in neoplasia (leaky tumor vessels) also used in vascular studies |
| how do air and bone appear on MRI? | both always dark |
| how does fat appear on MRI? | always relatively brignt |
| how does fluid appear on MRI? | dark on T1 weighted images bright on T2 |
| how does brain tissue appear on MRI? | T1: white matter brighter than gray matter T2: white matter darker than gray matter |
| distinguish hyper, iso, and hypointense on an MRI | hypointense: dark hyperintense: bright |
| what is unique about contrast imaging with MRI? | don't image the contrast medium itself: image its influence on the local magnetic field where it accumulates shortens T1: tissue becomes hyperintense |
| what contrast media is used with MRI | Gadolinium-chelates (Gd-DTPA) |
| how is MRI contrast media administered? | intravascular and intraarticular injection |
| In MRI, what interaction does T1 emphasize? | spin-lattice: rate at which excited nuclei dissipate excess energy to the environment (regrowth of longitudinal magnetization) |
| how does fluid appear in a T1 weighted MRI image? | always dark |
| In MRI, what interaction does T2 emphasize? | spin-spin interaction: characterizes at which rate excited spins exchange energy and go out of phase with each other loss of transverse magnetization (loss of phase in the x-y direction) |
| how does fluid appear in a T2 weighted image? | fluid is bright |
| how do liver, spleen and kidney compare in terms of echogenicity on ultrasound? | spleen: most echogenic liver: next most echogenic kidney: least echogenic note: with Kidney cortex, it can equal or exceed liver echogenicity |
| where in the abdomen can the left adrenal gland be found? | region of the left kidney, bordered by the aorta, left renal artery, celiac and cranial mesenteric arteries |
| define the borders used to find the left adrenal gland with ultrasound | aorta in long axis forms the medial border left renal artery (shepherd's crook) forms the caudal border cross sections of the celiac and cranial mesenteric arteries form the cranial borders |
| how does the prostate of an intact male compare to a neutered male on ultrasound | intact male prostate is larger, rounder, and hyperechoic to surrounding fat |
| how should you measure the thickness of the small intestinal wall on ultrasound? | no absolute measurement for individual layers: measure the thickness of the entire wall on the long axis image |
| normal jejunal thicknesses for dogs according to body weight | <4.1mm for dogs<20kg <4.4mm for dogs >= 20 and < 40kg <4.7mm for dogs>40kg |
| normal duodenal thickness for dogs according to body weight | <5.1mm for dogs< 20kg <5.3 for dogs>= 20 and < 30kg <6.0mm for dogs > 30kg |
| what might cause a focal thickening or loss of layering in the intestine that can be measured on ultrasound? | neoplasia: lymphosarcoma (or carcinoma) |
| what might cause symmetrical thickening of the intestine with intact layers (focal, regional, or extensive) as seen on ultrasound? | benign: IBD neoplastic: lymphosarcoma |
| how thick should the stomach wall be on ultrasound? | <5mm |
| describe a general sweep of the abdomen for ultrasound | dorsal to ventral with marker for cranial strip wise approach sector/curvilinear medium depth mid/deep focal zone masses lymph nodes free fluid Left limb of pancreas fat echogenicity |
| what organs/structures should you look at in a dogs abdomen for ultrasound on the right side? | liver and gallbladder right kidney right adrenal gland intestines medial iliac lymph nodes bladder duodenum pancreas |
| describe the borders used to find the right adrenal gland with ultrasound | ventromedial: caudal vena cava cross sections of celiac and cranial mesenteric arteries (cranial?) just dorsal to CVC |
| for which adrenal gland is doppler confirmation and phrenicoabdomial vessels more useful? | left adrenal (more difficult on the right) |
| identification hints for ultrasound of the descending duodenum (7) | superficial slightly thicker straight and easy to follow broad caudal flexure slish-slosh of contents 1st SI loop ventral to right kidney cranial connection to pylorus |
| length of kidney in a cat | 3.2-4.2cm |
| feline GI measurements (jejunum, duodenum, stomach) | jejunum: <2.5mm duodenum: <3mm stomach: <4mm |
| define contrast medium | substance applied to enhance the natural contrast of an organ of interest |
| what should procede every contrast study? | a survey study (baseline study to assess contrast enhancement) |
| contrast media used in conventional radiography | negative: gas (air, CO2) positive: barium sulfate, iodine compunds |
| how is negative contrast media used? | do not absorb x-rays, so appear radioluscent purpose: outlining of hollow organ walls (displacement, distension, wall mass) |
| applications of negative contrast studies | pneumo/capnocystogram pneumocolon pneumogastrogram |
| possible adverse effects of gas contrast study | overdistension and rupture gas embolism (with air) |
| purpose of positive contrast media with conventional radiography | outlining inner surface of hollow organs, vessels, and ducts enhancing parenchymal contrast filling defects |
| applications of barium sulfate positive contrast studies | oral: upper GI studies, esophagram rectal: barium enema studies |
| how does barium sulfate contrast work? | outlines the wall and the lumen of the GI tract coats mucosa so you can see mucosal detail provides outlining of mass effect |
| how does the body process barium sulfate? | its biologically inert: not hypertonic, metabolized or absorbed NEVER PUT IT IN VENOUS AREAS |
| what are BIPS and what are they used for? | Barium Impregnated Polyethylene Spheres: used to determine GI emptying and intestinal clearing time they can also highlight gastric obstruction |
| what is an additional positivie effect of Barium sulfate outside of its use in contrast studies? | provides a mucoprotective coating that binds toxins |
| adverse effects of barium sulfate | causes granuloma/ adhesion in peritoneal cavity causes aspiration (a lot) which can lead to airway obstruction and hypoxia |
| compare the osmolarity of ionic and non-ionic iodinated compounds | ionic: hyperosmolar non-ionic: iso or low osmolar |
| how are iodinated compounds excreted? | over 90% renal via glomerular filtration specific contrast media for biliary excretion alternative biliary and GI excretion in cases of renal failure |
| adverse reactions to iodinated contrast media | allergy: rare in small animals reported: acute renal failure, pulmonary edema, bronchospasm, vomiting, hypotension, seizures (due to intrathecal application) |
| how can you reduce the potential side effects of iodinated contrast media? | use non-ionic form |
| applications for iodinated contrast media (8-9) | myelogram (non-ionic only!) intravenous urogram positive contrast cystography retrograde urethrogram retrograde vaginogram angiography portography gastrogram duodenogram |
| how is positive contrast used to find filling defects? | structures surrounded by positive contrast will appear lucent if less opaque than contrast media= filling defect, while they appear opaque without contrast media |
| how are filling defects "overshadowed"? | by large amounts of positive contrast |
| what is a double contrast study? | study that uses both positive and negative contrast media |
| what are the applications of a double contrast study? | applications: esophagus, stomach, colon, urinary bladder highlights mucosal detail with positive contrast while providing dark background with negative contrast demonstrates filling defects in positive contrast puddle without overshadowing |
| define filling defect | any localized defect in the contour of the stomach, duodenum, or intestine, as seen in the radiograph after a barium enema |
| applications of iodinated contrast media to CT | IV: angiogram, parenchymal entrapment, excretory studies (excretory urogram) others: myelogram |
| for what situations are iodinated contrast media useful in angiography? | identifying vascular anatomy and anomalies thrombus |
| for what situations areiodinated contrast media useful in parenchymal enhancement? | neoplasia, inflammation, abscess, cysts |
| how is barium sulfate used for CT contrast studies? | defines external markings (scar) for radiation therapy planning used as a guide for biopsies and aspirates |
| what is the major contrast media used with MRI? | paramagnetic substances such as rare earth metals: Gadolinium (used in chelate form because gadolinium itself is toxic) |
| principles of contrast media in MRI | acts as a paramagnetic substance enhances magnetic properties of neighboring atoms shortens T1 relaxation |
| what features increase contrast media uptake in an MRI study? | leaky vessels: due to inflammation or selective disruption of the BBB note: MRI can facilitate much of this without contrast media by applying specific sequences |
| how are gas bubbles used in ultrasound? | gas bubbles cause sound reflection, can be used with IV injection for blood flow enhancement |
| how are bubbles best seen with ultrasound? | best seen with tissue harmonic imaging get a maximal signal is the bubble is destroyed sonographically |
| uses of contrast media in ultrasound | portosystemic shunts perfusion imaging (myocardial, renal grafts, tumor perfusion) echocardiography |
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nickrobl50