Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
249 Cards in this Set
- Front
- Back
|
which two views are used the most?
|
right lateral and VD
|
|
|
T/F: fluid and soft tissue have the same radiopacity
|
true
|
|
|
fat is less or more opaque than soft tissue and fluid?
|
less
|
|
|
name Pasquini's radiopacities in descending order
|
bullet (metal), bone (mineral), blood (fluid/soft tissue), blubber (blubber), bubbles (air)
|
|
|
define serosal detail
|
the ability to see the serosal margin (contour) of abdominal organs
|
|
|
why is it harder to see radiographs on fat puppies than on fat adults?
|
fat usually causes better serosal detail on a radiograph however puppy fat contains more water and is therefore more radiopaque, decreasing serosal detail
|
|
|
what happens to serosal detail with peritoneal inflammation or infiltration?
|
loss of serosal detail may be focal or diffuse
|
|
|
what happens to serosal detail w/ascited?
|
effacement of serosal detail (won't see margins)
|
|
|
5 types of peritoneal fluid
|
blood, urine, bile, transudate, exudate
|
|
|
with severe ascites in the peritoneal cavity...
|
-poor abdominal contrast, serosal detail is indistinct
-*intestinal gas shadows lie in the center of the abdominal cavity -*pendulous abdominal wall margins |
|
|
which is better for finding fluid: radiograph or US?
|
US - but cannot ID fluid - must be tapped and sent for cysto
|
|
|
fluid color/echogenicity on US depends on what?
|
cellularity
|
|
|
anechoic (black) fluid is usually ?
|
clear transudate
|
|
|
swirling-snowy appearing (echogenic) fluid could be ?
|
cellular fluids such as blood, pus
|
|
|
define anechoic
|
not having or producing echoes
|
|
|
define echogenic
|
structures that reflect high-frequency sound waves and thus can be imaged by ultrasound techniques
|
|
|
describe radiograph w/peritonitis
|
-poor abdominal contrast and serosal detail
-often localized around pancreas -may be generalized if severe or diffuse and large (if ascites present) |
|
|
describe US w/peritonitis
|
-anechoic areas outlining serosal surfaces of abdominal structures
-hyperechoic fat -could see a swirling-snowy appearance -fibrin tags may be ID'd |
|
|
seen in peritonitis on VD view
|
duodenum may be displaced laterally
|
|
|
seen in peritonitis on lateral view
|
colon may be displaced caudally away from stomach
|
|
|
which is better in dogs w/pancreatitis: US or radiograph
|
US
|
|
|
pancreatitis: where will you find fluid on US what type of fluid?
|
-in the immediate vicinity of the duodenum in the right cranioventral section of the abdomen
-hypoechoic or anechoic fluid |
|
|
what is the key to US?
|
know your anatomy very well
|
|
|
radiographic appearance of free peritoneal gas
|
-serosal surfaces outlined (liver separated from diaphragm by gas outline)
-gas seen under costal arch -gas shadows surrounding and enhancing renal silhouette -unusual gas patterns (bubbles or streaks) scattered through abdomen and not assoc. w/lumen of GI tract |
|
|
what is the best way to confirm free peritoneal gas?
|
use of horizontal beam w/animal in left lateral recumbency
|
|
|
which is better for fluid in the peritoneal cavity: US or radiograph?
|
radiograph - less obvious on US bc looks kinda of like gas in intestines (scan the upper or non-dependent region and may see a
reflective hyperechoic area) |
|
|
liver opacity and position
|
-soft tissue opacity
-most cr abd organ, partly w/i ribcage, ca to diaphgram, cr to stomach |
|
|
where should the caudal margin of the liver be on a radiograph?
|
within the costal arch or protruding slightly
|
|
|
how should the gastric axis be?
|
parallel to the ribs
|
|
|
what does it mean if the gastric axis is displaced caudally?
|
hepatomegally
|
|
|
what does it mean if the gastric axis is displaced cranially?
|
microhepatica
|
|
|
in what type of animal is the gastric axis sometimes cranially displaced?
|
deep-chested dogs
|
|
|
what does the liver look like on US?
|
-coarse, finely granular, and has a thin hyperechoic capsule
|
|
|
what do the liver vessels look like in US?
|
-portal vein: hyperechoic walls (look like little rings)
-hepatic veins: no walls visible (anechoic) -hepatic arteries: not seen in B-mode |
|
|
what does the GB look like on US and where is it?
|
round, globe-like on the right side
|
|
|
where is it easier to see hepatomegally: radiograph or US?
-when should a radiograph be taken? |
radiograph (fat)
-expiratory (inspiratory may cause liver to lie caudal to the costal arch |
|
|
radiographic signs of hepatomegally
|
-gastric axis displaced caudally
-rounding of caudal margin of the liver -liver protruding beyond costal arch -abd organs displaced caudally |
|
|
US signs of hepatomegally
|
-liver echotexture may be incr
-liver edges rounded or deformed |
|
|
radiograph: microhepatica
|
-inability to find ventral-caudal liver margin
-**gastric axis displaced cranially |
|
|
organ displacement w/right liver masses
|
-dorsomedial displacement of pylorus
-caudodorsal displacement of SI |
|
|
PSS is likely to be intrahepatic if ?
|
-shunt is cranial to the body of T13
|
|
|
technique for PSS diagnosis and assessment
|
Nuclear scintigraphy
|
|
|
head of the spleen is usually found where?
|
fixed between the left kidney, the fundus, and the liver
|
|
|
in which radiographic view is it easiest to find the head of the spleen and where on the view do you find it?
|
-VD
-left cranial |
|
|
in which radiographic view is it easiest to find the tail of the spleen and where will you find it?
|
-lateral
-just caudal to the liver in the ventral abdomen |
|
|
T/F: spleen is not normally seen in healthy cats
|
true
|
|
|
how does the spleen look on US?
|
-finely granular, homogenous, hyperechoic capsule (when compared to liver and kidneys)
-medium to high echogenicity (looks like a very pixelated static black and white tv) |
|
|
T/F: splenomegally can be both physiologic and pathologic
|
true: could be caused by anemia, anesthesia, neoplasia, cysts, abscesses, hematomas
|
|
|
what is known as the "mass effect?"
|
a mass in the abdomen will push and displace away movable organs
|
|
|
what can mask the presence of masses?
|
fluid
|
|
|
what does a ventral hernia look like?
|
abdominal organs laying outside the abdominal cavity just under the skin
|
|
|
what does a traumatic ventral hernia look like?
|
Intestines are present in the large hernia sac
|
|
|
what does a perineal hernia look like? what may be useful to find it?
|
-bladder absent in caudal abdomen. -Contrast cystography
|
|
|
what is a hiatal hernia?
|
protrusion of part of the stomach through the oesophaheal hiatus of the diaphragm.
|
|
|
what may be contained in an inguinal hernia?
|
may contain fat, bladder, uterus or intestine
|
|
|
the long axis of the stomach is usually where on a radiograph?
|
paralled to the 10th intercostal space
|
|
|
Gas flows to the ____ point in the stomach on radiographs. Barium flows to the ____ point in the stomach on radiographs.
|
-highest (pylorus on LLR or fundus on RLR)
-lowest (pylorus on RLR or fundus on LLR) |
|
|
where is the stomach on a VD radiograph in the dog? int he cat?
|
-dog: lies at right angles to the vertebral column)
-cat: lies completely on the left side in a C shape |
|
|
what one drug can cause marked gastric dilation?
|
xylazine
|
|
|
causes of gastric outflow obstruction that could cause gastric dilation
|
pyloric foreign bodies, obstruction due to pyloric stenosis or neoplasia and secondary extrinsic obstruction due to severe pancreatitis or pancreatic neoplasia
|
|
|
what else might you see on a radiograph with GDV or gastric torsion?
|
-small intestine may be seen in the dorso-cranial section of the
abdomen -air may be seen throughout the rest of the intestine -may see an associated megaoesophagus |
|
|
where will the pylorus be seen on a radiograph of a partial gastric torsion?
|
in the dorsocranial abdomen and the left cranial aspect of the abdominal cavity.
|
|
|
good indicator of compartmentalization in gastric torsion/volvulus on a radiograph?
|
soft tissue stripe (white)
|
|
|
normal SI diameter
|
two rib widths or less than 1.6 times the vertical body of L5
|
|
|
normal GI transit time for barium
when should the tract be empty? |
-between 30 and 120 minutes
-between 3 – 5 hours post administration |
|
|
best way to see different layers of GI
|
use the highest frequency possible
|
|
|
T/F: Outpouchings along the antimesenteric border of the duodenum are normal in dogs
|
true: they are Peyer's patched (aka "pseudoulcers")
|
|
|
what does the duodenum of a cat normally look like?
|
has a "string of pearls" conformation
|
|
|
T/F: "fimbriation" of the SI mucosal border is not normal
|
false: normal
|
|
|
the 5 layers of the stomach and intestines in US
-in which part of the GI are those layers not as clearly defined? |
lumen, mucosa, submucosa, muscularis, serosa
-colon |
|
|
***what do each of the 5 layers of the GI tract look like in an US
|
-serosa/subserosa: thin, hyperechoic
-muscularis: thin, hypoechoic -submucosa: thin, hyperechoic -mucosa: broad, hypoechoic -lumen interface: thin, hyperechoic (empty GI) |
|
|
how do you tell the difference between the SI and LI in an US?
|
-SI: mucosa is the thickest layer
|
|
|
how do you tell the difference between neoplasia and inflammation of the SI in an US?
|
-SI:
---layering pattern is preserved ---wall thickening and/or incr mucosal echogenicity ---generally diffuse ---any layer affected ---rarely causes obstruction -neoplasia: ---layering pattern is disrupted in most cases ---generally focal ---may or may not cause obstruction |
|
|
normal wall thickness of the stomach
|
-depends on degree of distension
<5/6mm |
|
|
normal wall thickness of the intestine
|
-almost dependent of distension
dog <4.5mm (duodenum <6mm) cat 2-2.5mm |
|
|
***describe mechanical distention/ileus of the SI
|
-severe, focal
-dogs >1.6xs midbody depth of L5 -cats > 1.2cm -"gravel sign" - mineral builds up cr to site of obstruction |
|
|
describe functional distention/ileus of the SI
|
-moderate generalized distension
-hyper or hypomotility on ultrasound (depends on cause) -underlying cause rarely identified (often assoc w/ ex. parvo-virus, peritonitis or chronic intestinal obstruction in the distal SI) |
|
|
what may resemble a coiled spring or "swiss cake roll" when a barium enema is given?
|
intussuception on US
|
|
|
what does a colon look like on US?
|
-thin wall (normally <2mm)
-layers not clearly differentiated like SI |
|
|
problem w/using US on the colon
|
US doesn't work well w/lots of gas and feces, therefore multiple artefacts are seen (shadows, reverberation, comet tails)
|
|
|
when may radiolucent gastric foreign bodies be seen in a radiograph?
|
when surrounded by air or barium is given
|
|
|
what does a gastric foreign body look like on US?
|
a sharp, radiopaque line creating acoustic shadow
|
|
|
in cases of severe constipation and megacolon, what do you assess?
|
pelvic canal and spine for possible primary lesions
|
|
|
define ultrasound
|
sound waves (consisting of a series of pulses made up of compressions and rarefactions) of frequency above the normal hearing range of the human ear (greater than 20,000 Hz)
|
|
|
what takes the most time with the piezo electric crystal in the US machine?
|
waiting for the reflected echoes to come back (only emits sound waves for approx 1% of the time)
|
|
|
US: velocity =
|
frequency x wavelength
|
|
|
the larger the difference in impedance...?
|
the larger the portion of reflected US
|
|
|
US: reflection occurs when ?
|
when an US beam encounters an interface between adjacent tissues with
different acoustic impedance |
|
|
when does specular reflection occur?
|
-occurs when the beam encounters large interfaces
-the US beam is reflected at an angle equal to the angle of incidence (parallel) (best at a 90 degree angle bc otherwise the entire reflected beam will not go back to transducer) |
|
|
define: scatter
-what does it contribute to? |
-occurs when US waves are reflected by small interfaces and
is not angle dependent -the parenchymal texture of multiple organs |
|
|
define: refraction
|
-the part of the beam that will be transmitted and change in speed according to the type of material or tissue (part of the beam reflects, part refracts)
(similar to the diffraction of light waves going through water or crystal) |
|
|
US: one of the most important things to take into account with absorption
|
frequency of the ultrasound beam
(higher frequency are attenuated more than lower frequency) |
|
|
higher frequency = ?
|
higher attenuation = less penetration
|
|
|
US frequency ranges
|
1,000,000 - 20,000,000 Hertz (1-20MHz)
|
|
|
speed of US depends on what?
|
type of tissue they're going through
|
|
|
speed of US in average soft tissue? air? fat?
|
-1540m/sec
-331m/sec -1450m/sec |
|
|
US: the greater the difference in acoustic impedance between two tissues...?
|
the stronger the returning echo
|
|
|
US: the transmission of US through air results in what?
-through bone? |
almost total reflection of sound waves
-absorbs 70-80%, reflects 20% |
|
|
US: acoustic shadowing
|
black shadow beyond the point of marked acoustic impedance
|
|
|
US: which weakens the beam more: fluid filled structures or soft tissue?
|
soft tissue
|
|
|
US: define: acoustic enhancement
|
the sound beam is relatively stronger when it exits a fluid structure surrounded by soft tissues
|
|
|
US: general ROT: higher frequency =
|
higher resolution (allows differentiation of smaller structures and improves image quality)
|
|
|
US: high frequency =
|
poor penetration = great image, high resolution
|
|
|
US: low frequency =
|
better penetration = worse image, worse resolution
|
|
|
US: benefits of electronic transducers
|
-lighter, smaller, less artefacts, allow focusing, less subject to wear
|
|
|
US: which type of transducer uses larger footprints? what do they display?
|
linear type
-large area of the near field of the image |
|
|
US: define: resolution
|
the ability to see 2 structures that are close together as 2 separate structures
|
|
|
US: how should the depth be adjusted
|
so the organs being examined occupy the maximum area of the field of view
|
|
|
US: focusing: the narrower the beam...
|
the higher the resolution
|
|
|
US: what does the general gain affect?
|
-the amplification of the signal generated by the returning echoes (too high = too bright, meaningless echoes; too low = too dark)
|
|
|
US: what is TGC and what does it do?
|
-time gain compensation
-allows control of the gain at different depths and should be adjusted so that the image is homogeneous in appearance (rather than darker as depth increases bc the signal from deeper structures is weaker) |
|
|
US: when does acoustic enhancement occur?
|
-when the beam travels through an area that attenuates the ultrasound
beam less than the surrounding tissues, such as the gall bladder surrounded by liver (produces an area of increased signal beyond the hypoattenuating structure) |
|
|
US: what is side lobe artefact?
|
where images obtained from the secondary beams are superimposed onto the image obtained from the primary beam bc the transducer assumes all imaged are from the primary beam
|
|
|
US: what is acoustic shadowing? what can cause it? what can it help with>
|
-complete reflection of the US beam where the area beyond the structure will appear black due to lack of echoes
-high echogenic structures -can help depict mineralization w/i soft tissues or ID foreign bodies |
|
|
US: what is seen with edge shadowing/refraction
|
-and echo free (anechoic) area will be displayed beyond the structure refracting the beam
|
|
|
US: why will the machine place structures deeper if they are reverberated?
|
-bc they take more time getting back to the transducer
|
|
|
US: what can help reduce reverberation artefacts?
|
-good transducer/skin apposition
-the use of coupling gel |
|
|
US: what creates comet tails?
|
-gas
-some metallic objects (such as biopsy needles) |
|
|
US: the term "echogenic" should only be used when?
|
to compare different regions of an image or to compare different organs (remember, it can be changed by incr or reducing the gain so just use it to compare structures on the same US)
-ex the liver is hypoechoic to the spleen |
|
|
US: in B-mode, the brightness is proportional to what?
|
the strength of the echo
|
|
|
US: one of the most common mistakes
|
too high gain
|
|
|
US: comet tails is a type of what?
|
reverberation (artefact)
|
|
|
US: what is the doppler shift? what is it proportional to?
|
-(emitted frequency) - (received frequency)
-proportional to speed of moving object |
|
|
electrons behave like ?
|
-waves that travel in straight lines, at a constant speed, the speed of light.
|
|
|
what % of the energy used is transformed into the actual x-ray?
|
1% (the rest is transformed into heat)
|
|
|
two principles in which x-rays are generated
|
Brehmsstraulung or braking electrons and characteristic radiation
|
|
|
continuous spectrum
|
Photons of all energies are produced up to a maximum, when an
electron loses all its energy in a single interaction. |
|
|
explain Brehmasstraulung/braking electrons
|
-High speed electrons interact with the atoms in the target. The electrons are deflected and slowed down due to these interactions. The energy lost by the electron during this process is released in the form of an X-ray (if an electron moves at 100eV and then is slowed to 20eV, the remaining 80eV becomes the x-ray
|
|
|
explain characteristic radiation
|
-A high speed electron collides with an electron in the target --> the electron in the target is ejected, leaving a shell with an empty space and an atom with a positive charge (ionization) --> one of the electrons in an outer shell of the atom will fall down to fill up the space --> when this happens, it loses energy which is released as a photon --> the released photon or X-ray will have an energy equal to the difference of energy between two sells
-ex Imagine electrons in the shell K have an energy of 50 eV and electrons in the L shell have 70eV. If a K shell electron is ejected and an L electron takes its place, a 20eV photon will be released. |
|
|
a difference between braking electrons and characteristic radiation
|
-as the energies of each shell of an atom are constant, the generated X-rays have always the same energy. This will create peaks of determined photon energy instead of a continuous spectrum
|
|
|
two basic components you need to generate an x-ray
|
-cathode (source of electrons) (-)
-anode (target) (+) |
|
|
define: thermionic emission
|
when a current is applied to the thin filament of the Tungsten cathode and an electron cloud is produced
|
|
|
what is the point of the focusing cup around the cathode?
|
electrons repel each other and have a tendency to spread when heading towards the anode so the focusing cup prevents this
|
|
|
problem w/stationary anodes
|
The electrons collide in the same spot of the target limiting the amount of X-rays generated.
|
|
|
what is the benefit of using rotating anodes?
|
-the area of impact of electrons is increased, and therefore the heat produced is distributed over a much larger area, allowing the use of higher mA
|
|
|
the one part of the metal case (part of the tube housing) that is NOT lined w/lead
|
the region opposite the target from which the x-ray beam will emerge
|
|
|
how do you generate the electrical potential for electrons to produce x-rays?
|
a high voltage direct current must be applied across the tube, which will
create a positive charge in the anode and a negative charge in the cathode |
|
|
a low voltage circuit has what and regulates what?
|
-cathode filament
-mA |
|
|
a high voltage circuit creates what and regulates what?
|
-electrical potential between cathode and anode
-kV |
|
|
4 x-ray controls
|
-kV
-mA -time -size of target |
|
|
higher kV =
|
incr in x-ray energy (bc higher energy potential across tube)
-also incr number of x-rays bc higher potential pulls more electrons from the filament |
|
|
higher mA =
|
incr quantity of x-rays (bc higher filament temperature, more electrons available)
|
|
|
the mA control regulates what?
|
the voltage applied to the
filament (cathode) and controls its temperature (Higher temperatures will result in larger numbers of available electrons. The larger number of electrons are available, the more X-rays are produced per unit of exposure time.) |
|
|
what does the exposure timer control?
longer exposure = ? |
-the length of time the high tension voltage is applied to the tube and therefore the length of time that X-rays are emitted.
-more electrons pulled from cathode = more x-rays |
|
|
mAs used by different types of x-ray machines
1. portable 2. mobile 3. fixed single phase 4. fixed three phase |
1. usually <100mA
2. up to 500mA 3. up to 1000mA 4. up to 1500/2000mA |
|
|
attenuation of an x-ray depends mainly on ?
|
-atomic number (Z)
-physical density and sp grav of the tissue -thickness of the tissue |
|
|
name the 3 main types of interaction resulting in attenuation
|
photoelectric effect
compton effect classical scatter (low energy radiation and doesn't contribute to image) |
|
|
name something very important for radiographic contrast
|
photoelectric absorption (barium, iodine)
|
|
|
probability of a photoelectric interaction is directly proportional to what? inversely proportional to what?
|
-the cube of the atomic number
-the kV (1/kV3) (as kV incr, PE decr) |
|
|
the benefits of photoelectric absorption?
the disclaimers of photoelectric absorption? |
benefits: magnifies the difference between tissues w/different Z, very important in radiograph contrast
disclaimer: deposits its energy in the patient |
|
|
what does the probability of the compton interaction depend on?
|
only on the specific gravity of the
absorbing tissue (C.E. ∝ Specific Gravity) and is INDEPENDENT of Atomic Number (Z). |
|
|
what si the compton interaction
|
when the x-ray knocks loose the electron and the energy from the recoil electron (the deflected proton) is deflected towards the x-ray
|
|
|
bad news about the compton effect:
|
scattered proton has a random direction outside the primary beam (safety hazard to personnel, decr radiographic contrast)
-scatter is more likely to reach the film |
|
|
result of the compton interaction in an x-ray
|
-a scattered, weakened photon
-a free electron and -a positively charged atom |
|
|
3 ways to control film scatter
|
-decreasing the amount of scatter produced.
-reducing the amount of scatter reaching the film. -reducing the effect of scattered radiation on the film. |
|
|
what happens in an x-ray at >70kV?
|
-incr in compton absorption, decr in PE absorption
-incr in scattered photons -decr in the differential absorption of different tissues -***poor radiograph contrast |
|
|
T/F: there is nothing good abut the compton effect
|
true!!
|
|
|
what materials are used in the intensifying screens of an x-ray?
|
-rare earth (more efficient at converting x-ray to light)
-calcium tungstate |
|
|
ways to increase speed of an x-ray? problem?
|
-larger crystals, thicker screen
-problem: incr in speed --> loss of sharpness |
|
|
4 layers of an x-ray film (outside to inside)
|
-supercoat (protection from damage)
-**emulsion (gelatin w/dispersed grains of silver halide - this is what turns black and gives you the image) - most important layer -subbing layer (adhesive) -film base (polyester, support for emulsion) |
|
|
advantage of single-sided emulsion film
-problem |
-1 image will look sharper (fine detail)
-need longer exposure bc only one image instead of two so needs more time to turn darker |
|
|
advantage of non-screen film
-problem |
-very very sharp image
-problem: large incr in mAs, problems w/automatic processors, thicker emulsion |
|
|
coating on the film
|
silver halide crystals (silver bromide pentagons)
|
|
|
lattice image (?)
|
cannot see it but the image is there and waiting to be developed
|
|
|
what does the developer do?
this process is dependent on what? |
the alkaline reducing agents can donate electrons --> penetrate the grains w/latent image --> neutralize all silver ions, converting them into metallic silver (black opaque silver)
-time and temperature (silver bromide turned into pure silver) |
|
|
what happens if you change the developer temperature?
|
incr in temperature develops radiograph quicker
(automatic processors use a higher temperature ~35 degree for 90-120sec) |
|
|
3 main functions of a fixer
-how long do you do it? -what will it look like it inadequately fixed? |
-stop continued development of silver halide
-remove unexposed and undeveloped grains of silver bromide (clearing the film) -hardens the gelatin -time: 10 minutes -the film will not be cleared or hardened - pink tinge dichroic fog |
|
|
resolution or a conventional radiograph has ___xs the resolution of a digital radiograph
|
4-5xs
|
|
|
what happens w/inadequate washing?
how long should you wash off the fixer the film? what happens if you wash it too much? |
silver sulphide formed will turn the film brown with age
-30 minutes -emulsion is soft, will slip off the film |
|
|
the most important thing in film quality?
|
film contrast
|
|
|
what is film density?
|
degree of film blackening
|
|
|
film density is determined by:
|
exposure settings (mA, time, kV) and film focal distance
|
|
|
what happens to overexposed film?
|
turns black
|
|
|
what is the effect of exposure (mA and kV) on film density?
|
-high mAs = more x-rays = more film density
-kV determines film contrast rather than film density ----however, incr kV = more electrons pulled from cathode = more protons = more film density |
|
|
film focal distance dramatically affects ?
if you double the FFD, what do you need to do to exposure? |
exposure
-incr by 4 (square it) (bc by the inverse square law, when you double the distance, the same amt of energy is distributed over an area 4xs the size) |
|
|
higher kV will produce what?
|
more penetrating X-rays that will be more likely to reach the film
|
|
|
what does mA do?
|
determines the number of available electrons at the filament per unit time. Higher mA = more X-rays
|
|
|
FFD is esp important in which spp?
|
horses
|
|
|
4 main types of unsharpness
|
-geometric
-movement -photographic -patient |
|
|
ways to minimize geometric unsharpness
|
-decr OFD
-incr FFD -smaller focal spot |
|
|
how to minimize movement unsharpness
|
-sedatives/anesthesia
-confine movement using sandbags, ties, etc -use stable x-ray machine stand and table -using shorter exposure times |
|
|
patient unsharpness is caused by:
|
-movement
-rounded margins of structures |
|
|
how to minimize image distortion?
|
keep object parallel to film and centered
|
|
|
causes of photographic unsharpness
|
-mainly by the size of AgBr crystals in film and phosphor crystals in screen (use high definition film/screen combinations when detail required
-also caused by double emulsion film (use single emulsion when fine detail needed) |
|
|
what will light crossover do?
|
decr sharpness in a similar manner to poor contact between film and screen
|
|
|
what does contrast depend on?
|
-quality of primary beam
-effect of scattered radiation -inherent film contrast -inherent patient contrast -film processing |
|
|
contrast and kV
|
low kV --> higher contrast (less scatter, PE effect dominates)
high kV --> low contrast, lots of scatter on film, compton predominated |
|
|
how to generate less scatter
|
-use low kV (PE dominates, less compton effect, means higher radiation dose as more absorption)
-beam collimation -decr thickness being radiographed (if possible) |
|
|
hot to decrease scatter reaching film
|
-use low kV (scatter is weaker and less aimed forward)
-use grids (stripes aligned w/primary beam, scatter gets absorbed by the grid) -use air gap technique |
|
|
what is the "grid factor"
|
the amt by which exposure needs to be incr when grid is used (bc grid stops some of the primary beam)
-generally between 2 and 3 (if 2, means exposure must be doubled, etc) |
|
|
advantage and disadvantages of the grid
|
advantage: improvement in contrast
disadvantage: incr in exposure factors (incr radiation, incr exposure time, more stress in equipment), grid lines w/stationary grid, possible artifacts w/poor grid alignment |
|
|
problem w/air gap technique to decr scatter
|
inconvenient, will cause magnification and blurring (though more scatter will miss the grid)
|
|
|
3 reasons film could be too dark
|
-overexposure
-overdevelopment -film fogging |
|
|
what can cause overexposure? what does it look like?
|
-too high mA, kV, or exposure time
-decr FFD -wrong film/screen -film too dark |
|
|
what might overdevelopment cause? what can cause it?
|
-may cause developemtn of crystals that were non sensitized/exposed (will turn black)
-radiograph being developed too long -developer temperature too high |
|
|
what can cause overall film fogging?
what does it look like? |
-chemicals, heat
-light (light leakage) -background radiator -overdevelopment -old film -film too dark |
|
|
what can cause localized film fogging?
|
-incorrect handling
-faulty cassette |
|
|
what can cause film to be too light?
|
-underexposure
-underdevelopment -wrong film/screen -exposure not adapted to grid -grid cutoff -anode failure |
|
|
causes of underexposure
|
-too low mA, kV, exposure time
-increased FFD |
|
|
causes of underdevelopment
|
-temperature too low or development time too short
-developed exhausted |
|
|
what can cause black marks on the film?
|
-developer splash
-bending or pressure on film (crescent shape common due to poor handling) -static discharge (looks like feathering) -cassette leakage |
|
|
what can cause uneven background density on a film?
|
-poorly mixed solutions
-exhausted developer |
|
|
what can cause yellow staining on a film?
|
-old developer
-poor washing |
|
|
what can cause double exposure on a film?
|
-pressing the button twice
-putting both legs on top of one another |
|
|
define ionizing radiation
-types |
radiation that is able to eject electrons from an atom or molecule
-electromagnetic and particulate |
|
|
name the 2 types of electromagnetic radiation
|
x-ray and gamma ray (radioactive decay)
|
|
|
direct effect of ionizing radiation
|
the electron interacts directly w/an important molecule of the tissue, generally DNA
|
|
|
indirect effect of electromagnetic radiation
|
the electron interacts w/another atom or molecule generating free radicls --> the free radicals attack relevant molecules (ex DNA)
|
|
|
which DNA damage is repairable: single strand breaks, double strand breaks, or both?
|
single strand breaks (sometimes double strand if the break is clean enough)
|
|
|
explain deterministic/non-stochastic biological damage from ionizing radiation
|
-dose dependent - higher dose, more severe effects
-below a certain dose, there is no damage -does NOT occur w/levels of radiation exposed to while taking radiographs of you or a patient -ex erythema, skin ulceration, hair loss, cataracts, etc |
|
|
explain stochastic biological damage from ionizing radiation
|
-more exposure to radiation = increased likelihood of developing side effects
-NO lower threshold level -amt of radiation does not determine severity but LIKELIHOOD |
|
|
two types of stochastic biological damage
|
-carcinogenic: long latent period and severity is unrelated to dose
-genetic effects: subsequent generations affected and severity unrelated to dose |
|
|
which tissues are more sensitive by radiation?
|
-rapidly dividing tissue (mitotic) have a greater sensitivity
-ex: fetus, bone marrow, epithelial tissues, skin basal layer, germinal cells -resistant tissues: liver, kidney, brain, bone, cartilage |
|
|
T/F: lead coated gloves, thyroid shields, and aprons are designed to protect you from primary radiation
|
FALSE
|
|
|
what is the only way to protect yourself completely from exposure to scatter?
|
don't enter the room
|
|
|
one thing you HAVE to remember when using a portable x-ray machine
|
NEVER HOLD THE X-RAY MACHINE
|
|
|
what is the "lead equivalent?"
|
the thickness of lead required to achieve the same shielding effect against radiation, under specific conditions, as that provided by a given material
|
|
|
types of dosimeters
|
-film badges: radiographic film
-thermo-luminescent dosimeters: lithium fluoride -ionization meters: give an immediate dose readout |
|
|
which type of dosimeter gives an immediate dose readout?
|
ionization meter
|
|
|
adequate wall shielding from radiation (for both vertical and horizontal beams)
|
vertical beam: single clay brick sufficient for scatter
horizontal beam: need additional shielding |
|
|
what radiograph system has the high spatial resolution unmatched by all other systems?
|
conventional radiography
|
|
|
advantages of digital radiography
|
-wide exposure latitude: digital radiography systems can compensate for over/under exposure
-increased dynamic range: ex can see soft tissue and bone in the same exposure -less artefacts related to exposure and development and increased dynamic range = less retakes |
|
|
speed of all three systems:
1. digital radiography 2. computerized radiography 3. conventional radiography |
1. few seconds, almost immediate
2. normally between 1.5-3 minutes 3. 5-10 minutes for manual development, though developer may be as fast as computerized (2-3 min) |
|
|
which radiograph systems use a cassette?
|
conventional and computerized radiograph systems
|
|
|
explain how a computerized radigoraph system works
|
isntead of radiographic film, the cassette contains a flexible image plate made out of photosensitive phosphor --> electrons in the crystalline phosphor are excited by the x-rays to a higher energy level where they are trapped --> the trapped electrons form a latent image similar to the latent image acquired on conventional x-ray film -->photosensitive phosphor is fed in to a reader --> lase scans the plate --> trapped electrons come back to their normal state at high energy level --> emit light while they do --> light is detected and measured by the system --> reader erases the place by prolonged exposure to light
|
|
|
how is the image captured on a digital radiograph? how large is each pixel in this image?
|
by a detector assembly
-the same size of a detector (so the image is limited by pixel size) |
|
|
two types of digital radiographs
|
-direct conversion (True DR)
-Indirect conversion: flat panel and charged couple device |
|
|
sequence of events with a Direct conversion digital radiograph
|
x-rays --> electric impulse --> readout
|
|
|
sequence of events with an Indirect conversion digital radiograph
|
x-rays --> light --> electrical impulse -->readout
|
|
|
sequence of events with a charged coupled detector digital radiograph
|
x-rays --> light --> lens -->CCD -->electric impulse --> readout
|
|
|
what is the problem with the indirect conversion and the charged coupled detectors in comparison with the direct conversion digital radiograph?
|
everytime you convert energy (so every step) you lose part of the image
|
|
|
how are each of the different types of radiographs limited in spatial resolution:
1. conventional radigoraph 2. computerized radiograph 3. direct radiograph |
1. limited to the size of the silver halide crystals
2. limited to the width of the laser in the reader (inferior to conventional) 3. limited to the size of detectors in the TFT (one detector = one pixel) (inferior to conventional) |
|
|
benefits or problems of computerized radiograph (over a direct/digital radiograph)
|
-cheaper
-no need for upgrade (DR needs to be synchronized w/x-ray generator) -can be reused many times (lifetime is limited) -one reader can be used in many x-ray rooms (just bring the cassettes) -slower -laser reader is sensitive to dust and moving parts, require repair and maintenance - |
|
|
benefits or problems of direct/digital radiograph (over a computerized radiograph)
|
-faster
-portable systems becoming more affordable -system needs to be synchronized w/x-ray generator -plates are sensitive to temperature changes (careful on farms) -plates are fragile, expensive, often fixed (one plate/system = one room) |
|
|
define quantum mottle
|
underexposed images appear grainy on digital x-ray
|
|
|
define digital burnout
|
severely overexposed areas will result in effacement of structure on digital x-ray
|
|
|
gloss over
|
v. explain away; cover up; deal with quickly in a cursory/perfunctory manner; hide No matter how hard he tried to talk around the issue, President Bush could not gloss over the fact that he had raised taxes after all.
|
|
|
why is a CT scan better than a radiograph for different opacities?
|
bc it can actually give value to the opacities and differentiate between those that can't be differentiated between in radiology (such as soft tissue and fluid, or even different types of fluids)
|
|
|
CT: what is it called when attenuation values are adjusted to a grey scale during review of the CT?
|
window level or windowing (can adjust to brain window, bone window, etc)
|
|
|
advantages of CT
|
-high detail cross sectional images, thus avoiding superimposition seen in conventional radiography.
-can process the image to give greater resolution of narrow contrast bands. -the ability to reformat the information. -post-processing can enhance an area of special interest. |
|
|
disadvantages of CT
|
-uses long X ray exposure times.
-contributes a radiation dose. -lower spatial resolution of low contrast objects. -expensive equipment. |
|
|
MRI stands for ?
|
Magnetic resonance imaging
|
|
|
MRI: air is black in which: T1 or T2?
|
T1
|
|
|
MRI: fat is bright in which: T1 or T2?
|
both (though moreso in T1)
|
|
|
MRI: air and bone are dark in which: T1 or T2?
|
both
|
|
|
main difference between MRI and CT
|
MRI can give you a slice in any plane along the body
CT is limited to transverse plane |
|
|
most common contrast agent used in MRI
-in which (T1 or T2) is it bright? |
Gadolinium
-T1 |
|
|
advantages of MRI
|
-has superior soft tissue resolution to CT.
-does NOT utilize ionizing radiations. |
|
|
disadvantages of MRI
|
-not so useful for the evaluation of bone.
-strong magnetic field used may affect pacemakers and metallic objects and create a safety hazard. -longer scanning times. -expensive equipment. |
